PubSub subscription callback

[UnderSampled]

Is your feature request related to a problem? Please describe.
I need to send a message to an MQTT topic after subscribing to it, so I can hear the response. Currently, I'd have to set a dumb timeout to give the broker just a little time to process the subscription request

Describe the solution you'd like
A callback/promise/connection event for PubSub.subscribe

Describe alternatives you've considered
I currently use a different MQTT library (the aws-iot-device-sdk), since it supports this sort of callback.

[UnderSampled]

It seems that Paho supports a success callback on the call to subscribe. It should be possible to await that in the call in Mqtt over WS.

[nzjoel1234]

Is there any possibility of this being done? The subscribe is not very useful without it.

[MikeSussman]

Any updates please as I am experiencing a similar issue in that my first Pub after subscribing to get the shadow state is not receiving data. If I wait and then manually trigger a pub I get the data.

[stocaaro]

Good news. We've added Hub events that you can now listen to to know when the IoT connection state changes, such as when it becomes Connected. Here are instructions on how to use this feature with a list of the different states you can watch for.

[leofolive]

@stocaaro
How can I verify that my subscription has successfully connected? I have 70+ in-app subscriptions on my mqtt client, but Hub.listen doesn't tell me specifically about each subscription.

I need to do this because I can only publish to a topic after being 100% connected with some subscriptions.

[stocaaro]

Hello @LFMAKER,

I added a reply to this question over on #2692.