前提条件
在本教程中，您将了解请求流水线模式及其优势。本教程要求您已熟悉编写和运行 FIDL 客户端与服务器的基础知识，这些内容在 Rust 使用入门教程中有所介绍。
概览
在 Fuchsia 上使用 FIDL 的一个常见方面是跨协议自行传递协议。许多 FIDL 消息都包含通道的客户端或服务器端，其中通道用于通过不同的 FIDL 协议进行通信。在这种情况下，客户端表示通道的远程端实现指定的协议，而服务器端表示远程端正在对指定协议发出请求。客户端和服务器端的另一组术语是协议和协议请求。
本教程涵盖以下内容：
- 在 FIDL 和 Rust FIDL 绑定中，这些客户端和服务器的使用就结束了。
- 请求管道模式及其优势。
本教程的完整示例代码位于 //examples/fidl/rust/request_pipelining。
FIDL 协议
本教程实现了 fuchsia.examples 库中的 EchoLauncher 协议：
@discoverable
closed protocol EchoLauncher {
strict GetEcho(struct {
echo_prefix string:MAX_STRING_LENGTH;
}) -> (resource struct {
response client_end:Echo;
});
strict GetEchoPipelined(resource struct {
echo_prefix string:MAX_STRING_LENGTH;
request server_end:Echo;
});
};
这是一个允许客户端检索 Echo 协议实例的协议。客户端可以指定一个前缀，生成的 Echo 实例会将该前缀添加到每个响应中。
可以使用以下两种方法完成此操作：
GetEcho：接受前缀作为请求，并使用连接到Echo协议实现的通道的客户端端进行响应。在响应中收到客户端后，客户端就可以开始使用客户端发出采用Echo协议的请求。GetEchoPipelined：将通道的前缀和服务器端作为请求，并将Echo的实现绑定到该请求。系统会假定发出请求的客户端已持有客户端，并将在调用GetEchoPipeliend之后开始在相应通道上发出Echo请求。
顾名思义，后一种方式使用称为协议请求流水线的模式，是首选方法。本教程同时实现了这两种方法。
实现服务器
实现 Echo 协议
这种 Echo 实现允许指定前缀，以区分 Echo 服务器的不同实例：
// An Echo implementation that adds a prefix to every response
async fn run_echo_server(stream: EchoRequestStream, prefix: &str) -> Result<(), Error> {
stream
.map(|result| result.context("failed request"))
.try_for_each(|request| async move {
match request {
// The SendString request is not used in this example, so just
// ignore it
EchoRequest::SendString { value: _, control_handle: _ } => {}
EchoRequest::EchoString { value, responder } => {
println!("Got echo request for prefix {}", prefix);
let response = format!("{}: {}", prefix, value);
responder.send(&response).context("error sending response")?;
}
}
Ok(())
})
.await
}
SendString 处理程序为空，因为客户端仅使用 EchoString。
实现 EchoLauncher 协议
一般结构与 Echo 实现类似，但一个区别在于使用的是 try_for_each_concurrent，而非 try_for_each。此示例中的客户端启动两个 Echo 实例，因此使用并发版本可以同时运行对 run_echo_server 的两次调用：
// The EchoLauncher implementation that launches Echo servers with the specified
// prefix
async fn run_echo_launcher_server(stream: EchoLauncherRequestStream) -> Result<(), Error> {
// Currently the client only connects at most two Echo clients for each EchoLauncher
stream
.map(|result| result.context("request error"))
.try_for_each_concurrent(2, |request| async move {
let (echo_prefix, server_end) = match request {
// In the non pipelined case, we need to initialize the
// communication channel ourselves
EchoLauncherRequest::GetEcho { echo_prefix, responder } => {
println!("Got non pipelined request");
let (client_end, server_end) = create_endpoints::<EchoMarker>();
responder.send(client_end)?;
(echo_prefix, server_end)
}
// In the pipelined case, the client is responsible for
// initializing the channel, and passes the server its end of
// the channel
EchoLauncherRequest::GetEchoPipelined {
echo_prefix,
request,
control_handle: _,
} => {
println!("Got pipelined request");
(echo_prefix, request)
}
};
// Run the Echo server with the specified prefix
run_echo_server(server_end.into_stream()?, &echo_prefix).await
})
.await
}
这两种 EchoLauncher 方法都通过在通道的服务器端调用 run_echo_server 来处理。不同之处在于，在 GetEcho 中，服务器负责初始化通道：它会将一端用作服务器端，并将另一端发送回客户端。在 GetEchoPipelined 中，服务器端作为请求的一部分提供，因此服务器无需执行任何其他工作，也无需响应。
// The EchoLauncher implementation that launches Echo servers with the specified
// prefix
async fn run_echo_launcher_server(stream: EchoLauncherRequestStream) -> Result<(), Error> {
