Inspect codelab

This document contains the codelab for Inspect in C++, Dart and Rust.

The code is available at:

This codelab is organized into several parts, each with their own subdirectory. The starting point for the codelab is part 1, and the code for each part contains the solution for the previous parts.

When working on this codelab, you may continue adding your solutions to "part_1", or you may skip around by building on the existing solutions.

Prerequisites

Set up your development environment.

This codelab assumes you have completed Getting Started and have:

A checked out and built Fuchsia tree.
A device or emulator (fx emu) that runs Fuchsia.
A workstation to serve components (fx serve) to your Fuchsia device or emulator.

To build and run the examples in this codelab, add the following arguments to your fx set invocation:

C++

fx set core.x64 \
--with //examples/diagnostics/inspect/codelab/cpp \
--with //examples/diagnostics/inspect/codelab/cpp:tests

Rust

fx set core.x64 \
--with //examples/diagnostics/inspect/codelab/rust \
--with //examples/diagnostics/inspect/codelab/rust:tests

Dart

fx set workstation.x64
--with //examples/diagnostics/inspect/codelab/dart \
--with //examples/diagnostics/inspect/codelab/dart:tests

Part 1: A buggy component

There is a component that serves a protocol called Reverser:

// Implementation of a string reverser.
@discoverable
protocol Reverser {
    // Returns the input string reversed character-by-character.
    Reverse(struct {
        input string:1024;
    }) -> (struct {
        response string:1024;
    });
};

This protocol has a single method, called "Reverse," that simply reverses any string passed to it. An implementation of the protocol is provided, but it has a critical bug. The bug makes clients who attempt to call the Reverse method see that their call hangs indefinitely. It is up to you to fix this bug.

Run the component

There is a client application that will launch the Reverser component and send the rest of its command line arguments as strings to Reverse:

See usage
C++

Depending on the part of the codelab you wish to run, you'd launch the client_i component, where i is a number in range [1, 5]. For example, to launch the client talking to the reverser from part 2 of the codelab:
```
ffx component run fuchsia-pkg://fuchsia.com/inspect_cpp_codelab#meta/client_part_2.cm
```
Rust

Depending on the part of the codelab you wish to run, you'd launch the client_i component, where i is a number in range [1, 5]. For example, to launch the client talking to the reverser from part 2 of the codelab:
```
ffx component run fuchsia-pkg://fuchsia.com/inspect_rust_codelab#meta/client_part_2.cm
```
Dart
```
fx run fuchsia-pkg://fuchsia.com/inspect-dart-codelab-client#meta/inspect-dart-codelab-client.cmx
```
Run part 1 code, and reverse the string "Hello"
C++

To specify the single string "Hello" modify the program.args section of the common.shard.cml, build and run the following:
```
ffx component run fuchsia-pkg://fuchsia.com/inspect_cpp_codelab#meta/client_part_1.cm
```
To see the command output take a look at the logs:
```
ffx log --tags inspect_cpp_codelab
```
This command prints some output containing errors.
Rust

To specify the single string "Hello" modify the program.args section of the common.shard.cml, build and run the following:
```
ffx component run fuchsia-pkg://fuchsia.com/inspect_rust_codelab#meta/client_part_1.cm
```
To see the command output take a look at the logs:
```
ffx log --tags inspect_rust_codelab
```
This command prints some output containing errors.
Dart
```
fx run fuchsia-pkg://fuchsia.com/inspect-dart-codelab-client#meta/inspect-dart-codelab-client.cmx 1 Hello
```
These commands hang.

Press Ctrl+C to stop the client and try running with more arguments:

C++

Add the string "World" to the program.args section of the the common.shard.cml:

{
    program: {
        args: [
            "Hello",
            "World",
        ],
    },
}

Build and run the following:

ffx component run fuchsia-pkg://fuchsia.com/inspect_cpp_codelab#meta/client_part_1.cm

Rust

Add the string "World" to the program.args section of the the common.shard.cml:

{
    program: {
        args: [
            "Hello",
            "World",
        ],
    },
}

Build and run the following:

ffx component run fuchsia-pkg://fuchsia.com/inspect_rust_codelab#meta/client_part_1.cm

Dart

fx run fuchsia-pkg://fuchsia.com/inspect-dart-codelab-client#meta/inspect-dart-codelab-client.cmx 1 Hello World

This command also prints no outputs.

These commands also hang.

You are now ready to look through the code to troubleshoot the issue.

Look through the code

Now that you can reproduce the problem, take a look at what the client is doing:

C++

In the client main:

// Repeatedly send strings to be reversed to the other component.
for (int i = 1; i < argc; i++) {
  FX_LOGS(INFO) << "Input: " << argv[i];

  std::string output;
  status = zx::make_status(reverser->Reverse(argv[i], &output));
  if (status.is_error()) {
    FX_LOGS(ERROR) << "Error: Failed to reverse string.";
    return status.status_value();
  }

  FX_LOGS(INFO) << "Output: " << output;
}

Rust

In the client main:

for string in args.strings {
    info!("Input: {}", string);
    match reverser.reverse(&string).await {
        Ok(output) => info!("Output: {}", output),
        Err(e) => error!(error = ?e, "Failed to reverse string"),
    }
}

Dart

In the client main:

for (int i = 1; i < args.length; i++) {
  print('Input: ${args[i]}');
  final response = await reverser.reverse(args[i]);
  print('Output: $response');
}

In this code snippet, the client calls the Reverse method but never seems to get a response. There doesn't seem to be an error message or output.

