gRPC概述

3/26/2016 9:16:08 AM

一直在寻找多平台多语言的通信框架，微软的WCF框架很强大和灵活，虽然也能通过自定义绑定和其他技术的客户端通信，但是始终没有实现多平台的技术框架的统一。google的gRPC是一个不错的选择，相比于类似框架Thrift等，google的解决方案更成熟和通用。不足的是由于刚刚开源，使用范围有限，国内资料更少。例如仅仅编译C++的gRPC，花了我两天的时间。在这个系列中，我会逐一介绍各个语言使用gRPC的细节。

gRPC是google2015年初开源的通信框架。

使用gRPC可以在客户端调用不同机器上的服务端的方法，而客户端和服务端的开发语言和运行环境可以有很多种，基本涵盖了主流语言和平台。双方交互的协议可以在proto文件中定义，客户端和服务端可以很方便的通过工具生成协议和代理代码。而消息的编码是采用google protocol buffer，数据量小、速度快。

下图是一个简单的gRPC使用的场景，服务端采用C++开发，客户端可以是anroid，和ruby。

gRPC具有以下特点：

• 基于 HTTP/2， 继而提供了连接多路复用、Body 和 Header 压缩等机制。可以节省带宽、降低TCP链接次数、节省CPU使用和延长电池寿命等。
• 支持主流开发语言（C, C++, Python, PHP, Ruby, NodeJS, C#, Objective-C、Golang、Java）
• IDL (Interface Definition Language) 层使用了 Protocol Buffers, 非常适合团队的接口设计

下面是C#、C++、java的客户端和服务端的例子，这些客户端都向服务端传递一个姓名XXX，服务端返回 hello XXX字符串。

作为通信协议的proto文件

无论使用何种语言创建客户端和服务端，都依照相同的proto文件。proto文件定义了协议接口和数据格式。不同的语言都依照proto文件生成服务端的接口和服务类、客户端的服务代理，只是生成工具的命令不同。
proto文件如下：

syntax = "proto3";

option java_multiple_files = true;
option java_package = "io.grpc.examples.helloworld";
option java_outer_classname = "HelloWorldProto";
option objc_class_prefix = "HLW";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

C#服务端和客户端代码

C#的客户端代理是由工具生成的，所以很简单。

客户端

public static void Main(string[] args)
{
    Channel channel = new Channel("127.0.0.1:50051", ChannelCredentials.Insecure);

    var client = Greeter.NewClient(channel);
    String user = "paul";

    var reply = client.SayHello(new HelloRequest { Name = user });
    Console.WriteLine("Greeting: " + reply.Message);

    channel.ShutdownAsync().Wait();
    Console.WriteLine("Press any key to exit...");
    Console.ReadKey();
}

服务端

class GreeterImpl : Greeter.IGreeter
{
    // Server side handler of the SayHello RPC
    public Task<HelloReply> SayHello(HelloRequest request, ServerCallContext context)
    {
        return Task.FromResult(new HelloReply { Message = "Hello " + request.Name });
    }
}



class Program
{
    const int Port = 50051;

    public static void Main(string[] args)
    {
        Server server = new Server
        {
            Services = { Greeter.BindService(new GreeterImpl()) },
            Ports = { new ServerPort("localhost", Port, ServerCredentials.Insecure) }
        };
        server.Start();

        Console.WriteLine("Greeter server listening on port " + Port);
        Console.WriteLine("Press any key to stop the server...");
        Console.ReadKey();

        server.ShutdownAsync().Wait();
    }
}

C++的服务端和客户端代码

C++的客户端代理无法通过工具生成，需要手动编写。

//C++客户端
class GreeterClient {
 public:
  GreeterClient(std::shared_ptr<Channel> channel)
      : stub_(Greeter::NewStub(channel)) {}

  // Assambles the client's payload, sends it and presents the response back
  // from the server.
  std::string SayHello(const std::string& user) {
    // Data we are sending to the server.
    HelloRequest request;
    request.set_name(user);

    // Container for the data we expect from the server.
    HelloReply reply;

    // Context for the client. It could be used to convey extra information to
    // the server and/or tweak certain RPC behaviors.
    ClientContext context;

    // The actual RPC.
    Status status = stub_->SayHello(&context, request, &reply);

    // Act upon its status.
    if (status.ok()) {
      return reply.message();
    } else {
      return "RPC failed";
    }
  }

 private:
  std::unique_ptr<Greeter::Stub> stub_;
};

int main(int argc, char** argv) {
  // Instantiate the client. It requires a channel, out of which the actual RPCs
  // are created. This channel models a connection to an endpoint (in this case,
  // localhost at port 50051). We indicate that the channel isn't authenticated
  // (use of InsecureChannelCredentials()).
  GreeterClient greeter(grpc::CreateChannel(
      "localhost:50051", grpc::InsecureChannelCredentials()));
  std::string user("world");
  std::string reply = greeter.SayHello(user);
  std::cout << "Greeter received: " << reply << std::endl;

  return 0;
}

//C++服务端
// Logic and data behind the server's behavior.
class GreeterServiceImpl final : public Greeter::Service {
  Status SayHello(ServerContext* context, const HelloRequest* request,
                  HelloReply* reply) override {
    std::string prefix("Hello ");
    reply->set_message(prefix + request->name());
    return Status::OK;
  }
};

void RunServer() {
  std::string server_address("0.0.0.0:50051");
  GreeterServiceImpl service;

