Mina、Netty、Twisted一起学（三）：TCP消息固定大小的前缀(Header)

在上一篇博文中，有介绍到用换行符分割消息的方法。但是这种方法有个小问题，如果消息中本身就包含换行符，那将会将这条消息分割成两条，结果就不对了。

本文介绍另外一种消息分割方式，即上一篇博文中讲的第2条：use a fixed length header that indicates the length of the body，用一个固定字节数的Header前缀来指定Body的字节数，以此来分割消息。

上面图中Header固定为4字节，Header中保存的是一个4字节（32位）的整数，例如12即为0x0000000C，这个整数用来指定Body的长度（字节数）。当读完这么多字节的Body之后，又是下一条消息的Header。

下面分别用MINA、Netty、Twisted来实现对这种消息的切合和解码。

MINA：

MINA提供了PrefixedStringCodecFactory来对这种类型的消息进行编码解码，PrefixedStringCodecFactory默认Header的大小是4字节，当然也可以指定成1或2。

public class TcpServer {public static void main(String[] args) throws IOException {IoAcceptor acceptor = new NioSocketAcceptor();// 4字节的Header指定Body的字节数，对这种消息的处理acceptor.getFilterChain().addLast("codec", new ProtocolCodecFilter(new PrefixedStringCodecFactory(Charset.forName("UTF-8"))));acceptor.setHandler(new TcpServerHandle());acceptor.bind(new InetSocketAddress(8080));}}class TcpServerHandle extends IoHandlerAdapter {@Overridepublic void exceptionCaught(IoSession session, Throwable cause)throws Exception {cause.printStackTrace();}// 接收到新的数据@Overridepublic void messageReceived(IoSession session, Object message)throws Exception {String msg = (String) message;System.out.println("messageReceived:" + msg);}@Overridepublic void sessionCreated(IoSession session) throws Exception {System.out.println("sessionCreated");}@Overridepublic void sessionClosed(IoSession session) throws Exception {System.out.println("sessionClosed");}}

Netty：

Netty使用LengthFieldBasedFrameDecoder来处理这种消息。下面代码中的new LengthFieldBasedFrameDecoder(80, 0, 4, 0, 4)中包含5个参数，分别是int maxFrameLength, int lengthFieldOffset, int lengthFieldLength, int lengthAdjustment, int initialBytesToStrip。maxFrameLength为消息的最大长度，lengthFieldOffset为Header的位置，lengthFieldLength为Header的长度，lengthAdjustment为长度调整（默认Header中的值表示Body的长度，并不包含Header自己），initialBytesToStrip为去掉字节数（默认解码后返回Header+Body的全部内容，这里设为4表示去掉4字节的Header，只留下Body）。

public class TcpServer {public static void main(String[] args) throws InterruptedException {EventLoopGroup bossGroup = new NioEventLoopGroup();EventLoopGroup workerGroup = new NioEventLoopGroup();try {ServerBootstrap b = new ServerBootstrap();b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).childHandler(new ChannelInitializer<SocketChannel>() {@Overridepublic void initChannel(SocketChannel ch)throws Exception {ChannelPipeline pipeline = ch.pipeline();// LengthFieldBasedFrameDecoder按行分割消息，取出bodypipeline.addLast(new LengthFieldBasedFrameDecoder(80, 0, 4, 0, 4));// 再按UTF-8编码转成字符串pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));pipeline.addLast(new TcpServerHandler());}});ChannelFuture f = b.bind(8080).sync();f.channel().closeFuture().sync();} finally {workerGroup.shutdownGracefully();bossGroup.shutdownGracefully();}}}class TcpServerHandler extends ChannelInboundHandlerAdapter {// 接收到新的数据@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) {String message = (String) msg;System.out.println("channelRead:" + message);}@Overridepublic void channelActive(ChannelHandlerContext ctx) {System.out.println("channelActive");}@Overridepublic void channelInactive(ChannelHandlerContext ctx) {System.out.println("channelInactive");}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {cause.printStackTrace();ctx.close();}}

Twisted：

在Twisted中需要继承Int32StringReceiver，不再继承Protocol。Int32StringReceiver表示固定32位（4字节）的Header，另外还有Int16StringReceiver、Int8StringReceiver等。而需要实现的接受数据事件的方法不再是dataReceived，也不是lineReceived，而是stringReceived。

# -*- coding:utf-8 –*-from twisted.protocols.basic import Int32StringReceiverfrom twisted.internet.protocol import Factoryfrom twisted.internet import reactorclass TcpServerHandle(Int32StringReceiver):    # 新的连接建立    def connectionMade(self):        print 'connectionMade'    # 连接断开    def connectionLost(self, reason):        print 'connectionLost'    # 接收到新的数据    def stringReceived(self, data):        print 'stringReceived:' + datafactory = Factory()factory.protocol = TcpServerHandlereactor.listenTCP(8080, factory)reactor.run()

下面是Java编写的一个客户端测试程序：

public class TcpClient {public static void main(String[] args) throws IOException {Socket socket = null;DataOutputStream out = null;try {socket = new Socket("localhost", 8080);out = new DataOutputStream(socket.getOutputStream());// 请求服务器String data1 = "牛顿";byte[] outputBytes1 = data1.getBytes("UTF-8");out.writeInt(outputBytes1.length); // write headerout.write(outputBytes1); // write bodyString data2 = "爱因斯坦";byte[] outputBytes2 = data2.getBytes("UTF-8");out.writeInt(outputBytes2.length); // write headerout.write(outputBytes2); // write bodyout.flush();} finally {// 关闭连接out.close();socket.close();}}}

MINA服务器输出结果：

sessionCreated
messageReceived:牛顿
messageReceived:爱因斯坦
sessionClosed

Netty服务器输出结果：

channelActive
channelRead:牛顿
channelRead:爱因斯坦
channelInactive

Twisted服务器输出结果：

connectionMade
stringReceived:牛顿
stringReceived:爱因斯坦
connectionLost

作者：叉叉哥   转载请注明出处：http://blog.csdn.net/xiao__gui/article/details/38752105