前提条件
本教程基于 C++ 入门教程。
概览
在 Fuchsia 上使用 FIDL 的一个常见方面是跨 协议许多 FIDL 消息都包含客户端或服务器端 信道,其中的信道用于通过不同的 FIDL 进行通信 协议。在这种情况下,客户端允许向指定的 协议,而服务器端必须实现指定的协议。一个 客户端和服务器端的备用术语是协议和协议 请求。
本教程涵盖以下内容:
- 这些客户端和服务器的使用结束,无论是在 FIDL 中还是在 C++ FIDL 绑定。
- 协议请求管道模式及其优势。
本教程的完整示例代码位于
//examples/fidl/cpp/request_pipelining
。
FIDL 协议
本教程将实现 EchoLauncher
协议
fuchsia.examples
库:
@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;
});
};
该协议可让客户端检索 Echo
的实例
协议。客户端可以指定前缀和生成的 Echo
实例
会向每个响应添加该前缀。
为此,您可以使用以下两种方法:
GetEcho
:接受前缀作为请求,并使用 连接到Echo
协议实现的通道。更新后 在响应收到客户端一端时,客户端可以开始发出请求 使用客户端的Echo
协议。GetEchoPipelined
:将通道的服务器端作为请求之一 参数,并将Echo
的实现与其绑定。客户 则视为客户端已发送请求,并且 在调用GetEchoPipelined
后开始对该频道发出Echo
请求。
顾名思义,后者使用一种称为协议请求的模式。 是首选方法本教程同时实现了 方法。
实现服务器
实现 Echo 协议
这种 Echo
实现允许指定前缀,以便
区分 Echo
服务器的不同实例:
// Implementation of the Echo protocol that prepends a prefix to every response.
class EchoImpl final : public fidl::Server<fuchsia_examples::Echo> {
public:
explicit EchoImpl(std::string prefix) : prefix_(prefix) {}
// This method is not used in the request pipelining example, so requests are ignored.
void SendString(SendStringRequest& request, SendStringCompleter::Sync& completer) override {}
void EchoString(EchoStringRequest& request, EchoStringCompleter::Sync& completer) override {
FX_LOGS(INFO) << "Got echo request for prefix " << prefix_;
completer.Reply(prefix_ + request.value());
}
const std::string prefix_;
};
SendString
处理程序为空,因为客户端仅使用 EchoString
。
实现 EchoLauncher 协议
// Implementation of EchoLauncher. Each method creates an instance of EchoImpl
// with the specified prefix.
class EchoLauncherImpl final : public fidl::Server<fuchsia_examples::EchoLauncher> {
public:
explicit EchoLauncherImpl(async_dispatcher_t* dispatcher) : dispatcher_(dispatcher) {}
void GetEcho(GetEchoRequest& request, GetEchoCompleter::Sync& completer) override {
FX_LOGS(INFO) << "Got non-pipelined request";
auto [client_end, server_end] = fidl::Endpoints<fuchsia_examples::Echo>::Create();
fidl::BindServer(dispatcher_, std::move(server_end),
std::make_unique<EchoImpl>(request.echo_prefix()));
completer.Reply(std::move(client_end));
}
void GetEchoPipelined(GetEchoPipelinedRequest& request,
GetEchoPipelinedCompleter::Sync& completer) override {
FX_LOGS(INFO) << "Got pipelined request";
fidl::BindServer(dispatcher_, std::move(request.request()),
std::make_unique<EchoImpl>(request.echo_prefix()));
}
async_dispatcher_t* dispatcher_;
};
对于 GetEcho
,代码首先需要实例化通道两端。它
然后,使用服务器端启动一个 Echo
实例,并发送响应
返回给客户端对于 GetEchoPipelined
,客户端已完成
都是创建频道两端的工作保留一端并超过
将另一个对象绑定到服务器,所以代码只需要将服务器端
移到新的 EchoImpl
。
提供 EchoLauncher 协议
主循环与
服务器教程,但提供 EchoLauncher
,而不是 Echo
。
int main(int argc, char** argv) {
async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
async_dispatcher_t* dispatcher = loop.dispatcher();
component::OutgoingDirectory outgoing = component::OutgoingDirectory(dispatcher);
zx::result result = outgoing.ServeFromStartupInfo();
if (result.is_error()) {
FX_LOGS(ERROR) << "Failed to serve outgoing directory: " << result.status_string();
return -1;
}
result = outgoing.AddUnmanagedProtocol<fuchsia_examples::EchoLauncher>(
[dispatcher](fidl::ServerEnd<fuchsia_examples::EchoLauncher> server_end) {
FX_LOGS(INFO) << "Incoming connection for "
<< fidl::DiscoverableProtocolName<fuchsia_examples::EchoLauncher>;
fidl::BindServer(dispatcher, std::move(server_end),
