Mqtt subscriber error

[Gustavo Junqueira]

I am experiencing an error that I can't figure it out why it is happening and where to go and try to fix it.

I am using the subscriber implementation on my nRF51, Raspberry Pi as router and broker.

To test it i'm using a python program on Raspberry to publish the "led/state" topic. I set the publisher to send a publish message every 0.5 seconds inside a loop to send 1200 packets, than it closes the connection.

I saw in wireshark that the broker send the publish message to the subscriber than the subscriber send Acknowledgement to the broker and the broker send an Acknowledgement to the subscriber.

So, around 1887 packets sent in this 3 way handshake, the subscriber stops executing and the broker disconnects it because of the timeout. But to get subscriber running again I have to restart and connect it again to the Rpi.

I ran this test publishing in many other ways and the subscriber halts every time around 1885 to 1890 packets.

Is there something on the mqtt code that I can change to not have this issue?

[Krishna Shingala]

Hello Gustavo,

There is no good reason in MQTT to stop exchanging packets after a while. I am however suspicious at the BLE level. Is it possible for you to capture BLE logs and notice if the Raspberry Pi is initiating a disconnection?

Thank you!

[Gustavo Junqueira]

Hi Krishna, Yes, the Broker stops sending the TCP ACK for every publish message to the subscriber client. And send TCP ACK only to a few messages and then the Broker and the client desynchronise. The TCP connection does not close, the Broker keeps retransmitting the publish messages and the client keep trying to acknowledge the last message before the Broker starts to retransmit. I have some .pcap logs if you want to check out.