Take a look at the server code for this part of the codelab. There is a lot of standard component setup:

C++

In the part 1 main:

Logging initialization

syslog::SetTags({"inspect_cpp_codelab", "part1"});

Creating an asynchronous executor

async::Loop loop(&kAsyncLoopConfigAttachToCurrentThread);
auto context = sys::ComponentContext::CreateAndServeOutgoingDirectory();

Serving a public service

context->outgoing()->AddPublicService(Reverser::CreateDefaultHandler());

Rust

In the part 1 main:

Logging initialization

#[fuchsia::component(logging_tags = ["inspect_rust_codelab", "part1"])]

ServiceFs initialization and collection
```
let mut fs = ServiceFs::new();
```

ServiceFs collection

let running_service_fs = fs.collect::<()>().map(Ok);

Serving a public service

fs.dir("svc").add_fidl_service(move |stream| reverser_factory.spawn_new(stream));
fs.take_and_serve_directory_handle()?;

Dart

In the part 1 main:

Logging initialization

setupLogger(name: 'inspect_dart_codelab', globalTags: ['part_1']);

Serving a public service

final context = ComponentContext.create();
context.outgoing
  ..addPublicService<fidl_codelab.Reverser>(
    ReverserImpl.getDefaultBinder(),
    fidl_codelab.Reverser.$serviceName,
  )
  ..serveFromStartupInfo();

See what the reverser definition is:

C++

In reverser.h:

class Reverser final : public fuchsia::examples::inspect::Reverser {
 public:
  // CODELAB: Create a new constructor for Reverser that takes an Inspect node.

  // Implementation of Reverser.Reverse().
  void Reverse(std::string input, ReverseCallback callback) override;

  // Return a request handler for the Reverser protocol that binds incoming requests to new
  // Reversers.
  static fidl::InterfaceRequestHandler<fuchsia::examples::inspect::Reverser> CreateDefaultHandler();
};

This class implements the Reverser protocol. A helper method called CreateDefaultHandler constructs an InterfaceRequestHandler that creates new Reversers for incoming requests.

Rust

In reverser.rs:

pub struct ReverserServerFactory {}

impl ReverserServerFactory {
    // CODELAB: Create a new() constructor that takes an Inspect node.
    pub fn new() -> Self {
        Self {}
    }

    pub fn spawn_new(&self, stream: ReverserRequestStream) {
        // CODELAB: Add stats about incoming connections.
        ReverserServer::new().spawn(stream);
    }
}

struct ReverserServer {}

impl ReverserServer {
    // CODELAB: Create a new() constructor that takes an Inspect node.
    fn new() -> Self {
        Self {}
    }

    pub fn spawn(self, mut stream: ReverserRequestStream) {
        fasync::Task::local(async move {
            while let Some(request) = stream.try_next().await.expect("serve reverser") {
                // CODELAB: Add stats about incoming requests.
                let ReverserRequest::Reverse { input, responder: _ } = request;
                let _result = input.chars().rev().collect::<String>();
                // Yes, this is silly. Just for codelab purposes.
                fasync::Timer::new(fasync::Time::after(10.hours())).await
            }
        })
        .detach();
    }
}

This struct serves the Reverser protocol. The ReverserServerFactory (will make more sense later) constructs a ReverserServer when a new connection to Reverser is established.

Dart

In reverser.dart:

typedef BindCallback = void Function(InterfaceRequest<fidl_codelab.Reverser>);
typedef VoidCallback = void Function();

class ReverserImpl extends fidl_codelab.Reverser {
  final _binding = fidl_codelab.ReverserBinding();

  // CODELAB: Create a constructor that takes an Inspect node.
  ReverserImpl();

  @override
  Future<String> reverse(String value) async {
    // CODELAB: Add stats about incoming requests.
    print(String.fromCharCodes(value.runes.toList().reversed));
    await Future.delayed(Duration(hours: 10));
    return '';
  }

  static final _bindingSet = <ReverserImpl>{};
  static BindCallback getDefaultBinder() {
    return (InterfaceRequest<fidl_codelab.Reverser> request) {
      // CODELAB: Add stats about incoming connections.
      final reverser = ReverserImpl()..bind(request, onClose: () {});
      _bindingSet.add(reverser);
    };
  }

  void bind(
    InterfaceRequest<fidl_codelab.Reverser> request, {
    @required VoidCallback onClose,
  }) {
    _binding.stateChanges.listen((state) {
      if (state == InterfaceState.closed) {
        dispose();
        onClose();
      }
    });
    _binding.bind(this, request);
  }

  void dispose() {}
}

This class implements the Reverser protocol. A helper method called getDefaultBinder returns a closure that creates new Reversers for incoming requests.

Add Inspect

Now that you know the code structure, you can start to instrument the code with Inspect to find the problem.

You may have previously debugged programs by printing or logging. While this is often effective, asynchronous Components that run persistently often output numerous logs about their internal state over time. This codelab shows how Inspect provides snapshots of your component's current state without needing to dig through logs.

Include Inspect dependencies:

C++

In BUILD.gn:

source_set("lib") {
  sources = [
    "reverser.cc",
    "reverser.h",
  ]

  public_deps = [
    "//examples/diagnostics/inspect/codelab/fidl:fuchsia.examples.inspect",
    "//sdk/lib/sys/inspect/cpp",
  ]
}

Rust

In BUILD.gn in deps under rustc_binary("bin"):

"//src/lib/diagnostics/inspect/runtime/rust",
"//src/lib/diagnostics/inspect/rust",
"//src/lib/fuchsia",
"//src/lib/zircon/rust:fuchsia-zircon",

Dart

In BUILD.gn in deps under dart_library("lib") and dart_app("bin"):

"//sdk/dart/fuchsia_inspect",

Initialize Inspect:

C++

In main.cc:

#include <lib/sys/inspect/cpp/component.h>
sys::ComponentInspector inspector(context.get());

Rust

In main.rs:

use fuchsia_inspect::component;
inspect_runtime::serve(component::inspector(), &mut fs)?;

Dart

In main.dart:

import 'package:fuchsia_inspect/inspect.dart' as inspect;
final inspector = inspect.Inspect()..serve(context.outgoing);

You are now using Inspect.

Add a simple "version" property to show which version is running:
C++
```
inspector.root().CreateString("version", "part2", &inspector);
```
This snippet does the following:
1. Obtain the "root" node of the Inspect hierarchy.
  
  The Inspect hierarchy for your component consists of a tree of Nodes, each of which contains any number of properties.
2. Create a new property using CreateString.
  
  This adds a new StringProperty on the root. This StringProperty is called "version", and its value is "part1".
3. Emplace the new property in the inspector.
  
