3.1.7.2 MQTT Service

The MQTT service provides an Application Programming Interface (API) to manage MQTT functionalities. These functionalities include, configuring the MQTT settings, connecting, disconnecting and reconnecting to the MQTT broker, publishing, subscribing and setting callbacks.

The MQTT service API example is as follows:

RNWF_RESULT_t RNWF_MQTT_SrvCtrl( RNWF_MQTT_SERVICE_t request, void *input)

It handles following services and reports the result to application over the return code or through the registered callback:

Table 3-4. MQTT Services
Service	Input	Description
`RNWF_MQTT_CONFIG`	Broker URL, Port, Client ID, Username, TLS configuration	Configures the MQTT server details along with the corresponding TLS configurations
`RNWF_MQTT_CONNECT`	None	Initiates the MQTT connection to the configured MQTT broker
`RNWF_MQTT_RECONNECT`	None	Triggers the re-connection to the configured MQTT broker
`RNWF_MQTT_DISCONNECT`	None	Disconnects from the connected MQTT broker
`RNWF_MQTT_SUBSCRIBE_QOS0`	Subscribe topic (String)	Subscribes to the given subscribe topic with QoS0
`RNWF_MQTT_SUBSCRIBE_QOS1`	Subscribe topic (String)	Subscribes to the given subscribe topic with QoS1
`RNWF_MQTT_SUBSCRIBE_QOS2`	Subscribe topic (String)	Subscribes to the given subscribe topic with QoS2
`RNWF_MQTT_PUBLISH`	New, QOS, Retain, topic, message	Publish the message on given publish topic and configuration
`RNWF_MQTT_SET_CALLBACK`	Callback Function Handler	Registers the MQTT callback to report the status to user application

The following list captures the MQTT Callback event codes and their arguments

Table 3-5. Callback Event codes
Event	Response Components	Comments
RNWF_MQTT_CONNECTED	None	Reported once connected to MQTT broker
RNWF_MQTT_DISCONNECTED	None	Event to report the MQTT broker disconnection
RNWF_MQTT_SUBCRIBE_MSG	dup, QoS, retain, topic, payload	Reports the received payload for the subscribed topic
RNWF_MQTT_SUBCRIBE_ACK	Integer string	Subscribe ack return code

MQTT Publish

User application can publish to the MQTT broker by creating the MQTT frame and then sending the frame using the RNWF_MQTT_SrvCtrl(RNWF_MQTT_PUBLISH, (void *)&mqtt_pub) API. The sequence chart is shown below.

MQTT Subscribe

The sequence for subscribing to a topic from the MQTT Broker is shown below. The user application needs to use the RNWF_MQTT_SrvCtrl(RNWF_MQTT_SUBSCRIBE_QOS0, buffer) API to subscribe to the topic with the appropriate QoS value.