netty解决TCP的拆包和粘包的解决办法

TCP粘包、拆包问题

熟悉tcp编程的可能知道，无论是服务端还是客户端，当我们读取或者发送数据的时候，都需要考虑TCP底层的粘包个拆包机制。
tcp是一个“流”协议，所谓流就是没有界限的传输数据，在业务上，一个完整的包可能会被TCP分成多个包进行发送，也可能把多个小包封装成一个大的数据包发送出去，这就是所谓的tcp粘包、拆包问题。
分析TCP粘包拆包问题的产生原因：
1. 应用程序write写入的字节大于套接口缓冲区的大小
2. 进行mss大小的TCP分段
3. 以太网的payload大于MTU进行IP分片
粘包拆包问题，根据业界主流协议，有三种主要方案：
1. 消息定长，例如每个报文的大小固定200个字节，如果不够，空位补空格
2. 在包尾部增加特殊字符进行分割，例如加回车等
3. 将消息分为消息头和消息体，在消息头中包含表示消息总长度的字段，然后进行业务逻辑的处理。

TCP粘包拆包之分隔符类 DellmiterBasedFrameDecoder(自定义分隔符)

代码在bhz.netty.ende1下
Server端

package com.weiyuan.test;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

public class Server {

    public static void main(String[] args) throws Exception{
        //1 创建2个线程，一个是负责接收客户端的连接。一个是负责进行数据传输的
        EventLoopGroup pGroup = new NioEventLoopGroup();
        EventLoopGroup cGroup = new NioEventLoopGroup();

        //2 创建服务器辅助类
        ServerBootstrap b = new ServerBootstrap();
        b.group(pGroup, cGroup)
         .channel(NioServerSocketChannel.class)
         .option(ChannelOption.SO_BACKLOG, 1024)
         .option(ChannelOption.SO_SNDBUF, 32*1024)
         .option(ChannelOption.SO_RCVBUF, 32*1024)
         .childHandler(new ChannelInitializer<SocketChannel>() {
            @Override
            protected void initChannel(SocketChannel sc) throws Exception {
                //设置特殊分隔符
                ByteBuf buf = Unpooled.copiedBuffer("$_".getBytes());
                sc.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, buf));
                //设置字符串形式的解码
                sc.pipeline().addLast(new StringDecoder());
                sc.pipeline().addLast(new ServerHandler());
            }
        });

        //4 绑定连接
        ChannelFuture cf = b.bind(8765).sync();

        //等待服务器监听端口关闭
        cf.channel().closeFuture().sync();
        pGroup.shutdownGracefully();
        cGroup.shutdownGracefully();

    }

}

ServerHandle端

package com.weiyuan.test;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;

public class ServerHandler extends ChannelHandlerAdapter {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println(" server channel active... ");
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String request = (String)msg;
        System.out.println("Server :" + msg);
        String response = "服务器响应：" + msg + "$_";
        ctx.writeAndFlush(Unpooled.copiedBuffer(response.getBytes()));
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {

    }

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

}

Client端

package com.weiyuan.test;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
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.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

public class Client {

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

        EventLoopGroup group = new NioEventLoopGroup();

        Bootstrap b = new Bootstrap();
        b.group(group)
         .channel(NioSocketChannel.class)
         .handler(new ChannelInitializer<SocketChannel>() {
            @Override
            protected void initChannel(SocketChannel sc) throws Exception {
                //
                ByteBuf buf = Unpooled.copiedBuffer("$_".getBytes());
                sc.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, buf));
                sc.pipeline().addLast(new StringDecoder());
                sc.pipeline().addLast(new ClientHandler());
            }
        });

        ChannelFuture cf = b.connect("127.0.0.1", 8765).sync();

        cf.channel().writeAndFlush(Unpooled.wrappedBuffer("bbbb$_".getBytes()));
        cf.channel().writeAndFlush(Unpooled.wrappedBuffer("cccc$_".getBytes()));

        //等待客户端端口关闭
        cf.channel().closeFuture().sync();
        group.shutdownGracefully();

