@Override
public void onOpen(Session session, EndpointConfig config) {
    String id = session.getId();
    log.debug("{}: open ws proxy ", id);
    try {
        ChannelFuture cf = backend.connect().sync();
        Channel channel = cf.channel();
        WebSocketClientProtocolHandler wscph = makeWsProtocolHandler(session);
        WebSocketClientHandshaker handshaker = wscph.handshaker();
        WsHandler handler = new WsHandler(handshaker, channel, session);
        channel.pipeline().addLast(new HttpObjectAggregator(1024 * 4),
          WebSocketClientCompressionHandler.INSTANCE,
          wscph,
          handler);
        handshaker.handshake(channel);
        log.debug("{}: wait messages", id);
        session.addMessageHandler(String.class, handler::onFrontString);
        session.addMessageHandler(ByteBuffer.class, handler::onFrontBytes);
    } catch (Exception e) {
        log.error("{}: can not establish ws connect with backed", id, e);
    }

}
 

@SuppressWarnings("FutureReturnValueIgnored")
final void withWebsocketSupport(WebsocketClientSpec websocketClientSpec, boolean compress) {
	URI url = websocketUri();
	//prevent further header to be sent for handshaking
	if (markSentHeaders()) {
		// Returned value is deliberately ignored
		addHandlerFirst(NettyPipeline.HttpAggregator, new HttpObjectAggregator(8192));
		removeHandler(NettyPipeline.HttpMetricsHandler);

		if (websocketClientSpec.compress()) {
			requestHeaders().remove(HttpHeaderNames.ACCEPT_ENCODING);
			// Returned value is deliberately ignored
			removeHandler(NettyPipeline.HttpDecompressor);
			// Returned value is deliberately ignored
			addHandlerFirst(NettyPipeline.WsCompressionHandler, WebSocketClientCompressionHandler.INSTANCE);
		}

		if (log.isDebugEnabled()) {
			log.debug(format(channel(), "Attempting to perform websocket handshake with {}"), url);
		}
		WebsocketClientOperations ops = new WebsocketClientOperations(url, websocketClientSpec, this);

		if (!rebind(ops)) {
			log.error(format(channel(), "Error while rebinding websocket in channel attribute: " +
					get(channel()) + " to " + ops));
		}
	}
}
 

/**
 * @return true if the handshake is done properly.
 * @throws URISyntaxException   throws if there is an error in the URI syntax.
 * @throws InterruptedException throws if the connecting the server is interrupted.
 */
public boolean handhshake() throws InterruptedException, URISyntaxException, SSLException, ProtocolException {
    boolean isSuccess;
    URI uri = new URI(url);
    String scheme = uri.getScheme() == null ? "ws" : uri.getScheme();
    final String host = uri.getHost() == null ? "127.0.0.1" : uri.getHost();
    final int port;
    if (uri.getPort() == -1) {
        if ("ws".equalsIgnoreCase(scheme)) {
            port = 80;
        } else if ("wss".equalsIgnoreCase(scheme)) {
            port = 443;
        } else {
            port = -1;
        }
    } else {
        port = uri.getPort();
    }

    if (!"ws".equalsIgnoreCase(scheme) && !"wss".equalsIgnoreCase(scheme)) {
        logger.error("Only WS(S) is supported.");
        return false;
    }

    final boolean ssl = "wss".equalsIgnoreCase(scheme);
    final SslContext sslCtx;
    if (ssl) {
        sslCtx = SslContextBuilder.forClient().trustManager(InsecureTrustManagerFactory.INSTANCE).build();
    } else {
        sslCtx = null;
    }

    group = new NioEventLoopGroup();

    HttpHeaders headers = new DefaultHttpHeaders();
    for (Map.Entry<String, String> entry : customHeaders.entrySet()) {
        headers.add(entry.getKey(), entry.getValue());
    }
    // Connect with V13 (RFC 6455 aka HyBi-17). You can change it to V08 or V00.
    // If you change it to V00, ping is not supported and remember to change
    // HttpResponseDecoder to WebSocketHttpResponseDecoder in the pipeline.
    handler = new WebSocketClientHandler(
            WebSocketClientHandshakerFactory.newHandshaker(uri, WebSocketVersion.V13, subProtocol, true, headers),
            latch);

    Bootstrap bootstrap = new Bootstrap();
    bootstrap.group(group).channel(NioSocketChannel.class).handler(new ChannelInitializer<SocketChannel>() {
        @Override
        protected void initChannel(SocketChannel ch) {
            ChannelPipeline p = ch.pipeline();
            if (sslCtx != null) {
                p.addLast(sslCtx.newHandler(ch.alloc(), host, port));
            }
            p.addLast(new HttpClientCodec(), new HttpObjectAggregator(8192),
                    WebSocketClientCompressionHandler.INSTANCE, handler);
        }
    });

    channel = bootstrap.connect(uri.getHost(), port).sync().channel();
    isSuccess = handler.handshakeFuture().sync().isSuccess();
    logger.info("WebSocket Handshake successful : " + isSuccess);
    return isSuccess;
}
 