// Currently the client only connects at most two Echo clients for each EchoLauncher
stream
.map(|result| result.context("request error"))
.try_for_each_concurrent(2, |request| async move {
let (echo_prefix, server_end) = match request {
// In the non pipelined case, we need to initialize the
// communication channel ourselves
EchoLauncherRequest::GetEcho { echo_prefix, responder } => {
println!("Got non pipelined request");
let (client_end, server_end) = create_endpoints::<EchoMarker>();
responder.send(client_end)?;
(echo_prefix, server_end)
}
// In the pipelined case, the client is responsible for
// initializing the channel, and passes the server its end of
// the channel
EchoLauncherRequest::GetEchoPipelined {
echo_prefix,
request,
control_handle: _,
} => {
println!("Got pipelined request");
(echo_prefix, request)
}
};
// Run the Echo server with the specified prefix
run_echo_server(server_end.into_stream()?, &echo_prefix).await
})
.await
}
提供 EchoLauncher 协议
主循环应与服务器教程中的相同，但提供的是 EchoLauncher，而不是 Echo。
enum IncomingService {
EchoLauncher(EchoLauncherRequestStream),
}
#[fuchsia::main]
async fn main() -> Result<(), Error> {
let mut fs = ServiceFs::new_local();
fs.dir("svc").add_fidl_service(IncomingService::EchoLauncher);
fs.take_and_serve_directory_handle()?;
const MAX_CONCURRENT: usize = 1000;
let fut = fs.for_each_concurrent(MAX_CONCURRENT, |IncomingService::EchoLauncher(stream)| {
run_echo_launcher_server(stream).unwrap_or_else(|e| println!("{:?}", e))
});
println!("Running echo launcher server");
fut.await;
Ok(())
}
构建服务器
（可选）如需检查内容是否正确，请尝试构建服务器：
配置您的 GN build 以包含该服务器：
fx set core.x64 --with //examples/fidl/rust/request_pipelining/server:echo-server构建 Fuchsia 映像：
fx build
实现客户端
连接到 EchoLauncher 服务器后，客户端代码会使用 GetEcho 连接到 Echo 的一个实例，使用 GetEchoPipelined 连接到另一个 Echo 实例，然后对每个实例发出 EchoString 请求。
以下是非流水线代码：
#[fuchsia::main]
async fn main() -> Result<(), Error> {
let echo_launcher =
connect_to_protocol::<EchoLauncherMarker>().context("Failed to connect to echo service")?;
// Create a future that obtains an Echo protocol using the non-pipelined
// GetEcho method
let non_pipelined_fut = async {
let client_end = echo_launcher.get_echo("not pipelined").await?;
// "Upgrade" the client end in the response into an Echo proxy, and
// make an EchoString request on it
let proxy = client_end.into_proxy()?;
proxy.echo_string("hello").map_ok(|val| println!("Got echo response {}", val)).await
};
// Create a future that obtains an Echo protocol using the pipelined GetEcho
// method
let (proxy, server_end) = create_proxy::<EchoMarker>()?;
echo_launcher.get_echo_pipelined("pipelined", server_end)?;
// We can make a request to the server right after sending the pipelined request
let pipelined_fut =
proxy.echo_string("hello").map_ok(|val| println!("Got echo response {}", val));
// Run the two futures to completion
let (non_pipelined_result, pipelined_result) = join!(non_pipelined_fut, pipelined_fut);
pipelined_result?;
non_pipelined_result?;
Ok(())
}
此代码将两个 Future 链接到一起。首先，它会向客户端发出 GetEcho 请求。然后，它会获取该 Future 的结果，接着用它来创建客户端对象 (proxy)，调用 EchoString，最后使用 await 阻塞结果。
尽管必须先初始化通道，但流水线代码要简单得多：
#[fuchsia::main]
async fn main() -> Result<(), Error> {
let echo_launcher =
connect_to_protocol::<EchoLauncherMarker>().context("Failed to connect to echo service")?;
// Create a future that obtains an Echo protocol using the non-pipelined
// GetEcho method
