QMqttClient Class
The QMqttClient class represents the central access communicating with an MQTT broker. More...
Header: | #include <QMqttClient> |
CMake: | find_package(Qt6 REQUIRED COMPONENTS Mqtt) target_link_libraries(mytarget PRIVATE Qt6::Mqtt) |
qmake: | QT += mqtt |
Inherits: | QObject |
Public Types
enum | ClientError { NoError, InvalidProtocolVersion, IdRejected, ServerUnavailable, BadUsernameOrPassword, …, Mqtt5SpecificError } |
enum | ClientState { Disconnected, Connecting, Connected } |
enum | ProtocolVersion { MQTT_3_1, MQTT_3_1_1, MQTT_5_0 } |
enum | TransportType { IODevice, AbstractSocket, SecureSocket } |
Properties
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Public Functions
QMqttClient(QObject *parent = nullptr) | |
virtual | ~QMqttClient() override |
void | authenticate(const QMqttAuthenticationProperties &prop) |
bool | autoKeepAlive() const |
bool | cleanSession() const |
QString | clientId() const |
void | connectToHost() |
void | connectToHostEncrypted(const QSslConfiguration &conf) |
QMqttConnectionProperties | connectionProperties() const |
void | disconnectFromHost() |
QMqttClient::ClientError | error() const |
QString | hostname() const |
quint16 | keepAlive() const |
QMqttLastWillProperties | lastWillProperties() const |
QString | password() const |
quint16 | port() const |
QMqttClient::ProtocolVersion | protocolVersion() const |
qint32 | publish(const QMqttTopicName &topic, const QByteArray &message = QByteArray(), quint8 qos = 0, bool retain = false) |
qint32 | publish(const QMqttTopicName &topic, const QMqttPublishProperties &properties, const QByteArray &message = QByteArray(), quint8 qos = 0, bool retain = false) |
bool | requestPing() |
QMqttServerConnectionProperties | serverConnectionProperties() const |
void | setConnectionProperties(const QMqttConnectionProperties &prop) |
void | setLastWillProperties(const QMqttLastWillProperties &prop) |
void | setTransport(QIODevice *device, QMqttClient::TransportType transport) |
QMqttClient::ClientState | state() const |
QMqttSubscription * | subscribe(const QMqttTopicFilter &topic, quint8 qos = 0) |
QMqttSubscription * | subscribe(const QMqttTopicFilter &topic, const QMqttSubscriptionProperties &properties, quint8 qos = 0) |
QIODevice * | transport() const |
void | unsubscribe(const QMqttTopicFilter &topic) |
void | unsubscribe(const QMqttTopicFilter &topic, const QMqttUnsubscriptionProperties &properties) |
QString | username() const |
QByteArray | willMessage() const |
quint8 | willQoS() const |
bool | willRetain() const |
QString | willTopic() const |
Public Slots
void | setAutoKeepAlive(bool autoKeepAlive) |
void | setCleanSession(bool cleanSession) |
void | setClientId(const QString &clientId) |
void | setError(QMqttClient::ClientError error) |
void | setHostname(const QString &hostname) |
void | setKeepAlive(quint16 keepAlive) |
void | setPassword(const QString &password) |
void | setPort(quint16 port) |
void | setProtocolVersion(QMqttClient::ProtocolVersion protocolVersion) |
void | setState(QMqttClient::ClientState state) |
void | setUsername(const QString &username) |
void | setWillMessage(const QByteArray &willMessage) |
void | setWillQoS(quint8 willQoS) |
void | setWillRetain(bool willRetain) |
void | setWillTopic(const QString &willTopic) |
Signals
void | authenticationFinished(const QMqttAuthenticationProperties &p) |
void | authenticationRequested(const QMqttAuthenticationProperties &p) |
void | autoKeepAliveChanged(bool autoKeepAlive) |
void | brokerSessionRestored() |
void | cleanSessionChanged(bool cleanSession) |
void | clientIdChanged(QString clientId) |
void | connected() |
void | disconnected() |
void | errorChanged(QMqttClient::ClientError error) |
void | hostnameChanged(QString hostname) |
void | keepAliveChanged(quint16 keepAlive) |
void | messageReceived(const QByteArray &message, const QMqttTopicName &topic = QMqttTopicName()) |
void | messageSent(qint32 id) |
void | messageStatusChanged(qint32 id, QMqtt::MessageStatus s, const QMqttMessageStatusProperties &properties) |
void | passwordChanged(QString password) |
void | pingResponseReceived() |
void | portChanged(quint16 port) |
void | protocolVersionChanged(QMqttClient::ProtocolVersion protocolVersion) |
void | stateChanged(QMqttClient::ClientState state) |
void | usernameChanged(QString username) |
void | willMessageChanged(QByteArray willMessage) |
void | willQoSChanged(quint8 willQoS) |
void | willRetainChanged(bool willRetain) |
void | willTopicChanged(QString willTopic) |
Detailed Description
An MQTT client is a program or device that uses MQTT to create a network connection to an MQTT server, also called a broker. The connection request must contain a unique client identifier. Optionally, it can contain a Will Topic, Will Message, user name, and password.
