| Subject: | Time::Timezone caching in tz_local_offset causes parsedate to return wrong values. |
| Date: | Thu, 30 May 2013 20:34:15 +0200 |
| To: | bug-Time-modules [...] rt.cpan.org |
| From: | Adam Schobelock <schobes [...] gmail.com> |
Time zone Europe/Moscow decided to permentantly move to
DST<http://en.wikipedia.org/wiki/Time_in_Russia#Daylight_saving_time>
on
2011-03-27. This was implemented in the IANA time zone database by changing
the UTC offset instead of leaving the UTC offset the same and leaving in
DST indefinitely.
In Time::Timezone sub tz_local_offset has a caching mechanism that saves
the offset for a time zone by caching it by the key of "TIMEZONE + ISDST".
This results in different UNIX timestamps being returned depending on which
non-dst definition is cached first.
Example: Returns proper UNIX timestamps for Europe/Moscow.
use strict;
use POSIX;
use Time::ParseDate;
$ENV{TZ} = 'Europe/Moscow';
POSIX::tzset();
print parsedate('2009-11-01').' 2009-11-01'."\n";
print parsedate('2013-05-30').' 2013-05-30'."\n";
This produces the following results.
$ perl correct_results.pl
1257022800 2009-11-01
1369861200 2013-05-30
Example: Returns the incorrect UNIX timestamps for Europe/Moscow.
#!/usr/bin/perl
use strict;
use POSIX;
use Time::ParseDate;
$ENV{TZ} = 'Europe/Moscow';
POSIX::tzset();
print parsedate('2013-05-30').' 2013-05-30'."\n";
print parsedate('2009-11-01').' 2009-11-01'."\n";
This produces the following results.
$ perl incorrect_results.pl
1369857600 2013-05-30
1257019200 2009-11-01
As you can see from the above when 2009-11-01 is ran through parsedate
before 2013-05-30 it results in a UNIX timestamp of 1257022800, but when
called after 2013-05-30, 1257019200 is returned.
Because of this behavior, I don't think it is possible to cache the
"TIMEZONE + ISDST" offset as it doesn't always result in the same offset
from UTC.