MQTT_ProcessLoop

Loop to receive packets from the transport interface. Handles keep alive.

MQTTStatus_t MQTT_ProcessLoop( MQTTContext_t * pContext,
                               uint32_t timeoutMs );

Note

Passing a timeout value of 0 will run the loop for a single iteration.

If a dummy timer function, MQTTGetCurrentTimeFunc_t, is passed to the library, then the keep-alive mechanism is not supported by the MQTT_ProcessLoop API. In that case, the MQTT_ReceiveLoop API function should be used instead.

Parameters

[in]	pContext	Initialized and connected MQTT context.
[in]	timeoutMs	Minimum time in milliseconds that the receive loop will run, unless an error occurs.

Note

Calling this function blocks the calling context for a time period that depends on the passed timeoutMs, the configuration macros, MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_RETRY_TIMEOUT_MS, and the underlying transport interface implementation timeouts, unless an error occurs. The blocking period also depends on the execution time of the MQTTEventCallback_t callback supplied to the library. It is recommended that the supplied MQTTEventCallback_t callback does not contain blocking operations to prevent potential non-deterministic blocking period of the MQTT_ProcessLoop API call.

Returns

MQTTBadParameter if context is NULL; MQTTRecvFailed if a network error occurs during reception; MQTTSendFailed if a network error occurs while sending an ACK or PINGREQ; MQTTBadResponse if an invalid packet is received; MQTTKeepAliveTimeout if the server has not sent a PINGRESP before MQTT_PINGRESP_TIMEOUT_MS milliseconds; MQTTIllegalState if an incoming QoS 1/2 publish or ack causes an invalid transition for the internal state machine; MQTTSuccess on success.

Example

// Variables used in this example.
MQTTStatus_t status;
uint32_t timeoutMs = 100;
// This context is assumed to be initialized and connected.
MQTTContext_t * pContext;
 
while( true )
{
     status = MQTT_ProcessLoop( pContext, timeoutMs );
 
     if( status != MQTTSuccess )
     {
         // Determine the error. It's possible we might need to disconnect
         // the underlying transport connection.
     }
     else
     {
         // Other application functions.
     }
}