Netty粘包/拆包（一）

￡神魔★判官ぃ 2022-05-12 15:20 257阅读 0赞

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（最大报文长度）大小的TCP分段(TCP报文长度-TCP头部长度>MSS的时候将发生拆包)；

3.以太网帧的payload大于MTU(最大数据包大小)进行IP分片。

![70][]

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();
        }
    }

![70 1][]

![70 2][]

![70 3][]

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();
        }
    }

![70 4][]

![70 5][]

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。

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