gRPC源码分析0-导读

时间:2022-04-23 07:49:49

gRPC是Google开源的新一代RPC框架,官网是http://www.grpc.io。正式发布于2016年8月,技术栈非常的新,基于HTTP/2,netty4.1,proto3。虽然目前在工程化方面gRPC还非常不足,但它也值得我们好好研究它,学习他。

1. 使用场景

按照Google的说法,使用广泛,但主要使用场景还是在移动端:

  1. Efficiently connecting polyglot services in microservices style architecture(微服务、多语言)

  2. Connecting mobile devices, browser clients to backend services

  3. Generating efficient client libraries

2. HTTP/2

HTTP/2,主要是基于Google发布的SPDY协议,是自HTTP/1.1从1999年发布16年后的首次更新。Servlet4.0将完全支持HTTP/2。目前支持HTTP/2的浏览器还不多,主要也只是支持基于TLS的HTTP/2。下图是在caniuse.com网站统计的支持HTTP/2的浏览器,可以看到chrome也是在41版本后开始的,IE根本不支持。

gRPC源码分析0-导读

 

HTTP/1.1会有什么问题呢?

假设一个网页需要加载几十个资源(css、js、jpg、等等),等到html文件加载成功后,浏览器会一个一个请求这些资源,并等待服务器按顺序一个一个返回。这将会非常耗时。

与HTTP/1.1标准比较,HTTP/2带来很多功能,如:

bidirectional streaming

flow control

header compression

multiplexing requests over a single TCP connection

在此不做详解,还不清楚的同学自行Google,推荐一些入门链接

http://www.ruanyifeng.com/blog/2016/08/http.html

https://imququ.com/post/protocol-negotiation-in-http2.html

3. HTTP/2局限性

gRPC源码分析0-导读

如上图,gRPC离真正可工程化的rpc框架还有一段路要走,缺的组件也很多,如

  1. Configuration(配置化)
  2. Service Discovery(服务发现)
  3. 服务治理等等

也就是目前gRPC想用到微服务后端,需要自己开发很多东西。

4. 使用样例

  • 下载gRPC源码

git clone git@github.com:grpc/grpc-java.git

gRPC支持了很多平台,当然我们讲解的是Java版本,目录结构如下图:

gRPC源码分析0-导读

 

  • 编译

首先我们先不编译grpc code generation plugin(主要用于proto3从.proto文件编译出Java文件的,一般不用修改)。在根目录下新建gradle.properties文件,然后添加skipCodegen=true这一行到文件中。

grpc-java has a C++ code generation plugin for protoc. Since many Java developers don't have C compilers installed and don't need to modify the codegen, the build can skip it. To skip, create the file <project-root>/gradle.properties and add skipCodegen=true.

Java、maven版本如下

Java版本需要1.8

maven 3.2

 

  • 编译代码

./gradlew build

  • 安装编译好的jar包到本地maven库

./gradlew install

  • 样例

先建立maven项目,定义服务.proto文件

 

在此默认大家对proto的语法已经熟悉,至少是可以使用的程度。借用Google官方的例子。

syntax = "proto3";

option java_multiple_files = true;
// 生产的Java的包
option java_package = "io.grpc.examples.helloworld.generated";
// 生产的Java类名
option java_outer_classname = "HelloWorldProto";
option objc_class_prefix = "HLW";

package helloworld;

// service 定义服务
service Greeter {
 // 服务的一个方法
 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;
}

添加依赖到pom.xml文件,使用刚才install的版本1.1.0-SNAPSHOT,build里的插件是用来由proto文件生产Java源码用的

gRPC源码分析0-导读

在测试项目文件夹下,生产Java代码

$ mvn compile

生产的代码在target下,将其拷贝到自己的项目里

gRPC源码分析0-导读

  • 编写测试代码,借用Google官方代码,懒得写了。

Server 

public class HelloWorldServer {
  private static final Logger logger = Logger.getLogger(HelloWorldServer.class.getName());

  private Server server;

  private void start() throws IOException {
    /* The port on which the server should run */
    int port = 50051;
    server = ServerBuilder.forPort(port)
        .addService(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();
  }

  static class GreeterImpl extends GreeterGrpc.GreeterImplBase {

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

Client

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) {
    this(ManagedChannelBuilder.forAddress(host, port)
        // Channels are secure by default (via SSL/TLS). For the example we disable TLS to avoid
        // needing certificates.
        .usePlaintext(true));
  }

  /** Construct client for accessing RouteGuide server using the existing channel. */
  HelloWorldClient(ManagedChannelBuilder<?> channelBuilder) {
    channel = channelBuilder.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();
    }
  }
}

如上可以看到,用gRPC编写服务是非常简单的。几行代码搞定。

源码分析导读

gRPC的代码与dubbo、rocketmq相比,还是很少的,主要是因为目前很多组件还没有。后面将会根据以下内容来讲解源码

  • 通信

  • 消息编解码

  • steam流

  • 框架

附录

gRPC 官方文档中文版

  • https://doc.oschina.net/grpc

GRPC的产生动机和设计原则

  • http://www.jianshu.com/p/8cc077f6dbb9

gRPC学习笔记

  • https://skyao.gitbooks.io/leaning-grpc/content/ 

gRPC源码分析0-导读