RFC 8536
The Time Zone Information Format (TZif)
6. Security Considerations
The Time Zone Information Format contains no executable code, and it does not define any extensible areas that could be used to store such code. TZif contains counted arrays of data elements. All counts should be checked when processing TZif objects, to guard against references past the end of the object. TZif provides no confidentiality or integrity protection. Time zone information is normally public and does not call for confidentiality protection. Since time zone information is used in many critical applications, integrity protection may be required and must be provided externally.7. Privacy Considerations
The Time Zone Information Format contains publicly available data, and it does not define any extensible areas that could be used to store private data. As discussed in Section 9 of [RFC7808], transmission of time zone data over an insecure communications channel could leak the past, current, or future location of a device or user. As such, TZif data transmitted over a public communications channel MUST be protected with a confidentiality layer such as that provided by Transport Layer Security (TLS) [RFC8446].8. IANA Considerations
This document defines two media types [RFC6838] for the exchange of data utilizing the Time Zone Information Format.8.1. application/tzif
Type name: application Subtype name: tzif Required parameters: none Optional parameters: none Encoding considerations: binary Security considerations: See Section 6 of RFC 8536.
Interoperability considerations: See Section 4 of RFC 8536. Published specification: This specification. Applications that use this media type: This media type is designed for widespread use by applications that need to use or exchange time zone information, such as the Time Zone Information Compiler (zic) [ZIC] and the GNU C Library [GNU-C]. The Time Zone Distribution Service [RFC7808] can directly use this media type. Fragment identifier considerations: N/A Additional information: Magic number(s): The first 4 octets are 0x54, 0x5A, 0x69, 0x66 File extensions(s): N/A Macintosh file type code(s): N/A Person & email address to contact for further information: Time Zone Database mailing list <tz@iana.org> Intended usage: COMMON Restrictions on usage: N/A Author: See the "Authors' Addresses" section of RFC 8536. Change controller: IETF8.2. application/tzif-leap
Type name: application Subtype name: tzif-leap Required parameters: none Optional parameters: none Encoding considerations: binary Security considerations: See Section 6 of RFC 8536. Interoperability considerations: See Section 4 of RFC 8536. Published specification: This specification.
Applications that use this media type: This media type is designed
for widespread use by applications that need to use or exchange
time zone information, such as the Time Zone Information Compiler
(zic) [ZIC] and the GNU C Library [GNU-C]. The Time Zone
Distribution Service [RFC7808] can directly use this media type.
Fragment identifier considerations: N/A
Additional information:
Magic number(s): The first 4 octets are 0x54, 0x5A, 0x69, 0x66
File extensions(s): N/A
Macintosh file type code(s): N/A
Person & email address to contact for further information:
Time Zone Database mailing list <tz@iana.org>
Intended usage: COMMON
Restrictions on usage: N/A
Author: See the "Authors' Addresses" section of RFC 8536.
Change controller: IETF
9. References
9.1. Normative References
[GNU-C] "The GNU C Library (glibc)",
<https://www.gnu.org/software/libc/>.
[POSIX] IEEE, "Standard for Information Technology--Portable
Operating System Interface (POSIX(R)) Base
Specifications, Issue 7", IEEE 1003.1-2017,
DOI 10.1109/IEEESTD.2018.8277153, January 2018,
<http://pubs.opengroup.org/onlinepubs/9699919799/>.
[RFC20] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<https://www.rfc-editor.org/info/rfc20>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, <https://www.rfc-editor.org/info/rfc6838>. [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, June 2014, <https://www.rfc-editor.org/info/rfc7231>. [RFC7808] Douglass, M. and C. Daboo, "Time Zone Data Distribution Service", RFC 7808, DOI 10.17487/RFC7808, March 2016, <https://www.rfc-editor.org/info/rfc7808>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>. [ZIC] Kerrisk, M., "ZIC(8)", man-pages release 4.16, February 2010, <http://man7.org/linux/man-pages/man8/zic.8.html>.9.2. Informative References
[EGGERT-TZ] "History for tz", October 2018, <https://github.com/eggert/tz/commits/master/tzfile.5>. [RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 5545, DOI 10.17487/RFC5545, September 2009, <https://www.rfc-editor.org/info/rfc5545>. [RFC6557] Lear, E. and P. Eggert, "Procedures for Maintaining the Time Zone Database", BCP 175, RFC 6557, DOI 10.17487/RFC6557, February 2012, <https://www.rfc-editor.org/info/rfc6557>. [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/info/rfc8446>. [tz-link] Eggert, P. and A. Olson, "Sources for Time Zone and Daylight Saving Time Data", 2018, <https://www.iana.org/time-zones/repository/ tz-link.html>.