Once a connection is created, a client can send messages that other clients might be interested in receiving, subscribe to request notifications on topics, unsubscribe to remove a request for notifications, and disconnect from the broker.
Member Type Documentation
enum QMqttClient::ClientError
This enum type specifies the error state of a client.
Constant | Value | Description |
---|---|---|
QMqttClient::NoError | 0 | No error occurred. |
QMqttClient::InvalidProtocolVersion | 1 | The broker does not accept a connection using the specified protocol version. |
QMqttClient::IdRejected | 2 | The client ID is malformed. This might be related to its length. |
QMqttClient::ServerUnavailable | 3 | The network connection has been established, but the service is unavailable on the broker side. |
QMqttClient::BadUsernameOrPassword | 4 | The data in the username or password is malformed. |
QMqttClient::NotAuthorized | 5 | The client is not authorized to connect. |
QMqttClient::TransportInvalid | 256 | The underlying transport caused an error. For example, the connection might have been interrupted unexpectedly. |
QMqttClient::ProtocolViolation | 257 | The client encountered a protocol violation, and therefore closed the connection. |
QMqttClient::UnknownError | 258 | An unknown error occurred. |
QMqttClient::Mqtt5SpecificError | 259 | The error is related to MQTT protocol level 5. A reason code might provide more details. |
enum QMqttClient::ClientState
This enum type specifies the states a client can enter.
Constant | Value | Description |
---|---|---|
QMqttClient::Disconnected | 0 | The client is disconnected from the broker. |
QMqttClient::Connecting | 1 | A connection request has been made, but the broker has not approved the connection yet. |
QMqttClient::Connected | 2 | The client is connected to the broker. |
enum QMqttClient::ProtocolVersion
This enum specifies the protocol version of the MQTT standard to use during communication with a broker.
Constant | Value | Description |
---|---|---|
QMqttClient::MQTT_3_1 | 3 | MQTT Standard 3.1 |
QMqttClient::MQTT_3_1_1 | 4 | MQTT Standard 3.1.1, publicly referred to as version 4 |
QMqttClient::MQTT_5_0 | 5 | MQTT Standard 5.0 |
enum QMqttClient::TransportType
This enum type specifies the connection method to be used to instantiate a connection to a broker.
Constant | Value | Description |
---|---|---|
QMqttClient::IODevice | 0 | The transport uses a class based on a QIODevice. |
QMqttClient::AbstractSocket | 1 | The transport uses a class based on a QAbstractSocket. |
QMqttClient::SecureSocket | 2 | The transport uses a class based on a QSslSocket. |
Property Documentation
autoKeepAlive : bool
This property holds whether the client will automatically manage keep alive messages to the server.
If this property is true
, then the client will automatically send a ping message to the server at the keepAlive interval.
Otherwise, a user will have to manually invoke requestPing within the specified interval of the connection. If no ping has been sent within the interval, the server will disconnect.
The default of this property is true
.
Access functions:
bool | autoKeepAlive() const |
void | setAutoKeepAlive(bool autoKeepAlive) |
Notifier signal:
void | autoKeepAliveChanged(bool autoKeepAlive) |
See also keepAlive(), requestPing(), serverConnectionProperties(), and pingResponseReceived().
cleanSession : bool
This property holds the state after connecting to a broker.
Access functions:
bool | cleanSession() const |
void | setCleanSession(bool cleanSession) |
Notifier signal:
void | cleanSessionChanged(bool cleanSession) |
clientId : QString
This property holds the client's identifier value.
