rfc8536.txt   draft-murchison-rfc8536bis-02.txt >
Internet Engineering Task Force (IETF) A. Olson Internet Engineering Task Force (IETF) A.D. Olson
Request for Comments: 8536 Internet-Draft
Category: Standards Track P. Eggert Obsoletes: 8536 (if approved) P. Eggert
ISSN: 2070-1721 UCLA Intended status: Standards Track UCLA
K. Murchison Expires: 23 March 2022 K. Murchison
FastMail Fastmail
February 2019 19 September 2021
The Time Zone Information Format (TZif) The Time Zone Information Format (TZif)
draft-murchison-rfc8536bis-02
Abstract Abstract
This document specifies the Time Zone Information Format (TZif) for This document specifies the Time Zone Information Format (TZif) for
representing and exchanging time zone information, independent of any representing and exchanging time zone information, independent of any
particular service or protocol. Two media types for this format are particular service or protocol. Two media types for this format are
also defined. also defined.
This document replaces and obsoletes RFC 8536.
Status of This Memo Status of This Memo
This is an Internet Standards Track document. This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
This document is a product of the Internet Engineering Task Force Internet-Drafts are working documents of the Internet Engineering
(IETF). It represents the consensus of the IETF community. It has Task Force (IETF). Note that other groups may also distribute
received public review and has been approved for publication by the working documents as Internet-Drafts. The list of current Internet-
Internet Engineering Steering Group (IESG). Further information on Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata, Internet-Drafts are draft documents valid for a maximum of six months
and how to provide feedback on it may be obtained at and may be updated, replaced, or obsoleted by other documents at any
https://www.rfc-editor.org/info/rfc8536. time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 23 March 2022.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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carefully, as they describe your rights and restrictions with respect and restrictions with respect to this document. Code Components
to this document. Code Components extracted from this document must extracted from this document must include Simplified BSD License text
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described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. The Time Zone Information Format (TZif) . . . . . . . . . . . 5 3. The Time Zone Information Format (TZif) . . . . . . . . . . . 5
3.1. TZif Header . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. TZif Header . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. TZif Data Block . . . . . . . . . . . . . . . . . . . . . 8 3.2. TZif Data Block . . . . . . . . . . . . . . . . . . . . . 8
3.3. TZif Footer . . . . . . . . . . . . . . . . . . . . . . . 12 3.3. TZif Footer . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.1. TZ String Extensions . . . . . . . . . . . . . . . . 13 3.3.1. TZ String Extensions . . . . . . . . . . . . . . . . 12
4. Interoperability Considerations . . . . . . . . . . . . . . . 13 4. Interoperability Considerations . . . . . . . . . . . . . . . 13
5. Use with the Time Zone Data Distribution Service . . . . . . 14 5. Use with the Time Zone Data Distribution Service . . . . . . 14
5.1. Truncating TZif Files . . . . . . . . . . . . . . . . . . 15 5.1. Truncating TZif Files . . . . . . . . . . . . . . . . . . 15
5.2. Example TZDIST Request for TZif Data . . . . . . . . . . 15 5.2. Example TZDIST Request for TZif Data . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 17 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8.1. application/tzif . . . . . . . . . . . . . . . . . . . . 17 8.1. application/tzif . . . . . . . . . . . . . . . . . . . . 18
8.2. application/tzif-leap . . . . . . . . . . . . . . . . . . 18 8.2. application/tzif-leap . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
9.1. Normative References . . . . . . . . . . . . . . . . . . 19 9.1. Normative References . . . . . . . . . . . . . . . . . . 21
9.2. Informative References . . . . . . . . . . . . . . . . . 20 9.2. Informative References . . . . . . . . . . . . . . . . . 22
Appendix A. Common Interoperability Issues . . . . . . . . . . . 21 Appendix A. Common Interoperability Issues . . . . . . . . . . . 22
Appendix B. Example TZif Files . . . . . . . . . . . . . . . . . 23 Appendix B. Example TZif Files . . . . . . . . . . . . . . . . . 25
B.1. Version 1 File Representing UTC (with Leap Seconds) . . . 24 B.1. Version 1 File Representing UTC (with Leap Seconds) . . . 25
B.2. Version 2 File Representing Pacific/Honolulu . . . . . . 28 B.2. Version 2 File Representing Pacific/Honolulu . . . . . . 31
B.3. Truncated Version 3 File Representing Asia/Jerusalem . . 33 B.3. Truncated Version 3 File Representing Asia/Jerusalem . . 38
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 34 B.4. Truncated Version 4 File Representing America/New_York . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 Appendix C. Changes from RFC 8536 . . . . . . . . . . . . . . . 44
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 44
D.1. Since rfc8536bis-01 . . . . . . . . . . . . . . . . . . . 44
D.2. Since rfc8536bis-00 . . . . . . . . . . . . . . . . . . . 44
D.3. Since RFC 8536 . . . . . . . . . . . . . . . . . . . . . 45
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45
1. Introduction 1. Introduction
Time zone data typically consists of offsets from universal time Time zone data typically consists of offsets from universal time
(UT), daylight saving transition rules, one or more local time (UT), daylight saving transition rules, one or more local time
designations (acronyms or abbreviations), and optional leap-second designations (acronyms or abbreviations), and optional leap-second
adjustments. One such format for conveying this information is adjustments. One such format for conveying this information is
iCalendar [RFC5545]. It is a text-based format used by calendaring iCalendar [RFC5545]. It is a text-based format used by calendaring
and scheduling systems. and scheduling systems.
