QTimeZone - Fix Windows Transitions

The Windows tz transition routines were not checking for a number of
invalid scenarios, in particular where there are no next transitions
able to be calcualted, leading to infinite loops.

Change-Id: I262b4321a95be1df4228774ada3908f8d3ed6c1a
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 89 insertions, 63 deletions

diff --git a/src/corelib/tools/qtimezoneprivate_win.cpp b/src/corelib/tools/qtimezoneprivate_win.cpp
index efdd6676fb..f411d35b3d 100644
--- a/src/corelib/tools/qtimezoneprivate_win.cpp
+++ b/src/corelib/tools/qtimezoneprivate_win.cpp
@@ -254,6 +254,10 @@ static QByteArray windowsSystemZoneId()
 
 static QDate calculateTransitionLocalDate(const SYSTEMTIME &rule, int year)
 {
+    // If month is 0 then there is no date
+    if (rule.wMonth == 0)
+        return QDate();
+
     SYSTEMTIME time = rule;
     // If the year isn't set, then the rule date is relative
     if (time.wYear == 0) {
@@ -269,9 +273,10 @@ static QDate calculateTransitionLocalDate(const SYSTEMTIME &rule, int year)
         while (date.month() != time.wMonth)
             date = date.addDays(-7);
         return date;
-    } else {
-        return QDate(time.wYear, time.wMonth, time.wDay);
     }
+
+    // If the year is set then is an absolute date
+    return QDate(time.wYear, time.wMonth, time.wDay);
 }
 
 // Converts a date/time value into msecs
@@ -285,19 +290,25 @@ static void calculateTransitionsForYear(const QWinTimeZonePrivate::QWinTransitio
                                        qint64 *stdMSecs, qint64 *dstMSecs)
 {
     // TODO Consider caching the calculated values
-
-    // The local time in Daylight Time when switches to Standard TIme
+    // The local time in Daylight Time when switches to Standard Time
     QDate standardDate = calculateTransitionLocalDate(rule.standardTimeRule, year);
     QTime standardTime = QTime(rule.standardTimeRule.wHour, rule.standardTimeRule.wMinute,
                                rule.standardTimeRule.wSecond);
-    // The local time in Standard Time when switches to Daylight TIme
+    if (standardDate.isValid() && standardTime.isValid()) {
+        *stdMSecs = timeToMSecs(standardDate, standardTime)
+                    + ((rule.standardTimeBias + rule.daylightTimeBias)  * 60000);
+    } else {
+        *stdMSecs = QTimeZonePrivate::invalidMSecs();
+    }
+
+    // The local time in Standard Time when switches to Daylight Time
     QDate daylightDate = calculateTransitionLocalDate(rule.daylightTimeRule, year);
     QTime daylightTime = QTime(rule.daylightTimeRule.wHour, rule.daylightTimeRule.wMinute,
                                rule.daylightTimeRule.wSecond);
-
-    *stdMSecs = timeToMSecs(standardDate, standardTime)
-                + ((rule.standardTimeBias + rule.daylightTimeBias)  * 60000);
-    *dstMSecs = timeToMSecs(daylightDate, daylightTime) + (rule.standardTimeBias * 60000);
+    if (standardDate.isValid() && standardTime.isValid())
+        *dstMSecs = timeToMSecs(daylightDate, daylightTime) + (rule.standardTimeBias * 60000);
+    else
+        *dstMSecs = QTimeZonePrivate::invalidMSecs();
 }
 
 static QLocale::Country userCountry()
@@ -465,15 +476,8 @@ bool QWinTimeZonePrivate::isDaylightTime(qint64 atMSecsSinceEpoch) const
 
