Converting Microsoft Timezone to standards timezone data in rails

Improved Answer

The functionality described in my original answer (below) is now available in my TimeZoneConverter library for .NET. All the hard work is done for you, and it is kept updated with changes to the world's time zones. The examples in the project readme show how to convert between Windows, IANA, and Rails identifiers.

Since the app described in the question is in Rails, I suggest running a background job in .NET to convert Windows time zone IDs to those needed in your Rails app and keep them in a separate column.

Original Answer

The resource you're looking for is the Windows to IANA mapping file maintained as part of the Unicode CLDR project. The file is located within the CLDR release at common/supplemental/windowsZones.xml, and you can find the current "development version" of it here.

Be aware of a few things:

  • The file does get updated as new time zones come out from Microsoft and from IANA, or occasionally when governments change their time zone rules significantly enough that a different mapping applies.

  • The offsets in your list would just be the standard offset - that is, the one that applies when daylight saving time is not in effect. A "time zone" is composed of the standard offsets, the daylight offsets, and the specific dates and times of the DST transitions, along with the history of changes for the offsets and transitions.

  • The Rails time zone names should not be used anywhere outside of Rails. My understanding is that they were actually created before Rails decided to use standard IANA/Olson time zones, then later when the Ruby tzinfo gem became viable, the Rails zones were retrofitted through the MAPPING constant shown on this page, then some were added afterwards as individual complaints arose. If possible, just use the IANA time zones directly, via the tzinfo gem. If not, then you will have two layers of mapping to go through (Microsoft -> IANA -> Rails).

  • I do not know of a Rails-specific implementation of the CLDR mappings. I checked a couple of CLDR for Rails projects, and found they didn't include that particular portion of the CLDR. However, if you have control over the Windows side of things, then you might consider using the .NET implementation I describe in this answer. You would do the Windows to IANA conversion on the Windows side, then either use the IANA zones directly with tzinfo, or map to Rails zones in your Rails app.

  • Also realize that the number of Rails time zones are significantly less than those supported by IANA. I haven't checked, but it's likely that some of the Windows zones map to IANA zones that aren't in Rails. Also, there are some Rails zones that have multiple Rails entries, but only one IANA mapping - essentially making them equivalent aliases.

  • Both Rails and Windows use "UTC" as a zone id, which Rails maps to "Etc/UTC", but CLDR maps to "Etc/GMT". You'll have to handle this one manually.

  • Lastly, recognize that the CLDR uses "stable" identifiers in a different way than IANA's "canonical" identifiers, which may cause some difficulties during the mapping.

    • As an example, consider that the Microsoft zone "India Standard Time" maps to "Asia/Calcutta" in the CLDR, because that's what the original IANA zone was. However, IANA changed the zone to "Asia/Kolkata", and set up a link for backward compatibility for "Asia/Calcutta". When you look in the Rails MAPPING constant, there are four Rails zones, "Chennai", "Kolkata", "Mumbai", and "New Delhi" - all of which are mapped to "Asia/Kolkata".

    • To overcome this, you will also need another file from the CLDR, common/bcp47/timezone.xml. You can use this file to find all of the links between aliased IANA zones, which can help you map back to the Rails zone.

So yes, it's possible - but it's not easy. ;)

I've performed the current mappings for you, which are as follows:

