Netty中处理TCP粘包和拆包

什么是粘包和拆包

TCP是个”流”协议，流其实就是没有界限的一串数据。
TCP底层中并不了解上层业务数据的具体含义，它会根据TCP缓冲区的实际情况进行包划分，所以在TCP中就有可能一个完整地包会被TCP拆分成多个包，也有可能吧多个小的包封装成一个大的数据包发送，这就是拆包和粘包的问题。

问题实例: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的字节数是不确定的，所以存在几种情况:
1.不存在粘包和分包的时候，服务端分两次读取到了两个独立的数据包。
2.存在粘包，一次读取了D1和D2。
3.存在拆包，第一次读取的是完整的D1包和部分D2包，第二次读取到了D2包的剩余内容。
4.第一次读取到了D1包的部分内容，第二次读取了D1剩下的内容和D2独立的包。

为什么会出现呢？

1.应用程序write写入的字节大小大于套接口发送缓冲区大小(出现拆包).
2,进行MSS大小的TCP分段
3.大于MTU进行分片

这里一般来说
MSS <=MTU-40(IPV4) MSS<= MTU -60 (IPV6)

解决策略

下面的策略都可以对应于我们Netty中的某个handler解决
1.消息定长.
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。
4.复杂的应用协议。

粘包导致的问题

我们可以设计一个类似Echo服务器的功能，客户端发出一百条，echo回显肯定也是一百条。这里有:

服务端代码

package time2;
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 time2.TimeServerHandler;
/**
* Created by lz on 2016/8/9.
*/
public class TimeServer {
public void bind(int port) throws Exception{
//配置服务端的NIO线程组,一个用于接收连接，一个用于处理连接
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 ChildChannerHanler());
//绑定端口，同步等待
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,释放线程资源
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
private class ChildChannerHanler extends ChannelInitializer<SocketChannel> {
@Override
protected void initChannel(SocketChannel socketChannel) throws Exception {
socketChannel.pipeline().addLast(new TimeServerHandler());
}
}
public static void main(String[] args) throws Exception {
int port = 8080;
new TimeServer().bind(port);
}
}

服务端handler

package time2;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
import java.util.Date;
/**
* Created by lz on 2016/8/10.
*/
public class TimeServerHandler extends ChannelHandlerAdapter{
private int counter;
@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,"UTF-8").substring(0,req.length-System.getProperty("line.separator").length());
System.out.println("Time Server得到了数据:" + body+";counter是:"+ ++counter);
String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date().toString():"BAD ORDER";
currentTime = currentTime + System.getProperty("line.separator");
ByteBuf
resp = Unpooled.copiedBuffer(currentTime.getBytes());
ctx.writeAndFlush(resp);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
ctx.close();
}
public static void main(String[] args) {
System.out.println("1"+System.getProperty("line.separator")+"1");
}
}

客户端代码

package time2;
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;
/**
* Created by lz on 2016/8/9.
*/
public class TimeClient {
public void connect(int port,String host) 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)
.handler(new ChannelInitializer<SocketChannel>(){
@Override
protected void initChannel(SocketChannel socketChannel) throws Exception {
socketChannel.pipeline().addLast(new TimeClientHandler());
}
});
//发起异步连接操作
ChannelFuture f = b.connect(host,port).sync();
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;
new TimeClient().connect(port,"127.0.0.1");
}
}

客户端Handler代码

package time2;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
/**
* Created by lz on 2016/8/10.
*/
public class TimeClientHandler extends ChannelHandlerAdapter {
private int counter;
private byte[] req;
public TimeClientHandler(){
req = ("QUERY TIME ORDER" + 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,"UTF-8");
System.out.println("Now is:"+body+";the counter is :" + ++counter);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
ctx.close();
}
}

进行测试分别运行客户端和服务器端，发现出现了粘包现象，客户端的counter只加了一次，这就出现了粘包问题，在我们初学的时候可以不考虑这个问题但是当压力上来后，发送大报文，就会出现粘包/拆包。
我们就需要我们的半包解码器。如下：

LineBasedFrameDecoder

这是一个一换行符为界限的解码器，如果有换行我们就把他标记为结束位置，这样就组成一个独立的包。我们可以设置最大长度。如果连续读取到最大长度后没有发现换行符，就会抛出异常，同时忽略掉之前读到的异常码流。代码如下：

Server端代码:

package time3;
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;
/**
* Created by lz on 2016/8/10.
*/
public class TimeServer {
public void bind(int port) throws Exception{
//配置服务端的NIO线程组,一个用于接收连接，一个用于处理连接
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 ChildChannelHandler());
//绑定端口，同步等待
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,释放线程资源
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
private class ChildChannelHandler extends ChannelInitializer<SocketChannel>{
@Override
protected void initChannel(SocketChannel socketChannel) throws Exception {
System.out.println("已经绑定");
socketChannel.pipeline().addLast(new LineBasedFrameDecoder(1024));
socketChannel.pipeline().addLast(new StringDecoder());
socketChannel.pipeline().addLast(new TimeServerHandler());
}
}
public static void main(String[] args) throws Exception {
int port = 8080;
new TimeServer().bind(port);
}
}