    }
}

ClientHandle端

package com.weiyuan.test;

import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
import io.netty.util.ReferenceCountUtil;

public class ClientHandler extends ChannelHandlerAdapter{

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("client channel active... ");
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        try {
            String response = (String)msg;
            System.out.println("Client: " + response);
        } finally {
            ReferenceCountUtil.release(msg);
        }
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
    }

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

}

先启动Server端，再启动Client端 
Client端输出

client channel active...
Client: 服务器响应：bbbb
Client: 服务器响应：cccc

server端输出

server channel active...
Server :bbbb
Server :cccc

TCP粘包拆包之FixedLengthFrameDecoder(定长)

和上面的代码类似 
Server端

package com.weiyuan.test;

import java.nio.ByteBuffer;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

public class Server {

    public static void main(String[] args) throws Exception{
        //1 创建2个线程，一个是负责接收客户端的连接。一个是负责进行数据传输的
        EventLoopGroup pGroup = new NioEventLoopGroup();
        EventLoopGroup cGroup = new NioEventLoopGroup();

        //2 创建服务器辅助类
        ServerBootstrap b = new ServerBootstrap();
        b.group(pGroup, cGroup)
         .channel(NioServerSocketChannel.class)
         .option(ChannelOption.SO_BACKLOG, 1024)
         .option(ChannelOption.SO_SNDBUF, 32*1024)
         .option(ChannelOption.SO_RCVBUF, 32*1024)
         .childHandler(new ChannelInitializer<SocketChannel>() {
            @Override
            protected void initChannel(SocketChannel sc) throws Exception {
                //设置定长字符串接收
                sc.pipeline().addLast(new FixedLengthFrameDecoder(5));
                //设置字符串形式的解码
                sc.pipeline().addLast(new StringDecoder());
                sc.pipeline().addLast(new ServerHandler());
            }
        });

        //4 绑定连接
        ChannelFuture cf = b.bind(8765).sync();

        //等待服务器监听端口关闭
        cf.channel().closeFuture().sync();
        pGroup.shutdownGracefully();
        cGroup.shutdownGracefully();

    }

}

ServerHandler

package com.weiyuan.test;

import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;

public class ServerHandler extends ChannelHandlerAdapter {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println(" server channel active... ");
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String request = (String)msg;
        System.out.println("Server rcv :" + msg);
        String response =  request ;
        ctx.writeAndFlush(Unpooled.copiedBuffer(response.getBytes()));
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {

    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable t) throws Exception {

    }

}

client端

package com.weiyuan.test;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
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.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

public class Client {

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

        EventLoopGroup group = new NioEventLoopGroup();

        Bootstrap b = new Bootstrap();
        b.group(group)
         .channel(NioSocketChannel.class)
         .handler(new ChannelInitializer<SocketChannel>() {
            @Override
            protected void initChannel(SocketChannel sc) throws Exception {
                sc.pipeline().addLast(new FixedLengthFrameDecoder(5));
                sc.pipeline().addLast(new StringDecoder());
                sc.pipeline().addLast(new ClientHandler());
            }
        });

        ChannelFuture cf = b.connect("127.0.0.1", 8765).sync();

        cf.channel().writeAndFlush(Unpooled.wrappedBuffer("aaaaabbbbb".getBytes()));
        cf.channel().writeAndFlush(Unpooled.copiedBuffer("ccccccc".getBytes()));

        //等待客户端端口关闭
        cf.channel().closeFuture().sync();
        group.shutdownGracefully();

    }
}

ClientHandler端

package com.weiyuan.test;

import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;

public class ClientHandler extends ChannelHandlerAdapter{

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("client channel active... ");
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String response = (String)msg;
        System.out.println("Client: " + response);
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
    }

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

}

先运行Server端，再运行Client端 
Client端输出

client channel active...
Client: aaaaa
Client: bbbbb
Client: ccccc

server端输出

server channel active...
Server rcv :aaaaa
Server rcv :bbbbb
Server rcv :ccccc

可以看到，每次定长都是5个字符， 有两个cc，由于不够五个，导致丢掉了

自定义协议粘包拆包

使用消息头和消息体， 暂未记录笔记。 TODO zhaikaishun

特别感谢互联网架构师白鹤翔老师，本文大多出自他的视频讲解。 
笔者主要是记录笔记，以便之后翻阅，正所谓好记性不如烂笔头，烂笔头不如云笔记