Netty中使用MessagePack时的TCP粘包问题与解决方案
通过下面的实例代码来演示在Netty中使用MessagPack时会出现的TCP粘包问题，为了学习的连贯性，参考了《Netty权威指南》第7章中的代码，但是需要注意的是，书中并没有提供完整代码，提供的代码都是片段性的，所以我根据自己的理解把服务端的代码和客户端的代码写了出来，可以作为参考。
仍然需要注意的是，我使用的是Netty 4.x的版本。
另外我在程序代码中写了非常详细的注释，所以这里不再进行更多的说明。
在使用MessagePack时的TCP粘包问题
编码器与解码器
MsgpackEncoder.java
package cn.xpleaf.msgpack;import org.msgpack.MessagePack;import io.netty.buffer.ByteBuf;import io.netty.channel.ChannelHandlerContext;import io.netty.handler.codec.MessageToByteEncoder;/** * MsgpackEncoder继承自Netty中的MessageToByteEncoder类， * 并重写抽象方法encode(ChannelHandlerContext ctx, Object msg, ByteBuf out) * 它负责将Object类型的POJO对象编码为byte数组，然后写入到ByteBuf中 * @author yeyonghao * */public class MsgpackEncoder extends MessageToByteEncoder<Object> { ???@Override ???protected void encode(ChannelHandlerContext ctx, Object msg, ByteBuf out) throws Exception { ???????// 创建MessagePack对象 ???????MessagePack msgpack = new MessagePack(); ???????// 将对象编码为MessagePack格式的字节数组 ???????byte[] raw = msgpack.write(msg); ???????// 将字节数组写入到ByteBuf中 ???????out.writeBytes(raw); ???}}MsgpackDecoder.java
package cn.xpleaf.msgpack;import java.util.List;import org.msgpack.MessagePack;import io.netty.buffer.ByteBuf;import io.netty.channel.ChannelHandlerContext;import io.netty.handler.codec.ByteToMessageDecoder;import io.netty.handler.codec.MessageToMessageDecoder;/** * MsgpackDecoder继承自Netty中的MessageToMessageDecoder类， * 并重写抽象方法decode(ChannelHandlerContext ctx, ByteBuf msg, List<Object> out) * 首先从数据报msg（数据类型取决于继承MessageToMessageDecoder时填写的泛型类型）中获取需要解码的byte数组 * 然后调用MessagePack的read方法将其反序列化（解码）为Object对象 * 将解码后的对象加入到解码列表out中，这样就完成了MessagePack的解码操作 * @author yeyonghao * */public class MsgpackDecoder extends MessageToMessageDecoder<ByteBuf> { ???@Override ???protected void decode(ChannelHandlerContext ctx, ByteBuf msg, List<Object> out) throws Exception { ???????// 从数据报msg中（这里的数据类型为ByteBuf，因为Netty的通信基于ByteBuf对象） ???????final byte[] array; ???????final int length = msg.readableBytes(); ???????array = new byte[length]; ???????/** ????????* 这里使用的是ByteBuf的getBytes方法来将ByteBuf对象转换为字节数组，前面是使用readBytes，直接传入一个接收的字节数组参数即可 ????????* 这里的参数比较多，第一个参数是index，关于readerIndex，说明如下： ????????* ByteBuf是通过readerIndex跟writerIndex两个位置指针来协助缓冲区的读写操作的，具体原理等到Netty源码分析时再详细学习一下 ????????* 第二个参数是接收的字节数组 ????????* 第三个参数是dstIndex the first index of the destination ????????* 第四个参数是length ??the number of bytes to transfer ????????*/ ???????msg.getBytes(msg.readerIndex(), array, 0, length); ???????// 创建一个MessagePack对象 ???????MessagePack msgpack = new MessagePack(); ???????// 解码并添加到解码列表out中 ???????out.add(msgpack.read(array)); ???}}服务端
EchoServer.java
package cn.xpleaf.echo;import cn.demo.simple.MsgPackDecode;import cn.xpleaf.msgpack.MsgpackDecoder;import cn.xpleaf.msgpack.MsgpackEncoder;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 EchoServer { ???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 ChannelInitializer<SocketChannel>() { ???????????????????@Override ???????????????????protected void initChannel(SocketChannel ch) throws Exception { ???????????????????????// 添加MesspagePack解码器 ???????????????????????ch.pipeline().addLast("msgpack decoder", new MsgPackDecode()); ???????????????????????// 添加MessagePack编码器 ???????????????????????ch.pipeline().addLast("msgpack encoder", new MsgpackEncoder()); ???????????????????????// 添加业务处理handler ???????????????????????ch.pipeline().addLast(new EchoServerHandler()); ???????????????????} ???????????????}); ???????????// 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(); ???????} ???} ???public static void main(String[] args) throws Exception { ???????int port = 8080; ???????if(args != null && args.length > 0) { ???????????try { ???????????????port = Integer.valueOf(port); ???????????} catch (NumberFormatException e) { ???????????????// TODO: handle exception ???????????} ???????} ???????new EchoServer().bind(port); ???}}EchoServerHandler.java
package cn.xpleaf.echo;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.ChannelInboundHandlerAdapter;public class EchoServerHandler extends ChannelInboundHandlerAdapter { ???@Override ???public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ???????System.out.println("Server receive the msgpack message : " + msg); ???????ctx.write(msg); ???} ???@Override ???public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ???????ctx.flush(); ???} ???@Override ???public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { ???????// 发生异常，关闭链路 ???????ctx.close(); ???}}客户端
