Netty粘包/拆包（一）

版权声明：版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/qq_37598011/article/details/83317161

TCP出现粘包拆包原因有三个：

1.应用程序write写入的字节大小大于套接口发送缓冲区大小；

2.进行MSS大小的TCP分段；

3.以太网帧的payload大于MTU进行IP分片。

粘包的解决方案：

1.消息定长，例如每个报文的大小为固定长度200字节，如果不够，空格补空格；

2.在包尾增加回车换行符进行分割，例如FTP协议；

3.将消息分为消息头和消息体，消息头中包含表示消息总长度（或者消息体长度）的字段，通常设计思路为消息头的第一个字段使用int32来表示消息的总长度；

4.更复杂的应用层协议。

首先使用未加Netty的半包解码器来看粘包拆包问题：

import io.netty.bootstrap.Bootstrap;
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.NioSocketChannel;

public class TimeClient {

    public void connect(int port, String host) throws Exception {
        // 配置客户端NIO线程组
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel arg0)
                                throws Exception {
                            System.out.println("客户端启动..");
                            arg0.pipeline().addLast(new TimeClientHandler());
                        }
                    });
            // 发起异步连接操作
            ChannelFuture f = b.connect(host, port).sync();
            // 等待客户端链路关闭
            f.channel().closeFuture().sync();
        } finally {
            // 优雅退出，释放NIO线程组
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;
        new TimeClient().connect(port, "127.0.0.1");
    }
}

import java.util.logging.Logger;

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

public class TimeClientHandler extends ChannelInboundHandlerAdapter {

    private static final Logger logger = Logger
            .getLogger(com.netty2.TimeClientHandler2.class.getName());

    private int counter;

    private byte[] req;

    public TimeClientHandler() {
        req = "QUERY TIME ORDER".getBytes();
//        firstMessage = Unpooled.buffer(req.length);
//        firstMessage.writeBytes(req);
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        //与服务端建立连接后
        System.out.println("客户端 channelActive..");
        ByteBuf message=null;
        for (int i=0;i<100;i++){
            message=Unpooled.buffer(req.length);
            message.writeBytes(req);
            ctx.writeAndFlush(message);
        }
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg)
            throws Exception {
        System.out.println("客户端 channelRead..");
        //服务端返回消息后
        ByteBuf buf = (ByteBuf) msg;
        byte[] req = new byte[buf.readableBytes()];
        buf.readBytes(req);
        String body = new String(req, "UTF-8");
        System.out.println("当前时间 :" + body +" 次数:"+ (++counter));
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
            throws Exception {
        System.out.println("客户端异常..");
        // 释放资源
        logger.warning("Unexpected exception from downstream:"
                + cause.getMessage());
        ctx.close();
    }

}

import io.netty.bootstrap.ServerBootstrap;
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;

public class TimeServer {

    public void bind(int port) throws Exception {
        //配置服务端的NIO线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .childHandler(new ChildChannelHandler());

            // 绑定端口，同步等待成功
            ChannelFuture f=b.bind(port).sync();

            //等待服务端监听端口关闭
            f.channel().closeFuture().sync();
        } finally {
            //退出，释放线程池资源
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    private class ChildChannelHandler extends ChannelInitializer<SocketChannel>{

        protected void initChannel(SocketChannel ch) throws Exception {
            System.out.println("服务端启动……");
            ch.pipeline().addLast(new TimeServerHandler());
        }
    }

    public static void main(String[] args) throws Exception {
        int port=8080;
        new TimeServer().bind(port);
    }
}

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

import java.util.Date;

public class TimeServerHandler extends ChannelInboundHandlerAdapter {

    private int counter;

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg)
            throws Exception {
        System.out.println("服务器启动..");
        ByteBuf buf = (ByteBuf) msg;
        byte[] req = new byte[buf.readableBytes()];
        buf.readBytes(req);
        String body = new String(req, "UTF-8");
        System.out.println("服务器接收数据:" + body+" 次数:"+ (++counter));
        String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(
                System.currentTimeMillis()).toString() : "BAD ORDER";
        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.writeAndFlush(resp);
    }
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        System.out.println("服务器读取完毕..");
        ctx.flush();//刷新后才将数据发出到SocketChannel
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
            throws Exception {
        System.out.println("服务器异常..");
        ctx.close();
    }
}