Each client needs to have a unique ID to be able to connect to an MQTT broker. If no client ID is specified by the user, one will be generated automatically when a connection is established.
Access functions:
QString | clientId() const |
void | setClientId(const QString &clientId) |
Notifier signal:
void | clientIdChanged(QString clientId) |
error : ClientError
Specifies the current error of the client.
Access functions:
QMqttClient::ClientError | error() const |
void | setError(QMqttClient::ClientError error) |
Notifier signal:
void | errorChanged(QMqttClient::ClientError error) |
hostname : QString
This property holds the hostname of the MQTT broker to connect to.
If no transport is specified via setTransport(), the client will instantiate a socket connection to the specified hostname itself.
Access functions:
QString | hostname() const |
void | setHostname(const QString &hostname) |
Notifier signal:
void | hostnameChanged(QString hostname) |
keepAlive : quint16
This property holds the interval at which regular ping messages are sent to the broker.
Once a connection to a broker is established, the client needs to send frequent updates to propagate it can still be reached. The interval between those updates is specified by this property.
The interval is specified in seconds.
If the broker does not respond within a grace period the connection will be closed.
Access functions:
quint16 | keepAlive() const |
void | setKeepAlive(quint16 keepAlive) |
Notifier signal:
void | keepAliveChanged(quint16 keepAlive) |
See also autoKeepAlive(), requestPing(), and pingResponseReceived().
password : QString
This property holds the password for connecting to a broker.
Access functions:
QString | password() const |
void | setPassword(const QString &password) |
Notifier signal:
void | passwordChanged(QString password) |
port : quint16
This property holds the port to connect to the MQTT broker.
If no transport is specified via setTransport(), the client will instantiate a socket connection to a host with this port number.
Access functions:
quint16 | port() const |
void | setPort(quint16 port) |
Notifier signal:
void | portChanged(quint16 port) |
protocolVersion : ProtocolVersion
This property holds the MQTT standard version to use for connections.
Specifies the version of the standard the client uses for connecting to a broker. Valid values are:
- 3: MQTT standard version 3.1.
- 4: MQTT standard version 3.1.1, often referred to MQTT 4.
- 5: MQTT Standard 5.0.
Access functions:
QMqttClient::ProtocolVersion | protocolVersion() const |
void | setProtocolVersion(QMqttClient::ProtocolVersion protocolVersion) |
Notifier signal:
void | protocolVersionChanged(QMqttClient::ProtocolVersion protocolVersion) |
state : ClientState
This property holds the current state of the client.
Access functions:
QMqttClient::ClientState | state() const |
void | setState(QMqttClient::ClientState state) |
Notifier signal:
void | stateChanged(QMqttClient::ClientState state) |
username : QString
This property holds the user name for connecting to a broker.
Access functions:
QString | username() const |
void | setUsername(const QString &username) |
Notifier signal:
void | usernameChanged(QString username) |
willMessage : QByteArray
This property holds the payload of a Will Message.
Access functions:
QByteArray | willMessage() const |
void | setWillMessage(const QByteArray &willMessage) |
Notifier signal:
void | willMessageChanged(QByteArray willMessage) |
willQoS : quint8
This property holds the level of QoS for sending and storing the Will Message.
Access functions:
quint8 | willQoS() const |
void | setWillQoS(quint8 willQoS) |
Notifier signal:
void | willQoSChanged(quint8 willQoS) |
willRetain : bool
This property holds whether the Will Message should be retained on the broker for future subscribers to receive.
Access functions:
bool | willRetain() const |
void | setWillRetain(bool willRetain) |
Notifier signal:
void | willRetainChanged(bool willRetain) |
willTopic : QString
This property holds the Will Topic.
Access functions:
QString | willTopic() const |
void | setWillTopic(const QString &willTopic) |
Notifier signal:
void | willTopicChanged(QString willTopic) |
Member Function Documentation
[explicit]
QMqttClient::QMqttClient(QObject *parent = nullptr)
Creates a new MQTT client instance with the specified parent.
[override virtual noexcept]
QMqttClient::~QMqttClient()
Deletes a MQTT client. If the MQTT client was not already disconnected from the MQTT broker, it will be disconnected from automatically.
void QMqttClient::authenticate(const QMqttAuthenticationProperties &prop)
Sends an authentication request to the broker. prop specifies the required information to fulfill the authentication request.
