Fix 500 on REPORT for recurring events with Windows timezone IDs
DAVx5 reported a 500 Internal Server Error on a time-range REPORT against a calendar containing a recurring event whose DTSTART/DTEND used a Windows-style TZID (e.g. "W. Europe Standard Time", as commonly written by Outlook/Exchange and some Thunderbird/Lightning setups) instead of an IANA zone name. go-ical resolves TZID via a plain time.LoadLocation call, which only understands IANA names. A simple decode of such an event succeeds (RRULE dates aren't parsed eagerly), but expanding its recurrence - which go-webdav's caldav.Filter does for every time-range REPORT - calls Component.RecurrenceSet, which does call time.LoadLocation(tzid) and fails with "ical: error parsing start time: unknown time zone ...". Add internal/icalfix, a small shared helper that rewrites recognized Windows timezone identifiers (TZID parameters and VTIMEZONE TZID: lines) to their IANA equivalent in raw ICS bytes before decoding. Wire it into every ical.NewDecoder call site: internal/caldav/backend.go's decodeObject (fixes the reported bug), internal/web/calendar.go's event rendering/ICS import, and internal/icssub's remote feed fetching, so a subscribed feed with the same issue doesn't hit it either. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Copilot
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// Package icalfix normalizes non-standard timezone identifiers in raw
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// iCalendar data before it's handed to go-ical's decoder.
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//
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// go-ical resolves a DTSTART/DTEND's TZID parameter (and, for recurring
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// events, the RRULE expansion's start time) via a direct
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// time.LoadLocation(tzid) call — see
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// github.com/emersion/go-ical@.../ical.go's Prop.DateTime and
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// components.go's Component.RecurrenceSet. That only understands IANA
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// zone names ("Europe/Berlin"), but Windows/Outlook (and anything built
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// on the Windows timezone database, e.g. Exchange, Thunderbird's Lightning
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// on some setups) commonly emits Windows zone names instead
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// ("W. Europe Standard Time"), which time.LoadLocation doesn't recognize.
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// A recurring event stored with such a TZID decodes fine (go-ical doesn't
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// eagerly parse RRULE dates), but fails later — as a 500 — the moment a
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// CalDAV client issues a time-range REPORT that has to expand its
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// recurrence, since that's when RecurrenceSet actually calls
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// time.LoadLocation.
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package icalfix
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import "regexp"
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// tzidParamRe matches a "TZID=<name>" (optionally quoted) parameter value
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// as it appears attached to any property (e.g. "DTSTART;TZID=W. Europe
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// Standard Time:..."). The name runs until the next ':' or ';' delimiter
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// or line break, so it captures the parameter's full value even though it
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// contains spaces and periods.
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var tzidParamRe = regexp.MustCompile(`TZID=("?)([^";:\r\n]+)("?)`)
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// tzidLineRe matches a standalone "TZID:<name>" property line, as found
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// inside a VTIMEZONE component.
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var tzidLineRe = regexp.MustCompile(`(?m)^TZID:([^\r\n]+)$`)
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// NormalizeTimeZones rewrites any recognized Windows timezone identifier
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// in data to its IANA equivalent, leaving everything else (including
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// unrecognized TZIDs) untouched. It's safe to call on data that has no
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// Windows TZIDs at all — such data passes through unchanged.
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func NormalizeTimeZones(data []byte) []byte {
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data = tzidParamRe.ReplaceAllFunc(data, func(m []byte) []byte {
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sub := tzidParamRe.FindSubmatch(m)
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name := string(sub[2])
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iana, ok := windowsToIANA[name]
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if !ok {
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return m
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}
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return []byte("TZID=" + string(sub[1]) + iana + string(sub[3]))
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})
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data = tzidLineRe.ReplaceAllFunc(data, func(m []byte) []byte {
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sub := tzidLineRe.FindSubmatch(m)
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name := string(sub[1])
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iana, ok := windowsToIANA[name]
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if !ok {
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return m
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}
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return []byte("TZID:" + iana)
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})
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return data
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}
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// windowsToIANA maps common Windows timezone identifiers (as found in the
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// CLDR windowsZones.xml "001"/default territory mapping) to an IANA zone
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// name recognized by Go's tzdata. It's not exhaustive, but covers the
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// zones seen in practice from Outlook/Exchange-generated ICS data.
