.NET TimeZoneInfo from Olson's Time Zone

Question

How to convert the following to System.TimeZone or System.TimeZoneInfo?

{ "timeZone": "America/Los_Angeles", "currentOffsetMs": -25200000 } 

This is the data that I receive from a third-party web service.

I assume the offset is a difference from UTC, and they tell me that America / Los_Angeles is Olson’s time zone. Java has no problem parsing this in Java TimeZone, but I need to parse this into a CZ TimeZoneInfo object.

Answer 1

This Unicode.org page contains the Olson timezone table in the Win32 time table. From there, I created a small C # helper function to display from an Olson timezone line in .NET TimeZoneInfo:

 /// <summary> /// Converts an Olson time zone ID to a Windows time zone ID. /// </summary> /// <param name="olsonTimeZoneId">An Olson time zone ID. See http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/zone_tzid.html. </param> /// <returns> /// The TimeZoneInfo corresponding to the Olson time zone ID, /// or null if you passed in an invalid Olson time zone ID. /// </returns> /// <remarks> /// See http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/zone_tzid.html /// </remarks> public static TimeZoneInfo OlsonTimeZoneToTimeZoneInfo(string olsonTimeZoneId) { var olsonWindowsTimes = new Dictionary<string, string>() { { "Africa/Bangui", "W. Central Africa Standard Time" }, { "Africa/Cairo", "Egypt Standard Time" }, { "Africa/Casablanca", "Morocco Standard Time" }, { "Africa/Harare", "South Africa Standard Time" }, { "Africa/Johannesburg", "South Africa Standard Time" }, { "Africa/Lagos", "W. Central Africa Standard Time" }, { "Africa/Monrovia", "Greenwich Standard Time" }, { "Africa/Nairobi", "E. Africa Standard Time" }, { "Africa/Windhoek", "Namibia Standard Time" }, { "America/Anchorage", "Alaskan Standard Time" }, { "America/Argentina/San_Juan", "Argentina Standard Time" }, { "America/Asuncion", "Paraguay Standard Time" }, { "America/Bahia", "Bahia Standard Time" }, { "America/Bogota", "SA Pacific Standard Time" }, { "America/Buenos_Aires", "Argentina Standard Time" }, { "America/Caracas", "Venezuela Standard Time" }, { "America/Cayenne", "SA Eastern Standard Time" }, { "America/Chicago", "Central Standard Time" }, { "America/Chihuahua", "Mountain Standard Time (Mexico)" }, { "America/Cuiaba", "Central Brazilian Standard Time" }, { "America/Denver", "Mountain Standard Time" }, { "America/Fortaleza", "SA Eastern Standard Time" }, { "America/Godthab", "Greenland Standard Time" }, { "America/Guatemala", "Central America Standard Time" }, { "America/Halifax", "Atlantic Standard Time" }, { "America/Indianapolis", "US Eastern Standard Time" }, { "America/Indiana/Indianapolis", "US Eastern Standard Time" }, { "America/La_Paz", "SA Western Standard Time" }, { "America/Los_Angeles", "Pacific Standard Time" }, { "America/Mexico_City", "Mexico Standard Time" }, { "America/Montevideo", "Montevideo Standard Time" }, { "America/New_York", "Eastern Standard Time" }, { "America/Noronha", "UTC-02" }, { "America/Phoenix", "US Mountain Standard Time" }, { "America/Regina", "Canada Central Standard Time" }, { "America/Santa_Isabel", "Pacific Standard Time (Mexico)" }, { "America/Santiago", "Pacific SA Standard Time" }, { "America/Sao_Paulo", "E. South America Standard Time" }, { "America/St_Johns", "Newfoundland Standard Time" }, { "America/Tijuana", "Pacific Standard Time" }, { "Antarctica/McMurdo", "New Zealand Standard Time" }, { "Atlantic/South_Georgia", "UTC-02" }, { "Asia/Almaty", "Central Asia Standard Time" }, { "Asia/Amman", "Jordan Standard Time" }, { "Asia/Baghdad", "Arabic Standard Time" }, { "Asia/Baku", "Azerbaijan Standard Time" }, { "Asia/Bangkok", "SE Asia Standard Time" }, { "Asia/Beirut", "Middle East Standard Time" }, { "Asia/Calcutta", "India Standard Time" }, { "Asia/Colombo", "Sri Lanka Standard Time" }, { "Asia/Damascus", "Syria Standard Time" }, { "Asia/Dhaka", "Bangladesh Standard Time" }, { "Asia/Dubai", "Arabian Standard Time" }, { "Asia/Irkutsk", "North Asia East Standard Time" }, { "Asia/Jerusalem", "Israel Standard