let non_pipelined_fut = async {
let client_end = echo_launcher.get_echo("not pipelined").await?;
// "Upgrade" the client end in the response into an Echo proxy, and
// make an EchoString request on it
let proxy = client_end.into_proxy()?;
proxy.echo_string("hello").map_ok(|val| println!("Got echo response {}", val)).await
};
// Create a future that obtains an Echo protocol using the pipelined GetEcho
// method
let (proxy, server_end) = create_proxy::<EchoMarker>()?;
echo_launcher.get_echo_pipelined("pipelined", server_end)?;
// We can make a request to the server right after sending the pipelined request
let pipelined_fut =
proxy.echo_string("hello").map_ok(|val| println!("Got echo response {}", val));
// Run the two futures to completion
let (non_pipelined_result, pipelined_result) = join!(non_pipelined_fut, pipelined_fut);
pipelined_result?;
non_pipelined_result?;
Ok(())
}
使用 create_proxy，这是创建通道的两端并将一端转换为代理的快捷方式。调用 GetEchoPipelined 后，客户端可以立即发出 EchoString 请求。
最后，与非流水线调用和流水线调用对应的两个 Future 会同时运行以完成操作，以查看哪个 Future 最先完成：
#[fuchsia::main]
async fn main() -> Result<(), Error> {
let echo_launcher =
connect_to_protocol::<EchoLauncherMarker>().context("Failed to connect to echo service")?;
// Create a future that obtains an Echo protocol using the non-pipelined
// GetEcho method
let non_pipelined_fut = async {
let client_end = echo_launcher.get_echo("not pipelined").await?;
// "Upgrade" the client end in the response into an Echo proxy, and
// make an EchoString request on it
let proxy = client_end.into_proxy()?;
proxy.echo_string("hello").map_ok(|val| println!("Got echo response {}", val)).await
};
// Create a future that obtains an Echo protocol using the pipelined GetEcho
// method
let (proxy, server_end) = create_proxy::<EchoMarker>()?;
echo_launcher.get_echo_pipelined("pipelined", server_end)?;
// We can make a request to the server right after sending the pipelined request
let pipelined_fut =
proxy.echo_string("hello").map_ok(|val| println!("Got echo response {}", val));
// Run the two futures to completion
let (non_pipelined_result, pipelined_result) = join!(non_pipelined_fut, pipelined_fut);
pipelined_result?;
non_pipelined_result?;
Ok(())
}
构建客户端
（可选）如需检查内容是否正确，请尝试构建客户端：
配置您的 GN build 以包含该服务器：
fx set core.x64 --with //examples/fidl/rust/request_pipelining/client:echo-client构建 Fuchsia 映像：
fx build
运行示例代码
fuchsia.examples.Echofuchsia.examples.EchoLauncher
配置 build 以添加所提供的包含 echo 领域、服务器和客户端的软件包：
fx set core.x64 --with //examples/fidl/rust:echo-launcher-rust构建 Fuchsia 映像：
fx build运行
echo_realm组件。这将创建客户端和服务器组件实例并路由功能：ffx component run /core/ffx-laboratory:echo_realm fuchsia-pkg://fuchsia.com/echo-launcher-rust#meta/echo_realm.cm启动
echo_client实例：ffx component start /core/ffx-laboratory:echo_realm/echo_client
当客户端尝试连接到 EchoLauncher 协议时，服务器组件便会启动。您应该会在设备日志 (ffx log) 中看到类似于以下内容的输出：
[echo_server][][I] Running echo launcher server
[echo_server][][I] Got pipelined request
[echo_server][][I] Got echo request for prefix pipelined
[echo_server][][I] Got non pipelined request
[echo_client][][I] Got echo response pipelined: hello
[echo_server][][I] Got echo request for prefix not pipelined
[echo_client][][I] Got echo response not pipelined: hello
根据打印订单，您可以看到，采用流水线的情形更快。即使先发送非流水线请求，也会先发送流水线用例的 echo 响应，因为请求流水线可以省去客户端与服务器之间的往返。请求管道也会简化代码。
如需详细了解协议请求流水线，包括如何处理可能失败的协议请求，请参阅 FIDL API 评分准则。
终止领域组件以停止执行并清理组件实例：
ffx component destroy /core/ffx-laboratory:echo_realm