"Windows","IANA","Rails"
"W. Central Africa Standard Time","Africa/Algiers","West Central Africa"
"Egypt Standard Time","Africa/Cairo","Cairo"
"Morocco Standard Time","Africa/Casablanca","Casablanca"
"South Africa Standard Time","Africa/Harare","Harare"
"South Africa Standard Time","Africa/Johannesburg","Pretoria"
"Greenwich Standard Time","Africa/Monrovia","Monrovia"
"E. Africa Standard Time","Africa/Nairobi","Nairobi"
"Argentina Standard Time","America/Argentina/Buenos_Aires","Buenos Aires"
"SA Pacific Standard Time","America/Bogota","Bogota"
"Venezuela Standard Time","America/Caracas","Caracas"
"Central Standard Time","America/Chicago","Central Time (US & Canada)"
"Mountain Standard Time (Mexico)","America/Chihuahua","Chihuahua"
"Mountain Standard Time","America/Denver","Mountain Time (US & Canada)"
"Greenland Standard Time","America/Godthab","Greenland"
"Central America Standard Time","America/Guatemala","Central America"
"SA Western Standard Time","America/Guyana","Georgetown"
"Atlantic Standard Time","America/Halifax","Atlantic Time (Canada)"
"US Eastern Standard Time","America/Indiana/Indianapolis","Indiana (East)"
"Alaskan Standard Time","America/Juneau","Alaska"
"SA Western Standard Time","America/La_Paz","La Paz"
"SA Pacific Standard Time","America/Lima","Lima"
"SA Pacific Standard Time","America/Lima","Quito"
"Pacific Standard Time","America/Los_Angeles","Pacific Time (US & Canada)"
"Mountain Standard Time (Mexico)","America/Mazatlan","Mazatlan"
"Central Standard Time (Mexico)","America/Mexico_City","Guadalajara"
"Central Standard Time (Mexico)","America/Mexico_City","Mexico City"
"Central Standard Time (Mexico)","America/Monterrey","Monterrey"
"Montevideo Standard Time","America/Montevideo","Montevideo"
"Eastern Standard Time","America/New_York","Eastern Time (US & Canada)"
"US Mountain Standard Time","America/Phoenix","Arizona"
"Canada Central Standard Time","America/Regina","Saskatchewan"
"Pacific SA Standard Time","America/Santiago","Santiago"
"E. South America Standard Time","America/Sao_Paulo","Brasilia"
"Newfoundland Standard Time","America/St_Johns","Newfoundland"
"Pacific Standard Time","America/Tijuana","Tijuana"
"Central Asia Standard Time","Asia/Almaty","Almaty"
"Arabic Standard Time","Asia/Baghdad","Baghdad"
"Azerbaijan Standard Time","Asia/Baku","Baku"
"SE Asia Standard Time","Asia/Bangkok","Bangkok"
"SE Asia Standard Time","Asia/Bangkok","Hanoi"
"China Standard Time","Asia/Chongqing","Chongqing"
"Sri Lanka Standard Time","Asia/Colombo","Sri Jayawardenepura"
"Bangladesh Standard Time","Asia/Dhaka","Astana"
"Bangladesh Standard Time","Asia/Dhaka","Dhaka"
"China Standard Time","Asia/Hong_Kong","Hong Kong"
"North Asia East Standard Time","Asia/Irkutsk","Irkutsk"
"SE Asia Standard Time","Asia/Jakarta","Jakarta"
"Israel Standard Time","Asia/Jerusalem","Jerusalem"
"Afghanistan Standard Time","Asia/Kabul","Kabul"
"Russia Time Zone 11","Asia/Kamchatka","Kamchatka"
"Pakistan Standard Time","Asia/Karachi","Islamabad"
"Pakistan Standard Time","Asia/Karachi","Karachi"
"Nepal Standard Time","Asia/Kathmandu","Kathmandu"
"India Standard Time","Asia/Kolkata","Chennai"
"India Standard Time","Asia/Kolkata","Kolkata"
"India Standard Time","Asia/Kolkata","Mumbai"
"India Standard Time","Asia/Kolkata","New Delhi"
"North Asia Standard Time","Asia/Krasnoyarsk","Krasnoyarsk"
"Singapore Standard Time","Asia/Kuala_Lumpur","Kuala Lumpur"
"Arab Standard Time","Asia/Kuwait","Kuwait"
"Magadan Standard Time","Asia/Magadan","Magadan"
"Arabian Standard Time","Asia/Muscat","Abu Dhabi"
"Arabian Standard Time","Asia/Muscat","Muscat"
"N. Central Asia Standard Time","Asia/Novosibirsk","Novosibirsk"
"Myanmar Standard Time","Asia/Rangoon","Rangoon"
"Arab Standard Time","Asia/Riyadh","Riyadh"
"Korea Standard Time","Asia/Seoul","Seoul"
"China Standard Time","Asia/Shanghai","Beijing"
"Singapore Standard Time","Asia/Singapore","Singapore"
"Russia Time Zone 10","Asia/Srednekolymsk","Srednekolymsk"
"Taipei Standard Time","Asia/Taipei","Taipei"
"West Asia Standard Time","Asia/Tashkent","Tashkent"
"Georgian Standard Time","Asia/Tbilisi","Tbilisi"
"Iran Standard Time","Asia/Tehran","Tehran"
"Tokyo Standard Time","Asia/Tokyo","Osaka"
"Tokyo Standard Time","Asia/Tokyo","Sapporo"
"Tokyo Standard Time","Asia/Tokyo","Tokyo"
"Ulaanbaatar Standard Time","Asia/Ulaanbaatar","Ulaanbaatar"
"Central Asia Standard Time","Asia/Urumqi","Urumqi"
"Vladivostok Standard Time","Asia/Vladivostok","Vladivostok"
"Yakutsk Standard Time","Asia/Yakutsk","Yakutsk"
"Ekaterinburg Standard Time","Asia/Yekaterinburg","Ekaterinburg"
"Caucasus Standard Time","Asia/Yerevan","Yerevan"
