netty 解决TCP粘包与拆包问题(一)

1.什么是TCP粘包与拆包

首先TCP是一个"流"协议，犹如河中水一样连成一片，没有严格的分界线。当我们在发送数据的时候就会出现多发送与少发送问题，也就是TCP粘包与拆包。得不到我们想要的效果。

所谓粘包：当你把A，B两个数据从甲发送到乙，本想A与B单独发送，但是你却把AB一起发送了，此时AB粘在一起，就是粘包了

所谓拆包: 如果发送数据的时候，你把A、B拆成了几份发，就是拆包了。当然数据不是你主动拆的，是TCP流自动拆的

2.TCP粘包与拆包产生原因

1.进行了MSS大小的TCP分段
2.以太网帧的plyload大与MTU进行了IP分片
3.应用程序write写入的字节大小大于套接口发送的缓冲区大小

3.解决方法

1.消息定长，比如把报文消息固定为500字节，不够用空格补位

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的字段

4.更复杂的应用层协议

4.netty 普通解决方法

这个是服务端代码

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) {
//配置服务端的nio线程组
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());
//绑定端口，同步等待成功
ChannelFuture f=b.bind(new InetSocketAddress(addr, port)).sync();
System.out.println("启动服务器:"+f.channel().localAddress());
//等等服务器端监听端口关闭
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());//增加解码器
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("服务端收到："+body+"，次数:"+ ++counter);
SimpleDateFormat  dateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String time=dateFormat.format(new Date());
String res="来自与服务端的回应,时间:"+ time;
ByteBuf resp=Unpooled.copiedBuffer(res.getBytes());
ctx.writeAndFlush(resp);

}

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

}

这个是客服端的代码

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 客户端模拟
* @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("连接服务器:"+f.channel().remoteAddress()+",本地地址:"+f.channel().localAddress());
f.channel().closeFuture().sync();//等待客户端关闭连接
} 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=("我是请求数据哦"+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+",响应次数:"+(++counter));
}

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

}

这次代码就是比上次的代码多了：LineBasedFrameDecoder,与StringDecoder的写法.

LineBasedFrameDecoder的原理是它依次遍历ByteBuf中的可读字节，判断是否有"\n"或"\r\n",如果有就以此为结束。它是以换行符为结束标志的解码器

StringDecoder的原理就是将接收到的对象转换为字符串，然后接着调用后面的handler。

LineBasedFrameDecoder+StringDecoder组合就是设计按行切换的文本解码器，被设计来支持TCP的粘包与拆包

当然，我们还可以用其余的分隔符来做，详情看下篇。觉得还行点个赞吧

生活就是拿来受虐的......