// Copyright (C) 2018 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \example websocketsubscription
    \examplecategory {Connectivity}
    \title WebSockets MQTT Subscription
    \ingroup qtmqtt-examples
    \brief Combining an MQTT client with a web socket connection.

    \e {WebSockets MQTT Subscription} shows how to design a custom
    QIODevice to combine a \l {Qt WebSockets}{web socket} connection with
    QMqttClient.

    \section1 Creating a Custom QIODevice

    The new custom device, \c WebSocketIODevice, has to be a subclass of
    \l QIODevice:

    \quotefromfile websocketsubscription/websocketiodevice.h
    \skipto WebSocketIODevice
    \printuntil }

    \section1 Designing a Class to Manage the Connection and Subscription

    \c WebSocketIODevice will be a private member of the \c ClientSubscription
    class alongside the QMqttClient and the QMqttSubscription:

    \quotefromfile websocketsubscription/clientsubscription.h
    \skipto private
    \printuntil m_version

    \section1 Subscribing to and Receiving Messages

    The main logic is implemented in the \c connectAndSubscribe() method of the
    \c ClientSubscription class. You need to verify that the web socket has
    successfully connected before you can initialize an MQTT connection over
    it. After the MQTT connection has been established, the QMqttClient can
    subscribe to the topic. If the subscription is successful, the
    QMqttSubscription can be used to receive messages from the subscribed topic
    that will be handled by the \c handleMessage() method of the
    \c ClientSubscription class.

    \quotefromfile websocketsubscription/clientsubscription.cpp
    \skipto connectAndSubscribe
    \printuntil Could
    \printuntil }
*/