  The lifetime of a property is tied to an object returned by Create, and destroying the object causes the property to disappear. The optional third parameter emplaces the new property in inspector rather than return it. As a result, the new property lives as long as the inspector itself (the entire execution of the component).
Rust
```
component::inspector().root().record_string("version", "part2");
```
This snippet does the following:
1. Obtain the "root" node of the Inspect hierarchy.
The Inspect hierarchy for your component consists of a tree of Nodes, each of which contains any number of properties.
1. Create a new property using record_string.
This adds a new StringProperty on the root. This StringProperty is called "version", and its value is "part1".
1. It records it in the root node.
The usual way of creating properties is through create_* methods on nodes. The lifetime of a property created with these methods is tied to the object returned and destroying the object causes the property to disappear. The library provides convenience methods record_* that perform creation of a property and tie the property lifetime to the node on which the method was called. As a result, the new property lives as long as the node itself (in this case, as long as the root node, so the entire execution of the component).
Dart
```
inspector.root.stringProperty('version').setValue('part2');
```
This snippet does the following:
1. Obtain the "root" node of the Inspect hierarchy.
The Inspect hierarchy for your component consists of a tree of Nodes, each of which contains any number of properties.
1. Create a new property using stringProperty(...).setValue(...).
This adds a new StringProperty on the root. This StringProperty is called "version", and its value is "part1".
1. It records it in the root node.
The lifetime of a property is tied to the lifetime of the node where it was created (in this case root, so the lifetime of the component). To delete the property one would have to call delete() on it.

Reading Inspect data

Now that you have added Inspect to your component, you can read what it says:

Rebuild and update the target system
```
fx build && fx ota
```

Run the client:

C++

ffx component run fuchsia-pkg://fuchsia.com/inspect_cpp_codelab#meta/client_part_1.cm
ffx log --tags inspect_cpp_codelab

Rust

ffx component run fuchsia-pkg://fuchsia.com/inspect_rust_codelab#meta/client_part_1.cm
ffx log --tags inspect_rust_codelab

Dart

fx run fuchsia-pkg://fuchsia.com/inspect-dart-codelab-client#meta/inspect-dart-codelab-client.cmx 1 Hello

Note that these should still hang.

Use ffx inspect to view your output:
```
ffx inspect show
```
This dumps all of the Inspect data for the entire system, which may be a lot of data.

Since ffx inspect supports glob matching, run:

C++

$ ffx inspect show 'core/ffx-laboratory\:client_part_1/reverser'
# or `ffx inspect show --manifest inspect_cpp_codelab`
metadata:
  filename = fuchsia.inspect.Tree
  component_url = fuchsia-pkg://fuchsia.com/inspect_cpp_codelab#meta/part_1.cm
  timestamp = 4728864898476
payload:
  root:
    version = part1

Rust

$ ffx inspect show 'core/ffx-laboratory\:client_part_1/reverser'
# or `ffx inspect show --manifest inspect_rust_codelab`
metadata:
  filename = fuchsia.inspect.Tree
  component_url = fuchsia-pkg://fuchsia.com/inspect_rust_codelab#meta/part_1.cm
  timestamp = 4728864898476
payload:
  root:
    version = part1

Dart

$ ffx inspect show 'codelab_*/inspect_dart_codelab_part_1.cmx'
# or `ffx inspect show --manifest inspect_dart_codelab`
metadata:
  filename = fuchsia.inspect.Tree
  component_url = fuchsia-pkg://fuchsia.com/inspect_dart_codelab#meta/inspect_dart_codelab_part_1.cmx
  timestamp = 4728864898476
payload:
  root:
    version = part1

You can also view the output as JSON:

C++

$ ffx inspect -f json show 'core/ffx-laboratory\:client_part_1/reverser'
[
  {
    "data_source": "Inspect",
    "metadata": {
      "errors": null,
      "filename": "fuchsia.inspect.Tree",
      "component_url": "fuchsia-pkg://fuchsia.com/inspect_pp_codelab#meta/part_1.cm",
      "timestamp": 5031116776282
    },
    "moniker": "core/ffx-laboratory\\:client_part_5/reverser",
    "payload": {
      "root": {
        "version": "part1",
    },
    "version": 1
  }
]

Rust

$ ffx inspect -f json show 'core/ffx-laboratory\:client_part_1/reverser'
[
  {
    "data_source": "Inspect",
    "metadata": {
      "errors": null,
      "filename": "fuchsia.inspect.Tree",
      "component_url": "fuchsia-pkg://fuchsia.com/inspect_rust_codelab#meta/part_1.cm",
      "timestamp": 5031116776282
    },
    "moniker": "core/ffx-laboratory\\:client_part_5/reverser",
    "payload": {
      "root": {
        "version": "part1",
    },
    "version": 1
  }
]

Dart

$ ffx inspect -f json show 'codelab_*/inspect_dart_codelab_part_1.cmx'
[
  {
    "data_source": "Inspect",
    "metadata": {
      "errors": null,
      "filename": "fuchsia.inspect.Tree",
      "component_url": "fuchsia-pkg://fuchsia.com/inspect_cpp_codelab#meta/inspect_dart_codelab_part_1.cmx",
      "timestamp": 5031116776282
    },
    "moniker": "codelab_1234/inspect_dart_codelab_part_1.cmx",
    "payload": {
      "root": {
        "version": "part1",
    },
    "version": 1
  }
]

Instrumenting the code to find the bug

Now that you have initialized Inspect and know how to read data, you are ready to instrument your code and uncover the bug.

The previous output shows you how the component is actually running and that the component is not hanging completely. Otherwise the Inspect read would hang.

Add new information per-connection to observe if the connection is even being handled by your component.

