Netty粘包/拆包（一）
TCP出现粘包拆包原因有三个：
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；
2.进行MSS（最大报文长度）大小的TCP分段(TCP报文长度-TCP头部长度>MSS的时候将发生拆包)；
3.以太网帧的payload大于MTU(最大数据包大小)进行IP分片。
粘包的解决方案：
1.消息定长，例如每个报文的大小为固定长度200字节，如果不够，空格补空格；
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（或者消息体长度）的字段，通常设计思路为消息头的第一个字段使用int32来表示消息的总长度；
4.更复杂的应用层协议。
首先使用未加Netty的半包解码器来看粘包拆包问题：
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;
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() {
@Override
protected void initChannel(SocketChannel arg0)
throws Exception {
System.out.println("客户端启动..");
arg0.pipeline().addLast(new TimeClientHandler());
}
});
// 发起异步连接操作
ChannelFuture f = b.connect(host, port).sync();
// 等待客户端链路关闭
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");
}
} import java.util.logging.Logger;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
public class TimeClientHandler extends ChannelInboundHandlerAdapter {
private static final Logger logger = Logger
.getLogger(com.netty2.TimeClientHandler2.class.getName());
private int counter;
private byte[] req;
public TimeClientHandler() {
req = "QUERY TIME ORDER".getBytes();
// firstMessage = Unpooled.buffer(req.length);
// firstMessage.writeBytes(req);
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
//与服务端建立连接后
System.out.println("客户端 channelActive..");
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 {
System.out.println("客户端 channelRead..");
//服务端返回消息后
ByteBuf buf = (ByteBuf) msg;
byte[] req = new byte[buf.readableBytes()];
buf.readBytes(req);
String body = new String(req, "UTF-8");
System.out.println("当前时间 :" + body +" 次数:"+ (++counter));
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
throws Exception {
System.out.println("客户端异常..");
// 释放资源
logger.warning("Unexpected exception from downstream:"
+ cause.getMessage());
ctx.close();
}
}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;
public class TimeServer {
public void bind(int port) throws Exception {
//配置服务端的NIO线程组
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，同步等待成功
ChannelFuture f=b.bind(port).sync();
//等待服务端监听端口关闭
f.channel().closeFuture().sync();
} finally {
//退出，释放线程池资源
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
private class ChildChannelHandler extends ChannelInitializer{
protected void initChannel(SocketChannel ch) throws Exception {
System.out.println("服务端启动……");
ch.pipeline().addLast(new TimeServerHandler());
}
}
public static void main(String[] args) throws Exception {
int port=8080;
new TimeServer().bind(port);
}
}
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import java.util.Date;
public class TimeServerHandler extends ChannelInboundHandlerAdapter {
private int counter;
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg)
throws Exception {
System.out.println("服务器启动..");
ByteBuf buf = (ByteBuf) msg;
byte[] req = new byte[buf.readableBytes()];
buf.readBytes(req);
String body = new String(req, "UTF-8");
System.out.println("服务器接收数据:" + body+" 次数:"+ (++counter));
String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(
System.currentTimeMillis()).toString() : "BAD ORDER";
ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
ctx.writeAndFlush(resp);
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
System.out.println("服务器读取完毕..");
ctx.flush();//刷新后才将数据发出到SocketChannel
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
throws Exception {
System.out.println("服务器异常..");
ctx.close();
}
}
可以看到它服务端和客户端只接收到了两次。
利用LineBasedFrameDecoder解决TCP粘包问题
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;
public class TimeClient2 {
public void connect(int port, String host) 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() {
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
ch.pipeline().addLast(new StringDecoder());
ch.pipeline().addLast(new TimeClientHandler2());
}
});
// 发起异步连接操作
ChannelFuture f = b.connect(host, port).sync();
// 等待客户端连接关闭
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 = 8082;
new TimeClient2().connect(port, "127.0.0.1");
}
} import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import java.util.logging.Logger;
public class TimeClientHandler2 extends ChannelInboundHandlerAdapter {
private static final Logger logger = Logger
.getLogger(TimeClientHandler2.class.getName());
private int counter;
private byte[] req;
public TimeClientHandler2() {
req = ("QUERY TIME ORDER" + System.getProperty("line.separator")).getBytes();
}
@Override
public void channelActive(ChannelHandlerContext ctx){
//与服务端建立连接后
System.out.println("客户端 channelActive..");
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) {
System.out.println("客户端 channelRead..");
//服务端返回消息后
String body = (String) msg;
System.out.println("当前时间 :" + body + " 次数:" + (++counter));
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
throws Exception {
System.out.println("客户端异常..");
// 释放资源
logger.warning("Unexpected exception from downstream:"
+ cause.getMessage());
ctx.close();
}
}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 TimeServer2 {
public void bind(int port) throws Exception {
// NIO线程组
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，同步等待成功
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，释放线程池资源
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
private class ChildChannelHandler extends ChannelInitializer {
@Override
protected void initChannel(SocketChannel arg0) throws Exception {
arg0.pipeline().addLast(new LineBasedFrameDecoder(1024));
arg0.pipeline().addLast(new StringDecoder());
arg0.pipeline().addLast(new TimeServerHandler2());
}
}
public static void main(String[] args) throws Exception {
int port=8082;
new TimeServer2().bind(port);
}
}
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import java.util.Date;
public class TimeServerHandler2 extends ChannelInboundHandlerAdapter {
private int counter;
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg){
System.out.println("服务器启动..");
String body = (String) msg;
System.out.println("服务器接收数据:" + body+" 次数:"+ (++counter));
String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(
System.currentTimeMillis()).toString() : "BAD ORDER";
if(counter%2==0)
currentTime = currentTime + System.getProperty("line.separator");
ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
ctx.writeAndFlush(resp);
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
System.out.println("服务器读取完毕..");
ctx.flush();//刷新后才将数据发出到SocketChannel
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
System.out.println("服务器异常..");
ctx.close();
}
}
LineBasedFrameDecoder的工作原理是它依次遍历ByteBuf中可读字节，判断看是否有“\n”或者“\r\n”，如果有就以此位置为结束位置，从可读索引到结束位置区间的字节就组成了一行。它是以换行符为结束标志的解码器，支持携带结束符或者不携带结束符两种解码方式，同时支持配置单行的最大长度。如果连续读取到最大长度后任然没有发现换行符就会抛出异常，同时忽略之前读取到的异常码流。
StringDecoder的功能非常简单，就是将接收到的对象转换成字符串，然后继续调用后面的Handler。LineBasedFrameDecoder+StringDecoder组合就是按行切换的文本解码器，他被设计用来支持TCP的粘包和拆包。