linkcheck: Use correct function to convert from UTC time to UNIX epoch

[mitya57]

Subject: linkcheck: Use correct function to convert from UTC time to UNIX epoch

Feature or Bugfix

• Bugfix

Purpose

After subtracting the offset, we get time in UTC. But time.mktime() expects a time struct in local time, not in UTC. Quoting the Python documentation:

Use the following functions to convert between time representations:

From	To	Use
seconds since the epoch	struct_time in UTC	gmtime()
seconds since the epoch	struct_time in local time	localtime()
struct_time in UTC	seconds since the epoch	calendar.timegm()
struct_time in local time	seconds since the epoch	mktime()

So in our case, the correct function to use is calendar.timegm().

This fixes hanging tests when the local timezone is to the west of UTC. One could test this using:

TZ=America/New_York python3 -m pytest -k test_too_many_requests_retry_after_HTTP_date

After applying this change, the test passes with timezones from both western and eastern hemispheres.

[AA-Turner]

Should we add a test for this? Please could you also add an entry to CHANGES, this will go into 7.2.3.

A

[mitya57]

Done.