Add a new child to your root node to contain statistics about the reverser service:

C++

context->outgoing()->AddPublicService(
    Reverser::CreateDefaultHandler(inspector.root().CreateChild("reverser_service")));

Rust

let reverser_factory =
    ReverserServerFactory::new(component::inspector().root().create_child("reverser_service"));

Dart

context.outgoing
  ..addPublicService<fidl_codelab.Reverser>(
    ReverserImpl.getDefaultBinder(inspector.root.child('reverser_service')),
    fidl_codelab.Reverser.$serviceName,
  )
  ..serveFromStartupInfo();

Update your server to accept this node:

C++

Update the definition of CreateDefaultHandler in reverser.h and [reverser.cc][part1-reverser-cc]:

#include <lib/inspect/cpp/inspect.h>
fidl::InterfaceRequestHandler<fuchsia::examples::inspect::Reverser> Reverser::CreateDefaultHandler(
    inspect::Node node) {

Rust

Update ReverserServerFactory::new to accept this node in reverser.rs:

use fuchsia_inspect as inspect;
pub struct ReverserServerFactory {
    node: inspect::Node,
    // ...
}

impl ReverserServerFactory {
    pub fn new(node: inspect::Node) -> Self {
        let request_count = Arc::new(node.create_uint("total_requests", 0));
        let connection_count = node.create_uint("connection_count", 0);
        Self {
            node,
            // ...
        }
    }

    // ...
}

Dart

Update the definition of getDefaultBinder in reverser.dart and [reverser.cc][part1-reverser-cc]:

import 'package:fuchsia_inspect/inspect.dart' as inspect;
static BindCallback getDefaultBinder(inspect.Node node) {

Add a property to keep track of the number of connections:

C++

fidl::InterfaceRequestHandler<fuchsia::examples::inspect::Reverser> Reverser::CreateDefaultHandler(
    inspect::Node node) {
  // ...

  // Return a handler for incoming FIDL connections to Reverser.
  //
  // The returned closure contains a binding set, which is used to bind incoming requests to a
  // particular implementation of a FIDL interface. This particular binding set is configured to
  // bind incoming requests to unique_ptr<Reverser>, which means the binding set itself takes
  // ownership of the created Reversers and frees them when the connection is closed.
  return [connection_count = node.CreateUint("connection_count", 0), node = std::move(node),
          // ...

Rust

use {
    // ...
    fuchsia_inspect::NumericProperty,
    // ...
};

pub struct ReverserServerFactory {
    node: inspect::Node,
    // ...
    connection_count: inspect::UintProperty,
}

impl ReverserServerFactory {
    pub fn new(node: inspect::Node) -> Self {
        // ...
        let connection_count = node.create_uint("connection_count", 0);
        Self {
            node,
            // ...
            connection_count,
        }
    }

    pub fn spawn_new(&self, stream: ReverserRequestStream) {
        self.connection_count.add(1);

Dart

static BindCallback getDefaultBinder(inspect.Node node) {
  // ...
  final glabalConnectionCount = node.intProperty('connection_count')
    ..setValue(0);
  return (InterfaceRequest<fidl_codelab.Reverser> request) {
    glabalConnectionCount.add(1);

This snippet demonstrates creating a new UintProperty (containing a 64 bit unsigned int) called connection_count and setting it to 0. In the handler (which runs for each connection), the property is incremented by 1.

Rebuild, re-run your component and then run ffx inspect:

C++

$ ffx inspect -f json show --manifest inspect_cpp_codelab

Rust

$ ffx inspect -f json show --manifest inspect_rust_codelab

Dart

$ ffx inspect -f json show --manifest inspect_dart_codelab_part_1

You should now see:

...
"payload": {
 "root": {
   "version": "part1",
   "reverser_service": {
     "connection_count": 1,
   }
 }
}

The output above demonstrates that the client successfully connected to the service, so the hanging problem must be caused by the Reverser implementation itself. In particular, it will be helpful to know:

If the connection is still open while the client is hanging.
If the Reverse method was called.

Exercise: Create a child node for each connection, and record "request_count" inside the Reverser.

Hint: There is a utility function for generating unique names:

C++

auto child = node.CreateChild(node.UniqueName("connection-"));

Rust

let node = self.node.create_child(inspect::unique_name("connection"));

Dart

final name = inspect.uniqueName('connection');

This will create unique names starting with "connection".

C++

Hint: You will find it helpful to create a constructor for Reverser that takes inspect::Node. Part 3 of this codelab explains why this is a useful pattern.

Rust

Hint: You will find it helpful to create a constructor for ReverserServer that takes inspect::Node for the same reason as we did for ReverserServerFactory.

Dart

Hint: You will find it helpful to create a constructor for ReverserImpl that takes inspect.Node. Part 3 of this codelab explains why this is a useful pattern.

Hint: You will need to create a member on Reverser to hold the request_count property. Its type will be inspect::UintProperty.
Follow up: Does request count give you all of the information you need? Add response_count as well.
Advanced: Can you add a count of all requests on all connections? The Reverser objects must share some state. You may find it helpful to refactor arguments to Reverser into a separate struct (See solution in part 2 for this approach).

After completing this exercise and running ffx inspect, you should see something like this:

...
"payload": {
  "root": {
    "version": "part1",
    "reverser_service": {
      "connection_count": 1,
      "connection0": {
        "request_count": 1,
      }
    }
  }
}

The output above shows that the connection is still open and it received one request.

C++

If you added "response_count" as well, you may have noticed the bug. The Reverse method receives a callback, but it is never called with the value of output.

Rust

If you added "response_count" as well, you may have noticed the bug. The Reverse method receives a responder, but it is never called with the value of result.

Dart

If you added "response_count" as well, you may have noticed the bug. The reverse method receives never returns the value of result.

Send the response:

C++

// At the end of Reverser::Reverse
callback(std::move(output));

Rust

responder.send(&result).expect("send reverse request response");

Dart

final result = String.fromCharCodes(value.runes.toList().reversed);
// ...
return result;

Run the client again:

C++

ffx component run fuchsia-pkg://fuchsia.com/inspect_cpp_codelab#meta/client_part_1.cm
Creating component instance: client_part_1

ffx log --tags inspect_cpp_codelab
[00039.129068][39163][39165][inspect_cpp_codelab, client] INFO: Input: Hello
[00039.194151][39163][39165][inspect_cpp_codelab, client] INFO: Output: olleH
[00039.194170][39163][39165][inspect_cpp_codelab, client] INFO: Input: World
[00039.194402][39163][39165][inspect_cpp_codelab, client] INFO: Output: dlroW
[00039.194407][39163][39165][inspect_cpp_codelab, client] INFO: Done reversing! Please use `ffx component stop`

Rust

ffx component run fuchsia-pkg://fuchsia.com/inspect_rust_codelab#meta/client_part_1.cm
Creating component instance: client_part_1

ffx log --tags inspect_rust_codelab
[00039.129068][39163][39165][inspect_rust_codelab, client] INFO: Input: Hello
[00039.194151][39163][39165][inspect_rust_codelab, client] INFO: Output: olleH
[00039.194170][39163][39165][inspect_rust_codelab, client] INFO: Input: World
[00039.194402][39163][39165][inspect_rust_codelab, client] INFO: Output: dlroW
[00039.194407][39163][39165][inspect_rust_codelab, client] INFO: Done reversing! Please use `ffx component stop`

Dart

fx run fuchsia-pkg://fuchsia.com/inspect-dart-codelab-client#meta/inspect-dart-codelab-client.cmx 1 hello
Input: hello
Output: olleh
Done. Press Ctrl+C to exit

The component continues running until Ctrl+C is pressed to give you a chance to run ffx inspect and observe your output.

