The functions used by the MQTT client to get and return buffers.

Overview

The MQTT client needs buffers for both transmitting and receiving messages. Whenever it needs a buffer, it invokes mqttconfigGET_FREE_BUFFER_FXN function to get a buffer and after it is done it invokes mqttconfigRETURN_BUFFER_FXN to return the buffer. By default, BUFFERPOOL_GetFreeBuffer and BUFFERPOOL_ReturnBuffer functions are used to get and return buffers from the central buffer pool. The user can change the buffer management functions for MQTT client by defining mqttconfigGET_FREE_BUFFER_FXN and mqttconfigRETURN_BUFFER_FXN macros. The user should implement the two functions having signatures same as BUFFERPOOL_GetFreeBuffer and BUFFERPOOL_ReturnBuffer and then define the macros in BufferPoolConfig.h:

* uint8_t* UserDefined_GetFreeBuffer( uint32_t *pulBufferLength );
* void UserDefined_ReturnBuffer( uint8_t * const pucBuffer );
*
* #define mqttconfigGET_FREE_BUFFER_FXN       UserDefined_GetFreeBuffer
* #define mqttconfigRETURN_BUFFER_FXN         UserDefined_ReturnBuffer
*