This function should only be called after a QMqttClient::authenticationRequested signal has been emitted.
Note: Extended authentication is part of the MQTT 5.0 standard and can only be used when the client specifies MQTT_5_0 as ProtocolVersion.
See also authenticationRequested() and authenticationFinished().
[signal]
void QMqttClient::authenticationFinished(const QMqttAuthenticationProperties &p)
This signal is emitted after extended authentication has finished. p specifies available details on the authentication process.
After successful authentication QMqttClient::connected is emitted.
Note: Extended authentication is part of the MQTT 5.0 standard and can only be used when the client specifies MQTT_5_0 as ProtocolVersion.
See also authenticationRequested() and authenticate().
[signal]
void QMqttClient::authenticationRequested(const QMqttAuthenticationProperties &p)
This signal is emitted after a client invoked QMqttClient::connectToHost or QMqttClient::connectToHostEncrypted and before the connection is established. In extended authentication, a broker might request additional details which need to be provided by invoking QMqttClient::authenticate. p specifies properties provided by the broker.
Note: Extended authentication is part of the MQTT 5.0 standard and can only be used when the client specifies MQTT_5_0 as ProtocolVersion.
See also authenticationFinished() and authenticate().
[signal]
void QMqttClient::brokerSessionRestored()
This signal is emitted after a client has successfully connected to a broker with the cleanSession property set to false
, and the broker has restored the session.
Sessions can be restored if a client has connected previously using the same clientId.
[invokable]
void QMqttClient::connectToHost()
Initiates a connection to the MQTT broker.
Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.
void QMqttClient::connectToHostEncrypted(const QSslConfiguration &conf)
Initiates an encrypted connection to the MQTT broker.
conf specifies the SSL configuration to be used for the connection
[signal]
void QMqttClient::connected()
This signal is emitted when a connection has been established.
QMqttConnectionProperties QMqttClient::connectionProperties() const
Returns the connection properties the client requests to the broker.
Note: QMqttConnectionProperties can only be used when the client specifies MQTT_5_0 as ProtocolVersion.
See also setConnectionProperties().
[invokable]
void QMqttClient::disconnectFromHost()
Disconnects from the MQTT broker.
Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.
[signal]
void QMqttClient::disconnected()
This signal is emitted when a connection has been closed. A connection may be closed when disconnectFromHost() is called or when the broker disconnects.
QMqttLastWillProperties QMqttClient::lastWillProperties() const
Returns the last will properties.
Note: QMqttLastWillProperties can only be used when the client specifies MQTT_5_0 as ProtocolVersion.
See also setLastWillProperties().
[signal]
void QMqttClient::messageReceived(const QByteArray &message, const QMqttTopicName &topic = QMqttTopicName())
This signal is emitted when a new message has been received. The category of the message is specified by topic with the content being message.
[signal]
void QMqttClient::messageSent(qint32 id)
Indicates that a message that was sent via the publish() function has been received by the broker. The id is the same as returned by publish()
to help tracking the status of the message.
[signal]
void QMqttClient::messageStatusChanged(qint32 id, QMqtt::MessageStatus s, const QMqttMessageStatusProperties &properties)
This signal is emitted when the status for the message identified by id changes. s specifies the new status of the message, and properties specify additional properties provided by the server.
[signal]
void QMqttClient::pingResponseReceived()
This signal is emitted after the broker responds to a requestPing() call or a keepAlive() ping message, and the connection is still valid.
[invokable]
qint32 QMqttClient::publish(const QMqttTopicName &topic, const QByteArray &message = QByteArray(), quint8 qos = 0, bool retain = false)
Publishes a message to the broker with the specified topic. qos specifies the QoS level required for transferring the message.
If retain is set to true
, the message will stay on the broker for other clients to connect and receive the message.
Returns an ID that is used internally to identify the message.
Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.
[invokable]
qint32 QMqttClient::publish(const QMqttTopicName &topic, const QMqttPublishProperties &properties, const QByteArray &message = QByteArray(), quint8 qos = 0, bool retain = false)
Publishes a message to the broker with the specified properties and topic. qos specifies the QoS level required for transferring the message.
If retain is set to true
, the message will stay on the broker for other clients to connect and receive the message.
Returns an ID that is used internally to identify the message.
