学习netty遇到的关于 LineBasedFrameDecoder 的问题

最近在看《Netty权威指南》这本书，关于TCP粘包/拆包，书中使用的是 LineBasedFrameDecoder 来解决的，但是我在实践的过程中出现了问题，上代码吧。

这个是 server 的代码

package com.cd.netty4.zhc.demo.ex01;

import java.text.SimpleDateFormat;

import java.util.Date;

import io.netty.bootstrap.ServerBootstrap;

import io.netty.buffer.ByteBuf;

import io.netty.buffer.Unpooled;

import io.netty.channel.ChannelFuture;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelInboundHandlerAdapter;

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;

import io.netty.util.CharsetUtil;

/**

 * 本例子参考《Netty权威指南（第2版）》第4章

 * 先运行 TimeServerExc02，然后运行 TimeClientExc02，可解决 TCP 粘包/拆包问题

 * 使用 LineBasedFrameDecoder + StringDecoder 解决 TCP 粘包/拆包问题

 * */

public class TimeServerExc02 {

    public static void main(String args[]) {

        System.out.println("---------------------- server 测试开始 ---------------------");

        new TimeServerExc02().bind("127.0.0.1", 1234);

        System.out.println("---------------------- server 测试end ---------------------");

    }

    public void bind(String host, int port) {

        EventLoopGroup bossGroup = new NioEventLoopGroup();

        EventLoopGroup workerGroup = new NioEventLoopGroup();

        ServerBootstrap serboot = new ServerBootstrap().group(bossGroup, workerGroup)

                .channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG, 1024)

                .childHandler(new ChannelInitializer<SocketChannel>() {

                    @Override

                    protected void initChannel(SocketChannel arg0) throws Exception {

                        arg0.pipeline().addLast(new LineBasedFrameDecoder(1024));

                        arg0.pipeline().addLast("decoder", new StringDecoder());

                        arg0.pipeline().addLast("handler", new TimeServerHandlerExc02());

                    }

                });

        try {

            // 绑定端口，同步等待成功

            ChannelFuture future = serboot.bind(host, port).sync();

            // 等待服务端监听端口关闭

            future.channel().closeFuture().sync();

        } catch (InterruptedException e) {

            e.printStackTrace();

        } finally {

            bossGroup.shutdownGracefully();

            workerGroup.shutdownGracefully();

        }

    }

}

class TimeServerHandlerExc02 extends ChannelInboundHandlerAdapter {

    @Override

    public void channelActive(ChannelHandlerContext ctx) throws Exception {

        System.out.println("server channelActive(有client连接上了)..");

        ctx.writeAndFlush(Unpooled.copiedBuffer("您已经成功连接上了 server!", CharsetUtil.UTF_8)); // 必须有flush

    }

    @Override

    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

        System.out.println("server channelRead..");

        String msgStr = msg.toString();

        System.out.println("读入client消息:" + msgStr);

        String currentTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());

        ByteBuf resp = Unpooled.copiedBuffer(currentTime, CharsetUtil.UTF_8);

        ctx.writeAndFlush(resp);

        System.out.println("向client发送消息:" + currentTime);

    }

    @Override

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

        cause.printStackTrace();

        ctx.close();

    }

}

这个是client的代码：

package com.cd.netty4.zhc.demo.ex01;

import io.netty.bootstrap.Bootstrap;

import io.netty.buffer.Unpooled;

import io.netty.channel.ChannelFuture;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelInboundHandlerAdapter;

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;

import io.netty.util.CharsetUtil;

/**

 * 本例子参考《Netty权威指南（第2版）》第4.2章

 * */

public class TimeClientExc02 {

    public static void main(String[] args) {

        try {

            System.out.println("---------------------- client 测试开始 ---------------------");

            new TimeClientExc02().connect("127.0.0.1", 1234);

            System.out.println("---------------------- client 测试end ---------------------");

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

    }

    private int count;

    public void connect(String host, int port) throws InterruptedException {

        EventLoopGroup group = new NioEventLoopGroup();

        try {

            Bootstrap boot = new Bootstrap().group(group).channel(NioSocketChannel.class)

