WebSockets MQTT Subscription Example

 // Copyright (C) 2017 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

 #include "clientsubscription.h"

 #include <QtCore/QCoreApplication>
 #include <QtCore/QCommandLineParser>
 #include <QtCore/QLoggingCategory>

 int main(int argc, char *argv[])
 {
     QCoreApplication a(argc, argv);
     QCoreApplication::setApplicationVersion("1.0");

     QCommandLineParser parser;
     parser.setApplicationDescription(QLatin1String("Websocket MQTT subscription tool"));
     auto help = parser.addHelpOption();

     // Use http://www.hivemq.com/demos/websocket-client/ in browser to publish
     QCommandLineOption urlOption(QStringList() << "host" << "url" << "broker",
                                  QStringLiteral("Host to connect to, eg ws://broker.hivemq.com:8000/mqtt"),
                                  "host");
     parser.addOption(urlOption);

     QCommandLineOption subscriptionOption(QStringList() << "t" << "topic",
                                           QStringLiteral("Topic to subscribe to"), "topic");
     parser.addOption(subscriptionOption);

     QCommandLineOption debugOption(QStringList() << "d" << "debug",
                                    QStringLiteral("Enable Debug mode"));
     parser.addOption(debugOption);

     QCommandLineOption versionOption(QStringList() << "v" << "version",
                                      QStringLiteral("MQTT protocol version.\n3: MQTT 3.1\n4: MQTT 3.1.1"),
                                      "version", "3");
     parser.addOption(versionOption);

     parser.process(a.arguments());

     const QString debugLog = QString::fromLatin1("qtdemo.websocket.mqtt*=%1").arg(
                                 parser.isSet(debugOption) ? "true" : "false");
     QLoggingCategory::setFilterRules(debugLog);

     ClientSubscription clientsub;
     clientsub.setUrl(QUrl(parser.value(urlOption)));
     clientsub.setTopic(parser.value(subscriptionOption));

     const QString versionString = parser.value(versionOption);

     if (versionString == "4") {
         clientsub.setVersion(4);
     } else if (versionString == "3") {
         clientsub.setVersion(3);
     } else {
         qInfo() << "Unknown MQTT version";
         return -2;
     }

     clientsub.connectAndSubscribe();
     return a.exec();
 }