Handling refresh tokens for FCM device groups

2018-07-03 15:21:52

I am trying to implement Firebase cloud messaging in my Android app through a Node.js server and I have got stuck at a usecase.

I saw the Firebase tutorial of creating a device group using registration tokens to send messages/notifications to all devices with the same user logged in, what I don't understand is what happens when one of the registration tokens get refreshed by onTokenRefresh() method.

How will I distinguish which token to change as all will be belonging to the same user?

Update:

Ok, so now I have got stucked on another blocking use case. I am creating a user group identified by the user id from my server. If user uninstalls and reinstalls the app immediately and another user logs in on the device, if I call a gcm message on the previous user group this device still receives it.

Is there any way for the gcm to identify is the device it is sending the notification to is logged in or not and if it is, is it logged in with the same user as for the group?

So I've been thinking about how to go with this scenario. First off, let's put in the instances when onRefreshToken() is called:

This will not be called very frequently , it is needed for key rotation and to handle Instance ID changes due to:

App deletes Instance ID

App is restored on a new device

User uninstalls/reinstall the app

User clears app data

Guess with that, you can say that 'onTokenRefresh()` will be called after one the above happens and if the device is online (of course it has to be online on order to get a new token). So I guess here's how I'd go on the scenario:

First off, upon registration, I would save the registration token and pair it along another identifier, let's say a deviceId (since we're in a scenario for a user with multiple devices) in my App Server.

So assume I add in 3 registration tokens, those are also paired with their deviceIds. I add them all to a device group.

Now say one of the devices triggers the onTokenRefresh() , I would immediately send a delete request to my App Server for the registration token that is currently paired to that deviceId (you should also delete it in any device group(s) it's connected to), replacing it with the new one, then re-add it to the corresponding device group(s).

That's the simplest way I can think of. The key here is for you to pair the registration tokens with another identifier and use it to find which registration token you need to replace.

at moment i use this method. in my database i create a node with devices id

deviceId: {
   uid1: deviceId,
   uid2: deviceId,
   uid3: deviceId
}

another node with the users that are subscribed to receive a notifications

newsSubscriber: {
   uid1: [array of subscribers],
   uid2: [array of subscribers],
   uid3: [array of subscribers]
}

when i can send a notification by my nodejs script i get all users that are saved in the newsSubscriber node, and for any user i get his deviceId and i put it into an array of devices to send a notification. There are only one problem, i read now that in this mode there are a limit of only 20 devices !.

but i think that this is a good easy method to have a corresponding deviceId for any user because when i use the logout or the login in my app i can change the correspondent deviceId for any user, so as to have consistency between user and device.

what happen if to bypass the limit of 20 devices i send the same notification to different groups of 20 devices?

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