Time" }, { "Asia/Kabul", "Afghanistan Standard Time" }, { "Asia/Kamchatka", "Kamchatka Standard Time" }, { "Asia/Karachi", "Pakistan Standard Time" }, { "Asia/Katmandu", "Nepal Standard Time" }, { "Asia/Kolkata", "India Standard Time" }, { "Asia/Krasnoyarsk", "North Asia Standard Time" }, { "Asia/Kuala_Lumpur", "Singapore Standard Time" }, { "Asia/Kuwait", "Arab Standard Time" }, { "Asia/Magadan", "Magadan Standard Time" }, { "Asia/Muscat", "Arabian Standard Time" }, { "Asia/Novosibirsk", "N. Central Asia Standard Time" }, { "Asia/Oral", "West Asia Standard Time" }, { "Asia/Rangoon", "Myanmar Standard Time" }, { "Asia/Riyadh", "Arab Standard Time" }, { "Asia/Seoul", "Korea Standard Time" }, { "Asia/Shanghai", "China Standard Time" }, { "Asia/Singapore", "Singapore Standard Time" }, { "Asia/Taipei", "Taipei Standard Time" }, { "Asia/Tashkent", "West Asia Standard Time" }, { "Asia/Tbilisi", "Georgian Standard Time" }, { "Asia/Tehran", "Iran Standard Time" }, { "Asia/Tokyo", "Tokyo Standard Time" }, { "Asia/Ulaanbaatar", "Ulaanbaatar Standard Time" }, { "Asia/Vladivostok", "Vladivostok Standard Time" }, { "Asia/Yakutsk", "Yakutsk Standard Time" }, { "Asia/Yekaterinburg", "Ekaterinburg Standard Time" }, { "Asia/Yerevan", "Armenian Standard Time" }, { "Atlantic/Azores", "Azores Standard Time" }, { "Atlantic/Cape_Verde", "Cape Verde Standard Time" }, { "Atlantic/Reykjavik", "Greenwich Standard Time" }, { "Australia/Adelaide", "Cen. Australia Standard Time" }, { "Australia/Brisbane", "E. Australia Standard Time" }, { "Australia/Darwin", "AUS Central Standard Time" }, { "Australia/Hobart", "Tasmania Standard Time" }, { "Australia/Perth", "W. Australia Standard Time" }, { "Australia/Sydney", "AUS Eastern Standard Time" }, { "Etc/GMT", "UTC" }, { "Etc/GMT+11", "UTC-11" }, { "Etc/GMT+12", "Dateline Standard Time" }, { "Etc/GMT+2", "UTC-02" }, { "Etc/GMT-12", "UTC+12" }, { "Europe/Amsterdam", "W. Europe Standard Time" }, { "Europe/Athens", "GTB Standard Time" }, { "Europe/Belgrade", "Central Europe Standard Time" }, { "Europe/Berlin", "W. Europe Standard Time" }, { "Europe/Brussels", "Romance Standard Time" }, { "Europe/Budapest", "Central Europe Standard Time" }, { "Europe/Dublin", "GMT Standard Time" }, { "Europe/Helsinki", "FLE Standard Time" }, { "Europe/Istanbul", "GTB Standard Time" }, { "Europe/Kiev", "FLE Standard Time" }, { "Europe/London", "GMT Standard Time" }, { "Europe/Minsk", "E. Europe Standard Time" }, { "Europe/Moscow", "Russian Standard Time" }, { "Europe/Paris", "Romance Standard Time" }, { "Europe/Sarajevo", "Central European Standard Time" }, { "Europe/Warsaw", "Central European Standard Time" }, { "Indian/Mauritius", "Mauritius Standard Time" }, { "Pacific/Apia", "Samoa Standard Time" }, { "Pacific/Auckland", "New Zealand Standard Time" }, { "Pacific/Fiji", "Fiji Standard Time" }, { "Pacific/Guadalcanal", "Central Pacific Standard Time" }, { "Pacific/Guam", "West Pacific Standard Time" }, { "Pacific/Honolulu", "Hawaiian Standard Time" }, { "Pacific/Pago_Pago", "UTC-11" }, { "Pacific/Port_Moresby", "West Pacific Standard Time" }, { "Pacific/Tongatapu", "Tonga Standard Time" } }; var windowsTimeZoneId = default(string); var windowsTimeZone = default(TimeZoneInfo); if (olsonWindowsTimes.TryGetValue(olsonTimeZoneId, out windowsTimeZoneId)) { try { windowsTimeZone = TimeZoneInfo.FindSystemTimeZoneById(windowsTimeZoneId); } catch (TimeZoneNotFoundException) { } catch (InvalidTimeZoneException) { } } return windowsTimeZone; } 

Answer 2

Here is the inverse mapping function (tzdb -> windows) using NodaTime :

 using NodaTime; using NodaTime.TimeZones; ... public TimeZoneInfo GetTimeZoneInfoForTzdbId(string tzdbId) { var mappings = TzdbDateTimeZoneSource.Default.WindowsMapping.MapZones; var map = mappings.FirstOrDefault(x => x.TzdbIds.Any(z => z.Equals(tzdbId, StringComparison.OrdinalIgnoreCase))); return map == null ? null : TimeZoneInfo.FindSystemTimeZoneById(map.WindowsId); } 

Note: it is possible that there is more than one mapping (in this case, it simply uses the first one found) or does not display at all (where it returns null).

