.opus file is rejected; same file with .ogg file extension is accepted

[BenLubar]

Steps to reproduce the problem

1. Upload an opus file to the post composer. Any file should work, example: repro.zip (GitHub won't let me upload a bare opus file)
2. Rename the file to have a .ogg extension and try again. This time, it works.

Expected behaviour

both files should be accepted

Actual behaviour

uploading the file with the .opus extension results in a pop-up that says "422 Validation failed: File content type is invalid, File is invalid"

Specifications

Server:
https://github.com/mastodon/mastodon/tree/2287eebae0c1d699436a8cf3218d7cfe990a3605

Client:
Google Chrome 102.0.4975.0 (Official Build) dev (64-bit)
Revision 9637db21d4426d633aafd3a8117272c5b37bc672-refs/branch-heads/4975
Platform 14658.0.0 (Official Build) dev-channel edgar
Firmware Version Google_Edgar.7287.167.156

[PoneyClairDeLune]

Why does this issue still exist...

[vmstan]

I think the issue is with the kt-paperclip Gem that handles upload processing.

Comparing the test file that @BenLubar attached, I can see from ffprobe how it is encoded:

vmstan@Sovereign ~/Code/mime-type $ ffprobe ~/Downloads/youre-a-girl.opus
...
Input #0, ogg, from '/Users/vmstan/Downloads/youre-a-girl.opus':
  Duration: 00:00:42.93, start: 0.000000, bitrate: 92 kb/s
  Stream #0:0(und): Audio: opus, 48000 Hz, stereo, fltp
    Metadata:
      handler_name    : SoundHandler
      encoder         : Lavc58.91.100 libopus
      major_brand     : isom
      minor_version   : 512
      compatible_brands: isomiso2avc1mp41

Using the file utility, it's properly identified as an audio/ogg file in both variations.

vmstan@Sovereign ~/Code/mime-type $ file --mime ~/Downloads/youre-a-girl.opus
/Users/vmstan/Downloads/youre-a-girl.opus: audio/ogg; charset=binary
vmstan@Sovereign ~/Code/mime-type $ file --mime ~/Downloads/youre-a-girl.ogg
/Users/vmstan/Downloads/youre-a-girl.ogg: audio/ogg; charset=binary

However when using kt-paperclip to do the identification (I hacked together a basic script to invoke the Gem to do it, so it's not Mastodon code doing any part of the processing) it shows a different result based on the file names, both of which differ from audio/ogg

vmstan@Sovereign ~/Code/mime-type $ ruby get_mime_type.rb ~/Downloads/youre-a-girl.ogg
The MIME type of the file is: audio/vorbis
vmstan@Sovereign ~/Code/mime-type $ ruby get_mime_type.rb ~/Downloads/youre-a-girl.opus
The MIME type of the file is: audio/opus

In the Mastodon file app/models/concerns/attachmentable.rb there is a specific bypass for audio/vorbis files to bypass the kt-paperclip identification method and use file. I suspect it's necessary to add an exemption for audio/opus -- I will test and report back.