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var windowsToIANA = map[string]string{
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"Dateline Standard Time": "Etc/GMT+12",
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"UTC-11": "Etc/GMT+11",
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"Aleutian Standard Time": "America/Adak",
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"Hawaiian Standard Time": "Pacific/Honolulu",
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"Marquesas Standard Time": "Pacific/Marquesas",
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"Alaskan Standard Time": "America/Anchorage",
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"UTC-09": "Etc/GMT+9",
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"Pacific Standard Time (Mexico)": "America/Tijuana",
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"UTC-08": "Etc/GMT+8",
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"Pacific Standard Time": "America/Los_Angeles",
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"US Mountain Standard Time": "America/Phoenix",
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"Mountain Standard Time (Mexico)": "America/Chihuahua",
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"Mountain Standard Time": "America/Denver",
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"Central America Standard Time": "America/Guatemala",
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"Central Standard Time": "America/Chicago",
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"Central Standard Time (Mexico)": "America/Mexico_City",
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"Canada Central Standard Time": "America/Regina",
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"SA Pacific Standard Time": "America/Bogota",
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"Eastern Standard Time (Mexico)": "America/Cancun",
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"Eastern Standard Time": "America/New_York",
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"Haiti Standard Time": "America/Port-au-Prince",
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"Cuba Standard Time": "America/Havana",
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"US Eastern Standard Time": "America/Indianapolis",
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"Turks And Caicos Standard Time": "America/Grand_Turk",
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"Paraguay Standard Time": "America/Asuncion",
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"Atlantic Standard Time": "America/Halifax",
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"Venezuela Standard Time": "America/Caracas",
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"Central Brazilian Standard Time": "America/Cuiaba",
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"SA Western Standard Time": "America/La_Paz",
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"Pacific SA Standard Time": "America/Santiago",
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"Newfoundland Standard Time": "America/St_Johns",
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"Tocantins Standard Time": "America/Araguaina",
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"E. South America Standard Time": "America/Sao_Paulo",
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"SA Eastern Standard Time": "America/Cayenne",
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"Argentina Standard Time": "America/Buenos_Aires",
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"Greenland Standard Time": "America/Godthab",
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"Montevideo Standard Time": "America/Montevideo",
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"Magallanes Standard Time": "America/Punta_Arenas",
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"Saint Pierre Standard Time": "America/Miquelon",
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"Bahia Standard Time": "America/Bahia",
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"UTC-02": "Etc/GMT+2",
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"Azores Standard Time": "Atlantic/Azores",
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"Cape Verde Standard Time": "Atlantic/Cape_Verde",
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"UTC": "Etc/UTC",
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"GMT Standard Time": "Europe/London",
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"Greenwich Standard Time": "Atlantic/Reykjavik",
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"Sao Tome Standard Time": "Africa/Sao_Tome",
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"Morocco Standard Time": "Africa/Casablanca",
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"W. Europe Standard Time": "Europe/Berlin",
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"Central Europe Standard Time": "Europe/Budapest",
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"Romance Standard Time": "Europe/Paris",
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"Central European Standard Time": "Europe/Warsaw",
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"W. Central Africa Standard Time": "Africa/Lagos",
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"Jordan Standard Time": "Asia/Amman",
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"GTB Standard Time": "Europe/Bucharest",
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"Middle East Standard Time": "Asia/Beirut",
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"Egypt Standard Time": "Africa/Cairo",
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"E. Europe Standard Time": "Europe/Chisinau",
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"Syria Standard Time": "Asia/Damascus",
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"West Bank Standard Time": "Asia/Hebron",
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"South Africa Standard Time": "Africa/Johannesburg",
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"FLE Standard Time": "Europe/Kiev",
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"Israel Standard Time": "Asia/Jerusalem",
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"Kaliningrad Standard Time": "Europe/Kaliningrad",
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"Sudan Standard Time": "Africa/Khartoum",
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"Libya Standard Time": "Africa/Tripoli",
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"Namibia Standard Time": "Africa/Windhoek",
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"Arabic Standard Time": "Asia/Baghdad",