This concludes part 1. You may commit your changes so far:

git commit -am "solution to part 1"

Part 2: Diagnosing inter-component problems

You received a bug report. The "FizzBuzz" team is saying they are not receiving data from your component.

In addition to serving the Reverser protocol, the component also reaches out to the "FizzBuzz" service and prints the response:

C++

fuchsia::examples::inspect::FizzBuzzPtr fizz_buzz;
context->svc()->Connect(fizz_buzz.NewRequest());
fizz_buzz->Execute(30, [](std::string result) { FX_LOGS(INFO) << "Got FizzBuzz: " << result; });

Rust

let fizzbuzz_fut = async move {
    let fizzbuzz = client::connect_to_protocol::<FizzBuzzMarker>()
        .context("failed to connect to fizzbuzz")?;
    match fizzbuzz.execute(30u32).await {
        Ok(result) => info!(%result, "Got FizzBuzz"),
        Err(_) => {}
    };
    Ok(())
};

Dart

final fizzBuzz = fidl_codelab.FizzBuzzProxy();
context.svc.connectToService(fizzBuzz);
final result = await fizzBuzz.execute(30);

If you see the logs, you will see that this log is never printed.

C++

ffx log --tags inspect_cpp_codelab

Rust

ffx log --tags inspect_rust_codelab

Dart

ffx log --tags inspect_dart_codelab_part_2

You will need to diagnose and solve this problem.

Diagnose the issue with Inspect

Run the component to see what is happening:

C++

ffx component run fuchsia-pkg://fuchsia.com/inspect_cpp_codelab#meta/client_part_2.cm

Rust

ffx component run fuchsia-pkg://fuchsia.com/inspect_rust_codelab#meta/client_part_2.cm

Dart

$ fx run fuchsia-pkg://fuchsia.com/inspect-dart-codelab-client#meta/inspect-dart-codelab-client.cmx 2 hello

Fortunately the FizzBuzz team instrumented their component using Inspect.

Read the FizzBuzz Inspect data using ffx inspect as before, you get:

"payload": {
    "root": {
        "fizzbuzz_service": {
            "closed_connection_count": 0,
            "incoming_connection_count": 0,
            "request_count": 0,
            ...

This output confirms that FizzBuzz is not receiving any connections.

Add Inspect to identify the problem:

C++

// CODELAB: Instrument our connection to FizzBuzz using Inspect. Is there an error?
fuchsia::examples::inspect::FizzBuzzPtr fizz_buzz;
context->svc()->Connect(fizz_buzz.NewRequest());
fizz_buzz.set_error_handler([&](zx_status_t status) {
  // CODELAB: Add Inspect here to see if there is a response.
});
fizz_buzz->Execute(30, [](std::string result) {
  // CODELAB: Add Inspect here to see if there was a response.
  FX_LOGS(INFO) << "Got FizzBuzz: " << result;
});

Rust

let fizzbuzz_fut = async move {
    let fizzbuzz = client::connect_to_protocol::<FizzBuzzMarker>()
        .context("failed to connect to fizzbuzz")?;
    match fizzbuzz.execute(30u32).await {
        Ok(result) => {
            // CODELAB: Add Inspect here to see if there is a response.
            info!(%result, "Got FizzBuzz");
        }
        Err(_) => {
            // CODELAB: Add Inspect here to see if there is an error
        }
    };
    Ok(())
};

Dart

final fizzBuzz = fidl_codelab.FizzBuzzProxy();
context.svc.connectToService(fizzBuzz);

fizzBuzz.execute(30).timeout(const Duration(seconds: 2), onTimeout: () {
  throw Exception('timeout');
}).then((result) {
  // CODELAB: Add Inspect here to see if there is a response.
  log.info('Got FizzBuzz: $result');
}).catchError((e) {
  // CODELAB: Instrument our connection to FizzBuzz using Inspect. Is there an error?
});

Exercise: Add Inspect to the FizzBuzz connection to identify the problem

Hint: Use the snippet above as a starting point, it provides an error handler for the connection attempt.

C++

Follow up: Can you store the status somewhere? You can convert it to a string using zx_status_get_string(status).

Advanced: inspector has a method called Health() that announces overall health status in a special location. Since our service is not healthy unless it can connect to FizzBuzz, can you incorporate this:

 /*
 "fuchsia.inspect.Health": {
     "status": "STARTING_UP"
 }
 */
 inspector.Health().StartingUp();

 /*
 "fuchsia.inspect.Health": {
     "status": "OK"
 }
 */
 inspector.Health().Ok();

 /*
 "fuchsia.inspect.Health": {
     "status": "UNHEALTHY",
     "message": "Something went wrong!"
 }
 */
 inspector.Health().Unhealthy("Something went wrong!");

Rust

Advanced: fuchsia_inspect::component has a function called health() that returns an object that announces overall health status in a special location (a node child of the root of the inspect tree). Since our service is not healthy unless it can connect to FizzBuzz, can you incorporate this:

/*
"fuchsia.inspect.Health": {
    "status": "STARTING_UP"
}
*/
fuchsia_inspect::component::health().set_starting_up();

/*
"fuchsia.inspect.Health": {
    "status": "OK"
}
*/
fuchsia_inspect::component::health().set_ok();

