FIDL 範例

這是一份 FIDL 範例目錄,旨在透過簡化實際軟體工作流程的實作方式,展示 FIDL 概念。

索引範例

以下範例會依序示範實用的 FIDL 概念。

計算機

計算機範例會顯示建立第一個 FIDL 通訊協定的基礎建構元素。

鍵/值儲存庫

鍵/值儲存庫範例會示範如何使用 FIDL 建構簡單的鍵/值儲存庫,以便瞭解該語言提供的各種資料類型。

畫布

畫布範例示範如何使用 FIDL 建構簡單的 2D 線條算繪畫布,以便瞭解常用的資料流程模式。

概念索引

FIDL 語言中的每個「概念」至少會在前一個章節列出的其中一個範例中示範。下一個章節將列出每個概念的快速參照資料,以及實作範例。

確認模式

FIDL 食譜:確認模式

確認模式是一種簡單的流程控制方法,可用於原本會是單向呼叫的方法。系統不會將方法設為單向呼叫,而是將其轉換為傳回值為空的雙向呼叫,也就是俗稱的 ack。回應的唯一目的,就是通知寄件者訊息已收到,以便寄件者決定後續處理方式。

這項確認的成本是透過管道新增的閒聊內容。如果用戶端在等待確認後才繼續下一個呼叫,這種模式也可能導致效能降低。

傳送不受限制的單向呼叫來回,可產生簡單的設計,但仍有潛在陷阱:如果伺服器處理更新的速度比用戶端傳送的速度慢得多,該怎麼辦?舉例來說,用戶端可能會載入由某個文字檔的數千行組成的圖表,並嘗試依序傳送這些圖表。我們如何將回壓力施加到用戶端,以免伺服器因這波更新而負荷過重?

透過使用確認模式,並將單向呼叫 AddLine(...); 轉換為雙向 AddLine(...) -> ();,我們就能向用戶端提供意見回饋。這樣一來,用戶端就能適當地節制輸出內容。在這個範例中,我們會讓用戶端等待 ack,然後再傳送等待中的下一個訊息,不過更複雜的設計可能會樂觀地傳送訊息,並且只在收到的非同步 ack 頻率低於預期時才節流。

首先,我們需要定義介面定義和測試裝置。FIDL、CML 和領域介面定義會設定可供任意實作項目使用的架構:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.canvas.addlinemetered;

/// A point in 2D space.
type Point = struct {
    x int64;
    y int64;
};

/// A line in 2D space.
alias Line = array<Point, 2>;

/// A bounding box in 2D space. This is the result of "drawing" operations on our canvas, and what
/// the server reports back to the client. These bounds are sufficient to contain all of the
/// lines (inclusive) on a canvas at a given time.
type BoundingBox = struct {
    top_left Point;
    bottom_right Point;
};

/// Manages a single instance of a canvas. Each session of this protocol is responsible for a new
/// canvas.
@discoverable
open protocol Instance {
    /// Add a line to the canvas.
    ///
    /// This method can be considered an improvement over the one-way case from a flow control
    /// perspective, as it is now much more difficult for a well-behaved client to "get ahead" of
    /// the server and overwhelm. This is because the client now waits for each request to be acked
    /// by the server before proceeding. This change represents a trade-off: we get much greater
    /// synchronization of message flow between the client and the server, at the cost of worse
    /// performance at the limit due to the extra wait imposed by each ack.
    flexible AddLine(struct {
        line Line;
    }) -> ();

    /// Update the client with the latest drawing state. The server makes no guarantees about how
    /// often this event occurs - it could occur multiple times per board state, for example.
    flexible -> OnDrawn(BoundingBox);
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.canvas.addlinemetered.Instance" },
    ],
    config: {
        // A script for the client to follow. Entries in the script may take one of two forms: a
        // pair of signed-integer coordinates like "-2,15:4,5", or the string "WAIT". The former
        // calls `AddLine(...)`, while the latter pauses execution until the next `->OnDrawn(...)`
        // event is received.
        //
        // TODO(https://fxbug.dev/42178362): It would absolve individual language implementations of a great
        //   deal of string parsing if we were able to use a vector of `union { Point; WaitEnum}`
        //   here.
        script: {
            type: "vector",
            max_count: 100,
            element: {
                type: "string",
                max_size: 64,
            },
        },
    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.canvas.addlinemetered.Instance" },
    ],
    expose: [
        {
            protocol: "examples.canvas.addlinemetered.Instance",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.canvas.addlinemetered.Instance",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{format_err, Context as _, Error};
use config::Config;
use fidl_examples_canvas_addlinemetered::{InstanceEvent, InstanceMarker, Point};
use fuchsia_component::client::connect_to_protocol;
use futures::TryStreamExt;
use std::{thread, time};

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send Instance requests
    // across the channel.
    let instance = connect_to_protocol::<InstanceMarker>()?;
    println!("Outgoing connection enabled");

    for action in config.script.into_iter() {
        // If the next action in the script is to "WAIT", block until an OnDrawn event is received
        // from the server.
        if action == "WAIT" {
            let mut event_stream = instance.take_event_stream();
            loop {
                match event_stream
                    .try_next()
                    .await
                    .context("Error getting event response from proxy")?
                    .ok_or_else(|| format_err!("Proxy sent no events"))?
                {
                    InstanceEvent::OnDrawn { top_left, bottom_right } => {
                        println!(
                            "OnDrawn event received: top_left: {:?}, bottom_right: {:?}",
                            top_left, bottom_right
                        );
                        break;
                    }
                    InstanceEvent::_UnknownEvent { ordinal, .. } => {
                        println!("Received an unknown event with ordinal {ordinal}");
                    }
                }
            }
            continue;
        }

        // If the action is not a "WAIT", we need to draw a line instead. Parse the string input,
        // making two points out of it.
        let mut points = action
            .split(":")
            .map(|point| {
                let integers = point
                    .split(",")
                    .map(|integer| integer.parse::<i64>().unwrap())
                    .collect::<Vec<i64>>();
                Point { x: integers[0], y: integers[1] }
            })
            .collect::<Vec<Point>>();

        // Assemble a line from the two points.
        let from = points.pop().ok_or_else(|| format_err!("line requires 2 points, but has 0"))?;
        let to = points.pop().ok_or_else(|| format_err!("line requires 2 points, but has 1"))?;
        let line = [from, to];

        // Draw a line to the canvas by calling the server, using the two points we just parsed
        // above as arguments.
        println!("AddLine request sent: {:?}", line);

        // By awaiting on the reply, we prevent the client from sending another request before the
        // server is ready to handle, thereby syncing the flow rate between the two parties over
        // this method.
        instance.add_line(&line).await.context("Error sending request")?;
        println!("AddLine response received");
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fidl::endpoints::RequestStream as _;
use fidl_examples_canvas_addlinemetered::{
    BoundingBox, InstanceRequest, InstanceRequestStream, Point,
};
use fuchsia_async::{MonotonicInstant, Timer};
use fuchsia_component::server::ServiceFs;

use futures::future::join;
use futures::prelude::*;
use std::sync::{Arc, Mutex};

// A struct that stores the two things we care about for this example: the bounding box the lines
// that have been added thus far, and bit to track whether or not there have been changes since the
// last `OnDrawn` event.
#[derive(Debug)]
struct CanvasState {
    // Tracks whether there has been a change since the last send, to prevent redundant updates.
    changed: bool,
    bounding_box: BoundingBox,
}

impl CanvasState {
    /// Handler for the `AddLine` method.
    fn add_line(&mut self, line: [Point; 2]) {
        // Update the bounding box to account for the new lines we've just "added" to the canvas.
        let bounds = &mut self.bounding_box;
        for point in line {
            if point.x < bounds.top_left.x {
                bounds.top_left.x = point.x;
            }
            if point.y > bounds.top_left.y {
                bounds.top_left.y = point.y;
            }
            if point.x > bounds.bottom_right.x {
                bounds.bottom_right.x = point.x;
            }
            if point.y < bounds.bottom_right.y {
                bounds.bottom_right.y = point.y;
            }
        }

        // Mark the state as "dirty", so that an update is sent back to the client on the next tick.
        self.changed = true
    }
}

/// Creates a new instance of the server, paired to a single client across a zircon channel.
async fn run_server(stream: InstanceRequestStream) -> Result<(), Error> {
    // Create a new in-memory state store for the state of the canvas. The store will live for the
    // lifetime of the connection between the server and this particular client.
    let state = Arc::new(Mutex::new(CanvasState {
        changed: true,
        bounding_box: BoundingBox {
            top_left: Point { x: 0, y: 0 },
            bottom_right: Point { x: 0, y: 0 },
        },
    }));

    // Take ownership of the control_handle from the stream, which will allow us to push events from
    // a different async task.
    let control_handle = stream.control_handle();

    // A separate watcher task periodically "draws" the canvas, and notifies the client of the new
    // state. We'll need a cloned reference to the canvas state to be accessible from the new
    // task.
    let state_ref = state.clone();
    let update_sender = || async move {
        loop {
            // Our server sends one update per second.
            Timer::new(MonotonicInstant::after(zx::MonotonicDuration::from_seconds(1))).await;
            let mut state = state_ref.lock().unwrap();
            if !state.changed {
                continue;
            }

            // After acquiring the lock, this is where we would draw the actual lines. Since this is
            // just an example, we'll avoid doing the actual rendering, and simply send the bounding
            // box to the client instead.
            let bounds = state.bounding_box;
            match control_handle.send_on_drawn(&bounds.top_left, &bounds.bottom_right) {
                Ok(_) => println!(
                    "OnDrawn event sent: top_left: {:?}, bottom_right: {:?}",
                    bounds.top_left, bounds.bottom_right
                ),
                Err(_) => return,
            }

            // Reset the change tracker.
            state.changed = false
        }
    };

    // Handle requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    let state_ref = &state;
    let request_handler =
        stream.map(|result| result.context("failed request")).try_for_each(|request| async move {
            // Match based on the method being invoked.
            match request {
                InstanceRequest::AddLine { line, responder } => {
                    println!("AddLine request received: {:?}", line);
                    state_ref.lock().unwrap().add_line(line);

                    // Because this is now a two-way method, we must use the generated `responder`
                    // to send an in this case empty reply back to the client. This is the mechanic
                    // which syncs the flow rate between the client and server on this method,
                    // thereby preventing the client from "flooding" the server with unacknowledged
                    // work.
                    responder.send().context("Error responding")?;
                    println!("AddLine response sent");
                } //
                InstanceRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        });

    // This await does not complete, and thus the function does not return, unless the server errors
    // out. The stream will await indefinitely, thereby creating a long-lived server. Here, we first
    // wait for the updater task to realize the connection has died, then bubble up the error.
    join(request_handler, update_sender()).await.0
}

// A helper enum that allows us to treat a `Instance` service instance as a value.
enum IncomingService {
    Instance(InstanceRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Instance` protocol - this will allow the client to see
    // the server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Instance);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Instance(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.addlinemetered/cpp/fidl.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/component/incoming/cpp/protocol.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <charconv>

#include <examples/fidl/new/canvas/add_line_metered/cpp_natural/client/config.h>

// The |EventHandler| is a derived class that we pass into the |fidl::WireClient| to handle incoming
// events asynchronously.
class EventHandler : public fidl::AsyncEventHandler<examples_canvas_addlinemetered::Instance> {
 public:
  // Handler for |OnDrawn| events sent from the server.
  void OnDrawn(fidl::Event<examples_canvas_addlinemetered::Instance::OnDrawn>& event) override {
    auto top_left = event.top_left();
    auto bottom_right = event.bottom_right();
    FX_LOGS(INFO) << "OnDrawn event received: top_left: Point { x: " << top_left.x()
                  << ", y: " << top_left.y() << " }, bottom_right: Point { x: " << bottom_right.x()
                  << ", y: " << bottom_right.y() << " }";
    loop_.Quit();
  }

  void on_fidl_error(fidl::UnbindInfo error) override { FX_LOGS(ERROR) << error; }

  void handle_unknown_event(
      fidl::UnknownEventMetadata<examples_canvas_addlinemetered::Instance> metadata) override {
    FX_LOGS(WARNING) << "Received an unknown event with ordinal " << metadata.event_ordinal;
  }

  explicit EventHandler(async::Loop& loop) : loop_(loop) {}

 private:
  async::Loop& loop_;
};

// A helper function that takes a coordinate in string form, like "123,-456", and parses it into a
// a struct of the form |{ in64 x; int64 y; }|.
::examples_canvas_addlinemetered::Point ParsePoint(std::string_view input) {
  int64_t x = 0;
  int64_t y = 0;
  size_t index = input.find(',');
  if (index != std::string::npos) {
    std::from_chars(input.data(), input.data() + index, x);
    std::from_chars(input.data() + index + 1, input.data() + input.length(), y);
  }
  return ::examples_canvas_addlinemetered::Point(x, y);
}

// A helper function that takes a coordinate pair in string form, like "1,2:-3,-4", and parses it
// into an array of 2 |Point| structs.
::std::array<::examples_canvas_addlinemetered::Point, 2> ParseLine(const std::string& action) {
  auto input = std::string_view(action);
  size_t index = input.find(':');
  if (index != std::string::npos) {
    return {ParsePoint(input.substr(0, index)), ParsePoint(input.substr(index + 1))};
  }
  return {};
}

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop and dispatcher.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace. This can fail so it's wrapped in a
  // |zx::result| and it must be checked for errors.
  zx::result client_end = component::Connect<examples_canvas_addlinemetered::Instance>();
  if (!client_end.is_ok()) {
    FX_LOGS(ERROR) << "Synchronous error when connecting to the |Instance| protocol: "
                   << client_end.status_string();
    return -1;
  }

  // Create an instance of the event handler.
  EventHandler event_handler(loop);

  // Create an asynchronous client using the newly-established connection.
  fidl::Client client(std::move(*client_end), dispatcher, &event_handler);
  FX_LOGS(INFO) << "Outgoing connection enabled";

  for (const auto& action : conf.script()) {
    // If the next action in the script is to "WAIT", block until an |OnDrawn| event is received
    // from the server.
    if (action == "WAIT") {
      loop.Run();
      loop.ResetQuit();
      continue;
    }

    // Draw a line to the canvas by calling the server, using the two points we just parsed
    // above as arguments.
    auto line = ParseLine(action);
    FX_LOGS(INFO) << "AddLine request sent: [Point { x: " << line[1].x() << ", y: " << line[1].y()
                  << " }, Point { x: " << line[0].x() << ", y: " << line[0].y() << " }]";

    client->AddLine(line).ThenExactlyOnce(
        [&](fidl::Result<examples_canvas_addlinemetered::Instance::AddLine>& result) {
          // Check if the FIDL call succeeded or not.
          if (!result.is_ok()) {
            // Check that our two-way call succeeded, and handle the error appropriately. In the
            // case of this example, there is nothing we can do to recover here, except to log an
            // error and exit the program.
            FX_LOGS(ERROR) << "Could not send AddLine request: "
                           << result.error_value().FormatDescription();
          }
          FX_LOGS(INFO) << "AddLine response received";

          // Quit the loop, thereby handing control back to the outer loop of actions being iterated
          // over.
          loop.Quit();
        });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.addlinemetered/cpp/fidl.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/async/cpp/task.h>
#include <lib/component/outgoing/cpp/outgoing_directory.h>
#include <lib/fidl/cpp/wire/channel.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <src/lib/fxl/macros.h>
#include <src/lib/fxl/memory/weak_ptr.h>

// A struct that stores the two things we care about for this example: the set of lines, and the
// bounding box that contains them.
struct CanvasState {
  // Tracks whether there has been a change since the last send, to prevent redundant updates.
  bool changed = true;
  examples_canvas_addlinemetered::BoundingBox bounding_box;
};

// An implementation of the |Instance| protocol.
class InstanceImpl final : public fidl::Server<examples_canvas_addlinemetered::Instance> {
 public:
  // Bind this implementation to a channel.
  InstanceImpl(async_dispatcher_t* dispatcher,
               fidl::ServerEnd<examples_canvas_addlinemetered::Instance> server_end)
      : binding_(fidl::BindServer(
            dispatcher, std::move(server_end), this,
            [this](InstanceImpl* impl, fidl::UnbindInfo info,
                   fidl::ServerEnd<examples_canvas_addlinemetered::Instance> server_end) {
              if (info.reason() != ::fidl::Reason::kPeerClosedWhileReading) {
                FX_LOGS(ERROR) << "Shutdown unexpectedly";
              }
              delete this;
            })),
        weak_factory_(this) {
    // Start the update timer on startup. Our server sends one update per second
    ScheduleOnDrawnEvent(dispatcher, zx::sec(1));
  }

  void AddLine(AddLineRequest& request, AddLineCompleter::Sync& completer) override {
    auto points = request.line();
    FX_LOGS(INFO) << "AddLine request received: [Point { x: " << points[1].x()
                  << ", y: " << points[1].y() << " }, Point { x: " << points[0].x()
                  << ", y: " << points[0].y() << " }]";

    // Update the bounding box to account for the new line we've just "added" to the canvas.
    auto& bounds = state_.bounding_box;
    for (const auto& point : request.line()) {
      if (point.x() < bounds.top_left().x()) {
        bounds.top_left().x() = point.x();
      }
      if (point.y() > bounds.top_left().y()) {
        bounds.top_left().y() = point.y();
      }
      if (point.x() > bounds.bottom_right().x()) {
        bounds.bottom_right().x() = point.x();
      }
      if (point.y() < bounds.bottom_right().y()) {
        bounds.bottom_right().y() = point.y();
      }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next |OnDrawn|
    // event.
    state_.changed = true;

    // Because this is now a two-way method, we must use the generated |completer| to send an in
    // this case empty reply back to the client. This is the mechanic which syncs the flow rate
    // between the client and server on this method, thereby preventing the client from "flooding"
    // the server with unacknowledged work.
    completer.Reply();
    FX_LOGS(INFO) << "AddLine response sent";
  }

  void handle_unknown_method(
      fidl::UnknownMethodMetadata<examples_canvas_addlinemetered::Instance> metadata,
      fidl::UnknownMethodCompleter::Sync& completer) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << metadata.method_ordinal;
  }

 private:
  // Each scheduled update waits for the allotted amount of time, sends an update if something has
  // changed, and schedules the next update.
  void ScheduleOnDrawnEvent(async_dispatcher_t* dispatcher, zx::duration after) {
    async::PostDelayedTask(
        dispatcher,
        [&, dispatcher, after, weak = weak_factory_.GetWeakPtr()] {
          // Halt execution if the binding has been deallocated already.
          if (!weak) {
            return;
          }

          // Schedule the next update if the binding still exists.
          weak->ScheduleOnDrawnEvent(dispatcher, after);

          // No need to send an update if nothing has changed since the last one.
          if (!weak->state_.changed) {
            return;
          }

          // This is where we would draw the actual lines. Since this is just an example, we'll
          // avoid doing the actual rendering, and simply send the bounding box to the client
          // instead.
          auto result = fidl::SendEvent(binding_)->OnDrawn(state_.bounding_box);
          if (!result.is_ok()) {
            return;
          }

          auto top_left = state_.bounding_box.top_left();
          auto bottom_right = state_.bounding_box.bottom_right();
          FX_LOGS(INFO) << "OnDrawn event sent: top_left: Point { x: " << top_left.x()
                        << ", y: " << top_left.y()
                        << " }, bottom_right: Point { x: " << bottom_right.x()
                        << ", y: " << bottom_right.y() << " }";

          // Reset the change tracker.
          state_.changed = false;
        },
        after);
  }

  fidl::ServerBindingRef<examples_canvas_addlinemetered::Instance> binding_;
  CanvasState state_ = CanvasState{};

  // Generates weak references to this object, which are appropriate to pass into asynchronous
  // callbacks that need to access this object. The references are automatically invalidated
  // if this object is destroyed.
  fxl::WeakPtrFactory<InstanceImpl> weak_factory_;
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component. This
  // directory is where the outgoing FIDL protocols are installed so that they can be provided to
  // other components.
  component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);

  // The `ServeFromStartupInfo()` function sets up the outgoing directory with the startup handle.
  // The startup handle is a handle provided to every component by the system, so that they can
  // serve capabilities (e.g. FIDL protocols) to other components.
  zx::result result = outgoing.ServeFromStartupInfo();
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
    return -1;
  }

  // Register a handler for components trying to connect to
  // |examples.canvas.addlinemetered.Instance|.
  result = outgoing.AddUnmanagedProtocol<examples_canvas_addlinemetered::Instance>(
      [dispatcher](fidl::ServerEnd<examples_canvas_addlinemetered::Instance> server_end) {
        // Create an instance of our InstanceImpl that destroys itself when the connection closes.
        new InstanceImpl(dispatcher, std::move(server_end));
      });
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to add Instance protocol: " << result.status_string();
    return -1;
  }

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

C++ (Wire)

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.addlinemetered/cpp/wire.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/component/incoming/cpp/protocol.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <charconv>

#include <examples/fidl/new/canvas/add_line_metered/cpp_wire/client/config.h>

// The |EventHandler| is a derived class that we pass into the |fidl::WireClient| to handle incoming
// events asynchronously.
class EventHandler : public fidl::WireAsyncEventHandler<examples_canvas_addlinemetered::Instance> {
 public:
  // Handler for |OnDrawn| events sent from the server.
  void OnDrawn(fidl::WireEvent<examples_canvas_addlinemetered::Instance::OnDrawn>* event) override {
    auto top_left = event->top_left;
    auto bottom_right = event->bottom_right;
    FX_LOGS(INFO) << "OnDrawn event received: top_left: Point { x: " << top_left.x
                  << ", y: " << top_left.y << " }, bottom_right: Point { x: " << bottom_right.x
                  << ", y: " << bottom_right.y << " }";
    loop_.Quit();
  }

  void on_fidl_error(fidl::UnbindInfo error) override { FX_LOGS(ERROR) << error; }

  void handle_unknown_event(
      fidl::UnknownEventMetadata<examples_canvas_addlinemetered::Instance> metadata) override {
    FX_LOGS(WARNING) << "Received an unknown event with ordinal " << metadata.event_ordinal;
  }

  explicit EventHandler(async::Loop& loop) : loop_(loop) {}

 private:
  async::Loop& loop_;
};

// A helper function that takes a coordinate in string form, like "123,-456", and parses it into a
// a struct of the form |{ in64 x; int64 y; }|.
::examples_canvas_addlinemetered::wire::Point ParsePoint(std::string_view input) {
  int64_t x = 0;
  int64_t y = 0;
  size_t index = input.find(',');
  if (index != std::string::npos) {
    std::from_chars(input.data(), input.data() + index, x);
    std::from_chars(input.data() + index + 1, input.data() + input.length(), y);
  }
  return ::examples_canvas_addlinemetered::wire::Point{.x = x, .y = y};
}

// A helper function that takes a coordinate pair in string form, like "1,2:-3,-4", and parses it
// into an array of 2 |Point| structs.
::fidl::Array<::examples_canvas_addlinemetered::wire::Point, 2> ParseLine(
    const std::string& action) {
  auto input = std::string_view(action);
  size_t index = input.find(':');
  if (index != std::string::npos) {
    return {ParsePoint(input.substr(0, index)), ParsePoint(input.substr(index + 1))};
  }
  return {};
}

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop and dispatcher.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace. This can fail so it's wrapped in a
  // |zx::result| and it must be checked for errors.
  zx::result client_end = component::Connect<examples_canvas_addlinemetered::Instance>();
  if (!client_end.is_ok()) {
    FX_LOGS(ERROR) << "Synchronous error when connecting to the |Instance| protocol: "
                   << client_end.status_string();
    return -1;
  }

  // Create an instance of the event handler.
  EventHandler event_handler(loop);

  // Create an asynchronous client using the newly-established connection.
  fidl::WireClient client(std::move(*client_end), dispatcher, &event_handler);
  FX_LOGS(INFO) << "Outgoing connection enabled";

  for (const auto& action : conf.script()) {
    // If the next action in the script is to "WAIT", block until an |OnDrawn| event is received
    // from the server.
    if (action == "WAIT") {
      loop.Run();
      loop.ResetQuit();
      continue;
    }

    // Draw a line to the canvas by calling the server, using the two points we just parsed
    // above as arguments.
    auto line = ParseLine(action);
    FX_LOGS(INFO) << "AddLine request sent: [Point { x: " << line[1].x << ", y: " << line[1].y
                  << " }, Point { x: " << line[0].x << ", y: " << line[0].y << " }]";

    client->AddLine(line).ThenExactlyOnce(
        [&](fidl::WireUnownedResult<examples_canvas_addlinemetered::Instance::AddLine>& result) {
          // Check if the FIDL call succeeded or not.
          if (!result.ok()) {
            // Check that our two-way call succeeded, and handle the error appropriately. In the
            // case of this example, there is nothing we can do to recover here, except to log an
            // error and exit the program.
            FX_LOGS(ERROR) << "Could not send AddLine request: " << result.status_string();
          }
          FX_LOGS(INFO) << "AddLine response received";

          // Quit the loop, thereby handing control back to the outer loop of actions being iterated
          // over.
          loop.Quit();
        });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.addlinemetered/cpp/wire.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/async/cpp/task.h>
#include <lib/component/outgoing/cpp/outgoing_directory.h>
#include <lib/fidl/cpp/wire/channel.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <src/lib/fxl/macros.h>
#include <src/lib/fxl/memory/weak_ptr.h>

// A struct that stores the two things we care about for this example: the set of lines, and the
// bounding box that contains them.
struct CanvasState {
  // Tracks whether there has been a change since the last send, to prevent redundant updates.
  bool changed = true;
  examples_canvas_addlinemetered::wire::BoundingBox bounding_box;
};

// An implementation of the |Instance| protocol.
class InstanceImpl final : public fidl::WireServer<examples_canvas_addlinemetered::Instance> {
 public:
  // Bind this implementation to a channel.
  InstanceImpl(async_dispatcher_t* dispatcher,
               fidl::ServerEnd<examples_canvas_addlinemetered::Instance> server_end)
      : binding_(fidl::BindServer(
            dispatcher, std::move(server_end), this,
            [this](InstanceImpl* impl, fidl::UnbindInfo info,
                   fidl::ServerEnd<examples_canvas_addlinemetered::Instance> server_end) {
              if (info.reason() != ::fidl::Reason::kPeerClosedWhileReading) {
                FX_LOGS(ERROR) << "Shutdown unexpectedly";
              }
              delete this;
            })),
        weak_factory_(this) {
    // Start the update timer on startup. Our server sends one update per second
    ScheduleOnDrawnEvent(dispatcher, zx::sec(1));
  }

  void AddLine(AddLineRequestView request, AddLineCompleter::Sync& completer) override {
    auto points = request->line;
    FX_LOGS(INFO) << "AddLine request received: [Point { x: " << points[1].x
                  << ", y: " << points[1].y << " }, Point { x: " << points[0].x
                  << ", y: " << points[0].y << " }]";

    // Update the bounding box to account for the new line we've just "added" to the canvas.
    auto& bounds = state_.bounding_box;
    for (const auto& point : request->line) {
      if (point.x < bounds.top_left.x) {
        bounds.top_left.x = point.x;
      }
      if (point.y > bounds.top_left.y) {
        bounds.top_left.y = point.y;
      }
      if (point.x > bounds.bottom_right.x) {
        bounds.bottom_right.x = point.x;
      }
      if (point.y < bounds.bottom_right.y) {
        bounds.bottom_right.y = point.y;
      }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next |OnDrawn|
    // event.
    state_.changed = true;

    // Because this is now a two-way method, we must use the generated |completer| to send an in
    // this case empty reply back to the client. This is the mechanic which syncs the flow rate
    // between the client and server on this method, thereby preventing the client from "flooding"
    // the server with unacknowledged work.
    completer.Reply();
    FX_LOGS(INFO) << "AddLine response sent";
  }

  void handle_unknown_method(
      fidl::UnknownMethodMetadata<examples_canvas_addlinemetered::Instance> metadata,
      fidl::UnknownMethodCompleter::Sync& completer) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << metadata.method_ordinal;
  }

 private:
  // Each scheduled update waits for the allotted amount of time, sends an update if something has
  // changed, and schedules the next update.
  void ScheduleOnDrawnEvent(async_dispatcher_t* dispatcher, zx::duration after) {
    async::PostDelayedTask(
        dispatcher,
        [&, dispatcher, after, weak = weak_factory_.GetWeakPtr()] {
          // Halt execution if the binding has been deallocated already.
          if (!weak) {
            return;
          }

          // Schedule the next update if the binding still exists.
          weak->ScheduleOnDrawnEvent(dispatcher, after);

          // No need to send an update if nothing has changed since the last one.
          if (!weak->state_.changed) {
            return;
          }

          // This is where we would draw the actual lines. Since this is just an example, we'll
          // avoid doing the actual rendering, and simply send the bounding box to the client
          // instead.
          auto top_left = weak->state_.bounding_box.top_left;
          auto bottom_right = weak->state_.bounding_box.bottom_right;
          fidl::Status status =
              fidl::WireSendEvent(weak->binding_)->OnDrawn(top_left, bottom_right);
          if (!status.ok()) {
            return;
          }
          FX_LOGS(INFO) << "OnDrawn event sent: top_left: Point { x: " << top_left.x
                        << ", y: " << top_left.y
                        << " }, bottom_right: Point { x: " << bottom_right.x
                        << ", y: " << bottom_right.y << " }";

          // Reset the change tracker.
          weak->state_.changed = false;
        },
        after);
  }

  fidl::ServerBindingRef<examples_canvas_addlinemetered::Instance> binding_;
  CanvasState state_ = CanvasState{};

  // Generates weak references to this object, which are appropriate to pass into asynchronous
  // callbacks that need to access this object. The references are automatically invalidated
  // if this object is destroyed.
  fxl::WeakPtrFactory<InstanceImpl> weak_factory_;
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component. This
  // directory is where the outgoing FIDL protocols are installed so that they can be provided to
  // other components.
  component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);

  // The `ServeFromStartupInfo()` function sets up the outgoing directory with the startup handle.
  // The startup handle is a handle provided to every component by the system, so that they can
  // serve capabilities (e.g. FIDL protocols) to other components.
  zx::result result = outgoing.ServeFromStartupInfo();
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
    return -1;
  }

  // Register a handler for components trying to connect to
  // |examples.canvas.addlinemetered.Instance|.
  result = outgoing.AddUnmanagedProtocol<examples_canvas_addlinemetered::Instance>(
      [dispatcher](fidl::ServerEnd<examples_canvas_addlinemetered::Instance> server_end) {
        // Create an instance of our InstanceImpl that destroys itself when the connection closes.
        new InstanceImpl(dispatcher, std::move(server_end));
      });
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to add Instance protocol: " << result.status_string();
    return -1;
  }

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

HLCPP

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/async-loop/cpp/loop.h>
#include <lib/sys/cpp/component_context.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <charconv>

#include <examples/canvas/addlinemetered/cpp/fidl.h>
#include <examples/fidl/new/canvas/add_line_metered/hlcpp/client/config.h>

#include "lib/fpromise/result.h"

// A helper function that takes a coordinate in string form, like "123,-456", and parses it into a
// a struct of the form |{ in64 x; int64 y; }|.
::examples::canvas::addlinemetered::Point ParsePoint(std::string_view input) {
  int64_t x = 0;
  int64_t y = 0;
  size_t index = input.find(',');
  if (index != std::string::npos) {
    std::from_chars(input.data(), input.data() + index, x);
    std::from_chars(input.data() + index + 1, input.data() + input.length(), y);
  }
  return ::examples::canvas::addlinemetered::Point{.x = x, .y = y};
}

// A helper function that takes a coordinate pair in string form, like "1,2:-3,-4", and parses it
// into an array of 2 |Point| structs.
::std::array<::examples::canvas::addlinemetered::Point, 2> ParseLine(const std::string& action) {
  auto input = std::string_view(action);
  size_t index = input.find(':');
  if (index != std::string::npos) {
    return {ParsePoint(input.substr(0, index)), ParsePoint(input.substr(index + 1))};
  }
  return {};
}

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace, then create an asynchronous client
  // using the newly-established connection.
  examples::canvas::addlinemetered::InstancePtr instance_proxy;
  auto context = sys::ComponentContext::Create();
  context->svc()->Connect(instance_proxy.NewRequest(dispatcher));
  FX_LOGS(INFO) << "Outgoing connection enabled";

  instance_proxy.set_error_handler([&loop](zx_status_t status) {
    FX_LOGS(ERROR) << "Shutdown unexpectedly";
    loop.Quit();
  });

  // Provide a lambda to handle incoming |OnDrawn| events asynchronously.
  instance_proxy.events().OnDrawn = [&loop](
                                        ::examples::canvas::addlinemetered::Point top_left,
                                        ::examples::canvas::addlinemetered::Point bottom_right) {
    FX_LOGS(INFO) << "OnDrawn event received: top_left: Point { x: " << top_left.x
                  << ", y: " << top_left.y << " }, bottom_right: Point { x: " << bottom_right.x
                  << ", y: " << bottom_right.y << " }";
    loop.Quit();
  };

  instance_proxy.events().handle_unknown_event = [](uint64_t ordinal) {
    FX_LOGS(WARNING) << "Received an unknown event with ordinal " << ordinal;
  };

  for (const auto& action : conf.script()) {
    // If the next action in the script is to "WAIT", block until an |OnDrawn| event is received
    // from the server.
    if (action == "WAIT") {
      loop.Run();
      loop.ResetQuit();
      continue;
    }

    // Draw a line to the canvas by calling the server, using the two points we just parsed
    // above as arguments.
    auto line = ParseLine(action);
    FX_LOGS(INFO) << "AddLine request sent: [Point { x: " << line[1].x << ", y: " << line[1].y
                  << " }, Point { x: " << line[0].x << ", y: " << line[0].y << " }]";

    instance_proxy->AddLine(line, [&](fpromise::result<void, fidl::FrameworkErr> result) {
      if (result.is_error()) {
        // Check that our flexible two-way call was known to the server and handle the case of an
        // unknown method appropriately. In the case of this example, there is nothing we can do to
        // recover here, except to log an error and exit the program.
        FX_LOGS(ERROR) << "Server does not implement AddLine";
      }
      FX_LOGS(INFO) << "AddLine response received";

      // Quit the loop, thereby handing control back to the outer loop of actions being iterated
      // over.
      loop.Quit();
    });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/async-loop/cpp/loop.h>
#include <lib/async-loop/default.h>
#include <lib/async/cpp/task.h>
#include <lib/fidl/cpp/binding.h>
#include <lib/sys/cpp/component_context.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <examples/canvas/addlinemetered/cpp/fidl.h>
#include <src/lib/fxl/macros.h>
#include <src/lib/fxl/memory/weak_ptr.h>

// A struct that stores the two things we care about for this example: the set of lines, and the
// bounding box that contains them.
struct CanvasState {
  // Tracks whether there has been a change since the last send, to prevent redundant updates.
  bool changed = true;
  examples::canvas::addlinemetered::BoundingBox bounding_box;
};

// An implementation of the |Instance| protocol.
class InstanceImpl final : public examples::canvas::addlinemetered::Instance {
 public:
  // Bind this implementation to an |InterfaceRequest|.
  InstanceImpl(async_dispatcher_t* dispatcher,
               fidl::InterfaceRequest<examples::canvas::addlinemetered::Instance> request)
      : binding_(fidl::Binding<examples::canvas::addlinemetered::Instance>(this)),
        weak_factory_(this) {
    binding_.Bind(std::move(request), dispatcher);

    // Gracefully handle abrupt shutdowns.
    binding_.set_error_handler([this](zx_status_t status) mutable {
      if (status != ZX_ERR_PEER_CLOSED) {
        FX_LOGS(ERROR) << "Shutdown unexpectedly";
      }
      delete this;
    });

    // Start the update timer on startup. Our server sends one update per second.
    ScheduleOnDrawnEvent(dispatcher, zx::sec(1));
  }

  void AddLine(::std::array<::examples::canvas::addlinemetered::Point, 2> line,
               AddLineCallback callback) override {
    FX_LOGS(INFO) << "AddLine request received: [Point { x: " << line[1].x << ", y: " << line[1].y
                  << " }, Point { x: " << line[0].x << ", y: " << line[0].y << " }]";

    // Update the bounding box to account for the new line we've just "added" to the canvas.
    auto& bounds = state_.bounding_box;
    for (const auto& point : line) {
      if (point.x < bounds.top_left.x) {
        bounds.top_left.x = point.x;
      }
      if (point.y > bounds.top_left.y) {
        bounds.top_left.y = point.y;
      }
      if (point.x > bounds.bottom_right.x) {
        bounds.bottom_right.x = point.x;
      }
      if (point.y < bounds.bottom_right.y) {
        bounds.bottom_right.y = point.y;
      }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next |OnDrawn|
    // event.
    state_.changed = true;

    // Because this is now a two-way method, we must use the generated |callback| to send an in
    // this case empty reply back to the client. This is the mechanic which syncs the flow rate
    // between the client and server on this method, thereby preventing the client from "flooding"
    // the server with unacknowledged work.
    callback(fpromise::ok());
    FX_LOGS(INFO) << "AddLine response sent";
  }

  void handle_unknown_method(uint64_t ordinal, bool method_has_response) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << ordinal;
  }

 private:
  // Each scheduled update waits for the allotted amount of time, sends an update if something has
  // changed, and schedules the next update.
  void ScheduleOnDrawnEvent(async_dispatcher_t* dispatcher, zx::duration after) {
    async::PostDelayedTask(
        dispatcher,
        [&, dispatcher, after, weak = weak_factory_.GetWeakPtr()] {
          // Halt execution if the binding has been deallocated already.
          if (!weak) {
            return;
          }

          // Schedule the next update if the binding still exists.
          weak->ScheduleOnDrawnEvent(dispatcher, after);

          // No need to send an update if nothing has changed since the last one.
          if (!weak->state_.changed) {
            return;
          }

          // This is where we would draw the actual lines. Since this is just an example, we'll
          // avoid doing the actual rendering, and simply send the bounding box to the client
          // instead.
          auto top_left = state_.bounding_box.top_left;
          auto bottom_right = state_.bounding_box.bottom_right;
          binding_.events().OnDrawn(top_left, bottom_right);
          FX_LOGS(INFO) << "OnDrawn event sent: top_left: Point { x: " << top_left.x
                        << ", y: " << top_left.y
                        << " }, bottom_right: Point { x: " << bottom_right.x
                        << ", y: " << bottom_right.y << " }";

          // Reset the change tracker.
          state_.changed = false;
        },
        after);
  }

  fidl::Binding<examples::canvas::addlinemetered::Instance> binding_;
  CanvasState state_ = CanvasState{};

  // Generates weak references to this object, which are appropriate to pass into asynchronous
  // callbacks that need to access this object. The references are automatically invalidated
  // if this object is destroyed.
  fxl::WeakPtrFactory<InstanceImpl> weak_factory_;
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  //
  // Note that unlike the new C++ bindings, HLCPP bindings rely on the async loop being attached to
  // the current thread via the |kAsyncLoopConfigAttachToCurrentThread| configuration.
  async::Loop loop(&kAsyncLoopConfigAttachToCurrentThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component.
  // This directory is where the outgoing FIDL protocols are installed so that they can be
  // provided to other components.
  auto context = sys::ComponentContext::CreateAndServeOutgoingDirectory();

  // Register a handler for components trying to connect to
  // |examples.canvas.addlinemetered.Instance|.
  context->outgoing()->AddPublicService(
      fidl::InterfaceRequestHandler<examples::canvas::addlinemetered::Instance>(
          [dispatcher](fidl::InterfaceRequest<examples::canvas::addlinemetered::Instance> request) {
            // Create an instance of our |InstanceImpl| that destroys itself when the connection
            // closes.
            new InstanceImpl(dispatcher, std::move(request));
          }));

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

別名

FIDL 食譜:別名

alias 是 FIDL 宣告,可為現有類型指派新名稱。這麼做有幾個好處:

  • 使用 alias 可確保別名類型代表的概念有單一可靠資料來源。
  • 它提供命名方式,特別是受限制的類型。
  • 對現在已建立別名的型別的不同用途,可能會連結為相同概念的例項。

請注意,別名目前不會傳遞至產生的繫結程式碼。換句話說,指派給 alias 宣告的名稱,絕不會在產生的 FIDL 程式碼中顯示為宣告名稱。

在本範例中,為 Key 新增 alias 可避免重複使用自訂名稱,同時向讀者清楚說明 Item 類型上的 key 值和 ReadItem 要求結構體中使用的 key 是刻意重複,而非巧合。

推理

原先的唯寫鍵/值儲存庫現在已擴充,可讀取儲存庫中的項目。

實作

套用至 FIDL 和 CML 定義的變更如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.addreaditem;

// Aliases for the key and value. Using aliases helps increase the readability of FIDL files and
// reduces likelihood of errors due to differing constraints.
alias Key = string:128;
alias Value = vector<byte>:64000;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key Key;
    value Value;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// An enumeration of things that may go wrong when trying to read a value out of our store.
type ReadError = flexible enum {
    UNKNOWN = 0;
    NOT_FOUND = 1;
};

/// A very basic key-value store - so basic, in fact, that one may only write to it, never read!
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;

    /// Reads an item from the store.
    flexible ReadItem(struct {
        key Key;
    }) -> (Item) error ReadError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.addreaditem.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        read_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.addreaditem.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.addreaditem.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.addreaditem.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

所有語言的用戶端和伺服器實作方式也都會變更:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use config::Config;
use fidl_examples_keyvaluestore_addreaditem::{Item, StoreMarker};
use fuchsia_component::client::connect_to_protocol;
use std::{str, thread, time};

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        match store.write_item(&Item { key: key, value: value.into_bytes() }).await? {
            Ok(_) => println!("WriteItem Success"),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // The structured config for this client contains `read_items`, a vector of strings, each of
    // which is meant to be read from the key-value store. We iterate over these keys, attempting to
    // read them in turn.
    for key in config.read_items.into_iter() {
        let res = store.read_item(key.as_str()).await;
        match res.unwrap() {
            Ok(val) => {
                println!("ReadItem Success: key: {}, value: {}", key, str::from_utf8(&val.1)?)
            }
            Err(err) => println!("ReadItem Error: {}", err.into_primitive()),
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    fidl_examples_keyvaluestore_addreaditem::{
        Item, ReadError, StoreRequest, StoreRequestStream, WriteError,
    },
    fuchsia_component::server::ServiceFs,
    futures::prelude::*,
    lazy_static::lazy_static,
    regex::Regex,
    std::cell::RefCell,
    std::collections::hash_map::Entry,
    std::collections::HashMap,
};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z][A-Za-z0-9_\./]{2,62}[A-Za-z0-9]$")
            .expect("Key validation regex failed to compile");
}

