How to set up UnifiedPush on Android for Nextcloud Talk: push notifications without Google Play Services

The problem with push notifications via Google Play Services

In the early days of Android, there was no dedicated, OS-level push mechanism, so developers who wanted to send notifications to users had to build their own. Some would let their apps poll their servers periodically, others would establish a constant connection in the background. This drained the battery fast.

To solve this problem, Google introduced «Cloud to Device Messaging» (C2DM), which was later replaced by «Google Cloud Messaging» (GCM) and finally «Firebase Cloud Messaging» (FCM), which is what most Android apps use today. It centralizes the infrastructure for processing notifications and only requires a single Google Play Services connection to push them to the phone.

However, since virtually every notification passes through Google’s servers, it can technically see metadata about when and how often you’re receiving notifications from which apps, even if it can’t read encrypted message content. Naturally, privacy-conscious users want to avoid this, which is why some Android apps use a different mechanism.

How privacy-focused Android apps handle push notifications

One app that minimizes the metadata Google can see is Signal. When a new message arrives for you, Signal’s own servers send FCM a payload that contains no sender info and no content. When it is delivered to your phone, it only tells your Signal app to wake up, nothing more. The app then reaches out to the Signal servers to fetch the actual end-to-end encrypted message.

Of course, this approach still involves Google’s FCM, so some apps keep their own connections running in the background or periodically check their servers to then generate the notifications locally once they detect something new. However, this can result in increased background activity, which makes the process more likely to be terminated by aggressive battery-optimization.

The privacy-respecting alternative: UnifiedPush

No matter how apps handle push notifications, they always involve a third-party server, be it Google’s or the app developers’ own. If you want to have full control over where your notifications are processed, you need to be able to specify your own server (including one you run yourself, if you prefer that), and UnifiedPush helps you with that.

UnifiedPush defines a set of interfaces specifying what messages get exchanged between which parties without dictating how each party is built internally (similar to how SMTP/IMAP works for email). To receive push notifications, you’ll also need a distributor app installed on your phone (e.g. NextPush, Sunup, or ntfy), a push server the distributor connects to (e.g. your Nextcloud, a third-party server like Mozilla’s, or your own self-hosted setup), and an app that supports receiving push notifications via UnifiedPush (like Nextcloud Talk for Android).

For a setup involving Sunup (which is the approach described in the next section), the process will then look like this:

When you receive a new message in Nextcloud Talk, the server running your Nextcloud sends the notification payload to your push server (in this case Mozilla’s), which then forwards it to Sunup (the distributor). Sunup hands it off to the Nextcloud Talk Android app, which displays it on your phone.

In this setup, Mozilla’s push server replaces Google’s FCM and Sunup replaces Google Play Services.