zulip/docs/production/mobile-push-notifications.md

# Mobile push notification service

Zulip's iOS and Android mobile apps support receiving push
notifications from Zulip servers to let users know when new messages
have arrived.  This is an important feature to having a great
experience using the Zulip mobile apps.

For technical reasons (explained below), in order to deliver mobile
push notifications in the app store versions of our mobile apps, you
will need to register your Zulip server with the Zulip mobile push
notification service.  This service will forward push notifications
generated by your server to the Zulip mobile app automatically.

## How to sign up

Starting with Zulip 1.6 for both Android and iOS, Zulip servers
support forwarding push notifications to a central push notification
forwarding service.  You can enable this for your Zulip server as
follows:

1. First, contact support@zulipchat.com with the `zulip_org_id` and
   `zulip_org_key` values from your `/etc/zulip/zulip-secrets.conf` file, as
   well as a `hostname` and `contact email` address you'd like us to use in case
   of any issues (we hope to have a nice web flow available for this soon).

2. We'll enable push notifications for your server on our end. Look for a
   reply from Zulipchat support within 24 hours.

3. Uncomment the `PUSH_NOTIFICATION_BOUNCER_URL = "https://push.zulipchat.com"`
   line in your `/etc/zulip/settings.py` file, and
   [restart your Zulip server](../production/maintain-secure-upgrade.html#updating-settings).
   Note that if you installed Zulip older than 1.6, you'll need to add
   the line (it won't be there to uncomment).

4. If you or your users have already set up the Zulip mobile app,
   you'll each need to log out and log back in again in order to start
   getting push notifications.

That should be all you need to do!

If you'd like to verify the full pipeline, you can do the following.
Please follow the instructions carefully:

* [Configure mobile push notifications to always be sent][notification-settings]
  (normally they're only sent if you're idle, which isn't ideal for
  this sort of testing).
* On an Android device, download and login to the
[Zulip Android app](https://play.google.com/store/apps/details?id=com.zulipmobile).
If you were already logged in before configuring the server, you'll
need to logout first, since the app only registers for push
notifications on login.
* Hit the home button, so Zulip is running in the background, and then
have **another user** send you a **private message** (By default,
Zulip only sends push notifications for private messages sent by other
users and messages mentioning you).  A push notification should appear
in the Android notification area.

[notification-settings]: https://zulipchat.com/help/configure-mobile-notifications

Note that use of the push notification bouncer is subject to the
[Zulipchat Terms of Service](https://zulipchat.com/terms/). By using push
notifications, you agree to those terms.

## Why this is necessary

Both Google's and Apple's push notification services have a security
model that does not support mutually untrusted self-hosted servers
sending push notifications to the same app.  In particular, when an
app is published to their respective app stores, one must compile into
the app a secret corresponding to the server that will be able to
publish push notifications for the app.  This means that it is
impossible for a single app in their stores to receive push
notifications from multiple, mutually untrusted, servers.

Zulip's solution to this problem is to provide a central push
notification forwarding service, which allows registered Zulip servers
to send push notifications to the Zulip app indirectly (through the
forwarding service).

## Security and privacy implications

We've designed this push notification bouncer service with security
and privacy in mind:

* A central design goal of the the Push Notification Service is to
  avoid any message content being stored or logged by the service,
  even in error cases.  We store only the necessary metadata for
  delivering the notifications.  This includes the tokens needed to
  push notifications to the devices, and user ID numbers generated by
  your Zulip server.  These user ID numbers are are opaque to the Push
  Notification Service, since it has no other data about those users.
* All of the network requests (both from Zulip servers to the Push
  Notification Service and from the Push Notification Service to the
  relevant Google and Apple services) are encrypted over the wire with
  SSL/TLS.
* The code for the push notification forwarding service is 100% open
  source and available as part of the
  [Zulip server project on GitHub](https://github.com/zulip/zulip).
* The push notification forwarding servers are professionally managed
  by a small team of security expert engineers.
* If you'd like an extra layer of protection, there's a
  `PUSH_NOTIFICATION_REDACT_CONTENT` setting available to disable any
  message content being sent via the push notification bouncer
  (i.e. message content will be replaced with `***REDACTED***`).  Note
  that this setting makes push notifications significantly less
  usable.  We plan to
  [replace this feature with end-to-end encryption](https://github.com/zulip/zulip/issues/6954)
  which would eliminate that usability tradeoff.

If you have any questions about the security model, contact
support@zulipchat.com.

## Sending push notifications directly from your server

As we discussed above, it is impossible for a single app in their
stores to receive push notifications from multiple, mutually
untrusted, servers.  The Mobile Push Notification Service is one of
the possible solutions to this problem.  The other possible solution
is for an individual Zulip server's administrators to build and
distribute their own copy of the Zulip mobile apps, hardcoding a key
that they possess.

This solution is possible with Zulip, but it requires the server
administrators to publish their own copies of
the Zulip mobile apps (and there's nothing the Zulip team can do to
eliminate this onorous requirement).

The main work is distributing your own copies of the Zulip mobile apps
configured to use APNS/GCM keys that you generate.  This is not for
the faint of heart!  If you haven't done this before, be warned that
one can easily spend hundreds of dollars (on things like a DUNS number
registration) and a week struggling through the hoops Apple requires
to build and distribute an app through the Apple app store, even if
you're making no code modifications to an app already present in the
store (as would be the case here). The Zulip mobile app also gets
frequent updates that you will have to either forgo or republish to
the app stores yourself.

If you've done that work, the Zulip server configuration for sending
push notifications through the new app is quite straightforward:
* Create a
  [GCM push notifications](https://developers.google.com/cloud-messaging/android/client)
  key in the Google Developer console and set `android_gcm_api_key` in
  `/etc/zulip/zulip-secrets.conf` to that key.
* Register for a
  [mobile push notification certificate][apple-docs]
  from Apple's developer console.  Set `APNS_SANDBOX=False` and
  `APNS_CERT_FILE` to be the path of your APNS certificate file in
  `/etc/zulip/settings.py`.
* Restart the Zulip server.

[apple-docs]: https://developer.apple.com/library/content/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/APNSOverview.html