std::make_unique<EchoLauncherImpl>(dispatcher));
});
if (result.is_error()) {
FX_LOGS(ERROR) << "Failed to add EchoLauncher protocol: " << result.status_string();
return -1;
}
FX_LOGS(INFO) << "Running echo launcher server" << std::endl;
loop.Run();
return 0;
}
构建服务器
(可选)要检查设置是否正确,请尝试构建服务器:
将您的 GN build 配置为包含服务器:
fx set core.x64 --with //examples/fidl/cpp/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
代码使用 GetEcho
连接到 Echo
的一个实例,使用 GetEcho
连接到另一个实例
GetEchoPipelined
,然后对每个实例发出 EchoString
请求。
非流水线客户端
以下是非流水线代码:
int main(int argc, const char** argv) {
async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
async_dispatcher_t* dispatcher = loop.dispatcher();
int num_responses = 0;
// Connect to the EchoLauncher protocol
zx::result launcher_client_end = component::Connect<fuchsia_examples::EchoLauncher>();
ZX_ASSERT(launcher_client_end.is_ok());
fidl::Client launcher(std::move(*launcher_client_end), dispatcher);
// Make a non-pipelined request to get an instance of Echo
launcher->GetEcho({"non pipelined: "})
.ThenExactlyOnce([&](fidl::Result<fuchsia_examples::EchoLauncher::GetEcho>& result) {
ZX_ASSERT(result.is_ok());
// Take the Echo client end in the response, bind it to another client, and
// make an EchoString request on it.
fidl::SharedClient echo(std::move(result->response()), dispatcher);
echo->EchoString({"hello!"})
.ThenExactlyOnce(
// Clone |echo| into the callback so that the client
// is only destroyed after we receive the response.
[&, echo = echo.Clone()](fidl::Result<fuchsia_examples::Echo::EchoString>& result) {
ZX_ASSERT(result.is_ok());
FX_LOGS(INFO) << "Got echo response " << result->response();
if (++num_responses == 2) {
loop.Quit();
}
});
});
auto [client_end, server_end] = fidl::Endpoints<fuchsia_examples::Echo>::Create();
// Make a pipelined request to get an instance of Echo
ZX_ASSERT(launcher->GetEchoPipelined({"pipelined: ", std::move(server_end)}).is_ok());
// A client can be initialized using the client end without waiting for a response
fidl::Client echo_pipelined(std::move(client_end), dispatcher);
echo_pipelined->EchoString({"hello!"})
.ThenExactlyOnce([&](fidl::Result<fuchsia_examples::Echo::EchoString>& result) {
ZX_ASSERT(result.is_ok());
FX_LOGS(INFO) << "Got echo response " << result->response();
if (++num_responses == 2) {
loop.Quit();
}
});
loop.Run();
return num_responses == 2 ? 0 : 1;
}
此代码有两层回调:
- 外层负责处理启动器
GetEcho
响应。 - 内层处理
EchoString
响应。
在 GetEcho
响应回调内,代码绑定返回的客户端
到 fidl::SharedClient<Echo>
,并将克隆放入 EchoString
回调,以便延长客户端的生命周期,直到收到 echo 响应
该事件很有可能是在顶级回调返回之后。
流水线客户端
尽管必须先创建一对端点,但流水线代码 更简单:
int main(int argc, const char** argv) {
async::Loop loop(&kAsyncLoopConfigNeverAttachToThread);
async_dispatcher_t* dispatcher = loop.dispatcher();
int num_responses = 0;
// Connect to the EchoLauncher protocol
zx::result launcher_client_end = component::Connect<fuchsia_examples::EchoLauncher>();
ZX_ASSERT(launcher_client_end.is_ok());
fidl::Client launcher(std::move(*launcher_client_end), dispatcher);
// Make a non-pipelined request to get an instance of Echo
launcher->GetEcho({"non pipelined: "})
.ThenExactlyOnce([&](fidl::Result<fuchsia_examples::EchoLauncher::GetEcho>& result) {
ZX_ASSERT(result.is_ok());
// Take the Echo client end in the response, bind it to another client, and
// make an EchoString request on it.
