[mosquitto-dev] Mosquitto c++ lib unexpected disconnect.

["Sunderman, Adam" <Adam.Sunderman@xxxxxxxxxxxx>]

Hi,

I am running Mosquitto lib version 1.4.8 and am handling a connection to a broker (rabbitMQ) with mqtt protocol version 3.1.1. 

I have all mosquitto functionality encapsulated in a c++ object (MQTT_Handler). I call mosquitto_lib_init() in the constructor. in MQTT_Handler::init() function, I use mosquitto_new() and use the this pointer as the obj parameter to re-scope the callbacks to my c++ object. I then proceed in the same function to call mosquitto_loop_start(), set the protocol version to 3.1.1, set relevant callbacks, mosquitto_reconnect_delay_set(), mosquitto_max_inflight_messages_set(). After my object is initialized, the function MQTT_Handler::connectToBroker() will eventually be called where I mosquitto_username_pw_set(), and mosquitto_connect_async().

After this point, most of the interaction with mosquitto happens via the callbacks fired. i.e. on the connect callback I subscribe to topics that my c++ object has been told to subscribe to, on the message_callback I pass the message onto the entity that cares about it, i.e. The only thing that my object does periodically outside of the callbacks is publish messages that other entities ask it to publish.

Everything works very well for a time. I am logging everything but DEBUG level messages (and am seeing nothing in that regard, so I may have to add DEBUG to pinpoint the cause of the issue). However after prolonged runtimes, I will occassionally get an unexpected disconnect (the disconnect callback will fire and reason will not be 0. note: timeout is 60 seconds). However, communication with the broker seems fine even after this occurs according to ping and the reconnect never seems to happen (well atleast not the connect callback) despite me setting up the reconnect info for the mosquitto thread. Making the issue stranger is the fact that at a low level, the connection seems to be fine and actually is running. I can perform a netstat -tapen and see that I still have an active connection to my broker. If I look in the rabbitmq management interface I also see that the queue still has a consumer (and the ip-port matches my netstat result). Furthermore, if I publish to this queue, the consumer even acks it despite my application not receiving any callbacks from mosquitto.

I have tried to be detailed in how I am utilizing mosquitto and the sequence of events, but I'm sure this won't be enough information alone. If I can be pointed in the right direction for what info I need to attain when the issue occurs, I can work towards gathering it. Unfortunately, it is tough to recreate at will, I just have to let it run for extended periods of time and then comb back through the logs to look for irregularities.

Any help is greatly appreciated!

Thanks,

Adam

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