手撸一个RPC

Posted 2021-07-17 Coder Club

RPC 全名为Remote Process Call，也就是远程过程调用，与本地过程调用相对，RPC应用多为分布式场景，简单的理解是一个节点请求另一个节点提供的服务。gRPC是Google公司开源的RPC框架，腾讯后台使用的RPC框架之一是tRPC，本节我们先来了解RPC的基本工作过程，采用Java语言实现。有关tRPC的相关内容，可参看CSDN腾讯技术工程：https://blog.csdn.net/Tencent_TEG/article/details/118686900?spm=1001.2014.3001.5501

RPC工作流程

RPC的工作流程可以用下图来概括：

img

1. Client通知Server欲调用的函数，并将函数映射为对应的 Call ID
2. Client向Server传参，与本地过程调用传参直接压栈不同，这里需要Client通过网络通信将调用参数转化为Byte流传给Server，Server再从Byte流中转化为自身能识别的格式，这其实就是序列化和反序列化的过程
3. Server处理后返回结果给Client，上述所有的C-S通信过程均采用TCP传输层和应用层完成

手撸一个RPC demo

序列化接口

首先定义一个序列化接口，

import java.io.Serializable;

/**
 * 空接口，实现序列化接口
 */
public interface IRpcService extends Serializable { }

定义远程调用接口及其实现类

/**
 * 远程调用的接口
 */
public interface IHelloService extends IRpcService {

    String sayHi(String name, String message);

}

/**
 * 实现空接口 IHelloService
 */
public class HelloServiceImpl implements IHelloService {

    private static final long serialVersionUID = 146468468464164698L;

    @Override
    public String sayHi(String name, String message) {
        return new StringBuilder().append(name).append(", ").append(message).toString();
    }

}

定义Server接口

import java.io.IOException;

public interface Server {

    int PORT = 8080;

    void start() throws IOException;

    void stop();

    void register(Class<? extends IRpcService> serviceInterface, Class<? extends IRpcService> impl);

}

定义服务中心

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Method;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class ServerCenter implements Server {

    private static ThreadPoolExecutor executor =
            new ThreadPoolExecutor(
                    5,
                    20,
                    200,
                    TimeUnit.MILLISECONDS,
                    new ArrayBlockingQueue<>(10));

    private static final Map<String, Class<?>> serviceRegistry = new HashMap<>();

    @Override
    public void start() throws IOException {
        ServerSocket server = new ServerSocket();
        server.bind(new InetSocketAddress(PORT));
        try {
            while (true) {
                executor.execute(new ServiceTask(server.accept()));
            }
        } finally {
            server.close();
        }
    }

    @Override
    public void stop() {
        executor.shutdown();
    }

    @Override
    public void register(Class<? extends IRpcService> serviceInterface, Class<? extends IRpcService> impl) {
        serviceRegistry.put(serviceInterface.getName(), impl);
    }

    private static class ServiceTask implements Runnable {

        Socket client = null;

        public ServiceTask(Socket client) {
            this.client = client;
        }

        @Override
        public void run() {
            ObjectInputStream input = null;
            ObjectOutputStream output = null;

            try {
                input = new ObjectInputStream(client.getInputStream());
                String serviceName = input.readUTF();
                String methodName = input.readUTF();
                Class<?>[] param = (Class<?>[]) input.readObject();
                Object[] arg = (Object[]) input.readObject();
                Class<?> serviceClass = serviceRegistry.get(serviceName);
                if (serviceClass == null) {
                    throw new ClassNotFoundException(serviceName + " not found");
                }
                Method method = serviceClass.getMethod(methodName, param);
                Object result = method.invoke(serviceClass.newInstance(), arg);
                output = new ObjectOutputStream(client.getOutputStream());
                output.writeObject(result);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                if (input != null) {
                    try {
                        input.close();
                    } catch(IOException e) {
                        e.printStackTrace();
                    }
                }
                if (output != null) {
                    try {
                        output.close();
                    } catch(IOException e) {
                        e.printStackTrace();
                    }
                }
                if (client != null) {
                    try {
                        client.close();
                    } catch(IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }

    public static void main(String[] args) throws Exception {
        ServerCenter center = new ServerCenter();
        center.register(IHelloService.class, new HelloServiceImpl().getClass());
        center.start();
    }

}

定义Client

import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.net.InetSocketAddress;
import java.net.Socket;

public class Client {

    @SuppressWarnings("unchecked")
    public static <T extends IRpcService> T getRemoteProxyObj(final Class<? extends IRpcService> serviceInterface, final InetSocketAddress addr) {
        return (T) Proxy.newProxyInstance(serviceInterface.getClassLoader(), new Class<?>[]{serviceInterface}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                Socket socket = null;
                ObjectInputStream input = null;
                ObjectOutputStream output = null;
                try {
                    socket = new Socket();
                    socket.connect(addr);
                    output = new ObjectOutputStream(socket.getOutputStream());
                    output.writeUTF(serviceInterface.getName());
                    output.writeUTF(method.getName());
                    output.writeObject(method.getParameterTypes());
                    output.writeObject(args);
                    input = new ObjectInputStream(socket.getInputStream());
                    return input.readObject();
                } catch(Exception e) {
                    e.printStackTrace();
                } finally {
                    if (socket != null) {
                        socket.close();
                    }
                    if (output != null) {
                        output.close();
                    }
                    if (input != null) {
                        input.close();
                    }
                }
                return null;
            }
        });
    }

}

测试

import java.net.InetSocketAddress;

public class RpcTest {

    public static void main(String[] args) {
        IHelloService service = Client.getRemoteProxyObj(IHelloService.class, new InetSocketAddress(8080));
        System.out.println(service.sayHi("Hello", "RPC"));
    }

}