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Fix conversion to UTC for DST changes

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The RepeatRuleDateTime constructor extracts the date's time zone then
passes it to the parent class DateTime. Because PHP's DateTime has full
support for time zones, it compensates for them when parsing a string.
Normally this isn't a problem, because the opposite occurs when a
DateTime is converted back into a string; the two adjustments cancel
each other.

Davical often converts a time to UTC by negating the time zone offset
and adding it to the underlying DateTime (keeping the time zone intact).
A problem occurs when the result is on the other side of a daylight-
saving-time transition. In that case the adjustments do not cancel and
an incorrect time string is returned.

This bug is tricky because the problem doesn't manifest during the DST
transition iself, but hours earlier or later depending on the original
time zone. For example, 2022-03-12T18:30:00-08:00 (America/Los_Angeles)
is 2022-03-13T02:30:00Z. Since 2022-03-13 is a 23-hour day in the Los
Angeles time zone (the 2AM-3AM hour is skipped) this becomes
2022-03-13T03:30:00-07:00 after adding the negated offset. FloatOrUTC()
would strip the new offset and simply return "20220313T033000".
This commit is contained in:
Chris S 2022-03-07 17:06:37 -08:00 committed by Andrew Ruthven
parent 5ef5c756f8
commit 069445579c
1 changed files with 1 additions and 3 deletions
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4
inc/RRule.php
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@ -410,9 +410,7 @@ class RepeatRuleDateTime extends DateTime {
public function FloatOrUTC($return_floating_times = false) {
$gmt = clone($this);
if ( !$return_floating_times && isset($this->tzid) && $this->tzid != 'UTC' ) {
$dtz = parent::getTimezone();
$offset = 0 - $dtz->getOffset($gmt);
$gmt->modify( $offset . ' seconds' );
$gmt->setTimezone('UTC');
}
if ( $this->is_date ) return $gmt->format('Ymd');
if ( $return_floating_times ) return $gmt->format('Ymd\THis');