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

 1 package com.ming.netty.nio;
 2
 3 import java.net.InetSocketAddress;
 4
 5 import io.netty.bootstrap.ServerBootstrap;
 6 import io.netty.channel.ChannelFuture;
 7 import io.netty.channel.ChannelInitializer;
 8 import io.netty.channel.ChannelOption;
 9 import io.netty.channel.EventLoopGroup;
10 import io.netty.channel.nio.NioEventLoopGroup;
11 import io.netty.channel.socket.SocketChannel;
12 import io.netty.channel.socket.nio.NioServerSocketChannel;
13 import io.netty.handler.codec.LineBasedFrameDecoder;
14 import io.netty.handler.codec.string.StringDecoder;
15
16 public class TimeServer {
17
18
19     public static void main(String[] args) throws Exception{
20         new TimeServer().bind("192.168.1.102", 8400);
21     }
22
23
24     public void bind(String addr,int port) {
25         //配置服务端的nio线程组
26         EventLoopGroup boosGroup=new NioEventLoopGroup();
27         EventLoopGroup workerGroup=new NioEventLoopGroup();
28         try {
29             ServerBootstrap b=new ServerBootstrap();
30             b.group(boosGroup,workerGroup);
31             b.channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG,1024)
32             .childHandler(new ChildChannelHandler());
33             //绑定端口，同步等待成功
34             ChannelFuture f=b.bind(new InetSocketAddress(addr, port)).sync();
35             System.out.println("启动服务器:"+f.channel().localAddress());
36             //等等服务器端监听端口关闭
37             f.channel().closeFuture().sync();
38         } catch (Exception e) {
39             // TODO: handle exception
40         }finally{
41             boosGroup.shutdownGracefully();
42             workerGroup.shutdownGracefully();
43         }
44     }
45
46     private class ChildChannelHandler extends ChannelInitializer<SocketChannel>{
47
48         @Override
49         protected void initChannel(SocketChannel ch) throws Exception {
50             System.out.println(ch.remoteAddress());
51             ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
52             ch.pipeline().addLast(new StringDecoder());//增加解码器
53             ch.pipeline().addLast(new TimeServerHandler());
54
55         }
56
57     }
58
59
60 }
61 package com.ming.netty.nio;
62
63 import java.nio.ByteBuffer;
64 import java.text.SimpleDateFormat;
65 import java.util.Date;
66
67 import io.netty.buffer.ByteBuf;
68 import io.netty.buffer.Unpooled;
69 import io.netty.channel.ChannelHandlerAdapter;
70 import io.netty.channel.ChannelHandlerContext;
71
72 public class TimeServerHandler extends ChannelHandlerAdapter {
73
74     private int counter;
75
76     @Override
77     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
78         String body=(String)msg;
79         System.out.println("服务端收到："+body+"，次数:"+ ++counter);
80         SimpleDateFormat  dateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
81         String time=dateFormat.format(new Date());
82         String res="来自与服务端的回应,时间:"+ time;
83         ByteBuf resp=Unpooled.copiedBuffer(res.getBytes());
84         ctx.writeAndFlush(resp);
85
86     }
87
88
89
90     @Override
91     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
92         ctx.close();
93     }
94
95
96
97
98 }

这个是客服端的代码

 1 package com.ming.netty.nio;
 2
 3 import io.netty.bootstrap.Bootstrap;
 4 import io.netty.channel.ChannelFuture;
 5 import io.netty.channel.ChannelInitializer;
 6 import io.netty.channel.ChannelOption;
 7 import io.netty.channel.EventLoopGroup;
 8 import io.netty.channel.nio.NioEventLoopGroup;
 9 import io.netty.channel.socket.SocketChannel;
10 import io.netty.channel.socket.nio.NioSocketChannel;
11 import io.netty.handler.codec.LineBasedFrameDecoder;
12 import io.netty.handler.codec.string.StringDecoder;
13
14 /**
15  * netty 客户端模拟
16  * @author mingge
17  *
18  */
19 public class TimeClient {
20
21
22     public static void main(String[] args) throws Exception{
23         new TimeClient().connect("192.168.1.102", 8400);
24     }
25
26     public void connect(String addr,int port) throws Exception{
27         EventLoopGroup group=new NioEventLoopGroup();
28         try {
29             Bootstrap b=new Bootstrap();
30             b.group(group).channel(NioSocketChannel.class)
31             .option(ChannelOption.TCP_NODELAY, true)
32             .handler(new ChannelInitializer<SocketChannel>() {
33                 public void initChannel(SocketChannel ch) throws Exception{
34                     ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
35                     ch.pipeline().addLast(new StringDecoder());
36                     ch.pipeline().addLast(new TimeClientHandler());
37                 }
38             });
39             ChannelFuture f=b.connect(addr,port).sync();
40             System.out.println("连接服务器:"+f.channel().remoteAddress()+",本地地址:"+f.channel().localAddress());
41             f.channel().closeFuture().sync();//等待客户端关闭连接
42         } catch (Exception e) {
43             e.printStackTrace();
44         }finally{
45
46             group.shutdownGracefully();
47         }
48     }
49 }
50 package com.ming.netty.nio;
51
52 import io.netty.buffer.ByteBuf;
53 import io.netty.buffer.Unpooled;
54 import io.netty.channel.ChannelHandlerAdapter;
55 import io.netty.channel.ChannelHandlerContext;
56
57 public class TimeClientHandler extends ChannelHandlerAdapter {
58
59     private int counter;
60
61     byte[] req;
62
63     public TimeClientHandler() {
64         req=("我是请求数据哦"+System.getProperty("line.separator")).getBytes();
65     }
66
67     @Override
68     public void channelActive(ChannelHandlerContext ctx) throws Exception {
69         ByteBuf message=null;
70         for(int i=0;i<100;i++){
71             message=Unpooled.buffer(req.length);
72             message.writeBytes(req);
73             ctx.writeAndFlush(message);
74         }
75
76     }
77
78     @Override
79     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
80         ByteBuf buf=(ByteBuf)msg;
81         byte[] req=new byte[buf.readableBytes()];
82         buf.readBytes(req);
83         String body=new String(req,"GBK");
84         System.out.println("body:"+body+",响应次数:"+(++counter));
85     }
86
87     @Override
88     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
89         //释放资源
90         ctx.close();
91     }
92
93
94 }

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