Netty系列（5）Netty中解决TCP粘包和拆包

2023-12-25 22:04:28

文章目录

1 TCP 粘包和拆包介绍
2 Netty 粘包演示
3 Netty中解决TCP粘包和拆包

1 TCP 粘包和拆包介绍

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
TCP 粘包、拆包图解

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：

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
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
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
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，这称之为 TCP 拆包。

2 Netty 粘包演示

服务端代码

package com.warybee.tcp;

import com.warybee.simple.NettyServerHandler;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;

/**
 */
public class MyServer {

    public static void main(String[] args) {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap bootstrap=new ServerBootstrap();
            bootstrap.group(bossGroup,workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG,128)
                    .childOption(ChannelOption.SO_KEEPALIVE,true)
                    .childHandler(new ChannelInitializer<SocketChannel>() {

                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new MyServerHandler());
                        }
                    });
            ChannelFuture channelFuture = bootstrap.bind(9999).sync();
            channelFuture.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

服务端handler

package com.warybee.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
    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, 回送一个随机id ,
        ByteBuf responseByteBuf = Unpooled.copiedBuffer(UUID.randomUUID().toString() + "\n",
                Charset.forName("utf-8"));
        ctx.writeAndFlush(responseByteBuf);
    }

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

服务端的 handler 主要逻辑是接收客户端发送过来的数据，看看是否是一条一条接收。然后每次接收到数据之后给客户端回复一个确认消息。

客户端

package com.warybee.tcp;

import com.warybee.simple.NettyClientHandler;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

/**
 * @description
 */
public class MyClient {

    public static void main(String[] args) {
        EventLoopGroup eventExecutors = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();

            bootstrap.group(eventExecutors)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            pipeline.addLast(new StringDecoder());
                            pipeline.addLast(new StringEncoder());
                            pipeline.addLast(new MyClientHandler());
                        }
                    });
            ChannelFuture cf = bootstrap.connect("127.0.0.1", 9999).sync();
            cf.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            eventExecutors.shutdownGracefully();
        }
    }
}

客户端Handler

package com.warybee.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;

/**
 * @author joy
 * @create 2021-10-27 14:50
 * @description
 */
public class MyClientHandler extends SimpleChannelInboundHandler<ByteBuf> {

    private int count;
    @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 channelActive(ChannelHandlerContext ctx) throws Exception {
        for (int i = 0; i < 20; ++i) {
            ByteBuf buffer = Unpooled.copiedBuffer("你好服务端：" + i+"rn", Charset.forName("utf-8"));
            ctx.writeAndFlush(buffer);
        }
    }
}

客户端 handler 主要逻辑是：循环20次给服务端发送测试消息。接收服务端的确认消息

启动项目之后服务端收到的消息结果：

这里能看到多条消息被粘到一起发送了。

3 Netty中解决TCP粘包和拆包

使用自定义协议+编解码器来解决。关键就是要解决服务器端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。

自定义消息协议

package com.warybee.tcp;

/**
 * @description 自定义协议包
 */
public class MessageProtocol {
    //消息长度
    private int len;
    /**
     * 消息
     */
    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;
    }
}

自定义编码器

package com.warybee.tcp;

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

/**
 * @description 自定义协议包编码
 */
public class MyMessageEncoder extends MessageToByteEncoder<MessageProtocol> {
    @Override
    protected void encode(ChannelHandlerContext ctx, MessageProtocol msg, ByteBuf out) throws Exception {
        out.writeInt(msg.getLen());
        out.writeBytes(msg.getContent());
    }
}

自定义解码器

package com.warybee.tcp;

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

import java.util.List;

/**
 * @description
 */
public class MyMessageDecoder extends ReplayingDecoder<Void> {

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        //需要将得到二进制字节码转化为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);
    }
}

服务端代码

package com.warybee.tcp;

import com.warybee.simple.NettyServerHandler;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;

/**
 * @author joy
 */
public class MyServer {

    public static void main(String[] args) {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap bootstrap=new ServerBootstrap();
            bootstrap.group(bossGroup,workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG,128)
                    .childOption(ChannelOption.SO_KEEPALIVE,true)
                    .childHandler(new ChannelInitializer<SocketChannel>() {

                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            //添加自定义编码器
                            pipeline.addLast("encoder",new MyMessageEncoder());
                            //添加自定义解码器
                            pipeline.addLast("decoder",new MyMessageDecoder());
                            pipeline.addLast(new MyServerHandler());
                        }
                    });
            ChannelFuture channelFuture = bootstrap.bind(9999).sync();
            channelFuture.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

服务端handler

package com.warybee.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;

/**
 * @description
 */
public class MyServerHandler extends SimpleChannelInboundHandler<MessageProtocol> {

    private int count;

    @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);
    }

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

服务端的 handler 主要逻辑是接收客户端发送过来的数据，看看是否是一条一条接收。然后每次接收到数据之后给客户端回复一个确认消息。**

客户端handler

package com.warybee.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;

/**
 * @author joy
 * @create 2021-10-27 14:50
 * @description
 */
public class MyClientHandler extends SimpleChannelInboundHandler<MessageProtocol> {

    private int count;
    @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 channelActive(ChannelHandlerContext ctx) throws Exception {
        //使用客户端发送5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);
        }
    }
}

码农公寓

文章目录

1 TCP 粘包和拆包介绍

2 Netty 粘包演示

3 Netty中解决TCP粘包和拆包

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