MQTTAgent_Subscribe

MQTTStatus_t MQTTAgent_Subscribe( const MQTTAgentContext_t * pMqttAgentContext,
                                  MQTTAgentSubscribeArgs_t * pSubscriptionArgs,
                                  const MQTTAgentCommandInfo_t * pCommandInfo );

Add a command to call MQTT_Subscribe() for an MQTT connection.

Parameters

[in]	pMqttAgentContext	The MQTT agent to use.
[in]	pSubscriptionArgs	Struct describing topic to subscribe to.
[in]	pCommandInfo	The information pertaining to the command, including: cmdCompleteCallback Optional callback to invoke when the command completes. pCmdCompleteCallbackContext Optional completion callback context. blockTimeMs The maximum amount of time in milliseconds to wait for the command to be posted to the MQTT agent, should the agent's event queue be full. Tasks wait in the Blocked state so don't use any CPU time.

Note

The context passed to the callback through pCmdContext member of pCommandInfo parameter MUST remain in scope at least until the callback has been executed by the agent task.

Returns

#MQTTSuccess if the command was posted to the MQTT agent's event queue. Otherwise an enumerated error code.

Example

// Variables used in this example.
MQTTAgentContext_t agentContext;
MQTTStatus_t status;
MQTTAgentCommandInfo_t commandInfo = { 0 };
MQTTSubscribeInfo_t subscribeInfo = { 0 };
MQTTAgentSubscribeArgs_t subscribeArgs = { 0 };
 
// Function for command complete callback.
void subscribeCmdCompleteCb( MQTTAgentCommandContext_t * pCmdCallbackContext,
                             MQTTAgentReturnInfo_t * pReturnInfo );
 
// Fill the command information.
commandInfo.CmdCompleteCallback = subscribeCmdCompleteCb;
commandInfo.blockTimeMs = 500;
 
// Fill the information for topic filters to subscribe to.
subscribeInfo.qos = Qos1;
subscribeInfo.pTopicFilter = "/foo/bar";
subscribeInfo.topicFilterLength = strlen("/foo/bar");
subscribeArgs.pSubscribeInfo = &subscribeInfo;
subscribeArgs.numSubscriptions = 1U;
 
status = MQTTAgent_Subscribe( &agentContext, &subscribeArgs, &commandInfo );
 
if( status == MQTTSuccess )
{
  // Command to send subscribe request to the server has been queued. Notification
  // about completion of the subscribe operation will be notified to application
  // through invocation of subscribeCmdCompleteCb().
}