"Azores Standard Time","Atlantic/Azores","Azores"
"Cape Verde Standard Time","Atlantic/Cape_Verde","Cape Verde Is."
"UTC-02","Atlantic/South_Georgia","Mid-Atlantic"
"Cen. Australia Standard Time","Australia/Adelaide","Adelaide"
"E. Australia Standard Time","Australia/Brisbane","Brisbane"
"AUS Central Standard Time","Australia/Darwin","Darwin"
"Tasmania Standard Time","Australia/Hobart","Hobart"
"AUS Eastern Standard Time","Australia/Melbourne","Canberra"
"AUS Eastern Standard Time","Australia/Melbourne","Melbourne"
"W. Australia Standard Time","Australia/Perth","Perth"
"AUS Eastern Standard Time","Australia/Sydney","Sydney"
"UTC","Etc/UTC","UTC"
"W. Europe Standard Time","Europe/Amsterdam","Amsterdam"
"GTB Standard Time","Europe/Athens","Athens"
"Central Europe Standard Time","Europe/Belgrade","Belgrade"
"W. Europe Standard Time","Europe/Berlin","Berlin"
"W. Europe Standard Time","Europe/Berlin","Bern"
"Central Europe Standard Time","Europe/Bratislava","Bratislava"
"Romance Standard Time","Europe/Brussels","Brussels"
"GTB Standard Time","Europe/Bucharest","Bucharest"
"Central Europe Standard Time","Europe/Budapest","Budapest"
"Romance Standard Time","Europe/Copenhagen","Copenhagen"
"GMT Standard Time","Europe/Dublin","Dublin"
"FLE Standard Time","Europe/Helsinki","Helsinki"
"Turkey Standard Time","Europe/Istanbul","Istanbul"
"Kaliningrad Standard Time","Europe/Kaliningrad","Kaliningrad"
"FLE Standard Time","Europe/Kiev","Kyiv"
"GMT Standard Time","Europe/Lisbon","Lisbon"
"Central Europe Standard Time","Europe/Ljubljana","Ljubljana"
"GMT Standard Time","Europe/London","Edinburgh"
"GMT Standard Time","Europe/London","London"
"Romance Standard Time","Europe/Madrid","Madrid"
"Belarus Standard Time","Europe/Minsk","Minsk"
"Russian Standard Time","Europe/Moscow","Moscow"
"Russian Standard Time","Europe/Moscow","St. Petersburg"
"Romance Standard Time","Europe/Paris","Paris"
"Central Europe Standard Time","Europe/Prague","Prague"
"FLE Standard Time","Europe/Riga","Riga"
"W. Europe Standard Time","Europe/Rome","Rome"
"Russia Time Zone 3","Europe/Samara","Samara"
"Central European Standard Time","Europe/Sarajevo","Sarajevo"
"Central European Standard Time","Europe/Skopje","Skopje"
"FLE Standard Time","Europe/Sofia","Sofia"
"W. Europe Standard Time","Europe/Stockholm","Stockholm"
"FLE Standard Time","Europe/Tallinn","Tallinn"
"W. Europe Standard Time","Europe/Vienna","Vienna"
"FLE Standard Time","Europe/Vilnius","Vilnius"
"Russian Standard Time","Europe/Volgograd","Volgograd"
"Central European Standard Time","Europe/Warsaw","Warsaw"
"Central European Standard Time","Europe/Zagreb","Zagreb"
"Samoa Standard Time","Pacific/Apia","Samoa"
"New Zealand Standard Time","Pacific/Auckland","Auckland"
"New Zealand Standard Time","Pacific/Auckland","Wellington"
"Tonga Standard Time","Pacific/Fakaofo","Tokelau Is."
"Fiji Standard Time","Pacific/Fiji","Fiji"
"Central Pacific Standard Time","Pacific/Guadalcanal","Solomon Is."
"West Pacific Standard Time","Pacific/Guam","Guam"
"Hawaiian Standard Time","Pacific/Honolulu","Hawaii"
"UTC+12","Pacific/Majuro","Marshall Is."
"UTC-11","Pacific/Midway","International Date Line West"
"UTC-11","Pacific/Midway","Midway Island"
"Central Pacific Standard Time","Pacific/Noumea","New Caledonia"
"UTC-11","Pacific/Pago_Pago","American Samoa"
"West Pacific Standard Time","Pacific/Port_Moresby","Port Moresby"
"Tonga Standard Time","Pacific/Tongatapu","Nuku'alofa"

Note that the above list includes entries where more than one Rails zone maps back to the same Windows zone. You may want to pick just one of these when mapping in the Windows-to-Rails direction.

Also, the above list does not include the zones that could not be mapped, which are as follows (CSV):

"Windows","IANA","Rails"
"","Pacific/Chatham","Chatham Is."
"Dateline Standard Time","Etc/GMT+12",""
"Pacific Standard Time (Mexico)","America/Santa_Isabel",""
"Eastern Standard Time (Mexico)","America/Cancun",""
"Paraguay Standard Time","America/Asuncion",""
"Central Brazilian Standard Time","America/Cuiaba",""
"SA Eastern Standard Time","America/Cayenne",""
"Bahia Standard Time","America/Bahia",""
"Namibia Standard Time","Africa/Windhoek",""
"Jordan Standard Time","Asia/Amman",""
"Middle East Standard Time","Asia/Beirut",""
"Syria Standard Time","Asia/Damascus",""
"E. Europe Standard Time","Etc/GMT-2",""
"Libya Standard Time","Africa/Tripoli",""
"Mauritius Standard Time","Indian/Mauritius",""
"Line Islands Standard Time","Pacific/Kiritimati",""

Tags:

Ruby On Rails

Timezone

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