skipping to change at page 3, line 25 skipping to change at page 3, line 16
Format (TZif). It is a binary format used by most UNIX systems to Format (TZif). It is a binary format used by most UNIX systems to
calculate local time. This format was introduced in the 1980s and calculate local time. This format was introduced in the 1980s and
has evolved since then into multiple upward-compatible versions. has evolved since then into multiple upward-compatible versions.
There is a wide variety of interoperable software capable of There is a wide variety of interoperable software capable of
generating and reading files in this format [tz-link]. generating and reading files in this format [tz-link].
This specification does not define the source of the data assembled This specification does not define the source of the data assembled
into a TZif file. One such source is the IANA-hosted time zone into a TZif file. One such source is the IANA-hosted time zone
database [RFC6557]. database [RFC6557].
This document obsoletes RFC 8536, providing editorial improvements,
new details, and errata fixes while keeping full compatibility with
the interchange format of RFC 8536. Additionally, a new version of
the format is defined. The changes from RFC 8536 are summarized in
Appendix C.
2. Conventions Used in This Document 2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
The following terms are used in this document (see "Sources for Time The following terms are used in this document (see "Sources for Time
Zone and Daylight Saving Time Data" [tz-link] for more detailed Zone and Daylight Saving Time Data" [tz-link] for more detailed
skipping to change at page 5, line 46 skipping to change at page 5, line 44
The version 1 header is followed by a variable-length version 1 data The version 1 header is followed by a variable-length version 1 data
block (Section 3.2) containing four-octet (32-bit) transition times block (Section 3.2) containing four-octet (32-bit) transition times
and leap-second occurrences. These 32-bit values are limited to and leap-second occurrences. These 32-bit values are limited to
representing time changes from 1901-12-13 20:45:52 through 2038-01-19 representing time changes from 1901-12-13 20:45:52 through 2038-01-19
03:14:07 UT, and the version 1 header and data block are present only 03:14:07 UT, and the version 1 header and data block are present only
for backward compatibility with obsolescent readers, as discussed in for backward compatibility with obsolescent readers, as discussed in
Common Interoperability Issues (Appendix A). Common Interoperability Issues (Appendix A).
Version 1 files terminate after the version 1 data block. Files from Version 1 files terminate after the version 1 data block. Files from
versions 2 and 3 extend the format by appending a second 44-octet versions 2 and higher extend the format by appending a second
version 2+ header, a variable-length version 2+ data block containing 44-octet version 2+ header, a variable-length version 2+ data block
eight-octet (64-bit) transition times and leap-second occurrences, containing eight-octet (64-bit) transition times and leap-second
and a variable-length footer (Section 3.3). These 64-bit values can occurrences, and a variable-length footer (Section 3.3). These
represent times approximately 292 billion years into the past or 64-bit values can represent times approximately 292 billion years
future. into the past or future.
NOTE: All multi-octet integer values MUST be stored in network octet NOTE: All multi-octet integer values MUST be stored in network octet
order format (high-order octet first, otherwise known as big-endian), order format (high-order octet first, otherwise known as big-endian),
with all bits significant. Signed integer values MUST be represented with all bits significant. Signed integer values MUST be represented
using two's complement. using two's complement.
