iOS: error publishing on the App Store due to private _AudioConvertHostTimeToNanos and _AudioGetCurrentHostTime

[mockersf]

When publishing an app on iOS through XCode / App Store Connect, I get rejected because of using private symbols:

Prepared archive for uploading
Upload failed
	error: Asset validation failed
The app references non-public symbols: _AudioConvertHostTimeToNanos, _AudioGetCurrentHostTime

If I remove all calls to these methods and always set the timestamps to 0, publication is successful.

It seems they are available on macOS, but not on iOS https://developer.apple.com/documentation/coreaudio/1422393-audioconverthosttimetonanos.

Is there a workaround that would keep the timestamps? It seems they are used only for sysex messages, would it be OK to put those calls behind a feature flag so that they can be ignored when not needed? I can submit and test a PR if that's the direction to take.

[Boddlnagg]

I think the timestamps are not only used for sysex messages (at least AudioConvertHostTimeToNanos is called in any case). But I agree that it would be great to find a workaround for the private symbols in order to allow iOS app publishing.

I'm open for a PR that disables these calls based on a feature flag (there are already two feature flags related to timestamps, so adding another one seems okay). It might even make sense to reuse the avoid_timestamping feature that's currently used for input on ALSA. However, because Cargo features shouldn't have negative semantics, it's probably better to have a default-on feature that can be opted out of (and is by default disabled on iOS). Maybe coremidi_receive_timestamped analogous to coremidi_send_timestamped?

If anyone knows an alternative solution that doesn't use the private symbols, that would be great too.