ServerHandler端代码:

package time3;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
import java.util.Date;
/**
* Created by lz on 2016/8/10.
*/
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("Time Server得到了数据:" + body+";counter是:"+ ++counter);
String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date().toString():"BAD ORDER";
currentTime = currentTime + System.getProperty("line.separator");
ByteBuf
resp = Unpooled.copiedBuffer(currentTime.getBytes());
ctx.writeAndFlush(resp);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
System.out.println(cause.getMessage());
ctx.close();
}
public static void main(String[] args) {
System.out.println("1"+System.getProperty("line.separator")+"1");
}
}

Client端代码:

package time3;
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;
/**
* Created by lz on 2016/8/10.
*/
public class TimeClient {
public void connect(int port,String host) 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)
.handler(new ChannelInitializer<SocketChannel>(){
@Override
protected void initChannel(SocketChannel socketChannel) throws Exception {
socketChannel.pipeline().addLast(new LineBasedFrameDecoder(1024));
socketChannel.pipeline().addLast(new StringDecoder());
socketChannel.pipeline().addLast(new TimeClientHandler());
}
});
//发起异步连接操作
ChannelFuture f = b.connect(host,port).sync();
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;
new TimeClient().connect(port,"127.0.0.1");
}
}

Client端Handler代码

package time3;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
/**
* Created by lz on 2016/8/10.
*/
public class TimeClientHandler extends ChannelHandlerAdapter {
private int counter;
private byte[] req;
public TimeClientHandler(){
System.out.println("初始化");
req = ("QUERY TIME ORDER" + System.getProperty("line.separator")).getBytes();
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
System.out.println("发送数据");
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 {
String body = (String) msg;
System.out.println("Now is:"+body+";the counter is :" + ++counter);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
System.out.println(cause.getMessage());
ctx.close();
}
}

通过我们的解码器我们的代码就简单了很多，部分地方有注释就不祥解了。

DelimiterBasedFrameDecoder

DelimiterBasedFrameDecoder允许我们设置特定的分隔符用来分隔，用法和上面类似，

 ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes()); //使用$_为分隔符
socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,delimiter));

上面就是以$_为分隔符，这里我们用echo服务器做测试:

EchoServer端代码

package echo1;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
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.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import time3.TimeServerHandler;
/**
* Created by lz on 2016/8/10.
*/
public class EchoServer {
public void bind(int port) throws Exception{
//配置服务端的NIO线程组,一个用于接收连接，一个用于处理连接
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) //设置accept的最大 也就是三次握手成功的队列长度
.handler(new LoggingHandler(LogLevel.INFO))
.childHandler(new ChildChannelHandler());
//绑定端口，同步等待
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,释放线程资源
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
private class ChildChannelHandler extends ChannelInitializer<SocketChannel> {
@Override
protected void initChannel(SocketChannel socketChannel) throws Exception {
System.out.println("已经绑定");
ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes()); //使用$_为分隔符
socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,delimiter));
socketChannel.pipeline().addLast(new StringDecoder());
socketChannel.pipeline().addLast(new EchoServerHandler());
}
}
public static void main(String[] args) throws Exception {
int port = 8080;
new EchoServer().bind(port);
}
}

EchoServer Handler代码

package echo1;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
/**
* Created by lz on 2016/8/10.
*/
public class EchoServerHandler extends ChannelHandlerAdapter {
int counter = 0;
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
String body = (String) msg;
System.out.println("第"+ ++counter +"次接收"+body);
body +="$_";
ByteBuf echo = Unpooled.copiedBuffer(body.getBytes());
ctx.writeAndFlush(echo);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();//发生异常，关闭链路
}
}

Echo Client端代码

package echo1;
import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
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.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import time3.TimeClientHandler;
/**
* Created by lz on 2016/8/10.
*/
public class EchoClient {
public void connect(int port,String host) 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)
.handler(new ChannelInitializer<SocketChannel>(){
@Override
protected void initChannel(SocketChannel socketChannel) throws Exception {
ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes()); //使用$_为分隔符
socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,delimiter));
socketChannel.pipeline().addLast(new StringDecoder());
socketChannel.pipeline().addLast(new EchoClientHandler());
}
});
//发起异步连接操作
ChannelFuture f = b.connect(host,port).sync();
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;
new EchoClient().connect(port,"127.0.0.1");
}
}

EchoClient Handler代码

package echo1;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
/**
* Created by lz on 2016/8/10.
*/
public class EchoClientHandler extends ChannelHandlerAdapter {
private int counter;
static final String ECHO_REQ = "Hi,lizhao$_";
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
for (int i = 0; i < 10; i++) {
ctx.writeAndFlush(Unpooled.copiedBuffer(ECHO_REQ.getBytes()));
}
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
System.out.println("这是第"+ ++counter + "次接收" + msg);
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
ctx.flush();
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}

运行上面的代码可以展示出正确的结果，我们当然不止这几个我们还有FixedLengthFrameDecoder固定长度的解码器，以及其他解码器，更多查看官方手册。

最后

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