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Fix potential memory leak in Encoder_init - #1040

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provinzkraut merged 2 commits into
msgspec:mainfrom
sobolevn:fix-leak-in-Encoder_init
Jun 10, 2026
Merged

Fix potential memory leak in Encoder_init#1040
provinzkraut merged 2 commits into
msgspec:mainfrom
sobolevn:fix-leak-in-Encoder_init

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@sobolevn

@sobolevn sobolevn commented Jun 7, 2026 •
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There was a potential memory leak in Encoder_init.

Why?

  1. Some valid callable is passed as enc_hook, it has +1 rc in Py_INCREF(enc_hook);
  2. Then, invalid order is checked, we return -1 from Encoder_init, but does not Py_DECREF(enc_hook);

We can just swap the check order. First check things that do not incref, lastly incref.

Repro:

>>> from msgspec.json import Encoder
>>> import sys
>>> def test(*args, **kwargs): ...
... 
>>> sys.getrefcount(test)
2
>>> Encoder(enc_hook=test, order='wrong')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: `order` must be one of `{None, 'deterministic', 'sorted'}`, got 'wrong'
>>> sys.getrefcount(test)
3

provinzkraut
provinzkraut approved these changes Jun 7, 2026
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@provinzkraut provinzkraut left a comment

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Good catch, thanks!

@provinzkraut
provinzkraut enabled auto-merge June 10, 2026 15:59
@provinzkraut
provinzkraut added this pull request to the merge queue Jun 10, 2026
Merged via the queue into msgspec:main with commit 4152dc1 Jun 10, 2026
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@sobolevn @provinzkraut