A TZif file is structured as follows: A TZif file is structured as follows:
Version 1 Versions 2 & 3 Version 1 Versions 2+
+-------------+ +-------------+ +-------------+ +-------------+
| Version 1 | | Version 1 | | Version 1 | | Version 1 |
| Header | | Header | | Header | | Header |
+-------------+ +-------------+ +-------------+ +-------------+
| Version 1 | | Version 1 | | Version 1 | | Version 1 |
| Data Block | | Data Block | | Data Block | | Data Block |
+-------------+ +-------------+ +-------------+ +-------------+
| Version 2+ | | Version 2+ |
| Header | | Header |
+-------------+ +-------------+
| Version 2+ | | Version 2+ |
| Data Block | | Data Block |
+-------------+ +-------------+
| Footer | | Footer |
+-------------+ +-------------+
General Format of TZif Files Figure 1: General Format of TZif Files
3.1. TZif Header 3.1. TZif Header
A TZif header is structured as follows (the lengths of multi-octet A TZif header is structured as follows (the lengths of multi-octet
fields are shown in parentheses): fields are shown in parentheses):
+---------------+---+ +---------------+---+
| magic (4) |ver| | magic (4) |ver|
+---------------+---+---------------------------------------+ +---------------+---+---------------------------------------+
| [unused - reserved for future use] (15) | | [unused - reserved for future use] (15) |
+---------------+---------------+---------------+-----------+ +---------------+---------------+---------------+-----------+
| isutcnt (4) | isstdcnt (4) | leapcnt (4) | | isutcnt (4) | isstdcnt (4) | leapcnt (4) |
+---------------+---------------+---------------+ +---------------+---------------+---------------+
| timecnt (4) | typecnt (4) | charcnt (4) | | timecnt (4) | typecnt (4) | charcnt (4) |
+---------------+---------------+---------------+ +---------------+---------------+---------------+
TZif Header Figure 2: TZif Header
The fields of the header are defined as follows: The fields of the header are defined as follows:
magic: The four-octet ASCII [RFC20] sequence "TZif" (0x54 0x5A 0x69 magic: The four-octet ASCII [RFC20] sequence "TZif" (0x54 0x5A 0x69
0x66), which identifies the file as utilizing the Time Zone 0x66), which identifies the file as utilizing the Time Zone
Information Format. Information Format.
ver(sion): An octet identifying the version of the file's format. ver(sion): An octet identifying the version of the file's format.
The value MUST be one of the following: The value MUST be one of the following:
NUL (0x00) Version 1 - The file contains only the version 1 NUL (0x00) Version 1 - The file contains only the version 1
header and data block. Version 1 files MUST NOT contain a header and data block. Version 1 files MUST NOT contain a
version 2+ header, data block, or footer. version 2+ header, data block, or footer.
'2' (0x32) Version 2 - The file MUST contain the version 1 header '2' (0x32) Version 2 - The file MUST contain the version 1 header
and data block, a version 2+ header and data block, and a and data block, a version 2+ header and data block, and a
footer. The TZ string in the footer (Section 3.3), if footer. The TZ string in the footer (Section 3.3), if
nonempty, MUST strictly adhere to the requirements for the TZ nonempty, MUST strictly adhere to the requirements for the TZ
environment variable as defined in Section 8.3 of the "Base environment variable as defined in Section 8.3 of the "Base
Definitions" volume of [POSIX] and MUST encode the POSIX Definitions" volume of [POSIX] and MUST encode the POSIX
portable character set as ASCII. portable character set as ASCII. The leap second table MUST
NOT be truncated at the start (Section 5.1), and MUST NOT
contain an expiration time.
'3' (0x33) Version 3 - The file MUST contain the version 1 header '3' (0x33) Version 3 - The file MUST conform to all version 2
and data block, a version 2+ header and data block, and a requirements, except that any TZ string in the footer
footer. The TZ string in the footer (Section 3.3), if (Section 3.3) MAY use the TZ string extensions described below
nonempty, MUST conform to POSIX requirements with ASCII (Section 3.3.1).
encoding, except that it MAY use the TZ string extensions
described below (Section 3.3.1). '4' (0x34) Version 4 - The file MUST conform to all version 3
requirements, except that the leap second table MAY be
truncated at the start, and MAY contain an expiration time.
isutcnt: A four-octet unsigned integer specifying the number of UT/ isutcnt: A four-octet unsigned integer specifying the number of UT/
local indicators contained in the data block -- MUST either be local indicators contained in the data block -- MUST either be
zero or equal to "typecnt". zero or equal to "typecnt".
