NRF modem 1.1.1 firmware, 1.2 SDK. Re-using sockets causes hang in nrf_connect.

[JVantol]

I'm porting a working app from SDK 1.1 to 1.2, and have noted that when I make an mqtt connection close it, and re-open (to a different mqtt server) that the call to nrf_connect hangs indefinitely.

The socket number is the same, which makes me think that when the first connection closes, it leaves something in a bad state.

The two separate mqtt connections work fine in isolation from each other, just not when the connections are made sequentially. (open, close, open)

Also, I've noted that when I modify the code to make both connections one after the other, forcing the use of another "new" socket for the second connection, things work fine.

This worked fine with modem firmware 1.1.1 and SDK 1.1, so it seems like it might be a new SDK 1.2 bug.

[Didrik Rokhaug]

Hi.

One of the changes between NCS v1.1.0 and NCS v1.2.0 is that the MQTT library now closes the socket in mqtt_disconnect, instead of after another call to mqtt_live.

How do you "re-use" the socket, and how do you "force" it to use another new socket?

Also, if you could capture a modem trace, that would help me track what happens to the sockets on the modem side.

You can learn how to capture a modem trace in this guide: https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/how-to-get-modem-trace-using-trace-collector-in-nrf-connect

Best regards,

Didrik

[JVantol]

Didrik and Johan,

I think both of you were wondering how I worked around this problem.

Here is the procedure.

Open MQTT Connection 1 (with TLS)

Open MQTT Connection 2 (with TLS)

Service connection 1 (in this case AWS FOTA)

Close Connection 1.

Service connection 2.

The time require to service connection 1 is short enough that connection 2 does not time out, it's well within the mqtt poll interval.

Didrik,

I'll try the modem log again.

Josh

[JVantol]

Here's a new trace. I think it's valid this time.

trace-2020-03-03T17-31-00.607Z.bin