Apple Push Notification Service - Multiple device tokens are valid for the same device
In order for us to send users iOS notifications the following flow occurs: a user installs our app, registers with APNS, and sends the registration token to our server to be used later to send notifications.
The above process is repeated for every device on which the user installs our app; we'd like them to get notifications on all their devices.
In addition to this, the process is repeated when a user uninstalls our app and reinstalls on the same device.
Every time the process repeats we get a new, distinct registration token. This is all well and good however, we noticed that only recently when our app is uninstalled, the device token remains valid after it is reinstalled and a new token is generated. It is our understanding that a single unique token can exist for a device.
Apple's documentation seems to suggest this as well (https://developer.apple.com/library/ios/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/Chapters/ApplePushService.html#//apple_ref/doc/uid/TP40008194-CH100-SW12)
The form of this phase of token trust ensures that only APNs generates the token which it will later honor, and it can assure itself that a token handed to it by a device is the same token that it previously provisioned for that particular device—and only for that device.
When a new token is generated after reinstall and sent to our backend, we've got two device tokens that point to the same device and as a result we send multiple notifications to that device. Are we misunderstanding the documentation? If so, what's the typical way of dealing with the reinstall scenario?
Thanks!
Answer
We just did a test here. On our iOS 8.4.1 test device after reinstalling our app we've received the same token, whereas on iOS 9.1 we always receive a new token after re-installing. This wouldn't be a problem if APNS invalidates the older device tokens, but as far as I can tell it does not. The result is that we're sending duplicate notifications to our users to the same device. Maybe it takes some time to invalidate older token?
We decided to do a server-side fix for this and remove duplicate tokens for one user from our database. Not a good and permanent solution, but a short-term fix for us since our users use the app usually on one device only.