                    .option(ChannelOption.TCP_NODELAY, true).handler(new ChannelInitializer<SocketChannel>() {

                        @Override

                        protected void initChannel(SocketChannel ch) throws Exception {

                            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));

                            ch.pipeline().addLast("decoder", new StringDecoder());

                            ch.pipeline().addLast(new TimeClientHandlerExc02());

                        }

                    });

            ChannelFuture future = boot.connect(host, port);

            // 等待客户端链路关闭

            future.channel().closeFuture().sync();

        } finally {

            // 优雅的退出，释放NIO线程组

            group.shutdownGracefully();

        }

    }

    class TimeClientHandlerExc02 extends ChannelInboundHandlerAdapter {

        @Override

        public void channelActive(ChannelHandlerContext ctx) throws Exception {

            System.out.println("client channelActive(client 连接成功)..");

            for (int i = 0; i < 50; i++) {

                System.out.print(i + ",");

                ctx.writeAndFlush(

                        Unpooled.copiedBuffer("It's a good day , I want to know time--" + i , CharsetUtil.UTF_8)); // 必须有flush

            }

            ctx.flush();

        }

        @Override

        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

            System.out.println("client channelRead.." + ++count);

            String msgStr = msg.toString();

            System.out.println("读入 server 消息:" + msgStr);

        }

        @Override

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

            cause.printStackTrace();

            ctx.close();

        }

    }

}

我先运行的是server，然后是client，发现 server 的 channelActive(..) 以及 client 的 channelActive(..) 都有运行到，但是后续的 channelRead(..) 方法却迟迟没有运行到，我把 LineBasedFrameDecoder 和 StringDecoder 这两个解码器去掉，则代码正常，但是会有 TCP 粘包/拆包问题。

在网上查了问题原因，无果，认真看了两遍书，发现 LineBasedFrameDecoder 的工作原理是“ 它依次遍历ByteBuf中的可读字节，判断看是否有‘\n’或者‘\r\n’，如果有，就在此位置为结束位置，从可读索引到结束位置区间的字节就组成了一行 ”。

所以，我的问题就出在消息结尾处没有加上换行符，修改代码后，可运行。修改后代码如下：

package com.cd.netty4.zhc.demo.ex01;

import java.text.SimpleDateFormat;

import java.util.Date;

import io.netty.bootstrap.ServerBootstrap;

import io.netty.buffer.ByteBuf;

import io.netty.buffer.Unpooled;

import io.netty.channel.ChannelFuture;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelInboundHandlerAdapter;

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;

import io.netty.util.CharsetUtil;

/**

 * 本例子参考《Netty权威指南（第2版）》第4章

 * 先运行 TimeServerExc02，然后运行 TimeClientExc02，可解决 TCP 粘包/拆包问题

 * 使用 LineBasedFrameDecoder + StringDecoder 解决 TCP 粘包/拆包问题

 * 注意：使用 LineBasedFrameDecoder时，发送的消息结尾一定要是\n（官方是 System.getProperty("line.separator")），server端 和 client 都必须如此

 * 因为LineBasedFrameDecoder 的工作原理是，依次遍历Bytebuf中的可读字节，判断是否有“\n”或者“\r\n”，如果有则在此位置结束

 * */

public class TimeServerExc02 {

    public static void main(String args[]) {

        System.out.println("---------------------- server 测试开始 ---------------------");

        new TimeServerExc02().bind("127.0.0.1", 1234);

        System.out.println("---------------------- server 测试end ---------------------");

    }

    public void bind(String host, int port) {

        EventLoopGroup bossGroup = new NioEventLoopGroup();

        EventLoopGroup workerGroup = new NioEventLoopGroup();

        ServerBootstrap serboot = new ServerBootstrap().group(bossGroup, workerGroup)

                .channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG, 1024)

                .childHandler(new ChannelInitializer<SocketChannel>() {

                    @Override

                    protected void initChannel(SocketChannel arg0) throws Exception {

                        arg0.pipeline().addLast(new LineBasedFrameDecoder(1024));

                        arg0.pipeline().addLast("decoder", new StringDecoder());

                        arg0.pipeline().addLast("handler", new TimeServerHandlerExc02());