/// Handler for the `WriteItem` method.
fn write_item(store: &mut HashMap<String, Vec<u8>>, attempt: Item) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Validate the value.
    if attempt.value.is_empty() {
        println!("Write error: INVALID_VALUE, For key: {}", attempt.key);
        return Err(WriteError::InvalidValue);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote value at key: {}", entry.key());
            entry.insert(attempt.value);
            Ok(())
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, Vec<u8>>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.borrow_mut(), attempt))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::ReadItem { key, responder } => {
                    println!("ReadItem request received");

                    // Read the item from the store, returning the appropriate error if it could not be found.
                    responder
                        .send(match store.borrow().get(&key) {
                            Some(found) => {
                                println!("Read value at key: {}", key);
                                Ok((&key, found))
                            }
                            None => {
                                println!("Read error: NOT_FOUND, For key: {}", key);
                                Err(ReadError::NotFound)
                            }
                        })
                        .context("error sending reply")?;
                    println!("ReadItem response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

匿名類型

FIDL 食譜:匿名型別

匿名類型是指定義與使用方式位於同一行,而非位於名為 type 的獨立宣告中的類型。使用匿名類型有兩個好處。首先,這可避免命名空間過度混淆,讓 FIDL 作者不必為只使用一次的類型命名。其次,由於無法透過名稱識別類型,因此可防止類型透過 using 宣告匯入至其他 FIDL 程式庫。

在這個變化版本中,我們允許鍵/值存放區將其他鍵/值存放區做為成員。簡而言之,我們會將其轉換為樹狀結構。我們會將 value 的原始定義替換為使用兩個成員 union 的定義:一個變化版本會使用與先前相同的 vector<byte> 類型儲存葉結點,另一個則會以其他巢狀儲存庫的形式儲存分支節點。

推理

這裡我們會看到幾種 optionality 的用法,我們可以宣告可能存在或不存在的型別。FIDL 中的選用性有三種:

  • 具有此類型一律會在網路上離線儲存,因此具有內建方式,可透過空值封套描述「缺席」。為這些類型啟用選用性不會影響所包含訊息的線路形狀,只會變更哪些值適用於該特定類型。您可以透過新增 :optional 限制,將 unionvector<T>client_endserver_endzx.Handle 類型設為選用。將 value union 設為選用項目後,我們就能以缺少 value 的形式,引入標準的「空值」項目。這表示空白的 bytes 和缺少/空白的 store 屬性是無效的值。
  • 與上述類型不同,struct 版面配置沒有可儲存空值標頭的額外空間。因此,您必須將其包裝在信封中,以便變更所附帶訊息的線上傳輸形狀。為確保這個線路修改效果易於解讀,Item struct 類型必須套用 box<T> 類型範本。
  • 最後,table 版面配置一律為選用。缺少的 table 只是沒有任何成員集。

樹狀圖是自然的自我參照資料結構:樹狀圖中的任何節點都可能包含純資料的葉節點 (在本例中為字串),或包含更多節點的子樹狀圖。這需要遞迴:Item 的定義現在會遞迴地依附自身!在 FIDL 中表示遞迴類型可能有點棘手,尤其是因為目前的支援有點受限。只要在透過自參照建立的循環中,至少有一個選用型別,我們就能支援這類型別。舉例來說,我們在此將 items struct 成員定義為 box<Item>,藉此中斷包含循環。

這些變更也大量使用匿名類型,也就是在使用點內嵌宣告而非命名的類型,以及頂層 type 宣告。根據預設,產生的語言繫結中匿名類型的名稱會取自其本機內容。舉例來說,新推出的 flexible union 會採用其擁有者成員的名稱 Value,新推出的 struct 會變成 Store,以此類推。由於這項啟發法的使用可能會導致衝突,因此 FIDL 提供逃逸處理程序,允許作者手動覆寫匿名類型的產生名稱。這項作業是透過 @generated_name 屬性完成,可讓使用者變更後端產生的名稱。我們可以在這裡使用一個,將原本的 Store 類型重新命名為 NestedStore,以免與使用相同名稱的 protocol 宣告發生名稱衝突。

實作

FIDL、CML 和領域介面定義的修改如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.supporttrees;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value strict union {
        // Keep the original `bytes` as one of the options in the new union. All leaf nodes in the
        // tree must be `bytes`, or absent unions (representing empty). Empty byte arrays are
        // disallowed.
        1: bytes vector<byte>:64000;

        // Allows a store within a store, thereby turning our flat key-value store into a tree
        // thereof. Note the use of `@generated_name` to prevent a type-name collision with the
        // `Store` protocol below, and the use of `box<T>` to ensure that there is a break in the
        // chain of recursion, thereby allowing `Item` to include itself in its own definition.
        //
        // This is a table so that added fields, like for example a `hash`, can be easily added in
        // the future.
        2: store @generated_name("nested_store") table {
            1: items vector<box<Item>>;
        };
    }:optional;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// A very basic key-value store.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.supporttrees.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A newline separated list nested entries. The first line should be the key
        // for the nested store, and each subsequent entry should be a pointer to a text file
        // containing the string value. The name of that text file (without the `.txt` suffix) will
        // serve as the entries key.
        write_nested: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A list of keys, all of which will be populated as null entries.
        write_null: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.supporttrees.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.supporttrees.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.supporttrees.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    config::Config,
    fidl_examples_keyvaluestore_supporttrees::{Item, NestedStore, StoreMarker, Value},
    fuchsia_component::client::connect_to_protocol,
    std::{thread, time},
};

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        let res = store
            .write_item(&Item {
                key: key.clone(),
                value: Some(Box::new(Value::Bytes(value.into_bytes()))),
            })
            .await;
        match res? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // Add nested entries to the key-value store as well. The entries are strings, where the first
    // line is the key of the entry, and each subsequent entry should be a pointer to a text file
    // containing the string value. The name of that text file (without the `.txt` suffix) will
    // serve as the entries key.
    for spec in config.write_nested.into_iter() {
        let mut items = vec![];
        let mut nested_store = NestedStore::default();
        let mut lines = spec.split("\n");
        let key = lines.next().unwrap();

        // For each entry, make a new entry in the `NestedStore` being built.
        for entry in lines {
            let path = format!("/pkg/data/{}.txt", entry);
            let contents = std::fs::read_to_string(path.clone())
                .with_context(|| format!("Failed to load {path}"))?;
            items.push(Some(Box::new(Item {
                key: entry.to_string(),
                value: Some(Box::new(Value::Bytes(contents.into()))),
            })));
        }
        nested_store.items = Some(items);

        // Send the `NestedStore`, represented as a vector of values.
        let res = store
            .write_item(&Item {
                key: key.to_string(),
                value: Some(Box::new(Value::Store(nested_store))),
            })
            .await;
        match res? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // Each entry in this list is a null value in the store.
    for key in config.write_null.into_iter() {
        match store.write_item(&Item { key: key.to_string(), value: None }).await? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Note: For the clarity of this example, allow code to be unused.
#![allow(dead_code)]

use {
    anyhow::{Context as _, Error},
    fidl_examples_keyvaluestore_supporttrees::{
        Item, StoreRequest, StoreRequestStream, Value, WriteError,
    },
    fuchsia_component::server::ServiceFs,
    futures::prelude::*,
    lazy_static::lazy_static,
    regex::Regex,
    std::cell::RefCell,
    std::collections::hash_map::Entry,
    std::collections::HashMap,
    std::str::from_utf8,
};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

// A representation of a key-value store that can contain an arbitrarily deep nesting of other
// key-value stores.
#[allow(clippy::box_collection, reason = "mass allow for https://fxbug.dev/381896734")]
enum StoreNode {
    Leaf(Option<Vec<u8>>),
    Branch(Box<HashMap<String, StoreNode>>),
}

/// Recursive item writer, which takes a `StoreNode` that may not necessarily be the root node, and
/// writes an entry to it.
fn write_item(
    store: &mut HashMap<String, StoreNode>,
    attempt: Item,
    path: &str,
) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            let key = format!("{}{}", &path, entry.key());
            match attempt.value {
                // Null entries are allowed.
                None => {
                    println!("Wrote value: NONE at key: {}", key);
                    entry.insert(StoreNode::Leaf(None));
                }
                Some(value) => match *value {
                    // If this is a nested store, recursively make a new store to insert at this
                    // position.
                    Value::Store(entry_list) => {
                        // Validate the value - absent stores, items lists with no children, or any
                        // of the elements within that list being empty boxes, are all not allowed.
                        if entry_list.items.is_some() {
                            let items = entry_list.items.unwrap();
                            if !items.is_empty() && items.iter().all(|i| i.is_some()) {
                                let nested_path = format!("{}/", key);
                                let mut nested_store = HashMap::<String, StoreNode>::new();
                                for item in items.into_iter() {
                                    write_item(&mut nested_store, *item.unwrap(), &nested_path)?;
                                }

                                println!("Created branch at key: {}", key);
                                entry.insert(StoreNode::Branch(Box::new(nested_store)));
                                return Ok(());
                            }
                        }

                        println!("Write error: INVALID_VALUE, For key: {}", key);
                        return Err(WriteError::InvalidValue);
                    }

                    // This is a simple leaf node on this branch.
                    Value::Bytes(value) => {
                        // Validate the value.
                        if value.is_empty() {
                            println!("Write error: INVALID_VALUE, For key: {}", key);
                            return Err(WriteError::InvalidValue);
                        }

                        println!("Wrote key: {}, value: {:?}", key, from_utf8(&value).unwrap());
                        entry.insert(StoreNode::Leaf(Some(value)));
                    }
                },
            }
            Ok(())
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, StoreNode>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.borrow_mut(), attempt, ""))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

位元

FIDL 食譜:位元

bits 類型是 FIDL 用來表示位元陣列的方式。這個方法用於需要一組布林值標記的情況。bits 陣列通常會「覆蓋」底層子類型,以便控制線路上的位元寬度。

推理

鍵/值儲存庫基準範例的實作方式是個不錯的起點,但其中一個主要缺點是資料會儲存為原始位元組。FIDL 是一種具有豐富型別的語言。強制將 UTF-8 字串等資料儲存為未指定類型的位元組陣列,會讓 *.fidl 檔案的讀者和使用產生繫結的程式設計師無法取得這類寶貴的類型資訊。

實作

這項變更的主要目標,是將基準案例的 vector<byte> 類型 value 成員,替換為可儲存多種可能類型的 union。事實上,隨著這項變更,FIDL 的類型也提供良好的調查結果:

  • 所有 FIDL 內建的純量類型都會用於 Value union 中的變數:booluint8uint16uint32uint64int8int16int32int64float32float64 (也稱為 FIDL 的原始類型),以及 string
  • 這個 union 也使用了 FIDL 內建的 array<T, N>vector<T> 類型範本。
  • 這個範例至少會使用一次 FIDL 的所有類型版面配置,也就是 bitsenumtableunionstruct

WriteItem 所使用的要求和回應酬載也已從 struct 變更為分別為命名的 table 和內嵌的 flexible union。事實上,這三種版面配置都可以用於要求/回應酬載。後兩者分別稱為表格酬載和 *聯合體酬載,在所有情況下皆為首選,但在對訊息大小最敏感的情況下除外。這是因為日後要以二進位相容方式擴充這些類別,會比較容易。

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.usegenericvalues;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value Value;
};

// Because the `Value` must be used both in the request and the response, we give it its own named
// type. The type is a `union` of all possible data types that we take as values, and is marked
// `flexible` to allow for the easy addition of new data types in the future.
type Value = flexible union {
    // Keep the original `bytes` as one of the options in the new union.
    1: bytes vector<byte>:64000;

    // A `string` is very similar to `vector<byte>` on the wire, with the extra constraint that
    // it enforces that it enforces that the byte vector in question is valid UTF-8.
    2: string string:64000;

    // All of FIDL's primitive types.
    3: bool bool;
    4: uint8 uint8;
    5: int8 int8;
    6: uint16 uint16;
    7: int16 int16;
    8: uint32 uint32;
    9: int32 int32;
    10: float32 float32;
    11: uint64 uint64;
    12: int64 int64;
    13: float64 float64;

    // FIDL does not natively support 128-bit integer types, so we have to define our own
    // representations.
    14: uint128 array<uint64, 2>;
};

// Because we now supoprt a richer range of types as values in our store, it is helpful to use a
// `flexible`, and therefore evolvable, `bits` type to store write options.
type WriteOptions = flexible bits : uint8 {
    // This flag allows us to overwrite existing data when there is a collision, rather than failing
    // with an `WriteError.ALREADY_EXISTS`.
    OVERWRITE = 0b1;
    // This flag allows us to concatenate to existing data when there is a collision, rather than
    // failing with an `WriteError.ALREADY_EXISTS`. "Concatenation" means addition for the numeric
    // variants and appending to the `bytes`/`string` variants. If no existing data can be found, we
    // "concatenate" to default values of zero and an empty vector, respectively. Attempting to
    // concatenate to an existing variant of a different type will return a
    // `WriteError.INVALID_VALUE` error.
    CONCAT = 0b10;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// A very basic key-value store.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    ///
    /// Since the value stored in the key-value store can now be different from the input (if the
    /// `WriteOptions.CONCAT` flag is set), we need to return the resulting `Value` to the
    /// requester.
    ///
    /// We use an (anonymous) `table` and a (named) `flexible union` as the request and response
    /// payload, respectively, to allow for easier future evolution. Both of these types are
    /// `flexible`, meaning that adding or removing members is binary-compatible. This makes them
    /// much easier to evolve that the `struct` types that were previously used, which cannot be
    /// changed after release without breaking ABI.
    flexible WriteItem(table {
        1: attempt Item;
        2: options WriteOptions;
    }) -> (Value) error WriteError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.usegenericvalues.Store" },
    ],
    config: {
        // A vector of values for every easily representible type in our key-value store. For
        // brevity's sake, the 8, 16, and 32 bit integer types and booleans are omitted.
        //
        // TODO(https://fxbug.dev/42178362): It would absolve individual language implementations of a great
        //   deal of string parsing if we were able to use all FIDL constructs directly here. In
        //   particular, floats and nested types are very difficult to represent, and have been
        //   excluded from this example for the time being.
        set_concat_option: { type: "bool" },
        set_overwrite_option: { type: "bool" },
        write_bytes: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },
        write_strings: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },
        write_uint64s: {
            type: "vector",
            max_count: 16,
            element: { type: "uint64" },
        },
        write_int64s: {
            type: "vector",
            max_count: 16,
            element: { type: "int64" },
        },

        // Note: due to the limitation of structured config not allowing vectors nested in vectors,
        // we only set the lower half of the uint128 for simplicity's sake.
        write_uint128s: {
            type: "vector",
            max_count: 16,
            element: { type: "uint64" },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.usegenericvalues.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.usegenericvalues.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.usegenericvalues.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    config::Config,
    fidl_examples_keyvaluestore_usegenericvalues::{
        Item, StoreMarker, StoreProxy, StoreWriteItemRequest, Value, WriteOptions,
    },
    fuchsia_component::client::connect_to_protocol,
    std::{thread, time},
};

// A helper function to sequentially write a single item to the key-value store and print a log when
// successful.
async fn write_next_item(
    store: &StoreProxy,
    key: &str,
    value: Value,
    options: WriteOptions,
) -> Result<(), Error> {
    // Create an empty request payload using `::default()`.
    let mut req = StoreWriteItemRequest::default();
    req.options = Some(options);

    // Fill in the `Item` we will be attempting to write.
    println!("WriteItem request sent: key: {}, value: {:?}", &key, &value);
    req.attempt = Some(Item { key: key.to_string(), value: value });

    // Send and async `WriteItem` request to the server.
    match store.write_item(&req).await.context("Error sending request")? {
        Ok(value) => println!("WriteItem response received: {:?}", &value),
        Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
    }
    Ok(())
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // All of our requests will have the same bitflags set. Pull these settings from the config.
    let mut options = WriteOptions::empty();
    options.set(WriteOptions::OVERWRITE, config.set_overwrite_option);
    options.set(WriteOptions::CONCAT, config.set_concat_option);

    // The structured config provides one input for most data types that can be stored in the data
    // store. Iterate through those inputs in the order we see them in the FIDL file.
    //
    // Note that FIDL unions are rendered as enums in Rust; for example, the `Value` union has now
    // become a `Value` Rust enum, with each member taking exactly one argument.
    for value in config.write_bytes.into_iter() {
        write_next_item(&store, "bytes", Value::Bytes(value.into()), options).await?;
    }
    for value in config.write_strings.into_iter() {
        write_next_item(&store, "string", Value::String(value), options).await?;
    }
    for value in config.write_uint64s.into_iter() {
        write_next_item(&store, "uint64", Value::Uint64(value), options).await?;
    }
    for value in config.write_int64s.into_iter() {
        write_next_item(&store, "int64", Value::Int64(value), options).await?;
    }
    for value in config.write_uint128s.into_iter() {
        write_next_item(&store, "uint128", Value::Uint128([0, value]), options).await?;
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fuchsia_component::server::ServiceFs;
use futures::prelude::*;
use lazy_static::lazy_static;
use regex::Regex;
use std::cell::RefCell;
use std::collections::hash_map::Entry;
use std::collections::HashMap;

use fidl_examples_keyvaluestore_usegenericvalues::{
    Item, StoreRequest, StoreRequestStream, Value, WriteError, WriteOptions,
};
use std::collections::hash_map::OccupiedEntry;
use std::ops::Add;

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

/// Sums any numeric type.
fn sum<T: Add + Add<Output = T> + Copy>(operands: [T; 2]) -> T {
    operands[0] + operands[1]
}

/// Clones and inserts an entry, so that the original (now concatenated) copy may be returned in the
/// response.
fn write(inserting: Value, mut entry: OccupiedEntry<'_, String, Value>) -> Value {
    entry.insert(inserting.clone());
    println!("Wrote key: {}, value: {:?}", entry.key(), &inserting);
    inserting
}

/// Handler for the `WriteItem` method.
fn write_item(
    store: &mut HashMap<String, Value>,
    attempt: Item,
    options: &WriteOptions,
) -> Result<Value, WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY for key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            // The `CONCAT` flag supersedes the `OVERWRITE` flag, so check it first.
            if options.contains(WriteOptions::CONCAT) {
                match entry.get() {
                    Value::Bytes(old) => {
                        if let Value::Bytes(new) = attempt.value {
                            let mut combined = old.clone();
                            combined.extend(new);
                            return Ok(write(Value::Bytes(combined), entry));
                        }
                    }
                    Value::String(old) => {
                        if let Value::String(new) = attempt.value {
                            return Ok(write(Value::String(format!("{}{}", old, &new)), entry));
                        }
                    }
                    Value::Uint64(old) => {
                        if let Value::Uint64(new) = attempt.value {
                            return Ok(write(Value::Uint64(sum([*old, new])), entry));
                        }
                    }
                    Value::Int64(old) => {
                        if let Value::Int64(new) = attempt.value {
                            return Ok(write(Value::Int64(sum([*old, new])), entry));
                        }
                    }
                    // Note: only works on the uint64 range in practice.
                    Value::Uint128(old) => {
                        if let Value::Uint128(new) = attempt.value {
                            return Ok(write(Value::Uint128([0, sum([old[1], new[1]])]), entry));
                        }
                    }
                    _ => {
                        panic!("actively unsupported type!")
                    }
                }

                // Only reachable if the type of the would be concatenated value did not match the
                // value already occupying this entry.
                println!("Write error: INVALID_VALUE for key: {}", entry.key());
                return Err(WriteError::InvalidValue);
            }

            // If we're not doing CONCAT, check for OVERWRITE next.
            if options.contains(WriteOptions::OVERWRITE) {
                return Ok(write(attempt.value, entry));
            }

            println!("Write error: ALREADY_EXISTS for key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote key: {}, value: {:?}", entry.key(), &attempt.value);
            entry.insert(attempt.value.clone());
            Ok(attempt.value)
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, Value>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                // Because we are using a table payload, there is an extra level of indirection. The
                // top-level container for the table itself is always called "payload".
                StoreRequest::WriteItem { payload, responder } => {
                    println!("WriteItem request received");

                    // Error out if either of the request table's members are not set.
                    let attempt = payload.attempt.context("required field 'attempt' is unset")?;
                    let options = payload.options.context("required field 'options' is unset")?;

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(
                            write_item(&mut store.borrow_mut(), attempt, &options)
                                .as_ref()
                                .map_err(|e| *e),
                        )
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

可供偵測

FIDL 食譜:@discoverable

@discoverable 屬性會為服務探索指定名稱。這樣一來,用戶端就能搜尋正確的名稱,而不需要手動確認查詢名稱是否與伺服器端傳遞的名稱相符。

在這個範例中,您將建立基本計算機伺服器和用戶端,說明先定義,然後提供及使用 FIDL 通訊協定所需的基本設定。

首先,您將定義介面定義和測試裝置。介面定義 (.fidl 檔案本身) 是任何新 FIDL 通訊協定的起點。此外,計算機還包含必要的 CML 和領域定義,可用於建立用戶端-伺服器模式,並用作任意實作項目的專案架構。

請參閱以下 FIDL 程式碼:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// The namespace for this FIDL protocol. This namespace is how both consumers (clients) and providers (servers) reference this protocol.
library examples.calculator.baseline;

// @discoverable indicates 'Calculator' is a protocol that will be served under the examples.calculator.baseline libarary namespace. https://fuchsia.dev/fuchsia-src/reference/fidl/language/attributes#discoverable . If @discoverable is missing, it will lead to a compile time error when trying to import the library.
@discoverable
// A limited-functionality calculator 'protocol' that adds and subtracts integers.
open protocol Calculator {
    // Takes as input a struct with two integers, and returns their sum: (a+b)=sum.  This method is infallible (no errors can be generated) as two int32's cannot overflow a result type of int64.
    flexible Add(struct {
        a int32;
        b int32;
    }) -> (struct {
        sum int64;
    });
    // Takes as input a struct with two integers, and returns their difference: (a-b)=difference.  This method is infallible (no errors can be generated) as two int32's cannot overflow a result type of int64.
    flexible Subtract(struct {
        a int32;
        b int32;
    }) -> (struct {
        difference int64;
    });
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.calculator.baseline.Calculator" },
    ],
    config: {},
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.calculator.baseline.Calculator" },
    ],
    expose: [
        {
            protocol: "examples.calculator.baseline.Calculator",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.calculator.baseline.Calculator",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to both children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// TODO(https://fxbug.dev/42063075): Rust implementation.

伺服器

// TODO(https://fxbug.dev/42063075): Rust implementation.

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42063075): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42063075): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42063075): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42063075): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42063075): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42063075): HLCPP implementation.

對於平台開發人員等特定開發人員而言,從頭開始建立 FIDL 通訊協定 (如本範例所示) 可能更常見。不過,其他類型的開發人員也能從學習如何建構 FIDL 通訊協定中受益,即使他們通常不會這麼做也一樣。這有助您瞭解 FIDL 的所有內容如何搭配運作,包括語法、文法、語言功能、如何提供及使用特定 FIDL 通訊協定,以及建構系統的運作方式。在後續步驟中,我們會根據這個基準提供範例,說明如何擴充現有的 FIDL 通訊協定,這應該是相當常見的做法。

Enum

FIDL 食譜:列舉

enum 是一種 FIDL 資料類型,用來表示可能常數的固定清單,例如一副撲克牌中的花色,或是使用者可從下拉式選單中選取的汽車品牌。接著,系統會將這個值清單對應至基礎整數類型,每個值都會對應至所列成員之一。

在下方範例中,我們在最適合使用列舉的情況下新增了 FIDL 列舉:列舉可能因失敗的函式呼叫而產生的錯誤值。ReadError 列舉有兩個成員:NOT_FOUND 用於指出在讀取嘗試期間無法比對搜尋鍵,而 UNKNOWN 則用於所有無法明確描述的情況,用來表示 grab-bag 錯誤。請注意,這個列舉標示為 flexible,方便日後輕鬆加入新成員。

推理

原先的唯寫鍵/值儲存庫現在已擴充,可讀取儲存庫中的項目。

實作

套用至 FIDL 和 CML 定義的變更如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.addreaditem;

// Aliases for the key and value. Using aliases helps increase the readability of FIDL files and
// reduces likelihood of errors due to differing constraints.
alias Key = string:128;
alias Value = vector<byte>:64000;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key Key;
    value Value;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// An enumeration of things that may go wrong when trying to read a value out of our store.
type ReadError = flexible enum {
    UNKNOWN = 0;
    NOT_FOUND = 1;
};

/// A very basic key-value store - so basic, in fact, that one may only write to it, never read!
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;

    /// Reads an item from the store.
    flexible ReadItem(struct {
        key Key;
    }) -> (Item) error ReadError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.addreaditem.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        read_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.addreaditem.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.addreaditem.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.addreaditem.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

所有語言的用戶端和伺服器實作方式也都會變更:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use config::Config;
use fidl_examples_keyvaluestore_addreaditem::{Item, StoreMarker};
use fuchsia_component::client::connect_to_protocol;
use std::{str, thread, time};

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        match store.write_item(&Item { key: key, value: value.into_bytes() }).await? {
            Ok(_) => println!("WriteItem Success"),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // The structured config for this client contains `read_items`, a vector of strings, each of
    // which is meant to be read from the key-value store. We iterate over these keys, attempting to
    // read them in turn.
    for key in config.read_items.into_iter() {
        let res = store.read_item(key.as_str()).await;
        match res.unwrap() {
            Ok(val) => {
                println!("ReadItem Success: key: {}, value: {}", key, str::from_utf8(&val.1)?)
            }
            Err(err) => println!("ReadItem Error: {}", err.into_primitive()),
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    fidl_examples_keyvaluestore_addreaditem::{
        Item, ReadError, StoreRequest, StoreRequestStream, WriteError,
    },
    fuchsia_component::server::ServiceFs,
    futures::prelude::*,
    lazy_static::lazy_static,
    regex::Regex,
    std::cell::RefCell,
    std::collections::hash_map::Entry,
    std::collections::HashMap,
};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z][A-Za-z0-9_\./]{2,62}[A-Za-z0-9]$")
            .expect("Key validation regex failed to compile");
}

/// Handler for the `WriteItem` method.
fn write_item(store: &mut HashMap<String, Vec<u8>>, attempt: Item) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Validate the value.
    if attempt.value.is_empty() {
        println!("Write error: INVALID_VALUE, For key: {}", attempt.key);
        return Err(WriteError::InvalidValue);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote value at key: {}", entry.key());
            entry.insert(attempt.value);
            Ok(())
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, Vec<u8>>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.borrow_mut(), attempt))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::ReadItem { key, responder } => {
                    println!("ReadItem request received");

                    // Read the item from the store, returning the appropriate error if it could not be found.
                    responder
                        .send(match store.borrow().get(&key) {
                            Some(found) => {
                                println!("Read value at key: {}", key);
                                Ok((&key, found))
                            }
                            None => {
                                println!("Read error: NOT_FOUND, For key: {}", key);
                                Err(ReadError::NotFound)
                            }
                        })
                        .context("error sending reply")?;
                    println!("ReadItem response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

動態饋給模式

FIDL 食譜:動態饋送模式

在 FIDL 通訊協定中,如果使用雙向方法搭配空回應來進行流量控制 (例如 DoSomething(...) -> ();),對於延遲敏感的通訊協定來說,這會帶來根本的缺點:呼叫端會在傳送下一個訊息前等待每個回應,因此會增加個別訊息的延遲時間,或者會忽略回應,導致空回應本身毫無意義。如果通訊協定需要流量控制,但不希望產生這些延遲成本,前饋模式就是不錯的替代方案。在這種設定中,一或多個單向方法會將資料寫入伺服器,而其他方法 (單向或雙向) 則用於「提交」工作,並在用戶端和伺服器之間同步處理。這表示可盡可能快速地傳輸任意數量的資料,但仍有一定程度的流程控制,因為同步處理方法會在繼續執行更多工作之前,強制用戶端停止。

改善 Instance 通訊協定效能的其中一種方法,是允許分批處理行:每當我們想要在畫布上新增一行時,不必每次都傳送單一 AddLine(...);,等待回應,然後再次為下一行執行這項操作,而是可以將多行分批處理,以便一次叫用新的 AddLines(...); 呼叫。用戶端現在可以決定如何最佳地區隔要繪製的大量線條集合。

若是採用簡單的實作方式,我們會發現伺服器和用戶端完全不同步:用戶端可能會以無限的 AddLines(...); 呼叫淹沒伺服器,而伺服器也可能會以超過用戶端處理能力的 -> OnDrawn(...); 事件淹沒用戶端。解決這兩個問題的方法,就是新增簡單的 Ready() -> (); 方法來進行同步處理。每當用戶端準備接收下一個繪圖更新時,就會呼叫這個方法,並透過伺服器的回應指出用戶端可以繼續執行更多要求。

我們現在在兩個方向都設有一些資料流控制。這項通訊協定現在實作了前饋模式,允許在某些同步「commit」呼叫觸發伺服器上的實際工作之前,進行許多未受控的呼叫。這可避免用戶端因工作量過大而癱瘓伺服器。同樣地,伺服器也不再允許傳送無限的 -> OnDrawn(...); 事件:每個事件都必須遵循來自用戶端的信號 (Ready() -> (); 呼叫),表示該事件已準備好執行更多工作。這就是所謂的「節流事件模式」

具體實作必須手動套用部分規則:如果用戶端收到未透過 Ready() -> (); 方法要求的 -> OnDrawn(...); 事件,就必須關閉連線。

FIDL、CML 和領域介面定義如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.canvas.clientrequesteddraw;

/// A point in 2D space.
type Point = struct {
    x int64;
    y int64;
};

/// A line in 2D space.
alias Line = array<Point, 2>;

/// A bounding box in 2D space. This is the result of "drawing" operations on our canvas, and what
/// the server reports back to the client. These bounds are sufficient to contain all of the
/// lines (inclusive) on a canvas at a given time.
type BoundingBox = struct {
    top_left Point;
    bottom_right Point;
};

/// Manages a single instance of a canvas. Each session of this protocol is responsible for a new
/// canvas.
@discoverable
open protocol Instance {
    /// Add multiple lines to the canvas. We are able to reduce protocol chatter and the number of
    /// requests needed by batching instead of calling the simpler `AddLine(...)` one line at a
    /// time.
    flexible AddLines(struct {
        lines vector<Line>;
    });

    /// Rather than the server randomly performing draws, or trying to guess when to do so, the
    /// client must explicitly ask for them. This creates a bit of extra chatter with the additional
    /// method invocation, but allows much greater client-side control of when the canvas is "ready"
    /// for a view update, thereby eliminating unnecessary draws.
    ///
    /// This method also has the benefit of "throttling" the `-> OnDrawn(...)` event - rather than
    /// allowing a potentially unlimited flood of `-> OnDrawn(...)` calls, we now have the runtime
    /// enforced semantic that each `-> OnDrawn(...)` call must follow a unique `Ready() -> ()` call
    /// from the client. An unprompted `-> OnDrawn(...)` is invalid, and should cause the channel to
    /// immediately close.
    flexible Ready() -> ();

    /// Update the client with the latest drawing state. The server makes no guarantees about how
    /// often this event occurs - it could occur multiple times per board state, for example.
    flexible -> OnDrawn(BoundingBox);
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.canvas.clientrequesteddraw.Instance" },
    ],
    config: {
        // A script for the client to follow. Entries in the script may take one of two forms: a
        // pair of signed-integer coordinates like "-2,15:4,5", or the string "READY". The former
        // builds a local vector sent via a single `AddLines(...)` call, while the latter sends a
        // `Ready() -> ()` call pauses execution until the next `->OnDrawn(...)` event is received.
        //
        // TODO(https://fxbug.dev/42178362): It would absolve individual language implementations of a great
        //   deal of string parsing if we were able to use a vector of `union { Point; Ready}` here.
        script: {
            type: "vector",
            max_count: 100,
            element: {
                type: "string",
                max_size: 64,
            },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.canvas.clientrequesteddraw.Instance" },
    ],
    expose: [
        {
            protocol: "examples.canvas.clientrequesteddraw.Instance",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.canvas.clientrequesteddraw.Instance",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{format_err, Context as _, Error};
use config::Config;
use fidl_examples_canvas_clientrequesteddraw::{InstanceEvent, InstanceMarker, Point};
use fuchsia_component::client::connect_to_protocol;
use futures::TryStreamExt;
use std::{thread, time};

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send Instance requests
    // across the channel.
    let instance = connect_to_protocol::<InstanceMarker>()?;
    println!("Outgoing connection enabled");

    let mut batched_lines = Vec::<[Point; 2]>::new();
    for action in config.script.into_iter() {
        // If the next action in the script is to "PUSH", send a batch of lines to the server.
        if action == "PUSH" {
            instance.add_lines(&batched_lines).context("Could not send lines")?;
            println!("AddLines request sent");
            batched_lines.clear();
            continue;
        }

        // If the next action in the script is to "WAIT", block until an OnDrawn event is received
        // from the server.
        if action == "WAIT" {
            let mut event_stream = instance.take_event_stream();
            loop {
                match event_stream
                    .try_next()
                    .await
                    .context("Error getting event response from proxy")?
                    .ok_or_else(|| format_err!("Proxy sent no events"))?
                {
                    InstanceEvent::OnDrawn { top_left, bottom_right } => {
                        println!(
                            "OnDrawn event received: top_left: {:?}, bottom_right: {:?}",
                            top_left, bottom_right
                        );
                        break;
                    }
                    InstanceEvent::_UnknownEvent { ordinal, .. } => {
                        println!("Received an unknown event with ordinal {ordinal}");
                    }
                }
            }

            // Now, inform the server that we are ready to receive more updates whenever they are
            // ready for us.
            println!("Ready request sent");
            instance.ready().await.context("Could not send ready call")?;
            println!("Ready success");
            continue;
        }

        // Add a line to the next batch. Parse the string input, making two points out of it.
        let mut points = action
            .split(":")
            .map(|point| {
                let integers = point
                    .split(",")
                    .map(|integer| integer.parse::<i64>().unwrap())
                    .collect::<Vec<i64>>();
                Point { x: integers[0], y: integers[1] }
            })
            .collect::<Vec<Point>>();

        // Assemble a line from the two points.
        let from = points.pop().ok_or_else(|| format_err!("line requires 2 points, but has 0"))?;
        let to = points.pop().ok_or_else(|| format_err!("line requires 2 points, but has 1"))?;
        let mut line: [Point; 2] = [from, to];

        // Batch a line for drawing to the canvas using the two points provided.
        println!("AddLines batching line: {:?}", &mut line);
        batched_lines.push(line);
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{anyhow, Context as _, Error};
use fidl::endpoints::RequestStream as _;
use fidl_examples_canvas_clientrequesteddraw::{
    BoundingBox, InstanceRequest, InstanceRequestStream, Point,
};
use fuchsia_async::{MonotonicInstant, Timer};
use fuchsia_component::server::ServiceFs;

use futures::future::join;
use futures::prelude::*;
use std::sync::{Arc, Mutex};

// A struct that stores the two things we care about for this example: the bounding box the lines
// that have been added thus far, and bit to track whether or not there have been changes since the
// last `OnDrawn` event.
#[derive(Debug)]
struct CanvasState {
    // Tracks whether there has been a change since the last send, to prevent redundant updates.
    changed: bool,
    // Tracks whether or not the client has declared itself ready to receive more updated.
    ready: bool,
    bounding_box: BoundingBox,
}

/// Handler for the `AddLines` method.
fn add_lines(state: &mut CanvasState, lines: Vec<[Point; 2]>) {
    // Update the bounding box to account for the new lines we've just "added" to the canvas.
    let bounds = &mut state.bounding_box;
    for line in lines {
        println!("AddLines printing line: {:?}", line);
        for point in line {
            if point.x < bounds.top_left.x {
                bounds.top_left.x = point.x;
            }
            if point.y > bounds.top_left.y {
                bounds.top_left.y = point.y;
            }
            if point.x > bounds.bottom_right.x {
                bounds.bottom_right.x = point.x;
            }
            if point.y < bounds.bottom_right.y {
                bounds.bottom_right.y = point.y;
            }
        }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next tick.
    state.changed = true
}

/// Creates a new instance of the server, paired to a single client across a zircon channel.
async fn run_server(stream: InstanceRequestStream) -> Result<(), Error> {
    // Create a new in-memory state store for the state of the canvas. The store will live for the
    // lifetime of the connection between the server and this particular client.
    let state = Arc::new(Mutex::new(CanvasState {
        changed: true,
        ready: true,
        bounding_box: BoundingBox {
            top_left: Point { x: 0, y: 0 },
            bottom_right: Point { x: 0, y: 0 },
        },
    }));

    // Take ownership of the control_handle from the stream, which will allow us to push events from
    // a different async task.
    let control_handle = stream.control_handle();

    // A separate watcher task periodically "draws" the canvas, and notifies the client of the new
    // state. We'll need a cloned reference to the canvas state to be accessible from the new
    // task.
    let state_ref = state.clone();
    let update_sender = || async move {
        loop {
            // Our server sends one update per second, but only if the client has declared that it
            // is ready to receive one.
            Timer::new(MonotonicInstant::after(zx::MonotonicDuration::from_seconds(1))).await;
            let mut state = state_ref.lock().unwrap();
            if !state.changed || !state.ready {
                continue;
            }

            // After acquiring the lock, this is where we would draw the actual lines. Since this is
            // just an example, we'll avoid doing the actual rendering, and simply send the bounding
            // box to the client instead.
            let bounds = state.bounding_box;
            match control_handle.send_on_drawn(&bounds.top_left, &bounds.bottom_right) {
                Ok(_) => println!(
                    "OnDrawn event sent: top_left: {:?}, bottom_right: {:?}",
                    bounds.top_left, bounds.bottom_right
                ),
                Err(_) => return,
            }

            // Reset the change and ready trackers.
            state.ready = false;
            state.changed = false;
        }
    };

    // Handle requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    let state_ref = &state;
    let request_handler =
        stream.map(|result| result.context("failed request")).try_for_each(|request| async move {
            // Match based on the method being invoked.
            match request {
                InstanceRequest::AddLines { lines, .. } => {
                    println!("AddLines request received");
                    add_lines(&mut state_ref.lock().unwrap(), lines);
                }
                InstanceRequest::Ready { responder, .. } => {
                    println!("Ready request received");
                    // The client must only call `Ready() -> ();` after receiving an `-> OnDrawn();`
                    // event; if two "consecutive" `Ready() -> ();` calls are received, this
                    // interaction has entered an invalid state, and should be aborted immediately.
                    let mut state = state_ref.lock().unwrap();
                    if state.ready == true {
                        return Err(anyhow!("Invalid back-to-back `Ready` requests received"));
                    }

                    state.ready = true;
                    responder.send().context("Error responding")?;
                } //
                InstanceRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        });

    // This line will only be reached if the server errors out. The stream will await indefinitely,
    // thereby creating a long-lived server. Here, we first wait for the updater task to realize the
    // connection has died, then bubble up the error.
    join(request_handler, update_sender()).await.0
}

// A helper enum that allows us to treat a `Instance` service instance as a value.
enum IncomingService {
    Instance(InstanceRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Instance` protocol - this will allow the client to see
    // the server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Instance);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Instance(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.clientrequesteddraw/cpp/fidl.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/component/incoming/cpp/protocol.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <charconv>

#include <examples/fidl/new/canvas/client_requested_draw/cpp_natural/client/config.h>

// The |EventHandler| is a derived class that we pass into the |fidl::WireClient| to handle incoming
// events asynchronously.
class EventHandler : public fidl::AsyncEventHandler<examples_canvas_clientrequesteddraw::Instance> {
 public:
  // Handler for |OnDrawn| events sent from the server.
  void OnDrawn(
      fidl::Event<examples_canvas_clientrequesteddraw::Instance::OnDrawn>& event) override {
    ::examples_canvas_clientrequesteddraw::Point top_left = event.top_left();
    ::examples_canvas_clientrequesteddraw::Point bottom_right = event.bottom_right();
    FX_LOGS(INFO) << "OnDrawn event received: top_left: Point { x: " << top_left.x()
                  << ", y: " << top_left.y() << " }, bottom_right: Point { x: " << bottom_right.x()
                  << ", y: " << bottom_right.y() << " }";
    loop_.Quit();
  }

  void on_fidl_error(fidl::UnbindInfo error) override { FX_LOGS(ERROR) << error; }

  void handle_unknown_event(
      fidl::UnknownEventMetadata<examples_canvas_clientrequesteddraw::Instance> metadata) override {
    FX_LOGS(WARNING) << "Received an unknown event with ordinal " << metadata.event_ordinal;
  }

  explicit EventHandler(async::Loop& loop) : loop_(loop) {}

 private:
  async::Loop& loop_;
};

// A helper function that takes a coordinate in string form, like "123,-456", and parses it into a
// a struct of the form |{ in64 x; int64 y; }|.
::examples_canvas_clientrequesteddraw::Point ParsePoint(std::string_view input) {
  int64_t x = 0;
  int64_t y = 0;
  size_t index = input.find(',');
  if (index != std::string::npos) {
    std::from_chars(input.data(), input.data() + index, x);
    std::from_chars(input.data() + index + 1, input.data() + input.length(), y);
  }
  return ::examples_canvas_clientrequesteddraw::Point(x, y);
}

using Line = ::std::array<::examples_canvas_clientrequesteddraw::Point, 2>;

// A helper function that takes a coordinate pair in string form, like "1,2:-3,-4", and parses it
// into an array of 2 |Point| structs.
Line ParseLine(const std::string& action) {
  auto input = std::string_view(action);
  size_t index = input.find(':');
  if (index != std::string::npos) {
    return {ParsePoint(input.substr(0, index)), ParsePoint(input.substr(index + 1))};
  }
  return {};
}

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop and dispatcher.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace. This can fail so it's wrapped in a
  // |zx::result| and it must be checked for errors.
  zx::result client_end = component::Connect<examples_canvas_clientrequesteddraw::Instance>();
  if (!client_end.is_ok()) {
    FX_LOGS(ERROR) << "Synchronous error when connecting to the |Instance| protocol: "
                   << client_end.status_string();
    return -1;
  }

