from_buffer() issue with file-5.47 #362

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1. ddelange commented on Mar 21, 2026

   

   ddelange

   on Mar 21, 2026

   Contributor

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   I can confirm this issue, just tried bumping to file-5.47 in #294 and the smoke test starts failing:

     Successfully installed python-magic-0.4.28
     + /bin/sh -c 'python -c "import magic; assert magic.Magic(mime=True).from_buffer(b'"'"'\x00\x00\x00\x1cftypiso5\x00\x00\x00\x01isomiso5hlsf\x00\x00'"'"') == '"'"'video/mp4'"'"'"'
     Traceback (most recent call last):
       File "<string>", line 1, in <module>
     AssertionError

   Sounds like an upstream issue because this library is just a CDLL wrapper.

   👍React with 👍1Reacted by RafayAK
2. ddelange

   added a commit that references this issue on Mar 21, 2026

   Revert "Bump to file-5.47" because of ahupp#362

   ...

   04d2587
3. bvergnaud commented on Apr 1, 2026

   

   bvergnaud

   on Apr 1, 2026

   Last edited by bvergnaud

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   Hiya,

   For anyone stumbling here, a similar problem was reported upstream here (requires creating an account).

   Date Submitted: 2026-03-04 12:58
   Last Update: 2026-04-01 08:54

   They seem to be on the right track. I spent some time digging tonight, I had identified a commit that messed with offset calculations in file_buffer(). I intended to report it, but I found that issue, and based on the latest comments from today, they found the same commit and code paths I was looking at.

   In the meantime:

   • Using magic.from_file() or magic.from_descriptor() works fine.
   • If you really want to use buffers (e.g. to avoid reading huge files), save the buffer to a temporary file and use magic.from_file() on that.
   • Or pin your file package ≤ 5.46, until further news.

   ---

   UPDATE: The bug is reported as patched by one of the maintainers, as of 2026-04-12 22:15 (UTC). All we need now is to wait for a 5.48 release. Which unfortunately might take a while: 5.47 landed Feb 26, 2026, 5.46 landed Nov 27, 2024. Let's hope we won't have to wait 1 more year. 😅

   👍React with 👍4Reacted by Wesley Moore, ddelange, pfcodes and RafayAK
4. Iamnotagenius

   added a commit that references this issue on Apr 8, 2026

   fix: use magic from file

   ...

   5fa1e3f
5. doronbehar commented on May 4, 2026

   

   doronbehar

   on May 4, 2026

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   Did anyone manage to figure out what upstream commit fixed the issue? I didn't find a clear candidate here:

   • https://bugs.astron.com/view.php?id=725

   I'd like to patch it for my distribution...
6. bvergnaud commented on May 4, 2026

   

   bvergnaud

   on May 4, 2026

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   Did anyone manage to figure out what upstream commit fixed the issue? I didn't find a clear candidate here:

   * https://bugs.astron.com/view.php?id=725
   

   I'd like to patch it for my distribution...

   Here you go:
   file/file@c546057

   ❤️React with ❤️1Reacted by Doron Behar
7. RafayAK commented on May 18, 2026

   

   RafayAK

   on May 18, 2026

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   Just faced this issue, for somereason audio/ogg is getting picked up as application/octet-stream

    python -u - <<'PY'
   import magic
   p='/Path/To/Audio-Notes/Q1.ogg'
   m=magic.Magic(mime=True)
   print('from_file', m.from_file(p))
   with open(p,'rb') as f:
       b=f.read(8192)
   print('from_buffer_2048', m.from_buffer(b[:2048]))
   print('from_buffer_8192', m.from_buffer(b))
   PY
   from_file audio/ogg
   from_buffer_2048 application/octet-stream
   from_buffer_8192 application/octet-stream