Incorrect handling of Retry-After (2.7)

[hodbn]

email.utils.parsedate_tz behaves differently on python2.7/3 if the input string has no timezone. On python3, the last item of the return value is 0 where on python2.7 it is None.

Since email.utils.mktime_tz assumes a None timezone to be the local timezone, the resulting date might be wrong when calculating Retry-After timeout of a value without a timezone.

To reproduce run the following test on a python2.7 machine with timezone != UTC:
test/test_retry.py::TestRetry::test_respect_retry_after_header_sleep[Mon Jun 3 11:30:12 2019-True-1812]

(Luckily, freezegun doesn't hide the issue since it freezes only the time using tz_offset but it doesn't patch the timezone.)

[sethmlarson]

Huh, wasn't seeing Python 2.7 failures on macOS. How'd you catch this issue?

[hodbn]

I ran it on my Linux VM which has a weird timezone set.
It seems our CI (at least actions and travis) runs on UTC.

[sethmlarson]

Ahhh makes sense, glad you caught this! :)