介绍websocket协议

WebSocket是HTML5开始提供的一种浏览器与服务器间进行全双工通信的网络技术，WebSocket通信协议于2011年被IETF定为

标准RFC6455，WebSocket API被W3C定为标准。

在WebSocket API中，浏览器和服务器只需要做一个握手的动作，然后，浏览器和服务器之间就形成了一条快速通道，两者就可

以直接互相传送数据了。WebSocket基于TCP双向全双工进行消息传递，在同一时刻，既可以发送消息，也可以接收消息，相比

HTTP的半双工协议，性能得到很大提升。

特点：

• 单一的TCP连接，采用全双工模式通信；
• 对代理、防火墙和路由器透明；
• 无头部信息、Cookie和身份验证；
• 无安全开销；
• 通过”ping/pong”帧保持链路激活；
• 服务器可以主动传递消息给客户端，不再需要客户端轮询。

http协议和websocket协议对比

同：

• 建立在TCP之上，通过TCP协议来传输数据。
• 都是可靠性传输协议。
• 都是应用层协议。

异：

• WebSocket是HTML5中的协议，支持持久连接，HTTP不支持持久连接
• HTTP是单向协议，只能由客户端发起，做不到服务器主动向客户端推送信息。

websocket的连接过程

为了建立一个WebSocket连接，客户端浏览器首先要向服务器发起一个HTTP请求，这个请求和通常的 HTTP请求不同，包含了一些附加头信息，其中附加头信息”Upgrade：WebSocket”表明这是一个申请协议升级的HTTP请求。服务器端解析这些附加的头信息，然后生成应答信息返回给客户端，客户端和服务器端的WebSocket连接就建立起来了，双方可以通过这个连接通道自由地传递信息，并且这个连接会持续存在直到客户端或者服务器端的某一方主动关闭连接。

代码

/*
 * Copyright 2013-2018 Lilinfeng.
 *  
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *  
 *      http://www.apache.org/licenses/LICENSE-2.0
 *  
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.phei.netty.protocol.websocket.server;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
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.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.stream.ChunkedWriteHandler;

/**
 * @author lilinfeng
 * @date 2014年2月14日
 * @version 1.0
 */
public class WebSocketServer {
    public void run(int port) throws Exception {
	EventLoopGroup bossGroup = new NioEventLoopGroup();
	EventLoopGroup workerGroup = new NioEventLoopGroup();
	try {
	    ServerBootstrap b = new ServerBootstrap();
	    b.group(bossGroup, workerGroup)
		    .channel(NioServerSocketChannel.class)
		    .childHandler(new ChannelInitializer<SocketChannel>() {

			@Override
			protected void initChannel(SocketChannel ch)
				throws Exception {
			    ChannelPipeline pipeline = ch.pipeline();
			    pipeline.addLast("http-codec",
				    new HttpServerCodec());
			    pipeline.addLast("aggregator",
				    new HttpObjectAggregator(65536));
			    ch.pipeline().addLast("http-chunked",
				    new ChunkedWriteHandler());
			    pipeline.addLast("handler",
				    new WebSocketServerHandler());
			}
		    });

	    Channel ch = b.bind(port).sync().channel();
	    System.out.println("Web socket server started at port " + port
		    + '.');
	    System.out
		    .println("Open your browser and navigate to http://localhost:"
			    + port + '/');

	    ch.closeFuture().sync();
	} finally {
	    bossGroup.shutdownGracefully();
	    workerGroup.shutdownGracefully();
	}
    }

    public static void main(String[] args) throws Exception {
	int port = 8080;
	if (args.length > 0) {
	    try {
		port = Integer.parseInt(args[0]);
	    } catch (NumberFormatException e) {
		e.printStackTrace();
	    }
	}
	new WebSocketServer().run(port);
    }
}

/*
 * Copyright 2013-2018 Lilinfeng.
 *  
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *  
 *      http://www.apache.org/licenses/LICENSE-2.0
 *  
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.phei.netty.protocol.websocket.server;

import static io.netty.handler.codec.http.HttpHeaders.isKeepAlive;
import static io.netty.handler.codec.http.HttpHeaders.setContentLength;
import static io.netty.handler.codec.http.HttpResponseStatus.BAD_REQUEST;
import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.DefaultFullHttpResponse;
import io.netty.handler.codec.http.FullHttpRequest;
import io.netty.handler.codec.http.FullHttpResponse;
import io.netty.handler.codec.http.websocketx.CloseWebSocketFrame;
import io.netty.handler.codec.http.websocketx.PingWebSocketFrame;
import io.netty.handler.codec.http.websocketx.PongWebSocketFrame;
import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketServerHandshaker;
import io.netty.handler.codec.http.websocketx.WebSocketServerHandshakerFactory;
import io.netty.util.CharsetUtil;

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

/**
 * @author lilinfeng
 * @date 2014年2月14日
 * @version 1.0
 */
public class WebSocketServerHandler extends SimpleChannelInboundHandler<Object> {
    private static final Logger logger = Logger
	    .getLogger(WebSocketServerHandler.class.getName());

    private WebSocketServerHandshaker handshaker;

