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Time: Prevent errors calculating the UTC offset

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Errors might occur on or near epoch or a transition to summer time.
This commit is contained in:
Anthony Nicholls 2025-06-27 15:40:54 +02:00 • committed by Anthony Nicholls
parent f5a6c510c0
commit 4ed15dbc9e
1 changed files with 42 additions and 36 deletions
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78
modules/juce_core/time/juce_Time.cpp
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@ -59,36 +59,6 @@ namespace TimeHelpers
#endif
}
static std::tm millisToUTC (int64 millis) noexcept
{
#if JUCE_WINDOWS
std::tm result;
millis /= 1000;
if (_gmtime64_s (&result, &millis) != 0)
zerostruct (result);
return result;
#else
std::tm result;
auto now = (time_t) (millis / 1000);
if (gmtime_r (&now, &result) == nullptr)
zerostruct (result);
return result;
#endif
}
static int getUTCOffsetSeconds (const int64 millis) noexcept
{
auto utc = millisToUTC (millis);
utc.tm_isdst = -1; // Treat this UTC time as local to find the offset
return (int) ((millis / 1000) - (int64) mktime (&utc));
}
static int extendedModulo (const int64 value, const int modulo) noexcept
{
return (int) (value >= 0 ? (value % modulo)
@ -181,6 +151,32 @@ namespace TimeHelpers
+ t.tm_sec;
}
static int64 mktime_local (const std::tm& t) noexcept
{
auto t1 = t;
const auto result = mktime (&t1);
// If any field changed in the struct passed to mktime, it indicates the
// original time was invalid or ambiguous in the local timezone.
//
// Common scenarios where this validation catches errors:
// Daylight Saving Time transitions:
// Times like 1:30 AM may not exist, mktime() may adjust them to
// 2:30 AM for example
// Invalid dates or out-of-range values:
// Feb 30, Apr 31, etc. may get normalised to valid dates
// hour=25, minute=70, etc. may get normalised to valid times
jassert ( t.tm_year == t1.tm_year
&& t.tm_mon == t1.tm_mon
&& t.tm_mday == t1.tm_mday
&& t.tm_hour == t1.tm_hour
&& t.tm_min == t1.tm_min
&& t.tm_sec == t1.tm_sec);
return (int64) result;
}
static Atomic<uint32> lastMSCounterValue { (uint32) 0 };
static String getUTCOffsetString (int utcOffsetSeconds, bool includeSemiColon)
@ -213,9 +209,9 @@ Time::Time (int year, int month, int day,
t.tm_hour = hours;
t.tm_min = minutes;
t.tm_sec = seconds;
t.tm_isdst = -1;
t.tm_isdst = useLocalTime ? -1 : 0;
millisSinceEpoch = 1000 * (useLocalTime ? (int64) mktime (&t)
millisSinceEpoch = 1000 * (useLocalTime ? TimeHelpers::mktime_local (t)
: TimeHelpers::mktime_utc (t))
+ milliseconds;
}
@ -383,7 +379,7 @@ String Time::getTimeZone() const
{
String zone[2];
#if JUCE_WINDOWS && (JUCE_MSVC || JUCE_CLANG)
#if JUCE_WINDOWS && (JUCE_MSVC || JUCE_CLANG)
_tzset();
for (int i = 0; i < 2; ++i)
@ -393,13 +389,13 @@ String Time::getTimeZone() const
_get_tzname (&length, name, sizeof (name) - 1, i);
zone[i] = name;
}
#else
#else
tzset();
auto zonePtr = (const char**) tzname;
zone[0] = zonePtr[0];
zone[1] = zonePtr[1];
#endif
#endif
if (isDaylightSavingTime())
{
@ -416,7 +412,9 @@ String Time::getTimeZone() const
int Time::getUTCOffsetSeconds() const noexcept
{
return TimeHelpers::getUTCOffsetSeconds (millisSinceEpoch);
// Treat local time as UTC to measure the difference
const auto local = TimeHelpers::millisToLocal (millisSinceEpoch);
return (int) (TimeHelpers::mktime_utc (local) - (millisSinceEpoch / 1000));
}
String Time::getUTCOffsetString (bool includeSemiColon) const
@ -640,6 +638,13 @@ public:
expect (t.getUTCOffsetString (true) == "Z" || t.getUTCOffsetString (true).length() == 6);
expect (t.getUTCOffsetString (false) == "Z" || t.getUTCOffsetString (false).length() == 5);
if (Time{}.getTimeZone() == "GMT")
{
// Tests the point of transition to BST
expect (Time (2025, 2, 30, 0, 59, 59, 999, false).toISO8601 (true) == "2025-03-30T00:59:59.999Z");
expect (Time (2025, 2, 30, 1, 00, 00, 000, false).toISO8601 (true) == "2025-03-30T02:00:00.000+01:00");
}
expect (TimeHelpers::getUTCOffsetString (-(3 * 60 + 15) * 60, true) == "-03:15");
expect (TimeHelpers::getUTCOffsetString (-(3 * 60 + 30) * 60, true) == "-03:30");
expect (TimeHelpers::getUTCOffsetString (-(3 * 60 + 45) * 60, true) == "-03:45");
@ -648,6 +653,7 @@ public:
expect (Time::fromISO8601 (t.toISO8601 (true)) == t);
expect (Time::fromISO8601 (t.toISO8601 (false)) == t);
expect (Time::fromISO8601 (Time (0).toISO8601 (true)) == Time (0));
expect (Time::fromISO8601 ("2016-02-16") == Time (2016, 1, 16, 0, 0, 0, 0, false));
expect (Time::fromISO8601 ("20160216Z") == Time (2016, 1, 16, 0, 0, 0, 0, false));