netty 解決TCP粘包與拆包問題(一)

1.什么是TCP粘包與拆包

首先TCP是一個"流"協議，猶如河中水一樣連成一片，沒有嚴格的分界線。當我們在發送數據的時候就會出現多發送與少發送問題，也就是TCP粘包與拆包。得不到我們想要的效果。

所謂粘包：當你把A，B兩個數據從甲發送到乙，本想A與B單獨發送，但是你卻把AB一起發送了，此時AB粘在一起，就是粘包了

所謂拆包: 如果發送數據的時候，你把A、B拆成了幾份發，就是拆包了。當然數據不是你主動拆的，是TCP流自動拆的

 

2.TCP粘包與拆包產生原因

1.進行了MSS大小的TCP分段
2.以太網幀的plyload大與MTU進行了IP分片
3.應用程序write寫入的字節大小大於套接口發送的緩沖區大小

 

3.解決方法

1.消息定長，比如把報文消息固定為500字節，不夠用空格補位

2.在包尾增加回車換行符進行分割，例如FTP協議

3.將消息分為消息頭和消息體，消息頭中包含表示消息總長度的字段

4.更復雜的應用層協議

 

4.netty 普通解決方法

 

這個是服務端代碼

package com.ming.netty.nio;

import java.net.InetSocketAddress;

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 TimeServer {
    
    
    public static void main(String[] args) throws Exception{
        new TimeServer().bind("192.168.1.102", 8400);
    }
    

    public void bind(String addr,int port) {
        //配置服務端的nio線程組
        EventLoopGroup boosGroup=new NioEventLoopGroup();
        EventLoopGroup workerGroup=new NioEventLoopGroup();
        try {
            ServerBootstrap b=new ServerBootstrap();
            b.group(boosGroup,workerGroup);
            b.channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG,1024)
            .childHandler(new ChildChannelHandler());
            //綁定端口，同步等待成功
            ChannelFuture f=b.bind(new InetSocketAddress(addr, port)).sync();
            System.out.println("啟動服務器:"+f.channel().localAddress());
            //等等服務器端監聽端口關閉
            f.channel().closeFuture().sync();
        } catch (Exception e) {
            // TODO: handle exception
        }finally{
            boosGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
    
    private class ChildChannelHandler extends ChannelInitializer<SocketChannel>{

        @Override
        protected void initChannel(SocketChannel ch) throws Exception {
            System.out.println(ch.remoteAddress());
            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
            ch.pipeline().addLast(new StringDecoder());//增加解碼器
            ch.pipeline().addLast(new TimeServerHandler());
            
        }
        
    }
    
    
}
package com.ming.netty.nio;

import java.nio.ByteBuffer;
import java.text.SimpleDateFormat;
import java.util.Date;

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

public class TimeServerHandler extends ChannelHandlerAdapter {

    private int counter;
    
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String body=(String)msg;
        System.out.println("服務端收到："+body+"，次數:"+ ++counter);
        SimpleDateFormat  dateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String time=dateFormat.format(new Date());
        String res="來自與服務端的回應,時間:"+ time;
        ByteBuf resp=Unpooled.copiedBuffer(res.getBytes());
        ctx.writeAndFlush(resp);
        
    }

    

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.close();
    }

    

    
}

 

這個是客服端的代碼

package com.ming.netty.nio;

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;

/**
 * netty 客戶端模擬
 * @author mingge
 *
 */
public class TimeClient {
    
    
    public static void main(String[] args) throws Exception{
        new TimeClient().connect("192.168.1.102", 8400);
    }

    public void connect(String addr,int port) 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>() {
                public void initChannel(SocketChannel ch) throws Exception{
                    ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
                    ch.pipeline().addLast(new StringDecoder());
                    ch.pipeline().addLast(new TimeClientHandler());
                }
            });
            ChannelFuture f=b.connect(addr,port).sync();
            System.out.println("連接服務器:"+f.channel().remoteAddress()+",本地地址:"+f.channel().localAddress());
            f.channel().closeFuture().sync();//等待客戶端關閉連接
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            
            group.shutdownGracefully();
        }
    }
}
package com.ming.netty.nio;

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

public class TimeClientHandler extends ChannelHandlerAdapter {
    
    private int counter;
    
    byte[] req;
    
    public TimeClientHandler() {
        req=("我是請求數據哦"+System.getProperty("line.separator")).getBytes();
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        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 {
        ByteBuf buf=(ByteBuf)msg;
        byte[] req=new byte[buf.readableBytes()];
        buf.readBytes(req);
        String body=new String(req,"GBK");
        System.out.println("body:"+body+",響應次數:"+(++counter));
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        //釋放資源
        ctx.close();
    }

    
}

 

這次代碼就是比上次的代碼多了：LineBasedFrameDecoder,與StringDecoder的寫法.

LineBasedFrameDecoder的原理是它依次遍歷ByteBuf中的可讀字節，判斷是否有"\n"或"\r\n",如果有就以此為結束。它是以換行符為結束標志的解碼器

StringDecoder的原理就是將接收到的對象轉換為字符串，然后接着調用后面的handler。

LineBasedFrameDecoder+StringDecoder組合就是設計按行切換的文本解碼器，被設計來支持TCP的粘包與拆包

 

當然，我們還可以用其余的分隔符來做，詳情看下篇。覺得還行點個贊吧

 

生活就是拿來受虐的......