 QTimeZonePrivate::Data QWinTimeZonePrivate::data(qint64 forMSecsSinceEpoch) const
 {
-    // Convert MSecs to year to get transitions for, but around 31 Dec/1 Jan may not be right year
-    // So get the year after we think we want transitions for, to be safe
-    QDate date = msecsToDate(forMSecsSinceEpoch);
-    int year;
-    int month;
-    int day;
-    date.getDate(&year, &month, &day);
-    if ((month == 12 && day == 31) || (month == 1 && day == 1))
-        ++year;
+    // Convert MSecs to year to get transitions for, assumes no transitions around 31 Dec/1 Jan
+    int year = msecsToDate(forMSecsSinceEpoch).year();
 
     qint64 first;
     qint64 second;
@@ -485,20 +489,22 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::data(qint64 forMSecsSinceEpoch) cons
         // Convert the transition rules into msecs for the year we want to try
         rule = ruleForYear(year);
         calculateTransitionsForYear(rule, year, &stdMSecs, &dstMSecs);
-        first = qMin(stdMSecs, dstMSecs);
-        second = qMax(stdMSecs, dstMSecs);
-        if (forMSecsSinceEpoch >= second)
+        if (stdMSecs < dstMSecs) {
+            first = stdMSecs;
+            second = dstMSecs;
+        } else {
+            first = dstMSecs;
+            second = stdMSecs;
+        }
+        if (forMSecsSinceEpoch >= second && second != invalidMSecs())
             next = second;
-        else if (forMSecsSinceEpoch >= first)
+        else if (forMSecsSinceEpoch >= first && first != invalidMSecs())
             next = first;
         // If didn't fall in this year, try the previous
         --year;
-    } while (forMSecsSinceEpoch < first && year >= MIN_YEAR);
+    } while (next == maxMSecs() && year >= MIN_YEAR);
 
-    if (next == dstMSecs)
-        return ruleToData(rule, forMSecsSinceEpoch, QTimeZone::DaylightTime);
-    else
-        return ruleToData(rule, forMSecsSinceEpoch, QTimeZone::StandardTime);
+    return ruleToData(rule, forMSecsSinceEpoch, (next == dstMSecs) ? QTimeZone::DaylightTime : QTimeZone::StandardTime);
 }
 
 bool QWinTimeZonePrivate::hasTransitions() const
@@ -512,79 +518,99 @@ bool QWinTimeZonePrivate::hasTransitions() const
 
 QTimeZonePrivate::Data QWinTimeZonePrivate::nextTransition(qint64 afterMSecsSinceEpoch) const
 {
-    // Convert MSecs to year to get transitions for, but around 31 Dec/1 Jan may not be right year
-    // Get the year before we think we want transitions for, to be safe
-    QDate date = msecsToDate(afterMSecsSinceEpoch);
-    int year;
-    int month;
-    int day;
-    date.getDate(&year, &month, &day);
-    if ((month == 12 && day == 31) || (month == 1 && day == 1))
-        --year;
+    // Convert MSecs to year to get transitions for, assumes no transitions around 31 Dec/1 Jan
+    int year = msecsToDate(afterMSecsSinceEpoch).year();
+
+    QWinTransitionRule rule;
+    // If the required year falls after the last rule start year and the last rule has no
+    // valid future transition calculations then there is no next transition
+    if (year > m_tranRules.last().startYear) {
+        rule = ruleForYear(year);
+        // If the rules have either a fixed year, or no month, then no future trans
+        if (rule.standardTimeRule.wYear != 0 || rule.daylightTimeRule.wYear != 0
+            || rule.standardTimeRule.wMonth == 0 || rule.daylightTimeRule.wMonth == 0) {
+            return invalidData();
+        }
+    }
 
+    // Otherwise we have a valid rule for the required year that can be used
+    // to calculate this year or next
     qint64 first;
     qint64 second;
     qint64 next = minMSecs();
     qint64 stdMSecs;
     qint64 dstMSecs;
-    QWinTransitionRule rule;
     do {
         // Convert the transition rules into msecs for the year we want to try
         rule = ruleForYear(year);
         calculateTransitionsForYear(rule, year, &stdMSecs, &dstMSecs);
         // Find the first and second transition for the year
-        first = qMin(stdMSecs, dstMSecs);
-        second = qMax(stdMSecs, dstMSecs);
+        if (stdMSecs < dstMSecs) {
+            first = stdMSecs;
+            second = dstMSecs;
+        } else {
+            first = dstMSecs;
+            second = stdMSecs;
+        }
         if (afterMSecsSinceEpoch < first)
             next = first;
         else if (afterMSecsSinceEpoch < second)
             next = second;
         // If didn't fall in this year, try the next
         ++year;
-    } while (afterMSecsSinceEpoch >= second && year <= MAX_YEAR);
+    } while (next == minMSecs() && year <= MAX_YEAR);
 
