九、TCP粘包和拆包及解决方案
9.1、TCP粘包和拆包基本介绍
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TCP是面向连接的，面向流的，提供高可靠性服务。收发两端（客户端和服务器端）都要有一一成对的Socket，因此，发送端为了将多个发给接收端的包，更有效的发给对方，使用了优化方法（Nagle算法），将多次间隔较小且数据量小的数据，合并成一个大的数据块，然后进行封包。这样做虽然提高了效率，但是接收端就难于分辩出完整的数据包了，因为面向流的通信是无消息保护边界的。
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由于TCP无消息保护边界，需要在接收端处理消息边界问题，也就是我们所说的粘包、拆包问题、
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TCP粘包、拆包示意图
ps：假设客户端分别发送了两个数据包D1和D2给服务端，由于服务端一次读取到字节数是不确定的，故可能存在以下四种情况
- 读取两个独立的数据包，分别是D1和D2，没有粘包和拆包
- 一次性接收两个数据包，D1和D2粘合在一起，称之为TCP粘包
- 服务端分两次读取到了数据包，第1次，读取完整的D1包和D2包的部分内容，第二次读取到了D2包的剩余部分，这就是TCP拆包
- 服务端分两次读取带了数据包，第1次，读取到了D1包的部分内容D1_1,第二次读取到了D1包的剩余部分内容D1_2和完整的D2包。
9.2、TCP粘包和拆包现象实例
编写Netty程序时，如果没有做处理，就会发生粘包和拆包的问题
package com.feng.netty.tcp;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
public class MyServer {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap serverBootstrap = new ServerBootstrap();
serverBootstrap.group(bossGroup,workerGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new MyServerHandler());
ChannelFuture channelFuture = serverBootstrap.bind(7000).sync();
channelFuture.channel().closeFuture().sync();
}finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
package com.feng.netty.tcp;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import java.nio.charset.Charset;
import java.util.UUID;
public class MyServerHandler extends SimpleChannelInboundHandler<ByteBuf> {
private int count;
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
ctx.close();
}
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
byte[] buffer = new byte[msg.readableBytes()];
msg.readBytes(buffer);
//将buffer转成字符串
String message = new String(buffer, Charset.forName("utf-8"));
System.out.println("服务器接收到数据 "+message);
System.out.println("服务器接收到消息量="+ (++this.count));
//服务器回送数据给客户端，回送一个数据id，
ByteBuf responseByteBuf = Unpooled.copiedBuffer(UUID.randomUUID().toString()+" ",Charset.forName("utf-8"));
ctx.writeAndFlush(responseByteBuf);
}
}
package com.feng.netty.tcp;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
public class MyServerInitializer extends ChannelInitializer<SocketChannel> {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new MyServerHandler());
}
}
package com.feng.netty.tcp;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
public class MyClient {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(group).channel(NioSocketChannel.class)
.handler(new MyClientInitializer()); //自定义一个初始化类
ChannelFuture channelFuture = bootstrap.connect("localhost", 7000).sync();
channelFuture.channel().closeFuture().sync();
}finally {
group.shutdownGracefully();
}
}
}
package com.feng.netty.tcp;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import java.nio.charset.Charset;
public class MyClientHandler extends SimpleChannelInboundHandler<ByteBuf> {
private int count;
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
//使用客户端发送10条数据 hello,server 编号
for(int i= 0; i< 10; ++i) {
ByteBuf buffer = Unpooled.copiedBuffer("hello,server " + i, Charset.forName("utf-8"));
ctx.writeAndFlush(buffer);
}
}
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
byte[] buffer = new byte[msg.readableBytes()];
msg.readBytes(buffer);
String message = new String(buffer, Charset.forName("utf-8"));
System.out.println("客户端接收到消息=" + message);
System.out.println("客户端接收消息数量=" + (++this.count));
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}
package com.feng.netty.tcp;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
public class MyClientInitializer extends ChannelInitializer<SocketChannel> {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new MyClientHandler());
}
}
9.3、TCP粘包和拆包解决方案
- 使用自定义协议+编码器来解决
- 关键就是要解决服务器每次读取数据长度的问题，这个问题解决，就不会出现服务器多读或少读数据的问题，从而避免的TCP粘包、拆包
9.4、具体实例
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要求客户端发送5个Message，客户端每次发送一个Message对象
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服务器端每次接收一个Message，分5次解码。每读取到一个Message，会回复一个Message对象给客户端
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代码演示
package com.feng.netty.protocoltcp; //协议包 public class MessageProtocol { private int len;//关键字 private byte[] content; public int getLen() { return len; } public void setLen(int len) { this.len = len; } public byte[] getContent() { return content; } public void setContent(byte[] content) { this.content = content; } }package com.feng.netty.protocoltcp; import io.netty.buffer.ByteBuf; import io.netty.channel.ChannelHandlerContext; import io.netty.handler.codec.MessageToByteEncoder; public class MyMessageEncoder extends MessageToByteEncoder<MessageProtocol> { @Override protected void encode(ChannelHandlerContext channelHandlerContext, MessageProtocol msg, ByteBuf out) throws Exception { System.out.println("MyMessageEncoder encode 方法被调用"); out.writeInt(msg.getLen()); out.writeBytes(msg.getContent()); } }package com.feng.netty.protocoltcp; import io.netty.buffer.ByteBuf; import io.netty.channel.ChannelHandlerContext; import io.netty.handler.codec.ReplayingDecoder; import java.util.List; public class MyMessageDecoder extends ReplayingDecoder<Void> { @Override protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception { System.out.println("MyMessageDecoder decode 被调用"); //需要将得到二进制字节码-> MessageProtocol数据包（对象） int length = in.readInt(); byte[] content = new byte[length]; in.readBytes(content); //封装成MessageProtocol对象。