nRF9160 MQTT with TLS disconnects if subscribing

[Jon Alvik]

Environment:
nrf9160DK v0.8.2
nRF Connect SDK v1.2.0
Modem firmware: v1.2.0
Toolchain: gcc-arm-none-eabi-9-2019-q4-major-win32

I started with the nrf mqtt_simple sample and modified it to enable TLS support.
Connection to the broker succeeds, and when doing only publish there are no problems, but if there are any subscriptions the second publish results in an error and disconnect.
The error occurs in client_write in mqtt.c  when calling mqtt_transport_write, errno is set to 128.
(mqtt_transport_write calls mqtt_client_tls_write which again calls nrf91_socket_offload_send).

The problem has been reproduced with two different brokers. The only message at the broker side is that the client has disconnected.
Using the same keys with mosquitto_pub/mosquitto_sub works fine.

Jon

[Håkon Alseth]

Hi Jon,

 

Although there has been several releases of bsdlib since tag v1.2.0 (which is based on v0.6.1), this does not sound like a previously known issue, as per the changelog:

https://github.com/NordicPlayground/nrfxlib/blob/master/bsdlib/doc/CHANGELOG.rst

 

Could you share your project?

If it holds any code that you do not want to share publicly, please let me know, and I can make this case private.

 

Kind regards,

Håkon

[Jon Alvik]

Hi Håkon, thank you for responding

I was able to resolve the issue by reverting to the mqtt_simple example and re-tracing my steps.

The cause of the issue was use of some uninitialized data when subscribing to one of the MQTT topics. There was no error message, but stepping through the offending code caused the debugger to disconnect while the code continued executing seemingly normal.

Jon