I think (reading between the lines on their docs) that you'll get throttled/dropped if you abuse the system by sending a regular push notification but do not notify the user. Apple doesn't like app developers using invisible notifications because it risks wasting device battery without the users being aware that their device is constantly being awakened by your app.
However, I was actually wrong more generally because Apple does have push notification type for this, Background Updates[1] are permitted to run invisibly. They say not to try sending more than 2-3 per hour, and that "the system may throttle the delivery of background notifications if the total number becomes excessive" - which sounds like you're permitted some unspecified small number between app launches.
These notifications seem to only be able to send a single boolean flag, so it doesn't seem like an awfully viable way of implementing a fixed rate message system (especially because you'd also want to be sending messages out on that same fixed rate to frustrate analysis)
Technically you can make malformed messages visible: store them in spambox and display their metadata or maybe even as a source of randomness, like random.org
I think (reading between the lines on their docs) that you'll get throttled/dropped if you abuse the system by sending a regular push notification but do not notify the user. Apple doesn't like app developers using invisible notifications because it risks wasting device battery without the users being aware that their device is constantly being awakened by your app.
However, I was actually wrong more generally because Apple does have push notification type for this, Background Updates[1] are permitted to run invisibly. They say not to try sending more than 2-3 per hour, and that "the system may throttle the delivery of background notifications if the total number becomes excessive" - which sounds like you're permitted some unspecified small number between app launches.
These notifications seem to only be able to send a single boolean flag, so it doesn't seem like an awfully viable way of implementing a fixed rate message system (especially because you'd also want to be sending messages out on that same fixed rate to frustrate analysis)
1: https://developer.apple.com/documentation/usernotifications/...
Technically you can make malformed messages visible: store them in spambox and display their metadata or maybe even as a source of randomness, like random.org