WebSockets MQTT 订阅

将 MQTT 客户端与网络套接字连接相结合。

WebSockets MQTT Subscription展示了如何设计一个自定义QIODevice ，将Web 套接字连接与QMqttClient 结合起来。

创建自定义 QIODevice

新的自定义设备WebSocketIODevice 必须是QIODevice 的子类：

class WebSocketIODevice : public QIODevice
{
    Q_OBJECT
public:
    WebSocketIODevice(QObject *parent = nullptr);

    bool isSequential() const override;
    qint64 bytesAvailable() const override;

    bool open(OpenMode mode) override;
    void close() override;

    qint64 readData(char *data, qint64 maxlen) override;
    qint64 writeData(const char *data, qint64 len) override;

    void setUrl(const QUrl &url);
    void setProtocol(const QByteArray &data);
Q_SIGNALS:
    void socketConnected();

public slots:
    void handleBinaryMessage(const QByteArray &msg);
    void onSocketConnected();

private:
    QByteArray m_protocol;
    QByteArray m_buffer;
    QWebSocket m_socket;
    QUrl m_url;
};

设计管理连接和订阅的类

WebSocketIODevice 将与和一起成为类的私有成员：QMqttClient QMqttSubscription ClientSubscription

private:
    QMqttClient m_client;
    QMqttSubscription *m_subscription;
    QUrl m_url;
    QString m_topic;
    WebSocketIODevice m_device;
    int m_version;

订阅和接收信息

主要逻辑在ClientSubscription 类的connectAndSubscribe() 方法中实现。在通过它初始化 MQTT 连接之前，您需要验证网络套接字是否已成功连接。建立 MQTT 连接后，QMqttClient 就可以订阅主题。如果订阅成功，QMqttSubscription 可用于接收来自订阅主题的消息，这些消息将由ClientSubscription 类的handleMessage() 方法处理。

voidClientSubscription::connectAndSubscribe() { qCDebug(lcWebSocketMqtt)<< "Connecting to broker at "<<m_url; m_device.setUrl(m_url); m_device.setProtocol(m_version== 3 ? "mqttv3.1":"mqtt"); connect(&m_device, &WebSocketIODevice::socketConnected, this, [this]() { qCDebug(lcWebSocketMqtt)<< "WebSocket 已连接，正在初始化 MQTT 连接"; m_client.setProtocolVersion(m_version== 3 ?QMqttClient::MQTT_3_1 ： QMqttClient::MQTT_3_1_1); m_client.setTransport(&m_device、 QMqttClientm_client.setTransport(&m_device, ::IODevice); connect(&m_client, &m_device, ::connected,this,[thisQMqttClient连接(&m_client, &::connected, this,[this]() { qCDebug(lcWebSocketMqtt)<< "MQTT 连接已建立"; m_subscription=m_client.subscribe(m_topic);if(!m_subscription) {                qDebug() << "Failed to subscribe to " << m_topic;
               emiterrorOccured(); } connect(m_subscription, &QMqttSubscription::stateChanged, [](QMqttSubscription::SubscriptionState s) { qCDebug(lcWebSocketMqtt)<< "Subscription state changed:"<<s; }); connect(m_subscription, &::messageReceived, [this](QMqttSubscription::messageReceived, [this](QMqttMessagemsg) { handleMessage(msg.payload()); }); }); m_client.connectToHost(); });if(!m_device.open(QIODevice::ReadWrite))        qDebug() << "Could not open socket device";
}

文件：

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