crash when initializing with an invalid model

[zaphoyd]

When Whisper.init(fromFileURL) is called with a file URL that is a file that exists, but not a valid model file, the error condition from the underlying whisper.cpp library is not handled.

Specifically:
self.whisperContext = fileURL.relativePath.withCString { whisper_init_from_file($0) }

whisper_init_from_file will return nullptr in this case. The attempted assignment produces the following error which crashes the program using the library.

whisper_init_from_file_no_state: loading model from '.'
whisper_model_load: loading model
whisper_model_load: invalid model data (bad magic)
whisper_init_no_state: failed to load model
SwiftWhisper/Whisper.swift:16: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value

I'd like to add a check to this initializer so my program can catch and safely handle this case. In theory, my program could attempt to figure out if this was a valid model file, but this would involve re-implementing the detection code from whisper.cpp that I am trying to wrap. Letting that code that is already doing the error handling just pass the error through seems like a better arrangement.

Doing so would probably require changing the init signature to a throwing one or a fail-able one. I understand that this would involve a change in API here. Is there a way to handle this that would be likely to be accepted as a PR? Is there a more general plan for how to handle this sort of error case?

[exPHAT]

As far as I'm aware, theres no way to catch fatally-throwing errors in Swift that originated from C. So I don't think a throwing initializer would be possible in this case.

If you know of a way that I'm not aware of, please let me know.

[zaphoyd]

Hi, the error is passed using the return value, not an exception. Here is the fix that I am using in a fork: master...uni-industries:SwiftWhisper:master

This allows checking the return value of the Whisper initializer. You don't get the precise reason in an exception (it IS printed to the console though by the underlying library). But you can check for this nil value and handle it rather than having the program crash with a null reference exception, which is the key thing I am trying to avoid.

Would be happy to submit a PR if this direction is useful.

[exPHAT]

Your branch looks good to me, though the tests and README will need to be updated to reflect it.

If you'd like to do that as well, I'd be happy to merge it in a PR.

[roei46]

I am running your fork yet Whisper is still nil: let whisper = Whisper(fromFileURL: recordedFile!)
What am i missing?