Service extensions are intended to act as middleware for push notifications. A service extension receives a notification before it's displayed to the user. This allows you to manipulate or enrich the notification's content before it's shown to the user.
A service extension is perfect if you're implementing end-to-end encryption, for example. Another great use for a service extension is to download a media attachment from a push notification, save it locally, and add it as a media attachment to the notification contents, because all media attachments that are shown in a notification must be stored locally on the device. This means that a push notification can't really have media attachments, unless a ...
