feat(odin): Allow collecting FCM device token in SDK & demonstrate it in sample app by odin-posthog · Pull Request #376 · PostHog/posthog-android

odin-posthog · 2026-01-20T17:16:22Z

💡 Motivation and Context

We want to allow customers to send push notifications to their users in workflows. For that, we need to enable the SDK to collect and update the FCM device token that must be used for pushing notifications.

We're not collecting it automatically when initializing so users that don't need this functionality aren't forced to install firebase dependencies, and they have control over which users have their tokens collected (eg. signed-in only)

💚 How did you test it?

Manually in my emulator through the sample app, and with some automated tests

📝 Checklist

I reviewed the submitted code.
I added tests to verify the changes.
I updated the docs if needed.
No breaking change or entry added to the changelog.
If there are related changes in the core package, I've already released them, or I'll release them before this one.

marandaneto · 2026-01-26T15:54:26Z

posthog/src/main/java/com/posthog/PostHog.kt

+        val storedToken = preferences.getValue(FCM_TOKEN) as? String
+        val lastUpdated = preferences.getValue(FCM_TOKEN_LAST_UPDATED) as? Long ?: 0L
+        val currentTime = config.dateProvider.currentDate().time
+        val oneHourInMillis = 60 * 60 * 1000L


this could be a static/global var so we dont have to compute on every method call

marandaneto · 2026-01-26T15:57:24Z

posthog/src/main/java/com/posthog/PostHog.kt

+        // Register with backend on a background thread to avoid StrictMode NetworkViolation
+        // The Firebase callback runs on the main thread, so we need to move the network call off it
+        return try {
+            val api = PostHogApi(config)


setup already creates a PostHogApi, lets make it global or create a class that receives the api instance as we do with many other things eg remoteConfigProvider

marandaneto · 2026-01-26T15:58:38Z

posthog/src/main/java/com/posthog/PostHog.kt

+            val distinctId = distinctId()
+
+            val executor =
+                Executors.newSingleThreadExecutor(


this should be a global instance and reused across calls eg queueExecutor
maybe within the class mentioned above https://github.com/PostHog/posthog-android/pull/376/files#r2728191619

marandaneto · 2026-01-26T16:01:56Z

posthog/src/main/java/com/posthog/PostHog.kt

+            } catch (e: java.util.concurrent.TimeoutException) {
+                config.logger.log("Failed to register FCM token: Timeout after 5 seconds")
+                future.cancel(true)
+                false
+            } catch (e: java.util.concurrent.ExecutionException) {
+                val cause = e.cause ?: e
+                config.logger.log("Failed to register FCM token: ${cause.message ?: "Unknown error"}")
+                false
+            } catch (e: Throwable) {
+                config.logger.log("Failed to register FCM token: ${e.message ?: "Unknown error"}")
+                false


you probably want this to be done within the PostHogApi class or inside the class mentioned above, also take a look at PostHogApi and how it throws PostHogApiError, you dont need to await the future, maybe this should should receive a callback to be called in case something goes wrong, but the method should be a fire and forget instead of awaiting for up to 5s, if the user calls this from the main thread, you are causing an ANR

marandaneto · 2026-01-26T16:27:59Z

posthog/src/main/java/com/posthog/PostHog.kt

        return PostHogSessionManager.isSessionActive()
    }

+    override fun registerPushToken(token: String): Boolean {


Does this method have to be atomic? what if multiple threads call this with multiple tokens? most likely, this will race and cause issues. do we have to protect against that?

odin-posthog · 2026-01-26T17:22:51Z

posthog-android/CHANGELOG.md

@@ -1,4 +1,5 @@
 ## Next


Is it correct to have the changelog in this PR already or should it be in the version bump PR? (or does it not matter?)

under next is correct, just do not add a version yet

ioannisj · 2026-01-27T07:15:31Z

posthog/src/main/java/com/posthog/PostHog.kt

+            preferences.setValue(FCM_TOKEN, token)
+            preferences.setValue(FCM_TOKEN_LAST_UPDATED, currentTime)


What happens when the API call fails right below here (L1283)?
Should we clear these preference values we set here?

Yeah, that's a good idea. Updated to clear preferences on error

ioannisj · 2026-01-27T07:20:39Z

posthog/src/main/java/com/posthog/PostHog.kt


+    override fun registerPushToken(
+        token: String,
+        callback: PostHogPushTokenCallback?,


Will BE allow integrating only with a single Firebase project? If we support multiple firebase projects, I would expect to register a firebase config identifier along with this token (So that BE would know which Firebase project to use)? Correct me if my rationale is wrong here, but for people using multiple apps within a specific PostHog project, this could be problematic?

