Messaging FCM token caching

[grigorigoldman]

I am trying to understand how getToken function works in react-native-firebase/messaging module.

From documentation, it implies that it retrieves the token from Firebase, however, I noticed that even if there is no network connection, I can still get the token. This suggests that perhaps it is stored somewhere on the device but I cannot see this documented anywhere.

I checked Firebase SDK documentation as well but there's no mention of storing the token on the device there either. In fact, the opposite is described. For example, retrieveFCMToken(forSenderID:) says that "This registration token is not cached by FIRMessaging."

How is it that calling getToken function without network connect returns a current, valid FCM token?

[mikehardy]

It sounds like you are referencing the iOS platform? I don't think I can be authoritative here so I humbly suggest you either ask this on stackoverflow (which gets responses from the upstream firebase developers - it's their most official support channel I think) or on the firebase-ios-sdk repo itself

[grigorigoldman]

I managed to track it down. It's buried in the FIRMessagingTokenStore module. The sequence of calls looks something like this:

[FIRMessaging retrieveFCMTokenForSenderID] calls [FIRMessagingTokenManager tokenWithAuthorizedEntity], which then calls [FIRMessagingTokenManager cachedTokenInfoWithAuthorizedEntity].

If the token does not exist or stale, only then does the call to Firebase is made.

I think the docs are somewhat misleading. Technically speaking, yes FIRMessaging does not cache the token but the module it uses does 🤷‍♂️