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ICU-13845 Windows timezone detection: When DST is off, map to an Etc/…
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…GMT+-hh zone.

The Windows 'Date and Time' Control Panel has a setting for "Automatically
adjust clock for DST". When this setting is manually unchecked, the DST
setting is considered OFF, and the clock does not adjust for DST.

This change detects when the setting is OFF and uses the non-DST offset
to map to an Etc/GMT+-hh zone.

- Also refactor uprv_detectWindowsTimeZone

Co-authored-by: Jungshik Shin <jshin@chromium.org>
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@jefgen @jungshik
jefgen and jungshik committed Sep 29, 2020
1 parent b2edfb8 commit b4d056a
Showing 1 changed file with 83 additions and 60 deletions.
143 changes: 83 additions & 60 deletions icu4c/source/common/wintz.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16,11 +16,12 @@
#if U_PLATFORM_USES_ONLY_WIN32_API

#include "wintz.h"
#include "charstr.h"
#include "cmemory.h"
#include "cstring.h"

#include "unicode/ures.h"
#include "unicode/ustring.h"
#include "unicode/unistr.h"
#include "uresimp.h"

#ifndef WIN32_LEAN_AND_MEAN
Expand All @@ -35,89 +36,111 @@

U_NAMESPACE_BEGIN

// The max size of TimeZoneKeyName is 128, defined in DYNAMIC_TIME_ZONE_INFORMATION
#define MAX_TIMEZONE_ID_LENGTH 128

/**
* Main Windows time zone detection function.
* Returns the Windows time zone converted to an ICU time zone as a heap-allocated buffer, or nullptr upon failure.
* Note: We use the Win32 API GetDynamicTimeZoneInformation to get the current time zone info.
* This API returns a non-localized time zone name, which we can then map to an ICU time zone name.
*
* Note: We use the Win32 API GetDynamicTimeZoneInformation (available since Vista+) to get the current time zone info.
* This API returns a non-localized time zone name, which is mapped to an ICU time zone ID (~ Olsen ID).
*/
U_CAPI const char* U_EXPORT2
uprv_detectWindowsTimeZone()
{
UErrorCode status = U_ZERO_ERROR;
char* icuid = nullptr;
char dynamicTZKeyName[MAX_TIMEZONE_ID_LENGTH];
char tmpid[MAX_TIMEZONE_ID_LENGTH];
int32_t len;
int id = GEOID_NOT_AVAILABLE;
int errorCode;
wchar_t ISOcodeW[3] = {}; /* 2 letter ISO code in UTF-16 */
char ISOcode[3] = {}; /* 2 letter ISO code in UTF-8 */

// Obtain the DYNAMIC_TIME_ZONE_INFORMATION info to get the non-localized time zone name.
DYNAMIC_TIME_ZONE_INFORMATION dynamicTZI;
uprv_memset(&dynamicTZI, 0, sizeof(dynamicTZI));
uprv_memset(dynamicTZKeyName, 0, sizeof(dynamicTZKeyName));
uprv_memset(tmpid, 0, sizeof(tmpid));
SYSTEMTIME systemTimeAllZero;
uprv_memset(&systemTimeAllZero, 0, sizeof(systemTimeAllZero));

/* Obtain TIME_ZONE_INFORMATION from the API and get the non-localized time zone name. */
if (TIME_ZONE_ID_INVALID == GetDynamicTimeZoneInformation(&dynamicTZI)) {
if (GetDynamicTimeZoneInformation(&dynamicTZI) == TIME_ZONE_ID_INVALID) {
return nullptr;
}

id = GetUserGeoID(GEOCLASS_NATION);
errorCode = GetGeoInfoW(id, GEO_ISO2, ISOcodeW, 3, 0);

// convert from wchar_t* (UTF-16 on Windows) to char* (UTF-8).
u_strToUTF8(ISOcode, UPRV_LENGTHOF(ISOcode), nullptr,
reinterpret_cast<const UChar*>(ISOcodeW), UPRV_LENGTHOF(ISOcodeW), &status);

LocalUResourceBundlePointer bundle(ures_openDirect(nullptr, "windowsZones", &status));
ures_getByKey(bundle.getAlias(), "mapTimezones", bundle.getAlias(), &status);
// If the DST setting has been turned off in the Control Panel, then return "Etc/GMT<offset>".
//
// Note: This logic is based on how the Control Panel itself determines if DST is 'off' on Windows.
// The code is somewhat convoluted; in a sort of pseudo-code it looks like this:
//
// IF (GetDynamicTimeZoneInformation != TIME_ZONE_ID_INVALID) && (DynamicDaylightTimeDisabled != 0) &&
// (StandardDate == DaylightDate) &&
// (
// (TimeZoneKeyName != Empty && StandardDate == 0) ||
// (TimeZoneKeyName == Empty && StandardDate != 0)
// )
// THEN
// DST setting is "Disabled".
//
if (dynamicTZI.DynamicDaylightTimeDisabled != 0 &&
uprv_memcmp(&dynamicTZI.StandardDate, &dynamicTZI.DaylightDate, sizeof(dynamicTZI.StandardDate)) == 0 &&
((dynamicTZI.TimeZoneKeyName[0] != L'\0' && uprv_memcmp(&dynamicTZI.StandardDate, &systemTimeAllZero, sizeof(systemTimeAllZero)) == 0) ||
(dynamicTZI.TimeZoneKeyName[0] == L'\0' && uprv_memcmp(&dynamicTZI.StandardDate, &systemTimeAllZero, sizeof(systemTimeAllZero)) != 0)))
{
LONG utcOffsetMins = dynamicTZI.Bias;
if (utcOffsetMins == 0) {
return uprv_strdup("Etc/UTC");
}