  ServerBuilder builder;
  // Listen on the given address without any authentication mechanism.
  builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
  // Register "service" as the instance through which we'll communicate with
  // clients. In this case it corresponds to an *synchronous* service.
  builder.RegisterService(&service);
  // Finally assemble the server.
  std::unique_ptr<Server> server(builder.BuildAndStart());
  std::cout << "Server listening on " << server_address << std::endl;

  // Wait for the server to shutdown. Note that some other thread must be
  // responsible for shutting down the server for this call to ever return.
  server->Wait();
}

int main(int argc, char** argv) {
  RunServer();

  return 0;
}

java的服务端和客户端代码

gRPC本身不支持java语言，但是使用java实现了gRPC，框架是gRPC-java。使用gRPC-java一样可以与gRPC的客户端和服务端进行交互。

java客户端代码：
和C++一样，java的客户端仍然不能直接自动生成服务代理类，需要手动创建。

package io.grpc.examples.helloworld;

import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import io.grpc.StatusRuntimeException;

import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * A simple client that requests a greeting from the {@link HelloWorldServer}.
 */
public class HelloWorldClient {
  private static final Logger logger = Logger.getLogger(HelloWorldClient.class.getName());

  private final ManagedChannel channel;
  private final GreeterGrpc.GreeterBlockingStub blockingStub;

  /** Construct client connecting to HelloWorld server at {@code host:port}. */
  public HelloWorldClient(String host, int port) {
    channel = ManagedChannelBuilder.forAddress(host, port)
        .usePlaintext(true)
        .build();
    blockingStub = GreeterGrpc.newBlockingStub(channel);
  }

  public void shutdown() throws InterruptedException {
    channel.shutdown().awaitTermination(5, TimeUnit.SECONDS);
  }

  /** Say hello to server. */
  public void greet(String name) {
    logger.info("Will try to greet " + name + " ...");
    HelloRequest request = HelloRequest.newBuilder().setName(name).build();
    HelloReply response;
    try {
      response = blockingStub.sayHello(request);
    } catch (StatusRuntimeException e) {
      logger.log(Level.WARNING, "RPC failed: {0}", e.getStatus());
      return;
    }
    logger.info("Greeting: " + response.getMessage());
  }

  /**
   * Greet server. If provided, the first element of {@code args} is the name to use in the
   * greeting.
   */
  public static void main(String[] args) throws Exception {
    HelloWorldClient client = new HelloWorldClient("localhost", 50051);
    try {
      /* Access a service running on the local machine on port 50051 */
      String user = "world";
      if (args.length > 0) {
        user = args[0]; /* Use the arg as the name to greet if provided */
      }
      client.greet(user);
    } finally {
      client.shutdown();
    }
  }
}

java服务端代码：

package io.grpc.examples.helloworld;

import io.grpc.Server;
import io.grpc.ServerBuilder;
import io.grpc.stub.StreamObserver;

import java.io.IOException;
import java.util.logging.Logger;

/**
 * Server that manages startup/shutdown of a {@code Greeter} server.
 */
public class HelloWorldServer {
  private static final Logger logger = Logger.getLogger(HelloWorldServer.class.getName());

  /* The port on which the server should run */
  private int port = 50051;
  private Server server;

  private void start() throws IOException {
    server = ServerBuilder.forPort(port)
        .addService(GreeterGrpc.bindService(new GreeterImpl()))
        .build()
        .start();
    logger.info("Server started, listening on " + port);
    Runtime.getRuntime().addShutdownHook(new Thread() {
      @Override
      public void run() {
        // Use stderr here since the logger may have been reset by its JVM shutdown hook.
        System.err.println("*** shutting down gRPC server since JVM is shutting down");
        HelloWorldServer.this.stop();
        System.err.println("*** server shut down");
      }
    });
  }

  private void stop() {
    if (server != null) {
      server.shutdown();
    }
  }

  /**
   * Await termination on the main thread since the grpc library uses daemon threads.
   */
  private void blockUntilShutdown() throws InterruptedException {
    if (server != null) {
      server.awaitTermination();
    }
  }

  /**
   * Main launches the server from the command line.
   */
  public static void main(String[] args) throws IOException, InterruptedException {
    final HelloWorldServer server = new HelloWorldServer();
    server.start();
    server.blockUntilShutdown();
  }

  private class GreeterImpl implements GreeterGrpc.Greeter {

    @Override
    public void sayHello(HelloRequest req, StreamObserver<HelloReply> responseObserver) {
      HelloReply reply = HelloReply.newBuilder().setMessage("Hello " + req.getName()).build();
      responseObserver.onNext(reply);
      responseObserver.onCompleted();
    }
  }
}

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