MQTT_Subscribe

Sends MQTT SUBSCRIBE for the given list of topic filters to the broker.

MQTTStatus_t MQTT_Subscribe( MQTTContext_t * pContext,
                             const MQTTSubscribeInfo_t * pSubscriptionList,
                             size_t subscriptionCount,
                             uint16_t packetId );

Parameters

[in]	pContext	Initialized MQTT context.
[in]	pSubscriptionList	List of MQTT subscription info.
[in]	subscriptionCount	The number of elements in pSubscriptionList.
[in]	packetId	Packet ID generated by MQTT_GetPacketId.

Returns

MQTTNoMemory if the MQTTContext_t.networkBuffer is too small to hold the MQTT packet; MQTTBadParameter if invalid parameters are passed; MQTTSendFailed if transport write failed; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTSubscribeInfo_t subscriptionList[ NUMBER_OF_SUBSCRIPTIONS ] = { 0 };
uint16_t packetId;
// This context is assumed to be initialized and connected.
MQTTContext_t * pContext;
// This is assumed to be a list of filters we want to subscribe to.
const char * filters[ NUMBER_OF_SUBSCRIPTIONS ];
 
// Set each subscription.
for( int i = 0; i < NUMBER_OF_SUBSCRIPTIONS; i++ )
{
     subscriptionList[ i ].qos = MQTTQoS0;
     // Each subscription needs a topic filter.
     subscriptionList[ i ].pTopicFilter = filters[ i ];
     subscriptionList[ i ].topicFilterLength = strlen( filters[ i ] );
}
 
// Obtain a new packet id for the subscription.
packetId = MQTT_GetPacketId( pContext );
 
status = MQTT_Subscribe( pContext, &subscriptionList[ 0 ], NUMBER_OF_SUBSCRIPTIONS, packetId );
 
if( status == MQTTSuccess )
{
     // We must now call MQTT_ReceiveLoop() or MQTT_ProcessLoop() to receive the SUBACK.
     // If the broker accepts the subscription we can now receive publishes
     // on the requested topics.
}