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描述

WebSocket是html5开始浏览器和服务端进行全双工通信的网络技术。在该协议下，与服务端只需要一次握手，之后建立一条快速通道，开始互相传输数据，实际是基于TCP双向全双工，比http半双工提高了很大的性能，常用于网络在线聊天室等。继续netty实例的学习，本期内容主要做WebSocket实例的实现和相关协议的验证。

WebSocket与http比较

代码示例和运行结果

服务端

服务端比较简单，是启动一个端口来处理请求。

主程序

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelInitializer;
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;
import org.junit.Test;

public class NettyWebSocketServer {

    public void run(final int port) {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap bootstrap = new ServerBootstrap();
            bootstrap.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline()
                                    .addLast(new HttpServerCodec())
                                    .addLast(new HttpObjectAggregator(65535))
                                    .addLast(new ChunkedWriteHandler())
                                    .addLast(new WebSocketServerHandler());
                        }
                    });
            Channel ch = bootstrap.bind(port).sync().channel();
            System.out.println("websocket @" + port);
            ch.closeFuture().sync();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Test
    public void runServer() {
        run(23123);
    }
}

请求处理handler

核心处理WebSocket请求，重点地方加了注释

import io.netty.buffer.ByteBufUtil;
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.*;
import io.netty.handler.codec.http.websocketx.*;

import java.time.LocalDateTime;
import java.util.concurrent.TimeUnit;

public class WebSocketServerHandler extends SimpleChannelInboundHandler<Object> {
    private WebSocketServerHandshaker handshaker;

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
        //首次请求之后先进行握手，通过http请求来实现
        if (msg instanceof FullHttpRequest) {
            handleHttpRequest(ctx, (FullHttpRequest) msg);
        } else if (msg instanceof WebSocketFrame) {
            handleWebSocketRequest(ctx, (WebSocketFrame) msg);
        }
    }

    private void handleHttpRequest(ChannelHandlerContext ctx, FullHttpRequest request) {
        //解码http失败返回
        if (!request.decoderResult().isSuccess()) {
            sendResponse(ctx, request, new DefaultFullHttpResponse(request.protocolVersion(), HttpResponseStatus.BAD_REQUEST, ctx.alloc().buffer()));
            return;
        }

        if (!HttpMethod.GET.equals(request.method())) {
            sendResponse(ctx, request, new DefaultFullHttpResponse(request.protocolVersion(), HttpResponseStatus.FORBIDDEN, ctx.alloc().buffer()));
            return;
        }

        //参数分别是ws地址，子协议，是否扩展，最大frame长度
        WebSocketServerHandshakerFactory factory = new WebSocketServerHandshakerFactory(getWebSocketLocation(request), null, true, 5 * 1024 * 1024);
        handshaker = factory.newHandshaker(request);
        if (handshaker == null) {
            WebSocketServerHandshakerFactory.sendUnsupportedVersionResponse(ctx.channel());
        } else {
            handshaker.handshake(ctx.channel(), request);
        }
    }

    //SSL支持采用wss://
    private String getWebSocketLocation(FullHttpRequest request) {
        String location = request.headers().get(HttpHeaderNames.HOST) + "/websocket";
        return "ws://" + location;
    }

    private void handleWebSocketRequest(ChannelHandlerContext ctx, WebSocketFrame frame) {
        //关闭
        if (frame instanceof CloseWebSocketFrame) {
            handshaker.close(ctx.channel(), (CloseWebSocketFrame) frame.retain());
            return;
        }

        //握手 PING/PONG
        if (frame instanceof PingWebSocketFrame) {
            ctx.write(new PongWebSocketFrame(frame.content().retain()));
            return;
        }

        //文本接收和发送
        if (frame instanceof TextWebSocketFrame) {
            String recv = ((TextWebSocketFrame) frame).text();
            String text = "now@" + LocalDateTime.now() + "\n recv:" + recv;

            //这里加了个循环，每隔一秒服务端主动发送内容给客户端
            for (int i = 0; i < 5; i++) {
                String res = i + "-" + text;
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                ctx.writeAndFlush(new TextWebSocketFrame(res));
            }
            System.out.println(recv);
            return;
        }

        if (frame instanceof BinaryWebSocketFrame) {
            ctx.write(frame.retain());
        }
    }

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

    private void sendResponse(ChannelHandlerContext ctx, FullHttpRequest req, FullHttpResponse resp) {
        HttpResponseStatus status = resp.status();
        if (status != HttpResponseStatus.OK) {
            ByteBufUtil.writeUtf8(resp.content(), status.toString());
            HttpUtil.setContentLength(req, resp.content().readableBytes());
        }
        boolean keepAlive = HttpUtil.isKeepAlive(req) && status == HttpResponseStatus.OK;
        HttpUtil.setKeepAlive(req, keepAlive);
        ChannelFuture future = ctx.write(resp);
        if (!keepAlive) {
            future.addListener(ChannelFutureListener.CLOSE);
        }
    }

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

客户端

<html>
<head>
    <meta charset="UTF-8">
</head>
<body>
<form onsubmit="return false;">
    <input type="text" name="message" value="test"/>
    <br/>
    <input type="button" value="send", onclick="send(this.form.message.value)"/>
    <hr/>
    resp:
    <br/>
    <textarea id="responseText" style="width: 200px;height:300px;"></textarea>
</form>

</form>
</body>
<script type="text/javascript">
 var socket;
 if (!window.WebSocket) {
 window.WebSocket = window.MozWebSocket;
 }
 if (window.WebSocket) {
 socket = new WebSocket("ws://127.0.0.1:23123/websocket");
 socket.onmessage = function (ev) {
 var ta = document.getElementById('responseText');
 ta.value = '';
 ta.value = ev.data;
 }

 socket.onopen = function (ev) {
 var ta = document.getElementById('responseText');
 ta.value = 'start open websocket ...';
 }

 socket.onclose = function (ev) {
 var ta = document.getElementById('responseText');
 ta.value = '';
 ta.value = 'close websocket ...';
 }
 }else {
 alert('not support websocket !')
 }

 function send(msg) {
 if (!window.WebSocket) {
 return;
 }
 if (socket.readyState == WebSocket.OPEN) {
 socket.send(msg);
 }else {
 alert('connect fail !')
 }
 }
</script>
</html>

试验结果

1. 请求抓包说明

   
   

   ws请求

   
   

   如图中，首先是TCP三次握手，然后HTTP请求，建立WebSocket连接。之后客户端请求一次，然后服务端每隔1秒发送内容到客户端。

   
   

   

   keepAlive

   
   上图是空闲时候的keepAlive调用

2. 客户端调用

   
   

   服务端关闭的时候效果

   
   

   服务端主动发送的效果

   
   

   上图是服务端主动发送的效果，随着内容不同数据会变化。

参考资料

结语

以上就是本期的内容，后面有时间会继续netty相关实例的文章，确实在网络方面有很多新的收获。