  // Create an instance of the event handler.
  EventHandler event_handler(loop);

  // Create an asynchronous client using the newly-established connection.
  fidl::Client client(std::move(*client_end), dispatcher, &event_handler);
  FX_LOGS(INFO) << "Outgoing connection enabled";

  std::vector<Line> batched_lines;
  for (const auto& action : conf.script()) {
    // If the next action in the script is to "PUSH", send a batch of lines to the server.
    if (action == "PUSH") {
      fit::result<fidl::Error> result = client->AddLines(batched_lines);
      if (!result.is_ok()) {
        // Check that our one-way call was enqueued successfully, and handle the error
        // appropriately. In the case of this example, there is nothing we can do to recover here,
        // except to log an error and exit the program.
        FX_LOGS(ERROR) << "Could not send AddLines request: " << result.error_value();
        return -1;
      }

      batched_lines.clear();
      FX_LOGS(INFO) << "AddLines request sent";
      continue;
    }

    // If the next action in the script is to "WAIT", block until an |OnDrawn| event is received
    // from the server.
    if (action == "WAIT") {
      loop.Run();
      loop.ResetQuit();

      // Now, inform the server that we are ready to receive more updates whenever they are
      // ready for us.
      FX_LOGS(INFO) << "Ready request sent";
      client->Ready().ThenExactlyOnce(
          [&](fidl::Result<examples_canvas_clientrequesteddraw::Instance::Ready> result) {
            // Check if the FIDL call succeeded or not.
            if (result.is_ok()) {
              FX_LOGS(INFO) << "Ready success";
            } else {
              FX_LOGS(ERROR) << "Could not send Ready request: " << result.error_value();
            }

            // Quit the loop, thereby handing control back to the outer loop of actions being
            // iterated over.
            loop.Quit();
          });

      // Run the loop until the callback is resolved, at which point we can continue from here.
      loop.Run();
      loop.ResetQuit();

      continue;
    }

    // Batch a line for drawing to the canvas using the two points provided.
    Line line = ParseLine(action);
    batched_lines.push_back(line);
    FX_LOGS(INFO) << "AddLines batching line: [Point { x: " << line[1].x() << ", y: " << line[1].y()
                  << " }, Point { x: " << line[0].x() << ", y: " << line[0].y() << " }]";
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.clientrequesteddraw/cpp/fidl.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/async/cpp/task.h>
#include <lib/component/outgoing/cpp/outgoing_directory.h>
#include <lib/fidl/cpp/wire/channel.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <src/lib/fxl/macros.h>
#include <src/lib/fxl/memory/weak_ptr.h>

// A struct that stores the two things we care about for this example: the set of lines, and the
// bounding box that contains them.
struct CanvasState {
  // Tracks whether there has been a change since the last send, to prevent redundant updates.
  bool changed = true;
  // Tracks whether or not the client has declared itself ready to receive more updated.
  bool ready = true;
  examples_canvas_clientrequesteddraw::BoundingBox bounding_box;
};

// An implementation of the |Instance| protocol.
class InstanceImpl final : public fidl::Server<examples_canvas_clientrequesteddraw::Instance> {
 public:
  // Bind this implementation to a channel.
  InstanceImpl(async_dispatcher_t* dispatcher,
               fidl::ServerEnd<examples_canvas_clientrequesteddraw::Instance> server_end)
      : binding_(dispatcher, std::move(server_end), this, std::mem_fn(&InstanceImpl::OnFidlClosed)),
        weak_factory_(this) {
    // Start the update timer on startup. Our server sends one update per second
    ScheduleOnDrawnEvent(dispatcher, zx::sec(1));
  }

  void OnFidlClosed(fidl::UnbindInfo info) {
    if (info.reason() != ::fidl::Reason::kPeerClosedWhileReading) {
      FX_LOGS(ERROR) << "Shutdown unexpectedly";
    }
    delete this;
  }

  void AddLines(AddLinesRequest& request, AddLinesCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "AddLines request received";
    for (const auto& points : request.lines()) {
      FX_LOGS(INFO) << "AddLines printing line: [Point { x: " << points[1].x()
                    << ", y: " << points[1].y() << " }, Point { x: " << points[0].x()
                    << ", y: " << points[0].y() << " }]";

      // Update the bounding box to account for the new line we've just "added" to the canvas.
      auto& bounds = state_.bounding_box;
      for (const auto& point : points) {
        if (point.x() < bounds.top_left().x()) {
          bounds.top_left().x() = point.x();
        }
        if (point.y() > bounds.top_left().y()) {
          bounds.top_left().y() = point.y();
        }
        if (point.x() > bounds.bottom_right().x()) {
          bounds.bottom_right().x() = point.x();
        }
        if (point.y() < bounds.bottom_right().y()) {
          bounds.bottom_right().y() = point.y();
        }
      }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next |OnDrawn|
    // event.
    state_.changed = true;
  }

  void Ready(ReadyCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "Ready request received";

    // The client must only call `Ready() -> ();` after receiving an `-> OnDrawn();` event; if two
    // "consecutive" `Ready() -> ();` calls are received, this interaction has entered an invalid
    // state, and should be aborted immediately.
    if (state_.ready == true) {
      FX_LOGS(ERROR) << "Invalid back-to-back `Ready` requests received";
    }

    state_.ready = true;
    completer.Reply();
  }

  void handle_unknown_method(
      fidl::UnknownMethodMetadata<examples_canvas_clientrequesteddraw::Instance> metadata,
      fidl::UnknownMethodCompleter::Sync& completer) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << metadata.method_ordinal;
  }

 private:
  // Each scheduled update waits for the allotted amount of time, sends an update if something has
  // changed, and schedules the next update.
  void ScheduleOnDrawnEvent(async_dispatcher_t* dispatcher, zx::duration after) {
    async::PostDelayedTask(
        dispatcher,
        [&, dispatcher, after, weak = weak_factory_.GetWeakPtr()] {
          // Halt execution if the binding has been deallocated already.
          if (!weak) {
            return;
          }

          // Schedule the next update if the binding still exists.
          weak->ScheduleOnDrawnEvent(dispatcher, after);

          // No need to send an update if nothing has changed since the last one, or the client has
          // not yet informed us that it is ready for more updates.
          if (!weak->state_.changed || !weak->state_.ready) {
            return;
          }

          // This is where we would draw the actual lines. Since this is just an example, we'll
          // avoid doing the actual rendering, and simply send the bounding box to the client
          // instead.
          auto result = fidl::SendEvent(binding_)->OnDrawn(state_.bounding_box);
          if (!result.is_ok()) {
            return;
          }

          auto top_left = state_.bounding_box.top_left();
          auto bottom_right = state_.bounding_box.bottom_right();
          FX_LOGS(INFO) << "OnDrawn event sent: top_left: Point { x: " << top_left.x()
                        << ", y: " << top_left.y()
                        << " }, bottom_right: Point { x: " << bottom_right.x()
                        << ", y: " << bottom_right.y() << " }";

          // Reset the change and ready trackers.
          state_.ready = false;
          state_.changed = false;
        },
        after);
  }

  fidl::ServerBinding<examples_canvas_clientrequesteddraw::Instance> binding_;
  CanvasState state_ = CanvasState{};

  // Generates weak references to this object, which are appropriate to pass into asynchronous
  // callbacks that need to access this object. The references are automatically invalidated
  // if this object is destroyed.
  fxl::WeakPtrFactory<InstanceImpl> weak_factory_;
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component. This
  // directory is where the outgoing FIDL protocols are installed so that they can be provided to
  // other components.
  component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);

  // The `ServeFromStartupInfo()` function sets up the outgoing directory with the startup handle.
  // The startup handle is a handle provided to every component by the system, so that they can
  // serve capabilities (e.g. FIDL protocols) to other components.
  zx::result result = outgoing.ServeFromStartupInfo();
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
    return -1;
  }

  // Register a handler for components trying to connect to
  // |examples.canvas.clientrequesteddraw.Instance|.
  result = outgoing.AddUnmanagedProtocol<examples_canvas_clientrequesteddraw::Instance>(
      [dispatcher](fidl::ServerEnd<examples_canvas_clientrequesteddraw::Instance> server_end) {
        // Create an instance of our InstanceImpl that destroys itself when the connection closes.
        new InstanceImpl(dispatcher, std::move(server_end));
      });
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to add Instance protocol: " << result.status_string();
    return -1;
  }

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

C++ (Wire)

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.clientrequesteddraw/cpp/wire.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/component/incoming/cpp/protocol.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <charconv>

#include <examples/fidl/new/canvas/client_requested_draw/cpp_wire/client/config.h>

// The |EventHandler| is a derived class that we pass into the |fidl::WireClient| to handle incoming
// events asynchronously.
class EventHandler
    : public fidl::WireAsyncEventHandler<examples_canvas_clientrequesteddraw::Instance> {
 public:
  // Handler for |OnDrawn| events sent from the server.
  void OnDrawn(
      fidl::WireEvent<examples_canvas_clientrequesteddraw::Instance::OnDrawn>* event) override {
    ::examples_canvas_clientrequesteddraw::wire::Point top_left = event->top_left;
    ::examples_canvas_clientrequesteddraw::wire::Point bottom_right = event->bottom_right;
    FX_LOGS(INFO) << "OnDrawn event received: top_left: Point { x: " << top_left.x
                  << ", y: " << top_left.y << " }, bottom_right: Point { x: " << bottom_right.x
                  << ", y: " << bottom_right.y << " }";
    loop_.Quit();
  }

  void on_fidl_error(fidl::UnbindInfo error) override { FX_LOGS(ERROR) << error; }

  void handle_unknown_event(
      fidl::UnknownEventMetadata<examples_canvas_clientrequesteddraw::Instance> metadata) override {
    FX_LOGS(WARNING) << "Received an unknown event with ordinal " << metadata.event_ordinal;
  }

  explicit EventHandler(async::Loop& loop) : loop_(loop) {}

 private:
  async::Loop& loop_;
};

// A helper function that takes a coordinate in string form, like "123,-456", and parses it into a
// a struct of the form |{ in64 x; int64 y; }|.
::examples_canvas_clientrequesteddraw::wire::Point ParsePoint(std::string_view input) {
  int64_t x = 0;
  int64_t y = 0;
  size_t index = input.find(',');
  if (index != std::string::npos) {
    std::from_chars(input.data(), input.data() + index, x);
    std::from_chars(input.data() + index + 1, input.data() + input.length(), y);
  }
  return ::examples_canvas_clientrequesteddraw::wire::Point{.x = x, .y = y};
}

using Line = ::fidl::Array<::examples_canvas_clientrequesteddraw::wire::Point, 2>;

// A helper function that takes a coordinate pair in string form, like "1,2:-3,-4", and parses it
// into an array of 2 |Point| structs.
Line ParseLine(const std::string& action) {
  auto input = std::string_view(action);
  size_t index = input.find(':');
  if (index != std::string::npos) {
    return {ParsePoint(input.substr(0, index)), ParsePoint(input.substr(index + 1))};
  }
  return {};
}

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop and dispatcher.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace. This can fail so it's wrapped in a
  // |zx::result| and it must be checked for errors.
  zx::result client_end = component::Connect<examples_canvas_clientrequesteddraw::Instance>();
  if (!client_end.is_ok()) {
    FX_LOGS(ERROR) << "Synchronous error when connecting to the |Instance| protocol: "
                   << client_end.status_string();
    return -1;
  }

  // Create an instance of the event handler.
  EventHandler event_handler(loop);

  // Create an asynchronous client using the newly-established connection.
  fidl::WireClient client(std::move(*client_end), dispatcher, &event_handler);
  FX_LOGS(INFO) << "Outgoing connection enabled";

  std::vector<Line> batched_lines;
  for (const auto& action : conf.script()) {
    // If the next action in the script is to "PUSH", send a batch of lines to the server.
    if (action == "PUSH") {
      fidl::Status status = client->AddLines(fidl::VectorView<Line>::FromExternal(batched_lines));
      if (!status.ok()) {
        // Check that our one-way call was enqueued successfully, and handle the error
        // appropriately. In the case of this example, there is nothing we can do to recover here,
        // except to log an error and exit the program.
        FX_LOGS(ERROR) << "Could not send AddLines request: " << status.error();
        return -1;
      }

      batched_lines.clear();
      FX_LOGS(INFO) << "AddLines request sent";
      continue;
    }

    // If the next action in the script is to "WAIT", block until an |OnDrawn| event is received
    // from the server.
    if (action == "WAIT") {
      loop.Run();
      loop.ResetQuit();

      // Now, inform the server that we are ready to receive more updates whenever they are
      // ready for us.
      FX_LOGS(INFO) << "Ready request sent";
      client->Ready().ThenExactlyOnce(
          [&](fidl::WireUnownedResult<examples_canvas_clientrequesteddraw::Instance::Ready>&
                  result) {
            // Check if the FIDL call succeeded or not.
            if (result.ok()) {
              FX_LOGS(INFO) << "Ready success";
            } else {
              FX_LOGS(ERROR) << "Could not send Ready request: " << result.error();
            }

            // Quit the loop, thereby handing control back to the outer loop of actions being
            // iterated over.
            loop.Quit();
          });

      // Run the loop until the callback is resolved, at which point we can continue from here.
      loop.Run();
      loop.ResetQuit();

      continue;
    }

    // Batch a line for drawing to the canvas using the two points provided.
    Line line = ParseLine(action);
    batched_lines.push_back(line);
    FX_LOGS(INFO) << "AddLines batching line: [Point { x: " << line[1].x << ", y: " << line[1].y
                  << " }, Point { x: " << line[0].x << ", y: " << line[0].y << " }]";
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.clientrequesteddraw/cpp/wire.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/async/cpp/task.h>
#include <lib/component/outgoing/cpp/outgoing_directory.h>
#include <lib/fidl/cpp/wire/channel.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <src/lib/fxl/macros.h>
#include <src/lib/fxl/memory/weak_ptr.h>

// A struct that stores the two things we care about for this example: the set of lines, and the
// bounding box that contains them.
struct CanvasState {
  // Tracks whether there has been a change since the last send, to prevent redundant updates.
  bool changed = true;
  // Tracks whether or not the client has declared itself ready to receive more updated.
  bool ready = true;
  examples_canvas_clientrequesteddraw::wire::BoundingBox bounding_box;
};

// An implementation of the |Instance| protocol.
class InstanceImpl final : public fidl::WireServer<examples_canvas_clientrequesteddraw::Instance> {
 public:
  // Bind this implementation to a channel.
  InstanceImpl(async_dispatcher_t* dispatcher,
               fidl::ServerEnd<examples_canvas_clientrequesteddraw::Instance> server_end)
      : binding_(dispatcher, std::move(server_end), this, std::mem_fn(&InstanceImpl::OnFidlClosed)),
        weak_factory_(this) {
    // Start the update timer on startup. Our server sends one update per second
    ScheduleOnDrawnEvent(dispatcher, zx::sec(1));
  }

  void OnFidlClosed(fidl::UnbindInfo info) {
    if (info.reason() != ::fidl::Reason::kPeerClosedWhileReading) {
      FX_LOGS(ERROR) << "Shutdown unexpectedly";
    }
    delete this;
  }

  void AddLines(AddLinesRequestView request, AddLinesCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "AddLines request received";
    for (const auto& points : request->lines) {
      FX_LOGS(INFO) << "AddLines printing line: [Point { x: " << points[1].x
                    << ", y: " << points[1].y << " }, Point { x: " << points[0].x
                    << ", y: " << points[0].y << " }]";

      // Update the bounding box to account for the new line we've just "added" to the canvas.
      auto& bounds = state_.bounding_box;
      for (const auto& point : points) {
        if (point.x < bounds.top_left.x) {
          bounds.top_left.x = point.x;
        }
        if (point.y > bounds.top_left.y) {
          bounds.top_left.y = point.y;
        }
        if (point.x > bounds.bottom_right.x) {
          bounds.bottom_right.x = point.x;
        }
        if (point.y < bounds.bottom_right.y) {
          bounds.bottom_right.y = point.y;
        }
      }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next |OnDrawn|
    // event.
    state_.changed = true;
  }

  void Ready(ReadyCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "Ready request received";

    // The client must only call `Ready() -> ();` after receiving an `-> OnDrawn();` event; if two
    // "consecutive" `Ready() -> ();` calls are received, this interaction has entered an invalid
    // state, and should be aborted immediately.
    if (state_.ready == true) {
      FX_LOGS(ERROR) << "Invalid back-to-back `Ready` requests received";
    }

    state_.ready = true;
    completer.Reply();
  }

  void handle_unknown_method(
      fidl::UnknownMethodMetadata<examples_canvas_clientrequesteddraw::Instance> metadata,
      fidl::UnknownMethodCompleter::Sync& completer) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << metadata.method_ordinal;
  }

 private:
  // Each scheduled update waits for the allotted amount of time, sends an update if something has
  // changed, and schedules the next update.
  void ScheduleOnDrawnEvent(async_dispatcher_t* dispatcher, zx::duration after) {
    async::PostDelayedTask(
        dispatcher,
        [&, dispatcher, after, weak = weak_factory_.GetWeakPtr()] {
          // Halt execution if the binding has been deallocated already.
          if (!weak) {
            return;
          }

          // Schedule the next update if the binding still exists.
          weak->ScheduleOnDrawnEvent(dispatcher, after);

          // No need to send an update if nothing has changed since the last one, or the client has
          // not yet informed us that it is ready for more updates.
          if (!weak->state_.changed || !weak->state_.ready) {
            return;
          }

          // This is where we would draw the actual lines. Since this is just an example, we'll
          // avoid doing the actual rendering, and simply send the bounding box to the client
          // instead.
          auto top_left = weak->state_.bounding_box.top_left;
          auto bottom_right = weak->state_.bounding_box.bottom_right;
          fidl::Status status =
              fidl::WireSendEvent(weak->binding_)->OnDrawn(top_left, bottom_right);
          if (!status.ok()) {
            return;
          }
          FX_LOGS(INFO) << "OnDrawn event sent: top_left: Point { x: " << top_left.x
                        << ", y: " << top_left.y
                        << " }, bottom_right: Point { x: " << bottom_right.x
                        << ", y: " << bottom_right.y << " }";

          // Reset the change and ready trackers.
          state_.ready = false;
          weak->state_.changed = false;
        },
        after);
  }

  fidl::ServerBinding<examples_canvas_clientrequesteddraw::Instance> binding_;
  CanvasState state_ = CanvasState{};

  // Generates weak references to this object, which are appropriate to pass into asynchronous
  // callbacks that need to access this object. The references are automatically invalidated
  // if this object is destroyed.
  fxl::WeakPtrFactory<InstanceImpl> weak_factory_;
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component. This
  // directory is where the outgoing FIDL protocols are installed so that they can be provided to
  // other components.
  component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);

  // The `ServeFromStartupInfo()` function sets up the outgoing directory with the startup handle.
  // The startup handle is a handle provided to every component by the system, so that they can
  // serve capabilities (e.g. FIDL protocols) to other components.
  zx::result result = outgoing.ServeFromStartupInfo();
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
    return -1;
  }

  // Register a handler for components trying to connect to
  // |examples.canvas.clientrequesteddraw.Instance|.
  result = outgoing.AddUnmanagedProtocol<examples_canvas_clientrequesteddraw::Instance>(
      [dispatcher](fidl::ServerEnd<examples_canvas_clientrequesteddraw::Instance> server_end) {
        // Create an instance of our InstanceImpl that destroys itself when the connection closes.
        new InstanceImpl(dispatcher, std::move(server_end));
      });
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to add Instance protocol: " << result.status_string();
    return -1;
  }

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

HLCPP

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/async-loop/cpp/loop.h>
#include <lib/sys/cpp/component_context.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <charconv>

#include <examples/canvas/clientrequesteddraw/cpp/fidl.h>
#include <examples/fidl/new/canvas/client_requested_draw/hlcpp/client/config.h>

// A helper function that takes a coordinate in string form, like "123,-456", and parses it into a
// a struct of the form |{ in64 x; int64 y; }|.
::examples::canvas::clientrequesteddraw::Point ParsePoint(std::string_view input) {
  int64_t x = 0;
  int64_t y = 0;
  size_t index = input.find(',');
  if (index != std::string::npos) {
    std::from_chars(input.data(), input.data() + index, x);
    std::from_chars(input.data() + index + 1, input.data() + input.length(), y);
  }
  return ::examples::canvas::clientrequesteddraw::Point{.x = x, .y = y};
}

using Line = ::std::array<::examples::canvas::clientrequesteddraw::Point, 2>;

// A helper function that takes a coordinate pair in string form, like "1,2:-3,-4", and parses it
// into an array of 2 |Point| structs.
Line ParseLine(const std::string& action) {
  auto input = std::string_view(action);
  size_t index = input.find(':');
  if (index != std::string::npos) {
    return {ParsePoint(input.substr(0, index)), ParsePoint(input.substr(index + 1))};
  }
  return {};
}

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace, then create an asynchronous client
  // using the newly-established connection.
  examples::canvas::clientrequesteddraw::InstancePtr instance_proxy;
  auto context = sys::ComponentContext::Create();
  context->svc()->Connect(instance_proxy.NewRequest(dispatcher));
  FX_LOGS(INFO) << "Outgoing connection enabled";

  instance_proxy.set_error_handler([&loop](zx_status_t status) {
    FX_LOGS(ERROR) << "Shutdown unexpectedly";
    loop.Quit();
  });

  // Provide a lambda to handle incoming |OnDrawn| events asynchronously.
  instance_proxy.events().OnDrawn =
      [&loop](::examples::canvas::clientrequesteddraw::Point top_left,
              ::examples::canvas::clientrequesteddraw::Point bottom_right) {
        FX_LOGS(INFO) << "OnDrawn event received: top_left: Point { x: " << top_left.x
                      << ", y: " << top_left.y << " }, bottom_right: Point { x: " << bottom_right.x
                      << ", y: " << bottom_right.y << " }";
        loop.Quit();
      };

  instance_proxy.events().handle_unknown_event = [](uint64_t ordinal) {
    FX_LOGS(WARNING) << "Received an unknown event with ordinal " << ordinal;
  };

  std::vector<Line> batched_lines;
  for (const auto& action : conf.script()) {
    // If the next action in the script is to "PUSH", send a batch of lines to the server.
    if (action == "PUSH") {
      instance_proxy->AddLines(batched_lines);
      batched_lines.clear();
      FX_LOGS(INFO) << "AddLines request sent";
      continue;
    }

    // If the next action in the script is to "WAIT", block until an |OnDrawn| event is received
    // from the server.
    if (action == "WAIT") {
      loop.Run();
      loop.ResetQuit();

      // Now, inform the server that we are ready to receive more updates whenever they are ready
      // for us.
      FX_LOGS(INFO) << "Ready request sent";
      instance_proxy->Ready([&](fpromise::result<void, fidl::FrameworkErr> result) {
        if (result.is_error()) {
          // Check that our flexible two-way call was known to the server and handle the case of an
          // unknown method appropriately. In the case of this example, there is nothing we can do
          // to recover here, except to log an error and exit the program.
          FX_LOGS(ERROR) << "Server does not implement AddLine";
        }

        FX_LOGS(INFO) << "Ready success";

        // Quit the loop, thereby handing control back to the outer loop of actions being iterated
        // over.
        loop.Quit();
      });

      // Run the loop until the callback is resolved, at which point we can continue from here.
      loop.Run();
      loop.ResetQuit();

      continue;
    }

    // Batch a line for drawing to the canvas using the two points provided.
    Line line = ParseLine(action);
    batched_lines.push_back(line);
    FX_LOGS(INFO) << "AddLines batching line: [Point { x: " << line[1].x << ", y: " << line[1].y
                  << " }, Point { x: " << line[0].x << ", y: " << line[0].y << " }]";
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/async-loop/cpp/loop.h>
#include <lib/async-loop/default.h>
#include <lib/async/cpp/task.h>
#include <lib/fidl/cpp/binding.h>
#include <lib/sys/cpp/component_context.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <examples/canvas/clientrequesteddraw/cpp/fidl.h>
#include <src/lib/fxl/macros.h>
#include <src/lib/fxl/memory/weak_ptr.h>

// A struct that stores the two things we care about for this example: the set of lines, and the
// bounding box that contains them.
struct CanvasState {
  // Tracks whether there has been a change since the last send, to prevent redundant updates.
  bool changed = true;
  // Tracks whether or not the client has declared itself ready to receive more updated.
  bool ready = true;
  examples::canvas::clientrequesteddraw::BoundingBox bounding_box;
};

using Line = ::std::array<::examples::canvas::clientrequesteddraw::Point, 2>;

// An implementation of the |Instance| protocol.
class InstanceImpl final : public examples::canvas::clientrequesteddraw::Instance {
 public:
  // Bind this implementation to an |InterfaceRequest|.
  InstanceImpl(async_dispatcher_t* dispatcher,
               fidl::InterfaceRequest<examples::canvas::clientrequesteddraw::Instance> request)
      : binding_(fidl::Binding<examples::canvas::clientrequesteddraw::Instance>(this)),
        weak_factory_(this) {
    binding_.Bind(std::move(request), dispatcher);

    // Gracefully handle abrupt shutdowns.
    binding_.set_error_handler([this](zx_status_t status) mutable {
      if (status != ZX_ERR_PEER_CLOSED) {
        FX_LOGS(ERROR) << "Shutdown unexpectedly";
      }
      delete this;
    });

    // Start the update timer on startup. Our server sends one update per second.
    ScheduleOnDrawnEvent(dispatcher, zx::sec(1));
  }

  void AddLines(std::vector<Line> lines) override {
    FX_LOGS(INFO) << "AddLines request received";
    for (const auto& points : lines) {
      FX_LOGS(INFO) << "AddLines printing line: [Point { x: " << points[1].x
                    << ", y: " << points[1].y << " }, Point { x: " << points[0].x
                    << ", y: " << points[0].y << " }]";

      // Update the bounding box to account for the new line we've just "added" to the canvas.
      auto& bounds = state_.bounding_box;
      for (const auto& point : points) {
        if (point.x < bounds.top_left.x) {
          bounds.top_left.x = point.x;
        }
        if (point.y > bounds.top_left.y) {
          bounds.top_left.y = point.y;
        }
        if (point.x > bounds.bottom_right.x) {
          bounds.bottom_right.x = point.x;
        }
        if (point.y < bounds.bottom_right.y) {
          bounds.bottom_right.y = point.y;
        }
      }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next
    // |OnDrawn| event.
    state_.changed = true;
  }

  void Ready(ReadyCallback callback) override {
    FX_LOGS(INFO) << "Ready request received";

    // The client must only call `Ready() -> ();` after receiving an `-> OnDrawn();` event; if
    // two "consecutive" `Ready() -> ();` calls are received, this interaction has entered an
    // invalid state, and should be aborted immediately.
    if (state_.ready == true) {
      FX_LOGS(ERROR) << "Invalid back-to-back `Ready` requests received";
    }

    state_.ready = true;
    callback(fpromise::ok());
  }

  void handle_unknown_method(uint64_t ordinal, bool method_has_response) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << ordinal;
  }

 private:
  // Each scheduled update waits for the allotted amount of time, sends an update if something
  // has changed, and schedules the next update.
  void ScheduleOnDrawnEvent(async_dispatcher_t* dispatcher, zx::duration after) {
    async::PostDelayedTask(
        dispatcher,
        [&, dispatcher, after, weak = weak_factory_.GetWeakPtr()] {
          // Halt execution if the binding has been deallocated already.
          if (!weak) {
            return;
          }

          // Schedule the next update if the binding still exists.
          weak->ScheduleOnDrawnEvent(dispatcher, after);

          // No need to send an update if nothing has changed since the last one, or the client
          // has not yet informed us that it is ready for more updates.
          if (!weak->state_.changed || !weak->state_.ready) {
            return;
          }

          // This is where we would draw the actual lines. Since this is just an example, we'll
          // avoid doing the actual rendering, and simply send the bounding box to the client
          // instead.
          auto top_left = state_.bounding_box.top_left;
          auto bottom_right = state_.bounding_box.bottom_right;
          binding_.events().OnDrawn(top_left, bottom_right);
          FX_LOGS(INFO) << "OnDrawn event sent: top_left: Point { x: " << top_left.x
                        << ", y: " << top_left.y
                        << " }, bottom_right: Point { x: " << bottom_right.x
                        << ", y: " << bottom_right.y << " }";

          // Reset the change and ready trackers.
          state_.ready = false;
          state_.changed = false;
        },
        after);
  }

  fidl::Binding<examples::canvas::clientrequesteddraw::Instance> binding_;
  CanvasState state_ = CanvasState{};

  // Generates weak references to this object, which are appropriate to pass into asynchronous
  // callbacks that need to access this object. The references are automatically invalidated
  // if this object is destroyed.
  fxl::WeakPtrFactory<InstanceImpl> weak_factory_;
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from
  // the client. The following initializes the loop, and obtains the dispatcher, which will be
  // used when binding the server implementation to a channel.
  //
  // Note that unlike the new C++ bindings, HLCPP bindings rely on the async loop being attached
  // to the current thread via the |kAsyncLoopConfigAttachToCurrentThread| configuration.
  async::Loop loop(&kAsyncLoopConfigAttachToCurrentThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component.
  // This directory is where the outgoing FIDL protocols are installed so that they can be
  // provided to other components.
  auto context = sys::ComponentContext::CreateAndServeOutgoingDirectory();

  // Register a handler for components trying to connect to
  // |examples.canvas.clientrequesteddraw.Instance|.
  context->outgoing()->AddPublicService(
      fidl::InterfaceRequestHandler<examples::canvas::clientrequesteddraw::Instance>(
          [dispatcher](
              fidl::InterfaceRequest<examples::canvas::clientrequesteddraw::Instance> request) {
            // Create an instance of our |InstanceImpl| that destroys itself when the connection
            // closes.
            new InstanceImpl(dispatcher, std::move(request));
          }));

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

產生的名稱

FIDL 食譜:產生的名稱

產生的名稱是 FIDL 編譯器為匿名類型指派的名稱。雖然匿名型別無法在 FIDL 檔案中命名,但在產生的繫結輸出內容中,必須要有某個名稱來參照這些型別,這樣使用者才能在繫結語言中建立型別的例項。

由於 FIDL 編譯器名稱產生演算法會使用本機內容 (成員名稱、方法名稱等) 為類型命名,因此可能會發生名稱衝突。如要解決這類衝突,請直接在類型宣告前方放置 @generated_name 屬性,指示編譯器應改用哪個名稱。

在這個變化版本中,我們允許鍵/值存放區將其他鍵/值存放區做為成員。簡而言之,我們會將其轉換為樹狀結構。我們會將 value 的原始定義替換為使用兩個成員 union 的定義:一個變化版本會使用與先前相同的 vector<byte> 類型儲存葉結點,另一個則會以其他巢狀儲存庫的形式儲存分支節點。

推理

這裡我們會看到幾種 optionality 的用法,我們可以宣告可能存在或不存在的型別。FIDL 中的選用性有三種:

  • 具有此類型一律會在網路上離線儲存,因此具有內建方式,可透過空值封套描述「缺席」。為這些類型啟用選用性不會影響所包含訊息的線路形狀,只會變更哪些值適用於該特定類型。您可以透過新增 :optional 限制,將 unionvector<T>client_endserver_endzx.Handle 類型設為選用。將 value union 設為選用項目後,我們就能以缺少 value 的形式,引入標準的「空值」項目。這表示空白的 bytes 和缺少/空白的 store 屬性是無效的值。
  • 與上述類型不同,struct 版面配置沒有可儲存空值標頭的額外空間。因此,您必須將其包裝在信封中,以便變更所附帶訊息的線上傳輸形狀。為確保這個線路修改效果易於解讀,Item struct 類型必須套用 box<T> 類型範本。
  • 最後,table 版面配置一律為選用。缺少的 table 只是沒有任何成員集。

樹狀圖是自然的自我參照資料結構:樹狀圖中的任何節點都可能包含純資料的葉節點 (在本例中為字串),或包含更多節點的子樹狀圖。這需要遞迴:Item 的定義現在會遞迴地依附自身!在 FIDL 中表示遞迴類型可能有點棘手,尤其是因為目前的支援有點受限。只要在透過自參照建立的循環中,至少有一個選用型別,我們就能支援這類型別。舉例來說,我們在此將 items struct 成員定義為 box<Item>,藉此中斷包含循環。

這些變更也大量使用匿名類型,也就是在使用點內嵌宣告而非命名的類型,以及頂層 type 宣告。根據預設,產生的語言繫結中匿名類型的名稱會取自其本機內容。舉例來說,新推出的 flexible union 會採用其擁有者成員的名稱 Value,新推出的 struct 會變成 Store,以此類推。由於這項啟發法的使用可能會導致衝突,因此 FIDL 提供逃逸處理程序,允許作者手動覆寫匿名類型的產生名稱。這項作業是透過 @generated_name 屬性完成,可讓使用者變更後端產生的名稱。我們可以在這裡使用一個,將原本的 Store 類型重新命名為 NestedStore,以免與使用相同名稱的 protocol 宣告發生名稱衝突。

實作

FIDL、CML 和領域介面定義的修改如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.supporttrees;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value strict union {
        // Keep the original `bytes` as one of the options in the new union. All leaf nodes in the
        // tree must be `bytes`, or absent unions (representing empty). Empty byte arrays are
        // disallowed.
        1: bytes vector<byte>:64000;

        // Allows a store within a store, thereby turning our flat key-value store into a tree
        // thereof. Note the use of `@generated_name` to prevent a type-name collision with the
        // `Store` protocol below, and the use of `box<T>` to ensure that there is a break in the
        // chain of recursion, thereby allowing `Item` to include itself in its own definition.
        //
        // This is a table so that added fields, like for example a `hash`, can be easily added in
        // the future.
        2: store @generated_name("nested_store") table {
            1: items vector<box<Item>>;
        };
    }:optional;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// A very basic key-value store.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.supporttrees.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A newline separated list nested entries. The first line should be the key
        // for the nested store, and each subsequent entry should be a pointer to a text file
        // containing the string value. The name of that text file (without the `.txt` suffix) will
        // serve as the entries key.
        write_nested: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A list of keys, all of which will be populated as null entries.
        write_null: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.supporttrees.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.supporttrees.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.supporttrees.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    config::Config,
    fidl_examples_keyvaluestore_supporttrees::{Item, NestedStore, StoreMarker, Value},
    fuchsia_component::client::connect_to_protocol,
    std::{thread, time},
};

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        let res = store
            .write_item(&Item {
                key: key.clone(),
                value: Some(Box::new(Value::Bytes(value.into_bytes()))),
            })
            .await;
        match res? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // Add nested entries to the key-value store as well. The entries are strings, where the first
    // line is the key of the entry, and each subsequent entry should be a pointer to a text file
    // containing the string value. The name of that text file (without the `.txt` suffix) will
    // serve as the entries key.
    for spec in config.write_nested.into_iter() {
        let mut items = vec![];
        let mut nested_store = NestedStore::default();
        let mut lines = spec.split("\n");
        let key = lines.next().unwrap();

        // For each entry, make a new entry in the `NestedStore` being built.
        for entry in lines {
            let path = format!("/pkg/data/{}.txt", entry);
            let contents = std::fs::read_to_string(path.clone())
                .with_context(|| format!("Failed to load {path}"))?;
            items.push(Some(Box::new(Item {
                key: entry.to_string(),
                value: Some(Box::new(Value::Bytes(contents.into()))),
            })));
        }
        nested_store.items = Some(items);

        // Send the `NestedStore`, represented as a vector of values.
        let res = store
            .write_item(&Item {
                key: key.to_string(),
                value: Some(Box::new(Value::Store(nested_store))),
            })
            .await;
        match res? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // Each entry in this list is a null value in the store.
    for key in config.write_null.into_iter() {
        match store.write_item(&Item { key: key.to_string(), value: None }).await? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Note: For the clarity of this example, allow code to be unused.
#![allow(dead_code)]

use {
    anyhow::{Context as _, Error},
    fidl_examples_keyvaluestore_supporttrees::{
        Item, StoreRequest, StoreRequestStream, Value, WriteError,
    },
    fuchsia_component::server::ServiceFs,
    futures::prelude::*,
    lazy_static::lazy_static,
    regex::Regex,
    std::cell::RefCell,
    std::collections::hash_map::Entry,
    std::collections::HashMap,
    std::str::from_utf8,
};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

// A representation of a key-value store that can contain an arbitrarily deep nesting of other
// key-value stores.
#[allow(clippy::box_collection, reason = "mass allow for https://fxbug.dev/381896734")]
enum StoreNode {
    Leaf(Option<Vec<u8>>),
    Branch(Box<HashMap<String, StoreNode>>),
}

/// Recursive item writer, which takes a `StoreNode` that may not necessarily be the root node, and
/// writes an entry to it.
fn write_item(
    store: &mut HashMap<String, StoreNode>,
    attempt: Item,
    path: &str,
) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            let key = format!("{}{}", &path, entry.key());
            match attempt.value {
                // Null entries are allowed.
                None => {
                    println!("Wrote value: NONE at key: {}", key);
                    entry.insert(StoreNode::Leaf(None));
                }
                Some(value) => match *value {
                    // If this is a nested store, recursively make a new store to insert at this
                    // position.
                    Value::Store(entry_list) => {
                        // Validate the value - absent stores, items lists with no children, or any
                        // of the elements within that list being empty boxes, are all not allowed.
                        if entry_list.items.is_some() {
                            let items = entry_list.items.unwrap();
                            if !items.is_empty() && items.iter().all(|i| i.is_some()) {
                                let nested_path = format!("{}/", key);
                                let mut nested_store = HashMap::<String, StoreNode>::new();
                                for item in items.into_iter() {
                                    write_item(&mut nested_store, *item.unwrap(), &nested_path)?;
                                }

                                println!("Created branch at key: {}", key);
                                entry.insert(StoreNode::Branch(Box::new(nested_store)));
                                return Ok(());
                            }
                        }

                        println!("Write error: INVALID_VALUE, For key: {}", key);
                        return Err(WriteError::InvalidValue);
                    }

                    // This is a simple leaf node on this branch.
                    Value::Bytes(value) => {
                        // Validate the value.
                        if value.is_empty() {
                            println!("Write error: INVALID_VALUE, For key: {}", key);
                            return Err(WriteError::InvalidValue);
                        }

                        println!("Wrote key: {}, value: {:?}", key, from_utf8(&value).unwrap());
                        entry.insert(StoreNode::Leaf(Some(value)));
                    }
                },
            }
            Ok(())
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, StoreNode>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.borrow_mut(), attempt, ""))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

處理權利

FIDL 食譜:處理權利

FIDL 句柄代表某些系統 (通常是 Zircon 核心) 中的獨特能力。句柄權利是指可用於 FIDL 的權限列舉,這些權限與能力相關,例如可否寫入、檢查、傳送信號等。

權利會在編碼和解碼時驗證,確保特定句柄具備介面作者為其分配的權限組合。

如要擴充鍵/值儲存庫以支援匯出備份,最簡單的方法就是新增可停止世界、序列化儲存庫狀態,並將其傳回為 FIDL vector<Item> 的新方法。不過,這種做法有兩個缺點。第一個原因是,備份作業的所有負擔都落在伺服器上 - 用戶端不必付費就能要求備份作業,但對伺服器來說,這項作業的成本非常高。第二個原因是,這項作業涉及大量複製作業:用戶端幾乎肯定會在收到備份檔案後,將產生的備份寫入某些備援資料儲存庫 (例如檔案或資料庫)。讓它解碼這個 (可能非常大的) FIDL 物件,只為了讓它在將實際儲存的任何通訊協定轉送給它時,能立即重新編碼,這非常浪費。

推理

更理想的做法是使用 zircon 的虛擬記憶體物件。我們可以使用桶連鎖方法,在用戶端上儲存備份資料,然後將其傳送至伺服器,再轉送回目標資料儲存庫,而不需要在過程中進行反序列化。只要目標資料儲存庫的通訊協定允許使用 VMO 傳輸資料,這就是完成這類耗用大量資源的作業的首選方式。事實上,Fuchsia 的檔案系統就是實作這個模式。這種做法的優點是,當用戶端要求伺服器執行耗用大量資源的作業時,會強制執行端執行一些工作,盡可能減少雙方之間的工作不平衡情形。

您可以使用 FIDL 資料儲存二進位格式,將 FIDL 值類型儲存至任何以位元組為導向的儲存媒體。我們會將新推出的 FIDL 類型 Exportable 儲存至 VMO。系統會對物件進行編碼並寫入儲存空間 (在本例中為稍後可儲存為檔案的 VMO),並在需要再次存取資料時進行解碼。這與透過 IPC 使用 FIDL 時,稍後對訊息進行編碼、傳輸及解碼的做法非常相似。

為了安全地執行這項操作並遵守最低權限原則,我們應限制代表 VMO 的句柄可能會攜帶的權限。輸入句柄權利,這是 FIDL 的一流方法,可說明特定句柄類型可用的權限。在這種情況下,我們允許在 Export 要求中傳遞至伺服器的 empty VMO 進行讀取、查詢大小、調整大小及寫入。當 VMO 傳回時,我們會移除調整大小和寫入權限,確保在系統傳輸過程中,任何程序 (甚至是某些遠端元件中的惡意行為者) 都無法修改這項資料。

實作

FIDL、CML 和領域介面定義如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.supportexports;

using zx;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value vector<byte>:64000;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// An enumeration of things that may go wrong when trying to mint an export.
type ExportError = flexible enum {
    UNKNOWN = 0;
    EMPTY = 1;
    STORAGE_TOO_SMALL = 2;
};

// A data type describing the structure of a single export. We never actually send this data type
// over the wire (we use the file's VMO instead), but whenever data needs to be written to/read from
// its backing storage as persistent FIDL, it will have this schema.
///
/// The items should be sorted in ascending order, following lexicographic ordering of their keys.
type Exportable = table {
    1: items vector<Item>;
};

/// A very basic key-value store - so basic, in fact, that one may only write to it, never read!
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;

