Adding timezone information to datetimes from systemd-journal

[Samuel-BF]

Currently, converters for timestamp fields (__REALTIME_TIMESTAMP, _SOURCE_REALTIME_TIMESTAMP, COREDUMPTIMESTAMP) produce datetimes object without timezone, losing information.

This PR fixes that.

Without this commit :

>>> from systemd import journal
>>> j = journal.Reader(flags = journal.CURRENT_USER)
>>> j.seek_tail()
>>> j.get_previous().isoformat()
>>> j.get_previous()['__REALTIME_TIMESTAMP'].isoformat()
'2022-01-08T20:44:23.000494'

And with this commit :

>>> j.get_previous()['__REALTIME_TIMESTAMP'].isoformat()
'2022-01-08T20:44:23.000494+01:00'

Reference: datetime.fromtimestamp :

If optional argument tz is None or not specified, the timestamp is converted to the platform’s local date and time, and the returned datetime object is naive.

[keszybz]

Sorry for the delay.

I'm looking at this, initially I wasn't sure if it's appropriate to attach the local time zone. After all, the timestamp that is stored in the journal is a timezone-less absolute timestamp. If anything, it'd be fair to say that it's UTC. But datetime.datetime.fromtimestamp does convert the timestamp to a local time, so, indeed, the resulting timestamp is in the local time zone. This begs the question why datetime.datetime.fromtimestamp does the conversion in this way: i.e. it actually selects a specific timezone to do the conversion, but then discards this information. I think it's a bug in datetime.datetime.fromtimestamp. But as far as a I know python, it'd take ages to get it fixed there, so applying this workaround here is appropriate.