// convert from wchar_t* (UTF-16 on Windows) to char* (UTF-8).
u_strToUTF8(dynamicTZKeyName, UPRV_LENGTHOF(dynamicTZKeyName), nullptr,
reinterpret_cast<const UChar*>(dynamicTZI.TimeZoneKeyName), -1, &status);
// No way to support when DST is turned off and the offset in minutes is not a multiple of 60.
if (utcOffsetMins % 60 == 0) {
char gmtOffsetTz[11] = {}; // "Etc/GMT+dd" is 11-char long with a terminal null.
// Note '-' before 'utcOffsetMin'. The timezone ID's sign convention
// is that a timezone ahead of UTC is Etc/GMT-<offset> and a timezone
// behind UTC is Etc/GMT+<offset>.
int ret = snprintf(gmtOffsetTz, UPRV_LENGTHOF(gmtOffsetTz), "Etc/GMT%+d", -utcOffsetMins / 60);
if (ret > 0 && ret < UPRV_LENGTHOF(gmtOffsetTz)) {
return uprv_strdup(gmtOffsetTz);
}
}
}

if (U_FAILURE(status)) {
// If DST is NOT disabled, but we have an empty TimeZoneKeyName, then it is unclear
// what we should do as this should not happen.
if (dynamicTZI.TimeZoneKeyName[0] == 0) {
return nullptr;
}

if (dynamicTZI.TimeZoneKeyName[0] != 0) {
StackUResourceBundle winTZ;
ures_getByKey(bundle.getAlias(), dynamicTZKeyName, winTZ.getAlias(), &status);

if (U_SUCCESS(status)) {
const UChar* icuTZ = nullptr;
if (errorCode != 0) {
icuTZ = ures_getStringByKey(winTZ.getAlias(), ISOcode, &len, &status);
}
if (errorCode == 0 || icuTZ == nullptr) {
/* fallback to default "001" and reset status */
status = U_ZERO_ERROR;
icuTZ = ures_getStringByKey(winTZ.getAlias(), "001", &len, &status);
}
CharString winTZ;
UErrorCode status = U_ZERO_ERROR;
winTZ.appendInvariantChars(UnicodeString(TRUE, dynamicTZI.TimeZoneKeyName, -1), status);

if (U_SUCCESS(status)) {
int index = 0;
// Map Windows Timezone name (non-localized) to ICU timezone ID (~ Olson timezone id).
StackUResourceBundle winTZBundle;
ures_openDirectFillIn(winTZBundle.getAlias(), nullptr, "windowsZones", &status);
ures_getByKey(winTZBundle.getAlias(), "mapTimezones", winTZBundle.getAlias(), &status);
ures_getByKey(winTZBundle.getAlias(), winTZ.data(), winTZBundle.getAlias(), &status);

while (!(*icuTZ == '\0' || *icuTZ == ' ')) {
// time zone IDs only contain ASCII invariant characters.
tmpid[index++] = (char)(*icuTZ++);
}
tmpid[index] = '\0';
}
if (U_FAILURE(status)) {
return nullptr;
}

// Note: Since the ISO 3166 country/region codes are all invariant ASCII chars, we can
// directly downcast from wchar_t to do the conversion.
// We could call the A version of the GetGeoInfo API, but that would be slightly slower than calling the W API,
// as the A version of the API will end up calling MultiByteToWideChar anyways internally.
wchar_t regionCodeW[3] = {};
char regionCode[3] = {}; // 2 letter ISO 3166 country/region code made entirely of invariant chars.
int geoId = GetUserGeoID(GEOCLASS_NATION);
int regionCodeLen = GetGeoInfoW(geoId, GEO_ISO2, regionCodeW, UPRV_LENGTHOF(regionCodeW), 0);

const UChar *icuTZ16 = nullptr;
int32_t tzLen;

if (regionCodeLen != 0) {
for (int i = 0; i < UPRV_LENGTHOF(regionCodeW); i++) {
regionCode[i] = static_cast<char>(regionCodeW[i]);
}
icuTZ16 = ures_getStringByKey(winTZBundle.getAlias(), regionCode, &tzLen, &status);
}

// Copy the timezone ID to icuid to be returned.
if (tmpid[0] != 0) {
icuid = uprv_strdup(tmpid);
if (regionCodeLen == 0 || U_FAILURE(status)) {
// fallback to default "001" (world)
status = U_ZERO_ERROR;
icuTZ16 = ures_getStringByKey(winTZBundle.getAlias(), "001", &tzLen, &status);
}

return icuid;
// Note: cloneData returns nullptr if the status is a failure, so this
// will return nullptr if the above look-up fails.
CharString icuTZStr;
return icuTZStr.appendInvariantChars(icuTZ16, tzLen, status).cloneData(status);
}

U_NAMESPACE_END
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