That's a good point! Until now I had assumed that users would have one firebase project per posthog project, and that's probably true for most users, but it would be much better to support multiple. I added the firebase app id

ioannisj · 2026-01-27T07:47:35Z

posthog/src/main/java/com/posthog/internal/PostHogPushSubscriptionRequest.kt

+ */
+@PostHogInternal
+public data class PostHogPushSubscriptionRequest(
+    val api_key: String,


Is snake_cased idiomatic to Kotlin @marandaneto? Probably okay since this is a boundary/network object, just felt weird to my eye. iirc, there's a @SerializedName attr we could use?

Turns out we do use that to transform to snake_case, updated the class to do that and keep the kotlin code camelCase

ioannisj · 2026-01-27T07:57:03Z

posthog/src/main/java/com/posthog/PostHog.kt

+            preferences.setValue(FCM_TOKEN_LAST_UPDATED, currentTime)
+        }
+
+        val distinctId = distinctId()


I feel there may be a race condition here where distinctId() may change between the synchronization block above and the api call below? This would mean we may send the token with the wrong distinctId. @marandaneto wdyt?

For our backend, we're okay with a "best effort to send correct distinctId", if we get a token for an outdated one and trigger a push notification of a more recent/correct distinctId, we query the persons db for past distinctIds associated with the user and find the token with the outdated distinctId

marandaneto · 2026-01-27T12:02:20Z

posthog/src/main/java/com/posthog/PostHog.kt

+        }
+
+        val distinctId = distinctId()
+        pushTokenExecutor.executeSafely {


this assumes connectivity, what if the device is offline or if something fails? how would the user know that they should call this again at some point? should we document this behaviour?

marandaneto · 2026-01-27T12:06:06Z

posthog/src/main/java/com/posthog/PostHogInterface.kt

+ * Callback for push token registration results.
+ * @param success `true` if registration succeeded, `false` if it failed, or `null` if registration was skipped (e.g., token unchanged).
+ */
+public typealias PostHogPushTokenCallback = (success: Boolean?) -> Unit


i think you should use a SAM interface here which is more friendly to java and kotlin users

fun interface PostHogPushTokenCallback { fun onComplete(success: Boolean?) }

also its common to create new files for classes/interfaces

marandaneto · 2026-01-27T12:09:35Z

posthog/src/test/java/com/posthog/PostHogTest.kt

+        // Wait for background thread to complete
+        Thread.sleep(100)


instead of using thread.sleep which slow down tests, you can use another approach
eg CountDownLatch, check the usage in tests and you'd see how to use it

marandaneto · 2026-01-27T12:11:42Z

posthog/src/main/java/com/posthog/PostHog.kt

        return PostHogSessionManager.isSessionActive()
    }

+    override fun registerPushToken(


i still think that this method code impl should live within another class, and this method just forwards to that class eg remoteConfig/replayQueue etc
this class is huge already and it should be a clean interface where users just call something and dont get distracted by its implementation

… in sample app

…etries

…we're actually using

…ests

marandaneto

Left a few small comments but LGTM regardless, thanks.

marandaneto · 2026-02-03T07:36:07Z

posthog-samples/posthog-android-sample/src/main/java/com/posthog/android/sample/MyApp.kt

 //        val apiKey = "_6SG-F7I1vCuZ-HdJL3VZQqjBlaSb1_20hDPwqMNnGI"
        // ManoelTesting:
-        val apiKey = "phc_6lqCaCDCBEWdIGieihq5R2dZpPVbAUFISA75vFZow06"
+        val apiKey = "phc_QFbR1y41s5sxnNTZoyKG2NJo2RlsCIWkUfdpawgb40D"


This is the rotated key, rollback

marandaneto · 2026-02-03T07:36:55Z

posthog/src/main/java/com/posthog/PostHog.kt


    private var remoteConfig: PostHogRemoteConfig? = null
    private var replayQueue: PostHogQueueInterface? = null
+    private lateinit var api: PostHogApi


I'd avoid lateinit otherwise you crash if you use it and its not init yet, nullable var is fine

marandaneto · 2026-02-03T07:37:54Z

posthog/src/main/java/com/posthog/PostHog.kt

+        callback: PostHogPushTokenCallback?,
+    ) {
+        if (!isEnabled()) {
+            pushTokenExecutor.executeSafely { callback?.onComplete(PostHogPushTokenError.SDK_DISABLED, null) }


