MQTT_ReceiveLoop

Loop to receive packets from the transport interface. Does not handle keep alive.

MQTTStatus_t MQTT_ReceiveLoop( MQTTContext_t * pContext,
                               uint32_t timeoutMs );

Note

Passing a timeout value of 0 will run the loop for a single iteration. If a dummy MQTTGetCurrentTimeFunc_t was passed to MQTT_Init, then the timeout value passed to the API MUST be 0, and the MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_RETRY_TIMEOUT_MS timeout configurations MUST be set to 0.

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_ReceiveLoop 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; 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;
uint32_t keepAliveMs = 60 * 1000;
// This context is assumed to be initialized and connected.
MQTTContext_t * pContext;
 
while( true )
{
     status = MQTT_ReceiveLoop( pContext, timeoutMs );
 
     if( status != MQTTSuccess )
     {
         // Determine the error. It's possible we might need to disconnect
         // the underlying transport connection.
     }
     else
     {
         // Since this function does not send pings, the application may need
         // to in order to comply with keep alive.
         if( ( pContext->getTime() - pContext->lastPacketTime ) > keepAliveMs )
         {
             status = MQTT_Ping( pContext );
         }
 
         // Other application functions.
     }
}