Note: properties will only be passed to the broker when the client specifies MQTT_5_0 as ProtocolVersion.
Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.
bool QMqttClient::requestPing()
Sends a ping message to the broker and expects a reply.
If the connection is active and autoKeepAlive is true
, then calling this function will fail as the client is responsible for managing this process.
Using requestPing()
manually requires a call every time within the keepAlive interval as long as the connection is active.
To check whether the ping is successful, connect to the pingResponseReceived() signal.
Returns true
if the ping request could be sent.
See also pingResponseReceived(), autoKeepAlive(), and keepAlive().
QMqttServerConnectionProperties QMqttClient::serverConnectionProperties() const
Returns the QMqttServerConnectionProperties the broker returned after a connection attempt.
This can be used to verify that client side connection properties set by QMqttClient::setConnectionProperties have been accepted by the broker. Also, in case of a failed connection attempt, it can be used for connection diagnostics.
Note: QMqttServerConnectionProperties can only be used when the client specifies MQTT_5_0 as ProtocolVersion.
See also connectionProperties().
void QMqttClient::setConnectionProperties(const QMqttConnectionProperties &prop)
Sets the connection properties to prop. QMqttConnectionProperties can be used to ask the server to use a specific feature set. After a connection request the server response can be obtained by calling QMqttClient::serverConnectionProperties.
Note: The connection properties can only be set if the MQTT client is in the Disconnected state.
Note: QMqttConnectionProperties can only be used when the client specifies MQTT_5_0 as ProtocolVersion.
See also connectionProperties().
void QMqttClient::setLastWillProperties(const QMqttLastWillProperties &prop)
Sets the last will properties to prop. QMqttLastWillProperties allows to set additional features for the last will message stored at the broker.
Note: The connection properties can only be set if the MQTT client is in the Disconnected state.
Note: QMqttLastWillProperties can only be used when the client specifies MQTT_5_0 as ProtocolVersion.
See also lastWillProperties().
void QMqttClient::setTransport(QIODevice *device, QMqttClient::TransportType transport)
Sets the transport to device. A transport can be either a socket type or derived from QIODevice and is specified by transport.
Note: The transport can only be exchanged if the MQTT client is in the Disconnected state.
Note: Setting a custom transport for a client does not pass over responsibility on connection management. The transport has to be opened for QIODevice based transports or connected for socket type transports before calling QMqttClient::connectToHost().
See also transport().
QMqttSubscription *QMqttClient::subscribe(const QMqttTopicFilter &topic, quint8 qos = 0)
Adds a new subscription to receive notifications on topic. The parameter qos specifies the level at which security messages are received. For more information about the available QoS levels, see Quality of Service.
This function returns a pointer to a QMqttSubscription. If the same topic is subscribed twice, the return value points to the same subscription instance. The MQTT client is the owner of the subscription.
QMqttSubscription *QMqttClient::subscribe(const QMqttTopicFilter &topic, const QMqttSubscriptionProperties &properties, quint8 qos = 0)
Adds a new subscription to receive notifications on topic. The parameter properties specifies additional subscription properties to be validated by the broker. The parameter qos specifies the level at which security messages are received. For more information about the available QoS levels, see Quality of Service.
This function returns a pointer to a QMqttSubscription. If the same topic is subscribed twice, the return value points to the same subscription instance. The MQTT client is the owner of the subscription.
Note: properties will only be passed to the broker when the client specifies MQTT_5_0 as ProtocolVersion.
QIODevice *QMqttClient::transport() const
Returns the transport used for communication with the broker.
See also setTransport().
void QMqttClient::unsubscribe(const QMqttTopicFilter &topic)
Unsubscribes from topic. No notifications will be sent to any of the subscriptions made by calling subscribe().
Note: If a client disconnects from a broker without unsubscribing, the broker will store all messages and publish them on the next reconnect.
void QMqttClient::unsubscribe(const QMqttTopicFilter &topic, const QMqttUnsubscriptionProperties &properties)
Unsubscribes from topic. No notifications will be sent to any of the subscriptions made by calling subscribe(). properties specifies additional user properties to be passed to the broker.
Note: If a client disconnects from a broker without unsubscribing, the broker will store all messages and publish them on the next reconnect.
Note: properties will only be passed to the broker when the client specifies MQTT_5_0 as ProtocolVersion.
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