EchoClient.java
package cn.xpleaf.echo;import cn.demo.simple.MsgPackDecode;import cn.xpleaf.msgpack.MsgpackDecoder;import cn.xpleaf.msgpack.MsgpackEncoder;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 EchoClient { ???public void connect(String host, int port, int sendNumber) 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) ???????????????// 设置TCP连接超时时间 ???????????????.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 3000) ???????????????.handler(new ChannelInitializer<SocketChannel>() { ???????????????????@Override ???????????????????protected void initChannel(SocketChannel ch) throws Exception { ???????????????????????// 添加MesspagePack解码器 ???????????????????????ch.pipeline().addLast("msgpack decoder", new MsgPackDecode()); ???????????????????????// 添加MessagePack编码器 ???????????????????????ch.pipeline().addLast("msgpack encoder", new MsgpackEncoder()); ???????????????????????// 添加业务处理handler ???????????????????????ch.pipeline().addLast(new EchoClientHandler(sendNumber)); ???????????????????} ???????????????}); ???????????// 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; ???????if(args != null && args.length > 0) { ???????????try { ???????????????port = Integer.valueOf(port); ???????????} catch (NumberFormatException e) { ???????????????// 采用默认值 ???????????} ???????} ???????int sendNumber = 1000; ???????new EchoClient().connect("localhost", port, sendNumber); ???}}EchoClientHander.java
package cn.xpleaf.echo;import cn.xpleaf.pojo.User;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.ChannelInboundHandlerAdapter;public class EchoClientHandler extends ChannelInboundHandlerAdapter { ???// sendNumber为写入发送缓冲区的对象数量 ???private int sendNumber; ???public EchoClientHandler(int sendNumber) { ???????this.sendNumber = sendNumber; ???} ???/** ????* 构建长度为userNum的User对象数组 ????* @param userNum ????* @return ????*/ ???private User[] getUserArray(int userNum) { ???????User[] users = new User[userNum]; ???????User user = null; ???????for(int i = 0; i < userNum; i++) { ???????????user = new User(); ???????????user.setName("ABCDEFG --->" + i); ???????????user.setAge(i); ???????????users[i] = user; ???????} ???????return users; ???} ???@Override ???public void channelActive(ChannelHandlerContext ctx) { ???????User[] users = getUserArray(sendNumber); ???????for (User user : users) { ???????????ctx.writeAndFlush(user); ???????} ???} ???@Override ???public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ???????System.out.println("Client receive the msgpack message : " + msg); ???} ???@Override ???public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ???????ctx.flush(); ???} ???@Override ???public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { ???????ctx.close(); ???}}POJO
User.java
package cn.xpleaf.pojo;import org.msgpack.annotation.Message;@Messagepublic class User { ???private String name; ???private int age; ???public String getName() { ???????return name; ???} ???public void setName(String name) { ???????this.name = name; ???} ???public int getAge() { ???????return age; ???} ???public void setAge(int age) { ???????this.age = age; ???} ???@Override ???public String toString() { ???????return "User [name=" + name + ", age=" + age + "]"; ???}}测试
当EchoClient.java中的sendNumber为1时，服务端和客户端都是正常工作的，此时，服务端和客户端的输出分别如下：
服务端：
Server receive the msgpack message : ["ABCDEFG --->0",0]客户端：
Client receive the msgpack message : ["ABCDEFG --->0",0]但是当sendNumber数字很大时，就不能正常工作了，比如可以设置为1000，此时输出结果如下：
服务端：
Server receive the msgpack message : ["ABCDEFG --->0",0]Server receive the msgpack message : ["ABCDEFG --->1",1]Server receive the msgpack message : ["ABCDEFG --->3",3]...省略输出...Server receive the msgpack message : ["ABCDEFG --->146",146]Server receive the msgpack message : 70Server receive the msgpack message : ["ABCDEFG --->156",156]Server receive the msgpack message : ["ABCDEFG --->157",157]...省略输出...客户端：
Client receive the msgpack message : ["ABCDEFG --->0",0]Client receive the msgpack message : 62Client receive the msgpack message : 68显然运行结果跟预期的不太一样，这是因为出现了TCP粘包问题。
