#3509: fix dst and utcOffset handling for Dublin time zone

Foundation/include/Poco/Timezone.h

@@ -58,6 +58,18 @@ public:
 
 	static std::string dstName();
 		/// Returns the timezone name if daylight saving time is in effect.
+
+#if !defined(POCO_OS_FAMILY_WINDOWS)
+	static int utcOffset(const Poco::Timestamp& timestamp);
+		/// Returns the offset of local time to UTC
+		/// for the given time, in seconds.
+		///     local time = UTC + utcOffset() + dst().
+
+	static int dst(const Poco::Timestamp& timestamp);
+		/// Returns the daylight saving time offset in seconds if
+		/// daylight saving time is in use for the given time.
+		///     local time = UTC + utcOffset() + dst().
+#endif
 };
 
 

Foundation/src/LocalDateTime.cpp

@@ -277,7 +277,7 @@ void LocalDateTime::determineTzd(bool adjust)
  		if (err) broken = nullptr;
 #endif
 		if (!broken) throw Poco::SystemException("cannot get local time");
-		_tzd = (Timezone::utcOffset() + ((broken->tm_isdst == 1) ? 3600 : 0));
+		_tzd = (Timezone::utcOffset() + Timezone::dst(_dateTime.timestamp()));
 #else
 		std::tm broken;
 #if defined(POCO_VXWORKS) && (defined(_VXWORKS_COMPATIBILITY_MODE) || (defined(_WRS_VXWORKS_MAJOR) && ((_WRS_VXWORKS_MAJOR < 6) || ((_WRS_VXWORKS_MAJOR == 6)  && (_WRS_VXWORKS_MINOR < 9)))))
@@ -318,7 +318,7 @@ std::time_t LocalDateTime::dstOffset(int& dstOffset) const
 	local = std::mktime(&broken);
 #endif
 
-	dstOffset = (broken.tm_isdst == 1) ? 3600 : 0;
+	dstOffset = (broken.tm_isdst == 1) ? Timezone::dst(_dateTime.timestamp()) : 0;
 	return local;
 }
 

Foundation/src/Timezone_UNIX.cpp

@@ -29,22 +29,12 @@ public:
 		tzset();
 	}
 
-	int timeZone()
+	static long gmtOffset(const struct std::tm& t)
 	{
-		Poco::FastMutex::ScopedLock lock(_mutex);
+	#if defined(__CYGWIN__)
-
+		return t.__TM_GMTOFF;
-	#if defined(__APPLE__)  || defined(__FreeBSD__) || defined (__OpenBSD__) || POCO_OS == POCO_OS_ANDROID // no timezone global var
-		std::time_t now = std::time(NULL);
-		struct std::tm t;
-		gmtime_r(&now, &t);
-		std::time_t utc = std::mktime(&t);
-		return now - utc;
-	#elif defined(__CYGWIN__)
-		tzset();
-		return -_timezone;
 	#else
-		tzset();
+		return t.tm_gmtoff;
-		return -timezone;
 	#endif
 	}
 
@@ -64,19 +54,39 @@ private:
 static TZInfo tzInfo;
 
 
+int Timezone::utcOffset(const Poco::Timestamp& timestamp)
+{
+	std::time_t time = timestamp.epochTime();
+	struct std::tm local;
+	if (!localtime_r(&time, &local))
+		throw Poco::SystemException("cannot get UTC offset");
+	struct std::tm utc;
+	gmtime_r(&time, &utc);
+	std::time_t utctime = std::mktime(&utc);
+	return time - utctime;
+}
+
+
 int Timezone::utcOffset()
 {
-	return tzInfo.timeZone();
+	return utcOffset(Poco::Timestamp());
 }
 
 
 int Timezone::dst()
 {
-	std::time_t now = std::time(NULL);
+	return dst(Poco::Timestamp());
-	struct std::tm t;
+}
-	if (!localtime_r(&now, &t))
+
+
+int Timezone::dst(const Poco::Timestamp& timestamp)
+{
+	std::time_t time = timestamp.epochTime();
+	struct std::tm local;
+	if (!localtime_r(&time, &local))
 		throw Poco::SystemException("cannot get local time DST offset");
-	return t.tm_isdst == 1 ? 3600 : 0;
+	long dst = TZInfo::gmtOffset(local) - utcOffset(timestamp);
+	return local.tm_isdst == 1 ? dst : 0;
 }
 
 

Foundation/testsuite/src/LocalDateTimeTest.cpp

@@ -454,6 +454,37 @@ void LocalDateTimeTest::testTimezone()
 }
 
 
+void LocalDateTimeTest::testTimezone2()
+{
+#if defined(POCO_OS_FAMILY_UNIX)
+	std::vector<std::string> timezones = {
+		"/usr/share/zoneinfo/America/Los_Angeles",
+		"/usr/share/zoneinfo/Europe/London",
+		"/usr/share/zoneinfo/Europe/Dublin", // special winter time of Ireland
+		"/usr/share/zoneinfo/Europe/Prague",
+	};
+
+	std::cout << "\n";
+
+	for (const std::string& tz : timezones)
+	{
+		setenv("TZ", tz.c_str(), 1); // POSIX-specific
+		std::vector<LocalDateTime> times = {
+			LocalDateTime(2022, 06, 29), // summer period
+			LocalDateTime(2022, 01, 29), // winter period
+		};
+		for (const LocalDateTime& ldt : times) {
+			std::time_t t = ldt.timestamp().epochTime();
+			std::tm then;
+			then = *std::localtime(&t);
+			assertTrue (then.tm_gmtoff == ldt.tzd());
+		}
+		unsetenv("TZ");
+	}
+#endif
+}
+
+
 void LocalDateTimeTest::setUp()
 {
 }
@@ -479,6 +510,7 @@ CppUnit::Test* LocalDateTimeTest::suite()
 	CppUnit_addTest(pSuite, LocalDateTimeTest, testArithmetics2);
 	CppUnit_addTest(pSuite, LocalDateTimeTest, testSwap);
 	CppUnit_addTest(pSuite, LocalDateTimeTest, testTimezone);
+	CppUnit_addTest(pSuite, LocalDateTimeTest, testTimezone2);
 
 	return pSuite;
 }

Foundation/testsuite/src/LocalDateTimeTest.h

@@ -35,6 +35,7 @@ public:
 	void testArithmetics2();
 	void testSwap();
 	void testTimezone();
+	void testTimezone2();
 
 	void setUp();
 	void tearDown();