sendBuffer may fail because of tick timer rollover

[dtaarondecker]

In core_mqtt.c, sendBuffer a timeout value is calculated by reading the current time and adding some timeout to that value.

coreMQTT/source/core_mqtt.c

Line 877 in 58d626a

timeoutMs = pContext->getTime() + MQTT_SEND_TIMEOUT_MS;

Take the case where current time is very close to, but not yet rolled over. We then add some timeout value causing a rollover on the timeoutMs variable.

We then check if the current time is greater than or equal to the timeout time

coreMQTT/source/core_mqtt.c

Line 912 in 58d626a

if( pContext->getTime() >= timeoutMs )

This check will erroneously fail.

For Example:

current time = 4294957296
timeoutMs = current time + 20000 = 20000

*continue executing*

Current Time = current time + ΔT where ΔT is less than 2^32 - current time 

currentTime >= timeoutMs = true until current time rolls over.

[paulbartell]

@dtaarondecker Thanks for the bug report. If you would like, feel free to open a pull request fixing the issue. Otherwise, we will get to it soon.