How to deal with old iOS notification tokens remaining valid after new token and vendorId are generated?

Question

I am using Azure Notification Hub to send remote notifications, at the moment only to iOS.

I initially realised that my device was receiving 5 notifications of the same notification event. I checked and debugged my code and it indeed correctly checks if the provided token to register is not already registered.

I then checked my database and realised that I do not have duplicates, but 5 different device tokens for the one device and user account. They each had been generated every-time I uninstall and then re-install the app on my device.

Given that, I would think that when an app is uninstalled, the token generated before is made invalid by Apples systems? I assumed this because upon re-installation, a new token is generated, different to the previous one. Why would the older tokens remain valid; whats the use case for such.

It seems other people are having this issue for iOS development, including Android too.

Using VendorId to identify a device is proving pointless, as some are finding out , that it also changes upon fresh installation. When I uninstall the app and reinstall I get a new vendorId plus a new notification token, leaving the previous ones still valid, opening up the ability to receive multiple of one instance of a notification (since the back end cannot match the new two values to anything existing in the database).

Any advice on this please? I am absolutely lost on this?

Update: I certainly need a user to have more than one device token at a time, in case they are logged in on multiple devices.

Answer 1

You are basically going to have to identify a device yourself, by saving an ID, using UUID, into Keychain. Keychain because the data persists over multiple installs.

Below is a quick rushed implementation using Locksmith :

import UIKit
import Locksmith


class Keychain
{
    private static let AccountName = "MyAppName";
    private static let CustomDeviceIdKey = "CustomDeviceIdKey";
    
    private static func AccountData() -> Dictionary<String, Any>?
    {
        return Locksmith.loadDataForUserAccount(userAccount: AccountName)
    }
    
    private static func GenerateCustomDeviceId() -> Bool
    {
        do{
            try Locksmith.saveData(data: [CustomDeviceIdKey: UUID().uuidString], forUserAccount: AccountName)
            return true
        }catch{
            print("Failed to save custom device id: \(error.localizedDescription)")
            return false
        }
    }
    
    static func CustomDeviceId() -> String
    {
        let data = AccountData()
        if let result = data?[CustomDeviceIdKey] as? String{
            return result
        }else{
            if GenerateCustomDeviceId(){
                return CustomDeviceId()
            }
            return ""
        }
    }
}

And then later you just go:

func SomeMethodThatNeedsDeviceId(){
    var customDeviceIdThatPersistsOverInstalls = Keychain.CustomDeviceId()
}

And that is what you use in place of VendorId

Answer 2

Answering from the Azure Notification Hubs perspective, we see each device id as a valid device id and only prevent future sends from targeting that device once we try to push to that device and Apple gives us the response of the device being expired/invalid. Hence, we have no visibility into whether or not different device ids may belong to the same device due to re-installs.

This is different than the case where a single notification may fetch the same device id multiple times. In this case, our service has de-duplication logic to prevent duplicate notifications.