                    }

                });

        try {

            // 绑定端口，同步等待成功

            ChannelFuture future = serboot.bind(host, port).sync();

            // 等待服务端监听端口关闭

            future.channel().closeFuture().sync();

        } catch (InterruptedException e) {

            e.printStackTrace();

        } finally {

            bossGroup.shutdownGracefully();

            workerGroup.shutdownGracefully();

        }

    }

}

class TimeServerHandlerExc02 extends ChannelInboundHandlerAdapter {

    @Override

    public void channelActive(ChannelHandlerContext ctx) throws Exception {

        System.out.println("server channelActive(有client连接上了)..");

        ctx.writeAndFlush(Unpooled.copiedBuffer("您已经成功连接上了 server!", CharsetUtil.UTF_8)); // 必须有flush

    }

    @Override

    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

        System.out.println("server channelRead..");

        String msgStr = msg.toString();

        System.out.println("读入client消息:" + msgStr);

        String currentTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());

        ByteBuf resp = Unpooled.copiedBuffer(currentTime + System.getProperty("line.separator"), CharsetUtil.UTF_8);

        ctx.writeAndFlush(resp);

        System.out.println("向client发送消息:" + currentTime);

    }

    @Override

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

        cause.printStackTrace();

        ctx.close();

    }

}

package com.cd.netty4.zhc.demo.ex01;

import io.netty.bootstrap.Bootstrap;

import io.netty.buffer.Unpooled;

import io.netty.channel.ChannelFuture;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelInboundHandlerAdapter;

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;

import io.netty.util.CharsetUtil;

/**

 * 本例子参考《Netty权威指南（第2版）》第4.2章

 * 注意：使用 LineBasedFrameDecoder时，发送的消息结尾一定要是\n（官方是 System.getProperty("line.separator")），server端 和 client 都必须如此

 * 因为LineBasedFrameDecoder 的工作原理是，依次遍历Bytebuf中的可读字节，判断是否有“\n”或者“\r\n”，如果有则在此位置结束

 * */

public class TimeClientExc02 {

    public static void main(String[] args) {

        try {

            System.out.println("---------------------- client 测试开始 ---------------------");

            new TimeClientExc02().connect("127.0.0.1", 1234);

            System.out.println("---------------------- client 测试end ---------------------");

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

    }

    private int count;

    public void connect(String host, int port) throws InterruptedException {

        EventLoopGroup group = new NioEventLoopGroup();

        try {

            Bootstrap boot = new Bootstrap().group(group).channel(NioSocketChannel.class)

                    .option(ChannelOption.TCP_NODELAY, true).handler(new ChannelInitializer<SocketChannel>() {

                        @Override

                        protected void initChannel(SocketChannel ch) throws Exception {

                            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));

                            ch.pipeline().addLast("decoder", new StringDecoder());

                            ch.pipeline().addLast(new TimeClientHandlerExc02());

                        }

                    });

            ChannelFuture future = boot.connect(host, port);

            // 等待客户端链路关闭

            future.channel().closeFuture().sync();

        } finally {

            // 优雅的退出，释放NIO线程组

            group.shutdownGracefully();

        }

    }

    class TimeClientHandlerExc02 extends ChannelInboundHandlerAdapter {

        @Override

        public void channelActive(ChannelHandlerContext ctx) throws Exception {

            System.out.println("client channelActive(client 连接成功)..");

            for (int i = 0; i < 50; i++) {

                System.out.print(i + ",");

                ctx.writeAndFlush(

                        Unpooled.copiedBuffer("It's a good day , I want to know time--" + i + "\n", CharsetUtil.UTF_8)); // 必须有flush

            }

            ctx.flush();

        }

        @Override

        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

            System.out.println("client channelRead.." + ++count);

            String msgStr = msg.toString();

            System.out.println("读入 server 消息:" + msgStr);

        }

        @Override

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

            cause.printStackTrace();

            ctx.close();

        }

    }

}

查看了 LineBasedFrameDecoder 的部分源码，确实是以换行作为分割符的。

巴特西

学习netty遇到的关于 LineBasedFrameDecoder 的问题

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