/*
"fuchsia.inspect.Health": {
    "status": "UNHEALTHY",
    "message": "Something went wrong!"
}
*/
fuchsia_inspect::component::health().set_unhealthy("something went wrong!");

Dart

Advanced: fuchsia_inspect::Inspect has a getter called health that returns an object that announces overall health status in a special location (a node child of the root of the inspect tree). Since our service is not healthy unless it can connect to FizzBuzz, can you incorporate this:

/*
"fuchsia.inspect.Health": {
    "status": "STARTING_UP"
}
*/
inspect.Inspect().health.setStartingUp();

/*
"fuchsia.inspect.Health": {
    "status": "OK"
}
*/
inspect.Inspect().health.setOk();

/*
"fuchsia.inspect.Health": {
    "status": "UNHEALTHY",
    "message": "Something went wrong!"
}
*/
inspect.Inspect().health.setUnhealthy('Something went wrong!');

Once you complete this exercise, you should see that the connection error handler is being called with a "not found" error. Inspect output showed that FizzBuzz is running, so maybe something is misconfigured. Unfortunately not everything uses Inspect (yet!) so look at the logs:

C++

$ ffx log --filter FizzBuzz
...
... Component fuchsia-pkg://fuchsia.com/inspect_cpp_codelab#meta/part_2.cm
is not allowed to connect to fuchsia.examples.inspect.FizzBuzz...

Rust

$ ffx log --filter FizzBuzz
...
... Component fuchsia-pkg://fuchsia.com/inspect_rust_codelab#meta/part_2.cm
is not allowed to connect to fuchsia.examples.inspect.FizzBuzz...

Dart

$ ffx log --filter FizzBuzz
...
... Component fuchsia-pkg://fuchsia.com/inspect_dart_codelab_part_2.cmx
is not allowed to connect to fuchsia.examples.inspect.FizzBuzz...

Sandboxing errors are a common pitfall that are sometimes difficult to uncover.

Looking at the sandbox in part2 meta, you can see it is missing the service:

C++

Find the sandbox meta in part_2/meta

Rust

Find the sandbox meta in part_2/meta

Dart

Find the sandbox meta in part_2/meta

"sandbox": {
    "services": [
        "fuchsia.logger.LogSink"
    ]
}

Add "fuchsia.examples.inspect.FizzBuzz" to the services array, rebuild, and run again. You should now see FizzBuzz in the logs and an OK status:

C++

$ ffx log --tags inspect_cpp_codelab
[inspect_cpp_codelab, part2] INFO: main.cc(57): Got FizzBuzz: 1 2 Fizz
4 Buzz Fizz 7 8 Fizz Buzz 11 Fizz 13 14 FizzBuzz 16 17 Fizz 19 Buzz Fizz
22 23 Fizz Buzz 26 Fizz 28 29 FizzBuzz

Rust

$ ffx log --tags inspect_rust_codelab
[inspect_rust_codelab, part2] INFO: main.rs(52): Got FizzBuzz: 1 2 Fizz
4 Buzz Fizz 7 8 Fizz Buzz 11 Fizz 13 14 FizzBuzz 16 17 Fizz 19 Buzz Fizz
22 23 Fizz Buzz 26 Fizz 28 29 FizzBuzz

Dart

$ ffx log --tags inspect_dart_codelab
[inspect_dart_codelab, part2] INFO: main.dart(35): Got FizzBuzz: 1 2 Fizz
4 Buzz Fizz 7 8 Fizz Buzz 11 Fizz 13 14 FizzBuzz 16 17 Fizz 19 Buzz Fizz
22 23 Fizz Buzz 26 Fizz 28 29 FizzBuzz

This concludes Part 2.

You can now commit your solution:

git commit -am "solution for part 2"

Part 3: Unit Testing for Inspect

All code on Fuchsia should be tested, and this applies to Inspect data as well.

While Inspect data is not required to be tested in general, you need to test Inspect data that is depended upon by other tools such as Triage or Feedback.

Reverser has a basic unit test. Run it:

C++

The unit tests is located in reverser_unittests.cc.

fx test inspect_cpp_codelab_unittests

Rust

The unit test is located in reverser.rs > mod tests.

fx test inspect_rust_codelab_unittests

Dart

The unit test is located in reverser_test.dart.

fx test inspect_dart_codelab_part_3_unittests

The unit test ensures that Reverser works properly (and doesn't hang!), but it does not check that the Inspect output is as expected.

Passing Nodes into constructors is a form of Dependency Injection, which allows you to pass in test versions of dependencies to check their state.

The code to open a Reverser looks like the following:

C++

binding_set_.AddBinding(std::make_unique<Reverser>(ReverserStats::CreateDefault()),
                        ptr.NewRequest());
// Alternatively
binding_set_.AddBinding(std::make_unique<Reverser>(inspect::Node()),
                        ptr.NewRequest());

Rust

let (proxy, stream) = fidl::endpoints::create_proxy_and_stream::<ReverserMarker>()?;
let reverser = ReverserServer::new(ReverserServerMetrics::default());
reverser.spawn(stream);

Dart

return ReverserImpl(ReverserStats.noop());

A default version of the Inspect Node is passed into the Reverser. This allows the reverser code to run properly in tests, but it does not support asserting on Inspect output.

C++

Exercise: Change OpenReverser to take the dependency for Reverser as an argument and use it when constructing Reverser.

Hint: Create an inspect::Inspector in the test function. You can get the root using inspector.GetRoot().
Hint: You will need to create a child on the root to pass in to OpenReverser.

Rust

Exercise: Change open_reverser to take the dependency for a ReverserServerFactory as an argument and use it when constructing Reverser.

Hint: Create a fuchsia_inspect::Inspector in the test function. You can get the root using inspector.root().
Note: Do not use component::inspector() directly in your tests, this creates a static inspector that will be alive in all your tests and can lead to flakes or unexpected behaviors. For unit tests, alwas prefer to use a new fuchsia_inspect::Inspector
Hint: You will need to create a child on the root to pass in to ReverserServerFactory::new.

Dart

Exercise: Change openReverser to take the dependency for an inspect.Node as an argument and use it when constructing Reverser.

Hint: Use inspect.Inspect.forTesting and FakeVmoHolder to create an Inspect object without fuchsia dependencies to run your test on host.
Hint: You will need to create a child on the root to pass in to openReverser.

