Netty——TCP粘包和拆包原理

摘要

TCP是面向连接的，面向流的，提供高可靠性服务。收发两端（客户端和服务器端)都要有——成对的socket，因此，发送端为了将多个发给接收端的包，更有效的发给对方，使用了优化方法(Nagle算法），将多次间隔较小且数据量小的数据，合并成一个大的数据块，然后进行封包。这样做虽然提高了效率，但是接收端就难于分辨出完整的数据包了，因为面向流的通信是无消息保护边界的。由于TCP无消息保护边界，需要在接收端处理消息边界问题，也就是我们所说的粘包、拆包问题。

粘包、拆包原理

假设客户端分别发送了两个数据包D1和D2给服务端，由于服务端一次读取到字节数是不确定的，故可能存在以下四种情况:

1)服务端分两次读取到了两个独立的数据包，分别是D1和D2，没有粘包和拆包
2)服务端一次接受到了两个数据包，D1和D2粘合在一起，称之为TCP粘包
3)服务端分两次读取到了数据包,第一次读,取到了完整的D1包和D2包的部分内容，第二次读取到了D2包的剩余内容，这称之为TCP拆包
4)服务端分两次读取到了数据包,第一次读,取到了D1包的部分内容D1_1，第二次读取到了D1包的剩余部分内容D1_2和完整的D2包。

粘包、拆包实战 server端

MyServer.java

package com.zhuangxiaoyan.netty.tcp;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;


public class MyServer {
    public static void main(String[] args) throws Exception {

        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {

            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).childHandler(new MyServerInitializer()); //自定义一个初始化类

            ChannelFuture channelFuture = serverBootstrap.bind(7000).sync();
            channelFuture.channel().closeFuture().sync();

        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }

    }
}

MyServerInitializer.java

package com.zhuangxiaoyan.netty.tcp;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;


public class MyServerInitializer extends ChannelInitializer {

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        pipeline.addLast(new MyServerHandler());
    }
}

MyServerHandler.java

package com.zhuangxiaoyan.netty.tcp;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.UUID;


public class MyServerHandler extends SimpleChannelInboundHandler {
    private int count;

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        //cause.printStackTrace();
        ctx.close();
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {

        byte[] buffer = new byte[msg.readableBytes()];
        msg.readBytes(buffer);

        //将buffer转成字符串
        String message = new String(buffer, StandardCharsets.UTF_8);

        System.out.println("服务器接收到数据 " + message);
        System.out.println("服务器接收到消息量=" + (++this.count));

        //服务器回送数据给客户端, 回送一个随机id ,
        ByteBuf responseByteBuf = Unpooled.copiedBuffer(UUID.randomUUID().toString() + " ", StandardCharsets.UTF_8);
        ctx.writeAndFlush(responseByteBuf);

    }
}

Client端

MyClient.java

package com.zhuangxiaoyan.netty.tcp;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;


public class MyClient {
    public static void main(String[] args) throws Exception {

        EventLoopGroup group = new NioEventLoopGroup();

        try {

            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group).channel(NioSocketChannel.class)
                    .handler(new MyClientInitializer()); //自定义一个初始化类

            ChannelFuture channelFuture = bootstrap.connect("localhost", 7000).sync();

            channelFuture.channel().closeFuture().sync();

        } finally {
            group.shutdownGracefully();
        }
    }
}

MyClientInitializer.java

package com.zhuangxiaoyan.netty.tcp;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;


public class MyClientInitializer extends ChannelInitializer {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {

        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast(new MyClientHandler());
    }
}

MyClientHandler.java

package com.zhuangxiaoyan.netty.tcp;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;


public class MyClientHandler extends SimpleChannelInboundHandler {

    private int count;

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        //使用客户端发送10条数据 hello,server 编号
        for (int i = 0; i < 10; ++i) {
            ByteBuf buffer = Unpooled.copiedBuffer("hello,server " + i, StandardCharsets.UTF_8);
            ctx.writeAndFlush(buffer);
        }
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
        byte[] buffer = new byte[msg.readableBytes()];
        msg.readBytes(buffer);

        String message = new String(buffer, StandardCharsets.UTF_8);
        System.out.println("客户端接收到消息=" + message);
        System.out.println("客户端接收消息数量=" + (++this.count));

    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

粘包、拆包解决方案

解决方法一：TCP提供了强制数据立即传送的操作指令push，TCP软件收到该操作指令后，就立即将本段数据发送出去，而不必等待发送缓冲区满；
解决方法二：发送固定长度的消息
解决方法三：把消息的尺寸与消息一块发送
解决方法四：双方约定每次传送的大小
解决方法五：双方约定使用特殊标记来区分消息间隔
解决方法六：标准协议按协议规则处理，如Sip协议

