Get all subscribed topics from firebase cloud messaging

Using the new FirebaseMessaging it's easy to un/subscribe to topics via:

FirebaseMessaging.getInstance().subscribeToTopic();
FirebaseMessaging.getInstance().unsubscribeFromTopic();

But is there any way to get all topics the current installation is subscribed to ?

I have searched Android API, asked questions for the same on SO but din't find anything. There is nothing in Android API to get all topics of a specific token.

However, you can do it through a GET request

HTTP GET Request

https://iid.googleapis.com/iid/info/<TOKEN>?details=true
Content-Type:application/json
Authorization:key=AAA....i1nM:APA9.....81gTPXCE55....JLPEG0wZobG_ile8lI35JTzHYE5MC..BmDD_Cxj5OxB1Yh....Rs5lo3UwLNL9h-WcocGV....b5bYWNI55kzNsrHK-7GljUDtMn 

TOKEN in url : FirebaseInstanceId.getInstance().getToken(senderId, scope);

key : can be found in firebase console: Your project -> settings -> Project settings -> Cloud messaging -> Server Key

Note: Be careful when finding key, dont use web api key its different.

senderId can be found in Settings -> Cloud Messaging -> Sender ID

scope is usually "FCM"

For those that would like to test it with command line CURL follow bellow the syntax that I have used:

#curl --location --request GET 'https://iid.googleapis.com/iid/info/yourFCMDeviceToken?details=true' \
--header 'Authorization: Bearer YourProject_CloudMessaging_ServerKey'

Response:

{
	applicationVersion: '4194309',
	application: 'com.domain.app',
	scope: '*',
	authorizedEntity: '913674269572',
	rel: { topics: { topicName: { addDate: '2020-08-19' } } },
	appSigner: 'ae7cbSomeHash23jsdfff34ac7ffd',
	platform: 'ANDROID'
} 

Never tried programmatically.

But you can do it by goto firebase console->your project->cloud messaging->new notification->target-> click on topic tab next to user segment just click on Message topic text box you will get list of subscribed topics

This topic is still relevant, still no API for this in the iOS SDK.

If your goal is to prevent a user from subscribing multiple times to the same topic and therefore getting notified multiple times for, say, a single comment in a group, my solution is a simple local cache using UserDefaults.

Pretty straightforward:

    func subscribeTo(topic: String){
        // first check that the user isn't already
        // subscribed, or they get multiple notifications
        let localFlag = UserDefaults.standard.bool(forKey: topic)
        if localFlag == true {
            print("user already subscribed to topic: \(topic)")
            return
        }
        print("attempting to subscribe user to topic: \(topic)")
        // Subscribe to comet chat push notifications through Firebase
        Messaging.messaging().subscribe(toTopic: topic) { error in
            if error == nil {
                print("subscribed CometChat user to topic: \(topic)")
                // set local flag as "already subbed"
                UserDefaults.standard.setValue(true, forKey: topic)
                return
            }
            print("attempt to subscribe CometChat user to topic \(topic) failed: \(error?.localizedDescription ?? "(no error provided)")")
        }
    }

The flow of my application logs a user in, and then automatically gets a list of topics associated with the user and auto-subscribes to the topic with each launch.

The reason for this is a high degree of assurance that the user is getting notified.

The flow: User launches app-> topics retrieved-> iterate & pass topic to subscribe func -> block if topic == true-> pass through if topic != true

And then of course we assign nil to the local bool at the topic key upon unsubscribe.

Unsubscribes are always successful without such blocking / checking, because it's better UX to be more conservative when a user does NOT want notifications.

Cheers.