Appendix A. Common Interoperability Issues
This section documents common problems in implementing this specification. Most of these are problems in generating TZif files for use by readers conforming to predecessors of this specification [EGGERT-TZ]. The goals of this section are: 1. to help TZif writers output files that avoid common pitfalls in older or buggy TZif readers, 2. to help TZif readers avoid common pitfalls when reading files generated by future TZif writers, and 3. to help any future specification authors see what sort of problems arise when the TZif format is changed. When new versions of the TZif format have been defined, a design goal has been that a reader can successfully use a TZif file even if the file is of a later TZif version than what the reader was designed for. When complete compatibility was not achieved, an attempt was made to limit glitches to rarely used timestamps and allow simple partial workarounds in writers designed to generate new-version data useful even for older-version readers. This section attempts to document these compatibility issues and workarounds, as well as documenting other common bugs in readers. Interoperability problems with TZif include the following: o Some readers examine only version 1 data. As a partial workaround, a writer can output as much version 1 data as possible. However, a reader should ignore version 1 data and use version 2+ data, even if the reader's native timestamps have only 32 bits. o Some readers designed for version 2 might mishandle timestamps after a version 3 file's last transition, because they cannot parse extensions to POSIX in the TZ-like string. As a partial workaround, a writer can output more transitions than necessary, so that only far-future timestamps are mishandled by version 2 readers. o Some readers designed for version 2 do not support permanent daylight saving time -- e.g., a TZ string "EST5EDT,0/0,J365/25" denoting permanent Eastern Daylight Time (-04). As a partial workaround, a writer can substitute standard time for the next time zone east -- e.g., "AST4" for permanent Atlantic Standard Time (-04).
o Some readers ignore the footer and instead predict future
timestamps from the time type of the last transition. As a
partial workaround, a writer can output more transitions than
necessary.
o Some readers do not use time type 0 for timestamps before the
first transition, in that they infer a time type using a heuristic
that does not always select time type 0. As a partial workaround,
a writer can output a dummy (no-op) first transition at an early
time.
o Some readers mishandle timestamps before the first transition that
has a timestamp not less than -2**31. Readers that support only
32-bit timestamps are likely to be more prone to this problem, for
example, when they process 64-bit transitions, only some of which
are representable in 32 bits. As a partial workaround, a writer
can output a dummy transition at timestamp -2**31.
o Some readers mishandle a transition if its timestamp has the
minimum possible signed 64-bit value. Timestamps less than -2**59
are not recommended.
o Some readers mishandle POSIX-style TZ strings that contain "<" or
">". As a partial workaround, a writer can avoid using '<' or '>'
for time zone abbreviations containing only alphabetic characters.
o Many readers mishandle time zone abbreviations that contain non-
ASCII characters. These characters are not recommended.
o Some readers may mishandle time zone abbreviations that contain
fewer than 3 or more than 6 characters, or that contain ASCII
characters other than alphanumerics, '-', and '+'. These
abbreviations are not recommended.
o Some readers mishandle TZif files that specify daylight saving
time UT offsets that are less than the UT offsets for the
corresponding standard time. These readers do not support
locations like Ireland, which uses the equivalent of the POSIX TZ
string "IST-1GMT0,M10.5.0,M3.5.0/1", observing standard time (IST,
+01) in summer and daylight saving time (GMT, +00) in winter. As
a partial workaround, a writer can output data for the equivalent
of the POSIX TZ string "GMT0IST,M3.5.0/1,M10.5.0", thus swapping
standard and daylight saving time. Although this workaround
misidentifies which part of the year uses daylight saving time, it
records UT offsets and time zone abbreviations correctly.