/**
 * @return true if the handshake is done properly.
 * @throws URISyntaxException   throws if there is an error in the URI syntax.
 * @throws InterruptedException throws if the connecting the server is interrupted.
 */
public boolean handhshake() throws InterruptedException, URISyntaxException, SSLException, ProtocolException {
    boolean isSuccess;
    URI uri = new URI(url);
    String scheme = uri.getScheme() == null ? "ws" : uri.getScheme();
    final String host = uri.getHost() == null ? "127.0.0.1" : uri.getHost();
    final int port;
    if (uri.getPort() == -1) {
        if ("ws".equalsIgnoreCase(scheme)) {
            port = 80;
        } else if ("wss".equalsIgnoreCase(scheme)) {
            port = 443;
        } else {
            port = -1;
        }
    } else {
        port = uri.getPort();
    }

    if (!"ws".equalsIgnoreCase(scheme) && !"wss".equalsIgnoreCase(scheme)) {
        logger.error("Only WS(S) is supported.");
        return false;
    }

    final boolean ssl = "wss".equalsIgnoreCase(scheme);
    final SslContext sslCtx;
    if (ssl) {
        sslCtx = SslContextBuilder.forClient().trustManager(InsecureTrustManagerFactory.INSTANCE).build();
    } else {
        sslCtx = null;
    }

    group = new NioEventLoopGroup();

    HttpHeaders headers = new DefaultHttpHeaders();
    for (Map.Entry<String, String> entry : customHeaders.entrySet()) {
        headers.add(entry.getKey(), entry.getValue());
    }
    // Connect with V13 (RFC 6455 aka HyBi-17). You can change it to V08 or V00.
    // If you change it to V00, ping is not supported and remember to change
    // HttpResponseDecoder to WebSocketHttpResponseDecoder in the pipeline.
    handler = new WebSocketClientHandler(
            WebSocketClientHandshakerFactory.newHandshaker(uri, WebSocketVersion.V13, subProtocol, true, headers),
            latch);

    Bootstrap bootstrap = new Bootstrap();
    bootstrap.group(group).channel(NioSocketChannel.class).handler(new ChannelInitializer<SocketChannel>() {
        @Override
        protected void initChannel(SocketChannel ch) {
            ChannelPipeline p = ch.pipeline();
            if (sslCtx != null) {
                p.addLast(sslCtx.newHandler(ch.alloc(), host, port));
            }
            p.addLast(new HttpClientCodec(), new HttpObjectAggregator(8192),
                    WebSocketClientCompressionHandler.INSTANCE, handler);
        }
    });

    channel = bootstrap.connect(uri.getHost(), port).sync().channel();
    isSuccess = handler.handshakeFuture().sync().isSuccess();
    logger.info("WebSocket Handshake successful : " + isSuccess);
    return isSuccess;
}
 

/**
 * @return true if the handshake is done properly.
 * @throws URISyntaxException throws if there is an error in the URI syntax.
 * @throws InterruptedException throws if the connecting the server is interrupted.
 */
public boolean handhshake() throws InterruptedException, URISyntaxException, SSLException {
    boolean isDone;
    URI uri = new URI(url);
    String scheme = uri.getScheme() == null ? "ws" : uri.getScheme();
    final String host = uri.getHost() == null ? "127.0.0.1" : uri.getHost();
    final int port;
    if (uri.getPort() == -1) {
        if ("ws".equalsIgnoreCase(scheme)) {
            port = 80;
        } else if ("wss".equalsIgnoreCase(scheme)) {
            port = 443;
        } else {
            port = -1;
        }
    } else {
        port = uri.getPort();
    }

    if (!"ws".equalsIgnoreCase(scheme) && !"wss".equalsIgnoreCase(scheme)) {
        logger.error("Only WS(S) is supported.");
        return false;
    }

    final boolean ssl = "wss".equalsIgnoreCase(scheme);
    final SslContext sslCtx;
    if (ssl) {
        sslCtx = SslContextBuilder.forClient()
                                  .trustManager(InsecureTrustManagerFactory.INSTANCE).build();
    } else {
        sslCtx = null;
    }

    group = new NioEventLoopGroup();

    HttpHeaders headers = new DefaultHttpHeaders();
    customHeaders.entrySet().forEach(
            header -> headers.add(header.getKey(), header.getValue())
    );
    try {
        // Connect with V13 (RFC 6455 aka HyBi-17). You can change it to V08 or V00.
        // If you change it to V00, ping is not supported and remember to change
        // HttpResponseDecoder to WebSocketHttpResponseDecoder in the pipeline.
        handler =
                new WebSocketClientHandler(
                        WebSocketClientHandshakerFactory.newHandshaker(
                                uri, WebSocketVersion.V13, subProtocol,
                                true, headers));

        Bootstrap b = new Bootstrap();
        b.group(group)
         .channel(NioSocketChannel.class)
         .handler(new ChannelInitializer<SocketChannel>() {
             @Override
             protected void initChannel(SocketChannel ch) {
                 ChannelPipeline p = ch.pipeline();
                 if (sslCtx != null) {
                     p.addLast(sslCtx.newHandler(ch.alloc(), host, port));
                 }
                 p.addLast(
                         new HttpClientCodec(),
                         new HttpObjectAggregator(8192),
                         WebSocketClientCompressionHandler.INSTANCE,
                         handler);
             }
         });

        channel = b.connect(uri.getHost(), port).sync().channel();
        isDone = handler.handshakeFuture().sync().isSuccess();
        logger.debug("WebSocket Handshake successful : " + isDone);
        return isDone;
    } catch (Exception e) {
        logger.error("Handshake unsuccessful : " + e.getMessage(), e);
        return false;
    }
}