MQTT How to know the Broker Status

Question

In a web application with MQTT in python (using paho-mqtt lib) I would like to know if there is a way to get the broker status in real time, because the only way that i find is to store the variable "rc" into the method on_connect but it's more like a client/connection state.

EDIT 1 : after reading mosquitto broker documentation, i found that you can subscribe to '$SYS/broker/connection/#' which is supposed to give you back 1 if the connection is up and 0 if it goes down. However when i do :

subscribe.callback(self.message_callback, '$SYS/broker/connection/#', port = port, hostname=broker, auth=authentication, protocol=client.MQTTv31, tls=TLS)

impossible to get payload and topic this message although i'm doing exactly the same command to get messages from my sensors except that the topic is '#' and it's working perfectly.

Does anyone knows why ?

Answer 1

There is no way to poll the state of the connection to the broker from the client.

The on_disconnect callback should be called when the connection to the broker is dropped.

This should be kicked off when the keep alive times out, but also as the result of a failure to publish (if you try to publish data before the timeout expires).

Also the rc from a call to the publish command will indicate if the connection has dropped.