    /// Exports the entire store as a persistent [`Exportable`] FIDL object into a VMO provided by
    /// the client.
    ///
    /// By having the client provide (and speculatively size) the VMO, we force the party requesting
    /// the relatively heavy load of generating a backup to acknowledge and bear some of the costs.
    ///
    /// This method operates by having the client supply an empty VMO, which the server then
    /// attempts to fill. Notice that the server removes the `zx.Rights.WRITE` and
    /// `zx.Rights.SET_PROPERTY` rights from the returned VMO - not even the requesting client may
    /// alter the backup once it has been minted by the server.
    flexible Export(resource struct {
        /// Note that the empty VMO has more rights than the filled one being returned: it has
        /// `zx.Rights.WRITE` (via `zx.RIGHTS_IO`) so that the VMO may be filled with exported data,
        /// and `zx.Rights.SET_PROPERTY` (via `zx.RIGHTS_PROPERTY`) so that it may be resized to
        /// truncate any remaining empty buffer.
        empty zx.Handle:<VMO, zx.RIGHTS_BASIC | zx.RIGHTS_PROPERTY | zx.RIGHTS_IO>;
    }) -> (resource struct {
        /// The `zx.Rights.WRITE` and `zx.Rights.SET_PROPERTY` rights have been removed from the now
        /// filled VMO. No one, not even the client that requested the export, is able to modify
        /// this VMO going forward.
        filled zx.Handle:<VMO, zx.RIGHTS_BASIC | zx.Rights.GET_PROPERTY | zx.Rights.READ>;
    }) error ExportError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.supportexports.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // The size, in bytes, allotted to the export VMO
        max_export_size: { type: "uint64" },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.supportexports.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.supportexports.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.supportexports.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use config::Config;
use fuchsia_component::client::connect_to_protocol;
use std::{thread, time};

use fidl::unpersist;
use fidl_examples_keyvaluestore_supportexports::{Exportable, Item, StoreMarker};
use zx::Vmo;

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        match store.write_item(&Item { key: key, value: value.into_bytes() }).await? {
            Ok(_) => println!("WriteItem Success"),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // If the `max_export_size` is 0, no export is possible, so just ignore this block. This check
    // isn't strictly necessary, but does avoid extra work down the line.
    if config.max_export_size > 0 {
        // Create a 100Kb VMO to store the resulting export. In a real implementation, we would
        // likely receive the VMO representing the to-be-written file from file system like vfs of
        // fxfs.
        let vmo = Vmo::create(config.max_export_size)?;

        // Send the VMO to the server, to be populated with the current state of the key-value
        // store.
        match store.export(vmo).await? {
            Err(err) => {
                println!("Export Error: {}", err.into_primitive());
            }
            Ok(output) => {
                println!("Export Success");

                // Read the exported data (encoded in byte form as persistent FIDL) from the
                // returned VMO. In a real implementation, instead of reading the VMO, we would
                // merely forward it to some other storage-handling process. Doing this using a VMO,
                // rather than FIDL IPC, would save us frivolous reads and writes at each hop.
                let content_size = output.get_content_size().unwrap();
                let mut encoded_bytes = vec![0; content_size as usize];
                output.read(&mut encoded_bytes, 0)?;

                // Decode the persistent FIDL that was just read from the file.
                let exportable = unpersist::<Exportable>(&encoded_bytes).unwrap();
                let items = exportable.items.expect("must always be set");

                // Log some information about the exported data.
                println!("Printing {} exported entries, which are:", items.len());
                for item in items.iter() {
                    println!("  * {}", item.key);
                }
            }
        };
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fuchsia_component::server::ServiceFs;
use futures::prelude::*;
use lazy_static::lazy_static;
use regex::Regex;
use std::cell::RefCell;
use std::collections::hash_map::Entry;
use std::collections::HashMap;

use fidl::{persist, Vmo};
use fidl_examples_keyvaluestore_supportexports::{
    ExportError, Exportable, Item, StoreRequest, StoreRequestStream, WriteError,
};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

/// Handler for the `WriteItem` method.
fn write_item(store: &mut HashMap<String, Vec<u8>>, attempt: Item) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Validate the value.
    if attempt.value.is_empty() {
        println!("Write error: INVALID_VALUE, For key: {}", attempt.key);
        return Err(WriteError::InvalidValue);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote value at key: {}", entry.key());
            entry.insert(attempt.value);
            Ok(())
        }
    }
}

/// Handler for the `Export` method.
fn export(store: &mut HashMap<String, Vec<u8>>, vmo: Vmo) -> Result<Vmo, ExportError> {
    // Empty stores cannot be exported.
    if store.is_empty() {
        return Err(ExportError::Empty);
    }

    // Build the `Exportable` vector locally. That means iterating over the map, and turning it into
    // a vector of items instead.
    let mut exportable = Exportable::default();
    let mut items = store
        .iter()
        .map(|entry| return Item { key: entry.0.clone(), value: entry.1.clone() })
        .collect::<Vec<Item>>();
    items.sort_by(|a, b| a.key.cmp(&b.key));
    exportable.items = Some(items);

    // Encode the bytes - there is a bug in persistent FIDL if this operation fails. Even if it
    // succeeds, make sure to check that the VMO has enough space to handle the encoded export data.
    let encoded_bytes = persist(&exportable).map_err(|_| ExportError::Unknown)?;
    if encoded_bytes.len() as u64 > vmo.get_content_size().map_err(|_| ExportError::Unknown)? {
        return Err(ExportError::StorageTooSmall);
    }

    // Write the (now encoded) persistent FIDL data to the VMO.
    vmo.set_content_size(&(encoded_bytes.len() as u64)).map_err(|_| ExportError::Unknown)?;
    vmo.write(&encoded_bytes, 0).map_err(|_| ExportError::Unknown)?;
    Ok(vmo)
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, Vec<u8>>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.borrow_mut(), attempt))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::Export { empty, responder } => {
                    println!("Export request received");

                    responder
                        .send(export(&mut store.borrow_mut(), empty))
                        .context("error sending reply")?;
                    println!("Export response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.keyvaluestore.supportexports/cpp/fidl.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/component/incoming/cpp/protocol.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <examples/fidl/new/key_value_store/support_exports/cpp_natural/client/config.h>
#include <src/lib/files/file.h>
#include <src/lib/fxl/strings/string_printf.h>

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop and dispatcher.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace. This can fail so it's wrapped in a
  // |zx::result| and it must be checked for errors.
  zx::result client_end = component::Connect<examples_keyvaluestore_supportexports::Store>();
  if (!client_end.is_ok()) {
    FX_LOGS(ERROR) << "Synchronous error when connecting to the |Store| protocol: "
                   << client_end.status_string();
    return -1;
  }

  // Create an asynchronous client using the newly-established connection.
  fidl::Client client(std::move(*client_end), dispatcher);
  FX_LOGS(INFO) << "Outgoing connection enabled";

  for (const auto& action : conf.write_items()) {
    std::string text;
    if (!files::ReadFileToString(fxl::StringPrintf("/pkg/data/%s.txt", action.c_str()), &text)) {
      FX_LOGS(ERROR) << "It looks like the correct `resource` dependency has not been packaged";
      break;
    }

    auto value = std::vector<uint8_t>(text.begin(), text.end());
    client->WriteItem(examples_keyvaluestore_supportexports::Item(action, value))
        .ThenExactlyOnce(
            [&](fidl::Result<examples_keyvaluestore_supportexports::Store::WriteItem> result) {
              // Check if the FIDL call succeeded or not.
              if (!result.is_ok()) {
                if (result.error_value().is_framework_error()) {
                  FX_LOGS(ERROR) << "Unexpected FIDL framework error: " << result.error_value();
                } else {
                  FX_LOGS(INFO) << "WriteItem Error: "
                                << fidl::ToUnderlying(result.error_value().domain_error());
                }
              } else {
                FX_LOGS(INFO) << "WriteItem Success";
              }

              // Quit the loop, thereby handing control back to the outer loop of actions being
              // iterated over.
              loop.Quit();
            });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // If the `max_export_size` is 0, no export is possible, so just ignore this block. This check
  // isn't strictly necessary, but does avoid extra work down the line.
  if (conf.max_export_size() > 0) {
    // Create a 100Kb VMO to store the resulting export. In a real implementation, we would
    // likely receive the VMO representing the to-be-written file from file system like vfs of
    // fxfs.
    zx::vmo vmo;
    if (zx_status_t status = zx::vmo::create(conf.max_export_size(), 0, &vmo); status != ZX_OK) {
      FX_PLOGS(ERROR, status) << "Failed to create VMO";
      return -1;
    }

    client->Export({std::move(vmo)})
        .ThenExactlyOnce(
            [&](fidl::Result<examples_keyvaluestore_supportexports::Store::Export>& result) {
              // Quit the loop, thereby handing control back to the outer loop of actions being
              // iterated over, when we return from this callback.
              loop.Quit();

              if (!result.is_ok()) {
                if (result.error_value().is_framework_error()) {
                  FX_LOGS(ERROR) << "Unexpected FIDL framework error: " << result.error_value();
                } else {
                  FX_LOGS(INFO) << "Export Error: "
                                << fidl::ToUnderlying(result.error_value().domain_error());
                }
                return;
              }

              FX_LOGS(INFO) << "Export Success";
              // Read the exported data (encoded in byte form as persistent FIDL) from the
              // returned VMO. In a real implementation, instead of reading the VMO, we would
              // merely forward it to some other storage-handling process. Doing this using a VMO,
              // rather than FIDL IPC, would save us frivolous reads and writes at each hop.
              size_t content_size = 0;
              zx::vmo vmo = std::move(result->filled());
              if (vmo.get_prop_content_size(&content_size) != ZX_OK) {
                return;
              }
              std::vector<uint8_t> encoded_bytes;
              encoded_bytes.resize(content_size);
              if (vmo.read(encoded_bytes.data(), 0, content_size) != ZX_OK) {
                return;
              }
              // Decode the persistent FIDL that was just read from the file.
              fit::result exportable =
                  fidl::Unpersist<examples_keyvaluestore_supportexports::Exportable>(
                      cpp20::span(encoded_bytes));
              if (exportable.is_error()) {
                FX_LOGS(ERROR) << "Failed to unpersist: " << exportable.error_value();
                return;
              }
              if (!exportable->items().has_value()) {
                FX_LOGS(INFO) << "Expected items to be set";
                return;
              }
              auto& items = exportable->items().value();

              // Log some information about the exported data.
              FX_LOGS(INFO) << "Printing " << items.size() << " exported entries, which are:";
              for (const auto& item : items) {
                FX_LOGS(INFO) << "  * " << item.key();
              }
            });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.keyvaluestore.supportexports/cpp/fidl.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/async/cpp/task.h>
#include <lib/component/outgoing/cpp/outgoing_directory.h>
#include <lib/fidl/cpp/wire/channel.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <algorithm>

#include <re2/re2.h>

// An implementation of the |Store| protocol.
class StoreImpl final : public fidl::Server<examples_keyvaluestore_supportexports::Store> {
 public:
  // Bind this implementation to a channel.
  StoreImpl(async_dispatcher_t* dispatcher,
            fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end)
      : binding_(fidl::BindServer(
            dispatcher, std::move(server_end), this,
            [this](StoreImpl* impl, fidl::UnbindInfo info,
                   fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end) {
              if (info.reason() != ::fidl::Reason::kPeerClosedWhileReading) {
                FX_LOGS(ERROR) << "Shutdown unexpectedly";
              }
              delete this;
            })) {}

  void WriteItem(WriteItemRequest& request, WriteItemCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "WriteItem request received";
    auto key = request.attempt().key();
    auto value = request.attempt().value();

    // Validate the key.
    if (!RE2::FullMatch(key, "^[A-Za-z]\\w+[A-Za-z0-9]$")) {
      FX_LOGS(INFO) << "Write error: INVALID_KEY, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kInvalidKey));
    }

    // Validate the value.
    if (value.empty()) {
      FX_LOGS(INFO) << "Write error: INVALID_VALUE, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kInvalidValue));
    }

    if (key_value_store_.find(key) != key_value_store_.end()) {
      FX_LOGS(INFO) << "Write error: ALREADY_EXISTS, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kAlreadyExists));
    }

    // Ensure that the value does not already exist in the store.
    key_value_store_.insert({key, value});
    FX_LOGS(INFO) << "Wrote value at key: " << key;
    FX_LOGS(INFO) << "WriteItem response sent";
    return completer.Reply(fit::ok());
  }

  void Export(ExportRequest& request, ExportCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "Export request received";
    completer.Reply(Export(std::move(request.empty())));
    FX_LOGS(INFO) << "Export response sent";
  }

  void handle_unknown_method(
      fidl::UnknownMethodMetadata<examples_keyvaluestore_supportexports::Store> metadata,
      fidl::UnknownMethodCompleter::Sync& completer) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << metadata.method_ordinal;
  }

 private:
  using ExportError = ::examples_keyvaluestore_supportexports::ExportError;
  using Exportable = ::examples_keyvaluestore_supportexports::Exportable;
  using Item = ::examples_keyvaluestore_supportexports::Item;

  fit::result<ExportError, zx::vmo> Export(zx::vmo vmo) {
    if (key_value_store_.empty()) {
      return fit::error(ExportError::kEmpty);
    }
    Exportable exportable;
    std::vector<Item> items;
    items.reserve(key_value_store_.size());
    for (const auto& [k, v] : key_value_store_) {
      items.push_back(Item{{.key = k, .value = v}});
    }
    std::sort(items.begin(), items.end(),
              [](const Item& a, const Item& b) { return a.key() < b.key(); });
    exportable.items(std::move(items));
    fit::result encoded = fidl::Persist(exportable);
    if (encoded.is_error()) {
      FX_LOGS(ERROR) << "Failed to encode in persistence convention: " << encoded.error_value();
      return fit::error(ExportError::kUnknown);
    }
    size_t content_size = 0;
    if (vmo.get_prop_content_size(&content_size) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    if (encoded->size() > content_size) {
      return fit::error(ExportError::kStorageTooSmall);
    }
    if (vmo.set_prop_content_size(encoded->size()) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    if (vmo.write(encoded->data(), 0, encoded->size()) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    return fit::ok(std::move(vmo));
  }

  fidl::ServerBindingRef<examples_keyvaluestore_supportexports::Store> binding_;

  // The map that serves as the per-connection instance of the key-value store.
  std::unordered_map<std::string, std::vector<uint8_t>> key_value_store_ = {};
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component. This
  // directory is where the outgoing FIDL protocols are installed so that they can be provided to
  // other components.
  component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);

  // The `ServeFromStartupInfo()` function sets up the outgoing directory with the startup handle.
  // The startup handle is a handle provided to every component by the system, so that they can
  // serve capabilities (e.g. FIDL protocols) to other components.
  zx::result result = outgoing.ServeFromStartupInfo();
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
    return -1;
  }

  // Register a handler for components trying to connect to |Store|.
  result = outgoing.AddUnmanagedProtocol<examples_keyvaluestore_supportexports::Store>(
      [dispatcher](fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end) {
        // Create an instance of our StoreImpl that destroys itself when the connection closes.
        new StoreImpl(dispatcher, std::move(server_end));
      });
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to add Store protocol: " << result.status_string();
    return -1;
  }

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

C++ (Wire)

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.keyvaluestore.supportexports/cpp/wire.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/component/incoming/cpp/protocol.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <examples/fidl/new/key_value_store/support_exports/cpp_wire/client/config.h>
#include <src/lib/files/file.h>
#include <src/lib/fxl/strings/string_printf.h>

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop and dispatcher.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace. This can fail so it's wrapped in a
  // |zx::result| and it must be checked for errors.
  zx::result client_end = component::Connect<examples_keyvaluestore_supportexports::Store>();
  if (!client_end.is_ok()) {
    FX_LOGS(ERROR) << "Synchronous error when connecting to the |Store| protocol: "
                   << client_end.status_string();
    return -1;
  }

  // Create an asynchronous client using the newly-established connection.
  fidl::WireClient client(std::move(*client_end), dispatcher);
  FX_LOGS(INFO) << "Outgoing connection enabled";

  for (const auto& key : conf.write_items()) {
    std::string text;
    if (!files::ReadFileToString(fxl::StringPrintf("/pkg/data/%s.txt", key.c_str()), &text)) {
      FX_LOGS(ERROR) << "It looks like the correct `resource` dependency has not been packaged";
      break;
    }

    auto value = std::vector<uint8_t>(text.begin(), text.end());
    client
        ->WriteItem(
            {fidl::StringView::FromExternal(key), fidl::VectorView<uint8_t>::FromExternal(value)})
        .ThenExactlyOnce(
            [&](fidl::WireUnownedResult<examples_keyvaluestore_supportexports::Store::WriteItem>&
                    result) {
              if (!result.ok()) {
                FX_LOGS(ERROR) << "Unexpected framework error";
              } else if (result->is_error()) {
                FX_LOGS(INFO) << "WriteItem Error: " << fidl::ToUnderlying(result->error_value());
              } else {
                FX_LOGS(INFO) << "WriteItem Success";
              }

              // Quit the loop, thereby handing control back to the outer loop of actions being
              // iterated over.
              loop.Quit();
            });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // If the `max_export_size` is 0, no export is possible, so just ignore this block. This check
  // isn't strictly necessary, but does avoid extra work down the line.
  if (conf.max_export_size() > 0) {
    // Create a 100Kb VMO to store the resulting export. In a real implementation, we would
    // likely receive the VMO representing the to-be-written file from file system like vfs of
    // fxfs.
    zx::vmo vmo;
    if (zx_status_t status = zx::vmo::create(conf.max_export_size(), 0, &vmo); status != ZX_OK) {
      FX_PLOGS(ERROR, status) << "Failed to create VMO";
      return -1;
    }

    client->Export(std::move(vmo))
        .ThenExactlyOnce(
            [&](fidl::WireUnownedResult<examples_keyvaluestore_supportexports::Store::Export>&
                    result) {
              // Quit the loop, thereby handing control back to the outer loop of actions being
              // iterated over, when we return from this callback.
              loop.Quit();

              if (!result.ok()) {
                FX_LOGS(ERROR) << "Unexpected FIDL framework error: " << result.error();
                return;
              }

              if (!result->is_ok()) {
                FX_LOGS(INFO) << "Export Error: " << fidl::ToUnderlying(result->error_value());
                return;
              }

              FX_LOGS(INFO) << "Export Success";
              // Read the exported data (encoded in byte form as persistent FIDL) from the
              // returned VMO. In a real implementation, instead of reading the VMO, we would
              // merely forward it to some other storage-handling process. Doing this using a VMO,
              // rather than FIDL IPC, would save us frivolous reads and writes at each hop.
              size_t content_size = 0;
              zx::vmo vmo = std::move(result->value()->filled);
              if (vmo.get_prop_content_size(&content_size) != ZX_OK) {
                return;
              }
              std::vector<uint8_t> encoded_bytes;
              encoded_bytes.resize(content_size);
              if (vmo.read(encoded_bytes.data(), 0, content_size) != ZX_OK) {
                return;
              }
              // Decode the persistent FIDL that was just read from the file.
              fit::result exportable =
                  fidl::InplaceUnpersist<examples_keyvaluestore_supportexports::wire::Exportable>(
                      cpp20::span(encoded_bytes));
              if (exportable.is_error()) {
                FX_LOGS(ERROR) << "Failed to unpersist: " << exportable.error_value();
                return;
              }
              if (!exportable->has_items()) {
                FX_LOGS(INFO) << "Expected items to be set";
                return;
              }
              auto& items = exportable->items();

              // Log some information about the exported data.
              FX_LOGS(INFO) << "Printing " << items.count() << " exported entries, which are:";
              for (const auto& item : items) {
                FX_LOGS(INFO) << "  * " << item.key.get();
              }
            });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.keyvaluestore.supportexports/cpp/wire.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/async/cpp/task.h>
#include <lib/component/outgoing/cpp/outgoing_directory.h>
#include <lib/fidl/cpp/wire/channel.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <algorithm>

#include <re2/re2.h>

// An implementation of the |Store| protocol.
class StoreImpl final : public fidl::WireServer<examples_keyvaluestore_supportexports::Store> {
 public:
  // Bind this implementation to a channel.
  StoreImpl(async_dispatcher_t* dispatcher,
            fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end)
      : binding_(fidl::BindServer(
            dispatcher, std::move(server_end), this,
            [this](StoreImpl* impl, fidl::UnbindInfo info,
                   fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end) {
              if (info.reason() != ::fidl::Reason::kPeerClosedWhileReading) {
                FX_LOGS(ERROR) << "Shutdown unexpectedly";
              }
              delete this;
            })) {}

  void WriteItem(WriteItemRequestView request, WriteItemCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "WriteItem request received";
    std::string key{request->attempt.key.get()};
    std::vector<uint8_t> value{request->attempt.value.begin(), request->attempt.value.end()};

    // Validate the key.
    if (!RE2::FullMatch(key, "^[A-Za-z]\\w+[A-Za-z0-9]$")) {
      FX_LOGS(INFO) << "Write error: INVALID_KEY, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kInvalidKey));
    }

    // Validate the value.
    if (value.empty()) {
      FX_LOGS(INFO) << "Write error: INVALID_VALUE, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kInvalidValue));
    }

    if (key_value_store_.find(key) != key_value_store_.end()) {
      FX_LOGS(INFO) << "Write error: ALREADY_EXISTS, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kAlreadyExists));
    }

    // Ensure that the value does not already exist in the store.
    key_value_store_.insert({key, value});
    FX_LOGS(INFO) << "Wrote value at key: " << key;
    FX_LOGS(INFO) << "WriteItem response sent";
    return completer.Reply(fit::success());
  }

  void Export(ExportRequestView request, ExportCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "Export request received";
    fit::result result = Export(std::move(request->empty));
    if (result.is_ok()) {
      completer.ReplySuccess(std::move(result.value()));
    } else {
      completer.ReplyError(result.error_value());
    }
    FX_LOGS(INFO) << "Export response sent";
  }

  using ExportError = ::examples_keyvaluestore_supportexports::wire::ExportError;
  using Exportable = ::examples_keyvaluestore_supportexports::wire::Exportable;
  using Item = ::examples_keyvaluestore_supportexports::wire::Item;

  fit::result<ExportError, zx::vmo> Export(zx::vmo vmo) {
    if (key_value_store_.empty()) {
      return fit::error(ExportError::kEmpty);
    }
    fidl::Arena arena;
    fidl::VectorView<Item> items;
    items.Allocate(arena, key_value_store_.size());
    size_t count = 0;
    for (auto& [k, v] : key_value_store_) {
      // Create a wire |Item| object that borrows from |k| and |v|.
      // Since |k| and |v| are references into the long living |key_value_store_|,
      // while |items| only live within the current function scope,
      // this operation is safe.
      items[count] = Item{
          .key = fidl::StringView::FromExternal(k),
          .value = fidl::VectorView<uint8_t>::FromExternal(v),
      };
      count++;
    }
    std::sort(items.begin(), items.end(),
              [](const Item& a, const Item& b) { return a.key.get() < b.key.get(); });
    Exportable exportable = Exportable::Builder(arena).items(items).Build();
    fit::result encoded = fidl::Persist(exportable);
    if (encoded.is_error()) {
      FX_LOGS(ERROR) << "Failed to encode in persistence convention: " << encoded.error_value();
      return fit::error(ExportError::kUnknown);
    }
    size_t content_size = 0;
    if (vmo.get_prop_content_size(&content_size) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    if (encoded->size() > content_size) {
      return fit::error(ExportError::kStorageTooSmall);
    }
    if (vmo.set_prop_content_size(encoded->size()) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    if (vmo.write(encoded->data(), 0, encoded->size()) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    return fit::ok(std::move(vmo));
  }

  void handle_unknown_method(
      fidl::UnknownMethodMetadata<examples_keyvaluestore_supportexports::Store> metadata,
      fidl::UnknownMethodCompleter::Sync& completer) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << metadata.method_ordinal;
  }

 private:
  fidl::ServerBindingRef<examples_keyvaluestore_supportexports::Store> binding_;

  // The map that serves as the per-connection instance of the key-value store.
  //
  // Out-of-line references in wire types are always mutable. Thus the
  // |const std::vector<uint8_t>| from the baseline needs to be changed to
  // non-const as we're making a vector view pointing to it during |Export|,
  // even though in practice the value is never mutated.
  std::unordered_map<std::string, std::vector<uint8_t>> key_value_store_ = {};
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component. This
  // directory is where the outgoing FIDL protocols are installed so that they can be provided to
  // other components.
  component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);

  // The `ServeFromStartupInfo()` function sets up the outgoing directory with the startup handle.
  // The startup handle is a handle provided to every component by the system, so that they can
  // serve capabilities (e.g. FIDL protocols) to other components.
  zx::result result = outgoing.ServeFromStartupInfo();
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
    return -1;
  }

  // Register a handler for components trying to connect to |Store|.
  result = outgoing.AddUnmanagedProtocol<examples_keyvaluestore_supportexports::Store>(
      [dispatcher](fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end) {
        // Create an instance of our StoreImpl that destroys itself when the connection closes.
        new StoreImpl(dispatcher, std::move(server_end));
      });
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to add Store protocol: " << result.status_string();
    return -1;
  }

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

無懈可擊的雙向方法

FIDL 作法:無懈可擊的雙向方法

無懈可擊的雙向方法是無法傳回錯誤值的 FIDL 方法。唯一可能的失敗模式是底層管道發生失敗 (例如無法連線至其中一個端點)。

在這個範例中,您將建立基本計算機伺服器和用戶端,說明先定義,然後提供及使用 FIDL 通訊協定所需的基本設定。

首先,您將定義介面定義和測試裝置。介面定義 (.fidl 檔案本身) 是任何新 FIDL 通訊協定的起點。此外,計算機還包含必要的 CML 和領域定義,可用於建立用戶端-伺服器模式,並用作任意實作項目的專案架構。

請參閱以下 FIDL 程式碼:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// The namespace for this FIDL protocol. This namespace is how both consumers (clients) and providers (servers) reference this protocol.
library examples.calculator.baseline;

// @discoverable indicates 'Calculator' is a protocol that will be served under the examples.calculator.baseline libarary namespace. https://fuchsia.dev/fuchsia-src/reference/fidl/language/attributes#discoverable . If @discoverable is missing, it will lead to a compile time error when trying to import the library.
@discoverable
// A limited-functionality calculator 'protocol' that adds and subtracts integers.
open protocol Calculator {
    // Takes as input a struct with two integers, and returns their sum: (a+b)=sum.  This method is infallible (no errors can be generated) as two int32's cannot overflow a result type of int64.
    flexible Add(struct {
        a int32;
        b int32;
    }) -> (struct {
        sum int64;
    });
    // Takes as input a struct with two integers, and returns their difference: (a-b)=difference.  This method is infallible (no errors can be generated) as two int32's cannot overflow a result type of int64.
    flexible Subtract(struct {
        a int32;
        b int32;
    }) -> (struct {
        difference int64;
    });
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.calculator.baseline.Calculator" },
    ],
    config: {},
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.calculator.baseline.Calculator" },
    ],
    expose: [
        {
            protocol: "examples.calculator.baseline.Calculator",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.calculator.baseline.Calculator",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to both children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// TODO(https://fxbug.dev/42063075): Rust implementation.

伺服器

// TODO(https://fxbug.dev/42063075): Rust implementation.

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42063075): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42063075): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42063075): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42063075): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42063075): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42063075): HLCPP implementation.

對於平台開發人員等特定開發人員而言,從頭開始建立 FIDL 通訊協定 (如本範例所示) 可能更常見。不過,其他類型的開發人員也能從學習如何建構 FIDL 通訊協定中受益,即使他們通常不會這麼做也一樣。這有助您瞭解 FIDL 的所有內容如何搭配運作,包括語法、文法、語言功能、如何提供及使用特定 FIDL 通訊協定,以及建構系統的運作方式。在後續步驟中,我們會根據這個基準提供範例,說明如何擴充現有的 FIDL 通訊協定,這應該是相當常見的做法。

命名的酬載

FIDL 食譜:命名的酬載

命名酬載structtableunion 類型,可直接用於方法要求或回應酬載。在方法酬載重複出現,或已是 FIDL 檔案中其他位置使用的命名型別時,可以使用這些值。

在下列範例中,新增的 ReadItem 方法與現有的 WriteItem 有明顯差異,因為它使用現有的命名類型做為酬載,而非重複的內嵌定義。

推理

原先的唯寫鍵/值儲存庫現在已擴充,可讀取儲存庫中的項目。

實作

套用至 FIDL 和 CML 定義的變更如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.addreaditem;

// Aliases for the key and value. Using aliases helps increase the readability of FIDL files and
// reduces likelihood of errors due to differing constraints.
alias Key = string:128;
alias Value = vector<byte>:64000;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key Key;
    value Value;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// An enumeration of things that may go wrong when trying to read a value out of our store.
type ReadError = flexible enum {
    UNKNOWN = 0;
    NOT_FOUND = 1;
};

/// A very basic key-value store - so basic, in fact, that one may only write to it, never read!
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;

    /// Reads an item from the store.
    flexible ReadItem(struct {
        key Key;
    }) -> (Item) error ReadError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.addreaditem.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        read_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.addreaditem.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.addreaditem.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.addreaditem.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

所有語言的用戶端和伺服器實作方式也都會變更:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use config::Config;
use fidl_examples_keyvaluestore_addreaditem::{Item, StoreMarker};
use fuchsia_component::client::connect_to_protocol;
use std::{str, thread, time};

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        match store.write_item(&Item { key: key, value: value.into_bytes() }).await? {
            Ok(_) => println!("WriteItem Success"),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // The structured config for this client contains `read_items`, a vector of strings, each of
    // which is meant to be read from the key-value store. We iterate over these keys, attempting to
    // read them in turn.
    for key in config.read_items.into_iter() {
        let res = store.read_item(key.as_str()).await;
        match res.unwrap() {
            Ok(val) => {
                println!("ReadItem Success: key: {}, value: {}", key, str::from_utf8(&val.1)?)
            }
            Err(err) => println!("ReadItem Error: {}", err.into_primitive()),
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    fidl_examples_keyvaluestore_addreaditem::{
        Item, ReadError, StoreRequest, StoreRequestStream, WriteError,
    },
    fuchsia_component::server::ServiceFs,
    futures::prelude::*,
    lazy_static::lazy_static,
    regex::Regex,
    std::cell::RefCell,
    std::collections::hash_map::Entry,
    std::collections::HashMap,
};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z][A-Za-z0-9_\./]{2,62}[A-Za-z0-9]$")
            .expect("Key validation regex failed to compile");
}

/// Handler for the `WriteItem` method.
fn write_item(store: &mut HashMap<String, Vec<u8>>, attempt: Item) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Validate the value.
    if attempt.value.is_empty() {
        println!("Write error: INVALID_VALUE, For key: {}", attempt.key);
        return Err(WriteError::InvalidValue);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote value at key: {}", entry.key());
            entry.insert(attempt.value);
            Ok(())
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, Vec<u8>>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.borrow_mut(), attempt))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::ReadItem { key, responder } => {
                    println!("ReadItem request received");

                    // Read the item from the store, returning the appropriate error if it could not be found.
                    responder
                        .send(match store.borrow().get(&key) {
                            Some(found) => {
                                println!("Read value at key: {}", key);
                                Ok((&key, found))
                            }
                            None => {
                                println!("Read error: NOT_FOUND, For key: {}", key);
                                Err(ReadError::NotFound)
                            }
                        })
                        .context("error sending reply")?;
                    println!("ReadItem response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

選填

FIDL 食譜:選用性

您可以透過新增 :optional 限制,讓特定 FIDL 類型變成選用,且不會變更所含訊息的線路形狀。此外,table 版面配置一律為選用,而 struct 版面配置則一律為必用。如要讓 struct 為選用,必須將其包裝在 box<T> 中,藉此變更其所含訊息的線形狀態。

基礎類型 選用版本 選用性會變更線路版面配置嗎?
struct {...} box<struct {...}>
table {...} table {...}
union {...} union {...}:optional
vector<T> vector<T>:optional
string string:optional
zx.Handle zx.Handle:optional
client_end:P client_end:<P, optional>
server_end:P server_end:<P, optional>

所有其他類型 (bitsenumarray<T, N> 和原始類型) 皆無法設為選用。

在這個變化版本中,我們允許鍵/值存放區將其他鍵/值存放區做為成員。簡而言之,我們會將其轉換為樹狀結構。我們會將 value 的原始定義替換為使用兩個成員 union 的定義:一個變化版本會使用與先前相同的 vector<byte> 類型儲存葉結點,另一個則會以其他巢狀儲存庫的形式儲存分支節點。

推理

這裡我們會看到幾種 optionality 的用法,我們可以宣告可能存在或不存在的型別。FIDL 中的選用性有三種:

  • 具有此類型一律會在網路上離線儲存,因此具有內建方式,可透過空值封套描述「缺席」。為這些類型啟用選用性不會影響所包含訊息的線路形狀,只會變更哪些值適用於該特定類型。您可以透過新增 :optional 限制,將 unionvector<T>client_endserver_endzx.Handle 類型設為選用。將 value union 設為選用項目後,我們就能以缺少 value 的形式,引入標準的「空值」項目。這表示空白的 bytes 和缺少/空白的 store 屬性是無效的值。
  • 與上述類型不同,struct 版面配置沒有可儲存空值標頭的額外空間。因此,您必須將其包裝在信封中,以便變更所附帶訊息的線上傳輸形狀。為確保這個線路修改效果易於解讀,Item struct 類型必須套用 box<T> 類型範本。
  • 最後,table 版面配置一律為選用。缺少的 table 只是沒有任何成員集。

樹狀圖是自然的自我參照資料結構:樹狀圖中的任何節點都可能包含純資料的葉節點 (在本例中為字串),或包含更多節點的子樹狀圖。這需要遞迴:Item 的定義現在會遞迴地依附自身!在 FIDL 中表示遞迴類型可能有點棘手,尤其是因為目前的支援有點受限。只要在透過自參照建立的循環中,至少有一個選用型別,我們就能支援這類型別。舉例來說,我們在此將 items struct 成員定義為 box<Item>,藉此中斷包含循環。

這些變更也大量使用匿名類型,也就是在使用點內嵌宣告而非命名的類型,以及頂層 type 宣告。根據預設,產生的語言繫結中匿名類型的名稱會取自其本機內容。舉例來說,新推出的 flexible union 會採用其擁有者成員的名稱 Value,新推出的 struct 會變成 Store,以此類推。由於這項啟發法的使用可能會導致衝突,因此 FIDL 提供逃逸處理程序,允許作者手動覆寫匿名類型的產生名稱。這項作業是透過 @generated_name 屬性完成,可讓使用者變更後端產生的名稱。我們可以在這裡使用一個,將原本的 Store 類型重新命名為 NestedStore,以免與使用相同名稱的 protocol 宣告發生名稱衝突。

實作

FIDL、CML 和領域介面定義的修改如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.supporttrees;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value strict union {
        // Keep the original `bytes` as one of the options in the new union. All leaf nodes in the
        // tree must be `bytes`, or absent unions (representing empty). Empty byte arrays are
        // disallowed.
        1: bytes vector<byte>:64000;

        // Allows a store within a store, thereby turning our flat key-value store into a tree
        // thereof. Note the use of `@generated_name` to prevent a type-name collision with the
        // `Store` protocol below, and the use of `box<T>` to ensure that there is a break in the
        // chain of recursion, thereby allowing `Item` to include itself in its own definition.
        //
        // This is a table so that added fields, like for example a `hash`, can be easily added in
        // the future.
        2: store @generated_name("nested_store") table {
            1: items vector<box<Item>>;
        };
    }:optional;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// A very basic key-value store.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.supporttrees.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A newline separated list nested entries. The first line should be the key
        // for the nested store, and each subsequent entry should be a pointer to a text file
        // containing the string value. The name of that text file (without the `.txt` suffix) will
        // serve as the entries key.
        write_nested: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A list of keys, all of which will be populated as null entries.
        write_null: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.supporttrees.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.supporttrees.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.supporttrees.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    config::Config,
    fidl_examples_keyvaluestore_supporttrees::{Item, NestedStore, StoreMarker, Value},
    fuchsia_component::client::connect_to_protocol,
    std::{thread, time},
};

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        let res = store
            .write_item(&Item {
                key: key.clone(),
                value: Some(Box::new(Value::Bytes(value.into_bytes()))),
            })
            .await;
        match res? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // Add nested entries to the key-value store as well. The entries are strings, where the first
    // line is the key of the entry, and each subsequent entry should be a pointer to a text file
    // containing the string value. The name of that text file (without the `.txt` suffix) will
    // serve as the entries key.
    for spec in config.write_nested.into_iter() {
        let mut items = vec![];
        let mut nested_store = NestedStore::default();
        let mut lines = spec.split("\n");
        let key = lines.next().unwrap();

        // For each entry, make a new entry in the `NestedStore` being built.
        for entry in lines {
            let path = format!("/pkg/data/{}.txt", entry);
            let contents = std::fs::read_to_string(path.clone())
                .with_context(|| format!("Failed to load {path}"))?;
            items.push(Some(Box::new(Item {
                key: entry.to_string(),
                value: Some(Box::new(Value::Bytes(contents.into()))),
            })));
        }
        nested_store.items = Some(items);

        // Send the `NestedStore`, represented as a vector of values.
        let res = store
            .write_item(&Item {
                key: key.to_string(),
                value: Some(Box::new(Value::Store(nested_store))),
            })
            .await;
        match res? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // Each entry in this list is a null value in the store.
    for key in config.write_null.into_iter() {
        match store.write_item(&Item { key: key.to_string(), value: None }).await? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Note: For the clarity of this example, allow code to be unused.
#![allow(dead_code)]

use {
    anyhow::{Context as _, Error},
    fidl_examples_keyvaluestore_supporttrees::{
        Item, StoreRequest, StoreRequestStream, Value, WriteError,
    },
    fuchsia_component::server::ServiceFs,
    futures::prelude::*,
    lazy_static::lazy_static,
    regex::Regex,
    std::cell::RefCell,
    std::collections::hash_map::Entry,
    std::collections::HashMap,
    std::str::from_utf8,
};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

// A representation of a key-value store that can contain an arbitrarily deep nesting of other
// key-value stores.
#[allow(clippy::box_collection, reason = "mass allow for https://fxbug.dev/381896734")]
enum StoreNode {
    Leaf(Option<Vec<u8>>),
    Branch(Box<HashMap<String, StoreNode>>),
}

/// Recursive item writer, which takes a `StoreNode` that may not necessarily be the root node, and
/// writes an entry to it.
fn write_item(
    store: &mut HashMap<String, StoreNode>,
    attempt: Item,
    path: &str,
) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            let key = format!("{}{}", &path, entry.key());
            match attempt.value {
                // Null entries are allowed.
                None => {
                    println!("Wrote value: NONE at key: {}", key);
                    entry.insert(StoreNode::Leaf(None));
                }
                Some(value) => match *value {
                    // If this is a nested store, recursively make a new store to insert at this
                    // position.
                    Value::Store(entry_list) => {
                        // Validate the value - absent stores, items lists with no children, or any
                        // of the elements within that list being empty boxes, are all not allowed.
                        if entry_list.items.is_some() {
                            let items = entry_list.items.unwrap();
                            if !items.is_empty() && items.iter().all(|i| i.is_some()) {
                                let nested_path = format!("{}/", key);
                                let mut nested_store = HashMap::<String, StoreNode>::new();
                                for item in items.into_iter() {
                                    write_item(&mut nested_store, *item.unwrap(), &nested_path)?;
                                }

                                println!("Created branch at key: {}", key);
                                entry.insert(StoreNode::Branch(Box::new(nested_store)));
                                return Ok(());
                            }
                        }

                        println!("Write error: INVALID_VALUE, For key: {}", key);
                        return Err(WriteError::InvalidValue);
                    }

                    // This is a simple leaf node on this branch.
                    Value::Bytes(value) => {
                        // Validate the value.
                        if value.is_empty() {
                            println!("Write error: INVALID_VALUE, For key: {}", key);
                            return Err(WriteError::InvalidValue);
                        }

                        println!("Wrote key: {}, value: {:?}", key, from_utf8(&value).unwrap());
                        entry.insert(StoreNode::Leaf(Some(value)));
                    }
                },
            }
            Ok(())
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, StoreNode>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.borrow_mut(), attempt, ""))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

分頁模式

FIDL 食譜:分頁模式

當您傳送的項目清單可能會變得非常龐大時,有一個實用的策略是透過分頁模式,將該清單分成多個呼叫。使用分頁功能可讓傳送者和接收者之間更精細地同步處理工作:傳送者不會向接收方傳送龐大的清單,而是一次傳送幾個項目,並等待系統回報郵件已處理完畢,再繼續執行。

在 FIDL 術語中,這表示 FIDL 作者應將其轉換為 vector<T>:N 的已確認訊息,而非傳送單一大型 vector<T>,以確保頁面大小和流量控管是 FIDL 合約的一部分。

鍵/值儲存庫的實用操作是依序疊代:也就是說,在指定鍵時,依序傳回鍵後方出現的元素清單 (通常分頁)。

推理

在 FIDL 中,建議使用疊代器執行這項操作,疊代器通常會實作為可執行此疊代的獨立通訊協定。使用獨立的通訊協定 (因此是獨立的管道) 有許多好處,包括將疊代拉取要求與透過主要通訊協定執行的其他作業分開。

通訊協定 P 管道連線的用戶端和伺服器端可分別以 FIDL 資料類型 client_end:Pserver_end:P 表示。這些類型統稱為「通訊協定端點」,代表透過現有 FIDL 連線,將 FIDL 用戶端連線至對應伺服器的其他 (非 @discoverable) 方式!

