FireBase Cloud Messaging (FCM) subscribing/unsubscribing to topic When OFFLINE

Question

Does FCM simply not send the subscribeToTopic(topic) and unsubscribeFromTopic(topic) when app has no internet access? Or does it store it locally and send as soon as internet connection is available?

If so what are the conditions for doing so (i.e. maximum time it waits for internet before it fails, if the app is closed does it still send the subscription or does it only happen when app is open or open in background)

Answer 1

subscribeToTopic(topic) and unsubscribeFromTopic(topic) operation are cached locally until they are successfully communicated to the FCM backend.

If the device is offline the subscribe/unsubscribe operations are stored on disk and performed when the device is connected and app is running (either in background or foreground). There is no maximum time for this to happen.