class QMqttClient

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

Synopsis

Properties

• autoKeepAliveᅟ - This property holds whether the client will automatically manage keep alive messages to the server

• cleanSessionᅟ - This property holds the state after connecting to a broker

• clientIdᅟ - This property holds the client’s identifier value

• errorᅟ - Specifies the current error of the client

• hostnameᅟ - This property holds the hostname of the MQTT broker to connect to

• keepAliveᅟ - This property holds the interval at which regular ping messages are sent to the broker

• passwordᅟ - This property holds the password for connecting to a broker

• portᅟ - This property holds the port to connect to the MQTT broker

• protocolVersionᅟ - This property holds the MQTT standard version to use for connections

• stateᅟ - This property holds the current state of the client

• usernameᅟ - This property holds the user name for connecting to a broker

• willMessageᅟ - This property holds the payload of a Will Message

• willQoSᅟ - This property holds the level of QoS for sending and storing the Will Message

• willRetainᅟ - This property holds whether the Will Message should be retained on the broker for future subscribers to receive

• willTopicᅟ - This property holds the Will Topic

Methods

• def __init__()

• def authenticate()

• def autoKeepAlive()

• def cleanSession()

• def clientId()

• def connectToHost()

• def connectToHostEncrypted()

• def connectionProperties()

• def disconnectFromHost()

• def error()

• def hostname()

• def keepAlive()

• def lastWillProperties()

• def password()

• def port()

• def protocolVersion()

• def publish()

• def requestPing()

• def serverConnectionProperties()

• def setConnectionProperties()

• def setLastWillProperties()

• def setTransport()

• def state()

• def subscribe()

• def transport()

• def unsubscribe()

• def username()

• def willMessage()

• def willQoS()

• def willRetain()

• def willTopic()

Slots

• def setAutoKeepAlive()

• def setCleanSession()

• def setClientId()

• def setError()

• def setHostname()

• def setKeepAlive()

• def setPassword()

• def setPort()

• def setProtocolVersion()

• def setState()

• def setUsername()

• def setWillMessage()

• def setWillQoS()

• def setWillRetain()

• def setWillTopic()

Signals

• def authenticationFinished()

• def authenticationRequested()

• def autoKeepAliveChanged()

• def brokerSessionRestored()

• def cleanSessionChanged()

• def clientIdChanged()

• def connected()

• def disconnected()

• def errorChanged()

• def hostnameChanged()

• def keepAliveChanged()

• def messageReceived()

• def messageSent()

• def messageStatusChanged()

• def passwordChanged()

• def pingResponseReceived()

• def portChanged()

• def protocolVersionChanged()

• def stateChanged()

• def usernameChanged()

• def willMessageChanged()

• def willQoSChanged()

• def willRetainChanged()

• def willTopicChanged()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

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.

class TransportType

This enum type specifies the connection method to be used to instantiate a connection to a broker.

Constant	Description
QMqttClient.IODevice	The transport uses a class based on a QIODevice.
QMqttClient.AbstractSocket	The transport uses a class based on a QAbstractSocket.
QMqttClient.SecureSocket	The transport uses a class based on a QSslSocket.

class ClientState

This enum type specifies the states a client can enter.

Constant	Description
QMqttClient.Disconnected	The client is disconnected from the broker.
QMqttClient.Connecting	A connection request has been made, but the broker has not approved the connection yet.
QMqttClient.Connected	The client is connected to the broker.

class ClientError

This enum type specifies the error state of a client.

Constant	Description
QMqttClient.NoError	No error occurred.
QMqttClient.InvalidProtocolVersion	The broker does not accept a connection using the specified protocol version.
QMqttClient.IdRejected	The client ID is malformed. This might be related to its length.
QMqttClient.ServerUnavailable	The network connection has been established, but the service is unavailable on the broker side.
QMqttClient.BadUsernameOrPassword	The data in the username or password is malformed.
QMqttClient.NotAuthorized	The client is not authorized to connect.
QMqttClient.TransportInvalid	The underlying transport caused an error. For example, the connection might have been interrupted unexpectedly.
QMqttClient.ProtocolViolation	The client encountered a protocol violation, and therefore closed the connection.
QMqttClient.UnknownError	An unknown error occurred.
QMqttClient.Mqtt5SpecificError	The error is related to MQTT protocol level 5. A reason code might provide more details.

class ProtocolVersion

This enum specifies the protocol version of the MQTT standard to use during communication with a broker.

