【Netty】WebSocket

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2024-09-27 22:52:39 214人阅读

一、前言

　　前面学习了codec和ChannelHandler之间的关系，接着学习WebSocket。

二、WebSocket

　　2.1. WebSocket介绍

　　WebSocket协议允许客户端和服务器随时传输消息，要求他们异步处理接收的消息，而几乎所有的浏览器都支持WebSocket协议，Netty支持WebSocket协议的所有实现，可以在应用中直接使用。

　　2.2. WebSocket应用示例

　　下面示例展示了如何使用WebSocket协议实现基于浏览器的实时聊天应用，示例逻辑图如下图所示。

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　　处理逻辑如下

　　　　· 客户端发送消息。

　　　　· 消息转发至其他所有客户端。

　　本示例中只实现服务端部分，客户端网页为index.html。

　　2.3 添加WebSocket支持

　　升级握手机制可用于从标准HTTP或HTTPS协议切换到WebSocket，使用WebSocket的应用程序以HTTP/S开头，当请求指定URL时将会启动该协议。本应用有如下惯例：如果URL请求以/ ws结尾，我们将使用升级的WebSocket协议，否则，将使用HTTP/S协议，连接升级后，所有数据将使用WebSocket传输。下图展示服务端的逻辑。

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　　1. 处理HTTP请求

　　首先我们实现处理HTTP请求的组件，该组件将为访问聊天室的页面提供服务，并显示连接的客户端发送的消息。下面是HttpRequestHandler代码，其继承SimpleChannelInboundHandler。　

public class HttpRequestHandler    extends SimpleChannelInboundHandler<FullHttpRequest> {    private final String wsUri;    private static final File INDEX;    static {        URL location = HttpRequestHandler.class            .getProtectionDomain()            .getCodeSource().getLocation();        try {            String path = location.toURI() + "index.html";            path = !path.contains("file:") ? path : path.substring(5);            INDEX = new File(path);        } catch (URISyntaxException e) {            throw new IllegalStateException(                "Unable to locate index.html", e);        }    }    public HttpRequestHandler(String wsUri) {        this.wsUri = wsUri;    }    @Override    public void channelRead0(ChannelHandlerContext ctx,        FullHttpRequest request) throws Exception {        if (wsUri.equalsIgnoreCase(request.getUri())) {            ctx.fireChannelRead(request.retain());        } else {            if (HttpHeaders.is100ContinueExpected(request)) {                send100Continue(ctx);            }            RandomAccessFile file = new RandomAccessFile(INDEX, "r");            HttpResponse response = new DefaultHttpResponse(            request.getProtocolVersion(), HttpResponseStatus.OK);            response.headers().set(                HttpHeaders.Names.CONTENT_TYPE,                "text/plain; charset=UTF-8");            boolean keepAlive = HttpHeaders.isKeepAlive(request);            if (keepAlive) {                response.headers().set(                    HttpHeaders.Names.CONTENT_LENGTH, file.length());                response.headers().set( HttpHeaders.Names.CONNECTION,                    HttpHeaders.Values.KEEP_ALIVE);            }            ctx.write(response);            if (ctx.pipeline().get(SslHandler.class) == null) {                ctx.write(new DefaultFileRegion(                file.getChannel(), 0, file.length()));            } else {                ctx.write(new ChunkedNioFile(file.getChannel()));            }            ChannelFuture future = ctx.writeAndFlush(                LastHttpContent.EMPTY_LAST_CONTENT);            if (!keepAlive) {                future.addListener(ChannelFutureListener.CLOSE);            }        }    }    private static void send100Continue(ChannelHandlerContext ctx) {        FullHttpResponse response = new DefaultFullHttpResponse(            HttpVersion.HTTP_1_1, HttpResponseStatus.CONTINUE);        ctx.writeAndFlush(response);    }    @Override    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)        throws Exception {        cause.printStackTrace();        ctx.close();    }}

　　上述代码用于处理纯HTTP请求，对于WebSocket而言，数据使用帧进行传输，完整的数据包含多帧。

　　2. 处理WebSocket帧

　　WebSocket定义了六种帧，如下图所示。

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　　对于聊天应用而言，其包含如下帧：CloseWebSocketFrame、PingWebSocketFrame、PongWebSocketFrame、TextWebSocketFrame。

　　下面代码展示了用于处理TextWebSocketFrames的ChannelHandler。　　

public class TextWebSocketFrameHandler    extends SimpleChannelInboundHandler<TextWebSocketFrame> {    private final ChannelGroup group;    public TextWebSocketFrameHandler(ChannelGroup group) {        this.group = group;    }    @Override    public void userEventTriggered(ChannelHandlerContext ctx,        Object evt) throws Exception {        if (evt == WebSocketServerProtocolHandler            .ServerHandshakeStateEvent.HANDSHAKE_COMPLETE) {            ctx.pipeline().remove(HttpRequestHandler.class);            group.writeAndFlush(new TextWebSocketFrame(                "Client " + ctx.channel() + " joined"));            group.add(ctx.channel());        } else {            super.userEventTriggered(ctx, evt);        }    }    @Override    public void channelRead0(ChannelHandlerContext ctx,        TextWebSocketFrame msg) throws Exception {        group.writeAndFlush(msg.retain());    }}

　　3. 初始化ChannelPipeline

　　为在ChannelPipeline中添加ChannelHandler，需要继承ChannelInitializer并且实现initChannel方法，下面是ChatServerInitializer的代码。　

public class ChatServerInitializer extends ChannelInitializer<Channel> {    private final ChannelGroup group;    public ChatServerInitializer(ChannelGroup group) {        this.group = group;    }    @Override    protected void initChannel(Channel ch) throws Exception {        ChannelPipeline pipeline = ch.pipeline();        pipeline.addLast(new HttpServerCodec());        pipeline.addLast(new ChunkedWriteHandler());        pipeline.addLast(new HttpObjectAggregator(64 * 1024));        pipeline.addLast(new HttpRequestHandler("/ws"));        pipeline.addLast(new WebSocketServerProtocolHandler("/ws"));        pipeline.addLast(new TextWebSocketFrameHandler(group));    }}