Some interoperability problems are reader bugs that are listed here
mostly as warnings to developers of readers.
o Some readers do not support negative timestamps. Developers of
distributed applications should keep this in mind if they need to
deal with pre-1970 data.
o Some readers mishandle timestamps before the first transition that
has a nonnegative timestamp. Readers that do not support negative
timestamps are likely to be more prone to this problem.
o Some readers mishandle time zone abbreviations like "-08" that
contain '+', '-', or digits.
o Some readers mishandle UT offsets that are out of the traditional
range of -12 through +12 hours and so do not support locations
like Kiritimati that are outside this range.
o Some readers mishandle UT offsets in the range [-3599, -1] seconds
from UT, because they integer-divide the offset by 3600 to get 0
and then display the hour part as "+00".
o Some readers mishandle UT offsets that are not a multiple of one
hour, 15 minutes, or 1 minute.
Appendix B. Example TZif Files
The following sections contain annotated hexadecimal dumps of example
TZif files.
Note that these examples should only be considered informative.
Although the example data entries are current as of the publication
date of this document, the data will likely change in the future as
leap seconds are added and changes are made to civil time.
B.1. Version 1 File Representing UTC (with Leap Seconds)
+-------+---------------+------------------+------------------------+ | File | Data Octets | Record Name / | Field Value | | Offset| (hexadecimal) | Field Name | | +-------+---------------+------------------+------------------------+ | 000 | 54 5a 69 66 | magic | "TZif" | | 004 | 00 | version | 0 (1) | | 005 | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 | | | | 020 | 00 00 00 01 | isutccnt | 1 | | 024 | 00 00 00 01 | isstdcnt | 1 | | 028 | 00 00 00 1b | isleapcnt | 27 | | 032 | 00 00 00 00 | timecnt | 0 | | 036 | 00 00 00 01 | typecnt | 1 | | 040 | 00 00 00 04 | charcnt | 4 | | | | | | | | | localtimetype[0] | | | 044 | 00 00 00 00 | utcoff | 00:00 | | 048 | 00 | isdst | 0 (no) | | 049 | 00 | desigidx | 0 | | | | | | | 050 | 55 54 43 00 | designations[0] | "UTC" | | | | | | | | | leapsecond[0] | | | 054 | 04 b2 58 00 | occurrence | 78796800 | | | | | (1972-06-30T23:59:60Z) | | 058 | 00 00 00 01 | correction | 1 | | | | | | | | | leapsecond[1] | | | 062 | 05 a4 ec 01 | occurrence | 94694401 | | | | | (1972-12-31T23:59:60Z) | | 066 | 00 00 00 02 | correction | 2 | | | | | | | | | leapsecond[2] | | | 070 | 07 86 1f 82 | occurrence | 126230402 | | | | | (1973-12-31T23:59:60Z) | | 074 | 00 00 00 03 | correction | 3 | | | | | | | | | leapsecond[3] | | | 078 | 09 67 53 03 | occurrence | 157766403 | | | | | (1974-12-31T23:59:60Z) | | 082 | 00 00 00 04 | correction | 4 | | | | | |
| | | leapsecond[4] | | | 086 | 0b 48 86 84 | occurrence | 189302404 | | | | | (1975-12-31T23:59:60Z) | | 090 | 00 00 00 05 | correction | 5 | | | | | | | | | leapsecond[5] | | | 094 | 0d 2b 0b 85 | occurrence | 220924805 | | | | | (1976-12-31T23:59:60Z) | | 098 | 00 00 00 06 | correction | 6 | | | | | | | | | leapsecond[6] | | | 102 | 0f 0c 3f 06 | occurrence | 252460806 | | | | | (1977-12-31T23:59:60Z) | | 106 | 00 00 00 07 | correction | 7 | | | | | | | | | leapsecond[7] | | | 110 | 10 ed 72 87 | occurrence | 283996807 | | | | | (1978-12-31T23:59:60Z) | | 114 | 00 00 00 08 | correction | 8 | | | | | | | | | leapsecond[8] | | | 118 | 12 ce a6 08 | occurrence | 315532808 | | | | | (1979-12-31T23:59:60Z) | | 122 | 00 00 00 09 | correction | 9 | | | | | | | | | leapsecond[9] | | | 126 | 15 9f ca 89 | occurrence | 362793609 | | | | | (1981-06-30T23:59:60Z) | | 130 | 00 00 00 0a | correction | 10 | | | | | | | | | leapsecond[10] | | | 134 | 17 80 fe 0a | occurrence | 394329610 | | | | | (1982-06-30T23:59:60Z) | | 138 | 00 00 00 0b | correction | 11 | | | | | | | | | leapsecond[11] | | | 142 | 19 62 31 8b | occurrence | 425865611 | | | | | (1983-06-30T23:59:60Z) | | 146 | 00 00 00 0c | correction | 12 | | | | | | | | | leapsecond[12] | | | 150 | 1d 25 ea 0c | occurrence | 489024012 | | | | | (1985-06-30T23:59:60Z) | | 154 | 00 00 00 0d | correction | 13 | | | | | | | | | leapsecond[13] | | | 158 | 21 da e5 0d | occurrence | 567993613 | | | | | (1987-12-31T23:59:60Z) |
| 162 | 00 00 00 0e | correction | 14 | | | | | | | | | leapsecond[14] | | | 166 | 25 9e 9d 8e | occurrence | 631152014 | | | | | (1989-12-31T23:59:60Z) | | 170 | 00 00 00 0f | correction | 15 | | | | | | | | | leapsecond[15] | | | 174 | 27 7f d1 0f | occurrence | 662688015 | | | | | (1990-12-31T23:59:60Z) | | 178 | 00 00 00 10 | correction | 16 | | | | | | | | | leapsecond[16] | | | 182 | 2a 50 f5 90 | occurrence | 709948816 | | | | | (1992-06-30T23:59:60Z) | | 186 | 00 00 00 11 | correction | 17 | | | | | | | | | leapsecond[17] | | | 190 | 2c 32 29 11 | occurrence | 741484817 | | | | | (1993-06-30T23:59:60Z) | | 194 | 00 00 00 12 | correction | 18 | | | | | | | | | leapsecond[18] | | | 198 | 2e 13 5c 92 | occurrence | 773020818 | | | | | (1994-06-30T23:59:60Z) | | 202 | 00 00 00 13 | correction | 19 | | | | | | | | | leapsecond[19] | | | 206 | 30 e7 24 13 | occurrence | 820454419 | | | | | (1995-12-31T23:59:60Z) | | 210 | 00 00 00 14 | correction | 20 | | | | | | | | | leapsecond[20] | | | 214 | 33 b8 48 94 | occurrence | 867715220 | | | | | (1997-06-30T23:59:60Z) | | 218 | 00 00 00 15 | correction | 21 | | | | | | | | | leapsecond[21] | | | 222 | 36 8c 10 15 | occurrence | 915148821 | | | | | (1998-12-31T23:59:60Z) | | 226 | 00 00 00 16 | correction | 22 | | | | | | | | | leapsecond[22] | | | 230 | 43 b7 1b 96 | occurrence | 1136073622 | | | | | (2005-12-31T23:59:60Z) | | 234 | 00 00 00 17 | correction | 23 | | | | | |
| | | leapsecond[23] | |
| 238 | 49 5c 07 97 | occurrence | 1230768023 |
| | | | (2008-12-31T23:59:60Z) |
| 242 | 00 00 00 18 | correction | 24 |
| | | | |
| | | leapsecond[24] | |
| 246 | 4f ef 93 18 | occurrence | 1341100824 |
| | | | (2012-06-30T23:59:60Z) |
| 250 | 00 00 00 19 | correction | 25 |
| | | | |
| | | leapsecond[25] | |
| 254 | 55 93 2d 99 | occurrence | 1435708825 |
| | | | (2015-06-30T23:59:60Z) |
| 258 | 00 00 00 1a | correction | 26 |
| | | | |
| | | leapsecond[26] | |
| 262 | 58 68 46 9a | occurrence | 1483228826 |
| | | | (2016-12-31T23:59:60Z) |
| 266 | 00 00 00 1b | correction | 27 |
| | | | |
| 270 | 00 | UT/local[0] | 0 (local) |
| | | | |
| 271 | 00 | standard/wall[0] | 0 (wall) |
+-------+---------------+------------------+------------------------+
To determine TAI corresponding to 2000-01-01T00:00:00Z
(UNIX time = 946684800), the following procedure would be followed:
1. Find the latest leap-second occurrence prior to the time of
interest (leapsecond[21]) and note the correction value
(LEAPCORR = 22).
2. Add LEAPCORR + 10 to the time of interest to yield TAI of
2000-01-01T00:00:32.
