`http.cookies` module does not parse obsolete RFC 850 date format

[Konano]

Bug report

Bug description:

Description: According to RFC 9110, a recipient that parses a timestamp value in an HTTP field MUST accept all three HTTP-date formats. This includes the obsolete RFC 850 format, e.g., Sunday, 06-Nov-94 08:49:37 GMT. However, the Python standard library module http.cookies currently fails to parse this format, which leads to the cookie being discarded entirely.

Steps to Reproduce:

1. Attempt to parse a cookie with a date in the obsolete RFC 850 format using the http.cookies module.
2. Observe that the module fails to parse the date, resulting in the cookie being discarded.

Code Example:

import http.cookies

cookie_string = 'example=value; expires=Sunday, 06-Nov-94 08:49:37 GMT'
cookie = http.cookies.SimpleCookie()
cookie.load(cookie_string)

# The expected behavior is that the cookie's expiration date is correctly parsed.
# However, the module fails to parse the date in the obsolete RFC 850 format,
# resulting in the cookie being discarded.
print(cookie['example'].get('expires'))

Expected Behavior:
The http.cookies module should correctly parse the obsolete RFC 850 date format and retain the cookie.

Actual Behavior:
The module fails to parse the date, resulting in a KeyError and the cookie being discarded.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-123401: Fix http.cookies module to support obsolete RFC 850 date format #123405
• [3.13] gh-123401: Fix http.cookies module to support obsolete RFC 850 date format (GH-123405) #127828
• [3.12] gh-123401: Fix http.cookies module to support obsolete RFC 850 date format (GH-123405) #127829

[vstinner]

Implemented by change 359389e.