IANA To/From Windows Ids Conversion APIs

src/libraries/Common/src/Interop/Interop.TimeZoneInfo.cs

@@ -16,7 +16,7 @@ internal static extern unsafe ResultCode GetTimeZoneDisplayName(
             int resultLength);
 
         [DllImport(Libraries.GlobalizationNative, CharSet = CharSet.Unicode, EntryPoint = "GlobalizationNative_WindowsIdToIanaId")]
-        internal static extern unsafe int WindowsIdToIanaId(string windowsId, char* ianaId, int ianaIdLength);
+        internal static extern unsafe int WindowsIdToIanaId(string windowsId, string? region, char* ianaId, int ianaIdLength);
 
         [DllImport(Libraries.GlobalizationNative, CharSet = CharSet.Unicode, EntryPoint = "GlobalizationNative_IanaIdToWindowsId")]
         internal static extern unsafe int IanaIdToWindowsId(string ianaId, char* windowsId, int windowsIdLength);

src/libraries/Native/Unix/System.Globalization.Native/pal_timeZoneInfo.c

@@ -21,13 +21,36 @@ static const UChar EXEMPLAR_CITY_PATTERN_UCHAR[] = {'V', 'V', 'V', '\0'};
 /*
 Convert Windows Time Zone Id to IANA Id
 */
-int32_t GlobalizationNative_WindowsIdToIanaId(const UChar* windowsId, UChar* ianaId, int32_t ianaIdLength)
+int32_t GlobalizationNative_WindowsIdToIanaId(const UChar* windowsId, const UChar* region, UChar* ianaId, int32_t ianaIdLength)
 {
     UErrorCode status = U_ZERO_ERROR;
 
     if (ucal_getTimeZoneIDForWindowsID_ptr != NULL)
     {
-        int32_t ianaIdFilledLength = ucal_getTimeZoneIDForWindowsID(windowsId, -1, NULL, ianaId, ianaIdLength, &status);
+        #define BUFFER_LENGTH 41 // enough length for the region code including the null termination
+        char buffer[BUFFER_LENGTH];
+        char* regionName = NULL;
+
+        if (region != NULL)
+        {
+            regionName = buffer;
+            int length = 0;
+            while (length < BUFFER_LENGTH - 1 && region[length] != '\0')
+            {
+                buffer[length] = (char)region[length];
+                length++;
+            }
+
+            if (length == BUFFER_LENGTH - 1)
+            {
+                // long region name which shouldn't be correct.
+                return 0;
+            }
+
+            buffer[length] = '\0';
+        }
+
+        int32_t ianaIdFilledLength = ucal_getTimeZoneIDForWindowsID(windowsId, -1, regionName, ianaId, ianaIdLength, &status);
         if (U_SUCCESS(status))
         {
             return ianaIdFilledLength;
@@ -91,7 +114,7 @@ static void GetTimeZoneDisplayName_FromPattern(const char* locale, const UChar*
     if (U_SUCCESS(*err))
     {
         udat_format(dateFormatter, timestamp, result, resultLength, NULL, err);
-        udat_close(dateFormatter);    
+        udat_close(dateFormatter);
     }
 }
 

src/libraries/Native/Unix/System.Globalization.Native/pal_timeZoneInfo.h

@@ -20,6 +20,6 @@ typedef enum
     TimeZoneDisplayName_ExemplarCity = 4,
 } TimeZoneDisplayNameType;
 
-PALEXPORT int32_t GlobalizationNative_WindowsIdToIanaId(const UChar* windowsId, UChar* ianaId, int32_t ianaIdLength);
+PALEXPORT int32_t GlobalizationNative_WindowsIdToIanaId(const UChar* windowsId, const UChar* region, UChar* ianaId, int32_t ianaIdLength);
 PALEXPORT int32_t GlobalizationNative_IanaIdToWindowsId(const UChar* ianaId, UChar* windowsId, int32_t windowsIdLength);
 PALEXPORT ResultCode GlobalizationNative_GetTimeZoneDisplayName(const UChar* localeName, const UChar* timeZoneId, TimeZoneDisplayNameType type, UChar* result, int32_t resultLength);

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.FullGlobalizationData.cs

@@ -231,36 +231,11 @@ private static string GetExemplarCityName(string timeZoneId, string uiCultureNam
             return timeZoneId.Substring(i + 1).Replace('_', ' ');
         }
 
