九、TCP粘包和拆包及解决方案

9.1、TCP粘包和拆包基本介绍

  1. 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)都要有一一成对的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辩出完整的数据包了,因为面向流的通信是无消息保护边界的。

  2. 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、

  3. TCP粘包、拆包示意图

九、TCP粘包和拆包及解决方案_第1张图片

ps: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. 读取两个独立的数据包,分别是D1和D2,没有粘包和拆包
  2. 一次性接收两个数据包,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1次,读取完整的D1包和D2包的部分内容,第二次读取到了D2包的剩余部分,这就是TCP拆包
  4. 服务端分两次读取带了数据包,第1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。

9.2、TCP粘包和拆包现象实例

​ 编写Netty程序时,如果没有做处理,就会发生粘包和拆包的问题

package com.feng.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 InterruptedException {
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup,workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new MyServerHandler());
            ChannelFuture channelFuture = serverBootstrap.bind(7000).sync();
            channelFuture.channel().closeFuture().sync();
        }finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

package com.feng.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.util.UUID;

public class MyServerHandler extends SimpleChannelInboundHandler<ByteBuf> {
    private  int count;

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        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, Charset.forName("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,回送一个数据id,
        ByteBuf responseByteBuf = Unpooled.copiedBuffer(UUID.randomUUID().toString()+" ",Charset.forName("utf-8"));
        ctx.writeAndFlush(responseByteBuf);
    }
}

package com.feng.netty.tcp;

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

public class MyServerInitializer extends ChannelInitializer<SocketChannel> {

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

package com.feng.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 InterruptedException {

        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();
        }
    }
}

package com.feng.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;

public class MyClientHandler extends SimpleChannelInboundHandler<ByteBuf> {

    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, Charset.forName("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, Charset.forName("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();
    }
}

package com.feng.netty.tcp;

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

public class MyClientInitializer extends ChannelInitializer<SocketChannel> {

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

9.3、TCP粘包和拆包解决方案

  1. 使用自定义协议+编码器来解决
  2. 关键就是要解决服务器每次读取数据长度的问题,这个问题解决,就不会出现服务器多读或少读数据的问题,从而避免的TCP粘包、拆包

9.4、具体实例

  1. 要求客户端发送5个Message,客户端每次发送一个Message对象

  2. 服务器端每次接收一个Message,分5次解码。每读取到一个Message,会回复一个Message对象给客户端

九、TCP粘包和拆包及解决方案_第2张图片

  1. 代码演示

    package com.feng.netty.protocoltcp;
    
    //协议包
    public class MessageProtocol {
        private int len;//关键字
        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;
        }
    }
    
    
    package com.feng.netty.protocoltcp;
    
    import io.netty.buffer.ByteBuf;
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.handler.codec.MessageToByteEncoder;
    
    public class MyMessageEncoder extends MessageToByteEncoder<MessageProtocol> {
        @Override
        protected void encode(ChannelHandlerContext channelHandlerContext, MessageProtocol msg, ByteBuf out) throws Exception {
            System.out.println("MyMessageEncoder encode 方法被调用");
            out.writeInt(msg.getLen());
            out.writeBytes(msg.getContent());
        }
    }
    
    
    package com.feng.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<Void> {
    
        @Override
        protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
            System.out.println("MyMessageDecoder decode 被调用");
            //需要将得到二进制字节码-> MessageProtocol数据包(对象)
            int length = in.readInt();
            byte[] content = new byte[length];
            in.readBytes(content);
            //封装成MessageProtocol对象。放入out。传递下一个handler业务处理
            MessageProtocol messageProtocol = new MessageProtocol();
            messageProtocol.setLen(length);
            messageProtocol.setContent(content);
            out.add(messageProtocol);
        }
    }
    
    
    package com.feng.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) {
            EventLoopGroup bossGroup = new NioEventLoopGroup(1);
            EventLoopGroup workGroup = new NioEventLoopGroup();
            try {
                ServerBootstrap serverBootstrap = new ServerBootstrap();
                serverBootstrap.group(bossGroup,workGroup)
                        .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();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                bossGroup.shutdownGracefully();
                workGroup.shutdownGracefully();
            }
        }
    }
    
    
    package com.feng.netty.protocoltcp;
    
    import io.netty.channel.ChannelInitializer;
    import io.netty.channel.ChannelPipeline;
    import io.netty.channel.socket.SocketChannel;
    
    public class MyServerInitializer extends ChannelInitializer<SocketChannel> {
    
        @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());
        }
    }
    
    
    package com.feng.netty.protocoltcp;
    
    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<MessageProtocol> {
    
        private int count;
        //处理业务的handler
        @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("内存="+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(Charset.forName("utf-8")).length;
            byte[] responseContent2 = responseContent.getBytes(Charset.forName("utf-8"));
            //构建一个协议包
            MessageProtocol messageProtocol = new MessageProtocol();
            messageProtocol.setLen(responseLen);
            messageProtocol.setContent(responseContent2);
            ctx.writeAndFlush(messageProtocol);
        }
    
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            ctx.close();
        }
    }
    
    
    package com.feng.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 InterruptedException {
    
            EventLoopGroup group = new NioEventLoopGroup();
            try {
                Bootstrap bootstrap = new Bootstrap();
                bootstrap.group(group)
                        .channel(NioSocketChannel.class)
                        .handler(new MyClientInitializer());
                ChannelFuture channelFuture = bootstrap.connect("localhost", 7000).sync();
                channelFuture.channel().closeFuture().sync();
            }finally {
                group.shutdownGracefully();
            }
        }
    }
    
    
    package com.feng.netty.protocoltcp;
    
    import io.netty.channel.ChannelInitializer;
    import io.netty.channel.ChannelPipeline;
    import io.netty.channel.socket.SocketChannel;
    
    public class MyClientInitializer extends ChannelInitializer<SocketChannel> {
    
        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());
        }
    }
    
    
    package com.feng.netty.protocoltcp;
    
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.channel.SimpleChannelInboundHandler;
    import java.nio.charset.Charset;
    
    
    public class MyClientHandler extends SimpleChannelInboundHandler<MessageProtocol> {
        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();
        }
    }
    
    

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