oc-calendar: Extract time zone from TimeZoneDefinition

All-day and recurrent events have a binary property that describes the time zone they take place in. We were using the user's time zone in the webmail, but it may not be equal to the one in the client. This difference eventually leads to time shifts in events.
2026-08-06 23:43:19 +00:00 · 2015-12-22 16:05:23 +01:00
parent 332508e2db
commit 4ae5feb131
5 changed files with 228 additions and 36 deletions
@@ -23,11 +23,15 @@
 #import <Foundation/NSArray.h>
 #import <Foundation/NSCalendarDate.h>
 #import <Foundation/NSString.h>
+#import <Foundation/NSTimeZone.h>
 #import <NGCards/iCalByDayMask.h>
+#import <NGCards/iCalDateTime.h>
 #import <NGCards/iCalTimeZonePeriod.h>
 #import <NGCards/iCalRecurrenceRule.h>

 #import "NSString+MAPIStore.h"
+#import "NSData+MAPIStore.h"
+#import "NSDate+MAPIStore.h"

 #include <stdbool.h>
 #include <stdint.h>
@@ -166,5 +170,186 @@
  return set_TimeZoneDefinition (memCtx, &definition);
 }

+- (NSString *) _offsetStringFromOffset: (NSInteger) offset
+{
+  NSInteger offsetHours, offsetMins;
+  NSString *offsetSign;
+
+  /* The offset format is, eg, "+0200" for 2 hours 0 minutes ahead */
+  if (offset < 0)
+    offsetSign = @"-";
+  else
+    offsetSign = @"+";
+  offsetHours = abs (offset) / 60;
+  offsetMins = abs (offset) % 60;
+
+  return [NSString stringWithFormat:  @"%@%d%d%d%d",
+           offsetSign, offsetHours / 10, offsetHours % 10,
+           offsetMins / 10, offsetMins % 10];
+
+}
+
+- (NSString *) _rRuleStringFromSystemTime: (struct SYSTEMTIME) date
+{
+  NSString *result, *byDay;
+
+  /* The conversion tables between the SYSTEMTIME fields and the RRULE ones
+     can be found at [MS-OXCICAL] 2.1.3.2.1 */
+  if (date.wDay == 5)
+    byDay = @"-1";
+  else
+    byDay = [NSString stringWithFormat: @"%d", date.wDay];
+
+  switch (date.wDayOfWeek)
+    {
+    case iCalWeekDaySunday:
+      byDay = [byDay stringByAppendingString: @"SU"];
+      break;
+    case iCalWeekDayMonday:
+      byDay = [byDay stringByAppendingString: @"MO"];
+      break;
+    case iCalWeekDayTuesday:
+      byDay = [byDay stringByAppendingString: @"TU"];
+      break;
+    case iCalWeekDayWednesday:
+      byDay = [byDay stringByAppendingString: @"WE"];
+      break;
+    case iCalWeekDayThursday:
+      byDay = [byDay stringByAppendingString: @"TH"];
+      break;
+    case iCalWeekDayFriday:
+      byDay = [byDay stringByAppendingString: @"FR"];
+      break;
+    case iCalWeekDaySaturday:
+      byDay = [byDay stringByAppendingString: @"SA"];
+      break;
+    }
+
+  result = [NSString stringWithFormat: @"FREQ=YEARLY;BYDAY=%@;BYMONTH=%d", byDay, date.wMonth];
+
+  return result;
+}
+
+- (iCalTimeZone *) iCalTimeZoneFromDefinition: (NSData *) value
+                              withDescription: (NSString *) description
+                                     inMemCtx: (TALLOC_CTX *) memCtx
+{
+  BOOL daylightDefined = NO, ruleFound = NO;
+  iCalDateTime *daylightStart, *standardStart;
+  iCalRecurrenceRule *daylightRRule, *standardRRule;
+  iCalTimeZone *tz = nil;
+  iCalTimeZonePeriod *daylight, *standard;
+  NSCalendarDate *dlStartValue, *stStartValue;
+  NSString *strOffsetFrom, *strOffsetTo, *tzID;
+  char *keyName;
+  struct Binary_r *binValue;
+  struct SYSTEMTIME initDate;
+  struct TimeZoneDefinition *definition;
+  struct TZRule rule;
+  uint16_t count;
+
+  binValue = [value asBinaryInMemCtx: memCtx];
+  definition = get_TimeZoneDefinition (memCtx, binValue);
+
+  if (!definition)
+    return nil;
+
+  if (!definition->cRules)
+    goto end;
+
+  for (count = 0; count < definition->cRules; count++)
+    {
+      /* ([MS-OXCICAL] 2.1.3.1.1.19) The TZRule with the
+         TZRULE_FLAG_EFFECTIVE_TZREG bit set in the TZRule flags field
+         is the one that MUST be exported */
