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gh-136547: refactor hashlib_helper for blocking and requesting digests #136762

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@picnixz picnixz commented Jul 18, 2025

I made some mistakes in my previous PR and the design I introduced for requesting hashes could actually be greatly simplified. As those two are tightly coupled, I've decided to do both the fix & refactoring at the same time.

Because of all build possibilities we can have, whether at runtime or not, and because some functions can't be given usedforsecurity, tests easily fail because of the underlying configurations. Default builds where we don't have some FIPS module are easy to test, but when FIPS mode is enabled, it's hard to know what is blocked and what is not.

One really annoying thing is the treatment of BLAKE-2 which always falls back to the built-in implementations. Thus, blocking BLAKE-2 may be quite hard and quite different. Well, if we block BLAKE-2 and we don't have OpenSSL at all, then tests don't pass because hashlib.py can't even be imported. Anywsay, I'm opening a draft for now and I'll continue working on this tomorrow.

@picnixz picnixz marked this pull request as ready for review July 19, 2025 17:46
@picnixz picnixz requested review from gpshead and tiran as code owners July 19, 2025 17:46
@picnixz picnixz marked this pull request as draft July 19, 2025 17:49
# re-import '_hashlib' in case it was mocked
_hashlib = try_import_module("_hashlib")
mod = _hashlib if openssl and _hashlib is not None else hashlib
constructor = partial(mod.new, digestname, **kwargs)
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I shouldn't return a partial function with "**kwargs" as it makes it impossible to use otherwise. I should only check if the call will succeed if I were to pass such keywords.

_hashlib = importlib.import_module("_hashlib")
except ImportError as exc:
raise SkipNoHash(digestname, "openssl") from exc
constructor = partial(_hashlib.new, digestname, **kwargs)
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Ditto.

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