Missing mqtt messages on persistent session restart

[jenia2007b]

Hello.

I am using aws iot device SDK cpp v1.15.2 undex Windows 7 and Windows 10.
I'm using ATS data type endpoint: the endpoint look like prefix-ats.iot.region.amazonaws.com

My test app is very close to basic_pub_sub SDK sample.
I am using MQTT Persistent session with cleanSession = false & QOS=1 with every SUB & PUB.
I connect to the Broker and subscribe to a topic successfully. I can publish and receive messages, all is OK while the device stay connected.
But if I disconnect from the broker (closing my app or disconnecting the network in my PC), then send one ore more messages via "MQTT test client" with QoS=1 and connect my app, I see, that session is resumed (sessionPresent comes "true"), but no messages are received.

I try to setup OnMessageReceivedHandler via SetOnMessageHandler() before I call connect() function in my app. But the problem is the same: it works OK when I send message with device connected, but does not work, if I send message while the device is offline.
I also try to update SDK up to version 1.18.2, but it does not help to me.

[jmklix]

What value are you using for the keepAliveTimeSecs? It might be that your session is expiring and you end up with a clean session because of that.

Docs:

Reconnection after a persistent session has expired

If a client doesn't reconnect to its persistent session before it expires, the session ends and its stored messages are discarded. When a client reconnects after the session has expired with a cleanSession flag to 0, the service creates a new persistent session. Any subscriptions or messages from the previous session are not available to this session because they were discarded when the previous session expired.

[jenia2007b]

I use value 120 (seconds). Does this parameter influence on persistent session lifetime? I think that it only set the interval of MQTT pings when device is connected, but does not publish anything.

I also see, that parameter sessionPresent in onConnectionCompleted callback comes "true", as if session does not expire.

[jmklix]

What changes did you make from the original basic_pub_sub? I incorrectly stated that the keepAlive value might affect this. Also what do you mean by closing my app?

[github-actions[bot]]

Hello! Reopening this discussion to make it searchable.