QMqttClient Class

The QMqttClient class represents the central access communicating with an MQTT broker. More...

Header:	#include <QMqttClient>
qmake:	QT += mqtt
Inherits:	QObject

• List of all members, including inherited members

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

autoKeepAlive : bool cleanSession : bool clientId : QString error : ClientError hostname : QString keepAlive : quint16 password : QString port : quint16

protocolVersion : ProtocolVersion state : ClientState username : QString willMessage : QByteArray willQoS : quint8 willRetain : bool willTopic : QString

Public Functions

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.

Member Function Documentation

[signal, since 5.12] 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.

This function was introduced in Qt 5.12.

See also authenticationRequested() and authenticate().

[signal, since 5.12] 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.

This function was introduced in Qt 5.12.

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.

[signal] void QMqttClient::connected()

This signal is emitted when a connection has been established.

[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.

[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, since 5.12] 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.

This function was introduced in Qt 5.12.

[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.

[override virtual] QMqttClient::~QMqttClient()

Deletes a MQTT client. If the MQTT client was not already disconnected from the MQTT broker, it will be disconnected from automatically.

[since 5.12] 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.

This function was introduced in Qt 5.12.

See also authenticationRequested() and authenticationFinished().

[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.

[since 5.14] 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

This function was introduced in Qt 5.14.

[since 5.12] QMqttConnectionProperties QMqttClient::connectionProperties() const

Returns the connection properties the client requests to the broker.

This function was introduced in Qt 5.12.

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.

[since 5.12] QMqttLastWillProperties QMqttClient::lastWillProperties() const

Returns the last will properties.

This function was introduced in Qt 5.12.

See also setLastWillProperties().

[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, since 5.12] 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: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

This function was introduced in Qt 5.12.

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().

[since 5.12] 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.

This function was introduced in Qt 5.12.

See also connectionProperties().

[since 5.12] 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.

This function was introduced in Qt 5.12.

See also connectionProperties().

[since 5.12] 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.

This function was introduced in Qt 5.12.

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.

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.

[since 5.12] 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.

This function was introduced in Qt 5.12.

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().

[since 5.12] 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.

This function was introduced in Qt 5.12.