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"Turkey Standard Time": "Europe/Istanbul",
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"Arab Standard Time": "Asia/Riyadh",
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"Belarus Standard Time": "Europe/Minsk",
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"Russian Standard Time": "Europe/Moscow",
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"E. Africa Standard Time": "Africa/Nairobi",
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"Volgograd Standard Time": "Europe/Volgograd",
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"Iran Standard Time": "Asia/Tehran",
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"Arabian Standard Time": "Asia/Dubai",
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"Astrakhan Standard Time": "Europe/Astrakhan",
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"Azerbaijan Standard Time": "Asia/Baku",
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"Russia Time Zone 3": "Europe/Samara",
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"Mauritius Standard Time": "Indian/Mauritius",
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"Saratov Standard Time": "Europe/Saratov",
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"Georgian Standard Time": "Asia/Tbilisi",
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"Caucasus Standard Time": "Asia/Yerevan",
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"Afghanistan Standard Time": "Asia/Kabul",
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"West Asia Standard Time": "Asia/Tashkent",
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"Ekaterinburg Standard Time": "Asia/Yekaterinburg",
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"Pakistan Standard Time": "Asia/Karachi",
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"Qyzylorda Standard Time": "Asia/Qyzylorda",
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"India Standard Time": "Asia/Calcutta",
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"Sri Lanka Standard Time": "Asia/Colombo",
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"Nepal Standard Time": "Asia/Katmandu",
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"Central Asia Standard Time": "Asia/Almaty",
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"Bangladesh Standard Time": "Asia/Dhaka",
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"Omsk Standard Time": "Asia/Omsk",
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"Myanmar Standard Time": "Asia/Rangoon",
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"SE Asia Standard Time": "Asia/Bangkok",
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"Altai Standard Time": "Asia/Barnaul",
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"W. Mongolia Standard Time": "Asia/Hovd",
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"North Asia Standard Time": "Asia/Krasnoyarsk",
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"N. Central Asia Standard Time": "Asia/Novosibirsk",
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"Tomsk Standard Time": "Asia/Tomsk",
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"China Standard Time": "Asia/Shanghai",
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"North Asia East Standard Time": "Asia/Irkutsk",
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"Singapore Standard Time": "Asia/Singapore",
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"W. Australia Standard Time": "Australia/Perth",
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"Taipei Standard Time": "Asia/Taipei",
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"Ulaanbaatar Standard Time": "Asia/Ulaanbaatar",
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"Aus Central W. Standard Time": "Australia/Eucla",
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"Transbaikal Standard Time": "Asia/Chita",
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"Tokyo Standard Time": "Asia/Tokyo",
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"North Korea Standard Time": "Asia/Pyongyang",
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"Korea Standard Time": "Asia/Seoul",
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"Yakutsk Standard Time": "Asia/Yakutsk",
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"Cen. Australia Standard Time": "Australia/Adelaide",
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"AUS Central Standard Time": "Australia/Darwin",
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"E. Australia Standard Time": "Australia/Brisbane",
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"AUS Eastern Standard Time": "Australia/Sydney",
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"West Pacific Standard Time": "Pacific/Port_Moresby",
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"Tasmania Standard Time": "Australia/Hobart",
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"Vladivostok Standard Time": "Asia/Vladivostok",
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"Lord Howe Standard Time": "Australia/Lord_Howe",
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"Bougainville Standard Time": "Pacific/Bougainville",
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"Russia Time Zone 10": "Asia/Srednekolymsk",
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"Magadan Standard Time": "Asia/Magadan",
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"Norfolk Standard Time": "Pacific/Norfolk",
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"Sakhalin Standard Time": "Asia/Sakhalin",
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"Central Pacific Standard Time": "Pacific/Guadalcanal",
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"Russia Time Zone 11": "Asia/Kamchatka",
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"New Zealand Standard Time": "Pacific/Auckland",
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"UTC+12": "Etc/GMT-12",
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"Fiji Standard Time": "Pacific/Fiji",
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"Kamchatka Standard Time": "Asia/Kamchatka",
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"Chatham Islands Standard Time": "Pacific/Chatham",
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"UTC+13": "Etc/GMT-13",
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"Tonga Standard Time": "Pacific/Tongatapu",
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"Samoa Standard Time": "Pacific/Apia",
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"Line Islands Standard Time": "Pacific/Kiritimati",
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}
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