Constant	Description
QMqttClient.MQTT_3_1	MQTT Standard 3.1
QMqttClient.MQTT_3_1_1	MQTT Standard 3.1.1, publicly referred to as version 4
QMqttClient.MQTT_5_0	MQTT Standard 5.0

Note

Properties can be used directly when from __feature__ import true_property is used or via accessor functions otherwise.

property autoKeepAliveᅟ: bool

This property holds 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.

See also

keepAlive() requestPing() serverConnectionProperties() pingResponseReceived()

Access functions:

• autoKeepAlive()

• setAutoKeepAlive()

• Signal autoKeepAliveChanged()

property cleanSessionᅟ: bool

This property holds This property holds the state after connecting to a broker..

Access functions:

• cleanSession()

• setCleanSession()

• Signal cleanSessionChanged()

property clientIdᅟ: str

This property holds 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:

• clientId()

• setClientId()

• Signal clientIdChanged()

property errorᅟ: QMqttClient.ClientError

This property Specifies the current error of the client..

Access functions:

• error()

• setError()

• Signal errorChanged()

property hostnameᅟ: str

This property holds 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:

• hostname()

• setHostname()

• Signal hostnameChanged()

property keepAliveᅟ: int

This property holds 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.

See also

autoKeepAlive() requestPing() pingResponseReceived()

Access functions:

• keepAlive()

• setKeepAlive()

• Signal keepAliveChanged()

property passwordᅟ: str

This property holds This property holds the password for connecting to a broker..

Access functions:

• password()

• setPassword()

• Signal passwordChanged()

property portᅟ: int

This property holds 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:

• port()

• setPort()

• Signal portChanged()

property protocolVersionᅟ: QMqttClient.ProtocolVersion

This property holds 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:

• protocolVersion()

• setProtocolVersion()

• Signal protocolVersionChanged()

property stateᅟ: QMqttClient.ClientState

This property holds This property holds the current state of the client..

Access functions:

• state()

• setState()

• Signal stateChanged()

property usernameᅟ: str

This property holds This property holds the user name for connecting to a broker..

Access functions:

• username()

• setUsername()

• Signal usernameChanged()

property willMessageᅟ: QByteArray

This property holds This property holds the payload of a Will Message..

Access functions:

• willMessage()

• setWillMessage()

• Signal willMessageChanged()

property willQoSᅟ: int

This property holds This property holds the level of QoS for sending and storing the Will Message..

Access functions:

• willQoS()

• setWillQoS()

• Signal willQoSChanged()

property willRetainᅟ: bool

This property holds This property holds whether the Will Message should be retained on the broker for future subscribers to receive..

Access functions:

• willRetain()

• setWillRetain()

• Signal willRetainChanged()

property willTopicᅟ: str

This property holds This property holds the Will Topic..

Access functions:

• willTopic()

• setWillTopic()

• Signal willTopicChanged()

__init__([parent=None])

Parameters:

parent – QObject

Creates a new MQTT client instance with the specified parent.

authenticate(prop)

Parameters:

prop – QMqttAuthenticationProperties

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 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() authenticationFinished()

authenticationFinished(p)

Parameters:

p – QMqttAuthenticationProperties

This signal is emitted after extended authentication has finished. p specifies available details on the authentication process.