-        // Helper function that returns an alternative ID using ICU data.  Used primarily for converting from Windows IDs.
-        private static unsafe string? GetAlternativeId(string id)
+        // Helper function that returns an alternative ID using ICU data. Used primarily for converting from Windows IDs.
+        private static unsafe string? GetAlternativeId(string id, out bool idIsIana)
         {
-            if (!GlobalizationMode.Invariant)
-            {
-                if (id.Equals("utc", StringComparison.OrdinalIgnoreCase))
-                {
-                    // Special case UTC, as previously ICU would convert it to "Etc/GMT" which is incorrect name for UTC.
-                    return "Etc/UTC";
-                }
-
-                foreach (char c in id)
-                {
-                    // ICU uses some characters as a separator and trim the id at that character.
-                    // while we should fail if the Id contained one of these characters.
-                    if (c == '\\' || c == '\n' || c == '\r')
-                    {
-                        return null;
-                    }
-                }
-
-                char* buffer = stackalloc char[100];
-                int length = Interop.Globalization.WindowsIdToIanaId(id, buffer, 100);
-                if (length > 0)
-                {
-                    return new string(buffer, 0, length);
-                }
-            }
-
-            return null;
+            idIsIana = false;
+            return TryConvertWindowsIdToIanaId(id, null, out string? ianaId) ? ianaId : null;
         }
     }
 }

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.MinimalGlobalizationData.cs

@@ -22,9 +22,10 @@ private static string GetUtcFullDisplayName(string timeZoneId, string standardDi
             return $"(UTC) {timeZoneId}";
         }
 
-        private static string? GetAlternativeId(string id)
+        private static string? GetAlternativeId(string id, out bool idIsIana)
         {
             // No alternative IDs in this target.
+            idIsIana = false;
             return null;
         }
     }

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Unix.cs

@@ -41,6 +41,8 @@ private TimeZoneInfo(byte[] data, string id, bool dstDisabled)
         {
             _id = id;
 
+            HasIanaId = true;
+
             // Handle UTC and its aliases
             if (StringArrayContains(_id, s_UtcAliases, StringComparison.OrdinalIgnoreCase))
             {

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Win32.cs

@@ -106,29 +106,10 @@ private static void PopulateAllSystemTimeZones(CachedData cachedData)
             }
         }
 
-        private static unsafe string? GetAlternativeId(string id)
+        private static string? GetAlternativeId(string id, out bool idIsIana)
         {
-            if (!GlobalizationMode.Invariant && !GlobalizationMode.UseNls)
-            {
-                foreach (char c in id)
-                {
-                    // ICU uses some characters as a separator and trim the id at that character.
-                    // while we should fail if the Id contained one of these characters.
-                    if (c == '\\' || c == '\n' || c == '\r')
-                    {
-                        return null;
-                    }
-                }
-
-                char* buffer = stackalloc char[100];
-                int length = Interop.Globalization.IanaIdToWindowsId(id, buffer, 100);
-                if (length > 0)
-                {
-                    return new string(buffer, 0, length);
-                }
-            }
-
-            return null;
+            idIsIana = true;
+            return TryConvertIanaIdToWindowsId(id, out string? windowsId) ? windowsId : null;
         }
 
         private TimeZoneInfo(in TIME_ZONE_INFORMATION zone, bool dstDisabled)

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs

@@ -6,6 +6,7 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
+using System.Runtime.InteropServices;
 using System.Runtime.Serialization;
 using System.Threading;
 
@@ -136,6 +137,11 @@ public DateTimeKind GetCorrespondingKind(TimeZoneInfo? timeZone)
 
         public string Id => _id;
 
+        /// <summary>
+        /// Returns true if this TimeZoneInfo object has IANA Id.
+        /// </summary>
+        public bool HasIanaId { get; }
+
         public string DisplayName => _displayName ?? string.Empty;
 
         public string StandardName => _standardDisplayName ?? string.Empty;
@@ -880,7 +886,8 @@ private TimeZoneInfo(
                 string? standardDisplayName,
                 string? daylightDisplayName,
                 AdjustmentRule[]? adjustmentRules,
-                bool disableDaylightSavingTime)
+                bool disableDaylightSavingTime,
+                bool hasIanaId = false)
         {
             ValidateTimeZoneInfo(id, baseUtcOffset, adjustmentRules, out bool adjustmentRulesSupportDst);
 
@@ -891,6 +898,8 @@ private TimeZoneInfo(
             _daylightDisplayName = disableDaylightSavingTime ? null : daylightDisplayName;
             _supportsDaylightSavingTime = adjustmentRulesSupportDst && !disableDaylightSavingTime;
             _adjustmentRules = adjustmentRules;
+
+            HasIanaId = _id.Equals(UtcId, StringComparison.OrdinalIgnoreCase) ? true : hasIanaId;
         }
 
