ssl: a failed assignment or deletion of _SSLContext._msg_callback clears the callback

[serhiy-storchaka]

Bug report

The setter of _ssl._SSLContext._msg_callback clears the current callback before validating the new value, so a rejected assignment or a deletion loses it.

>>> import ssl, _ssl
>>> ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
>>> descr = _ssl._SSLContext.__dict__['_msg_callback']
>>> descr.__set__(ctx, lambda *args: None)
>>> descr.__delete__(ctx)
Traceback (most recent call last):
  ...
TypeError: not a callable object
>>> print(descr.__get__(ctx))
None

Deleting the attribute should raise AttributeError, like for keylog_filename (gh-156099) and row_factory (gh-149738), and neither a failed deletion nor a failed assignment should change the value.

ssl.SSLContext wraps the attribute in a property which checks the value and has no deleter, so this is only reachable through the C type.

Linked PRs

• gh-156166: Fix setting and deleting SSLContext._msg_callback #156167
• [3.15] gh-156166: Fix setting and deleting SSLContext._msg_callback (GH-156167) #156171
• [3.14] gh-156166: Fix setting and deleting SSLContext._msg_callback (GH-156167) #156174
• [3.13] gh-156166: Fix setting and deleting SSLContext._msg_callback (GH-156167) #156175