[mosquitto-dev] lwt and connection status for bridge

[Greg Troxel <gdt@xxxxxxxxxx>]

I have a broker on a computer A, and another broker on a computer C in a
differerent place.  The C broker is configured to bridge to the A broker
and this works fine.

I would like to know, at A, if the bridge is connected.   So I'd like
the bridge when connecting to post to /sensor/B/bridge/online as ON with
a lwt to write OFF.

Reading the man pages, I see in the bridge config:

       notifications [ true | false ]
           If set to true, publish notification messages to the local and
           remote brokers giving information about the state of the bridge
           connection. Retained messages are published to the topic
           $SYS/broker/connection/<remote_clientid>/state unless otherwise set
           with notification_topics. If the message is 1 then the connection
           is active, or 0 if the connection has failed. Defaults to true.

           This uses the Last Will and Testament (LWT) feature.

and I see that topic on A with value 1.

I interpret the LWT comment as being that if the broker at C is shut
down or disconnected for any reaosn (clean shutdown, crash, loss of
network connectivity, then I should see the topic value change to 0, and
can use that as a binary sensor in HA (to alert on loss of bridge).

Is that the right interpretation?