MQTT_GetIncomingPacketTypeAndLength

Extract the MQTT packet type and length from incoming packet.

MQTTStatus_t MQTT_GetIncomingPacketTypeAndLength( TransportRecv_t readFunc,
                                                  NetworkContext_t * pNetworkContext,
                                                  MQTTPacketInfo_t * pIncomingPacket );

This function must be called for every incoming packet to retrieve the MQTTPacketInfo_t.type and MQTTPacketInfo_t.remainingLength. A MQTTPacketInfo_t is not valid until this routine has been invoked.

Parameters

[in]	readFunc	Transport layer read function pointer.
[in]	pNetworkContext	The network context pointer provided by the application.
[out]	pIncomingPacket	Pointer to MQTTPacketInfo_t structure. This is where type, remaining length and packet identifier are stored.

Returns

MQTTSuccess on successful extraction of type and length, MQTTBadParameter if pIncomingPacket is invalid, MQTTRecvFailed on transport receive failure, MQTTBadResponse if an invalid packet is read, and MQTTNoDataAvailable if there is nothing to read.

Example

// TransportRecv_t function for reading from the network.
int32_t socket_recv(
     NetworkContext_t * pNetworkContext,
     void * pBuffer,
     size_t bytesToRecv
);
// Some context to be used with above transport receive function.
NetworkContext_t networkContext;
 
// Struct to hold the incoming packet information.
MQTTPacketInfo_t incomingPacket;
MQTTStatus_t status = MQTTSuccess;
int32_t bytesRecvd;
// Buffer to hold the remaining data of the incoming packet.
uint8_t buffer[ BUFFER_SIZE ];
 
// Loop until data is available to be received.
do{
     status = MQTT_GetIncomingPacketTypeAndLength(
         socket_recv,
         &networkContext,
         &incomingPacket
     );
} while( status == MQTTNoDataAvailable );
 
assert( status == MQTTSuccess );
 
// Receive the rest of the incoming packet.
assert( incomingPacket.remainingLength <= BUFFER_SIZE );
bytesRecvd = socket_recv(
     &networkContext,
     ( void * ) buffer,
     incomingPacket.remainingLength
);
 
// Set the remaining data field.
incomingPacket.pRemainingData = buffer;