Using FirebaseApp.delete() results in unusable Messaging singleton

[cooksimo]

Describe your environment

• Xcode version: 10.2.1
• Firebase SDK version: 6.5.0
• Firebase Component: Messaging
• Component version: 4.1.1

Describe the problem

We have several projects set up, representing different environments for remote config. We use Messaging to enable real time remote config updates. When a user switches the firebase environment within the app, we delete the default app, and attempt to recreate it.

FirebaseApp.delete({ _ in })
FirebaseApp.configure(options: options)

Once this has been done any interaction with Messaging will not work. We have encountered this because we were running a very old version of Firebase (4.13.0) & Messaging (2.2.0) and we're trying to update to the latest. This approach worked in those versions.

This problem looks to be in the implementation of messaging(), there is a dispatch_once block to actually set everything up, this doesn't make sense if the singleton object can actually be deallocated and recreated.

I have attempted to solve this by calling start manually, and this seems to fix some things, but the new Messaging instance never gets notified of the fcmToken being available so cannot subscribe to anything.

[morganchen12]

IIRC this has never been an officially supported use case, though we also don't explicitly label deleteApp: as unrecoverable. We can revisit this behavior in API review, but in the meantime, what use case are you trying to accomplish by deleting and reconstructing the Firebase app?

[cooksimo]

Our use case is to have production, staging and sandbox environments for Firebase, with an in-app option to toggle between these environments for debug builds.

[cooksimo]

I have managed to workaround this and get it working again, but it's very hacky.

When we switch environments we do this:

var oldMessaging: Messaging? = nil
if FirebaseApp.app() != nil {
    oldMessaging = Messaging.messaging()
}

...

// If we are switching environments, we need to delete the old FirebaseApp and recreate a new one
if let app = FirebaseApp.app() {
    app.delete({ _  in })

    FirebaseApp.configure(options: options)

    if oldMessaging != nil {
        Messaging.messaging().perform(Selector("start"))
        let notification = Notification(name: Notification.Name(rawValue: "com.firebase.iid.notif.fcm-token"), object: Messaging.messaging().fcmToken, userInfo: nil) // The Messaging instance does know its token, things just didn't get wired back up properly
        NotificationQueue.default.enqueue(notification, postingStyle: .asap)
        Messaging.messaging().delegate = oldMessaging?.delegate
        Messaging.messaging().apnsToken = oldMessaging?.apnsToken
    }
}
else {
    FirebaseApp.configure(options: options)
}

[ryanwilson]

Thanks @cooksimo for the detailed write-up and investigation into what the cause was!

[nordfogel]

Is it intended not taking the delegate into account by recreating the Messaging singleton after a FirebaseApp is deleted and recreated?

@property(nonatomic, weak, nullable) id<FIRMessagingDelegate> delegate;