Gmscore: [Feature Request] Provide app-side library implementation of fcm

[cRaZy-bisCuiT]

If possible, please provide a app-side library implementation of FCM so it's possible to implement fully open source apps to use FCM.

[tobiasKaminsky]

This would be very good to have.
If you need someone to test it, feel free to ping me :+1:

For us, we would need:
FirebaseMessagingService
FirebaseInstanceIdService

[rugk]

Google is slowly open sourcing all the Firebase-* things, so I expect messaging to follow soon so there will be no need for client-side microg.

@mario in https://github.com/nextcloud/android/issues/3333#issuecomment-446490133

So well… if Firebase is open-source this would obviously help here, at least – if not obsolete this lib.

[ale5000-git]

FCM is GCM with some extensions, most apps that use FCM are already working with microG.

[Bubu]

@ale5000-git

But they cannot work with this clientside library because it doesn't implement the firebase classes currently.