MQTT_Init

Initialize an MQTT context.

MQTTStatus_t MQTT_Init( MQTTContext_t * pContext,
                        const TransportInterface_t * pTransportInterface,
                        MQTTGetCurrentTimeFunc_t getTimeFunction,
                        MQTTEventCallback_t userCallback,
                        const MQTTFixedBuffer_t * pNetworkBuffer );

This function must be called on a MQTTContext_t before any other function.

Note

The MQTTGetCurrentTimeFunc_t function for querying time must be defined. If there is no time implementation, it is the responsibility of the application to provide a dummy function to always return 0, provide 0 timeouts for all calls to MQTT_Connect, MQTT_ProcessLoop, and MQTT_ReceiveLoop and configure the MQTT_RECV_POLLING_TIMEOUT_MS and MQTT_SEND_RETRY_TIMEOUT_MS configurations to be 0. This will result in loop functions running for a single iteration, and MQTT_Connect relying on MQTT_MAX_CONNACK_RECEIVE_RETRY_COUNT to receive the CONNACK packet.

Parameters

[in]	pContext	The context to initialize.
[in]	pTransportInterface	The transport interface to use with the context.
[in]	getTimeFunction	The time utility function to use with the context.
[in]	userCallback	The user callback to use with the context to notify about incoming packet events.
[in]	pNetworkBuffer	Network buffer provided for the context.

Returns

MQTTBadParameter if invalid parameters are passed; MQTTSuccess otherwise.

Example

// Function for obtaining a timestamp.
uint32_t getTimeStampMs();
// Callback function for receiving packets.
void eventCallback(
     MQTTContext_t * pContext,
     MQTTPacketInfo_t * pPacketInfo,
     MQTTDeserializedInfo_t * pDeserializedInfo
);
// Network send.
int32_t networkSend( NetworkContext_t * pContext, const void * pBuffer, size_t bytes );
// Network receive.
int32_t networkRecv( NetworkContext_t * pContext, void * pBuffer, size_t bytes );
 
MQTTContext_t mqttContext;
TransportInterface_t transport;
MQTTFixedBuffer_t fixedBuffer;
uint8_t buffer[ 1024 ];
 
// Clear context.
memset( ( void * ) &mqttContext, 0x00, sizeof( MQTTContext_t ) );
 
// Set transport interface members.
transport.pNetworkContext = &someTransportContext;
transport.send = networkSend;
transport.recv = networkRecv;
 
// Set buffer members.
fixedBuffer.pBuffer = buffer;
fixedBuffer.size = 1024;
 
status = MQTT_Init( &mqttContext, &transport, getTimeStampMs, eventCallback, &fixedBuffer );
 
if( status == MQTTSuccess )
{
     // Do something with mqttContext. The transport and fixedBuffer structs were
     // copied into the context, so the original structs do not need to stay in scope.
}