粘包、拆包解决方案实战 Server端

Myserver.java

package com.zhuangxiaoyan.netty.protocoltcp;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;


public class MyServer {
    public static void main(String[] args) throws Exception {

        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {

            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).childHandler(new MyServerInitializer()); //自定义一个初始化类

            ChannelFuture channelFuture = serverBootstrap.bind(7000).sync();
            channelFuture.channel().closeFuture().sync();

        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }

    }
}

MyServerInitializer.java

package com.zhuangxiaoyan.netty.protocoltcp;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;


public class MyServerInitializer extends ChannelInitializer {

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        pipeline.addLast(new MyMessageDecoder());//解码器
        pipeline.addLast(new MyMessageEncoder());//编码器
        pipeline.addLast(new MyServerHandler());
    }
}

MyServerHandler.java

package com.zhuangxiaoyan.netty.protocoltcp;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.nio.charset.Charset;
import java.util.UUID;


//处理业务的handler
public class MyServerHandler extends SimpleChannelInboundHandler {
    private int count;

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        //cause.printStackTrace();
        ctx.close();
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, MessageProtocol msg) throws Exception {

        //接收到数据，并处理
        int len = msg.getLen();
        byte[] content = msg.getContent();

        System.out.println();
        System.out.println();
        System.out.println();
        System.out.println("服务器接收到信息如下");
        System.out.println("长度=" + len);
        System.out.println("内容=" + new String(content, Charset.forName("utf-8")));

        System.out.println("服务器接收到消息包数量=" + (++this.count));

        //回复消息

        String responseContent = UUID.randomUUID().toString();
        int responseLen = responseContent.getBytes("utf-8").length;
        byte[] responseContent2 = responseContent.getBytes("utf-8");
        //构建一个协议包
        MessageProtocol messageProtocol = new MessageProtocol();
        messageProtocol.setLen(responseLen);
        messageProtocol.setContent(responseContent2);

        ctx.writeAndFlush(messageProtocol);

    }
}

Client端

MessageProtocol.java

package com.zhuangxiaoyan.netty.protocoltcp;


//协议包
public class MessageProtocol {
    private int len; //关键
    private byte[] content;

    public int getLen() {
        return len;
    }

    public void setLen(int len) {
        this.len = len;
    }

    public byte[] getContent() {
        return content;
    }

    public void setContent(byte[] content) {
        this.content = content;
    }
}

Myclient.java

package com.zhuangxiaoyan.netty.protocoltcp;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;


public class MyClient {
    public static void main(String[] args) throws Exception {

        EventLoopGroup group = new NioEventLoopGroup();

        try {

            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group).channel(NioSocketChannel.class)
                    .handler(new MyClientInitializer()); //自定义一个初始化类

            ChannelFuture channelFuture = bootstrap.connect("localhost", 7000).sync();

            channelFuture.channel().closeFuture().sync();

        } finally {
            group.shutdownGracefully();
        }
    }
}

MyClientInitializer.java

package com.zhuangxiaoyan.netty.protocoltcp;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;


public class MyClientInitializer extends ChannelInitializer {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {

        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast(new MyMessageEncoder()); //加入编码器
        pipeline.addLast(new MyMessageDecoder()); //加入解码器
        pipeline.addLast(new MyClientHandler());
    }
}

MyClientHandler.java

package com.zhuangxiaoyan.netty.protocoltcp;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.nio.charset.Charset;


public class MyClientHandler extends SimpleChannelInboundHandler {

    private int count;

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        //使用客户端发送10条数据 "今天天气冷，吃火锅" 编号

        for (int i = 0; i < 5; i++) {
            String mes = "今天天气冷，吃火锅";
            byte[] content = mes.getBytes(Charset.forName("utf-8"));
            int length = mes.getBytes(Charset.forName("utf-8")).length;

            //创建协议包对象
            MessageProtocol messageProtocol = new MessageProtocol();
            messageProtocol.setLen(length);
            messageProtocol.setContent(content);
            ctx.writeAndFlush(messageProtocol);

        }

    }

    //    @Override
    protected void channelRead0(ChannelHandlerContext ctx, MessageProtocol msg) throws Exception {

        int len = msg.getLen();
        byte[] content = msg.getContent();

        System.out.println("客户端接收到消息如下");
        System.out.println("长度=" + len);
        System.out.println("内容=" + new String(content, Charset.forName("utf-8")));

        System.out.println("客户端接收消息数量=" + (++this.count));

    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println("异常消息=" + cause.getMessage());
        ctx.close();
    }
}

编码器与解码器

MyMessageDecoder.java

package com.zhuangxiaoyan.netty.protocoltcp;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ReplayingDecoder;

import java.util.List;


public class MyMessageDecoder extends ReplayingDecoder {
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List

Netty——TCP粘包和拆包原理

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