Follow up: Create multiple reverser connections and test them independently.

Following this exercise, your unit test will set real values in an Inspect hierarchy.

Add code to test the output in Inspect:

C++

#include <lib/inspect/testing/cpp/inspect.h>
fpromise::result<inspect::Hierarchy> hierarchy =
    RunPromise(inspect::ReadFromInspector(inspector));
ASSERT_TRUE(hierarchy.is_ok());

The snippet above reads the underlying virtual memory object (VMO) containing Inspect data and parses it into a readable hierarchy.

You can now read individual properties and children as follows:

auto* global_count =
    hierarchy.value().node().get_property<inspect::UintPropertyValue>("request_count");
ASSERT_TRUE(global_count);
EXPECT_EQ(3u, global_count->value());

auto* connection_0 = hierarchy.value().GetByPath({"connection_0x0"});
ASSERT_TRUE(connection_0);
auto* requests_0 =
    connection_0->node().get_property<inspect::UintPropertyValue>("request_count");
ASSERT_TRUE(requests_0);
EXPECT_EQ(2u, requests_0->value());

Rust

fuchsia_inspect::{self, assert_data_tree},
let inspector = inspect::Inspector::new();
assert_data_tree!(inspector, root: {
    reverser_service: {
        total_requests: 3u64,
        connection_count: 2u64,
        "connection0": {
            request_count: 2u64,
            response_count: 2u64,
        },
        "connection1": {
            request_count: 1u64,
            response_count: 1u64,
        },
    }
});

Dart

test('reverser', () async {
  // ...

The VmoMatcher is a convenient utility for testing inspect integrations. It allows to assert existing properties and children and missing ones, among other features.

The snippets above read a snapshot from the underlying virtual memory object (VMO) containing Inspect data and parses it into a readable hierarchy.

Exercise: Add assertions for the rest of your Inspect data.

This concludes Part 3.

You may commit your changes:

git commit -am "solution to part 3"

Part 4: Integration Testing for Inspect

Integration testing is an important part of the software development workflow for Fuchsia. Integration tests allow you to observe the behavior of your actual component when it runs on the system.

Running integration tests

You can run the integration tests for the codelab as follows:

C++

$ fx test inspect_cpp_codelab_integration_tests

Rust

$ fx test inspect_rust_codelab_integration_tests

Dart

$ fx test inspect_dart_codelab_part_4_integration_tests

View the code

Look at how the integration test is setup:

View the component manifest for the integration test:
C++

Find the component manifest (cml) in part_4/meta
```
{
   ...
   use: [
       { protocol: "fuchsia.diagnostics.ArchiveAccessor" },
   ]
}
```
This file uses the protocol fuchsia.diagnostics.ArchiveAccessor from parent. This protocol is available to all tests to enable to read diagnostics about all components under the test realm.
Rust

Find the component manifest (cml) in part_4/meta
```
{
   ...
   use: [
       { protocol: "fuchsia.diagnostics.ArchiveAccessor" },
   ]
}
```
This file uses the protocol fuchsia.diagnostics.ArchiveAccessor from parent. This protocol is available to all tests to enable to read diagnostics about all components under the test realm.
Dart
Find the component manifest (cmx) in dart/part_4/meta
```
{
    "facets": {
        "fuchsia.test": {
            "injected-services": {
                "fuchsia.diagnostics.ArchiveAccessor":
                    "fuchsia-pkg://fuchsia.com/archivist-for-embedding#meta/archivist-for-embedding.cmx"
            }
        }
    },
    "program": {
        "binary": "test/integration_part_4"
    },
    "sandbox": {
        "services": [
            "fuchsia.logger.LogSink",
            "fuchsia.sys.Loader",
            "fuchsia.sys.Environment"
            ...
        ]
    }
}
```
The important parts of this file are:
- Injected services: The fuchsia.test facet includes configuration for tests. In this file, the fuchsia.diagnostics.ArchiveAccessor service is injected and points to a component called archivist-for-embedding.cmx. The Archivist collects information from all components in your test environment and provides a reading interface. You can use this information to look at your Inspect output.
- Sandbox services: Integration tests need to start other components in the test environment and wire them up. For this you need fuchsia.sys.Loader and fuchsia.sys.Environment.

Look at the integration test itself. The individual test cases are fairly straightforward:

C++

Locate the integration test in part4/tests/integration_test.cc.

TEST_F(IntegrationTestPart4, StartWithFizzBuzz) {
  auto ptr = ConnectToReverser({.include_fizzbuzz = true});

  bool error = false;
  ptr.set_error_handler([&](zx_status_t unused) { error = true; });

  bool done = false;
  std::string result;
  ptr->Reverse("hello", [&](std::string value) {
    result = std::move(value);
    done = true;
  });
  RunLoopUntil([&] { return done || error; });

  ASSERT_FALSE(error);
  EXPECT_EQ("olleh", result);

  // CODELAB: Check that the component was connected to FizzBuzz.
}

StartComponentAndConnect is responsible for creating a new test environment and starting the codelab component inside of it. The include_fizzbuzz_service option instructs the method to optionally include FizzBuzz. This feature tests that your Inspect output is as expected in case it fails to connect to FizzBuzz as in Part 2.

Rust

Locate the integration test in part4/tests/integration_test.rs.

#[fuchsia::test]
async fn start_with_fizzbuzz() -> Result<(), Error> {
    let test = IntegrationTest::start(4, TestOptions::default()).await?;
    let reverser = test.connect_to_reverser()?;
    let result = reverser.reverse("hello").await?;
    assert_eq!(result, "olleh");

    // CODELAB: Check that the component was connected to FizzBuzz.

    Ok(())
}

IntegrationTest::start is responsible for creating a new test environment and starting the codelab component inside of it. The include_fizzbuzz option instructs the method to optionally launch the FizzBuzz component. This feature tests that your Inspect output is as expected in case it fails to connect to FizzBuzz as in Part 2.