fidl::SharedClient echo(std::move(result->response()), dispatcher);
echo->EchoString({"hello!"})
.ThenExactlyOnce(
// Clone |echo| into the callback so that the client
// is only destroyed after we receive the response.
[&, echo = echo.Clone()](fidl::Result<fuchsia_examples::Echo::EchoString>& result) {
ZX_ASSERT(result.is_ok());
FX_LOGS(INFO) << "Got echo response " << result->response();
if (++num_responses == 2) {
loop.Quit();
}
});
});
auto [client_end, server_end] = fidl::Endpoints<fuchsia_examples::Echo>::Create();
// Make a pipelined request to get an instance of Echo
ZX_ASSERT(launcher->GetEchoPipelined({"pipelined: ", std::move(server_end)}).is_ok());
// A client can be initialized using the client end without waiting for a response
fidl::Client echo_pipelined(std::move(client_end), dispatcher);
echo_pipelined->EchoString({"hello!"})
.ThenExactlyOnce([&](fidl::Result<fuchsia_examples::Echo::EchoString>& result) {
ZX_ASSERT(result.is_ok());
FX_LOGS(INFO) << "Got echo response " << result->response();
if (++num_responses == 2) {
loop.Quit();
}
});
loop.Run();
return num_responses == 2 ? 0 : 1;
}
与客户端教程不同,异步循环会完整运行 一次,即同时运行非流水线代码和流水线代码, 并注意观察操作顺序客户端会跟踪 这样,当没有更多消息时,它就可以退出循环 预期。
构建客户端
(可选)要检查是否正确,请尝试构建客户端:
将您的 GN build 配置为包含服务器:
fx set core.x64 --with //examples/fidl/cpp/request_pipelining/client:echo-client
构建 Fuchsia 映像:
fx build
运行示例代码
在本教程中,
领域
组件是
用于声明
fuchsia.examples.Echo
和 fuchsia.examples.EchoLauncher
。
配置 build,使其包含提供的软件包,其中包含 echo 领域、服务器和客户端:
fx set core.x64 --with //examples/fidl/cpp/request_pipelining
构建 Fuchsia 映像:
fx build
运行
echo_realm
组件。这会创建客户端和服务器组件 并路由功能:ffx component run /core/ffx-laboratory:echo_realm fuchsia-pkg://fuchsia.com/echo-launcher-cpp#meta/echo_realm.cm
启动
echo_client
实例:ffx component start /core/ffx-laboratory:echo_realm/echo_client
在客户端尝试连接到
EchoLauncher
协议。您应该会看到类似如下所示的输出
在设备日志 (ffx log
) 中:
[echo_server][I] Running echo launcher server
[echo_server][I] Incoming connection for fuchsia.examples.EchoLauncher
[echo_server][I] Got non-pipelined request
[echo_server][I] Got pipelined request
[echo_server][I] Got echo request for prefix pipelined:
[echo_server][I] Got echo request for prefix non pipelined:
[echo_client][I] Got echo response pipelined: hello!
[echo_client][I] Got echo response non pipelined: hello!
根据打印顺序,您可以看到流水线处理速度较快。通过 echo 响应首先到达流水线,即使非 流水线请求首先发送,因为请求流水线可以节省往返时间 客户端和服务器之间的通信请求管道也能简化代码。
有关协议请求管道(包括如何处理 则请参阅 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