iOS Action Extension share from GarageBand - ios

Question

I am building an action extension for GarageBand on iOS which transforms and uploads audio but no matter what I try, I just could not get to the exported file.
Let’s consider the following code — it should:
find and load shared audio from extensionContext
initialise audio player
play the sound
It works if I run the extension in Voice Memos.app — the url to the file looks like this: file:///tmp/com.apple.VoiceMemos/New%20Recording%202.m4a
Now, If I run the code in GarageBand.app, the url points to (what I presume) is GarageBand’s app container, as the url looks something like /var/…/Containers/…/Project.band/audio/Project.m4a, and the audio will not be loaded and cannot therefore be manipulated in any way.
// edit: If I try to load contents of the audio file, it looks like the data only contains aac header (?) but the rest of the file is empty
What is interesting is this: The extension renders a react-native view and if I pass the view the fileUrl (/var/…Project.band/audio/Project.m4a) and then pass it down to XMLHTTPRequest, the file gets uploaded. So it looks like the file can be accessed in some way?
I’m new to Swift/iOS development so this is kind of frustrating for me, I feel like I tried just about everything.
The code:
override func viewDidLoad() {
super.viewDidLoad()
var audioFound :Bool = false
for inputItem: Any in self.extensionContext!.inputItems {
let extensionItem = inputItem as! NSExtensionItem
for attachment: Any in extensionItem.attachments! {
print("attachment = \(attachment)")
let itemProvider = attachment as! NSItemProvider
if itemProvider.hasItemConformingToTypeIdentifier(kUTTypeAudio as String) {
itemProvider.loadItem(forTypeIdentifier: kUTTypeAudio as String,
options: nil, completionHandler: { (audioURL, error) in
OperationQueue.main.addOperation {
if let audioURL = audioURL as? NSURL {
print("audioUrl = \(audioURL)")
// in our sample code we just present and play the audio in our app extension
let theAVPlayer :AVPlayer = AVPlayer(url: audioURL as URL)
let theAVPlayerViewController :AVPlayerViewController = AVPlayerViewController()
theAVPlayerViewController.player = theAVPlayer
self.present(theAVPlayerViewController, animated: true) {
theAVPlayerViewController.player!.play()
}
}
}
})
audioFound = true
break
}
}
if (audioFound) {
break
}
}
}