         /// <summary>
@@ -902,14 +911,17 @@ public static TimeZoneInfo CreateCustomTimeZone(
             string? displayName,
             string? standardDisplayName)
         {
+            bool hasIanaId = TimeZoneInfo.TryConvertIanaIdToWindowsId(id, out string _);
+
             return new TimeZoneInfo(
                 id,
                 baseUtcOffset,
                 displayName,
                 standardDisplayName,
                 standardDisplayName,
                 adjustmentRules: null,
-                disableDaylightSavingTime: false);
+                disableDaylightSavingTime: false,
+                hasIanaId);
         }
 
         /// <summary>
@@ -950,14 +962,111 @@ public static TimeZoneInfo CreateCustomTimeZone(
                 adjustmentRules = (AdjustmentRule[])adjustmentRules.Clone();
             }
 
+            bool hasIanaId = TimeZoneInfo.TryConvertIanaIdToWindowsId(id, out string _);
+
             return new TimeZoneInfo(
                 id,
                 baseUtcOffset,
                 displayName,
                 standardDisplayName,
                 daylightDisplayName,
                 adjustmentRules,
-                disableDaylightSavingTime);
+                disableDaylightSavingTime,
+                hasIanaId);
+        }
+
+        /// <summary>
+        /// Tries to convert IANA time zone Id to Windows Id.
+        /// </summary>
+        /// <param name="ianaId">The IANA time zone Id.</param>
+        /// <param name="windowsId">String object hold the Windows Id which resulted from the IANA Id conversion.</param>
+        /// <returns>True if the Id conversion succeed, false otherwise .</returns>
+        public static unsafe bool TryConvertIanaIdToWindowsId(string ianaId, out string? windowsId)
+        {
+            windowsId = null;
+
+            // This functionality is not enabled in the browser for the sake of size reduction.
+#if !TARGET_BROWSER
+            if (GlobalizationMode.Invariant || GlobalizationMode.UseNls || ianaId is null)
+            {
+                return false;
+            }
+
+            foreach (char c in ianaId)
+            {
+                // ICU uses some characters as a separator and trim the id at that character.
+                // while we should fail if the Id contained one of these characters.
+                if (c == '\\' || c == '\n' || c == '\r')
+                {
+                    return false;
+                }
+            }
+
+            char* buffer = stackalloc char[100];
+            int length = Interop.Globalization.IanaIdToWindowsId(ianaId, buffer, 100);
+            if (length > 0)
+            {
+                windowsId = new string(buffer, 0, length);
+                return true;
+            }
+#endif // !TARGET_BROWSER
+
+            return false;
+        }
+
+        /// <summary>
+        /// Tries to convert Windows time zone Id to IANA Id.
+        /// </summary>
+        /// <param name="windowsId">The Windows time zone Id.</param>
+        /// <param name="ianaId">String object hold the IANA Id which resulted from the Windows Id conversion.</param>
+        /// <returns>True if the Id conversion succeed, false otherwise .</returns>
+        public static bool TryConvertWindowsIdToIanaId(string windowsId, out string? ianaId) => TryConvertWindowsIdToIanaId(windowsId, null, out ianaId);
+
+        /// <summary>
+        /// Tries to convert Windows time zone Id to IANA Id.
+        /// </summary>
+        /// <param name="windowsId">The Windows time zone Id.</param>
+        /// <param name="region">The ISO 3166 for the country/region.</param>
+        /// <param name="ianaId">String object hold the IANA Id which resulted from the Windows Id conversion.</param>
+        /// <returns>True if the Id conversion succeed, false otherwise .</returns>
+        public static unsafe bool TryConvertWindowsIdToIanaId(string windowsId, string? region, out string? ianaId)
+        {
+            ianaId = null;
+
+            // This functionality is not enabled in the browser for the sake of size reduction.
+#if !TARGET_BROWSER
+            if (GlobalizationMode.Invariant || GlobalizationMode.UseNls || windowsId is null)
+            {
+                return false;
+            }
+
+            if (windowsId.Equals("utc", StringComparison.OrdinalIgnoreCase))
+            {
+                // Special case UTC, as previously ICU would convert it to "Etc/GMT" which is incorrect name for UTC.
+                ianaId = "Etc/UTC";
+                return true;
+            }
+
+            foreach (char c in windowsId)
+            {
+                // ICU uses some characters as a separator and trim the id at that character.
+                // while we should fail if the Id contained one of these characters.
+                if (c == '\\' || c == '\n' || c == '\r')
+                {
+                    return false;
+                }
+            }
+
+            char* buffer = stackalloc char[100];
+            int length = Interop.Globalization.WindowsIdToIanaId(windowsId, region, buffer, 100);
+            if (length > 0)
+            {
+                ianaId = new string(buffer, 0, length);
+                return true;
+            }
+#endif // !TARGET_BROWSER
+
+            return false;
         }
 
