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authorLars Henriksen <LarsHenriksen@get2net.dk>2019-09-08 08:41:42 +0200
committerLukas Fleischer <lfleischer@calcurse.org>2019-10-18 16:29:34 -0400
commit0e46881746c1a639933d1b794bd2438a430c9c3a (patch)
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parent1db1108e86ff41a5efc7268145a092fc36418d63 (diff)
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DST and recurrent items
The patch adresses two issues with the function recur_item_find ocurrence(), one major: mktime(), and one minor: item duration. In addition, some refactoring is done. The following recurrent appointments demonstrate the problems (as described in the message) and are used as test cases in the associated test commit. 03/29/2019 @ 12:00 -> 03/30/2019 @ 11:00 {2D -> 04/03/2019} |two-day - every other day - not on 1/4 03/31/2019 @ 12:00 -> 03/31/2019 @ 13:00 {1D -> 04/01/2019} |daily - not on 31/3, twice on 1/4 03/31/2019 @ 04:00 -> 03/31/2019 @ 05:00 {1W} |weekly - appears after one week 03/31/2019 @ 12:00 -> 03/31/2019 @ 12:00 {1M} |monthly - never appears 03/31/2019 @ 12:00 -> 03/31/2019 @ 12:00 {1Y} |yearly - never appears 10/20/2019 @ 00:00 -> 10/21/2019 @ 01:00 {1W -> 11/03/2019} |25 hours - ends on 27th, but continues on 28th 03/24/2019 @ 00:00 -> 03/25/2019 @ 00:00 {1W -> 04/07/2019} |24 hours - does not continue on April 1 The root cause is two mktime() calls in recur_item_find_occurrence(), both of which use an inherited tm_isdst value in the tm structure. In such cases mktime() will "normalize" the tm stucture if tm_isdst is 0 or 1 and in disagreement with the rest of the tm contents (just like 32 May will be normalized to 1 June). Example. In 2019 DST started on 31/3 at 02:00:00 (in the European Union). If the (local) time "31/3/2018 00:00:00" is passed to mktime() with tm_isdst = 0, the return value is (say) T sec and the tm structure is unchanged, because DST is not in effect at midnight. If the same call is performed with tm_isdst = 1, the return value becomes (T - 3600) sec and the tm structure is normalized to "30/3/2018 23:00:00", tm_isdst = 0. In recur_item_find_occurrence(), the normalized tm structure with wrong day and time is used in ensuing calculations, leading to wrong dates and the errors observed. The first mktime() call is used to calculate the "day span" of the occurrence before the occurrence itself has been determined. But once the occurence is known, the "day span" is easily determined, and there is no need for the first mktime() call. Events have no explicit duration. However, recur_event_find_occurrence() and recur_event_inday() set the duration of an event to DAYINSEC before passing it on to recur_item_find_occurrence(). The value is not correct on the day when DST begins or ends. The interpretation of the daylength should be left to the called function. Hence, duration is set to -1 to signal no (explicit) duration. Signed-off-by: Lars Henriksen <LarsHenriksen@get2net.dk> Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>
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