Dart

Locate the integration test in part_4/test/integration_test.dart.

setUp(() async {
  env = CodelabEnvironment();
  await env.create();
});

tearDown(() async {
  env.dispose();
});

test('start with fizzbuzz', () async {
  final reverser = await startComponentAndConnect(includeFizzbuzz: true);
  final result = await reverser.reverse('hello');
  expect(result, equals('olleh'));
  // CODELAB: Check that the component was connected to FizzBuzz.
});

env.create() is responsible for creating a new test environment. startComponentAndConnect launches the reverser component and optionally launches the FizzBuzz component. This feature tests that the Inspect output is as expected in case it fails to connect to FizzBuzz as in Part 2.

Add the following method to your test fixture to read from the ArchiveAccessor service:

C++

#include <rapidjson/document.h>
#include <rapidjson/pointer.h>
std::string GetInspectJson() {
  fuchsia::diagnostics::ArchiveAccessorPtr archive;
  auto svc = sys::ServiceDirectory::CreateFromNamespace();
  svc->Connect(archive.NewRequest());

  while (true) {
    ContentVector current_entries;

    fuchsia::diagnostics::BatchIteratorPtr iterator;
    fuchsia::diagnostics::StreamParameters stream_parameters;
    stream_parameters.set_data_type(fuchsia::diagnostics::DataType::INSPECT);
    stream_parameters.set_stream_mode(fuchsia::diagnostics::StreamMode::SNAPSHOT);
    stream_parameters.set_format(fuchsia::diagnostics::Format::JSON);

    {
      std::vector<fuchsia::diagnostics::SelectorArgument> args;
      args.emplace_back();
      args[0].set_raw_selector(ReverserMonikerForSelectors() + ":root");

      fuchsia::diagnostics::ClientSelectorConfiguration client_selector_config;
      client_selector_config.set_selectors(std::move(args));
      stream_parameters.set_client_selector_configuration(std::move(client_selector_config));
    }
    archive->StreamDiagnostics(std::move(stream_parameters), iterator.NewRequest());

    bool done = false;
    iterator->GetNext([&](auto result) {
      auto res =
          fpromise::result<ContentVector, fuchsia::diagnostics::ReaderError>(std::move(result));
      if (res.is_ok()) {
        current_entries = res.take_value();
      }

      done = true;
    });

    RunLoopUntil([&] { return done; });

    // Should be at most one component.
    ZX_ASSERT(current_entries.size() <= 1);
    if (!current_entries.empty()) {
      std::string json;
      fsl::StringFromVmo(current_entries[0].json(), &json);
      // Ensure the component is either OK or UNHEALTHY.
      if (json.find("OK") != std::string::npos || json.find("UNHEALTHY") != std::string::npos) {
        return json;
      }
    }

    // Retry with delay until the data appears.
    usleep(150000);
  }

  return "";
}

Rust

use {
    anyhow::format_err,
    diagnostics_reader::{
        assert_data_tree, AnyProperty, ArchiveReader, DiagnosticsHierarchy, Inspect,
    },
};
async fn get_inspect_hierarchy(test: &IntegrationTest) -> Result<DiagnosticsHierarchy, Error> {
    let moniker = test.reverser_moniker_for_selectors();
    ArchiveReader::new()
        .add_selector(format!("{}:root", moniker))
        .snapshot::<Inspect>()
        .await?
        .into_iter()
        .next()
        .and_then(|result| result.payload)
        .ok_or(format_err!("expected one inspect hierarchy"))
}

Dart

// NOTE: this test is currently commented out in the BUILD.gn file.
// TODO(fxb/45831): re-enable
import 'dart:convert';
import 'package:fidl_fuchsia_diagnostics/fidl_async.dart';
import 'package:fidl_fuchsia_mem/fidl_async.dart';
import 'package:fuchsia_services/services.dart';
import 'package:zircon/zircon.dart';
String readBuffer(Buffer buffer) {
  final dataVmo = SizedVmo(buffer.vmo.handle, buffer.size);
  final data = dataVmo.read(buffer.size);
  return utf8.decode(data.bytesAsUint8List());
}

Future<Map<String, dynamic>> getInspectHierarchy() async {
  final archive = ArchiveAccessorProxy();
  final incoming = Incoming.fromSvcPath()..connectToService(archive);

  final params = StreamParameters(
    dataType: DataType.inspect,
    streamMode: StreamMode.snapshot,
    format: Format.json,
    clientSelectorConfiguration: ClientSelectorConfiguration.withSelectors([
      SelectorArgument.withRawSelector('${env.label}/$serverName.cmx:root'),
    ]),
  );

  // ignore: literal_only_boolean_expressions
  while (true) {
    final iterator = BatchIteratorProxy();
    await archive.streamDiagnostics(params, iterator.ctrl.request());
    final batch = await iterator.getNext();
    for (final entry in batch) {
      final jsonData = readBuffer(entry.json);
      if (jsonData.contains('fuchsia.inspect.Health') &&
          !jsonData.contains('STARTING_UP')) {
        await incoming.close();
        return json.decode(jsonData);
      }
    }
    iterator.ctrl.close();
    await Future.delayed(Duration(milliseconds: 150));
  }
}

Exercise. Use the returned data in your tests and add assertions to the returned data:
C++
```
rapidjson::Document document;
document.Parse(GetInspectJson());
```
Add assertions on the returned JSON data.
- Hint: It may help to print the JSON output to view the schema.
- Hint: You can read values by path as follows:
- Hint: You can EXPECT_EQ by passing in the expected value as a rapidjson::Value: rapidjson::Value("OK").
```
rapidjson::GetValueByPointerWithDefault(
    document, "/payload/root/fuchsia.inspect.Health/status", "")
```
Rust
```
let hierarchy = get_inspect_hierarchy(&test).await?;
```
Add assertions on the returned DiagnosticsHierarchy.
- Hint: It may help to print the JSON output to view the schema.
Dart
```
final inspectData = await getInspectHierarchy();
```
Add assertions on the returned Map data.
- Hint: It may help to print the JSON output to view the schema.

Your integration test will now ensure your inspect output is correct.

This concludes Part 4.

You may commit your solution:

git commit -am "solution to part 4"

Part 5: Feedback Selectors

This section is under construction.

TODO: Writing a feedback selector and adding tests to your integration test.
TODO: Selectors for Feedback and other pipelines