hashlib.algorithms_available doesn't account for backends loaded dynamically at runtime

[mgorny]

Bug report

If additional OpenSSL backends are loaded at runtime (this happens e.g. when importing PyOpenSSL), the hashlib.algorithms_available doesn't get updated for the newly available hashes.

Trivial reproducer:

>>> import ctypes, hashlib
>>> ctypes.CDLL("libssl.so").OSSL_PROVIDER_load(None, b"legacy")
-1311283920
>>> "md4" in hashlib.algorithms_available
False
>>> hashlib.new("md4")
<md4 _hashlib.HASH object @ 0x7f404308faf0>

Your environment

• CPython versions tested on: 3.11.0b1, 3.10.4 with 1b6acaa backported, 3.9.12
• Operating system and architecture: Gentoo Linux amd64
• OpenSSL version: 3.0.3

[jakirkham]

This looks very similar to issue ( #92876 ). Should one of these be closed? Or am I missing some difference between these?

[mgorny]

No, not really. Solving #92876 would somewhat avoid one particular example but the issue would persist if one of the libraries loaded yet another provider.

[picnixz]

One way to mitigate this is to add a function that can modify the hashlib.algorithms_available set. It would be too complicate to make it automatic. Would it help solving your issue?

[mgorny]

I don't think it's really worth the effort. I wouldn't really call it an issue, rather an observed inconsistency.

A simpler way to avoid it would be to make hashlib.new() reject algorithms not in algorithms_available, but that probably has more downsides than real benefits.