通訊協定端點是一般 FIDL 概念的特定例項:資源類型。資源類型旨在包含 FIDL 句柄,因此必須對該類型的使用方式施加額外限制。類型必須一律是唯一的,因為基礎資源是由其他某些能力管理工具 (通常是 Zircon 核心) 調解。因此,如果不透過管理員,就無法透過簡單的記憶體內複製作業複製這類資源。為避免重複,FIDL 中的所有資源類型一律為只移動型。

最後,Iterator 通訊協定本身的 Get() 方法會在傳回酬載上使用大小限制。這項限制可限制單一提取作業中可能傳輸的資料量,讓您可以控制資源使用量。它也會建立自然的分頁邊界:伺服器只需一次準備小批次,而非一次處理所有結果。

實作

FIDL、CML 和領域介面定義如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.additerator;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value vector<byte>:64000;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// An enumeration of things that may go wrong when trying to create an iterator.
type IterateConnectionError = flexible enum {
    /// The starting key was not found.
    UNKNOWN_START_AT = 1;
};

/// A key-value store which supports insertion and iteration.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;

    /// Iterates over the items in the store, using lexicographic ordering over the keys.
    ///
    /// The [`iterator`] is [pipelined][pipelining] to the server, such that the client can
    /// immediately send requests over the new connection.
    ///
    /// [pipelining]: https://fuchsia.dev/fuchsia-src/development/api/fidl?hl=en#request-pipelining
    flexible Iterate(resource struct {
        /// If present, requests to start the iteration at this item.
        starting_at string:<128, optional>;

        /// The [`Iterator`] server endpoint. The client creates both ends of the channel and
        /// retains the `client_end` locally to use for pulling iteration pages, while sending the
        /// `server_end` off to be fulfilled by the server.
        iterator server_end:Iterator;
    }) -> () error IterateConnectionError;
};

/// An iterator for the key-value store. Note that this protocol makes no guarantee of atomicity -
/// the values may change between pulls from the iterator. Unlike the `Store` protocol above, this
/// protocol is not `@discoverable`: it is not independently published by the component that
/// implements it, but rather must have one of its two protocol ends transmitted over an existing
/// FIDL connection.
///
/// As is often the case with iterators, the client indicates that they are done with an instance of
/// the iterator by simply closing their end of the connection.
///
/// Since the iterator is associated only with the Iterate method, it is declared as closed rather
/// than open. This is because changes to how iteration works are more likely to require replacing
/// the Iterate method completely (which is fine because that method is flexible) rather than
/// evolving the Iterator protocol.
closed protocol Iterator {
    /// Gets the next batch of keys.
    ///
    /// The client pulls keys rather than having the server proactively push them, to implement
    /// [flow control][flow-control] over the messages.
    ///
    /// [flow-control]:
    ///     https://fuchsia.dev/fuchsia-src/development/api/fidl?hl=en#prefer_pull_to_push
    strict Get() -> (struct {
        /// A list of keys. If the iterator has reached the end of iteration, the list will be
        /// empty. The client is expected to then close the connection.
        entries vector<string:128>:10;
    });
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.additerator.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A key to iterate from, after all items in `write_items` have been written.
        iterate_from: {
            type: "string",
            max_size: 64,
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.additerator.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.additerator.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.additerator.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use config::Config;
use fuchsia_component::client::connect_to_protocol;
use std::{thread, time};

use fidl::endpoints::create_proxy;
use fidl_examples_keyvaluestore_additerator::{Item, IteratorMarker, StoreMarker};
use futures::join;

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        match store.write_item(&Item { key: key, value: value.into_bytes() }).await? {
            Ok(_) => println!("WriteItem Success"),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    if !config.iterate_from.is_empty() {
        // This helper creates a channel, and returns two protocol ends: the `client_end` is already
        // conveniently bound to the correct FIDL protocol, `Iterator`, while the `server_end` is
        // unbound and ready to be sent over the wire.
        let (iterator, server_end) = create_proxy::<IteratorMarker>();

        // There is no need to wait for the iterator to connect before sending the first `Get()`
        // request - since we already hold the `client_end` of the connection, we can start queuing
        // requests on it immediately.
        let connect_to_iterator = store.iterate(Some(config.iterate_from.as_str()), server_end);
        let first_get = iterator.get();

        // Wait until both the connection and the first request resolve - an error in either case
        // triggers an immediate resolution of the combined future.
        let (connection, first_page) = join!(connect_to_iterator, first_get);

        // Handle any connection error. If this has occurred, it is impossible for the first `Get()`
        // call to have resolved successfully, so check this error first.
        if let Err(err) = connection.context("Could not connect to Iterator")? {
            println!("Iterator Connection Error: {}", err.into_primitive());
        } else {
            println!("Iterator Connection Success");

            // Consecutively repeat the `Get()` request if the previous response was not empty.
            let mut entries = first_page.context("Could not get page from Iterator")?;
            while !&entries.is_empty() {
                for entry in entries.iter() {
                    println!("Iterator Entry: {}", entry);
                }
                entries = iterator.get().await.context("Could not get page from Iterator")?;
            }
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fuchsia_component::server::ServiceFs;
use futures::prelude::*;
use lazy_static::lazy_static;
use regex::Regex;

use fidl_examples_keyvaluestore_additerator::{
    Item, IterateConnectionError, IteratorRequest, IteratorRequestStream, StoreRequest,
    StoreRequestStream, WriteError,
};
use fuchsia_async as fasync;
use std::collections::btree_map::Entry;
use std::collections::BTreeMap;
use std::ops::Bound::*;
use std::sync::{Arc, Mutex};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

/// Handler for the `WriteItem` method.
fn write_item(store: &mut BTreeMap<String, Vec<u8>>, attempt: Item) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Validate the value.
    if attempt.value.is_empty() {
        println!("Write error: INVALID_VALUE, For key: {}", attempt.key);
        return Err(WriteError::InvalidValue);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote value at key: {}", entry.key());
            entry.insert(attempt.value);
            Ok(())
        }
    }
}

/// Handler for the `Iterate` method, which deals with validating that the requested start position
/// exists, and then sets up the asynchronous side channel for the actual iteration to occur over.
fn iterate(
    store: Arc<Mutex<BTreeMap<String, Vec<u8>>>>,
    starting_at: Option<String>,
    stream: IteratorRequestStream,
) -> Result<(), IterateConnectionError> {
    // Validate that the starting key, if supplied, actually exists.
    if let Some(start_key) = starting_at.clone() {
        if !store.lock().unwrap().contains_key(&start_key) {
            return Err(IterateConnectionError::UnknownStartAt);
        }
    }

    // Spawn a detached task. This allows the method call to return while the iteration continues in
    // a separate, unawaited task.
    fasync::Task::spawn(async move {
        // Serve the iteration requests. Note that access to the underlying store is behind a
        // contended `Mutex`, meaning that the iteration is not atomic: page contents could shift,
        // change, or disappear entirely between `Get()` requests.
        stream
            .map(|result| result.context("failed request"))
            .try_fold(
                match starting_at {
                    Some(start_key) => Included(start_key),
                    None => Unbounded,
                },
                |mut lower_bound, request| async {
                    match request {
                        IteratorRequest::Get { responder } => {
                            println!("Iterator page request received");

                            // The `page_size` should be kept in sync with the size constraint on
                            // the iterator's response, as defined in the FIDL protocol.
                            static PAGE_SIZE: usize = 10;

                            // An iterator, beginning at `lower_bound` and tracking the pagination's
                            // progress through iteration as each page is pulled by a client-sent
                            // `Get()` request.
                            let held_store = store.lock().unwrap();
                            let mut entries = held_store.range((lower_bound.clone(), Unbounded));
                            let mut current_page = vec![];
                            for _ in 0..PAGE_SIZE {
                                match entries.next() {
                                    Some(entry) => {
                                        current_page.push(entry.0.clone());
                                    }
                                    None => break,
                                }
                            }

                            // Update the `lower_bound` - either inclusive of the next item in the
                            // iteration, or exclusive of the last seen item if the iteration has
                            // finished. This `lower_bound` will be passed to the next request
                            // handler as its starting point.
                            lower_bound = match entries.next() {
                                Some(next) => Included(next.0.clone()),
                                None => match current_page.last() {
                                    Some(tail) => Excluded(tail.clone()),
                                    None => lower_bound,
                                },
                            };

                            // Send the page. At the end of this scope, the `held_store` lock gets
                            // dropped, and therefore released.
                            responder.send(&current_page).context("error sending reply")?;
                            println!("Iterator page sent");
                        }
                    }
                    Ok(lower_bound)
                },
            )
            .await
            .ok();
    })
    .detach();

    Ok(())
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    //
    // Note that we now use an `Arc<Mutex<BTreeMap>>`, replacing the previous `RefCell<HashMap>`.
    // The `BTreeMap` is used because we want an ordered map, to better facilitate iteration. The
    // `Arc<Mutex<...>>` is used because there are now multiple async tasks accessing the: one main
    // task which handles communication over the protocol, and one additional task per iterator
    // protocol. `Arc<Mutex<...>>` is the simplest way to synchronize concurrent access between
    // these racing tasks.
    let store = &Arc::new(Mutex::new(BTreeMap::<String, Vec<u8>>::new()));

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.clone().lock().unwrap(), attempt))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::Iterate { starting_at, iterator, responder } => {
                    println!("Iterate request received");

                    // The `iterate` handler does a quick check to see that the request is valid,
                    // then spins up a separate worker task to serve the newly minted `Iterator`
                    // protocol instance, allowing this call to return immediately and continue the
                    // request stream with other work.
                    responder
                        .send(iterate(store.clone(), starting_at, iterator.into_stream()))
                        .context("error sending reply")?;
                    println!("Iterate response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

保留

FIDL 食譜:持久性

「Persistent」PersistentFIDL 是指沒有基礎傳輸機制的線路編碼二進位 FIDL 資料。而是使用持續性的位元組導向介面 (例如檔案或資料庫項目),將資料儲存一段不定時間。

如要擴充鍵/值儲存庫以支援匯出備份,最簡單的方法就是新增可停止世界、序列化儲存庫狀態,並將其傳回為 FIDL vector<Item> 的新方法。不過,這種做法有兩個缺點。第一個原因是,備份作業的所有負擔都落在伺服器上 - 用戶端不必付費就能要求備份作業,但對伺服器來說,這項作業的成本非常高。第二個原因是,這項作業涉及大量複製作業:用戶端幾乎肯定會在收到備份檔案後,將產生的備份寫入某些備援資料儲存庫 (例如檔案或資料庫)。讓它解碼這個 (可能非常大的) FIDL 物件,只為了讓它在將實際儲存的任何通訊協定轉送給它時,能立即重新編碼,這非常浪費。

推理

更理想的做法是使用 zircon 的虛擬記憶體物件。我們可以使用桶連鎖方法,在用戶端上儲存備份資料,然後將其傳送至伺服器,再轉送回目標資料儲存庫,而不需要在過程中進行反序列化。只要目標資料儲存庫的通訊協定允許使用 VMO 傳輸資料,這就是完成這類耗用大量資源的作業的首選方式。事實上,Fuchsia 的檔案系統就是實作這個模式。這種做法的優點是,當用戶端要求伺服器執行耗用大量資源的作業時,會強制執行端執行一些工作,盡可能減少雙方之間的工作不平衡情形。

您可以使用 FIDL 資料儲存二進位格式,將 FIDL 值類型儲存至任何以位元組為導向的儲存媒體。我們會將新推出的 FIDL 類型 Exportable 儲存至 VMO。系統會對物件進行編碼並寫入儲存空間 (在本例中為稍後可儲存為檔案的 VMO),並在需要再次存取資料時進行解碼。這與透過 IPC 使用 FIDL 時,稍後對訊息進行編碼、傳輸及解碼的做法非常相似。

為了安全地執行這項操作並遵守最低權限原則,我們應限制代表 VMO 的句柄可能會攜帶的權限。輸入句柄權利,這是 FIDL 的一流方法,可說明特定句柄類型可用的權限。在這種情況下,我們允許在 Export 要求中傳遞至伺服器的 empty VMO 進行讀取、查詢大小、調整大小及寫入。當 VMO 傳回時,我們會移除調整大小和寫入權限,確保在系統傳輸過程中,任何程序 (甚至是某些遠端元件中的惡意行為者) 都無法修改這項資料。

實作

FIDL、CML 和領域介面定義如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.supportexports;

using zx;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value vector<byte>:64000;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// An enumeration of things that may go wrong when trying to mint an export.
type ExportError = flexible enum {
    UNKNOWN = 0;
    EMPTY = 1;
    STORAGE_TOO_SMALL = 2;
};

// A data type describing the structure of a single export. We never actually send this data type
// over the wire (we use the file's VMO instead), but whenever data needs to be written to/read from
// its backing storage as persistent FIDL, it will have this schema.
///
/// The items should be sorted in ascending order, following lexicographic ordering of their keys.
type Exportable = table {
    1: items vector<Item>;
};

/// A very basic key-value store - so basic, in fact, that one may only write to it, never read!
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;

    /// Exports the entire store as a persistent [`Exportable`] FIDL object into a VMO provided by
    /// the client.
    ///
    /// By having the client provide (and speculatively size) the VMO, we force the party requesting
    /// the relatively heavy load of generating a backup to acknowledge and bear some of the costs.
    ///
    /// This method operates by having the client supply an empty VMO, which the server then
    /// attempts to fill. Notice that the server removes the `zx.Rights.WRITE` and
    /// `zx.Rights.SET_PROPERTY` rights from the returned VMO - not even the requesting client may
    /// alter the backup once it has been minted by the server.
    flexible Export(resource struct {
        /// Note that the empty VMO has more rights than the filled one being returned: it has
        /// `zx.Rights.WRITE` (via `zx.RIGHTS_IO`) so that the VMO may be filled with exported data,
        /// and `zx.Rights.SET_PROPERTY` (via `zx.RIGHTS_PROPERTY`) so that it may be resized to
        /// truncate any remaining empty buffer.
        empty zx.Handle:<VMO, zx.RIGHTS_BASIC | zx.RIGHTS_PROPERTY | zx.RIGHTS_IO>;
    }) -> (resource struct {
        /// The `zx.Rights.WRITE` and `zx.Rights.SET_PROPERTY` rights have been removed from the now
        /// filled VMO. No one, not even the client that requested the export, is able to modify
        /// this VMO going forward.
        filled zx.Handle:<VMO, zx.RIGHTS_BASIC | zx.Rights.GET_PROPERTY | zx.Rights.READ>;
    }) error ExportError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.supportexports.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // The size, in bytes, allotted to the export VMO
        max_export_size: { type: "uint64" },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.supportexports.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.supportexports.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.supportexports.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use config::Config;
use fuchsia_component::client::connect_to_protocol;
use std::{thread, time};

use fidl::unpersist;
use fidl_examples_keyvaluestore_supportexports::{Exportable, Item, StoreMarker};
use zx::Vmo;

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        match store.write_item(&Item { key: key, value: value.into_bytes() }).await? {
            Ok(_) => println!("WriteItem Success"),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // If the `max_export_size` is 0, no export is possible, so just ignore this block. This check
    // isn't strictly necessary, but does avoid extra work down the line.
    if config.max_export_size > 0 {
        // Create a 100Kb VMO to store the resulting export. In a real implementation, we would
        // likely receive the VMO representing the to-be-written file from file system like vfs of
        // fxfs.
        let vmo = Vmo::create(config.max_export_size)?;

        // Send the VMO to the server, to be populated with the current state of the key-value
        // store.
        match store.export(vmo).await? {
            Err(err) => {
                println!("Export Error: {}", err.into_primitive());
            }
            Ok(output) => {
                println!("Export Success");

                // Read the exported data (encoded in byte form as persistent FIDL) from the
                // returned VMO. In a real implementation, instead of reading the VMO, we would
                // merely forward it to some other storage-handling process. Doing this using a VMO,
                // rather than FIDL IPC, would save us frivolous reads and writes at each hop.
                let content_size = output.get_content_size().unwrap();
                let mut encoded_bytes = vec![0; content_size as usize];
                output.read(&mut encoded_bytes, 0)?;

                // Decode the persistent FIDL that was just read from the file.
                let exportable = unpersist::<Exportable>(&encoded_bytes).unwrap();
                let items = exportable.items.expect("must always be set");

                // Log some information about the exported data.
                println!("Printing {} exported entries, which are:", items.len());
                for item in items.iter() {
                    println!("  * {}", item.key);
                }
            }
        };
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fuchsia_component::server::ServiceFs;
use futures::prelude::*;
use lazy_static::lazy_static;
use regex::Regex;
use std::cell::RefCell;
use std::collections::hash_map::Entry;
use std::collections::HashMap;

use fidl::{persist, Vmo};
use fidl_examples_keyvaluestore_supportexports::{
    ExportError, Exportable, Item, StoreRequest, StoreRequestStream, WriteError,
};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

/// Handler for the `WriteItem` method.
fn write_item(store: &mut HashMap<String, Vec<u8>>, attempt: Item) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Validate the value.
    if attempt.value.is_empty() {
        println!("Write error: INVALID_VALUE, For key: {}", attempt.key);
        return Err(WriteError::InvalidValue);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote value at key: {}", entry.key());
            entry.insert(attempt.value);
            Ok(())
        }
    }
}

/// Handler for the `Export` method.
fn export(store: &mut HashMap<String, Vec<u8>>, vmo: Vmo) -> Result<Vmo, ExportError> {
    // Empty stores cannot be exported.
    if store.is_empty() {
        return Err(ExportError::Empty);
    }

    // Build the `Exportable` vector locally. That means iterating over the map, and turning it into
    // a vector of items instead.
    let mut exportable = Exportable::default();
    let mut items = store
        .iter()
        .map(|entry| return Item { key: entry.0.clone(), value: entry.1.clone() })
        .collect::<Vec<Item>>();
    items.sort_by(|a, b| a.key.cmp(&b.key));
    exportable.items = Some(items);

    // Encode the bytes - there is a bug in persistent FIDL if this operation fails. Even if it
    // succeeds, make sure to check that the VMO has enough space to handle the encoded export data.
    let encoded_bytes = persist(&exportable).map_err(|_| ExportError::Unknown)?;
    if encoded_bytes.len() as u64 > vmo.get_content_size().map_err(|_| ExportError::Unknown)? {
        return Err(ExportError::StorageTooSmall);
    }

    // Write the (now encoded) persistent FIDL data to the VMO.
    vmo.set_content_size(&(encoded_bytes.len() as u64)).map_err(|_| ExportError::Unknown)?;
    vmo.write(&encoded_bytes, 0).map_err(|_| ExportError::Unknown)?;
    Ok(vmo)
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, Vec<u8>>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.borrow_mut(), attempt))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::Export { empty, responder } => {
                    println!("Export request received");

                    responder
                        .send(export(&mut store.borrow_mut(), empty))
                        .context("error sending reply")?;
                    println!("Export response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.keyvaluestore.supportexports/cpp/fidl.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/component/incoming/cpp/protocol.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <examples/fidl/new/key_value_store/support_exports/cpp_natural/client/config.h>
#include <src/lib/files/file.h>
#include <src/lib/fxl/strings/string_printf.h>

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop and dispatcher.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace. This can fail so it's wrapped in a
  // |zx::result| and it must be checked for errors.
  zx::result client_end = component::Connect<examples_keyvaluestore_supportexports::Store>();
  if (!client_end.is_ok()) {
    FX_LOGS(ERROR) << "Synchronous error when connecting to the |Store| protocol: "
                   << client_end.status_string();
    return -1;
  }

  // Create an asynchronous client using the newly-established connection.
  fidl::Client client(std::move(*client_end), dispatcher);
  FX_LOGS(INFO) << "Outgoing connection enabled";

  for (const auto& action : conf.write_items()) {
    std::string text;
    if (!files::ReadFileToString(fxl::StringPrintf("/pkg/data/%s.txt", action.c_str()), &text)) {
      FX_LOGS(ERROR) << "It looks like the correct `resource` dependency has not been packaged";
      break;
    }

    auto value = std::vector<uint8_t>(text.begin(), text.end());
    client->WriteItem(examples_keyvaluestore_supportexports::Item(action, value))
        .ThenExactlyOnce(
            [&](fidl::Result<examples_keyvaluestore_supportexports::Store::WriteItem> result) {
              // Check if the FIDL call succeeded or not.
              if (!result.is_ok()) {
                if (result.error_value().is_framework_error()) {
                  FX_LOGS(ERROR) << "Unexpected FIDL framework error: " << result.error_value();
                } else {
                  FX_LOGS(INFO) << "WriteItem Error: "
                                << fidl::ToUnderlying(result.error_value().domain_error());
                }
              } else {
                FX_LOGS(INFO) << "WriteItem Success";
              }

              // Quit the loop, thereby handing control back to the outer loop of actions being
              // iterated over.
              loop.Quit();
            });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // If the `max_export_size` is 0, no export is possible, so just ignore this block. This check
  // isn't strictly necessary, but does avoid extra work down the line.
  if (conf.max_export_size() > 0) {
    // Create a 100Kb VMO to store the resulting export. In a real implementation, we would
    // likely receive the VMO representing the to-be-written file from file system like vfs of
    // fxfs.
    zx::vmo vmo;
    if (zx_status_t status = zx::vmo::create(conf.max_export_size(), 0, &vmo); status != ZX_OK) {
      FX_PLOGS(ERROR, status) << "Failed to create VMO";
      return -1;
    }

    client->Export({std::move(vmo)})
        .ThenExactlyOnce(
            [&](fidl::Result<examples_keyvaluestore_supportexports::Store::Export>& result) {
              // Quit the loop, thereby handing control back to the outer loop of actions being
              // iterated over, when we return from this callback.
              loop.Quit();

              if (!result.is_ok()) {
                if (result.error_value().is_framework_error()) {
                  FX_LOGS(ERROR) << "Unexpected FIDL framework error: " << result.error_value();
                } else {
                  FX_LOGS(INFO) << "Export Error: "
                                << fidl::ToUnderlying(result.error_value().domain_error());
                }
                return;
              }

              FX_LOGS(INFO) << "Export Success";
              // Read the exported data (encoded in byte form as persistent FIDL) from the
              // returned VMO. In a real implementation, instead of reading the VMO, we would
              // merely forward it to some other storage-handling process. Doing this using a VMO,
              // rather than FIDL IPC, would save us frivolous reads and writes at each hop.
              size_t content_size = 0;
              zx::vmo vmo = std::move(result->filled());
              if (vmo.get_prop_content_size(&content_size) != ZX_OK) {
                return;
              }
              std::vector<uint8_t> encoded_bytes;
              encoded_bytes.resize(content_size);
              if (vmo.read(encoded_bytes.data(), 0, content_size) != ZX_OK) {
                return;
              }
              // Decode the persistent FIDL that was just read from the file.
              fit::result exportable =
                  fidl::Unpersist<examples_keyvaluestore_supportexports::Exportable>(
                      cpp20::span(encoded_bytes));
              if (exportable.is_error()) {
                FX_LOGS(ERROR) << "Failed to unpersist: " << exportable.error_value();
                return;
              }
              if (!exportable->items().has_value()) {
                FX_LOGS(INFO) << "Expected items to be set";
                return;
              }
              auto& items = exportable->items().value();

              // Log some information about the exported data.
              FX_LOGS(INFO) << "Printing " << items.size() << " exported entries, which are:";
              for (const auto& item : items) {
                FX_LOGS(INFO) << "  * " << item.key();
              }
            });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.keyvaluestore.supportexports/cpp/fidl.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/async/cpp/task.h>
#include <lib/component/outgoing/cpp/outgoing_directory.h>
#include <lib/fidl/cpp/wire/channel.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <algorithm>

#include <re2/re2.h>

// An implementation of the |Store| protocol.
class StoreImpl final : public fidl::Server<examples_keyvaluestore_supportexports::Store> {
 public:
  // Bind this implementation to a channel.
  StoreImpl(async_dispatcher_t* dispatcher,
            fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end)
      : binding_(fidl::BindServer(
            dispatcher, std::move(server_end), this,
            [this](StoreImpl* impl, fidl::UnbindInfo info,
                   fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end) {
              if (info.reason() != ::fidl::Reason::kPeerClosedWhileReading) {
                FX_LOGS(ERROR) << "Shutdown unexpectedly";
              }
              delete this;
            })) {}

  void WriteItem(WriteItemRequest& request, WriteItemCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "WriteItem request received";
    auto key = request.attempt().key();
    auto value = request.attempt().value();

    // Validate the key.
    if (!RE2::FullMatch(key, "^[A-Za-z]\\w+[A-Za-z0-9]$")) {
      FX_LOGS(INFO) << "Write error: INVALID_KEY, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kInvalidKey));
    }

    // Validate the value.
    if (value.empty()) {
      FX_LOGS(INFO) << "Write error: INVALID_VALUE, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kInvalidValue));
    }

    if (key_value_store_.find(key) != key_value_store_.end()) {
      FX_LOGS(INFO) << "Write error: ALREADY_EXISTS, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kAlreadyExists));
    }

    // Ensure that the value does not already exist in the store.
    key_value_store_.insert({key, value});
    FX_LOGS(INFO) << "Wrote value at key: " << key;
    FX_LOGS(INFO) << "WriteItem response sent";
    return completer.Reply(fit::ok());
  }

  void Export(ExportRequest& request, ExportCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "Export request received";
    completer.Reply(Export(std::move(request.empty())));
    FX_LOGS(INFO) << "Export response sent";
  }

  void handle_unknown_method(
      fidl::UnknownMethodMetadata<examples_keyvaluestore_supportexports::Store> metadata,
      fidl::UnknownMethodCompleter::Sync& completer) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << metadata.method_ordinal;
  }

 private:
  using ExportError = ::examples_keyvaluestore_supportexports::ExportError;
  using Exportable = ::examples_keyvaluestore_supportexports::Exportable;
  using Item = ::examples_keyvaluestore_supportexports::Item;

  fit::result<ExportError, zx::vmo> Export(zx::vmo vmo) {
    if (key_value_store_.empty()) {
      return fit::error(ExportError::kEmpty);
    }
    Exportable exportable;
    std::vector<Item> items;
    items.reserve(key_value_store_.size());
    for (const auto& [k, v] : key_value_store_) {
      items.push_back(Item{{.key = k, .value = v}});
    }
    std::sort(items.begin(), items.end(),
              [](const Item& a, const Item& b) { return a.key() < b.key(); });
    exportable.items(std::move(items));
    fit::result encoded = fidl::Persist(exportable);
    if (encoded.is_error()) {
      FX_LOGS(ERROR) << "Failed to encode in persistence convention: " << encoded.error_value();
      return fit::error(ExportError::kUnknown);
    }
    size_t content_size = 0;
    if (vmo.get_prop_content_size(&content_size) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    if (encoded->size() > content_size) {
      return fit::error(ExportError::kStorageTooSmall);
    }
    if (vmo.set_prop_content_size(encoded->size()) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    if (vmo.write(encoded->data(), 0, encoded->size()) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    return fit::ok(std::move(vmo));
  }

  fidl::ServerBindingRef<examples_keyvaluestore_supportexports::Store> binding_;

  // The map that serves as the per-connection instance of the key-value store.
  std::unordered_map<std::string, std::vector<uint8_t>> key_value_store_ = {};
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component. This
  // directory is where the outgoing FIDL protocols are installed so that they can be provided to
  // other components.
  component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);

  // The `ServeFromStartupInfo()` function sets up the outgoing directory with the startup handle.
  // The startup handle is a handle provided to every component by the system, so that they can
  // serve capabilities (e.g. FIDL protocols) to other components.
  zx::result result = outgoing.ServeFromStartupInfo();
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
    return -1;
  }

  // Register a handler for components trying to connect to |Store|.
  result = outgoing.AddUnmanagedProtocol<examples_keyvaluestore_supportexports::Store>(
      [dispatcher](fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end) {
        // Create an instance of our StoreImpl that destroys itself when the connection closes.
        new StoreImpl(dispatcher, std::move(server_end));
      });
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to add Store protocol: " << result.status_string();
    return -1;
  }

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

C++ (Wire)

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.keyvaluestore.supportexports/cpp/wire.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/component/incoming/cpp/protocol.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <examples/fidl/new/key_value_store/support_exports/cpp_wire/client/config.h>
#include <src/lib/files/file.h>
#include <src/lib/fxl/strings/string_printf.h>

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop and dispatcher.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace. This can fail so it's wrapped in a
  // |zx::result| and it must be checked for errors.
  zx::result client_end = component::Connect<examples_keyvaluestore_supportexports::Store>();
  if (!client_end.is_ok()) {
    FX_LOGS(ERROR) << "Synchronous error when connecting to the |Store| protocol: "
                   << client_end.status_string();
    return -1;
  }

  // Create an asynchronous client using the newly-established connection.
  fidl::WireClient client(std::move(*client_end), dispatcher);
  FX_LOGS(INFO) << "Outgoing connection enabled";

  for (const auto& key : conf.write_items()) {
    std::string text;
    if (!files::ReadFileToString(fxl::StringPrintf("/pkg/data/%s.txt", key.c_str()), &text)) {
      FX_LOGS(ERROR) << "It looks like the correct `resource` dependency has not been packaged";
      break;
    }

    auto value = std::vector<uint8_t>(text.begin(), text.end());
    client
        ->WriteItem(
            {fidl::StringView::FromExternal(key), fidl::VectorView<uint8_t>::FromExternal(value)})
        .ThenExactlyOnce(
            [&](fidl::WireUnownedResult<examples_keyvaluestore_supportexports::Store::WriteItem>&
                    result) {
              if (!result.ok()) {
                FX_LOGS(ERROR) << "Unexpected framework error";
              } else if (result->is_error()) {
                FX_LOGS(INFO) << "WriteItem Error: " << fidl::ToUnderlying(result->error_value());
              } else {
                FX_LOGS(INFO) << "WriteItem Success";
              }

              // Quit the loop, thereby handing control back to the outer loop of actions being
              // iterated over.
              loop.Quit();
            });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // If the `max_export_size` is 0, no export is possible, so just ignore this block. This check
  // isn't strictly necessary, but does avoid extra work down the line.
  if (conf.max_export_size() > 0) {
    // Create a 100Kb VMO to store the resulting export. In a real implementation, we would
    // likely receive the VMO representing the to-be-written file from file system like vfs of
    // fxfs.
    zx::vmo vmo;
    if (zx_status_t status = zx::vmo::create(conf.max_export_size(), 0, &vmo); status != ZX_OK) {
      FX_PLOGS(ERROR, status) << "Failed to create VMO";
      return -1;
    }

    client->Export(std::move(vmo))
        .ThenExactlyOnce(
            [&](fidl::WireUnownedResult<examples_keyvaluestore_supportexports::Store::Export>&
                    result) {
              // Quit the loop, thereby handing control back to the outer loop of actions being
              // iterated over, when we return from this callback.
              loop.Quit();

              if (!result.ok()) {
                FX_LOGS(ERROR) << "Unexpected FIDL framework error: " << result.error();
                return;
              }

              if (!result->is_ok()) {
                FX_LOGS(INFO) << "Export Error: " << fidl::ToUnderlying(result->error_value());
                return;
              }

              FX_LOGS(INFO) << "Export Success";
              // Read the exported data (encoded in byte form as persistent FIDL) from the
              // returned VMO. In a real implementation, instead of reading the VMO, we would
              // merely forward it to some other storage-handling process. Doing this using a VMO,
              // rather than FIDL IPC, would save us frivolous reads and writes at each hop.
              size_t content_size = 0;
              zx::vmo vmo = std::move(result->value()->filled);
              if (vmo.get_prop_content_size(&content_size) != ZX_OK) {
                return;
              }
              std::vector<uint8_t> encoded_bytes;
              encoded_bytes.resize(content_size);
              if (vmo.read(encoded_bytes.data(), 0, content_size) != ZX_OK) {
                return;
              }
              // Decode the persistent FIDL that was just read from the file.
              fit::result exportable =
                  fidl::InplaceUnpersist<examples_keyvaluestore_supportexports::wire::Exportable>(
                      cpp20::span(encoded_bytes));
              if (exportable.is_error()) {
                FX_LOGS(ERROR) << "Failed to unpersist: " << exportable.error_value();
                return;
              }
              if (!exportable->has_items()) {
                FX_LOGS(INFO) << "Expected items to be set";
                return;
              }
              auto& items = exportable->items();

              // Log some information about the exported data.
              FX_LOGS(INFO) << "Printing " << items.count() << " exported entries, which are:";
              for (const auto& item : items) {
                FX_LOGS(INFO) << "  * " << item.key.get();
              }
            });

    // Run the loop until the callback is resolved, at which point we can continue from here.
    loop.Run();
    loop.ResetQuit();
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.keyvaluestore.supportexports/cpp/wire.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/async/cpp/task.h>
#include <lib/component/outgoing/cpp/outgoing_directory.h>
#include <lib/fidl/cpp/wire/channel.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <algorithm>

#include <re2/re2.h>

// An implementation of the |Store| protocol.
class StoreImpl final : public fidl::WireServer<examples_keyvaluestore_supportexports::Store> {
 public:
  // Bind this implementation to a channel.
  StoreImpl(async_dispatcher_t* dispatcher,
            fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end)
      : binding_(fidl::BindServer(
            dispatcher, std::move(server_end), this,
            [this](StoreImpl* impl, fidl::UnbindInfo info,
                   fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end) {
              if (info.reason() != ::fidl::Reason::kPeerClosedWhileReading) {
                FX_LOGS(ERROR) << "Shutdown unexpectedly";
              }
              delete this;
            })) {}

  void WriteItem(WriteItemRequestView request, WriteItemCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "WriteItem request received";
    std::string key{request->attempt.key.get()};
    std::vector<uint8_t> value{request->attempt.value.begin(), request->attempt.value.end()};

    // Validate the key.
    if (!RE2::FullMatch(key, "^[A-Za-z]\\w+[A-Za-z0-9]$")) {
      FX_LOGS(INFO) << "Write error: INVALID_KEY, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kInvalidKey));
    }

    // Validate the value.
    if (value.empty()) {
      FX_LOGS(INFO) << "Write error: INVALID_VALUE, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kInvalidValue));
    }

    if (key_value_store_.find(key) != key_value_store_.end()) {
      FX_LOGS(INFO) << "Write error: ALREADY_EXISTS, For key: " << key;
      FX_LOGS(INFO) << "WriteItem response sent";
      return completer.Reply(
          fit::error(examples_keyvaluestore_supportexports::WriteError::kAlreadyExists));
    }

    // Ensure that the value does not already exist in the store.
    key_value_store_.insert({key, value});
    FX_LOGS(INFO) << "Wrote value at key: " << key;
    FX_LOGS(INFO) << "WriteItem response sent";
    return completer.Reply(fit::success());
  }

  void Export(ExportRequestView request, ExportCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "Export request received";
    fit::result result = Export(std::move(request->empty));
    if (result.is_ok()) {
      completer.ReplySuccess(std::move(result.value()));
    } else {
      completer.ReplyError(result.error_value());
    }
    FX_LOGS(INFO) << "Export response sent";
  }

  using ExportError = ::examples_keyvaluestore_supportexports::wire::ExportError;
  using Exportable = ::examples_keyvaluestore_supportexports::wire::Exportable;
  using Item = ::examples_keyvaluestore_supportexports::wire::Item;

  fit::result<ExportError, zx::vmo> Export(zx::vmo vmo) {
    if (key_value_store_.empty()) {
      return fit::error(ExportError::kEmpty);
    }
    fidl::Arena arena;
    fidl::VectorView<Item> items;
    items.Allocate(arena, key_value_store_.size());
    size_t count = 0;
    for (auto& [k, v] : key_value_store_) {
      // Create a wire |Item| object that borrows from |k| and |v|.
      // Since |k| and |v| are references into the long living |key_value_store_|,
      // while |items| only live within the current function scope,
      // this operation is safe.
      items[count] = Item{
          .key = fidl::StringView::FromExternal(k),
          .value = fidl::VectorView<uint8_t>::FromExternal(v),
      };
      count++;
    }
    std::sort(items.begin(), items.end(),
              [](const Item& a, const Item& b) { return a.key.get() < b.key.get(); });
    Exportable exportable = Exportable::Builder(arena).items(items).Build();
    fit::result encoded = fidl::Persist(exportable);
    if (encoded.is_error()) {
      FX_LOGS(ERROR) << "Failed to encode in persistence convention: " << encoded.error_value();
      return fit::error(ExportError::kUnknown);
    }
    size_t content_size = 0;
    if (vmo.get_prop_content_size(&content_size) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    if (encoded->size() > content_size) {
      return fit::error(ExportError::kStorageTooSmall);
    }
    if (vmo.set_prop_content_size(encoded->size()) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    if (vmo.write(encoded->data(), 0, encoded->size()) != ZX_OK) {
      return fit::error(ExportError::kUnknown);
    }
    return fit::ok(std::move(vmo));
  }

  void handle_unknown_method(
      fidl::UnknownMethodMetadata<examples_keyvaluestore_supportexports::Store> metadata,
      fidl::UnknownMethodCompleter::Sync& completer) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << metadata.method_ordinal;
  }

 private:
  fidl::ServerBindingRef<examples_keyvaluestore_supportexports::Store> binding_;

  // The map that serves as the per-connection instance of the key-value store.
  //
  // Out-of-line references in wire types are always mutable. Thus the
  // |const std::vector<uint8_t>| from the baseline needs to be changed to
  // non-const as we're making a vector view pointing to it during |Export|,
  // even though in practice the value is never mutated.
  std::unordered_map<std::string, std::vector<uint8_t>> key_value_store_ = {};
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component. This
  // directory is where the outgoing FIDL protocols are installed so that they can be provided to
  // other components.
  component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);

  // The `ServeFromStartupInfo()` function sets up the outgoing directory with the startup handle.
  // The startup handle is a handle provided to every component by the system, so that they can
  // serve capabilities (e.g. FIDL protocols) to other components.
  zx::result result = outgoing.ServeFromStartupInfo();
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
    return -1;
  }

  // Register a handler for components trying to connect to |Store|.
  result = outgoing.AddUnmanagedProtocol<examples_keyvaluestore_supportexports::Store>(
      [dispatcher](fidl::ServerEnd<examples_keyvaluestore_supportexports::Store> server_end) {
        // Create an instance of our StoreImpl that destroys itself when the connection closes.
        new StoreImpl(dispatcher, std::move(server_end));
      });
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to add Store protocol: " << result.status_string();
    return -1;
  }

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

通訊協定結束

FIDL 食譜:通訊協定結束

「通訊協定端」代表管道連線的一個端點,可透過該端點傳送特定的 FIDL 通訊協定。此連線的伺服器端為 server_end,而用戶端端為 client_end

通訊協定端點有必要的限制,可指定透過連線使用的 FIDL 通訊協定。舉例來說,client_end:Foo 代表 Zircon 管道的用戶端端點,透過該端點交換的所有訊息都會符合該 FIDL 通訊協定定義的方法和事件,而 server_end:Foo 則代表相反的端點。

鍵/值儲存庫的實用操作是依序疊代:也就是說,在指定鍵時,依序傳回鍵後方出現的元素清單 (通常分頁)。

推理

在 FIDL 中,建議使用疊代器執行這項操作,疊代器通常會實作為可執行此疊代的獨立通訊協定。使用獨立的通訊協定 (因此是獨立的管道) 有許多好處,包括將疊代拉取要求與透過主要通訊協定執行的其他作業分開。

通訊協定 P 管道連線的用戶端和伺服器端可分別以 FIDL 資料類型 client_end:Pserver_end:P 表示。這些類型統稱為「通訊協定端點」,代表透過現有 FIDL 連線,將 FIDL 用戶端連線至對應伺服器的其他 (非 @discoverable) 方式!