    @Override
    public void messageReceived(ChannelHandlerContext ctx, Object msg)
	    throws Exception {
	// 传统的HTTP接入
	if (msg instanceof FullHttpRequest) {
	    handleHttpRequest(ctx, (FullHttpRequest) msg);
	}
	// WebSocket接入
	else if (msg instanceof WebSocketFrame) {
	    handleWebSocketFrame(ctx, (WebSocketFrame) msg);
	}
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
	ctx.flush();
    }

    private void handleHttpRequest(ChannelHandlerContext ctx,
	    FullHttpRequest req) throws Exception {

	// 如果HTTP解码失败，返回HHTP异常
	if (!req.getDecoderResult().isSuccess()
		|| (!"websocket".equals(req.headers().get("Upgrade")))) {
	    sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HTTP_1_1,
		    BAD_REQUEST));
	    return;
	}

	// 构造握手响应返回，本机测试
	WebSocketServerHandshakerFactory wsFactory = new WebSocketServerHandshakerFactory(
		"ws://localhost:8080/websocket", null, false);
	handshaker = wsFactory.newHandshaker(req);
	if (handshaker == null) {
	    WebSocketServerHandshakerFactory
		    .sendUnsupportedWebSocketVersionResponse(ctx.channel());
	} else {
	    handshaker.handshake(ctx.channel(), req);
	}
    }

    private void handleWebSocketFrame(ChannelHandlerContext ctx,
	    WebSocketFrame frame) {

	// 判断是否是关闭链路的指令
	if (frame instanceof CloseWebSocketFrame) {
	    handshaker.close(ctx.channel(),
		    (CloseWebSocketFrame) frame.retain());
	    return;
	}
	// 判断是否是Ping消息
	if (frame instanceof PingWebSocketFrame) {
	    ctx.channel().write(
		    new PongWebSocketFrame(frame.content().retain()));
	    return;
	}
	// 本例程仅支持文本消息，不支持二进制消息
	if (!(frame instanceof TextWebSocketFrame)) {
	    throw new UnsupportedOperationException(String.format(
		    "%s frame types not supported", frame.getClass().getName()));
	}

	// 返回应答消息
	String request = ((TextWebSocketFrame) frame).text();
	if (logger.isLoggable(Level.FINE)) {
	    logger.fine(String.format("%s received %s", ctx.channel(), request));
	}
	ctx.channel().write(
		new TextWebSocketFrame(request
			+ " , 欢迎使用Netty WebSocket服务，现在时刻："
			+ new java.util.Date().toString()));
    }

    private static void sendHttpResponse(ChannelHandlerContext ctx,
	    FullHttpRequest req, FullHttpResponse res) {
	// 返回应答给客户端
	if (res.getStatus().code() != 200) {
	    ByteBuf buf = Unpooled.copiedBuffer(res.getStatus().toString(),
		    CharsetUtil.UTF_8);
	    res.content().writeBytes(buf);
	    buf.release();
	    setContentLength(res, res.content().readableBytes());
	}

	// 如果是非Keep-Alive，关闭连接
	ChannelFuture f = ctx.channel().writeAndFlush(res);
	if (!isKeepAlive(req) || res.getStatus().code() != 200) {
	    f.addListener(ChannelFutureListener.CLOSE);
	}
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
	    throws Exception {
	cause.printStackTrace();
	ctx.close();
    }
}

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
Netty WebSocket 时间服务器
</head>
<br>
<body>
<br>
<script type="text/javascript">
var socket;
if (!window.WebSocket) 
{
	window.WebSocket = window.MozWebSocket;
}
if (window.WebSocket) {
	socket = new WebSocket("ws://localhost:8080/websocket");
	socket.onmessage = function(event) {
		var ta = document.getElementById('responseText');
		ta.value="";
		ta.value = event.data
	};
	socket.onopen = function(event) {
		var ta = document.getElementById('responseText');
		ta.value = "打开WebSocket服务正常，浏览器支持WebSocket!";
	};
	socket.onclose = function(event) {
		var ta = document.getElementById('responseText');
		ta.value = "";
		ta.value = "WebSocket 关闭!"; 
	};
}
else
	{
	alert("抱歉，您的浏览器不支持WebSocket协议!");
	}

function send(message) {
	if (!window.WebSocket) { return; }
	if (socket.readyState == WebSocket.OPEN) {
		socket.send(message);
	}
	else
		{
		  alert("WebSocket连接没有建立成功!");
		}
}
</script>
<form onsubmit="return false;">
<input type="text" name="message" value="Netty最佳实践"/>
<br><br>
<input type="button" value="发送WebSocket请求消息" onclick="send(this.form.message.value)"/>
<hr color="blue"/>
<h3>服务端返回的应答消息</h3>
<textarea id="responseText" style="width:500px;height:300px;"></textarea>
</form>
</body>
</html>