B.2. Version 2 File Representing Pacific/Honolulu
+--------+--------------+------------------+------------------------+ | File | Hexadecimal | Record Name / | Field Value | | Offset | Octets | Field Name | | +--------+--------------+------------------+------------------------+ | 000 | 54 5a 69 66 | magic | "TZif" | | 004 | 32 | version | '2' (2) | | 005 | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 | | | | 020 | 00 00 00 06 | isutccnt | 6 | | 024 | 00 00 00 06 | isstdcnt | 6 | | 028 | 00 00 00 00 | isleapcnt | 0 | | 032 | 00 00 00 07 | timecnt | 7 | | 036 | 00 00 00 06 | typecnt | 6 | | 040 | 00 00 00 14 | charcnt | 20 | | | | | | | 044 | 80 00 00 00 | trans time[0] | -2147483648 | | | | | (1901-12-13T20:45:52Z) | | 048 | bb 05 43 48 | trans time[1] | -1157283000 | | | | | (1933-04-30T12:30:00Z) | | 052 | bb 21 71 58 | trans time[2] | -1155436200 | | | | | (1933-05-21T21:30:00Z) | | 056 | cb 89 3d c8 | trans time[3] | -880198200 | | | | | (1942-02-09T12:30:00Z) | | 060 | d2 23 f4 70 | trans time[4] | -769395600 | | | | | (1945-08-14T23:00:00Z) | | 064 | d2 61 49 38 | trans time[5] | -765376200 | | | | | (1945-09-30T11:30:00Z) | | 068 | d5 8d 73 48 | trans time[6] | -712150200 | | | | | (1947-06-08T12:30:00Z) | | | | | | | 072 | 01 | trans type[0] | 1 | | 073 | 02 | trans type[1] | 2 | | 074 | 01 | trans type[2] | 1 | | 075 | 03 | trans type[3] | 3 | | 076 | 04 | trans type[4] | 4 | | 077 | 01 | trans type[5] | 1 | | 078 | 05 | trans type[6] | 5 | | | | | | | | | localtimetype[0] | | | 079 | ff ff 6c 02 | utcoff | -37886 (-10:21:26) | | 083 | 00 | isdst | 0 (no) | | 084 | 00 | desigidx | 0 | | | | | |
| | | localtimetype[1] | | | 085 | ff ff 6c 58 | utcoff | -37800 (-10:30) | | 089 | 00 | isdst | 0 (no) | | 090 | 04 | desigidx | 4 | | | | | | | | | localtimetype[2] | | | 091 | ff ff 7a 68 | utcoff | -34200 (-09:30) | | 095 | 01 | isdst | 1 (yes) | | 096 | 08 | desigidx | 8 | | | | | | | | | localtimetype[3] | | | 097 | ff ff 7a 68 | utcoff | -34200 (-09:30) | | 101 | 01 | isdst | 1 (yes) | | 102 | 0c | desigidx | 12 | | | | | | | | | localtimetype[4] | | | 103 | ff ff 7a 68 | utcoff | -34200 (-09:30) | | 107 | 01 | isdst | 1 (yes) | | 108 | 10 | desigidx | 16 | | | | | | | | | localtimetype[5] | | | 109 | ff ff 73 60 | utcoff | -36000 (-10:00) | | 113 | 00 | isdst | 0 (no) | | 114 | 04 | desigidx | 4 | | | | | | | 115 | 4c 4d 54 00 | designations[0] | "LMT" | | 119 | 48 53 54 00 | designations[4] | "HST" | | 123 | 48 44 54 00 | designations[8] | "HDT" | | 127 | 48 57 54 00 | designations[12] | "HWT" | | 131 | 48 50 54 00 | designations[16] | "HPT" | | | | | | | 135 | 00 | UT/local[0] | 1 (UT) | | 136 | 00 | UT/local[1] | 0 (local) | | 137 | 00 | UT/local[2] | 0 (local) | | 138 | 00 | UT/local[3] | 0 (local) | | 139 | 01 | UT/local[4] | 1 (UT) | | 140 | 00 | UT/local[5] | 0 (local) | | | | | | | 141 | 00 | standard/wall[0] | 1 (standard) | | 142 | 00 | standard/wall[1] | 0 (wall) | | 143 | 00 | standard/wall[2] | 0 (wall) | | 144 | 00 | standard/wall[3] | 0 (wall) | | 145 | 01 | standard/wall[4] | 1 (standard) | | 146 | 00 | standard/wall[5] | 0 (wall) | | | | | | | 147 | 54 5a 69 66 | magic | "TZif" | | 151 | 32 | version | '2' (2) |
