Netty傻瓜教程（三）：拆包、粘包。用神器protobuf！

关于TCP/IP协议粘包的问题自行百度，我举个例子，服务器发出的消息本来为：“你好，我是服务端。”，客户端接收的时候可能变成了：“你好，我是服”，这就是拆包了。

因此服务端和客户端数据交互要避免这些问题。幸亏，谷歌公司有个神器，叫作protobuf，能够完美解决这个问题，此外还有交互数据小，代码生成简单，支持多种语言等特性。

在Mac上安装protobuf请参考：http://blog.csdn.net/dfqin/article/details/8198341

而后编写一个后缀名为proto的文件，定义消息格式，而后用proto命令生成java文件：

Auth.proto文件以下

option java_package = "com.hengzecn.protobuf";

package auth;

message AuthRequest{ // (1)
	required string user_id=1;
	required string password=2;
}

message AuthResponse{ //(2)
	required int32 result_code=1;
	required string result_message=2;
}

1. 包名自定义，也能够不加，将生成的文件拖进相应的包中便可。

MAC里的编译命令以下：

proto --proto_path=/Users/nantongribao/Desktop --java_out=/Users/nantongribao/Desktop /Users/nantongribao/Desktop/Auth.proto

最后生成Auth.java文件。

咱们将要实现，客户端登陆验证功能，客户端向服务端发送用户名和密码，服务端验证正确，向客户端返回success信息，否错返回错误信息。

服务器代码：

package com.hengzecn.protobuf;

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.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.LengthFieldPrepender;
import io.netty.handler.codec.protobuf.ProtobufDecoder;
import io.netty.handler.codec.protobuf.ProtobufEncoder;

import java.util.logging.Level;
import java.util.logging.Logger;

public class AuthServer {
	private static Logger logger = Logger.getLogger(AuthServerInitHandler.class
			.getName());

	public void start(int port) throws Exception {
		EventLoopGroup bossGroup = new NioEventLoopGroup();// (1)
		EventLoopGroup workerGroup = new NioEventLoopGroup();// (2)
		try {
			ServerBootstrap b = new ServerBootstrap();// (3)
			b.group(bossGroup, workerGroup); // (4)
			b.channel(NioServerSocketChannel.class);
			b.childHandler(new ChannelInitializer<SocketChannel>() {
				@Override
				protected void initChannel(SocketChannel ch) throws Exception {
					//decoded
					ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024, 0, 4, 0, 4));
					ch.pipeline().addLast(new ProtobufDecoder(Auth.AuthRequest.getDefaultInstance()));
					//encoded
					ch.pipeline().addLast(new LengthFieldPrepender(4));
					ch.pipeline().addLast(new ProtobufEncoder());
					// register handler
					ch.pipeline().addLast(new AuthServerInitHandler());
				}
			});
			b.option(ChannelOption.SO_BACKLOG, 128);
			b.childOption(ChannelOption.SO_KEEPALIVE, true);
			//bind port, wait for success sync
			ChannelFuture f = b.bind(port).sync();
			//wait for channel close sync
			f.channel().closeFuture().sync();
		} finally {
			workerGroup.shutdownGracefully();
			bossGroup.shutdownGracefully();
		}
	}

	public static void main(String[] args) throws Exception {
		logger.log(Level.INFO, "AuthServer start...");
		new AuthServer().start(5555);
	}
}

1. LengthFieldBasedFrameDecoder定义了最大帧长度，以及指示包长度的头部以及须要忽略掉的字节，详见：http://docs.jboss.org/netty/3.1/api/org/jboss/netty/handler/codec/frame/LengthFieldBasedFrameDecoder.html

2. ProtobufDecoder引入定义的请求数据定义

3. LengthFieldPrepender在数据包中加入长度头

下面是服务端的Handler：

package com.hengzecn.protobuf;

import java.util.logging.Level;
import java.util.logging.Logger;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class AuthServerInitHandler extends ChannelInboundHandlerAdapter {
	private Logger logger=Logger.getLogger(AuthServerInitHandler.class.getName());

	@Override
	public void channelRead(ChannelHandlerContext ctx, Object msg)
			throws Exception {
		logger.log(Level.INFO, "AuthServerInitHandler channelRead");
		Auth.AuthRequest request=(Auth.AuthRequest)msg;
		System.out.println("request: userId="+request.getUserId()+", password="+request.getPassword());
		Auth.AuthResponse response=Auth.AuthResponse.newBuilder()
	                                                    .setResultCode(0)
							    .setResultMessage("success")
							    .build();
		ctx.writeAndFlush(response);
		//ctx.close();
	}

	@Override
	public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
		logger.log(Level.INFO, "AuthServerInitHandler channelReadComplete");
		ctx.flush();
	}

	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
			throws Exception {
		logger.log(Level.INFO, "AuthServerInitHandler exceptionCaught");
		cause.printStackTrace();
		ctx.close();
	}

}

1. Handler不判断用户名和密码是否正确，只是简单地回复success，后续会加入数据库验证。

客户端的Client文件和服务端差很少，详情参看第二节中的介绍。

客户端的Handler文件以下：

package com.hengzecn.protobuf;

import java.util.logging.Level;
import java.util.logging.Logger;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class AuthClientInitHandler extends ChannelInboundHandlerAdapter {
	private Logger logger=Logger.getLogger(AuthClientInitHandler.class.getName());

	@Override
	public void channelActive(ChannelHandlerContext ctx) throws Exception {
		logger.log(Level.INFO, "AuthClientInitHandler exceptionCaught");
		Auth.AuthRequest request=Auth.AuthRequest.newBuilder()
							 .setUserId("010203")
							 .setPassword("abcde")
							 .build();
		ctx.writeAndFlush(request);
	}

	@Override
	public void channelRead(ChannelHandlerContext ctx, Object msg)
			throws Exception {
		logger.log(Level.INFO, "AuthClientInitHandler channelRead");
		Auth.AuthResponse response=(Auth.AuthResponse)msg;
		System.out.println("response: code="+response.getResultCode()+", message="+response.getResultMessage());
		//ctx.close();
	}
}

1. 设置用户名和密码，并发送请求，这里用到了channelActive。

2. 读取服务器的回复信息。