After successful authentication 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() authenticate()

authenticationRequested(p)

Parameters:

p – QMqttAuthenticationProperties

This signal is emitted after a client invoked connectToHost or connectToHostEncrypted and before the connection is established. In extended authentication, a broker might request additional details which need to be provided by invoking 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() authenticate()

autoKeepAlive()

Return type:

bool

See also

setAutoKeepAlive()

Getter of property autoKeepAliveᅟ .

autoKeepAliveChanged(autoKeepAlive)

Parameters:

autoKeepAlive – bool

Notification signal of property autoKeepAliveᅟ .

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 .

cleanSession()

Return type:

bool

See also

setCleanSession()

Getter of property cleanSessionᅟ .

cleanSessionChanged(cleanSession)

Parameters:

cleanSession – bool

Notification signal of property cleanSessionᅟ .

clientId()

Return type:

str

See also

setClientId()

Getter of property clientIdᅟ .

clientIdChanged(clientId)

Parameters:

clientId – str

Notification signal of property clientIdᅟ .

connectToHost()

Initiates a connection to the MQTT broker.

connectToHostEncrypted(conf)

Parameters:

conf – QSslConfiguration

Initiates an encrypted connection to the MQTT broker.

conf specifies the SSL configuration to be used for the connection

connected()

This signal is emitted when a connection has been established.

connectionProperties()

Return type:

QMqttConnectionProperties

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()

disconnectFromHost()

Disconnects from the MQTT broker.

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.

error()

Return type:

ClientError

See also

setError()

Getter of property errorᅟ .

errorChanged(error)

Parameters:

error – ClientError

Notification signal of property errorᅟ .

hostname()

Return type:

str

See also

setHostname()

Getter of property hostnameᅟ .

hostnameChanged(hostname)

Parameters:

hostname – str

Notification signal of property hostnameᅟ .

keepAlive()

Return type:

int

See also

setKeepAlive()

Getter of property keepAliveᅟ .

keepAliveChanged(keepAlive)

Parameters:

keepAlive – int

Notification signal of property keepAliveᅟ .

lastWillProperties()

Return type:

QMqttLastWillProperties

Returns the last will properties.

Note

QMqttLastWillProperties can only be used when the client specifies MQTT_5_0 as ProtocolVersion .

See also

setLastWillProperties()

messageReceived(message[, topic=QMqttTopicName()])

Parameters:

• message – QByteArray

• 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.

messageSent(id)

Parameters:

id – int

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.

messageStatusChanged(id, s, properties)

Parameters:

• id – int

• s – MessageStatus

• properties – QMqttMessageStatusProperties

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.

password()

Return type:

str

See also

setPassword()

Getter of property passwordᅟ .

passwordChanged(password)

Parameters:

password – str

Notification signal of property passwordᅟ .

pingResponseReceived()

This signal is emitted after the broker responds to a requestPing() call or a keepAlive() ping message, and the connection is still valid.

port()

Return type:

int

See also

setPort()

Getter of property portᅟ .

portChanged(port)

Parameters:

port – int

Notification signal of property portᅟ .

protocolVersion()

Return type:

ProtocolVersion

See also

setProtocolVersion()

Getter of property protocolVersionᅟ .

protocolVersionChanged(protocolVersion)

Parameters:

protocolVersion – ProtocolVersion

Notification signal of property protocolVersionᅟ .

publish(topic[, message=QByteArray()[, qos=0[, retain=false]]])

Parameters:

• topic – QMqttTopicName

• message – QByteArray

• qos – int

• retain – bool

Return type:

int

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.

publish(topic, properties[, message=QByteArray()[, qos=0[, retain=false]]])

Parameters:

• topic – QMqttTopicName

• properties – QMqttPublishProperties

• message – QByteArray

• qos – int

• retain – bool

Return type:

int

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 .

requestPing()

Return type:

bool

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() keepAlive()

serverConnectionProperties()

Return type:

QMqttServerConnectionProperties

Returns the QMqttServerConnectionProperties the broker returned after a connection attempt.