| 152 | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 | | | | 167 | 00 00 00 06 | isutccnt | 6 | | 171 | 00 00 00 06 | isstdcnt | 6 | | 175 | 00 00 00 00 | isleapcnt | 0 | | 179 | 00 00 00 07 | timecnt | 7 | | 183 | 00 00 00 06 | typecnt | 6 | | 187 | 00 00 00 14 | charcnt | 20 | | | | | | | 191 | ff ff ff ff | trans time[0] | -2334101314 | | | 74 e0 70 be | | (1896-01-13T22:31:26Z) | | 199 | ff ff ff ff | trans time[1] | -1157283000 | | | bb 05 43 48 | | (1933-04-30T12:30:00Z) | | 207 | ff ff ff ff | trans time[2] | -1155436200 | | | bb 21 71 58 | | (1933-05-21T21:30:00Z) | | 215 | ff ff ff ff | trans time[3] | -880198200 | | | cb 89 3d c8 | | (1942-02-09T12:30:00Z) | | 223 | ff ff ff ff | trans time[4] | -769395600 | | | d2 23 f4 70 | | (1945-08-14T23:00:00Z) | | 231 | ff ff ff ff | trans time[5] | -765376200 | | | d2 61 49 38 | | (1945-09-30T11:30:00Z) | | 239 | ff ff ff ff | trans time[6] | -712150200 | | | d5 8d 73 48 | | (1947-06-08T12:30:00Z) | | | | | | | 247 | 01 | trans type[0] | 1 | | 248 | 02 | trans type[1] | 2 | | 249 | 01 | trans type[2] | 1 | | 250 | 03 | trans type[3] | 3 | | 251 | 04 | trans type[4] | 4 | | 252 | 01 | trans type[5] | 1 | | 253 | 05 | trans type[6] | 5 | | | | | | | | | localtimetype[0] | | | 254 | ff ff 6c 02 | utcoff | -37886 (-10:21:26) | | 258 | 00 | isdst | 0 (no) | | 259 | 00 | desigidx | 0 | | | | | | | | | localtimetype[1] | | | 260 | ff ff 6c 58 | utcoff | -37800 (-10:30) | | 264 | 00 | isdst | 0 (no) | | 265 | 04 | desigidx | 4 | | | | | | | | | localtimetype[2] | | | 266 | ff ff 7a 68 | utcoff | -34200 (-09:30) | | 270 | 01 | isdst | 1 (yes) | | 271 | 08 | desigidx | 8 |
| | | | | | | | localtimetype[3] | | | 272 | ff ff 7a 68 | utcoff | -34200 (-09:30) | | 276 | 01 | isdst | 1 (yes) | | 277 | 0c | desigidx | 12 | | | | | | | | | localtimetype[4] | | | 278 | ff ff 7a 68 | utcoff | -34200 (-09:30) | | 282 | 01 | isdst | 1 (yes) | | 283 | 10 | desigidx | 16 | | | | | | | | | localtimetype[5] | | | 284 | ff ff 73 60 | utcoff | -36000 (-10:00) | | 288 | 00 | isdst | 0 (no) | | 289 | 04 | desigidx | 4 | | | | | | | 290 | 4c 4d 54 00 | designations[0] | "LMT" | | 294 | 48 53 54 00 | designations[4] | "HST" | | 298 | 48 44 54 00 | designations[8] | "HDT" | | 302 | 48 57 54 00 | designations[12] | "HWT" | | 306 | 48 50 54 00 | designations[16] | "HPT" | | | | | | | 310 | 00 | UT/local[0] | 0 (local) | | 311 | 00 | UT/local[1] | 0 (local) | | 312 | 00 | UT/local[2] | 0 (local) | | 313 | 00 | UT/local[3] | 0 (local) | | 314 | 01 | UT/local[4] | 1 (UT) | | 315 | 00 | UT/local[5] | 0 (local) | | | | | | | 316 | 00 | standard/wall[0] | 0 (wall) | | 317 | 00 | standard/wall[1] | 0 (wall) | | 318 | 00 | standard/wall[2] | 0 (wall) | | 319 | 00 | standard/wall[3] | 0 (wall) | | 320 | 01 | standard/wall[4] | 1 (standard) | | 321 | 00 | standard/wall[5] | 0 (wall) | | | | | | | 322 | 0a | NL | '\n' | | 323 | 48 53 54 31 | TZ string | "HST10" | | | 30 | | | | 328 | 0a | NL | '\n' | +--------+--------------+------------------+------------------------+
To determine the local time in this time zone corresponding to
1933-05-04T12:00:00Z (UNIX time = -1156939200), the following
procedure would be followed:
1. Find the latest time transition prior to the time of interest
(trans time[1]).
