### Problem
The `MQTT_ProcessLoop` and `MQTT_ReceiveLoop` read incoming MQTT packet payload over the network by calling the `recvExact` function. The `recvExact` function can be called multiple times to read the expected number of bytes for the MQTT packet but it also implements a timeout functionality of receiving the expected number of payload within the timeout value passed to the function.
This causes problems when the `Transport_Recv` call returns less than requested number of bytes, and there is a timeout (for example, when calling `MQTT_ProcessLoop` with 0ms duration) which causes the function to assume failure instead of reading the remaining payload of the MQTT packet by calling `Transport_Recv` again. Thus, in such cases, the MQTT connection is severed prematurely even though there is a high probability of receiving the remaining bytes of the MQTT packet over the network.
### Solution
Instead of implementing a timeout on the entire duration of receiving the expected number of remaining MQTT packet bytes in `recvExact`, the use of timeout is being changed to be relevant only on the total time of receiving 0 bytes over the network over multiple calls to `Transport_Recv`.
As this modified meaning of the timeout duration is now unrelated to the timeout duration that the `MQTT_ProcessLoop` or `MQTT_ReceiveLoop` functions are called, a new configuration constant for the `recvExact` timeout value, `MQTT_RECV_POLLING_TIMEOUT_MS`, has been added to the library which will carry a default value of 10ms.
Co-authored-by: Sarena Meas <sarem@amazon.com>
This follows changes from FreeRTOS/FreeRTOS@398abba. The const qualifier is removed from send/recv because there are transport implementations that require a member of the network context to be modified such as in the case of mbedtls.
This updates the coreMQTT library so as to resend a PUBACK and PUBREC for an incoming duplicate publish packet, irrespective of the broker setting the DUP flag.
* Set publish payload to NULL when zero length
* Add unit test for zero length payload
* Fix unit tests for deserialize publish
* Rename setupWillInfo to setupPublishInfo
* Remove void * from memset
* Add version numbers
* Add missing @file tags
* Update lexicon.txt
* Update @brief tag for MQTT cbmc state
Co-authored-by: Gary Wicker <14828980+gkwicker@users.noreply.github.com>