可以看到它服务端和客户端只接收到了两次。

利用LineBasedFrameDecoder解决TCP粘包问题

import io.netty.bootstrap.Bootstrap;
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.NioSocketChannel;
import io.netty.handler.codec.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;

public class TimeClient2 {

    public void connect(int port, String host) throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();

            b.group(group)
                    .channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new TimeClientHandler2());
                        }
                    });

            // 发起异步连接操作
            ChannelFuture f = b.connect(host, port).sync();
            // 等待客户端连接关闭
            f.channel().closeFuture().sync();
        } finally {
            // 优雅退出，释放NIO线程组
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8082;
        new TimeClient2().connect(port, "127.0.0.1");
    }
}

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

import java.util.logging.Logger;

public class TimeClientHandler2 extends ChannelInboundHandlerAdapter {

    private static final Logger logger = Logger
            .getLogger(TimeClientHandler2.class.getName());

    private int counter;

    private byte[] req;

    public TimeClientHandler2() {
        req = ("QUERY TIME ORDER" + System.getProperty("line.separator")).getBytes();
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx){
        //与服务端建立连接后
        System.out.println("客户端 channelActive..");
        ByteBuf message=null;
        for (int i=0;i<100;i++){
            message=Unpooled.buffer(req.length);
            message.writeBytes(req);
            ctx.writeAndFlush(message);
        }
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        System.out.println("客户端 channelRead..");
        //服务端返回消息后
        String body = (String) msg;
        System.out.println("当前时间 :" + body + " 次数:" + (++counter));
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
            throws Exception {
        System.out.println("客户端异常..");
        // 释放资源
        logger.warning("Unexpected exception from downstream:"
                + cause.getMessage());
        ctx.close();
    }

}

import io.netty.bootstrap.ServerBootstrap;
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.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;

public class TimeServer2 {

    public void bind(int port) throws Exception {
        // NIO线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .childHandler(new ChildChannelHandler());

            // 绑定端口，同步等待成功
            ChannelFuture f = b.bind(port).sync();
            // 等待服务端监听端口关闭
            f.channel().closeFuture().sync();
        } finally {
            // 优雅退出，释放线程池资源
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    private class ChildChannelHandler extends ChannelInitializer<SocketChannel> {
        @Override
        protected void initChannel(SocketChannel arg0) throws Exception {
            arg0.pipeline().addLast(new LineBasedFrameDecoder(1024));
            arg0.pipeline().addLast(new StringDecoder());
            arg0.pipeline().addLast(new TimeServerHandler2());
        }
    }

    public static void main(String[] args) throws Exception {
        int port=8082;
        new TimeServer2().bind(port);
    }
}

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

import java.util.Date;

public class TimeServerHandler2 extends ChannelInboundHandlerAdapter {

    private int counter;

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg){
        System.out.println("服务器启动..");
        String body = (String) msg;
        System.out.println("服务器接收数据:" + body+" 次数:"+ (++counter));
        String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(
                System.currentTimeMillis()).toString() : "BAD ORDER";
        if(counter%2==0)
            currentTime = currentTime + System.getProperty("line.separator");
        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.writeAndFlush(resp);
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        System.out.println("服务器读取完毕..");
        ctx.flush();//刷新后才将数据发出到SocketChannel
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        System.out.println("服务器异常..");
        ctx.close();
    }
}

    LineBasedFrameDecoder的工作原理是它依次遍历ByteBuf中可读字节，判断看是否有“\n”或者“\r\n”，如果有就以此位置为结束位置，从可读索引到结束位置区间的字节就组成了一行。它是以换行符为结束标志的解码器，支持携带结束符或者不携带结束符两种解码方式，同时支持配置单行的最大长度。如果连续读取到最大长度后任然没有发现换行符就会抛出异常，同时忽略之前读取到的异常码流。

    StringDecoder的功能非常简单，就是将接收到的对象转换成字符串，然后继续调用后面的Handler。LineBasedFrameDecoder+StringDecoder组合就是按行切换的文本解码器，他被设计用来支持TCP的粘包和拆包。