+      if (definition->TZRules[count].flags & TZRULE_FLAG_EFFECTIVE_TZREG)
+        {
+          rule = definition->TZRules[count];
+          ruleFound = YES;
+          break;
+        }
+    }
+
+  if (!ruleFound)
+    goto end;
+
+  if (!description)
+    {
+      /* The cbHeader field contains the size, in bytes of the Reserved (2b),
+         cchKeyName (2b) keyName (variable Unicode string) and cRules (2b)
+         ([MS-OXOCAL] 2.2.1.41). The keyName field is a non-NULL-terminated
+         char array. */
+      keyName = talloc_strndup (memCtx, definition->keyName, (definition->cbHeader - 6) / 2);
+      tzID = [NSString stringWithCString: keyName
+                                encoding: [NSString defaultCStringEncoding]];
+      talloc_free (keyName);
+    }
+  else
+    tzID = [NSString stringWithString: description];
+
+  tz = [iCalTimeZone groupWithTag: @"vtimezone"];
+  [tz addChild: [CardElement simpleElementWithTag: @"tzid"
+                                            value: tzID]];
+
+  if (rule.stStandardDate.wMonth != 0)
+    daylightDefined = YES;
+
+  /* STANDARD TIME ([MS-OXCICAL] 2.1.3.1.1.19.2) */
+  standard = [iCalTimeZonePeriod groupWithTag: @"standard"];
+
+  /* TZOFFSETFROM = -1 * (PidLidTimeZoneStruct.lBias + PidLidTimeZoneStruct.lDaylightBias) */
+  strOffsetFrom = [self _offsetStringFromOffset: -1 * (rule.lBias + rule.lDaylightBias)];
+  [standard addChild: [CardElement simpleElementWithTag: @"tzoffsetfrom"
+                                                  value: strOffsetFrom]];
+
+  /* TZOFFSETTO = -1 * (PidLidTimeZoneStruct.lBias + PidLidTimeZoneStruct.lStandardBias) */
+  strOffsetTo = [self _offsetStringFromOffset: -1 * (rule.lBias + rule.lStandardBias)];
+  [standard addChild: [CardElement simpleElementWithTag: @"tzoffsetto"
+                                                  value: strOffsetTo]];
+
+  /* DTSTART & RRULE are derived from the stStandardDate and wYear properties */
+  standardStart = [iCalDateTime elementWithTag: @"dtstart"];
+
+  initDate = rule.stStandardDate;
+  stStartValue = [NSCalendarDate dateFromSystemTime: initDate
+                                        andRuleYear: rule.wYear];
+
+  [standardStart setDateTime: stStartValue];
+  [standard addChild: standardStart];
+
+  if (daylightDefined)
+    {
+      standardRRule = [[iCalRecurrenceRule alloc] initWithString: [self _rRuleStringFromSystemTime: initDate]];
+      [standard addChild: standardRRule];
+
+      /* DAYLIGHT SAVING TIME ([MS-OXCICAL] 2.1.3.1.1.19.3) */
+      daylight = [iCalTimeZonePeriod groupWithTag: @"daylight"];
+      /* TZOFFSETFROM = -1 * (PidLidTimeZoneStruct.lBias + PidLidTimeZoneStruct.lStandardBias) */
+      [daylight addChild: [CardElement simpleElementWithTag: @"tzoffsetfrom"
+                                                      value: strOffsetTo]];
+      /* TZOFFSETTO = -1 * (PidLidTimeZoneStruct.lBias + PidLidTimeZoneStruct.lDaylightBias) */
+      [daylight addChild: [CardElement simpleElementWithTag: @"tzoffsetto"
+                                                      value: strOffsetFrom]];
+
+      /* DTSTART & RRULE are derived from the stDaylightDate and wYear properties */
+      daylightStart = [iCalDateTime elementWithTag: @"dtstart"];
+      initDate = rule.stDaylightDate;
+      dlStartValue = [NSCalendarDate dateFromSystemTime: initDate
+                                            andRuleYear: rule.wYear];
+
+      [daylightStart setDateTime: dlStartValue];
+      [daylight addChild: daylightStart];
+
+      daylightRRule = [[iCalRecurrenceRule alloc] initWithString: [self _rRuleStringFromSystemTime: initDate]];
+      [daylight addChild: daylightRRule];
+      [tz addChild: daylight];
+    }
+  [tz addChild: standard];
+
+end:
+
+  talloc_free (definition);
+  return tz;
+}

@end