-    if (next == dstMSecs)
-        return ruleToData(rule, next, QTimeZone::DaylightTime);
-    else
-        return ruleToData(rule, next, QTimeZone::StandardTime);
+    if (next == minMSecs() || next == invalidMSecs())
+        return invalidData();
+
+    return ruleToData(rule, next, (next == dstMSecs) ? QTimeZone::DaylightTime : QTimeZone::StandardTime);
 }
 
 QTimeZonePrivate::Data QWinTimeZonePrivate::previousTransition(qint64 beforeMSecsSinceEpoch) const
 {
-    // Convert MSecs to year to get transitions for, but around 31 Dec/1 Jan may not be right year
-    // So get the year after we think we want transitions for, to be safe
-    QDate date = msecsToDate(beforeMSecsSinceEpoch);
-    int year;
-    int month;
-    int day;
-    date.getDate(&year, &month, &day);
-    if ((month == 12 && day == 31) || (month == 1 && day == 1))
-        ++year;
+    // Convert MSecs to year to get transitions for, assumes no transitions around 31 Dec/1 Jan
+    int year = msecsToDate(beforeMSecsSinceEpoch).year();
+
+    QWinTransitionRule rule;
+    // If the required year falls before the first rule start year and the first rule has no
+    // valid transition calculations then there is no previous transition
+    if (year < m_tranRules.first().startYear) {
+        rule = ruleForYear(year);
+        // If the rules have either a fixed year, or no month, then no previous trans
+        if (rule.standardTimeRule.wYear != 0 || rule.daylightTimeRule.wYear != 0
+            || rule.standardTimeRule.wMonth == 0 || rule.daylightTimeRule.wMonth == 0) {
+            return invalidData();
+        }
+    }
 
     qint64 first;
     qint64 second;
     qint64 next = maxMSecs();
     qint64 stdMSecs;
     qint64 dstMSecs;
-    QWinTransitionRule rule;
     do {
         // Convert the transition rules into msecs for the year we want to try
         rule = ruleForYear(year);
         calculateTransitionsForYear(rule, year, &stdMSecs, &dstMSecs);
-        first = qMin(stdMSecs, dstMSecs);
-        second = qMax(stdMSecs, dstMSecs);
-        if (beforeMSecsSinceEpoch > second)
+        if (stdMSecs < dstMSecs) {
+            first = stdMSecs;
+            second = dstMSecs;
+        } else {
+            first = dstMSecs;
+            second = stdMSecs;
+        }
+        if (beforeMSecsSinceEpoch > second && second != invalidMSecs())
             next = second;
-        else if (beforeMSecsSinceEpoch > first)
+        else if (beforeMSecsSinceEpoch > first && first != invalidMSecs())
             next = first;
         // If didn't fall in this year, try the previous
         --year;
-    } while (beforeMSecsSinceEpoch < first && year >= MIN_YEAR);
+    } while (next == maxMSecs() && year >= MIN_YEAR);
 
-    if (next == dstMSecs)
-        return ruleToData(rule, next, QTimeZone::DaylightTime);
-    else
-        return ruleToData(rule, next, QTimeZone::StandardTime);
+    if (next == maxMSecs())
+        return invalidData();
+
+    return ruleToData(rule, next, (next == dstMSecs) ? QTimeZone::DaylightTime : QTimeZone::StandardTime);
 }
 
 QByteArray QWinTimeZonePrivate::systemTimeZoneId() const