MQTT_GetUnsubscribePacketSize

Get packet size and Remaining Length of an MQTT UNSUBSCRIBE packet.

MQTTStatus_t MQTT_GetUnsubscribePacketSize( const MQTTSubscribeInfo_t * pSubscriptionList,
                                            size_t subscriptionCount,
                                            size_t * pRemainingLength,
                                            size_t * pPacketSize );

This function must be called before MQTT_SerializeUnsubscribe in order to get the size of the MQTT UNSUBSCRIBE packet that is generated from the list of MQTTSubscribeInfo_t. The size of the MQTTFixedBuffer_t supplied to MQTT_SerializeUnsubscribe must be at least pPacketSize. The provided pSubscriptionList is valid for serialization with MQTT_SerializeUnsubscribe only if this function returns MQTTSuccess. The remaining length returned in pRemainingLength and the packet size returned in pPacketSize are valid only if this function returns MQTTSuccess.

Parameters

[in]	pSubscriptionList	List of MQTT subscription info.
[in]	subscriptionCount	The number of elements in pSubscriptionList.
[out]	pRemainingLength	The Remaining Length of the MQTT UNSUBSCRIBE packet.
[out]	pPacketSize	The total size of the MQTT UNSUBSCRIBE packet.

Returns

MQTTBadParameter if the packet would exceed the size allowed by the MQTT spec; MQTTSuccess otherwise.

Example

// Variables used in this example.
MQTTStatus_t status;
MQTTSubscribeInfo_t subscriptionList[ NUMBER_OF_SUBSCRIPTIONS ] = { 0 };
size_t remainingLength = 0, packetSize = 0;
 
// Initialize the subscribe info. The details are out of scope for this example.
initializeSubscribeInfo( &subscriptionList[ 0 ] );
 
// Get the size requirement for the unsubscribe packet.
status = MQTT_GetUnsubscribePacketSize(
     &subscriptionList[ 0 ], NUMBER_OF_SUBSCRIPTIONS, &remainingLength, &packetSize
);
 
if( status == MQTTSuccess )
{
     // The application should allocate or use a static #MQTTFixedBuffer_t
     // of size >= packetSize to serialize the unsubscribe request.
}