放入out。传递下一个handler业务处理 MessageProtocol messageProtocol = new MessageProtocol(); messageProtocol.setLen(length); messageProtocol.setContent(content); out.add(messageProtocol); } }package com.feng.netty.protocoltcp; import io.netty.bootstrap.ServerBootstrap; import io.netty.channel.ChannelFuture; import io.netty.channel.EventLoopGroup; import io.netty.channel.nio.NioEventLoopGroup; import io.netty.channel.socket.nio.NioServerSocketChannel; public class MyServer { public static void main(String[] args) { EventLoopGroup bossGroup = new NioEventLoopGroup(1); EventLoopGroup workGroup = new NioEventLoopGroup(); try { ServerBootstrap serverBootstrap = new ServerBootstrap(); serverBootstrap.group(bossGroup,workGroup) .channel(NioServerSocketChannel.class) .childHandler(new MyServerInitializer());//自定义一个初始化类 ChannelFuture channelFuture = serverBootstrap.bind(7000).sync(); channelFuture.channel().closeFuture().sync(); } catch (InterruptedException e) { e.printStackTrace(); } finally { bossGroup.shutdownGracefully(); workGroup.shutdownGracefully(); } } }package com.feng.netty.protocoltcp; import io.netty.channel.ChannelInitializer; import io.netty.channel.ChannelPipeline; import io.netty.channel.socket.SocketChannel; public class MyServerInitializer extends ChannelInitializer<SocketChannel> { @Override protected void initChannel(SocketChannel ch) throws Exception { ChannelPipeline pipeline = ch.pipeline(); pipeline.addLast(new MyMessageDecoder());//解码器 pipeline.addLast(new MyMessageEncoder());//编码器 pipeline.addLast(new MyServerHandler()); } }package com.feng.netty.protocoltcp; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.SimpleChannelInboundHandler; import java.nio.charset.Charset; import java.nio.charset.StandardCharsets; import java.util.UUID; public class MyServerHandler extends SimpleChannelInboundHandler<MessageProtocol> { private int count; //处理业务的handler @Override protected void channelRead0(ChannelHandlerContext ctx, MessageProtocol msg) throws Exception { //接收到数据，并处理 int len = msg.getLen(); byte[] content = msg.getContent(); System.out.println(); System.out.println(); System.out.println(); System.out.println("服务器接收到信息如下"); System.out.println("长度="+len); System.out.println("内存="+new String(content, Charset.forName("utf-8"))); System.out.println("服务器接收到消息包数量="+(++this.count)); //回复消息 String responseContent = UUID.randomUUID().toString(); int responseLen = responseContent.getBytes(Charset.forName("utf-8")).length; byte[] responseContent2 = responseContent.getBytes(Charset.forName("utf-8")); //构建一个协议包 MessageProtocol messageProtocol = new MessageProtocol(); messageProtocol.setLen(responseLen); messageProtocol.setContent(responseContent2); ctx.writeAndFlush(messageProtocol); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { ctx.close(); } }package com.feng.netty.protocoltcp; import io.netty.bootstrap.Bootstrap; import io.netty.channel.ChannelFuture; import io.netty.channel.EventLoopGroup; import io.netty.channel.nio.NioEventLoopGroup; import io.netty.channel.socket.nio.NioSocketChannel; public class MyClient { public static void main(String[] args) throws InterruptedException { EventLoopGroup group = new NioEventLoopGroup(); try { Bootstrap bootstrap = new Bootstrap(); bootstrap.group(group) .channel(NioSocketChannel.class) .handler(new MyClientInitializer()); ChannelFuture channelFuture = bootstrap.connect("localhost", 7000).sync(); channelFuture.channel().closeFuture().sync(); }finally { group.shutdownGracefully(); } } }package com.feng.netty.protocoltcp; import io.netty.channel.ChannelInitializer; import io.netty.channel.ChannelPipeline; import io.netty.channel.socket.SocketChannel; public class MyClientInitializer extends ChannelInitializer<SocketChannel> { protected void initChannel(SocketChannel ch) throws Exception { ChannelPipeline pipeline = ch.pipeline(); pipeline.addLast(new MyMessageEncoder());//加入编码器 pipeline.addLast(new MyMessageDecoder());//加入解码器 pipeline.addLast(new MyClientHandler()); } }package com.feng.netty.protocoltcp; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.SimpleChannelInboundHandler; import java.nio.charset.Charset; public class MyClientHandler extends SimpleChannelInboundHandler<MessageProtocol> { private int count; @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { //使用客户端发送10条数据，"今天天气冷，吃火锅" 编号 for (int i=0;i<5;i++){ String mes = "今天天气冷，吃火锅"; byte[] content = mes.getBytes(Charset.forName("utf-8")); int length = mes.getBytes(Charset.forName("utf-8")).length; //创建协议包对象 MessageProtocol messageProtocol = new MessageProtocol(); messageProtocol.setLen(length); messageProtocol.setContent(content); ctx.writeAndFlush(messageProtocol); } } @Override protected void channelRead0(ChannelHandlerContext ctx, MessageProtocol msg) throws Exception { int len = msg.getLen(); byte[] content = msg.getContent(); System.out.println("客户端接收到消息如下"); System.out.println("长度="+ len); System.out.println("内容="+ new String(content,Charset.forName("utf-8"))); System.out.println("客户端接收消息数量="+(++this.count)); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { System.out.println("异常消息="+cause.getMessage()); ctx.close(); } }