This can be used to verify that client side connection properties set by 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()

setAutoKeepAlive(autoKeepAlive)

Parameters:

autoKeepAlive – bool

See also

autoKeepAlive()

Setter of property autoKeepAliveᅟ .

setCleanSession(cleanSession)

Parameters:

cleanSession – bool

See also

cleanSession()

Setter of property cleanSessionᅟ .

setClientId(clientId)

Parameters:

clientId – str

See also

clientId()

Setter of property clientIdᅟ .

setConnectionProperties(prop)

Parameters:

prop – QMqttConnectionProperties

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 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()

setError(error)

Parameters:

error – ClientError

See also

error()

Setter of property errorᅟ .

setHostname(hostname)

Parameters:

hostname – str

See also

hostname()

Setter of property hostnameᅟ .

setKeepAlive(keepAlive)

Parameters:

keepAlive – int

See also

keepAlive()

Setter of property keepAliveᅟ .

setLastWillProperties(prop)

Parameters:

prop – QMqttLastWillProperties

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()

setPassword(password)

Parameters:

password – str

See also

password()

Setter of property passwordᅟ .

setPort(port)

Parameters:

port – int

See also

port()

Setter of property portᅟ .

setProtocolVersion(protocolVersion)

Parameters:

protocolVersion – ProtocolVersion

See also

protocolVersion()

Setter of property protocolVersionᅟ .

setState(state)

Parameters:

state – ClientState

See also

state()

Setter of property stateᅟ .

setTransport(device, transport)

Parameters:

• device – QIODevice

• transport – TransportType

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 connectToHost() .

See also

transport()

setUsername(username)

Parameters:

username – str

See also

username()

Setter of property usernameᅟ .

setWillMessage(willMessage)

Parameters:

willMessage – QByteArray

See also

willMessage()

Setter of property willMessageᅟ .

setWillQoS(willQoS)

Parameters:

willQoS – int

See also

willQoS()

Setter of property willQoSᅟ .

setWillRetain(willRetain)

Parameters:

willRetain – bool

See also

willRetain()

Setter of property willRetainᅟ .

setWillTopic(willTopic)

Parameters:

willTopic – str

See also

willTopic()

Setter of property willTopicᅟ .

state()

Return type:

ClientState

See also

setState()

Getter of property stateᅟ .

stateChanged(state)

Parameters:

state – ClientState

Notification signal of property stateᅟ .

subscribe(topic[, qos=0])

Parameters:

• topic – QMqttTopicFilter

• qos – int

Return type:

QMqttSubscription

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.

subscribe(topic, properties[, qos=0])

Parameters:

• topic – QMqttTopicFilter

• properties – QMqttSubscriptionProperties

• qos – int

Return type:

QMqttSubscription

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 .

transport()

Return type:

QIODevice

Returns the transport used for communication with the broker.

See also

setTransport()

unsubscribe(topic)

Parameters:

topic – QMqttTopicFilter

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.

unsubscribe(topic, properties)

Parameters:

• topic – QMqttTopicFilter

• properties – QMqttUnsubscriptionProperties

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 .

username()

Return type:

str

See also

setUsername()

Getter of property usernameᅟ .

usernameChanged(username)

Parameters:

username – str

Notification signal of property usernameᅟ .

willMessage()

Return type:

QByteArray

See also

setWillMessage()

Getter of property willMessageᅟ .

willMessageChanged(willMessage)

Parameters:

willMessage – QByteArray

Notification signal of property willMessageᅟ .

willQoS()

Return type:

int

See also

setWillQoS()

Getter of property willQoSᅟ .

willQoSChanged(willQoS)

Parameters:

willQoS – int

Notification signal of property willQoSᅟ .

willRetain()

Return type:

bool

See also

setWillRetain()

Getter of property willRetainᅟ .

willRetainChanged(willRetain)

Parameters:

willRetain – bool

Notification signal of property willRetainᅟ .

willTopic()

Return type:

str

See also

setWillTopic()

Getter of property willTopicᅟ .

willTopicChanged(willTopic)

Parameters:

willTopic – str

Notification signal of property willTopicᅟ .