You dont need to execute the callback always within the executor, i'd just run the callback on whatever thread it is

marandaneto · 2026-02-03T07:38:27Z

posthog/src/main/java/com/posthog/PostHog.kt


        private val apiKeys = mutableSetOf<String>()

+        private const val ONE_HOUR_IN_MILLIS = 60 * 60 * 1000L


Const usually goes within the companion object in kotlin

marandaneto · 2026-02-03T10:54:48Z

posthog/src/main/java/com/posthog/PostHogPushTokenCallback.kt

+ * @param throwable When [error] is one of [PostHogPushTokenError.NETWORK_ERROR], [PostHogPushTokenError.INVALID_INPUT], [PostHogPushTokenError.UNAUTHORIZED], [PostHogPushTokenError.SERVER_ERROR], or [PostHogPushTokenError.OTHER], the exception that caused the failure; otherwise `null`.
+ */
+public fun interface PostHogPushTokenCallback {
+    public fun onComplete(


should this method have a boolean param like success: true|false?
right now the user needs to check both error and throwable to understand if it worked or not
the other option is an interface with 2 methods, onSuccess and onError, so its clear what happened

odin-posthog self-assigned this Jan 20, 2026

odin-posthog mentioned this pull request Jan 26, 2026

feat(odin): Allow collecting FCM device token in SDK core #396

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odin-posthog force-pushed the odin/feature-add-push-notification-token-upload branch from 95772c0 to f8a4c90 Compare January 26, 2026 14:54

marandaneto reviewed Jan 26, 2026

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odin-posthog marked this pull request as ready for review January 26, 2026 16:21

odin-posthog requested a review from a team January 26, 2026 16:21

marandaneto reviewed Jan 26, 2026

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odin-posthog commented Jan 26, 2026

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odin-posthog force-pushed the odin/feature-add-push-notification-token-upload branch from 6f3c3c0 to 09a500b Compare January 26, 2026 17:25

odin-posthog requested a review from marandaneto January 26, 2026 17:42

ioannisj reviewed Jan 27, 2026

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marandaneto reviewed Jan 27, 2026

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odin-posthog force-pushed the odin/feature-add-push-notification-token-upload branch from 7ea7efe to 92906d6 Compare January 30, 2026 14:30

odin-posthog added 11 commits January 30, 2026 16:23

feat(odin): Allow collecting FCM device token in SDK & demonstrate it…

4e28e38

… in sample app

Update changelogs

20f5e50

feat: allow collecting FCM tokens for push notifications in core

51dcb52

Update PR in changelog

ddb4a2e

chore: remove non-core changes, keep only posthog/ module changes

ae8a3df

Fix up minor issues

7405f85

Fix CI issues (formatting, code cleanliness)

9c5fb6b

Update API file

c59ba16

Add registerPushToken to PostHogFake.kt

4c7bcea

Fix tests

4e9a08b

Update changelogs

286a45f

odin-posthog added 7 commits January 30, 2026 16:23

Address PR comments

e81be16

Apply spotless formatting

ff00334

Update api file

7fb293f

Add firebaseAppId to request

4ef12d3

Clear token from preferences after failed API calls to enable swift r…

d2027af

…etries

Use SerializedName to snake-case PostHogPushSubscriptionRequest

b2398b4

Include firebase app id, refactor to keep PostHog.kt clean

3c67b45

odin-posthog force-pushed the odin/feature-add-push-notification-token-upload branch from 92906d6 to 3c67b45 Compare January 30, 2026 15:24

odin-posthog added 5 commits January 30, 2026 20:56

Rename "firebase app id" to "firebase project id", since that's what …

da3b7f2

…we're actually using

Reupload token every 24h instead of 1h

95cc19f

Remove strict mode tagging (only needed locally)

65d8ff7

Apply spotless formatting

8069e27

Rename firebaseProjectId to fcmProjectId (as in backend), fix flaky t…

9ed0b2d

…ests

marandaneto approved these changes Feb 3, 2026

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marandaneto reviewed Feb 3, 2026

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		preferences.setValue(FCM_TOKEN, token)
		preferences.setValue(FCM_TOKEN_LAST_UPDATED, currentTime)


		private val apiKeys = mutableSetOf<String>()

		private const val ONE_HOUR_IN_MILLIS = 60 * 60 * 1000L

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odin-posthog commented Jan 20, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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💡 Motivation and Context

💚 How did you test it?

📝 Checklist

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ioannisj Jan 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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odin-posthog commented Jan 20, 2026 •

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