In the most commonly used time zones, this should work quite well. But the best solution would be to skip using TimeZoneInfo in general, and just use NodaTime throughout the application, directly in the TZDB zone.

See also: How to translate between Windows time zones and IANA?

Answer 3

Perhaps you should take a look at Jon Skeet Noda-Time and opt out of TimeZoneInfo altogether. Noda-Time uses Olson's watches, so your mapping will be a piece of cake. There are other reasons why you can use it:

What happened to DateTime anyway?

My question was to use Noda-Time

Answer 4

A small snippet that I came up with to get an olson list for Windows timezone mappings from xml at http://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml p>

 private static void LoadMappingsO() { var file = new FileInfo("windowsZones.xml"); if (!file.Exists) { return; } var map = new Dictionary<string, string>(); using (var reader = file.OpenText()) { var readerSettings = new XmlReaderSettings { XmlResolver = null, ProhibitDtd = false }; using (var xmlReader = XmlReader.Create(reader, readerSettings)) { var document = new XPathDocument(xmlReader); var navigator = document.CreateNavigator(); var nodes = navigator.Select("/supplementalData/windowsZones/mapTimezones/mapZone"); while (nodes.MoveNext()) { var node = nodes.Current; if (node == null) continue; var olsonNames = node.GetAttribute("type", "").Split(' '); var windowsName = node.GetAttribute("other", ""); foreach (var olsonName in olsonNames) { if (!map.ContainsKey(olsonName)) { map.Add(olsonName, windowsName); } } } } } using (TextWriter tw = new StreamWriter("dict.txt", false)) { foreach (var key in map.Keys) { tw.WriteLine(string.Format("{{\"{0}\", \"{1}\"}},", key, map[key])); } } } 

UPDATE (using Linq Xml):

 private static void LoadMappings() { var map = new Dictionary<string, string>(); var xdoc = XDocument.Load("windowsZones.xml"); var zones = xdoc.XPathSelectElements("/supplementalData/windowsZones/mapTimezones/mapZone"); foreach (var zone in zones) { var olsonNames = zone.Attribute("type")?.Value.Split(' '); if (olsonNames == null) continue; var windowsName = zone.Attribute("other")?.Value; if (string.IsNullOrWhiteSpace(windowsName)) continue; foreach (var olsonName in olsonNames) { map[olsonName] = windowsName; } } using (TextWriter tw = new StreamWriter("dict.txt", false)) { foreach (var key in map.Keys) { tw.WriteLine($"{{\"{key}\", \"{map[key]}\"}},"); } } } 

Answer 5

After converting currentOffsetMs to hours and the remaining minutes, you can list specific TimeZoneInfo objects:

 foreach (TimeZoneInfo nextZone in TimeZoneInfo.GetSystemTimeZones()) { int nextHours = nextZone.BaseUtcOffset.Hours + 24; // To prevent negative numbers int nextMinutes = nextZone.BaseUtcOffset.Minutes; if (tzHours == nextHours && tzMinutes == nextMinutes) { myTimeZoneInfo = nextZone; break; } } 

Answer 6

UPDATE: I removed the URL from the script. Please send the file manually. This script is not intended to continuously load unnecessary load on unicode.org. See comments below.

This Powershell script can be used to create a case statement using the current XML file from unicode.org. It generates mappings from IANA names in TimeZoneInfoId.

  # Download the xml file. $xml = [Xml] /// Load the XML content here # Parse the fields we want from the XML. $mappings1 = $xml.supplementalData.windowsZones.mapTimezones.mapZone | select Type,Other # Extrapolate extra rows for entries that contain more than one IANA name seperated by spaces. # Example: |<mapZone other="Alaskan Standard Time" territory="US" type="America/Anchorage America/Juneau America/Nome America/Sitka America/Yakutat"/> $mappings2 = $mappings1 | %{ $mapping = $_ $_.Type.Split(" ") | %{ New-Object PSObject -Property @{type = $_; other = $mapping.other} } } # Remove dup's $mappings3 = $mappings2 | sort type -Unique # Generate the case statements. $mappings3 | %{ [String]::Format("case @""{0}"": return @""{1}"";", $_.Type, $_.Other)}