粘包问题解决方案
在前面代码的基础上，只需要对EchoServer.java和EchoClient.java中的代码进行修改即可。
EchoServer.java
package cn.xpleaf.echo02;import cn.demo.simple.MsgPackDecode;import cn.xpleaf.msgpack.MsgpackDecoder;import cn.xpleaf.msgpack.MsgpackEncoder;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.LengthFieldBasedFrameDecoder;import io.netty.handler.codec.LengthFieldPrepender;public class EchoServer { ???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 ChannelInitializer<SocketChannel>() { ???????????????????@Override ???????????????????protected void initChannel(SocketChannel ch) throws Exception { ???????????????????????// 添加长度字段解码器 ???????????????????????// 在MessagePack解码器之前增加LengthFieldBasedFrameDecoder，用于处理半包消息 ???????????????????????// 它会解析消息头部的长度字段信息，这样后面的MsgpackDecoder接收到的永远是整包消息 ???????????????????????ch.pipeline().addLast("frameDecoder", new LengthFieldBasedFrameDecoder(65535, 0, 2, 0, 2)); ???????????????????????// 添加MesspagePack解码器 ???????????????????????ch.pipeline().addLast("msgpack decoder", new MsgPackDecode()); ???????????????????????// 添加长度字段编码器 ???????????????????????// 在MessagePack编码器之前增加LengthFieldPrepender，它将在ByteBuf之前增加2个字节的消息长度字段 ???????????????????????ch.pipeline().addLast("frameEncoder", new LengthFieldPrepender(2)); ???????????????????????// 添加MessagePack编码器 ???????????????????????ch.pipeline().addLast("msgpack encoder", new MsgpackEncoder()); ???????????????????????// 添加业务处理handler ???????????????????????ch.pipeline().addLast(new EchoServerHandler()); ???????????????????} ???????????????}); ???????????// 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(); ???????} ???} ???public static void main(String[] args) throws Exception { ???????int port = 8080; ???????if(args != null && args.length > 0) { ???????????try { ???????????????port = Integer.valueOf(port); ???????????} catch (NumberFormatException e) { ???????????????// TODO: handle exception ???????????} ???????} ???????new EchoServer().bind(port); ???}}EchoClient.java
package cn.xpleaf.echo02;import cn.demo.simple.MsgPackDecode;import cn.xpleaf.msgpack.MsgpackDecoder;import cn.xpleaf.msgpack.MsgpackEncoder;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.LengthFieldBasedFrameDecoder;import io.netty.handler.codec.LengthFieldPrepender;public class EchoClient { ???public void connect(String host, int port, int sendNumber) 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) ???????????????// 设置TCP连接超时时间 ???????????????.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 3000) ???????????????.handler(new ChannelInitializer<SocketChannel>() { ???????????????????@Override ???????????????????protected void initChannel(SocketChannel ch) throws Exception { ???????????????????????// 添加长度字段解码器 ???????????????????????// 在MessagePack解码器之前增加LengthFieldBasedFrameDecoder，用于处理半包消息 ???????????????????????// 它会解析消息头部的长度字段信息，这样后面的MsgpackDecoder接收到的永远是整包消息 ???????????????????????ch.pipeline().addLast("frameDecoder", new LengthFieldBasedFrameDecoder(65535, 0, 2, 0, 2)); ???????????????????????// 添加MesspagePack解码器 ???????????????????????ch.pipeline().addLast("msgpack decoder", new MsgPackDecode()); ???????????????????????// 添加长度字段编码器 ???????????????????????// 在MessagePack编码器之前增加LengthFieldPrepender，它将在ByteBuf之前增加2个字节的消息长度字段 ???????????????????????ch.pipeline().addLast("frameEncoder", new LengthFieldPrepender(2)); ???????????????????????// 添加MessagePack编码器 ???????????????????????ch.pipeline().addLast("msgpack encoder", new MsgpackEncoder()); ???????????????????????// 添加业务处理handler ???????????????????????ch.pipeline().addLast(new EchoClientHandler(sendNumber)); ???????????????????} ???????????????}); ???????????// 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; ???????if(args != null && args.length > 0) { ???????????try { ???????????????port = Integer.valueOf(port); ???????????} catch (NumberFormatException e) { ???????????????// 采用默认值 ???????????} ???????} ???????int sendNumber = 1000; ???????new EchoClient().connect("localhost", port, sendNumber); ???}}测试
可以将EchoClient.java中sendNumber设置为1000或更大，此时服务端和客户端的输出结果跟预期的都是一样的。
测试结果为，服务端和客户端都会打印1000行的信息（假设sendNumber为1000），这里不再给出运行结果。
Netty中使用MessagePack时的TCP粘包问题与解决方案
原文地址：http://blog.51cto.com/xpleaf/2071688