7.MQTT网页客户端连接MQTT服务器的问题WebSocket connection to 'ws://XXX:1883/' failed: Connection closed before receiving a handshake response

问题描述：
MQTT.js提供了连接MQTT的一套javascipt的方法，可供前端连接到MQTT服务器，也可以作为脚本测试。
以脚本形式，用nodejs运行，是没有问题的，能够正常连接并且发送报文。
但是如果把js代码放到HTML文件中，就不能正常完成连接，提示：
客户端提示：

服务器提示：

问题解决；
根据客户端提示，是无法完成握手连接，根据服务器提示，是因为解包的时候，包不符合格式，导致了连接拒绝。
通过查阅文献，发现普通的socket和websocket是不一样的。
直接运行脚本使用的是socket.io 而 浏览器使用的是websocket，而处理这两种报文是不一样的。
所以猜测是MQTT并没有打开websocket支持，而是把过来的包当做普通的socket包处理了。
查阅代码发现：
我服务器使用的是moquette，里面的nettyAcceptor已经明确说明了TCP和websocket的不同处理，可以看到代码中websocket是关闭的：

private void initializePlainTCPTransport(final NettyMQTTHandler handler, IConfig props) throws IOException {
final MoquetteIdleTimeoutHandler timeoutHandler = new MoquetteIdleTimeoutHandler();
String host = props.getProperty(BrokerConstants.HOST_PROPERTY_NAME);
String tcpPortProp = props.getProperty(PORT_PROPERTY_NAME, DISABLED_PORT_BIND);
if (DISABLED_PORT_BIND.equals(tcpPortProp)) {
LOG.info("tcp MQTT is disabled because the value for the property with key {}", BrokerConstants.PORT_PROPERTY_NAME);
return;
}
int port = Integer.parseInt(tcpPortProp);
initFactory(host, port, new PipelineInitializer() {
@Override
void init(ChannelPipeline pipeline) {
pipeline.addFirst("idleStateHandler", new IdleStateHandler(0, 0, Constants.DEFAULT_CONNECT_TIMEOUT));
pipeline.addAfter("idleStateHandler", "idleEventHandler", timeoutHandler);
// pipeline.addLast("logger", new LoggingHandler("Netty", LogLevel.ERROR));
pipeline.addFirst("bytemetrics", new BytesMetricsHandler(m_bytesMetricsCollector));
pipeline.addLast("decoder", new MQTTDecoder());
pipeline.addLast("encoder", new MQTTEncoder());
pipeline.addLast("metrics", new MessageMetricsHandler(m_metricsCollector));
// pipeline.addLast("messageLogger", new MQTTMessageLogger());
pipeline.addLast("handler", handler);
}
});
}

private void initializeWebSocketTransport(final NettyMQTTHandler handler, IConfig props) throws IOException {
String webSocketPortProp = props.getProperty(WEB_SOCKET_PORT_PROPERTY_NAME, DISABLED_PORT_BIND);
if (DISABLED_PORT_BIND.equals(webSocketPortProp)) {
//Do nothing no WebSocket configured
LOG.info("WebSocket is disabled");
return;
}
else{
LOG.info("WebSocket is enable");
}
int port = Integer.valueOf(webSocketPortProp);

final MoquetteIdleTimeoutHandler timeoutHandler = new MoquetteIdleTimeoutHandler();

String host = props.getProperty(BrokerConstants.HOST_PROPERTY_NAME);
initFactory(host, port, new PipelineInitializer() {
@Override
void init(ChannelPipeline pipeline) {
pipeline.addLast("httpEncoder", new HttpResponseEncoder());
pipeline.addLast("httpDecoder", new HttpRequestDecoder());
pipeline.addLast("aggregator", new HttpObjectAggregator(65536));
pipeline.addLast("webSocketHandler", new WebSocketServerProtocolHandler("/mqtt", MQTT_SUBPROTOCOL_CSV_LIST));
pipeline.addLast("ws2bytebufDecoder", new WebSocketFrameToByteBufDecoder());
pipeline.addLast("bytebuf2wsEncoder", new ByteBufToWebSocketFrameEncoder());
pipeline.addFirst("idleStateHandler", new IdleStateHandler(0, 0, Constants.DEFAULT_CONNECT_TIMEOUT));
pipeline.addAfter("idleStateHandler", "idleEventHandler", timeoutHandler);
pipeline.addFirst("bytemetrics", new BytesMetricsHandler(m_bytesMetricsCollector));
pipeline.addLast("decoder", new MQTTDecoder());
pipeline.addLast("encoder", new MQTTEncoder());
pipeline.addLast("metrics", new MessageMetricsHandler(m_metricsCollector));
pipeline.addLast("handler", handler);
}
});
}

解决方法：
设置一个端口，我设为1885，将websocket服务打开就可以了。

String webSocketPortProp = props.getProperty(WEB_SOCKET_PORT_PROPERTY_NAME);
        if (DISABLED_PORT_BIND.equals(webSocketPortProp)) {
            //Do nothing no WebSocket configured
            LOG.info("WebSocket is disabled");
            return;
        }
        else{
            LOG.info("WebSocket is enable");
        }
        int port = Integer.valueOf(webSocketPortProp);