Publisher callback for new subscriber

[kdkavanagh]

Is there any mechanism for a publication to receive a notification that a new subscriber has joined to the stream? Polling Publication::isConnected isnt sufficient, as that only indicates that there is 1+ subscribers, rather than the subscriber count or other more-detailed information about the subscribers.

I assume that the publisher does have this information under the hood to support flow-control - Wondering if it's exposed in a public API somewhere

[vyazelenko]

@kdkavanagh What are you trying to achieve?

[kdkavanagh]

My specific interest here is for the publisher to be notified of a new subscriber and publish a conceptual "hello" message over the stream every time a new subscriber joins. Specifically, it's important for this message to be in the same stream that the subscriber has joined (vs some side-band channel, where a request/response protocol could be implemented), to allow the hello message to be sequenced amongst the other messages flowing thru the stream

(It's okay for all other existing consumers of the same stream to receive the hello message, in this case).

I could achieve this by having the publisher continually poll a separate stream which new subscribers ping when they join the main stream, but this feels like overkill, especially since I think the media driver already has sufficient info to alert on new subscribers

It would also be helpful to have for logging / observability purposes

[mark-b2c2]

That sounds like a very interesting use case. Did you ever manage to find a solution to this @kdkavanagh?