　　对于使用HTTP协议（升级前）和WebSocket协议（升级后）的管道中的处理器分别如下图所示。

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　　4. Bootstrapping

　　ChatServer类用于启动服务器并且安装ChatServerInitializer，其代码如下。　　

public class ChatServer {    private final ChannelGroup channelGroup =        new DefaultChannelGroup(ImmediateEventExecutor.INSTANCE);    private final EventLoopGroup group = new NioEventLoopGroup();    private Channel channel;    public ChannelFuture start(InetSocketAddress address) {        ServerBootstrap bootstrap = new ServerBootstrap();        bootstrap.group(group)            .channel(NioServerSocketChannel.class)            .childHandler(createInitializer(channelGroup));        ChannelFuture future = bootstrap.bind(address);        future.syncUninterruptibly();        channel = future.channel();        return future;    }    protected ChannelInitializer<Channel> createInitializer(        ChannelGroup group) {        return new ChatServerInitializer(group);    }    public void destroy() {        if (channel != null) {            channel.close();        }        channelGroup.close();        group.shutdownGracefully();    }    public static void main(String[] args) throws Exception {        if (args.length != 1) {            System.err.println("Please give port as argument");            System.exit(1);        }        int port = Integer.parseInt(args[0]);        final ChatServer endpoint = new ChatServer();        ChannelFuture future = endpoint.start(            new InetSocketAddress(port));        Runtime.getRuntime().addShutdownHook(new Thread() {            @Override            public void run() {                endpoint.destroy();            }        });        future.channel().closeFuture().syncUninterruptibly();    }}

　　上述代码就完成了服务端的所有代码，接着进行测试。

　　2.4 加密应用

　　上述代码中可正常进行通信，但是并未加密，首先需要添加SecureChatServerInitializer，其代码如下。　　

public class SecureChatServerInitializer extends ChatServerInitializer {    private final SslContext context;    public SecureChatServerInitializer(ChannelGroup group,        SslContext context) {        super(group);        this.context = context;    }        @Override    protected void initChannel(Channel ch) throws Exception {        super.initChannel(ch);        SSLEngine engine = context.newEngine(ch.alloc());        ch.pipeline().addFirst(new SslHandler(engine));    }}

　　然后添加SecureChatServerInitializer，代码如下。　　

public class SecureChatServer extends ChatServer {    private final SslContext context;    public SecureChatServer(SslContext context) {        this.context = context;    }    @Override    protected ChannelInitializer<Channel> createInitializer(        ChannelGroup group) {        return new SecureChatServerInitializer(group, context);    }    public static void main(String[] args) throws Exception {        if (args.length != 1) {            System.err.println("Please give port as argument");            System.exit(1);        }        int port = Integer.parseInt(args[0]);        SelfSignedCertificate cert = new SelfSignedCertificate();        SslContext context = SslContext.newServerContext(        cert.certificate(), cert.privateKey());        final SecureChatServer endpoint = new SecureChatServer(context);        ChannelFuture future = endpoint.start(new InetSocketAddress(port));        Runtime.getRuntime().addShutdownHook(new Thread() {            @Override            public void run() {                endpoint.destroy();            }        });        future.channel().closeFuture().syncUninterruptibly();    }}

　　2.5 测试应用

　　在编译的classes文件夹中加入index.html（客户端），其中index.html的源码如下　　

<!DOCTYPE html><html><head><meta charset="UTF-8"><title>WebSocket Chat</title></head><body>    <script type="text/javascript">        var socket;        if (!window.WebSocket) {            window.WebSocket = window.MozWebSocket;        }        if (window.WebSocket) {            socket = new WebSocket("ws://localhost:8080/ws");            socket.onmessage = function(event) {                var ta = document.getElementById(‘responseText‘);                ta.value = ta.value + ‘\n‘ + event.data            };            socket.onopen = function(event) {                var ta = document.getElementById(‘responseText‘);                ta.value = "connected!";            };            socket.onclose = function(event) {                var ta = document.getElementById(‘responseText‘);                ta.value = ta.value + "connection is shutdown";            };        } else {            alert("your broswer do not support WebSocket！");        }        function send(message) {            if (!window.WebSocket) {                return;            }            if (socket.readyState == WebSocket.OPEN) {                socket.send(message);            } else {                alert("connection is not start.");            }        }    </script>    <form onsubmit="return false;">        <h3>WebSocket ChatRoom:</h3>        <textarea id="responseText" style="width: 500px; height: 300px;"></textarea>        <br>         <input type="text" name="message"  style="width: 300px" value="">        <input type="button" value="http://www.mamicode.com/Send Message" onclick="send(this.form.message.value)">        <input type="button" onclick="javascript:document.getElementById(‘responseText‘).value=http://www.mamicode.com/‘‘" value="http://www.mamicode.com/Clear message">    </form>    <br>     <br> </body></html>

　　然后启动ChatServer（非加密方式），最后在浏览器中访问localhost:8080（可打开多个窗口，多个客户端），其运行效果如下。　　

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　　可以看到两个客户端之间可以正常进行通信，互相发送消息。

三、总结

　　本篇博文通过一个示例讲解了WebSocket协议的具体使用，可完成不同客户端之间的通信，也谢谢各位园友的观看~

【Netty】WebSocket

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