INFO-3 Subscription channels remain open after token expiration

[lukasmittag]

This fixes that a subscription channel stays open after the token of the subscriber has expired. We need to decide if we want to fix this. Currently it is only fixed for ChangeSubscription which the new API uses. If we want to do it for the old query subscription as well it can be done similiar. To test it take a jwt token of kuksa-val/jwt/ and use a timestamp that expires in the near future -> go to https://www.epochconverter.com/ for timestamps ;)

It is not that pretty in code I think so do not now if we want to fix this in this way/at all. One observation I made was that even if the channel is kept open somehow if you update the token new updates do not come in in the databroker-cli again. Haven't figured out why yet.

[lukasmittag]

and I opted for closing if a new notification would be sent out so no general repeated check. This means if you do not update soem things channel can stay open a while.

[rafaeling]

Code looks fine to me, tested with python sdk and the channel closes correclty

[erikbosch]

Looks ok for me. But I did not really understood one of the comment, see below. Is that one still valid, or do you think the code is pretty enough (kenough) now?

"It is not that pretty in code I think so do not now if we want to fix this in this way/at all."

[lukasmittag]

I just thought that it's maybe not the ideal way code wise. But since @argerus had nothing to complain yet :) From my side we can merge.

[argerus]

It would probably be a lot easier to treat expired permissions the same way we treat channels that have been closed:

e.g. add a check to Subscriptions::cleanup() that will remove all subscriptions with expired permissions. This will be triggered both periodically, and whenever a SubscriptionError is returned when when calling notify.

new changes

[erikbosch]

Databroker has been migrated to https://github.com/eclipse-kuksa/kuksa-databroker.
Please open a new pull request in that repo.