通訊協定端點是一般 FIDL 概念的特定例項:資源類型。資源類型旨在包含 FIDL 句柄,因此必須對該類型的使用方式施加額外限制。類型必須一律是唯一的,因為基礎資源是由其他某些能力管理工具 (通常是 Zircon 核心) 調解。因此,如果不透過管理員,就無法透過簡單的記憶體內複製作業複製這類資源。為避免重複,FIDL 中的所有資源類型一律為只移動型。

最後,Iterator 通訊協定本身的 Get() 方法會在傳回酬載上使用大小限制。這項限制可限制單一提取作業中可能傳輸的資料量,讓您可以控制資源使用量。它也會建立自然的分頁邊界:伺服器只需一次準備小批次,而非一次處理所有結果。

實作

FIDL、CML 和領域介面定義如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.additerator;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value vector<byte>:64000;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// An enumeration of things that may go wrong when trying to create an iterator.
type IterateConnectionError = flexible enum {
    /// The starting key was not found.
    UNKNOWN_START_AT = 1;
};

/// A key-value store which supports insertion and iteration.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;

    /// Iterates over the items in the store, using lexicographic ordering over the keys.
    ///
    /// The [`iterator`] is [pipelined][pipelining] to the server, such that the client can
    /// immediately send requests over the new connection.
    ///
    /// [pipelining]: https://fuchsia.dev/fuchsia-src/development/api/fidl?hl=en#request-pipelining
    flexible Iterate(resource struct {
        /// If present, requests to start the iteration at this item.
        starting_at string:<128, optional>;

        /// The [`Iterator`] server endpoint. The client creates both ends of the channel and
        /// retains the `client_end` locally to use for pulling iteration pages, while sending the
        /// `server_end` off to be fulfilled by the server.
        iterator server_end:Iterator;
    }) -> () error IterateConnectionError;
};

/// An iterator for the key-value store. Note that this protocol makes no guarantee of atomicity -
/// the values may change between pulls from the iterator. Unlike the `Store` protocol above, this
/// protocol is not `@discoverable`: it is not independently published by the component that
/// implements it, but rather must have one of its two protocol ends transmitted over an existing
/// FIDL connection.
///
/// As is often the case with iterators, the client indicates that they are done with an instance of
/// the iterator by simply closing their end of the connection.
///
/// Since the iterator is associated only with the Iterate method, it is declared as closed rather
/// than open. This is because changes to how iteration works are more likely to require replacing
/// the Iterate method completely (which is fine because that method is flexible) rather than
/// evolving the Iterator protocol.
closed protocol Iterator {
    /// Gets the next batch of keys.
    ///
    /// The client pulls keys rather than having the server proactively push them, to implement
    /// [flow control][flow-control] over the messages.
    ///
    /// [flow-control]:
    ///     https://fuchsia.dev/fuchsia-src/development/api/fidl?hl=en#prefer_pull_to_push
    strict Get() -> (struct {
        /// A list of keys. If the iterator has reached the end of iteration, the list will be
        /// empty. The client is expected to then close the connection.
        entries vector<string:128>:10;
    });
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.additerator.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A key to iterate from, after all items in `write_items` have been written.
        iterate_from: {
            type: "string",
            max_size: 64,
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.additerator.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.additerator.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.additerator.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use config::Config;
use fuchsia_component::client::connect_to_protocol;
use std::{thread, time};

use fidl::endpoints::create_proxy;
use fidl_examples_keyvaluestore_additerator::{Item, IteratorMarker, StoreMarker};
use futures::join;

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        match store.write_item(&Item { key: key, value: value.into_bytes() }).await? {
            Ok(_) => println!("WriteItem Success"),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    if !config.iterate_from.is_empty() {
        // This helper creates a channel, and returns two protocol ends: the `client_end` is already
        // conveniently bound to the correct FIDL protocol, `Iterator`, while the `server_end` is
        // unbound and ready to be sent over the wire.
        let (iterator, server_end) = create_proxy::<IteratorMarker>();

        // There is no need to wait for the iterator to connect before sending the first `Get()`
        // request - since we already hold the `client_end` of the connection, we can start queuing
        // requests on it immediately.
        let connect_to_iterator = store.iterate(Some(config.iterate_from.as_str()), server_end);
        let first_get = iterator.get();

        // Wait until both the connection and the first request resolve - an error in either case
        // triggers an immediate resolution of the combined future.
        let (connection, first_page) = join!(connect_to_iterator, first_get);

        // Handle any connection error. If this has occurred, it is impossible for the first `Get()`
        // call to have resolved successfully, so check this error first.
        if let Err(err) = connection.context("Could not connect to Iterator")? {
            println!("Iterator Connection Error: {}", err.into_primitive());
        } else {
            println!("Iterator Connection Success");

            // Consecutively repeat the `Get()` request if the previous response was not empty.
            let mut entries = first_page.context("Could not get page from Iterator")?;
            while !&entries.is_empty() {
                for entry in entries.iter() {
                    println!("Iterator Entry: {}", entry);
                }
                entries = iterator.get().await.context("Could not get page from Iterator")?;
            }
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fuchsia_component::server::ServiceFs;
use futures::prelude::*;
use lazy_static::lazy_static;
use regex::Regex;

use fidl_examples_keyvaluestore_additerator::{
    Item, IterateConnectionError, IteratorRequest, IteratorRequestStream, StoreRequest,
    StoreRequestStream, WriteError,
};
use fuchsia_async as fasync;
use std::collections::btree_map::Entry;
use std::collections::BTreeMap;
use std::ops::Bound::*;
use std::sync::{Arc, Mutex};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

/// Handler for the `WriteItem` method.
fn write_item(store: &mut BTreeMap<String, Vec<u8>>, attempt: Item) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Validate the value.
    if attempt.value.is_empty() {
        println!("Write error: INVALID_VALUE, For key: {}", attempt.key);
        return Err(WriteError::InvalidValue);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote value at key: {}", entry.key());
            entry.insert(attempt.value);
            Ok(())
        }
    }
}

/// Handler for the `Iterate` method, which deals with validating that the requested start position
/// exists, and then sets up the asynchronous side channel for the actual iteration to occur over.
fn iterate(
    store: Arc<Mutex<BTreeMap<String, Vec<u8>>>>,
    starting_at: Option<String>,
    stream: IteratorRequestStream,
) -> Result<(), IterateConnectionError> {
    // Validate that the starting key, if supplied, actually exists.
    if let Some(start_key) = starting_at.clone() {
        if !store.lock().unwrap().contains_key(&start_key) {
            return Err(IterateConnectionError::UnknownStartAt);
        }
    }

    // Spawn a detached task. This allows the method call to return while the iteration continues in
    // a separate, unawaited task.
    fasync::Task::spawn(async move {
        // Serve the iteration requests. Note that access to the underlying store is behind a
        // contended `Mutex`, meaning that the iteration is not atomic: page contents could shift,
        // change, or disappear entirely between `Get()` requests.
        stream
            .map(|result| result.context("failed request"))
            .try_fold(
                match starting_at {
                    Some(start_key) => Included(start_key),
                    None => Unbounded,
                },
                |mut lower_bound, request| async {
                    match request {
                        IteratorRequest::Get { responder } => {
                            println!("Iterator page request received");

                            // The `page_size` should be kept in sync with the size constraint on
                            // the iterator's response, as defined in the FIDL protocol.
                            static PAGE_SIZE: usize = 10;

                            // An iterator, beginning at `lower_bound` and tracking the pagination's
                            // progress through iteration as each page is pulled by a client-sent
                            // `Get()` request.
                            let held_store = store.lock().unwrap();
                            let mut entries = held_store.range((lower_bound.clone(), Unbounded));
                            let mut current_page = vec![];
                            for _ in 0..PAGE_SIZE {
                                match entries.next() {
                                    Some(entry) => {
                                        current_page.push(entry.0.clone());
                                    }
                                    None => break,
                                }
                            }

                            // Update the `lower_bound` - either inclusive of the next item in the
                            // iteration, or exclusive of the last seen item if the iteration has
                            // finished. This `lower_bound` will be passed to the next request
                            // handler as its starting point.
                            lower_bound = match entries.next() {
                                Some(next) => Included(next.0.clone()),
                                None => match current_page.last() {
                                    Some(tail) => Excluded(tail.clone()),
                                    None => lower_bound,
                                },
                            };

                            // Send the page. At the end of this scope, the `held_store` lock gets
                            // dropped, and therefore released.
                            responder.send(&current_page).context("error sending reply")?;
                            println!("Iterator page sent");
                        }
                    }
                    Ok(lower_bound)
                },
            )
            .await
            .ok();
    })
    .detach();

    Ok(())
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    //
    // Note that we now use an `Arc<Mutex<BTreeMap>>`, replacing the previous `RefCell<HashMap>`.
    // The `BTreeMap` is used because we want an ordered map, to better facilitate iteration. The
    // `Arc<Mutex<...>>` is used because there are now multiple async tasks accessing the: one main
    // task which handles communication over the protocol, and one additional task per iterator
    // protocol. `Arc<Mutex<...>>` is the simplest way to synchronize concurrent access between
    // these racing tasks.
    let store = &Arc::new(Mutex::new(BTreeMap::<String, Vec<u8>>::new()));

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.clone().lock().unwrap(), attempt))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::Iterate { starting_at, iterator, responder } => {
                    println!("Iterate request received");

                    // The `iterate` handler does a quick check to see that the request is valid,
                    // then spins up a separate worker task to serve the newly minted `Iterator`
                    // protocol instance, allowing this call to return immediately and continue the
                    // request stream with other work.
                    responder
                        .send(iterate(store.clone(), starting_at, iterator.into_stream()))
                        .context("error sending reply")?;
                    println!("Iterate response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

通訊協定

FIDL 食譜:通訊協定

通訊協定會說明一組可透過管道傳送訊息來叫用的相關方法。它會說明用戶端和伺服器之間可交換 FIDL 資料的介面。

在這個範例中,您將建立基本計算機伺服器和用戶端,說明先定義,然後提供及使用 FIDL 通訊協定所需的基本設定。

首先,您將定義介面定義和測試裝置。介面定義 (.fidl 檔案本身) 是任何新 FIDL 通訊協定的起點。此外,計算機還包含必要的 CML 和領域定義,可用於建立用戶端-伺服器模式,並用作任意實作項目的專案架構。

請參閱以下 FIDL 程式碼:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// The namespace for this FIDL protocol. This namespace is how both consumers (clients) and providers (servers) reference this protocol.
library examples.calculator.baseline;

// @discoverable indicates 'Calculator' is a protocol that will be served under the examples.calculator.baseline libarary namespace. https://fuchsia.dev/fuchsia-src/reference/fidl/language/attributes#discoverable . If @discoverable is missing, it will lead to a compile time error when trying to import the library.
@discoverable
// A limited-functionality calculator 'protocol' that adds and subtracts integers.
open protocol Calculator {
    // Takes as input a struct with two integers, and returns their sum: (a+b)=sum.  This method is infallible (no errors can be generated) as two int32's cannot overflow a result type of int64.
    flexible Add(struct {
        a int32;
        b int32;
    }) -> (struct {
        sum int64;
    });
    // Takes as input a struct with two integers, and returns their difference: (a-b)=difference.  This method is infallible (no errors can be generated) as two int32's cannot overflow a result type of int64.
    flexible Subtract(struct {
        a int32;
        b int32;
    }) -> (struct {
        difference int64;
    });
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.calculator.baseline.Calculator" },
    ],
    config: {},
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.calculator.baseline.Calculator" },
    ],
    expose: [
        {
            protocol: "examples.calculator.baseline.Calculator",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.calculator.baseline.Calculator",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to both children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// TODO(https://fxbug.dev/42063075): Rust implementation.

伺服器

// TODO(https://fxbug.dev/42063075): Rust implementation.

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42063075): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42063075): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42063075): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42063075): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42063075): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42063075): HLCPP implementation.

對於平台開發人員等特定開發人員而言,從頭開始建立 FIDL 通訊協定 (如本範例所示) 可能更常見。不過,其他類型的開發人員也能從學習如何建構 FIDL 通訊協定中受益,即使他們通常不會這麼做也一樣。這有助您瞭解 FIDL 的所有內容如何搭配運作,包括語法、文法、語言功能、如何提供及使用特定 FIDL 通訊協定,以及建構系統的運作方式。在後續步驟中,我們會根據這個基準提供範例,說明如何擴充現有的 FIDL 通訊協定,這應該是相當常見的做法。

遞迴型別

FIDL 食譜:遞迴型別

遞迴類型是指在其定義中間接參照自身的類型。當型別直接參照自身,或參照某些鏈結型別,並以間接方式包含該型別時,就可能發生這種情況。舉例來說,在經典的樹狀結構中,每個節點可能只包含資料 (「葉節點」),或是資料和更多子節點的參照 (「分支節點」)。在後一種情況下,節點會遞迴地包含巢狀樹狀定義,並視需要重複到更深層的層級。

只要包含週期中至少有一條鏈結 (也就是可選的類型定義鏈結,可導回原始類型),FIDL 就會支援遞迴類型。如果鏈結中沒有任何類型為選用類型,則該類型將無法編碼,因為每個類型例項都需要至少一個內部類型,無限循環。

在這個變化版本中,我們允許鍵/值存放區將其他鍵/值存放區做為成員。簡而言之,我們會將其轉換為樹狀結構。我們會將 value 的原始定義替換為使用兩個成員 union 的定義:一個變化版本會使用與先前相同的 vector<byte> 類型儲存葉結點,另一個則會以其他巢狀儲存庫的形式儲存分支節點。

推理

這裡我們會看到幾種 optionality 的用法,我們可以宣告可能存在或不存在的型別。FIDL 中的選用性有三種:

  • 具有此類型一律會在網路上離線儲存,因此具有內建方式,可透過空值封套描述「缺席」。為這些類型啟用選用性不會影響所包含訊息的線路形狀,只會變更哪些值適用於該特定類型。您可以透過新增 :optional 限制,將 unionvector<T>client_endserver_endzx.Handle 類型設為選用。將 value union 設為選用項目後,我們就能以缺少 value 的形式,引入標準的「空值」項目。這表示空白的 bytes 和缺少/空白的 store 屬性是無效的值。
  • 與上述類型不同,struct 版面配置沒有可儲存空值標頭的額外空間。因此,您必須將其包裝在信封中,以便變更所附帶訊息的線上傳輸形狀。為確保這個線路修改效果易於解讀,Item struct 類型必須套用 box<T> 類型範本。
  • 最後,table 版面配置一律為選用。缺少的 table 只是沒有任何成員集。

樹狀圖是自然的自我參照資料結構:樹狀圖中的任何節點都可能包含純資料的葉節點 (在本例中為字串),或包含更多節點的子樹狀圖。這需要遞迴:Item 的定義現在會遞迴地依附自身!在 FIDL 中表示遞迴類型可能有點棘手,尤其是因為目前的支援有點受限。只要在透過自參照建立的循環中,至少有一個選用型別,我們就能支援這類型別。舉例來說,我們在此將 items struct 成員定義為 box<Item>,藉此中斷包含循環。

這些變更也大量使用匿名類型,也就是在使用點內嵌宣告而非命名的類型,以及頂層 type 宣告。根據預設,產生的語言繫結中匿名類型的名稱會取自其本機內容。舉例來說,新推出的 flexible union 會採用其擁有者成員的名稱 Value,新推出的 struct 會變成 Store,以此類推。由於這項啟發法的使用可能會導致衝突,因此 FIDL 提供逃逸處理程序,允許作者手動覆寫匿名類型的產生名稱。這項作業是透過 @generated_name 屬性完成,可讓使用者變更後端產生的名稱。我們可以在這裡使用一個,將原本的 Store 類型重新命名為 NestedStore,以免與使用相同名稱的 protocol 宣告發生名稱衝突。

實作

FIDL、CML 和領域介面定義的修改如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.supporttrees;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value strict union {
        // Keep the original `bytes` as one of the options in the new union. All leaf nodes in the
        // tree must be `bytes`, or absent unions (representing empty). Empty byte arrays are
        // disallowed.
        1: bytes vector<byte>:64000;

        // Allows a store within a store, thereby turning our flat key-value store into a tree
        // thereof. Note the use of `@generated_name` to prevent a type-name collision with the
        // `Store` protocol below, and the use of `box<T>` to ensure that there is a break in the
        // chain of recursion, thereby allowing `Item` to include itself in its own definition.
        //
        // This is a table so that added fields, like for example a `hash`, can be easily added in
        // the future.
        2: store @generated_name("nested_store") table {
            1: items vector<box<Item>>;
        };
    }:optional;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// A very basic key-value store.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.supporttrees.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A newline separated list nested entries. The first line should be the key
        // for the nested store, and each subsequent entry should be a pointer to a text file
        // containing the string value. The name of that text file (without the `.txt` suffix) will
        // serve as the entries key.
        write_nested: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A list of keys, all of which will be populated as null entries.
        write_null: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.supporttrees.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.supporttrees.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.supporttrees.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    config::Config,
    fidl_examples_keyvaluestore_supporttrees::{Item, NestedStore, StoreMarker, Value},
    fuchsia_component::client::connect_to_protocol,
    std::{thread, time},
};

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        let res = store
            .write_item(&Item {
                key: key.clone(),
                value: Some(Box::new(Value::Bytes(value.into_bytes()))),
            })
            .await;
        match res? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // Add nested entries to the key-value store as well. The entries are strings, where the first
    // line is the key of the entry, and each subsequent entry should be a pointer to a text file
    // containing the string value. The name of that text file (without the `.txt` suffix) will
    // serve as the entries key.
    for spec in config.write_nested.into_iter() {
        let mut items = vec![];
        let mut nested_store = NestedStore::default();
        let mut lines = spec.split("\n");
        let key = lines.next().unwrap();

        // For each entry, make a new entry in the `NestedStore` being built.
        for entry in lines {
            let path = format!("/pkg/data/{}.txt", entry);
            let contents = std::fs::read_to_string(path.clone())
                .with_context(|| format!("Failed to load {path}"))?;
            items.push(Some(Box::new(Item {
                key: entry.to_string(),
                value: Some(Box::new(Value::Bytes(contents.into()))),
            })));
        }
        nested_store.items = Some(items);

        // Send the `NestedStore`, represented as a vector of values.
        let res = store
            .write_item(&Item {
                key: key.to_string(),
                value: Some(Box::new(Value::Store(nested_store))),
            })
            .await;
        match res? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // Each entry in this list is a null value in the store.
    for key in config.write_null.into_iter() {
        match store.write_item(&Item { key: key.to_string(), value: None }).await? {
            Ok(_) => println!("WriteItem Success at key: {}", key),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Note: For the clarity of this example, allow code to be unused.
#![allow(dead_code)]

use {
    anyhow::{Context as _, Error},
    fidl_examples_keyvaluestore_supporttrees::{
        Item, StoreRequest, StoreRequestStream, Value, WriteError,
    },
    fuchsia_component::server::ServiceFs,
    futures::prelude::*,
    lazy_static::lazy_static,
    regex::Regex,
    std::cell::RefCell,
    std::collections::hash_map::Entry,
    std::collections::HashMap,
    std::str::from_utf8,
};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

// A representation of a key-value store that can contain an arbitrarily deep nesting of other
// key-value stores.
#[allow(clippy::box_collection, reason = "mass allow for https://fxbug.dev/381896734")]
enum StoreNode {
    Leaf(Option<Vec<u8>>),
    Branch(Box<HashMap<String, StoreNode>>),
}

/// Recursive item writer, which takes a `StoreNode` that may not necessarily be the root node, and
/// writes an entry to it.
fn write_item(
    store: &mut HashMap<String, StoreNode>,
    attempt: Item,
    path: &str,
) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            let key = format!("{}{}", &path, entry.key());
            match attempt.value {
                // Null entries are allowed.
                None => {
                    println!("Wrote value: NONE at key: {}", key);
                    entry.insert(StoreNode::Leaf(None));
                }
                Some(value) => match *value {
                    // If this is a nested store, recursively make a new store to insert at this
                    // position.
                    Value::Store(entry_list) => {
                        // Validate the value - absent stores, items lists with no children, or any
                        // of the elements within that list being empty boxes, are all not allowed.
                        if entry_list.items.is_some() {
                            let items = entry_list.items.unwrap();
                            if !items.is_empty() && items.iter().all(|i| i.is_some()) {
                                let nested_path = format!("{}/", key);
                                let mut nested_store = HashMap::<String, StoreNode>::new();
                                for item in items.into_iter() {
                                    write_item(&mut nested_store, *item.unwrap(), &nested_path)?;
                                }

                                println!("Created branch at key: {}", key);
                                entry.insert(StoreNode::Branch(Box::new(nested_store)));
                                return Ok(());
                            }
                        }

                        println!("Write error: INVALID_VALUE, For key: {}", key);
                        return Err(WriteError::InvalidValue);
                    }

                    // This is a simple leaf node on this branch.
                    Value::Bytes(value) => {
                        // Validate the value.
                        if value.is_empty() {
                            println!("Write error: INVALID_VALUE, For key: {}", key);
                            return Err(WriteError::InvalidValue);
                        }

                        println!("Wrote key: {}, value: {:?}", key, from_utf8(&value).unwrap());
                        entry.insert(StoreNode::Leaf(Some(value)));
                    }
                },
            }
            Ok(())
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, StoreNode>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.borrow_mut(), attempt, ""))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

資源類型

FIDL 食譜:資源類型

FIDL 資源類型是用於間接攜帶句柄的類型。由於 FIDL 句柄是功能的唯一參照,因此任何包含一個句柄的類型都會繼承這項行為:也無法複製。因此,資源性質會傳染:如果值類型成為資源類型,則所有間接包含該類型的類型也必須如此。

鍵/值儲存庫的實用操作是依序疊代:也就是說,在指定鍵時,依序傳回鍵後方出現的元素清單 (通常分頁)。

推理

在 FIDL 中,建議使用疊代器執行這項操作,疊代器通常會實作為可執行此疊代的獨立通訊協定。使用獨立的通訊協定 (因此是獨立的管道) 有許多好處,包括將疊代拉取要求與透過主要通訊協定執行的其他作業分開。

通訊協定 P 管道連線的用戶端和伺服器端可分別以 FIDL 資料類型 client_end:Pserver_end:P 表示。這些類型統稱為「通訊協定端點」,代表透過現有 FIDL 連線,將 FIDL 用戶端連線至對應伺服器的其他 (非 @discoverable) 方式!

通訊協定端點是一般 FIDL 概念的特定例項:資源類型。資源類型旨在包含 FIDL 句柄,因此必須對該類型的使用方式施加額外限制。類型必須一律是唯一的,因為基礎資源是由其他某些能力管理工具 (通常是 Zircon 核心) 調解。因此,如果不透過管理員,就無法透過簡單的記憶體內複製作業複製這類資源。為避免重複,FIDL 中的所有資源類型一律為只移動型。

最後,Iterator 通訊協定本身的 Get() 方法會在傳回酬載上使用大小限制。這項限制可限制單一提取作業中可能傳輸的資料量,讓您可以控制資源使用量。它也會建立自然的分頁邊界:伺服器只需一次準備小批次,而非一次處理所有結果。

實作

FIDL、CML 和領域介面定義如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.additerator;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value vector<byte>:64000;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// An enumeration of things that may go wrong when trying to create an iterator.
type IterateConnectionError = flexible enum {
    /// The starting key was not found.
    UNKNOWN_START_AT = 1;
};

/// A key-value store which supports insertion and iteration.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;

    /// Iterates over the items in the store, using lexicographic ordering over the keys.
    ///
    /// The [`iterator`] is [pipelined][pipelining] to the server, such that the client can
    /// immediately send requests over the new connection.
    ///
    /// [pipelining]: https://fuchsia.dev/fuchsia-src/development/api/fidl?hl=en#request-pipelining
    flexible Iterate(resource struct {
        /// If present, requests to start the iteration at this item.
        starting_at string:<128, optional>;

        /// The [`Iterator`] server endpoint. The client creates both ends of the channel and
        /// retains the `client_end` locally to use for pulling iteration pages, while sending the
        /// `server_end` off to be fulfilled by the server.
        iterator server_end:Iterator;
    }) -> () error IterateConnectionError;
};

/// An iterator for the key-value store. Note that this protocol makes no guarantee of atomicity -
/// the values may change between pulls from the iterator. Unlike the `Store` protocol above, this
/// protocol is not `@discoverable`: it is not independently published by the component that
/// implements it, but rather must have one of its two protocol ends transmitted over an existing
/// FIDL connection.
///
/// As is often the case with iterators, the client indicates that they are done with an instance of
/// the iterator by simply closing their end of the connection.
///
/// Since the iterator is associated only with the Iterate method, it is declared as closed rather
/// than open. This is because changes to how iteration works are more likely to require replacing
/// the Iterate method completely (which is fine because that method is flexible) rather than
/// evolving the Iterator protocol.
closed protocol Iterator {
    /// Gets the next batch of keys.
    ///
    /// The client pulls keys rather than having the server proactively push them, to implement
    /// [flow control][flow-control] over the messages.
    ///
    /// [flow-control]:
    ///     https://fuchsia.dev/fuchsia-src/development/api/fidl?hl=en#prefer_pull_to_push
    strict Get() -> (struct {
        /// A list of keys. If the iterator has reached the end of iteration, the list will be
        /// empty. The client is expected to then close the connection.
        entries vector<string:128>:10;
    });
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.additerator.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A key to iterate from, after all items in `write_items` have been written.
        iterate_from: {
            type: "string",
            max_size: 64,
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.additerator.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.additerator.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.additerator.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use config::Config;
use fuchsia_component::client::connect_to_protocol;
use std::{thread, time};

use fidl::endpoints::create_proxy;
use fidl_examples_keyvaluestore_additerator::{Item, IteratorMarker, StoreMarker};
use futures::join;

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        match store.write_item(&Item { key: key, value: value.into_bytes() }).await? {
            Ok(_) => println!("WriteItem Success"),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    if !config.iterate_from.is_empty() {
        // This helper creates a channel, and returns two protocol ends: the `client_end` is already
        // conveniently bound to the correct FIDL protocol, `Iterator`, while the `server_end` is
        // unbound and ready to be sent over the wire.
        let (iterator, server_end) = create_proxy::<IteratorMarker>();

        // There is no need to wait for the iterator to connect before sending the first `Get()`
        // request - since we already hold the `client_end` of the connection, we can start queuing
        // requests on it immediately.
        let connect_to_iterator = store.iterate(Some(config.iterate_from.as_str()), server_end);
        let first_get = iterator.get();

        // Wait until both the connection and the first request resolve - an error in either case
        // triggers an immediate resolution of the combined future.
        let (connection, first_page) = join!(connect_to_iterator, first_get);

        // Handle any connection error. If this has occurred, it is impossible for the first `Get()`
        // call to have resolved successfully, so check this error first.
        if let Err(err) = connection.context("Could not connect to Iterator")? {
            println!("Iterator Connection Error: {}", err.into_primitive());
        } else {
            println!("Iterator Connection Success");

            // Consecutively repeat the `Get()` request if the previous response was not empty.
            let mut entries = first_page.context("Could not get page from Iterator")?;
            while !&entries.is_empty() {
                for entry in entries.iter() {
                    println!("Iterator Entry: {}", entry);
                }
                entries = iterator.get().await.context("Could not get page from Iterator")?;
            }
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fuchsia_component::server::ServiceFs;
use futures::prelude::*;
use lazy_static::lazy_static;
use regex::Regex;

use fidl_examples_keyvaluestore_additerator::{
    Item, IterateConnectionError, IteratorRequest, IteratorRequestStream, StoreRequest,
    StoreRequestStream, WriteError,
};
use fuchsia_async as fasync;
use std::collections::btree_map::Entry;
use std::collections::BTreeMap;
use std::ops::Bound::*;
use std::sync::{Arc, Mutex};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

/// Handler for the `WriteItem` method.
fn write_item(store: &mut BTreeMap<String, Vec<u8>>, attempt: Item) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Validate the value.
    if attempt.value.is_empty() {
        println!("Write error: INVALID_VALUE, For key: {}", attempt.key);
        return Err(WriteError::InvalidValue);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote value at key: {}", entry.key());
            entry.insert(attempt.value);
            Ok(())
        }
    }
}

/// Handler for the `Iterate` method, which deals with validating that the requested start position
/// exists, and then sets up the asynchronous side channel for the actual iteration to occur over.
fn iterate(
    store: Arc<Mutex<BTreeMap<String, Vec<u8>>>>,
    starting_at: Option<String>,
    stream: IteratorRequestStream,
) -> Result<(), IterateConnectionError> {
    // Validate that the starting key, if supplied, actually exists.
    if let Some(start_key) = starting_at.clone() {
        if !store.lock().unwrap().contains_key(&start_key) {
            return Err(IterateConnectionError::UnknownStartAt);
        }
    }

    // Spawn a detached task. This allows the method call to return while the iteration continues in
    // a separate, unawaited task.
    fasync::Task::spawn(async move {
        // Serve the iteration requests. Note that access to the underlying store is behind a
        // contended `Mutex`, meaning that the iteration is not atomic: page contents could shift,
        // change, or disappear entirely between `Get()` requests.
        stream
            .map(|result| result.context("failed request"))
            .try_fold(
                match starting_at {
                    Some(start_key) => Included(start_key),
                    None => Unbounded,
                },
                |mut lower_bound, request| async {
                    match request {
                        IteratorRequest::Get { responder } => {
                            println!("Iterator page request received");

                            // The `page_size` should be kept in sync with the size constraint on
                            // the iterator's response, as defined in the FIDL protocol.
                            static PAGE_SIZE: usize = 10;

                            // An iterator, beginning at `lower_bound` and tracking the pagination's
                            // progress through iteration as each page is pulled by a client-sent
                            // `Get()` request.
                            let held_store = store.lock().unwrap();
                            let mut entries = held_store.range((lower_bound.clone(), Unbounded));
                            let mut current_page = vec![];
                            for _ in 0..PAGE_SIZE {
                                match entries.next() {
                                    Some(entry) => {
                                        current_page.push(entry.0.clone());
                                    }
                                    None => break,
                                }
                            }

                            // Update the `lower_bound` - either inclusive of the next item in the
                            // iteration, or exclusive of the last seen item if the iteration has
                            // finished. This `lower_bound` will be passed to the next request
                            // handler as its starting point.
                            lower_bound = match entries.next() {
                                Some(next) => Included(next.0.clone()),
                                None => match current_page.last() {
                                    Some(tail) => Excluded(tail.clone()),
                                    None => lower_bound,
                                },
                            };

                            // Send the page. At the end of this scope, the `held_store` lock gets
                            // dropped, and therefore released.
                            responder.send(&current_page).context("error sending reply")?;
                            println!("Iterator page sent");
                        }
                    }
                    Ok(lower_bound)
                },
            )
            .await
            .ok();
    })
    .detach();

    Ok(())
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    //
    // Note that we now use an `Arc<Mutex<BTreeMap>>`, replacing the previous `RefCell<HashMap>`.
    // The `BTreeMap` is used because we want an ordered map, to better facilitate iteration. The
    // `Arc<Mutex<...>>` is used because there are now multiple async tasks accessing the: one main
    // task which handles communication over the protocol, and one additional task per iterator
    // protocol. `Arc<Mutex<...>>` is the simplest way to synchronize concurrent access between
    // these racing tasks.
    let store = &Arc::new(Mutex::new(BTreeMap::<String, Vec<u8>>::new()));

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.clone().lock().unwrap(), attempt))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::Iterate { starting_at, iterator, responder } => {
                    println!("Iterate request received");

                    // The `iterate` handler does a quick check to see that the request is valid,
                    // then spins up a separate worker task to serve the newly minted `Iterator`
                    // protocol instance, allowing this call to return immediately and continue the
                    // request stream with other work.
                    responder
                        .send(iterate(store.clone(), starting_at, iterator.into_stream()))
                        .context("error sending reply")?;
                    println!("Iterate response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

純量型別

FIDL 食譜:純量類型

FIDL 的純量類型是一種類型,其中包含所有內建原始類型,以及內建的非原始類型 string

推理

鍵/值儲存庫基準範例的實作方式是個不錯的起點,但其中一個主要缺點是資料會儲存為原始位元組。FIDL 是一種具有豐富型別的語言。強制將 UTF-8 字串等資料儲存為未指定類型的位元組陣列,會讓 *.fidl 檔案的讀者和使用產生繫結的程式設計師無法取得這類寶貴的類型資訊。

實作

這項變更的主要目標,是將基準案例的 vector<byte> 類型 value 成員,替換為可儲存多種可能類型的 union。事實上,隨著這項變更,FIDL 的類型也提供良好的調查結果:

  • 所有 FIDL 內建的純量類型都會用於 Value union 中的變數:booluint8uint16uint32uint64int8int16int32int64float32float64 (也稱為 FIDL 的原始類型),以及 string
  • 這個 union 也使用了 FIDL 內建的 array<T, N>vector<T> 類型範本。
  • 這個範例至少會使用一次 FIDL 的所有類型版面配置,也就是 bitsenumtableunionstruct

WriteItem 所使用的要求和回應酬載也已從 struct 變更為分別為命名的 table 和內嵌的 flexible union。事實上,這三種版面配置都可以用於要求/回應酬載。後兩者分別稱為表格酬載和 *聯合體酬載,在所有情況下皆為首選,但在對訊息大小最敏感的情況下除外。這是因為日後要以二進位相容方式擴充這些類別,會比較容易。

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.usegenericvalues;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value Value;
};

// Because the `Value` must be used both in the request and the response, we give it its own named
// type. The type is a `union` of all possible data types that we take as values, and is marked
// `flexible` to allow for the easy addition of new data types in the future.
type Value = flexible union {
    // Keep the original `bytes` as one of the options in the new union.
    1: bytes vector<byte>:64000;

    // A `string` is very similar to `vector<byte>` on the wire, with the extra constraint that
    // it enforces that it enforces that the byte vector in question is valid UTF-8.
    2: string string:64000;

    // All of FIDL's primitive types.
    3: bool bool;
    4: uint8 uint8;
    5: int8 int8;
    6: uint16 uint16;
    7: int16 int16;
    8: uint32 uint32;
    9: int32 int32;
    10: float32 float32;
    11: uint64 uint64;
    12: int64 int64;
    13: float64 float64;

    // FIDL does not natively support 128-bit integer types, so we have to define our own
    // representations.
    14: uint128 array<uint64, 2>;
};

// Because we now supoprt a richer range of types as values in our store, it is helpful to use a
// `flexible`, and therefore evolvable, `bits` type to store write options.
type WriteOptions = flexible bits : uint8 {
    // This flag allows us to overwrite existing data when there is a collision, rather than failing
    // with an `WriteError.ALREADY_EXISTS`.
    OVERWRITE = 0b1;
    // This flag allows us to concatenate to existing data when there is a collision, rather than
    // failing with an `WriteError.ALREADY_EXISTS`. "Concatenation" means addition for the numeric
    // variants and appending to the `bytes`/`string` variants. If no existing data can be found, we
    // "concatenate" to default values of zero and an empty vector, respectively. Attempting to
    // concatenate to an existing variant of a different type will return a
    // `WriteError.INVALID_VALUE` error.
    CONCAT = 0b10;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// A very basic key-value store.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    ///
    /// Since the value stored in the key-value store can now be different from the input (if the
    /// `WriteOptions.CONCAT` flag is set), we need to return the resulting `Value` to the
    /// requester.
    ///
    /// We use an (anonymous) `table` and a (named) `flexible union` as the request and response
    /// payload, respectively, to allow for easier future evolution. Both of these types are
    /// `flexible`, meaning that adding or removing members is binary-compatible. This makes them
    /// much easier to evolve that the `struct` types that were previously used, which cannot be
    /// changed after release without breaking ABI.
    flexible WriteItem(table {
        1: attempt Item;
        2: options WriteOptions;
    }) -> (Value) error WriteError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.usegenericvalues.Store" },
    ],
    config: {
        // A vector of values for every easily representible type in our key-value store. For
        // brevity's sake, the 8, 16, and 32 bit integer types and booleans are omitted.
        //
        // TODO(https://fxbug.dev/42178362): It would absolve individual language implementations of a great
        //   deal of string parsing if we were able to use all FIDL constructs directly here. In
        //   particular, floats and nested types are very difficult to represent, and have been
        //   excluded from this example for the time being.
        set_concat_option: { type: "bool" },
        set_overwrite_option: { type: "bool" },
        write_bytes: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },
        write_strings: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },
        write_uint64s: {
            type: "vector",
            max_count: 16,
            element: { type: "uint64" },
        },
        write_int64s: {
            type: "vector",
            max_count: 16,
            element: { type: "int64" },
        },

        // Note: due to the limitation of structured config not allowing vectors nested in vectors,
        // we only set the lower half of the uint128 for simplicity's sake.
        write_uint128s: {
            type: "vector",
            max_count: 16,
            element: { type: "uint64" },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.usegenericvalues.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.usegenericvalues.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.usegenericvalues.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    config::Config,
    fidl_examples_keyvaluestore_usegenericvalues::{
        Item, StoreMarker, StoreProxy, StoreWriteItemRequest, Value, WriteOptions,
    },
    fuchsia_component::client::connect_to_protocol,
    std::{thread, time},
};

// A helper function to sequentially write a single item to the key-value store and print a log when
// successful.
async fn write_next_item(
    store: &StoreProxy,
    key: &str,
    value: Value,
    options: WriteOptions,
) -> Result<(), Error> {
    // Create an empty request payload using `::default()`.
    let mut req = StoreWriteItemRequest::default();
    req.options = Some(options);

    // Fill in the `Item` we will be attempting to write.
    println!("WriteItem request sent: key: {}, value: {:?}", &key, &value);
    req.attempt = Some(Item { key: key.to_string(), value: value });

    // Send and async `WriteItem` request to the server.
    match store.write_item(&req).await.context("Error sending request")? {
        Ok(value) => println!("WriteItem response received: {:?}", &value),
        Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
    }
    Ok(())
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // All of our requests will have the same bitflags set. Pull these settings from the config.
    let mut options = WriteOptions::empty();
    options.set(WriteOptions::OVERWRITE, config.set_overwrite_option);
    options.set(WriteOptions::CONCAT, config.set_concat_option);

    // The structured config provides one input for most data types that can be stored in the data
    // store. Iterate through those inputs in the order we see them in the FIDL file.
    //
    // Note that FIDL unions are rendered as enums in Rust; for example, the `Value` union has now
    // become a `Value` Rust enum, with each member taking exactly one argument.
    for value in config.write_bytes.into_iter() {
        write_next_item(&store, "bytes", Value::Bytes(value.into()), options).await?;
    }
    for value in config.write_strings.into_iter() {
        write_next_item(&store, "string", Value::String(value), options).await?;
    }
    for value in config.write_uint64s.into_iter() {
        write_next_item(&store, "uint64", Value::Uint64(value), options).await?;
    }
    for value in config.write_int64s.into_iter() {
        write_next_item(&store, "int64", Value::Int64(value), options).await?;
    }
    for value in config.write_uint128s.into_iter() {
        write_next_item(&store, "uint128", Value::Uint128([0, value]), options).await?;
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fuchsia_component::server::ServiceFs;
use futures::prelude::*;
use lazy_static::lazy_static;
use regex::Regex;
use std::cell::RefCell;
use std::collections::hash_map::Entry;
use std::collections::HashMap;

use fidl_examples_keyvaluestore_usegenericvalues::{
    Item, StoreRequest, StoreRequestStream, Value, WriteError, WriteOptions,
};
use std::collections::hash_map::OccupiedEntry;
use std::ops::Add;

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

/// Sums any numeric type.
fn sum<T: Add + Add<Output = T> + Copy>(operands: [T; 2]) -> T {
    operands[0] + operands[1]
}

/// Clones and inserts an entry, so that the original (now concatenated) copy may be returned in the
/// response.
fn write(inserting: Value, mut entry: OccupiedEntry<'_, String, Value>) -> Value {
    entry.insert(inserting.clone());
    println!("Wrote key: {}, value: {:?}", entry.key(), &inserting);
    inserting
}

/// Handler for the `WriteItem` method.
fn write_item(
    store: &mut HashMap<String, Value>,
    attempt: Item,
    options: &WriteOptions,
) -> Result<Value, WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY for key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            // The `CONCAT` flag supersedes the `OVERWRITE` flag, so check it first.
            if options.contains(WriteOptions::CONCAT) {
                match entry.get() {
                    Value::Bytes(old) => {
                        if let Value::Bytes(new) = attempt.value {
                            let mut combined = old.clone();
                            combined.extend(new);
                            return Ok(write(Value::Bytes(combined), entry));
                        }
                    }
                    Value::String(old) => {
                        if let Value::String(new) = attempt.value {
                            return Ok(write(Value::String(format!("{}{}", old, &new)), entry));
                        }
                    }
                    Value::Uint64(old) => {
                        if let Value::Uint64(new) = attempt.value {
                            return Ok(write(Value::Uint64(sum([*old, new])), entry));
                        }
                    }
                    Value::Int64(old) => {
                        if let Value::Int64(new) = attempt.value {
                            return Ok(write(Value::Int64(sum([*old, new])), entry));
                        }
                    }
                    // Note: only works on the uint64 range in practice.
                    Value::Uint128(old) => {
                        if let Value::Uint128(new) = attempt.value {
                            return Ok(write(Value::Uint128([0, sum([old[1], new[1]])]), entry));
                        }
                    }
                    _ => {
                        panic!("actively unsupported type!")
                    }
                }

                // Only reachable if the type of the would be concatenated value did not match the
                // value already occupying this entry.
                println!("Write error: INVALID_VALUE for key: {}", entry.key());
                return Err(WriteError::InvalidValue);
            }

            // If we're not doing CONCAT, check for OVERWRITE next.
            if options.contains(WriteOptions::OVERWRITE) {
                return Ok(write(attempt.value, entry));
            }

            println!("Write error: ALREADY_EXISTS for key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote key: {}, value: {:?}", entry.key(), &attempt.value);
            entry.insert(attempt.value.clone());
            Ok(attempt.value)
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, Value>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                // Because we are using a table payload, there is an extra level of indirection. The
                // top-level container for the table itself is always called "payload".
                StoreRequest::WriteItem { payload, responder } => {
                    println!("WriteItem request received");

                    // Error out if either of the request table's members are not set.
                    let attempt = payload.attempt.context("required field 'attempt' is unset")?;
                    let options = payload.options.context("required field 'options' is unset")?;

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(
                            write_item(&mut store.borrow_mut(), attempt, &options)
                                .as_ref()
                                .map_err(|e| *e),
                        )
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

大小限制

FIDL 食譜:大小限制

FIDL 向量和字串可能會攜帶大小限制,這會指定型別可包含的成員數量上限。在向量情況下,這會是向量中儲存的元素數量,而在字串情況下,則是字串包含的 字節數

我們強烈建議您使用大小限制,因為這可為原本無上限的大型型別設定上限。

鍵/值儲存庫的實用操作是依序疊代:也就是說,在指定鍵時,依序傳回鍵後方出現的元素清單 (通常分頁)。

推理

在 FIDL 中,建議使用疊代器執行這項操作,疊代器通常會實作為可執行此疊代的獨立通訊協定。使用獨立的通訊協定 (因此是獨立的管道) 有許多好處,包括將疊代拉取要求與透過主要通訊協定執行的其他作業分開。

通訊協定 P 管道連線的用戶端和伺服器端可分別以 FIDL 資料類型 client_end:Pserver_end:P 表示。這些類型統稱為「通訊協定端點」,代表透過現有 FIDL 連線,將 FIDL 用戶端連線至對應伺服器的其他 (非 @discoverable) 方式!