2. Reference the corresponding transition type (trans type[1]) to
determine the local time type index (2).
3. Reference the corresponding local time type (localtimetype[2]) to
determine the offset from UTC (-09:30), the daylight saving
indicator (1 = yes), and the index into the time zone designation
strings (8).
4. Look up the corresponding time zone designation string
(designations[8] = "HDT").
5. Add the UTC offset to the time of interest to yield a local
daylight saving time of 1933-05-04T02:30:00-09:30 (HDT).
To determine the local time in this time zone corresponding to
2019-01-01T00:00:00Z (UNIX time = 1546300800), the following
procedure would be followed:
1. Find the latest time transition prior to the time of interest
(there is no such transition).
2. Look up the TZ string in the footer ("HST10"), which indicates
that the time zone designation is "HST" year-round, and the
offset to UTC is 10:00.
3. Subtract the UTC offset from the time of interest to yield a
standard local time of 2018-12-31T14:00:00-10:00 (HST).
B.3. Truncated Version 3 File Representing Asia/Jerusalem
The following TZif file has been truncated to start on 2038-01-01T00:00:00Z. +--------+--------------+------------------+------------------------+ | File | Hexadecimal | Record Name / | Field Value | | Offset | Octets | Field Name | | +--------+--------------+------------------+------------------------+ | 000 | 54 5a 69 66 | magic | "TZif" | | 004 | 33 | version | '3' (3) | | 005 | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 | | | | 020 | 00 00 00 00 | isutccnt | 0 | | 024 | 00 00 00 00 | isstdcnt | 0 | | 028 | 00 00 00 00 | isleapcnt | 0 | | 032 | 00 00 00 00 | timecnt | 0 | | 036 | 00 00 00 00 | typecnt | 0 | | 040 | 00 00 00 00 | charcnt | 0 | | | | | | | 044 | 54 5a 69 66 | magic | "TZif" | | 048 | 33 | version | '3' (3) | | 049 | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 | | | | 064 | 00 00 00 03 | isutccnt | 1 | | 068 | 00 00 00 03 | isstdcnt | 1 | | 072 | 00 00 00 00 | isleapcnt | 0 | | 076 | 00 00 00 03 | timecnt | 1 | | 080 | 00 00 00 03 | typecnt | 1 | | 084 | 00 00 00 08 | charcnt | 4 | | | | | | | 088 | 00 00 00 00 | trans time[0] | 2145916800 | | | 7f e8 17 80 | | (2038-01-01T00:00:00Z) | | | | | | | 096 | 00 | trans type[0] | 0 | | | | | | | | | localtimetype[0] | | | 097 | 00 00 1c 20 | utcoff | 7200 (+02:00) | | 101 | 00 | isdst | 0 (no) | | 102 | 00 | desigidx | 0 | | | | | | | 103 | 49 53 54 00 | designations[0] | "IST" | | | | | | | 107 | 01 | UT/local[0] | 1 (UT) |
| | | | | | 108 | 01 | standard/wall[0] | 1 (standard) | | | | | | | 109 | 0a | NL | '\n' | | 110 | 49 53 54 2d | TZ string | "IST-2IDT, | | | 32 49 44 54 | | M3.4.4/26,M10.5.0" | | | 2c 4d 33 2e | | | | | 34 2e 34 2f | | | | | 32 36 2c 4d | | | | | 31 30 2e 35 | | | | | 2e 30 | | | | 136 | 0a | NL | '\n' | +--------+--------------+------------------+------------------------+Acknowledgments
The authors would like to thank the following individuals for contributing their ideas and support for writing this specification: Michael Douglass, Ned Freed, Guy Harris, Eliot Lear, and Alexey Melnikov.Authors' Addresses
Arthur David Olson Email: arthurdavidolson@gmail.com Paul Eggert University of California, Los Angeles Email: eggert@cs.ucla.edu Kenneth Murchison FastMail US LLC Email: murch@fastmailteam.com