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add section on notifications

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Daniel Micay 2021-04-06 22:03:07 -04:00
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@ -110,6 +110,7 @@
<li><a href="#updates">How do I keep the OS updated?</a></li>
<li><a href="#updates-sideloading">How do I update without connecting the
device to the internet?</a></li>
<li><a href="#notifications">Do notifications properly work on GrapheneOS?</a></li>
</ul>
</li>
<li><a href="#features">What features does GrapheneOS implement?</a></li>
@ -1062,6 +1063,60 @@
<p>Updates can be <a href="/usage#updates-sideloading">sideloaded via
recovery</a>.</p>
</article>
<article id="notifications">
<h2><a href="#notifications">Do notifications work properly on GrapheneOS?</a></h2>
<p>Yes, notifications work properly on GrapheneOS. Portable apps avoiding a
hard dependency on Google Play services for their functionality have fully
working notifications on GrapheneOS. Apps that are not fully portable across
Android implementations often lack support for background notifications due to
only bothering to implement support for it via Google Play services.</p>
<p>Most apps that able to run without Google Play services will have working
notifications when they're in the foreground. Unfortunately, many apps don't
implement a service to continue receiving events from their server in the
background. On the stock OS, they rely on receiving events through Google
servers via Firebase Cloud Messaging (FCM) in the background, and sometimes
also in the foreground.</p>
<p>Polling is the traditional pull-based approach of checking for new events
at an interval. This is badly suited to mobile devices for anything more than
very infrequent checks. Apps using infrequent polling are supposed to use the
JobScheduler service. A minority of apps may only be able to use Firebase
WorkManager or the legacy Firebase JobDispatcher. Most apps doing this should
work fine on GrapheneOS. An example of an app needing to use this approach is
a feed reader for RSS/Atom feeds or an email client dealing with legacy email
servers without IMAP IDLE push support.</p>
<p>Push messaging is the modern push-based model of receiving events from the
server as they occur by keeping open a connection to it. Push messaging still
uses occasional polling to keep the connection from being killed by a network
using a stateful firewall or some form of NAT. IPv4 mobile networks use large
scale NAT (CGNAT) to work around IPv4 addresses running out. The occasional
polling will also detect a silently dropped connection. An efficient push
implementation will figure out that it's on a reliable network and throttle
the polling to be very infrequent.</p>
<p>In order to properly implement either push messaging or frequent polling
themselves, an app needs to run a foreground service. This is displayed as a
persistent notification. It will normally be marked as a silent notification
with the lowest possible priority, so it will be collapsed as the bottom and
won't show up as an icon in the status bar or on the lockscreen. A battery
optimization exception is also needed for the app to bypass device idle states
and run while the device is idle. If you can tolerate delays while the device
is idle, then the battery optimization exception isn't mandatory.</p>
<p>FairEmail and Signal are examples of apps using the proper approach of a
foreground service combined with an optional battery optimization exception.
Signal doesn't have an optimized implementation throttling the polling used to
keep the connection alive, but it does work well. Signal always uses their own
push implementation in the foreground, but switches to FCM in the background
when it's available. FairEmail uses the IMAP IDLE push feature provided by
email servers. Most email servers don't provide FCM-based push in the first
place, and the only way for an email app to provide push via FCM would be to
give the user's credentials to their own server to act as a middleman.</p>
</article>
</section>
<article id="features">