通訊協定端點是一般 FIDL 概念的特定例項:資源類型。資源類型旨在包含 FIDL 句柄,因此必須對該類型的使用方式施加額外限制。類型必須一律是唯一的,因為基礎資源是由其他某些能力管理工具 (通常是 Zircon 核心) 調解。因此,如果不透過管理員,就無法透過簡單的記憶體內複製作業複製這類資源。為避免重複,FIDL 中的所有資源類型一律為只移動型。

最後,Iterator 通訊協定本身的 Get() 方法會在傳回酬載上使用大小限制。這項限制可限制單一提取作業中可能傳輸的資料量,讓您可以控制資源使用量。它也會建立自然的分頁邊界:伺服器只需一次準備小批次,而非一次處理所有結果。

實作

FIDL、CML 和領域介面定義如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.additerator;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value vector<byte>:64000;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// An enumeration of things that may go wrong when trying to create an iterator.
type IterateConnectionError = flexible enum {
    /// The starting key was not found.
    UNKNOWN_START_AT = 1;
};

/// A key-value store which supports insertion and iteration.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    flexible WriteItem(struct {
        attempt Item;
    }) -> () error WriteError;

    /// Iterates over the items in the store, using lexicographic ordering over the keys.
    ///
    /// The [`iterator`] is [pipelined][pipelining] to the server, such that the client can
    /// immediately send requests over the new connection.
    ///
    /// [pipelining]: https://fuchsia.dev/fuchsia-src/development/api/fidl?hl=en#request-pipelining
    flexible Iterate(resource struct {
        /// If present, requests to start the iteration at this item.
        starting_at string:<128, optional>;

        /// The [`Iterator`] server endpoint. The client creates both ends of the channel and
        /// retains the `client_end` locally to use for pulling iteration pages, while sending the
        /// `server_end` off to be fulfilled by the server.
        iterator server_end:Iterator;
    }) -> () error IterateConnectionError;
};

/// An iterator for the key-value store. Note that this protocol makes no guarantee of atomicity -
/// the values may change between pulls from the iterator. Unlike the `Store` protocol above, this
/// protocol is not `@discoverable`: it is not independently published by the component that
/// implements it, but rather must have one of its two protocol ends transmitted over an existing
/// FIDL connection.
///
/// As is often the case with iterators, the client indicates that they are done with an instance of
/// the iterator by simply closing their end of the connection.
///
/// Since the iterator is associated only with the Iterate method, it is declared as closed rather
/// than open. This is because changes to how iteration works are more likely to require replacing
/// the Iterate method completely (which is fine because that method is flexible) rather than
/// evolving the Iterator protocol.
closed protocol Iterator {
    /// Gets the next batch of keys.
    ///
    /// The client pulls keys rather than having the server proactively push them, to implement
    /// [flow control][flow-control] over the messages.
    ///
    /// [flow-control]:
    ///     https://fuchsia.dev/fuchsia-src/development/api/fidl?hl=en#prefer_pull_to_push
    strict Get() -> (struct {
        /// A list of keys. If the iterator has reached the end of iteration, the list will be
        /// empty. The client is expected to then close the connection.
        entries vector<string:128>:10;
    });
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.additerator.Store" },
    ],
    config: {
        write_items: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },

        // A key to iterate from, after all items in `write_items` have been written.
        iterate_from: {
            type: "string",
            max_size: 64,
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.additerator.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.additerator.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.additerator.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use config::Config;
use fuchsia_component::client::connect_to_protocol;
use std::{thread, time};

use fidl::endpoints::create_proxy;
use fidl_examples_keyvaluestore_additerator::{Item, IteratorMarker, StoreMarker};
use futures::join;

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // This client's structured config has one parameter, a vector of strings. Each string is the
    // path to a resource file whose filename is a key and whose contents are a value. We iterate
    // over them and try to write each key-value pair to the remote store.
    for key in config.write_items.into_iter() {
        let path = format!("/pkg/data/{}.txt", key);
        let value = std::fs::read_to_string(path.clone())
            .with_context(|| format!("Failed to load {path}"))?;
        match store.write_item(&Item { key: key, value: value.into_bytes() }).await? {
            Ok(_) => println!("WriteItem Success"),
            Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
        }
    }

    if !config.iterate_from.is_empty() {
        // This helper creates a channel, and returns two protocol ends: the `client_end` is already
        // conveniently bound to the correct FIDL protocol, `Iterator`, while the `server_end` is
        // unbound and ready to be sent over the wire.
        let (iterator, server_end) = create_proxy::<IteratorMarker>();

        // There is no need to wait for the iterator to connect before sending the first `Get()`
        // request - since we already hold the `client_end` of the connection, we can start queuing
        // requests on it immediately.
        let connect_to_iterator = store.iterate(Some(config.iterate_from.as_str()), server_end);
        let first_get = iterator.get();

        // Wait until both the connection and the first request resolve - an error in either case
        // triggers an immediate resolution of the combined future.
        let (connection, first_page) = join!(connect_to_iterator, first_get);

        // Handle any connection error. If this has occurred, it is impossible for the first `Get()`
        // call to have resolved successfully, so check this error first.
        if let Err(err) = connection.context("Could not connect to Iterator")? {
            println!("Iterator Connection Error: {}", err.into_primitive());
        } else {
            println!("Iterator Connection Success");

            // Consecutively repeat the `Get()` request if the previous response was not empty.
            let mut entries = first_page.context("Could not get page from Iterator")?;
            while !&entries.is_empty() {
                for entry in entries.iter() {
                    println!("Iterator Entry: {}", entry);
                }
                entries = iterator.get().await.context("Could not get page from Iterator")?;
            }
        }
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fuchsia_component::server::ServiceFs;
use futures::prelude::*;
use lazy_static::lazy_static;
use regex::Regex;

use fidl_examples_keyvaluestore_additerator::{
    Item, IterateConnectionError, IteratorRequest, IteratorRequestStream, StoreRequest,
    StoreRequestStream, WriteError,
};
use fuchsia_async as fasync;
use std::collections::btree_map::Entry;
use std::collections::BTreeMap;
use std::ops::Bound::*;
use std::sync::{Arc, Mutex};

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

/// Handler for the `WriteItem` method.
fn write_item(store: &mut BTreeMap<String, Vec<u8>>, attempt: Item) -> Result<(), WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY, For key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    // Validate the value.
    if attempt.value.is_empty() {
        println!("Write error: INVALID_VALUE, For key: {}", attempt.key);
        return Err(WriteError::InvalidValue);
    }

    // Write to the store, validating that the key did not already exist.
    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            println!("Write error: ALREADY_EXISTS, For key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote value at key: {}", entry.key());
            entry.insert(attempt.value);
            Ok(())
        }
    }
}

/// Handler for the `Iterate` method, which deals with validating that the requested start position
/// exists, and then sets up the asynchronous side channel for the actual iteration to occur over.
fn iterate(
    store: Arc<Mutex<BTreeMap<String, Vec<u8>>>>,
    starting_at: Option<String>,
    stream: IteratorRequestStream,
) -> Result<(), IterateConnectionError> {
    // Validate that the starting key, if supplied, actually exists.
    if let Some(start_key) = starting_at.clone() {
        if !store.lock().unwrap().contains_key(&start_key) {
            return Err(IterateConnectionError::UnknownStartAt);
        }
    }

    // Spawn a detached task. This allows the method call to return while the iteration continues in
    // a separate, unawaited task.
    fasync::Task::spawn(async move {
        // Serve the iteration requests. Note that access to the underlying store is behind a
        // contended `Mutex`, meaning that the iteration is not atomic: page contents could shift,
        // change, or disappear entirely between `Get()` requests.
        stream
            .map(|result| result.context("failed request"))
            .try_fold(
                match starting_at {
                    Some(start_key) => Included(start_key),
                    None => Unbounded,
                },
                |mut lower_bound, request| async {
                    match request {
                        IteratorRequest::Get { responder } => {
                            println!("Iterator page request received");

                            // The `page_size` should be kept in sync with the size constraint on
                            // the iterator's response, as defined in the FIDL protocol.
                            static PAGE_SIZE: usize = 10;

                            // An iterator, beginning at `lower_bound` and tracking the pagination's
                            // progress through iteration as each page is pulled by a client-sent
                            // `Get()` request.
                            let held_store = store.lock().unwrap();
                            let mut entries = held_store.range((lower_bound.clone(), Unbounded));
                            let mut current_page = vec![];
                            for _ in 0..PAGE_SIZE {
                                match entries.next() {
                                    Some(entry) => {
                                        current_page.push(entry.0.clone());
                                    }
                                    None => break,
                                }
                            }

                            // Update the `lower_bound` - either inclusive of the next item in the
                            // iteration, or exclusive of the last seen item if the iteration has
                            // finished. This `lower_bound` will be passed to the next request
                            // handler as its starting point.
                            lower_bound = match entries.next() {
                                Some(next) => Included(next.0.clone()),
                                None => match current_page.last() {
                                    Some(tail) => Excluded(tail.clone()),
                                    None => lower_bound,
                                },
                            };

                            // Send the page. At the end of this scope, the `held_store` lock gets
                            // dropped, and therefore released.
                            responder.send(&current_page).context("error sending reply")?;
                            println!("Iterator page sent");
                        }
                    }
                    Ok(lower_bound)
                },
            )
            .await
            .ok();
    })
    .detach();

    Ok(())
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    //
    // Note that we now use an `Arc<Mutex<BTreeMap>>`, replacing the previous `RefCell<HashMap>`.
    // The `BTreeMap` is used because we want an ordered map, to better facilitate iteration. The
    // `Arc<Mutex<...>>` is used because there are now multiple async tasks accessing the: one main
    // task which handles communication over the protocol, and one additional task per iterator
    // protocol. `Arc<Mutex<...>>` is the simplest way to synchronize concurrent access between
    // these racing tasks.
    let store = &Arc::new(Mutex::new(BTreeMap::<String, Vec<u8>>::new()));

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                StoreRequest::WriteItem { attempt, responder } => {
                    println!("WriteItem request received");

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(write_item(&mut store.clone().lock().unwrap(), attempt))
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                }
                StoreRequest::Iterate { starting_at, iterator, responder } => {
                    println!("Iterate request received");

                    // The `iterate` handler does a quick check to see that the request is valid,
                    // then spins up a separate worker task to serve the newly minted `Iterator`
                    // protocol instance, allowing this call to return immediately and continue the
                    // request stream with other work.
                    responder
                        .send(iterate(store.clone(), starting_at, iterator.into_stream()))
                        .context("error sending reply")?;
                    println!("Iterate response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

結構體酬載

FIDL 食譜:結構體酬載

結構體酬載是使用 struct 版面配置的 FIDL 方法酬載。struct 是型別欄位的簡單序列,類似於 C 結構體的運作方式。

在這個範例中,您將建立基本計算機伺服器和用戶端,說明先定義,然後提供及使用 FIDL 通訊協定所需的基本設定。

首先,您將定義介面定義和測試裝置。介面定義 (.fidl 檔案本身) 是任何新 FIDL 通訊協定的起點。此外,計算機還包含必要的 CML 和領域定義,可用於建立用戶端-伺服器模式,並用作任意實作項目的專案架構。

請參閱以下 FIDL 程式碼:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// The namespace for this FIDL protocol. This namespace is how both consumers (clients) and providers (servers) reference this protocol.
library examples.calculator.baseline;

// @discoverable indicates 'Calculator' is a protocol that will be served under the examples.calculator.baseline libarary namespace. https://fuchsia.dev/fuchsia-src/reference/fidl/language/attributes#discoverable . If @discoverable is missing, it will lead to a compile time error when trying to import the library.
@discoverable
// A limited-functionality calculator 'protocol' that adds and subtracts integers.
open protocol Calculator {
    // Takes as input a struct with two integers, and returns their sum: (a+b)=sum.  This method is infallible (no errors can be generated) as two int32's cannot overflow a result type of int64.
    flexible Add(struct {
        a int32;
        b int32;
    }) -> (struct {
        sum int64;
    });
    // Takes as input a struct with two integers, and returns their difference: (a-b)=difference.  This method is infallible (no errors can be generated) as two int32's cannot overflow a result type of int64.
    flexible Subtract(struct {
        a int32;
        b int32;
    }) -> (struct {
        difference int64;
    });
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.calculator.baseline.Calculator" },
    ],
    config: {},
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.calculator.baseline.Calculator" },
    ],
    expose: [
        {
            protocol: "examples.calculator.baseline.Calculator",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.calculator.baseline.Calculator",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to both children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// TODO(https://fxbug.dev/42063075): Rust implementation.

伺服器

// TODO(https://fxbug.dev/42063075): Rust implementation.

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42063075): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42063075): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42063075): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42063075): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42063075): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42063075): HLCPP implementation.

對於平台開發人員等特定開發人員而言,從頭開始建立 FIDL 通訊協定 (如本範例所示) 可能更常見。不過,其他類型的開發人員也能從學習如何建構 FIDL 通訊協定中受益,即使他們通常不會這麼做也一樣。這有助您瞭解 FIDL 的所有內容如何搭配運作,包括語法、文法、語言功能、如何提供及使用特定 FIDL 通訊協定,以及建構系統的運作方式。在後續步驟中,我們會根據這個基準提供範例,說明如何擴充現有的 FIDL 通訊協定,這應該是相當常見的做法。

表格酬載

FIDL 食譜:表格酬載

表格酬載是使用 table 版面配置的 FIDL 方法酬載。用於方法酬載的頂層類型必須使用 structtableunion 做為其版面配置。值得注意的是,部分產生的繫結會「扁平化」傳遞至 struct 方法酬載的引數,以便將每個成員視為呼叫簽章中的函式引數。使用 tableunion 的酬載則不會這麼做,而是一律傳遞單一引數 (稱為 payload)。

推理

鍵/值儲存庫基準範例的實作方式是個不錯的起點,但其中一個主要缺點是資料會儲存為原始位元組。FIDL 是一種具有豐富型別的語言。強制將 UTF-8 字串等資料儲存為未指定類型的位元組陣列,會讓 *.fidl 檔案的讀者和使用產生繫結的程式設計師無法取得這類寶貴的類型資訊。

實作

這項變更的主要目標,是將基準案例的 vector<byte> 類型 value 成員,替換為可儲存多種可能類型的 union。事實上,隨著這項變更,FIDL 的類型也提供良好的調查結果:

  • 所有 FIDL 內建的純量類型都會用於 Value union 中的變數:booluint8uint16uint32uint64int8int16int32int64float32float64 (也稱為 FIDL 的原始類型),以及 string
  • 這個 union 也使用了 FIDL 內建的 array<T, N>vector<T> 類型範本。
  • 這個範例至少會使用一次 FIDL 的所有類型版面配置,也就是 bitsenumtableunionstruct

WriteItem 所使用的要求和回應酬載也已從 struct 變更為分別為命名的 table 和內嵌的 flexible union。事實上,這三種版面配置都可以用於要求/回應酬載。後兩者分別稱為表格酬載和 *聯合體酬載,在所有情況下皆為首選,但在對訊息大小最敏感的情況下除外。這是因為日後要以二進位相容方式擴充這些類別,會比較容易。

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.usegenericvalues;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value Value;
};

// Because the `Value` must be used both in the request and the response, we give it its own named
// type. The type is a `union` of all possible data types that we take as values, and is marked
// `flexible` to allow for the easy addition of new data types in the future.
type Value = flexible union {
    // Keep the original `bytes` as one of the options in the new union.
    1: bytes vector<byte>:64000;

    // A `string` is very similar to `vector<byte>` on the wire, with the extra constraint that
    // it enforces that it enforces that the byte vector in question is valid UTF-8.
    2: string string:64000;

    // All of FIDL's primitive types.
    3: bool bool;
    4: uint8 uint8;
    5: int8 int8;
    6: uint16 uint16;
    7: int16 int16;
    8: uint32 uint32;
    9: int32 int32;
    10: float32 float32;
    11: uint64 uint64;
    12: int64 int64;
    13: float64 float64;

    // FIDL does not natively support 128-bit integer types, so we have to define our own
    // representations.
    14: uint128 array<uint64, 2>;
};

// Because we now supoprt a richer range of types as values in our store, it is helpful to use a
// `flexible`, and therefore evolvable, `bits` type to store write options.
type WriteOptions = flexible bits : uint8 {
    // This flag allows us to overwrite existing data when there is a collision, rather than failing
    // with an `WriteError.ALREADY_EXISTS`.
    OVERWRITE = 0b1;
    // This flag allows us to concatenate to existing data when there is a collision, rather than
    // failing with an `WriteError.ALREADY_EXISTS`. "Concatenation" means addition for the numeric
    // variants and appending to the `bytes`/`string` variants. If no existing data can be found, we
    // "concatenate" to default values of zero and an empty vector, respectively. Attempting to
    // concatenate to an existing variant of a different type will return a
    // `WriteError.INVALID_VALUE` error.
    CONCAT = 0b10;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// A very basic key-value store.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    ///
    /// Since the value stored in the key-value store can now be different from the input (if the
    /// `WriteOptions.CONCAT` flag is set), we need to return the resulting `Value` to the
    /// requester.
    ///
    /// We use an (anonymous) `table` and a (named) `flexible union` as the request and response
    /// payload, respectively, to allow for easier future evolution. Both of these types are
    /// `flexible`, meaning that adding or removing members is binary-compatible. This makes them
    /// much easier to evolve that the `struct` types that were previously used, which cannot be
    /// changed after release without breaking ABI.
    flexible WriteItem(table {
        1: attempt Item;
        2: options WriteOptions;
    }) -> (Value) error WriteError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.usegenericvalues.Store" },
    ],
    config: {
        // A vector of values for every easily representible type in our key-value store. For
        // brevity's sake, the 8, 16, and 32 bit integer types and booleans are omitted.
        //
        // TODO(https://fxbug.dev/42178362): It would absolve individual language implementations of a great
        //   deal of string parsing if we were able to use all FIDL constructs directly here. In
        //   particular, floats and nested types are very difficult to represent, and have been
        //   excluded from this example for the time being.
        set_concat_option: { type: "bool" },
        set_overwrite_option: { type: "bool" },
        write_bytes: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },
        write_strings: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },
        write_uint64s: {
            type: "vector",
            max_count: 16,
            element: { type: "uint64" },
        },
        write_int64s: {
            type: "vector",
            max_count: 16,
            element: { type: "int64" },
        },

        // Note: due to the limitation of structured config not allowing vectors nested in vectors,
        // we only set the lower half of the uint128 for simplicity's sake.
        write_uint128s: {
            type: "vector",
            max_count: 16,
            element: { type: "uint64" },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.usegenericvalues.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.usegenericvalues.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.usegenericvalues.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    config::Config,
    fidl_examples_keyvaluestore_usegenericvalues::{
        Item, StoreMarker, StoreProxy, StoreWriteItemRequest, Value, WriteOptions,
    },
    fuchsia_component::client::connect_to_protocol,
    std::{thread, time},
};

// A helper function to sequentially write a single item to the key-value store and print a log when
// successful.
async fn write_next_item(
    store: &StoreProxy,
    key: &str,
    value: Value,
    options: WriteOptions,
) -> Result<(), Error> {
    // Create an empty request payload using `::default()`.
    let mut req = StoreWriteItemRequest::default();
    req.options = Some(options);

    // Fill in the `Item` we will be attempting to write.
    println!("WriteItem request sent: key: {}, value: {:?}", &key, &value);
    req.attempt = Some(Item { key: key.to_string(), value: value });

    // Send and async `WriteItem` request to the server.
    match store.write_item(&req).await.context("Error sending request")? {
        Ok(value) => println!("WriteItem response received: {:?}", &value),
        Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
    }
    Ok(())
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // All of our requests will have the same bitflags set. Pull these settings from the config.
    let mut options = WriteOptions::empty();
    options.set(WriteOptions::OVERWRITE, config.set_overwrite_option);
    options.set(WriteOptions::CONCAT, config.set_concat_option);

    // The structured config provides one input for most data types that can be stored in the data
    // store. Iterate through those inputs in the order we see them in the FIDL file.
    //
    // Note that FIDL unions are rendered as enums in Rust; for example, the `Value` union has now
    // become a `Value` Rust enum, with each member taking exactly one argument.
    for value in config.write_bytes.into_iter() {
        write_next_item(&store, "bytes", Value::Bytes(value.into()), options).await?;
    }
    for value in config.write_strings.into_iter() {
        write_next_item(&store, "string", Value::String(value), options).await?;
    }
    for value in config.write_uint64s.into_iter() {
        write_next_item(&store, "uint64", Value::Uint64(value), options).await?;
    }
    for value in config.write_int64s.into_iter() {
        write_next_item(&store, "int64", Value::Int64(value), options).await?;
    }
    for value in config.write_uint128s.into_iter() {
        write_next_item(&store, "uint128", Value::Uint128([0, value]), options).await?;
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fuchsia_component::server::ServiceFs;
use futures::prelude::*;
use lazy_static::lazy_static;
use regex::Regex;
use std::cell::RefCell;
use std::collections::hash_map::Entry;
use std::collections::HashMap;

use fidl_examples_keyvaluestore_usegenericvalues::{
    Item, StoreRequest, StoreRequestStream, Value, WriteError, WriteOptions,
};
use std::collections::hash_map::OccupiedEntry;
use std::ops::Add;

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

/// Sums any numeric type.
fn sum<T: Add + Add<Output = T> + Copy>(operands: [T; 2]) -> T {
    operands[0] + operands[1]
}

/// Clones and inserts an entry, so that the original (now concatenated) copy may be returned in the
/// response.
fn write(inserting: Value, mut entry: OccupiedEntry<'_, String, Value>) -> Value {
    entry.insert(inserting.clone());
    println!("Wrote key: {}, value: {:?}", entry.key(), &inserting);
    inserting
}

/// Handler for the `WriteItem` method.
fn write_item(
    store: &mut HashMap<String, Value>,
    attempt: Item,
    options: &WriteOptions,
) -> Result<Value, WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY for key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            // The `CONCAT` flag supersedes the `OVERWRITE` flag, so check it first.
            if options.contains(WriteOptions::CONCAT) {
                match entry.get() {
                    Value::Bytes(old) => {
                        if let Value::Bytes(new) = attempt.value {
                            let mut combined = old.clone();
                            combined.extend(new);
                            return Ok(write(Value::Bytes(combined), entry));
                        }
                    }
                    Value::String(old) => {
                        if let Value::String(new) = attempt.value {
                            return Ok(write(Value::String(format!("{}{}", old, &new)), entry));
                        }
                    }
                    Value::Uint64(old) => {
                        if let Value::Uint64(new) = attempt.value {
                            return Ok(write(Value::Uint64(sum([*old, new])), entry));
                        }
                    }
                    Value::Int64(old) => {
                        if let Value::Int64(new) = attempt.value {
                            return Ok(write(Value::Int64(sum([*old, new])), entry));
                        }
                    }
                    // Note: only works on the uint64 range in practice.
                    Value::Uint128(old) => {
                        if let Value::Uint128(new) = attempt.value {
                            return Ok(write(Value::Uint128([0, sum([old[1], new[1]])]), entry));
                        }
                    }
                    _ => {
                        panic!("actively unsupported type!")
                    }
                }

                // Only reachable if the type of the would be concatenated value did not match the
                // value already occupying this entry.
                println!("Write error: INVALID_VALUE for key: {}", entry.key());
                return Err(WriteError::InvalidValue);
            }

            // If we're not doing CONCAT, check for OVERWRITE next.
            if options.contains(WriteOptions::OVERWRITE) {
                return Ok(write(attempt.value, entry));
            }

            println!("Write error: ALREADY_EXISTS for key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote key: {}, value: {:?}", entry.key(), &attempt.value);
            entry.insert(attempt.value.clone());
            Ok(attempt.value)
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, Value>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                // Because we are using a table payload, there is an extra level of indirection. The
                // top-level container for the table itself is always called "payload".
                StoreRequest::WriteItem { payload, responder } => {
                    println!("WriteItem request received");

                    // Error out if either of the request table's members are not set.
                    let attempt = payload.attempt.context("required field 'attempt' is unset")?;
                    let options = payload.options.context("required field 'options' is unset")?;

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(
                            write_item(&mut store.borrow_mut(), attempt, &options)
                                .as_ref()
                                .map_err(|e| *e),
                        )
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

節流事件模式

FIDL 食譜:節流事件模式

事件是從伺服器啟動的 FIDL 呼叫。由於這些呼叫沒有內建用戶端端回應,因此不會進行流程控制:伺服器可能會為大量這類呼叫排隊,並淹沒用戶端。解決這個問題的方法之一是使用節流事件模式。這個模式會新增用戶端呼叫的 FIDL 方法,做為一或多個事件的確認點。

在接收來自用戶端的下一個確認呼叫之前,伺服器應避免傳送更多受限速的事件 (此處的確切語義取決於實作通訊協定)。同樣地,如果伺服器在用戶端確認之前傳送的節制事件數量超過允許數量,用戶端也應關閉連線。這些限制並未內建於 FIDL 執行階段,因此需要由用戶端/伺服器實作端手動實作,才能確保正確的行為。

改善 Instance 通訊協定效能的其中一種方法,是允許分批處理行:每當我們想要在畫布上新增一行時,不必每次都傳送單一 AddLine(...);,等待回應,然後再次為下一行執行這項操作,而是可以將多行分批處理,以便一次叫用新的 AddLines(...); 呼叫。用戶端現在可以決定如何最佳地區隔要繪製的大量線條集合。

若是採用簡單的實作方式,我們會發現伺服器和用戶端完全不同步:用戶端可能會以無限的 AddLines(...); 呼叫淹沒伺服器,而伺服器也可能會以超過用戶端處理能力的 -> OnDrawn(...); 事件淹沒用戶端。解決這兩個問題的方法,就是新增簡單的 Ready() -> (); 方法來進行同步處理。每當用戶端準備接收下一個繪圖更新時,就會呼叫這個方法,並透過伺服器的回應指出用戶端可以繼續執行更多要求。

我們現在在兩個方向都設有一些資料流控制。這項通訊協定現在實作了前饋模式,允許在某些同步「commit」呼叫觸發伺服器上的實際工作之前,進行許多未受控的呼叫。這可避免用戶端因工作量過大而癱瘓伺服器。同樣地,伺服器也不再允許傳送無限的 -> OnDrawn(...); 事件:每個事件都必須遵循來自用戶端的信號 (Ready() -> (); 呼叫),表示該事件已準備好執行更多工作。這就是所謂的「節流事件模式」

具體實作必須手動套用部分規則:如果用戶端收到未透過 Ready() -> (); 方法要求的 -> OnDrawn(...); 事件,就必須關閉連線。

FIDL、CML 和領域介面定義如下:

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.canvas.clientrequesteddraw;

/// A point in 2D space.
type Point = struct {
    x int64;
    y int64;
};

/// A line in 2D space.
alias Line = array<Point, 2>;

/// A bounding box in 2D space. This is the result of "drawing" operations on our canvas, and what
/// the server reports back to the client. These bounds are sufficient to contain all of the
/// lines (inclusive) on a canvas at a given time.
type BoundingBox = struct {
    top_left Point;
    bottom_right Point;
};

/// Manages a single instance of a canvas. Each session of this protocol is responsible for a new
/// canvas.
@discoverable
open protocol Instance {
    /// Add multiple lines to the canvas. We are able to reduce protocol chatter and the number of
    /// requests needed by batching instead of calling the simpler `AddLine(...)` one line at a
    /// time.
    flexible AddLines(struct {
        lines vector<Line>;
    });

    /// Rather than the server randomly performing draws, or trying to guess when to do so, the
    /// client must explicitly ask for them. This creates a bit of extra chatter with the additional
    /// method invocation, but allows much greater client-side control of when the canvas is "ready"
    /// for a view update, thereby eliminating unnecessary draws.
    ///
    /// This method also has the benefit of "throttling" the `-> OnDrawn(...)` event - rather than
    /// allowing a potentially unlimited flood of `-> OnDrawn(...)` calls, we now have the runtime
    /// enforced semantic that each `-> OnDrawn(...)` call must follow a unique `Ready() -> ()` call
    /// from the client. An unprompted `-> OnDrawn(...)` is invalid, and should cause the channel to
    /// immediately close.
    flexible Ready() -> ();

    /// Update the client with the latest drawing state. The server makes no guarantees about how
    /// often this event occurs - it could occur multiple times per board state, for example.
    flexible -> OnDrawn(BoundingBox);
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.canvas.clientrequesteddraw.Instance" },
    ],
    config: {
        // A script for the client to follow. Entries in the script may take one of two forms: a
        // pair of signed-integer coordinates like "-2,15:4,5", or the string "READY". The former
        // builds a local vector sent via a single `AddLines(...)` call, while the latter sends a
        // `Ready() -> ()` call pauses execution until the next `->OnDrawn(...)` event is received.
        //
        // TODO(https://fxbug.dev/42178362): It would absolve individual language implementations of a great
        //   deal of string parsing if we were able to use a vector of `union { Point; Ready}` here.
        script: {
            type: "vector",
            max_count: 100,
            element: {
                type: "string",
                max_size: 64,
            },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.canvas.clientrequesteddraw.Instance" },
    ],
    expose: [
        {
            protocol: "examples.canvas.clientrequesteddraw.Instance",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.canvas.clientrequesteddraw.Instance",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{format_err, Context as _, Error};
use config::Config;
use fidl_examples_canvas_clientrequesteddraw::{InstanceEvent, InstanceMarker, Point};
use fuchsia_component::client::connect_to_protocol;
use futures::TryStreamExt;
use std::{thread, time};

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send Instance requests
    // across the channel.
    let instance = connect_to_protocol::<InstanceMarker>()?;
    println!("Outgoing connection enabled");

    let mut batched_lines = Vec::<[Point; 2]>::new();
    for action in config.script.into_iter() {
        // If the next action in the script is to "PUSH", send a batch of lines to the server.
        if action == "PUSH" {
            instance.add_lines(&batched_lines).context("Could not send lines")?;
            println!("AddLines request sent");
            batched_lines.clear();
            continue;
        }

        // If the next action in the script is to "WAIT", block until an OnDrawn event is received
        // from the server.
        if action == "WAIT" {
            let mut event_stream = instance.take_event_stream();
            loop {
                match event_stream
                    .try_next()
                    .await
                    .context("Error getting event response from proxy")?
                    .ok_or_else(|| format_err!("Proxy sent no events"))?
                {
                    InstanceEvent::OnDrawn { top_left, bottom_right } => {
                        println!(
                            "OnDrawn event received: top_left: {:?}, bottom_right: {:?}",
                            top_left, bottom_right
                        );
                        break;
                    }
                    InstanceEvent::_UnknownEvent { ordinal, .. } => {
                        println!("Received an unknown event with ordinal {ordinal}");
                    }
                }
            }

            // Now, inform the server that we are ready to receive more updates whenever they are
            // ready for us.
            println!("Ready request sent");
            instance.ready().await.context("Could not send ready call")?;
            println!("Ready success");
            continue;
        }

        // Add a line to the next batch. Parse the string input, making two points out of it.
        let mut points = action
            .split(":")
            .map(|point| {
                let integers = point
                    .split(",")
                    .map(|integer| integer.parse::<i64>().unwrap())
                    .collect::<Vec<i64>>();
                Point { x: integers[0], y: integers[1] }
            })
            .collect::<Vec<Point>>();

        // Assemble a line from the two points.
        let from = points.pop().ok_or_else(|| format_err!("line requires 2 points, but has 0"))?;
        let to = points.pop().ok_or_else(|| format_err!("line requires 2 points, but has 1"))?;
        let mut line: [Point; 2] = [from, to];

        // Batch a line for drawing to the canvas using the two points provided.
        println!("AddLines batching line: {:?}", &mut line);
        batched_lines.push(line);
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{anyhow, Context as _, Error};
use fidl::endpoints::RequestStream as _;
use fidl_examples_canvas_clientrequesteddraw::{
    BoundingBox, InstanceRequest, InstanceRequestStream, Point,
};
use fuchsia_async::{MonotonicInstant, Timer};
use fuchsia_component::server::ServiceFs;

use futures::future::join;
use futures::prelude::*;
use std::sync::{Arc, Mutex};

// A struct that stores the two things we care about for this example: the bounding box the lines
// that have been added thus far, and bit to track whether or not there have been changes since the
// last `OnDrawn` event.
#[derive(Debug)]
struct CanvasState {
    // Tracks whether there has been a change since the last send, to prevent redundant updates.
    changed: bool,
    // Tracks whether or not the client has declared itself ready to receive more updated.
    ready: bool,
    bounding_box: BoundingBox,
}

/// Handler for the `AddLines` method.
fn add_lines(state: &mut CanvasState, lines: Vec<[Point; 2]>) {
    // Update the bounding box to account for the new lines we've just "added" to the canvas.
    let bounds = &mut state.bounding_box;
    for line in lines {
        println!("AddLines printing line: {:?}", line);
        for point in line {
            if point.x < bounds.top_left.x {
                bounds.top_left.x = point.x;
            }
            if point.y > bounds.top_left.y {
                bounds.top_left.y = point.y;
            }
            if point.x > bounds.bottom_right.x {
                bounds.bottom_right.x = point.x;
            }
            if point.y < bounds.bottom_right.y {
                bounds.bottom_right.y = point.y;
            }
        }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next tick.
    state.changed = true
}

/// Creates a new instance of the server, paired to a single client across a zircon channel.
async fn run_server(stream: InstanceRequestStream) -> Result<(), Error> {
    // Create a new in-memory state store for the state of the canvas. The store will live for the
    // lifetime of the connection between the server and this particular client.
    let state = Arc::new(Mutex::new(CanvasState {
        changed: true,
        ready: true,
        bounding_box: BoundingBox {
            top_left: Point { x: 0, y: 0 },
            bottom_right: Point { x: 0, y: 0 },
        },
    }));

    // Take ownership of the control_handle from the stream, which will allow us to push events from
    // a different async task.
    let control_handle = stream.control_handle();

    // A separate watcher task periodically "draws" the canvas, and notifies the client of the new
    // state. We'll need a cloned reference to the canvas state to be accessible from the new
    // task.
    let state_ref = state.clone();
    let update_sender = || async move {
        loop {
            // Our server sends one update per second, but only if the client has declared that it
            // is ready to receive one.
            Timer::new(MonotonicInstant::after(zx::MonotonicDuration::from_seconds(1))).await;
            let mut state = state_ref.lock().unwrap();
            if !state.changed || !state.ready {
                continue;
            }

            // After acquiring the lock, this is where we would draw the actual lines. Since this is
            // just an example, we'll avoid doing the actual rendering, and simply send the bounding
            // box to the client instead.
            let bounds = state.bounding_box;
            match control_handle.send_on_drawn(&bounds.top_left, &bounds.bottom_right) {
                Ok(_) => println!(
                    "OnDrawn event sent: top_left: {:?}, bottom_right: {:?}",
                    bounds.top_left, bounds.bottom_right
                ),
                Err(_) => return,
            }

            // Reset the change and ready trackers.
            state.ready = false;
            state.changed = false;
        }
    };

    // Handle requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    let state_ref = &state;
    let request_handler =
        stream.map(|result| result.context("failed request")).try_for_each(|request| async move {
            // Match based on the method being invoked.
            match request {
                InstanceRequest::AddLines { lines, .. } => {
                    println!("AddLines request received");
                    add_lines(&mut state_ref.lock().unwrap(), lines);
                }
                InstanceRequest::Ready { responder, .. } => {
                    println!("Ready request received");
                    // The client must only call `Ready() -> ();` after receiving an `-> OnDrawn();`
                    // event; if two "consecutive" `Ready() -> ();` calls are received, this
                    // interaction has entered an invalid state, and should be aborted immediately.
                    let mut state = state_ref.lock().unwrap();
                    if state.ready == true {
                        return Err(anyhow!("Invalid back-to-back `Ready` requests received"));
                    }

                    state.ready = true;
                    responder.send().context("Error responding")?;
                } //
                InstanceRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        });

    // This line will only be reached if the server errors out. The stream will await indefinitely,
    // thereby creating a long-lived server. Here, we first wait for the updater task to realize the
    // connection has died, then bubble up the error.
    join(request_handler, update_sender()).await.0
}

// A helper enum that allows us to treat a `Instance` service instance as a value.
enum IncomingService {
    Instance(InstanceRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Instance` protocol - this will allow the client to see
    // the server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Instance);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Instance(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.clientrequesteddraw/cpp/fidl.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/component/incoming/cpp/protocol.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <charconv>

#include <examples/fidl/new/canvas/client_requested_draw/cpp_natural/client/config.h>

// The |EventHandler| is a derived class that we pass into the |fidl::WireClient| to handle incoming
// events asynchronously.
class EventHandler : public fidl::AsyncEventHandler<examples_canvas_clientrequesteddraw::Instance> {
 public:
  // Handler for |OnDrawn| events sent from the server.
  void OnDrawn(
      fidl::Event<examples_canvas_clientrequesteddraw::Instance::OnDrawn>& event) override {
    ::examples_canvas_clientrequesteddraw::Point top_left = event.top_left();
    ::examples_canvas_clientrequesteddraw::Point bottom_right = event.bottom_right();
    FX_LOGS(INFO) << "OnDrawn event received: top_left: Point { x: " << top_left.x()
                  << ", y: " << top_left.y() << " }, bottom_right: Point { x: " << bottom_right.x()
                  << ", y: " << bottom_right.y() << " }";
    loop_.Quit();
  }

  void on_fidl_error(fidl::UnbindInfo error) override { FX_LOGS(ERROR) << error; }

  void handle_unknown_event(
      fidl::UnknownEventMetadata<examples_canvas_clientrequesteddraw::Instance> metadata) override {
    FX_LOGS(WARNING) << "Received an unknown event with ordinal " << metadata.event_ordinal;
  }

  explicit EventHandler(async::Loop& loop) : loop_(loop) {}

 private:
  async::Loop& loop_;
};

// A helper function that takes a coordinate in string form, like "123,-456", and parses it into a
// a struct of the form |{ in64 x; int64 y; }|.
::examples_canvas_clientrequesteddraw::Point ParsePoint(std::string_view input) {
  int64_t x = 0;
  int64_t y = 0;
  size_t index = input.find(',');
  if (index != std::string::npos) {
    std::from_chars(input.data(), input.data() + index, x);
    std::from_chars(input.data() + index + 1, input.data() + input.length(), y);
  }
  return ::examples_canvas_clientrequesteddraw::Point(x, y);
}

using Line = ::std::array<::examples_canvas_clientrequesteddraw::Point, 2>;

// A helper function that takes a coordinate pair in string form, like "1,2:-3,-4", and parses it
// into an array of 2 |Point| structs.
Line ParseLine(const std::string& action) {
  auto input = std::string_view(action);
  size_t index = input.find(':');
  if (index != std::string::npos) {
    return {ParsePoint(input.substr(0, index)), ParsePoint(input.substr(index + 1))};
  }
  return {};
}

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop and dispatcher.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace. This can fail so it's wrapped in a
  // |zx::result| and it must be checked for errors.
  zx::result client_end = component::Connect<examples_canvas_clientrequesteddraw::Instance>();
  if (!client_end.is_ok()) {
    FX_LOGS(ERROR) << "Synchronous error when connecting to the |Instance| protocol: "
                   << client_end.status_string();
    return -1;
  }

  // Create an instance of the event handler.
  EventHandler event_handler(loop);

  // Create an asynchronous client using the newly-established connection.
  fidl::Client client(std::move(*client_end), dispatcher, &event_handler);
  FX_LOGS(INFO) << "Outgoing connection enabled";

  std::vector<Line> batched_lines;
  for (const auto& action : conf.script()) {
    // If the next action in the script is to "PUSH", send a batch of lines to the server.
    if (action == "PUSH") {
      fit::result<fidl::Error> result = client->AddLines(batched_lines);
      if (!result.is_ok()) {
        // Check that our one-way call was enqueued successfully, and handle the error
        // appropriately. In the case of this example, there is nothing we can do to recover here,
        // except to log an error and exit the program.
        FX_LOGS(ERROR) << "Could not send AddLines request: " << result.error_value();
        return -1;
      }

      batched_lines.clear();
      FX_LOGS(INFO) << "AddLines request sent";
      continue;
    }

    // If the next action in the script is to "WAIT", block until an |OnDrawn| event is received
    // from the server.
    if (action == "WAIT") {
      loop.Run();
      loop.ResetQuit();

      // Now, inform the server that we are ready to receive more updates whenever they are
      // ready for us.
      FX_LOGS(INFO) << "Ready request sent";
      client->Ready().ThenExactlyOnce(
          [&](fidl::Result<examples_canvas_clientrequesteddraw::Instance::Ready> result) {
            // Check if the FIDL call succeeded or not.
            if (result.is_ok()) {
              FX_LOGS(INFO) << "Ready success";
            } else {
              FX_LOGS(ERROR) << "Could not send Ready request: " << result.error_value();
            }

            // Quit the loop, thereby handing control back to the outer loop of actions being
            // iterated over.
            loop.Quit();
          });

      // Run the loop until the callback is resolved, at which point we can continue from here.
      loop.Run();
      loop.ResetQuit();

      continue;
    }

    // Batch a line for drawing to the canvas using the two points provided.
    Line line = ParseLine(action);
    batched_lines.push_back(line);
    FX_LOGS(INFO) << "AddLines batching line: [Point { x: " << line[1].x() << ", y: " << line[1].y()
                  << " }, Point { x: " << line[0].x() << ", y: " << line[0].y() << " }]";
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.clientrequesteddraw/cpp/fidl.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/async/cpp/task.h>
#include <lib/component/outgoing/cpp/outgoing_directory.h>
#include <lib/fidl/cpp/wire/channel.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <src/lib/fxl/macros.h>
#include <src/lib/fxl/memory/weak_ptr.h>

// A struct that stores the two things we care about for this example: the set of lines, and the
// bounding box that contains them.
struct CanvasState {
  // Tracks whether there has been a change since the last send, to prevent redundant updates.
  bool changed = true;
  // Tracks whether or not the client has declared itself ready to receive more updated.
  bool ready = true;
  examples_canvas_clientrequesteddraw::BoundingBox bounding_box;
};

// An implementation of the |Instance| protocol.
class InstanceImpl final : public fidl::Server<examples_canvas_clientrequesteddraw::Instance> {
 public:
  // Bind this implementation to a channel.
  InstanceImpl(async_dispatcher_t* dispatcher,
               fidl::ServerEnd<examples_canvas_clientrequesteddraw::Instance> server_end)
      : binding_(dispatcher, std::move(server_end), this, std::mem_fn(&InstanceImpl::OnFidlClosed)),
        weak_factory_(this) {
    // Start the update timer on startup. Our server sends one update per second
    ScheduleOnDrawnEvent(dispatcher, zx::sec(1));
  }

  void OnFidlClosed(fidl::UnbindInfo info) {
    if (info.reason() != ::fidl::Reason::kPeerClosedWhileReading) {
      FX_LOGS(ERROR) << "Shutdown unexpectedly";
    }
    delete this;
  }

  void AddLines(AddLinesRequest& request, AddLinesCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "AddLines request received";
    for (const auto& points : request.lines()) {
      FX_LOGS(INFO) << "AddLines printing line: [Point { x: " << points[1].x()
                    << ", y: " << points[1].y() << " }, Point { x: " << points[0].x()
                    << ", y: " << points[0].y() << " }]";

      // Update the bounding box to account for the new line we've just "added" to the canvas.
      auto& bounds = state_.bounding_box;
      for (const auto& point : points) {
        if (point.x() < bounds.top_left().x()) {
          bounds.top_left().x() = point.x();
        }
        if (point.y() > bounds.top_left().y()) {
          bounds.top_left().y() = point.y();
        }
        if (point.x() > bounds.bottom_right().x()) {
          bounds.bottom_right().x() = point.x();
        }
        if (point.y() < bounds.bottom_right().y()) {
          bounds.bottom_right().y() = point.y();
        }
      }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next |OnDrawn|
    // event.
    state_.changed = true;
  }

  void Ready(ReadyCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "Ready request received";

