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Netty中使用MessagePack时的TCP粘包问题与解决方案

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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;

@Message
public 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 : 70
Server 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 : 62
Client 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.javaEchoClient.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.javasendNumber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

标签:private   pri   delay   read   complete   bcd   资源   tina   object   

原文:http://blog.51cto.com/xpleaf/2071688

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