Netty-源碼分析WebSocketClient客戶端

WebSocketClient客戶端使用Netty實現的源碼分析

EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap(); // (1)
            b.group(workerGroup); // (2)
            b.channel(NioSocketChannel.class); // (3)
            b.option(ChannelOption.SO_KEEPALIVE, true); // (4)
            b.handler(new ChannelInitializer<SocketChannel>() {
                @Override
                public void initChannel(SocketChannel ch) throws Exception {
                    //處理http請求的編解碼器
                    ch.pipeline().addLast("http-codec", new HttpClientCodec());
                    ch.pipeline().addLast("aggregator", new HttpObjectAggregator(655360));
                    ch.pipeline().addLast("http-chunked", new ChunkedWriteHandler());
                    ch.pipeline().addLast("ws", new WebSocketClientProtocolHandler(URI.create("ws://192.168.80.110:8080/websocket"),
                            WebSocketVersion.V08, "", true, new DefaultHttpHeaders(), Integer.MAX_VALUE));
                    ch.pipeline().addLast("handler", new WsClientHandler());
                }
            });
            ChannelFuture f = b.connect("192.168.80.110", 8080).sync();
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
        }

最核心的地方在於這個Handler。

 ch.pipeline().addLast("ws", new WebSocketClientProtocolHandler(URI.create("ws://192.168.80.110:8080/websocket"),
                            WebSocketVersion.V08, "", true, new DefaultHttpHeaders(), Integer.MAX_VALUE));

WebSocketClientProtocolHandler關鍵代碼片段如下：

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) {
        ChannelPipeline cp = ctx.pipeline();
        if (cp.get(WebSocketClientProtocolHandshakeHandler.class) == null) {
            // Add the WebSocketClientProtocolHandshakeHandler before this one.
            ctx.pipeline().addBefore(ctx.name(), WebSocketClientProtocolHandshakeHandler.class.getName(),
                                     new WebSocketClientProtocolHandshakeHandler(handshaker, handshakeTimeoutMillis));
        }
        if (cp.get(Utf8FrameValidator.class) == null) {
            // Add the UFT8 checking before this one.
            ctx.pipeline().addBefore(ctx.name(), Utf8FrameValidator.class.getName(),
                    new Utf8FrameValidator());
        }
    }

在handlerAdded事件中，動態的掛載了WebSocketClientProtocolHandshakeHandler到ppLine中。

 

 

WebSocketClientProtocolHandshakeHandler關鍵代碼

@Override
    public void channelActive(final ChannelHandlerContext ctx) throws Exception {
        super.channelActive(ctx);
        handshaker.handshake(ctx.channel()).addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) throws Exception {
                if (!future.isSuccess()) {
                    handshakePromise.tryFailure(future.cause());
                    ctx.fireExceptionCaught(future.cause());
                } else {
                    ctx.fireUserEventTriggered(
                            WebSocketClientProtocolHandler.ClientHandshakeStateEvent.HANDSHAKE_ISSUED);
                }
            }
        });
        applyHandshakeTimeout();
    }

在channelActive事件（tcp連接建立後觸發），會發送http握手請求，升級websocket協議。

 @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        if (!(msg instanceof FullHttpResponse)) {
            ctx.fireChannelRead(msg);
            return;
        }

        FullHttpResponse response = (FullHttpResponse) msg;
        try {
            if (!handshaker.isHandshakeComplete()) {
                handshaker.finishHandshake(ctx.channel(), response);
                handshakePromise.trySuccess();
                ctx.fireUserEventTriggered(
                        WebSocketClientProtocolHandler.ClientHandshakeStateEvent.HANDSHAKE_COMPLETE);
                ctx.pipeline().remove(this);
                return;
            }
            throw new IllegalStateException("WebSocketClientHandshaker should have been non finished yet");
        } finally {
            response.release();
        }
    }

在上面方法中，讀取服務器端返回的Http響應，完成ws握手，移除當前Handler。

 

public final ChannelFuture handshake(Channel channel, final ChannelPromise promise) {
        ChannelPipeline pipeline = channel.pipeline();
        HttpResponseDecoder decoder = pipeline.get(HttpResponseDecoder.class);
        if (decoder == null) {
            HttpClientCodec codec = pipeline.get(HttpClientCodec.class);
            if (codec == null) {
               promise.setFailure(new IllegalStateException("ChannelPipeline does not contain " +
                       "an HttpResponseDecoder or HttpClientCodec"));
               return promise;
            }
        }

        FullHttpRequest request = newHandshakeRequest();

        channel.writeAndFlush(request).addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) {
                if (future.isSuccess()) {
                    ChannelPipeline p = future.channel().pipeline();
                    ChannelHandlerContext ctx = p.context(HttpRequestEncoder.class);
                    if (ctx == null) {
                        ctx = p.context(HttpClientCodec.class);
                    }
                    if (ctx == null) {
                        promise.setFailure(new IllegalStateException("ChannelPipeline does not contain " +
                                "an HttpRequestEncoder or HttpClientCodec"));
                        return;
                    }
                    p.addAfter(ctx.name(), "ws-encoder", newWebSocketEncoder());

                    promise.setSuccess();
                } else {
                    promise.setFailure(future.cause());
                }
            }
        });
        return promise;
    }

發送http請求到服務器端（ws客戶端握手請求）

掛載websocket編碼器。

 

   @Override
    protected FullHttpRequest newHandshakeRequest() {
        URI wsURL = uri();

        // Get 16 bit nonce and base 64 encode it
        byte[] nonce = WebSocketUtil.randomBytes(16);
        String key = WebSocketUtil.base64(nonce);

        String acceptSeed = key + MAGIC_GUID;
        byte[] sha1 = WebSocketUtil.sha1(acceptSeed.getBytes(CharsetUtil.US_ASCII));
        expectedChallengeResponseString = WebSocketUtil.base64(sha1);

        if (logger.isDebugEnabled()) {
            logger.debug(
                    "WebSocket version 08 client handshake key: {}, expected response: {}",
                    key, expectedChallengeResponseString);
        }

        // Format request
        FullHttpRequest request = new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.GET, upgradeUrl(wsURL),
                Unpooled.EMPTY_BUFFER);
        HttpHeaders headers = request.headers();

        if (customHeaders != null) {
            headers.add(customHeaders);
        }

        headers.set(HttpHeaderNames.UPGRADE, HttpHeaderValues.WEBSOCKET)
               .set(HttpHeaderNames.CONNECTION, HttpHeaderValues.UPGRADE)
               .set(HttpHeaderNames.SEC_WEBSOCKET_KEY, key)
               .set(HttpHeaderNames.HOST, websocketHostValue(wsURL));

        if (!headers.contains(HttpHeaderNames.SEC_WEBSOCKET_ORIGIN)) {
            headers.set(HttpHeaderNames.SEC_WEBSOCKET_ORIGIN, websocketOriginValue(wsURL));
        }

        String expectedSubprotocol = expectedSubprotocol();
        if (expectedSubprotocol != null && !expectedSubprotocol.isEmpty()) {
            headers.set(HttpHeaderNames.SEC_WEBSOCKET_PROTOCOL, expectedSubprotocol);
        }

        headers.set(HttpHeaderNames.SEC_WEBSOCKET_VERSION, "8");
        return request;
    }

構造握手的http請求信息。