    // The client must only call `Ready() -> ();` after receiving an `-> OnDrawn();` event; if two
    // "consecutive" `Ready() -> ();` calls are received, this interaction has entered an invalid
    // state, and should be aborted immediately.
    if (state_.ready == true) {
      FX_LOGS(ERROR) << "Invalid back-to-back `Ready` requests received";
    }

    state_.ready = true;
    completer.Reply();
  }

  void handle_unknown_method(
      fidl::UnknownMethodMetadata<examples_canvas_clientrequesteddraw::Instance> metadata,
      fidl::UnknownMethodCompleter::Sync& completer) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << metadata.method_ordinal;
  }

 private:
  // Each scheduled update waits for the allotted amount of time, sends an update if something has
  // changed, and schedules the next update.
  void ScheduleOnDrawnEvent(async_dispatcher_t* dispatcher, zx::duration after) {
    async::PostDelayedTask(
        dispatcher,
        [&, dispatcher, after, weak = weak_factory_.GetWeakPtr()] {
          // Halt execution if the binding has been deallocated already.
          if (!weak) {
            return;
          }

          // Schedule the next update if the binding still exists.
          weak->ScheduleOnDrawnEvent(dispatcher, after);

          // No need to send an update if nothing has changed since the last one, or the client has
          // not yet informed us that it is ready for more updates.
          if (!weak->state_.changed || !weak->state_.ready) {
            return;
          }

          // This is where we would draw the actual lines. Since this is just an example, we'll
          // avoid doing the actual rendering, and simply send the bounding box to the client
          // instead.
          auto result = fidl::SendEvent(binding_)->OnDrawn(state_.bounding_box);
          if (!result.is_ok()) {
            return;
          }

          auto top_left = state_.bounding_box.top_left();
          auto bottom_right = state_.bounding_box.bottom_right();
          FX_LOGS(INFO) << "OnDrawn event sent: top_left: Point { x: " << top_left.x()
                        << ", y: " << top_left.y()
                        << " }, bottom_right: Point { x: " << bottom_right.x()
                        << ", y: " << bottom_right.y() << " }";

          // Reset the change and ready trackers.
          state_.ready = false;
          state_.changed = false;
        },
        after);
  }

  fidl::ServerBinding<examples_canvas_clientrequesteddraw::Instance> binding_;
  CanvasState state_ = CanvasState{};

  // Generates weak references to this object, which are appropriate to pass into asynchronous
  // callbacks that need to access this object. The references are automatically invalidated
  // if this object is destroyed.
  fxl::WeakPtrFactory<InstanceImpl> weak_factory_;
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component. This
  // directory is where the outgoing FIDL protocols are installed so that they can be provided to
  // other components.
  component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);

  // The `ServeFromStartupInfo()` function sets up the outgoing directory with the startup handle.
  // The startup handle is a handle provided to every component by the system, so that they can
  // serve capabilities (e.g. FIDL protocols) to other components.
  zx::result result = outgoing.ServeFromStartupInfo();
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
    return -1;
  }

  // Register a handler for components trying to connect to
  // |examples.canvas.clientrequesteddraw.Instance|.
  result = outgoing.AddUnmanagedProtocol<examples_canvas_clientrequesteddraw::Instance>(
      [dispatcher](fidl::ServerEnd<examples_canvas_clientrequesteddraw::Instance> server_end) {
        // Create an instance of our InstanceImpl that destroys itself when the connection closes.
        new InstanceImpl(dispatcher, std::move(server_end));
      });
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to add Instance protocol: " << result.status_string();
    return -1;
  }

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

C++ (Wire)

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.clientrequesteddraw/cpp/wire.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/component/incoming/cpp/protocol.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <charconv>

#include <examples/fidl/new/canvas/client_requested_draw/cpp_wire/client/config.h>

// The |EventHandler| is a derived class that we pass into the |fidl::WireClient| to handle incoming
// events asynchronously.
class EventHandler
    : public fidl::WireAsyncEventHandler<examples_canvas_clientrequesteddraw::Instance> {
 public:
  // Handler for |OnDrawn| events sent from the server.
  void OnDrawn(
      fidl::WireEvent<examples_canvas_clientrequesteddraw::Instance::OnDrawn>* event) override {
    ::examples_canvas_clientrequesteddraw::wire::Point top_left = event->top_left;
    ::examples_canvas_clientrequesteddraw::wire::Point bottom_right = event->bottom_right;
    FX_LOGS(INFO) << "OnDrawn event received: top_left: Point { x: " << top_left.x
                  << ", y: " << top_left.y << " }, bottom_right: Point { x: " << bottom_right.x
                  << ", y: " << bottom_right.y << " }";
    loop_.Quit();
  }

  void on_fidl_error(fidl::UnbindInfo error) override { FX_LOGS(ERROR) << error; }

  void handle_unknown_event(
      fidl::UnknownEventMetadata<examples_canvas_clientrequesteddraw::Instance> metadata) override {
    FX_LOGS(WARNING) << "Received an unknown event with ordinal " << metadata.event_ordinal;
  }

  explicit EventHandler(async::Loop& loop) : loop_(loop) {}

 private:
  async::Loop& loop_;
};

// A helper function that takes a coordinate in string form, like "123,-456", and parses it into a
// a struct of the form |{ in64 x; int64 y; }|.
::examples_canvas_clientrequesteddraw::wire::Point ParsePoint(std::string_view input) {
  int64_t x = 0;
  int64_t y = 0;
  size_t index = input.find(',');
  if (index != std::string::npos) {
    std::from_chars(input.data(), input.data() + index, x);
    std::from_chars(input.data() + index + 1, input.data() + input.length(), y);
  }
  return ::examples_canvas_clientrequesteddraw::wire::Point{.x = x, .y = y};
}

using Line = ::fidl::Array<::examples_canvas_clientrequesteddraw::wire::Point, 2>;

// A helper function that takes a coordinate pair in string form, like "1,2:-3,-4", and parses it
// into an array of 2 |Point| structs.
Line ParseLine(const std::string& action) {
  auto input = std::string_view(action);
  size_t index = input.find(':');
  if (index != std::string::npos) {
    return {ParsePoint(input.substr(0, index)), ParsePoint(input.substr(index + 1))};
  }
  return {};
}

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop and dispatcher.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace. This can fail so it's wrapped in a
  // |zx::result| and it must be checked for errors.
  zx::result client_end = component::Connect<examples_canvas_clientrequesteddraw::Instance>();
  if (!client_end.is_ok()) {
    FX_LOGS(ERROR) << "Synchronous error when connecting to the |Instance| protocol: "
                   << client_end.status_string();
    return -1;
  }

  // Create an instance of the event handler.
  EventHandler event_handler(loop);

  // Create an asynchronous client using the newly-established connection.
  fidl::WireClient client(std::move(*client_end), dispatcher, &event_handler);
  FX_LOGS(INFO) << "Outgoing connection enabled";

  std::vector<Line> batched_lines;
  for (const auto& action : conf.script()) {
    // If the next action in the script is to "PUSH", send a batch of lines to the server.
    if (action == "PUSH") {
      fidl::Status status = client->AddLines(fidl::VectorView<Line>::FromExternal(batched_lines));
      if (!status.ok()) {
        // Check that our one-way call was enqueued successfully, and handle the error
        // appropriately. In the case of this example, there is nothing we can do to recover here,
        // except to log an error and exit the program.
        FX_LOGS(ERROR) << "Could not send AddLines request: " << status.error();
        return -1;
      }

      batched_lines.clear();
      FX_LOGS(INFO) << "AddLines request sent";
      continue;
    }

    // If the next action in the script is to "WAIT", block until an |OnDrawn| event is received
    // from the server.
    if (action == "WAIT") {
      loop.Run();
      loop.ResetQuit();

      // Now, inform the server that we are ready to receive more updates whenever they are
      // ready for us.
      FX_LOGS(INFO) << "Ready request sent";
      client->Ready().ThenExactlyOnce(
          [&](fidl::WireUnownedResult<examples_canvas_clientrequesteddraw::Instance::Ready>&
                  result) {
            // Check if the FIDL call succeeded or not.
            if (result.ok()) {
              FX_LOGS(INFO) << "Ready success";
            } else {
              FX_LOGS(ERROR) << "Could not send Ready request: " << result.error();
            }

            // Quit the loop, thereby handing control back to the outer loop of actions being
            // iterated over.
            loop.Quit();
          });

      // Run the loop until the callback is resolved, at which point we can continue from here.
      loop.Run();
      loop.ResetQuit();

      continue;
    }

    // Batch a line for drawing to the canvas using the two points provided.
    Line line = ParseLine(action);
    batched_lines.push_back(line);
    FX_LOGS(INFO) << "AddLines batching line: [Point { x: " << line[1].x << ", y: " << line[1].y
                  << " }, Point { x: " << line[0].x << ", y: " << line[0].y << " }]";
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fidl/examples.canvas.clientrequesteddraw/cpp/wire.h>
#include <lib/async-loop/cpp/loop.h>
#include <lib/async/cpp/task.h>
#include <lib/component/outgoing/cpp/outgoing_directory.h>
#include <lib/fidl/cpp/wire/channel.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <src/lib/fxl/macros.h>
#include <src/lib/fxl/memory/weak_ptr.h>

// A struct that stores the two things we care about for this example: the set of lines, and the
// bounding box that contains them.
struct CanvasState {
  // Tracks whether there has been a change since the last send, to prevent redundant updates.
  bool changed = true;
  // Tracks whether or not the client has declared itself ready to receive more updated.
  bool ready = true;
  examples_canvas_clientrequesteddraw::wire::BoundingBox bounding_box;
};

// An implementation of the |Instance| protocol.
class InstanceImpl final : public fidl::WireServer<examples_canvas_clientrequesteddraw::Instance> {
 public:
  // Bind this implementation to a channel.
  InstanceImpl(async_dispatcher_t* dispatcher,
               fidl::ServerEnd<examples_canvas_clientrequesteddraw::Instance> server_end)
      : binding_(dispatcher, std::move(server_end), this, std::mem_fn(&InstanceImpl::OnFidlClosed)),
        weak_factory_(this) {
    // Start the update timer on startup. Our server sends one update per second
    ScheduleOnDrawnEvent(dispatcher, zx::sec(1));
  }

  void OnFidlClosed(fidl::UnbindInfo info) {
    if (info.reason() != ::fidl::Reason::kPeerClosedWhileReading) {
      FX_LOGS(ERROR) << "Shutdown unexpectedly";
    }
    delete this;
  }

  void AddLines(AddLinesRequestView request, AddLinesCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "AddLines request received";
    for (const auto& points : request->lines) {
      FX_LOGS(INFO) << "AddLines printing line: [Point { x: " << points[1].x
                    << ", y: " << points[1].y << " }, Point { x: " << points[0].x
                    << ", y: " << points[0].y << " }]";

      // Update the bounding box to account for the new line we've just "added" to the canvas.
      auto& bounds = state_.bounding_box;
      for (const auto& point : points) {
        if (point.x < bounds.top_left.x) {
          bounds.top_left.x = point.x;
        }
        if (point.y > bounds.top_left.y) {
          bounds.top_left.y = point.y;
        }
        if (point.x > bounds.bottom_right.x) {
          bounds.bottom_right.x = point.x;
        }
        if (point.y < bounds.bottom_right.y) {
          bounds.bottom_right.y = point.y;
        }
      }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next |OnDrawn|
    // event.
    state_.changed = true;
  }

  void Ready(ReadyCompleter::Sync& completer) override {
    FX_LOGS(INFO) << "Ready request received";

    // The client must only call `Ready() -> ();` after receiving an `-> OnDrawn();` event; if two
    // "consecutive" `Ready() -> ();` calls are received, this interaction has entered an invalid
    // state, and should be aborted immediately.
    if (state_.ready == true) {
      FX_LOGS(ERROR) << "Invalid back-to-back `Ready` requests received";
    }

    state_.ready = true;
    completer.Reply();
  }

  void handle_unknown_method(
      fidl::UnknownMethodMetadata<examples_canvas_clientrequesteddraw::Instance> metadata,
      fidl::UnknownMethodCompleter::Sync& completer) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << metadata.method_ordinal;
  }

 private:
  // Each scheduled update waits for the allotted amount of time, sends an update if something has
  // changed, and schedules the next update.
  void ScheduleOnDrawnEvent(async_dispatcher_t* dispatcher, zx::duration after) {
    async::PostDelayedTask(
        dispatcher,
        [&, dispatcher, after, weak = weak_factory_.GetWeakPtr()] {
          // Halt execution if the binding has been deallocated already.
          if (!weak) {
            return;
          }

          // Schedule the next update if the binding still exists.
          weak->ScheduleOnDrawnEvent(dispatcher, after);

          // No need to send an update if nothing has changed since the last one, or the client has
          // not yet informed us that it is ready for more updates.
          if (!weak->state_.changed || !weak->state_.ready) {
            return;
          }

          // This is where we would draw the actual lines. Since this is just an example, we'll
          // avoid doing the actual rendering, and simply send the bounding box to the client
          // instead.
          auto top_left = weak->state_.bounding_box.top_left;
          auto bottom_right = weak->state_.bounding_box.bottom_right;
          fidl::Status status =
              fidl::WireSendEvent(weak->binding_)->OnDrawn(top_left, bottom_right);
          if (!status.ok()) {
            return;
          }
          FX_LOGS(INFO) << "OnDrawn event sent: top_left: Point { x: " << top_left.x
                        << ", y: " << top_left.y
                        << " }, bottom_right: Point { x: " << bottom_right.x
                        << ", y: " << bottom_right.y << " }";

          // Reset the change and ready trackers.
          state_.ready = false;
          weak->state_.changed = false;
        },
        after);
  }

  fidl::ServerBinding<examples_canvas_clientrequesteddraw::Instance> binding_;
  CanvasState state_ = CanvasState{};

  // Generates weak references to this object, which are appropriate to pass into asynchronous
  // callbacks that need to access this object. The references are automatically invalidated
  // if this object is destroyed.
  fxl::WeakPtrFactory<InstanceImpl> weak_factory_;
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from the
  // client. The following initializes the loop, and obtains the dispatcher, which will be used when
  // binding the server implementation to a channel.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component. This
  // directory is where the outgoing FIDL protocols are installed so that they can be provided to
  // other components.
  component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);

  // The `ServeFromStartupInfo()` function sets up the outgoing directory with the startup handle.
  // The startup handle is a handle provided to every component by the system, so that they can
  // serve capabilities (e.g. FIDL protocols) to other components.
  zx::result result = outgoing.ServeFromStartupInfo();
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
    return -1;
  }

  // Register a handler for components trying to connect to
  // |examples.canvas.clientrequesteddraw.Instance|.
  result = outgoing.AddUnmanagedProtocol<examples_canvas_clientrequesteddraw::Instance>(
      [dispatcher](fidl::ServerEnd<examples_canvas_clientrequesteddraw::Instance> server_end) {
        // Create an instance of our InstanceImpl that destroys itself when the connection closes.
        new InstanceImpl(dispatcher, std::move(server_end));
      });
  if (result.is_error()) {
    FX_LOGS(ERROR) << "Failed to add Instance protocol: " << result.status_string();
    return -1;
  }

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

HLCPP

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/async-loop/cpp/loop.h>
#include <lib/sys/cpp/component_context.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <charconv>

#include <examples/canvas/clientrequesteddraw/cpp/fidl.h>
#include <examples/fidl/new/canvas/client_requested_draw/hlcpp/client/config.h>

// A helper function that takes a coordinate in string form, like "123,-456", and parses it into a
// a struct of the form |{ in64 x; int64 y; }|.
::examples::canvas::clientrequesteddraw::Point ParsePoint(std::string_view input) {
  int64_t x = 0;
  int64_t y = 0;
  size_t index = input.find(',');
  if (index != std::string::npos) {
    std::from_chars(input.data(), input.data() + index, x);
    std::from_chars(input.data() + index + 1, input.data() + input.length(), y);
  }
  return ::examples::canvas::clientrequesteddraw::Point{.x = x, .y = y};
}

using Line = ::std::array<::examples::canvas::clientrequesteddraw::Point, 2>;

// A helper function that takes a coordinate pair in string form, like "1,2:-3,-4", and parses it
// into an array of 2 |Point| structs.
Line ParseLine(const std::string& action) {
  auto input = std::string_view(action);
  size_t index = input.find(':');
  if (index != std::string::npos) {
    return {ParsePoint(input.substr(0, index)), ParsePoint(input.substr(index + 1))};
  }
  return {};
}

int main(int argc, const char** argv) {
  FX_LOGS(INFO) << "Started";

  // Retrieve component configuration.
  auto conf = config::Config::TakeFromStartupHandle();

  // Start up an async loop.
  async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Connect to the protocol inside the component's namespace, then create an asynchronous client
  // using the newly-established connection.
  examples::canvas::clientrequesteddraw::InstancePtr instance_proxy;
  auto context = sys::ComponentContext::Create();
  context->svc()->Connect(instance_proxy.NewRequest(dispatcher));
  FX_LOGS(INFO) << "Outgoing connection enabled";

  instance_proxy.set_error_handler([&loop](zx_status_t status) {
    FX_LOGS(ERROR) << "Shutdown unexpectedly";
    loop.Quit();
  });

  // Provide a lambda to handle incoming |OnDrawn| events asynchronously.
  instance_proxy.events().OnDrawn =
      [&loop](::examples::canvas::clientrequesteddraw::Point top_left,
              ::examples::canvas::clientrequesteddraw::Point bottom_right) {
        FX_LOGS(INFO) << "OnDrawn event received: top_left: Point { x: " << top_left.x
                      << ", y: " << top_left.y << " }, bottom_right: Point { x: " << bottom_right.x
                      << ", y: " << bottom_right.y << " }";
        loop.Quit();
      };

  instance_proxy.events().handle_unknown_event = [](uint64_t ordinal) {
    FX_LOGS(WARNING) << "Received an unknown event with ordinal " << ordinal;
  };

  std::vector<Line> batched_lines;
  for (const auto& action : conf.script()) {
    // If the next action in the script is to "PUSH", send a batch of lines to the server.
    if (action == "PUSH") {
      instance_proxy->AddLines(batched_lines);
      batched_lines.clear();
      FX_LOGS(INFO) << "AddLines request sent";
      continue;
    }

    // If the next action in the script is to "WAIT", block until an |OnDrawn| event is received
    // from the server.
    if (action == "WAIT") {
      loop.Run();
      loop.ResetQuit();

      // Now, inform the server that we are ready to receive more updates whenever they are ready
      // for us.
      FX_LOGS(INFO) << "Ready request sent";
      instance_proxy->Ready([&](fpromise::result<void, fidl::FrameworkErr> result) {
        if (result.is_error()) {
          // Check that our flexible two-way call was known to the server and handle the case of an
          // unknown method appropriately. In the case of this example, there is nothing we can do
          // to recover here, except to log an error and exit the program.
          FX_LOGS(ERROR) << "Server does not implement AddLine";
        }

        FX_LOGS(INFO) << "Ready success";

        // Quit the loop, thereby handing control back to the outer loop of actions being iterated
        // over.
        loop.Quit();
      });

      // Run the loop until the callback is resolved, at which point we can continue from here.
      loop.Run();
      loop.ResetQuit();

      continue;
    }

    // Batch a line for drawing to the canvas using the two points provided.
    Line line = ParseLine(action);
    batched_lines.push_back(line);
    FX_LOGS(INFO) << "AddLines batching line: [Point { x: " << line[1].x << ", y: " << line[1].y
                  << " }, Point { x: " << line[0].x << ", y: " << line[0].y << " }]";
  }

  // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
  // referenced bug has been resolved, we can remove the sleep.
  sleep(2);
  return 0;
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/async-loop/cpp/loop.h>
#include <lib/async-loop/default.h>
#include <lib/async/cpp/task.h>
#include <lib/fidl/cpp/binding.h>
#include <lib/sys/cpp/component_context.h>
#include <lib/syslog/cpp/macros.h>
#include <unistd.h>

#include <examples/canvas/clientrequesteddraw/cpp/fidl.h>
#include <src/lib/fxl/macros.h>
#include <src/lib/fxl/memory/weak_ptr.h>

// A struct that stores the two things we care about for this example: the set of lines, and the
// bounding box that contains them.
struct CanvasState {
  // Tracks whether there has been a change since the last send, to prevent redundant updates.
  bool changed = true;
  // Tracks whether or not the client has declared itself ready to receive more updated.
  bool ready = true;
  examples::canvas::clientrequesteddraw::BoundingBox bounding_box;
};

using Line = ::std::array<::examples::canvas::clientrequesteddraw::Point, 2>;

// An implementation of the |Instance| protocol.
class InstanceImpl final : public examples::canvas::clientrequesteddraw::Instance {
 public:
  // Bind this implementation to an |InterfaceRequest|.
  InstanceImpl(async_dispatcher_t* dispatcher,
               fidl::InterfaceRequest<examples::canvas::clientrequesteddraw::Instance> request)
      : binding_(fidl::Binding<examples::canvas::clientrequesteddraw::Instance>(this)),
        weak_factory_(this) {
    binding_.Bind(std::move(request), dispatcher);

    // Gracefully handle abrupt shutdowns.
    binding_.set_error_handler([this](zx_status_t status) mutable {
      if (status != ZX_ERR_PEER_CLOSED) {
        FX_LOGS(ERROR) << "Shutdown unexpectedly";
      }
      delete this;
    });

    // Start the update timer on startup. Our server sends one update per second.
    ScheduleOnDrawnEvent(dispatcher, zx::sec(1));
  }

  void AddLines(std::vector<Line> lines) override {
    FX_LOGS(INFO) << "AddLines request received";
    for (const auto& points : lines) {
      FX_LOGS(INFO) << "AddLines printing line: [Point { x: " << points[1].x
                    << ", y: " << points[1].y << " }, Point { x: " << points[0].x
                    << ", y: " << points[0].y << " }]";

      // Update the bounding box to account for the new line we've just "added" to the canvas.
      auto& bounds = state_.bounding_box;
      for (const auto& point : points) {
        if (point.x < bounds.top_left.x) {
          bounds.top_left.x = point.x;
        }
        if (point.y > bounds.top_left.y) {
          bounds.top_left.y = point.y;
        }
        if (point.x > bounds.bottom_right.x) {
          bounds.bottom_right.x = point.x;
        }
        if (point.y < bounds.bottom_right.y) {
          bounds.bottom_right.y = point.y;
        }
      }
    }

    // Mark the state as "dirty", so that an update is sent back to the client on the next
    // |OnDrawn| event.
    state_.changed = true;
  }

  void Ready(ReadyCallback callback) override {
    FX_LOGS(INFO) << "Ready request received";

    // The client must only call `Ready() -> ();` after receiving an `-> OnDrawn();` event; if
    // two "consecutive" `Ready() -> ();` calls are received, this interaction has entered an
    // invalid state, and should be aborted immediately.
    if (state_.ready == true) {
      FX_LOGS(ERROR) << "Invalid back-to-back `Ready` requests received";
    }

    state_.ready = true;
    callback(fpromise::ok());
  }

  void handle_unknown_method(uint64_t ordinal, bool method_has_response) override {
    FX_LOGS(WARNING) << "Received an unknown method with ordinal " << ordinal;
  }

 private:
  // Each scheduled update waits for the allotted amount of time, sends an update if something
  // has changed, and schedules the next update.
  void ScheduleOnDrawnEvent(async_dispatcher_t* dispatcher, zx::duration after) {
    async::PostDelayedTask(
        dispatcher,
        [&, dispatcher, after, weak = weak_factory_.GetWeakPtr()] {
          // Halt execution if the binding has been deallocated already.
          if (!weak) {
            return;
          }

          // Schedule the next update if the binding still exists.
          weak->ScheduleOnDrawnEvent(dispatcher, after);

          // No need to send an update if nothing has changed since the last one, or the client
          // has not yet informed us that it is ready for more updates.
          if (!weak->state_.changed || !weak->state_.ready) {
            return;
          }

          // This is where we would draw the actual lines. Since this is just an example, we'll
          // avoid doing the actual rendering, and simply send the bounding box to the client
          // instead.
          auto top_left = state_.bounding_box.top_left;
          auto bottom_right = state_.bounding_box.bottom_right;
          binding_.events().OnDrawn(top_left, bottom_right);
          FX_LOGS(INFO) << "OnDrawn event sent: top_left: Point { x: " << top_left.x
                        << ", y: " << top_left.y
                        << " }, bottom_right: Point { x: " << bottom_right.x
                        << ", y: " << bottom_right.y << " }";

          // Reset the change and ready trackers.
          state_.ready = false;
          state_.changed = false;
        },
        after);
  }

  fidl::Binding<examples::canvas::clientrequesteddraw::Instance> binding_;
  CanvasState state_ = CanvasState{};

  // Generates weak references to this object, which are appropriate to pass into asynchronous
  // callbacks that need to access this object. The references are automatically invalidated
  // if this object is destroyed.
  fxl::WeakPtrFactory<InstanceImpl> weak_factory_;
};

int main(int argc, char** argv) {
  FX_LOGS(INFO) << "Started";

  // The event loop is used to asynchronously listen for incoming connections and requests from
  // the client. The following initializes the loop, and obtains the dispatcher, which will be
  // used when binding the server implementation to a channel.
  //
  // Note that unlike the new C++ bindings, HLCPP bindings rely on the async loop being attached
  // to the current thread via the |kAsyncLoopConfigAttachToCurrentThread| configuration.
  async::Loop loop(&kAsyncLoopConfigAttachToCurrentThread);
  async_dispatcher_t* dispatcher = loop.dispatcher();

  // Create an |OutgoingDirectory| instance.
  //
  // The |component::OutgoingDirectory| class serves the outgoing directory for our component.
  // This directory is where the outgoing FIDL protocols are installed so that they can be
  // provided to other components.
  auto context = sys::ComponentContext::CreateAndServeOutgoingDirectory();

  // Register a handler for components trying to connect to
  // |examples.canvas.clientrequesteddraw.Instance|.
  context->outgoing()->AddPublicService(
      fidl::InterfaceRequestHandler<examples::canvas::clientrequesteddraw::Instance>(
          [dispatcher](
              fidl::InterfaceRequest<examples::canvas::clientrequesteddraw::Instance> request) {
            // Create an instance of our |InstanceImpl| that destroys itself when the connection
            // closes.
            new InstanceImpl(dispatcher, std::move(request));
          }));

  // Everything is wired up. Sit back and run the loop until an incoming connection wakes us up.
  FX_LOGS(INFO) << "Listening for incoming connections";
  loop.Run();
  return 0;
}

Union 酬載

FIDL 食譜:Union 酬載

聯集酬載是使用 union 版面配置的 FIDL 方法酬載。用於方法酬載的頂層類型必須使用 structtableunion 做為其版面配置。值得注意的是,部分產生的繫結會「扁平化」傳遞至 struct 方法酬載的引數,以便將每個成員視為呼叫簽章中的函式引數。使用 tableunion 的酬載則不會這麼做,而是一律傳遞單一引數 (稱為 payload)。

推理

鍵/值儲存庫基準範例的實作方式是個不錯的起點,但其中一個主要缺點是資料會儲存為原始位元組。FIDL 是一種具有豐富型別的語言。強制將 UTF-8 字串等資料儲存為未指定類型的位元組陣列,會讓 *.fidl 檔案的讀者和使用產生繫結的程式設計師無法取得這類寶貴的類型資訊。

實作

這項變更的主要目標,是將基準案例的 vector<byte> 類型 value 成員,替換為可儲存多種可能類型的 union。事實上,隨著這項變更,FIDL 的類型也提供良好的調查結果:

  • 所有 FIDL 內建的純量類型都會用於 Value union 中的變數:booluint8uint16uint32uint64int8int16int32int64float32float64 (也稱為 FIDL 的原始類型),以及 string
  • 這個 union 也使用了 FIDL 內建的 array<T, N>vector<T> 類型範本。
  • 這個範例至少會使用一次 FIDL 的所有類型版面配置,也就是 bitsenumtableunionstruct

WriteItem 所使用的要求和回應酬載也已從 struct 變更為分別為命名的 table 和內嵌的 flexible union。事實上,這三種版面配置都可以用於要求/回應酬載。後兩者分別稱為表格酬載和 *聯合體酬載,在所有情況下皆為首選,但在對訊息大小最敏感的情況下除外。這是因為日後要以二進位相容方式擴充這些類別,會比較容易。

FIDL

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library examples.keyvaluestore.usegenericvalues;

/// An item in the store. The key must match the regex `^[A-z][A-z0-9_\.\/]{2,62}[A-z0-9]$`. That
/// is, it must start with a letter, end with a letter or number, contain only letters, numbers,
/// periods, and slashes, and be between 4 and 64 characters long.
type Item = struct {
    key string:128;
    value Value;
};

// Because the `Value` must be used both in the request and the response, we give it its own named
// type. The type is a `union` of all possible data types that we take as values, and is marked
// `flexible` to allow for the easy addition of new data types in the future.
type Value = flexible union {
    // Keep the original `bytes` as one of the options in the new union.
    1: bytes vector<byte>:64000;

    // A `string` is very similar to `vector<byte>` on the wire, with the extra constraint that
    // it enforces that it enforces that the byte vector in question is valid UTF-8.
    2: string string:64000;

    // All of FIDL's primitive types.
    3: bool bool;
    4: uint8 uint8;
    5: int8 int8;
    6: uint16 uint16;
    7: int16 int16;
    8: uint32 uint32;
    9: int32 int32;
    10: float32 float32;
    11: uint64 uint64;
    12: int64 int64;
    13: float64 float64;

    // FIDL does not natively support 128-bit integer types, so we have to define our own
    // representations.
    14: uint128 array<uint64, 2>;
};

// Because we now supoprt a richer range of types as values in our store, it is helpful to use a
// `flexible`, and therefore evolvable, `bits` type to store write options.
type WriteOptions = flexible bits : uint8 {
    // This flag allows us to overwrite existing data when there is a collision, rather than failing
    // with an `WriteError.ALREADY_EXISTS`.
    OVERWRITE = 0b1;
    // This flag allows us to concatenate to existing data when there is a collision, rather than
    // failing with an `WriteError.ALREADY_EXISTS`. "Concatenation" means addition for the numeric
    // variants and appending to the `bytes`/`string` variants. If no existing data can be found, we
    // "concatenate" to default values of zero and an empty vector, respectively. Attempting to
    // concatenate to an existing variant of a different type will return a
    // `WriteError.INVALID_VALUE` error.
    CONCAT = 0b10;
};

/// An enumeration of things that may go wrong when trying to write a value to our store.
type WriteError = flexible enum {
    UNKNOWN = 0;
    INVALID_KEY = 1;
    INVALID_VALUE = 2;
    ALREADY_EXISTS = 3;
};

/// A very basic key-value store.
@discoverable
open protocol Store {
    /// Writes an item to the store.
    ///
    /// Since the value stored in the key-value store can now be different from the input (if the
    /// `WriteOptions.CONCAT` flag is set), we need to return the resulting `Value` to the
    /// requester.
    ///
    /// We use an (anonymous) `table` and a (named) `flexible union` as the request and response
    /// payload, respectively, to allow for easier future evolution. Both of these types are
    /// `flexible`, meaning that adding or removing members is binary-compatible. This makes them
    /// much easier to evolve that the `struct` types that were previously used, which cannot be
    /// changed after release without breaking ABI.
    flexible WriteItem(table {
        1: attempt Item;
        2: options WriteOptions;
    }) -> (Value) error WriteError;
};

CML

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/client_bin",
    },
    use: [
        { protocol: "examples.keyvaluestore.usegenericvalues.Store" },
    ],
    config: {
        // A vector of values for every easily representible type in our key-value store. For
        // brevity's sake, the 8, 16, and 32 bit integer types and booleans are omitted.
        //
        // TODO(https://fxbug.dev/42178362): It would absolve individual language implementations of a great
        //   deal of string parsing if we were able to use all FIDL constructs directly here. In
        //   particular, floats and nested types are very difficult to represent, and have been
        //   excluded from this example for the time being.
        set_concat_option: { type: "bool" },
        set_overwrite_option: { type: "bool" },
        write_bytes: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },
        write_strings: {
            type: "vector",
            max_count: 16,
            element: {
                type: "string",
                max_size: 64,
            },
        },
        write_uint64s: {
            type: "vector",
            max_count: 16,
            element: { type: "uint64" },
        },
        write_int64s: {
            type: "vector",
            max_count: 16,
            element: { type: "int64" },
        },

        // Note: due to the limitation of structured config not allowing vectors nested in vectors,
        // we only set the lower half of the uint128 for simplicity's sake.
        write_uint128s: {
            type: "vector",
            max_count: 16,
            element: { type: "uint64" },
        },

    },
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/server_bin",
    },
    capabilities: [
        { protocol: "examples.keyvaluestore.usegenericvalues.Store" },
    ],
    expose: [
        {
            protocol: "examples.keyvaluestore.usegenericvalues.Store",
            from: "self",
        },
    ],
}

運作範圍

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
{
    children: [
        {
            name: "client",
            url: "#meta/client.cm",
        },
        {
            name: "server",
            url: "#meta/server.cm",
        },
    ],
    offer: [
        // Route the protocol under test from the server to the client.
        {
            protocol: "examples.keyvaluestore.usegenericvalues.Store",
            from: "#server",
            to: "#client",
        },

        // Route diagnostics support to all children.
        {
            dictionary: "diagnostics",
            from: "parent",
            to: [
                "#client",
                "#server",
            ],
        },
    ],
}

接著,您可以使用任何支援的語言編寫用戶端和伺服器實作項目:

荒漠油廠

用戶端

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use {
    anyhow::{Context as _, Error},
    config::Config,
    fidl_examples_keyvaluestore_usegenericvalues::{
        Item, StoreMarker, StoreProxy, StoreWriteItemRequest, Value, WriteOptions,
    },
    fuchsia_component::client::connect_to_protocol,
    std::{thread, time},
};

// A helper function to sequentially write a single item to the key-value store and print a log when
// successful.
async fn write_next_item(
    store: &StoreProxy,
    key: &str,
    value: Value,
    options: WriteOptions,
) -> Result<(), Error> {
    // Create an empty request payload using `::default()`.
    let mut req = StoreWriteItemRequest::default();
    req.options = Some(options);

    // Fill in the `Item` we will be attempting to write.
    println!("WriteItem request sent: key: {}, value: {:?}", &key, &value);
    req.attempt = Some(Item { key: key.to_string(), value: value });

    // Send and async `WriteItem` request to the server.
    match store.write_item(&req).await.context("Error sending request")? {
        Ok(value) => println!("WriteItem response received: {:?}", &value),
        Err(err) => println!("WriteItem Error: {}", err.into_primitive()),
    }
    Ok(())
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Load the structured config values passed to this component at startup.
    let config = Config::take_from_startup_handle();

    // Use the Component Framework runtime to connect to the newly spun up server component. We wrap
    // our retained client end in a proxy object that lets us asynchronously send `Store` requests
    // across the channel.
    let store = connect_to_protocol::<StoreMarker>()?;
    println!("Outgoing connection enabled");

    // All of our requests will have the same bitflags set. Pull these settings from the config.
    let mut options = WriteOptions::empty();
    options.set(WriteOptions::OVERWRITE, config.set_overwrite_option);
    options.set(WriteOptions::CONCAT, config.set_concat_option);

    // The structured config provides one input for most data types that can be stored in the data
    // store. Iterate through those inputs in the order we see them in the FIDL file.
    //
    // Note that FIDL unions are rendered as enums in Rust; for example, the `Value` union has now
    // become a `Value` Rust enum, with each member taking exactly one argument.
    for value in config.write_bytes.into_iter() {
        write_next_item(&store, "bytes", Value::Bytes(value.into()), options).await?;
    }
    for value in config.write_strings.into_iter() {
        write_next_item(&store, "string", Value::String(value), options).await?;
    }
    for value in config.write_uint64s.into_iter() {
        write_next_item(&store, "uint64", Value::Uint64(value), options).await?;
    }
    for value in config.write_int64s.into_iter() {
        write_next_item(&store, "int64", Value::Int64(value), options).await?;
    }
    for value in config.write_uint128s.into_iter() {
        write_next_item(&store, "uint128", Value::Uint128([0, value]), options).await?;
    }

    // TODO(https://fxbug.dev/42156498): We need to sleep here to make sure all logs get drained. Once the
    // referenced bug has been resolved, we can remove the sleep.
    thread::sleep(time::Duration::from_secs(2));
    Ok(())
}

伺服器

// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{Context as _, Error};
use fuchsia_component::server::ServiceFs;
use futures::prelude::*;
use lazy_static::lazy_static;
use regex::Regex;
use std::cell::RefCell;
use std::collections::hash_map::Entry;
use std::collections::HashMap;

use fidl_examples_keyvaluestore_usegenericvalues::{
    Item, StoreRequest, StoreRequestStream, Value, WriteError, WriteOptions,
};
use std::collections::hash_map::OccupiedEntry;
use std::ops::Add;

lazy_static! {
    static ref KEY_VALIDATION_REGEX: Regex =
        Regex::new(r"^[A-Za-z]\w+[A-Za-z0-9]$").expect("Key validation regex failed to compile");
}

/// Sums any numeric type.
fn sum<T: Add + Add<Output = T> + Copy>(operands: [T; 2]) -> T {
    operands[0] + operands[1]
}

/// Clones and inserts an entry, so that the original (now concatenated) copy may be returned in the
/// response.
fn write(inserting: Value, mut entry: OccupiedEntry<'_, String, Value>) -> Value {
    entry.insert(inserting.clone());
    println!("Wrote key: {}, value: {:?}", entry.key(), &inserting);
    inserting
}

/// Handler for the `WriteItem` method.
fn write_item(
    store: &mut HashMap<String, Value>,
    attempt: Item,
    options: &WriteOptions,
) -> Result<Value, WriteError> {
    // Validate the key.
    if !KEY_VALIDATION_REGEX.is_match(attempt.key.as_str()) {
        println!("Write error: INVALID_KEY for key: {}", attempt.key);
        return Err(WriteError::InvalidKey);
    }

    match store.entry(attempt.key) {
        Entry::Occupied(entry) => {
            // The `CONCAT` flag supersedes the `OVERWRITE` flag, so check it first.
            if options.contains(WriteOptions::CONCAT) {
                match entry.get() {
                    Value::Bytes(old) => {
                        if let Value::Bytes(new) = attempt.value {
                            let mut combined = old.clone();
                            combined.extend(new);
                            return Ok(write(Value::Bytes(combined), entry));
                        }
                    }
                    Value::String(old) => {
                        if let Value::String(new) = attempt.value {
                            return Ok(write(Value::String(format!("{}{}", old, &new)), entry));
                        }
                    }
                    Value::Uint64(old) => {
                        if let Value::Uint64(new) = attempt.value {
                            return Ok(write(Value::Uint64(sum([*old, new])), entry));
                        }
                    }
                    Value::Int64(old) => {
                        if let Value::Int64(new) = attempt.value {
                            return Ok(write(Value::Int64(sum([*old, new])), entry));
                        }
                    }
                    // Note: only works on the uint64 range in practice.
                    Value::Uint128(old) => {
                        if let Value::Uint128(new) = attempt.value {
                            return Ok(write(Value::Uint128([0, sum([old[1], new[1]])]), entry));
                        }
                    }
                    _ => {
                        panic!("actively unsupported type!")
                    }
                }

                // Only reachable if the type of the would be concatenated value did not match the
                // value already occupying this entry.
                println!("Write error: INVALID_VALUE for key: {}", entry.key());
                return Err(WriteError::InvalidValue);
            }

            // If we're not doing CONCAT, check for OVERWRITE next.
            if options.contains(WriteOptions::OVERWRITE) {
                return Ok(write(attempt.value, entry));
            }

            println!("Write error: ALREADY_EXISTS for key: {}", entry.key());
            Err(WriteError::AlreadyExists)
        }
        Entry::Vacant(entry) => {
            println!("Wrote key: {}, value: {:?}", entry.key(), &attempt.value);
            entry.insert(attempt.value.clone());
            Ok(attempt.value)
        }
    }
}

/// Creates a new instance of the server. Each server has its own bespoke, per-connection instance
/// of the key-value store.
async fn run_server(stream: StoreRequestStream) -> Result<(), Error> {
    // Create a new in-memory key-value store. The store will live for the lifetime of the
    // connection between the server and this particular client.
    let store = RefCell::new(HashMap::<String, Value>::new());

    // Serve all requests on the protocol sequentially - a new request is not handled until its
    // predecessor has been processed.
    stream
        .map(|result| result.context("failed request"))
        .try_for_each(|request| async {
            // Match based on the method being invoked.
            match request {
                // Because we are using a table payload, there is an extra level of indirection. The
                // top-level container for the table itself is always called "payload".
                StoreRequest::WriteItem { payload, responder } => {
                    println!("WriteItem request received");

                    // Error out if either of the request table's members are not set.
                    let attempt = payload.attempt.context("required field 'attempt' is unset")?;
                    let options = payload.options.context("required field 'options' is unset")?;

                    // The `responder` parameter is a special struct that manages the outgoing reply
                    // to this method call. Calling `send` on the responder exactly once will send
                    // the reply.
                    responder
                        .send(
                            write_item(&mut store.borrow_mut(), attempt, &options)
                                .as_ref()
                                .map_err(|e| *e),
                        )
                        .context("error sending reply")?;
                    println!("WriteItem response sent");
                } //
                StoreRequest::_UnknownMethod { ordinal, .. } => {
                    println!("Received an unknown method with ordinal {ordinal}");
                }
            }
            Ok(())
        })
        .await
}

// A helper enum that allows us to treat a `Store` service instance as a value.
enum IncomingService {
    Store(StoreRequestStream),
}

#[fuchsia::main]
async fn main() -> Result<(), Error> {
    println!("Started");

    // Add a discoverable instance of our `Store` protocol - this will allow the client to see the
    // server and connect to it.
    let mut fs = ServiceFs::new_local();
    fs.dir("svc").add_fidl_service(IncomingService::Store);
    fs.take_and_serve_directory_handle()?;
    println!("Listening for incoming connections");

    // The maximum number of concurrent clients that may be served by this process.
    const MAX_CONCURRENT: usize = 10;

    // Serve each connection simultaneously, up to the `MAX_CONCURRENT` limit.
    fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::Store(stream)| {
        run_server(stream).unwrap_or_else(|e| println!("{:?}", e))
    })
    .await;

    Ok(())
}

C++ (自然)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Natural) implementation.

C++ (Wire)

用戶端

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

伺服器

// TODO(https://fxbug.dev/42060656): C++ (Wire) implementation.

HLCPP

用戶端

// TODO(https://fxbug.dev/42060656): HLCPP implementation.

伺服器

// TODO(https://fxbug.dev/42060656): HLCPP implementation.