         void IDeserializationCallback.OnDeserialization(object? sender)
@@ -1794,7 +1903,7 @@ private static TimeZoneInfoResult TryGetTimeZone(string id, bool dstDisabled, ou
             TimeZoneInfoResult result = TryGetTimeZoneUsingId(id, dstDisabled, out value, out e, cachedData, alwaysFallbackToLocalMachine);
             if (result != TimeZoneInfoResult.Success)
             {
-                string? alternativeId = GetAlternativeId(id);
+                string? alternativeId = GetAlternativeId(id, out bool idIsIana);
                 if (alternativeId != null)
                 {
                     result = TryGetTimeZoneUsingId(alternativeId, dstDisabled, out value, out e, cachedData, alwaysFallbackToLocalMachine);
@@ -1804,7 +1913,7 @@ private static TimeZoneInfoResult TryGetTimeZone(string id, bool dstDisabled, ou
                         if (value!._equivalentZones == null)
                         {
                             zone = new TimeZoneInfo(id, value!._baseUtcOffset, value!._displayName, value!._standardDisplayName,
-                                                    value!._daylightDisplayName, value!._adjustmentRules, dstDisabled && value!._supportsDaylightSavingTime);
+                                                    value!._daylightDisplayName, value!._adjustmentRules, dstDisabled && value!._supportsDaylightSavingTime, idIsIana);
                             value!._equivalentZones = new List<TimeZoneInfo>();
                             lock (value!._equivalentZones)
                             {
@@ -1824,7 +1933,7 @@ private static TimeZoneInfoResult TryGetTimeZone(string id, bool dstDisabled, ou
                             if (zone == null)
                             {
                                 zone = new TimeZoneInfo(id, value!._baseUtcOffset, value!._displayName, value!._standardDisplayName,
-                                                        value!._daylightDisplayName, value!._adjustmentRules, dstDisabled && value!._supportsDaylightSavingTime);
+                                                        value!._daylightDisplayName, value!._adjustmentRules, dstDisabled && value!._supportsDaylightSavingTime, idIsIana);
                                 lock (value!._equivalentZones)
                                 {
                                     value!._equivalentZones.Add(zone);
@@ -1861,7 +1970,7 @@ private static TimeZoneInfoResult TryGetTimeZoneUsingId(string id, bool dstDisab
                     else
                     {
                         value = new TimeZoneInfo(match._id, match._baseUtcOffset, match._displayName, match._standardDisplayName,
-                                              match._daylightDisplayName, match._adjustmentRules, disableDaylightSavingTime: false);
+                                              match._daylightDisplayName, match._adjustmentRules, disableDaylightSavingTime: false, match.HasIanaId);
                     }
 
                     return result;

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -3851,6 +3851,7 @@ internal TimeZoneInfo() { }
         public System.TimeSpan BaseUtcOffset { get { throw null; } }
         public string DaylightName { get { throw null; } }
         public string DisplayName { get { throw null; } }
+        public bool HasIanaId { get; }
         public string Id { get { throw null; } }
         public static System.TimeZoneInfo Local { get { throw null; } }
         public string StandardName { get { throw null; } }
@@ -3890,6 +3891,9 @@ void System.Runtime.Serialization.IDeserializationCallback.OnDeserialization(obj
         void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         public string ToSerializedString() { throw null; }
         public override string ToString() { throw null; }
+        public static bool TryConvertIanaIdToWindowsId(string ianaId, out string windowsId) { throw null; }
+        public static bool TryConvertWindowsIdToIanaId(string windowsId, out string? ianaId) { throw null; }
+        public static bool TryConvertWindowsIdToIanaId(string windowsId, string? region, out string? ianaId) { throw null; }
         public sealed partial class AdjustmentRule : System.IEquatable<System.TimeZoneInfo.AdjustmentRule?>, System.Runtime.Serialization.IDeserializationCallback, System.Runtime.Serialization.ISerializable
         {
             internal AdjustmentRule() { }