Low level hardware access for opening a file and a network port? Those are some of the first lessons in any programming tutorial. If they aren't available, what is the OS even doing?

Also, for all intents and purposes, GMS is part of the Android OS, but Google had to branch it off, to keep it closed source.

AirDrop doesn't open a network port, it creates a WiFi Aware advertisement and a WiFi Direct connection. However I thought this also should not need OS-level changes, just android.permission.NEARBY_WIFI_DEVICES permission.