isstdcnt: A four-octet unsigned integer specifying the number of isstdcnt: A four-octet unsigned integer specifying the number of
standard/wall indicators contained in the data block -- MUST standard/wall indicators contained in the data block -- MUST
either be zero or equal to "typecnt". either be zero or equal to "typecnt".
leapcnt: A four-octet unsigned integer specifying the number of leapcnt: A four-octet unsigned integer specifying the number of
skipping to change at page 8, line 22 skipping to change at page 8, line 26
which is a series of items. The number of items in each series is which is a series of items. The number of items in each series is
determined by the corresponding count field in the header. The total determined by the corresponding count field in the header. The total
length of each element is calculated by multiplying the number of length of each element is calculated by multiplying the number of
items by the size of each item. Therefore, implementations that do items by the size of each item. Therefore, implementations that do
not wish to parse or use the version 1 data block can calculate its not wish to parse or use the version 1 data block can calculate its
total length and skip directly to the header of the version 2+ data total length and skip directly to the header of the version 2+ data
block. block.
In the version 1 data block, time values are 32 bits (TIME_SIZE = 4 In the version 1 data block, time values are 32 bits (TIME_SIZE = 4
octets). In the version 2+ data block, present only in version 2 and octets). In the version 2+ data block, present only in version 2 and
3 files, time values are 64 bits (TIME_SIZE = 8 octets). higher files, time values are 64 bits (TIME_SIZE = 8 octets).
The data block is structured as follows (the lengths of multi-octet The data block is structured as follows (the lengths of multi-octet
fields are shown in parentheses): fields are shown in parentheses):
+---------------------------------------------------------+ +---------------------------------------------------------+
| transition times (timecnt x TIME_SIZE) | | transition times (timecnt x TIME_SIZE) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| transition types (timecnt) | | transition types (timecnt) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| local time type records (typecnt x 6) | | local time type records (typecnt x 6) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| time zone designations (charcnt) | | time zone designations (charcnt) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| leap-second records (leapcnt x (TIME_SIZE + 4)) | | leap-second records (leapcnt x (TIME_SIZE + 4)) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| standard/wall indicators (isstdcnt) | | standard/wall indicators (isstdcnt) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| UT/local indicators (isutcnt) | | UT/local indicators (isutcnt) |
+---------------------------------------------------------+ +---------------------------------------------------------+
TZif Data Block Figure 3: TZif Data Block
The elements of the data block are defined as follows: The elements of the data block are defined as follows:
transition times: A series of four- or eight-octet UNIX leap-time transition times: A series of four- or eight-octet UNIX leap-time
values sorted in strictly ascending order. Each value is used as values sorted in strictly ascending order. Each value is used as
a transition time at which the rules for computing local time may a transition time at which the rules for computing local time may
change. The number of time values is specified by the "timecnt" change. The number of time values is specified by the "timecnt"
field in the header. Each time value SHOULD be at least -2**59. field in the header. Each time value SHOULD be at least -2**59.
(-2**59 is the greatest negated power of 2 that predates the Big (-2**59 is the greatest negated power of 2 that predates the Big
Bang, and avoiding earlier timestamps works around known TZif Bang, and avoiding earlier timestamps works around known TZif
reader bugs relating to outlandishly negative timestamps.) reader bugs relating to outlandishly negative timestamps.)
transition types: A series of one-octet unsigned integers specifying transition types: A series of one-octet unsigned integers specifying
the type of local time of the corresponding transition time. the type of local time of the corresponding transition time.
These values serve as zero-based indices into the array of local These values serve as zero-based indices into the array of local
time type records. The number of type indices is specified by the time type records. The number of type indices is specified by the
"timecnt" field in the header. Each type index MUST be in the "timecnt" field in the header. Each type index MUST be in the
range [0, "typecnt" - 1]. range [0, "typecnt" - 1].
skipping to change at page 10, line 21 skipping to change at page 10, line 21
leap-second records: A series of eight- or twelve-octet records leap-second records: A series of eight- or twelve-octet records
specifying the corrections that need to be applied to UTC in order specifying the corrections that need to be applied to UTC in order
to determine TAI. The records are sorted by the occurrence time to determine TAI. The records are sorted by the occurrence time
in strictly ascending order. The number of records is specified in strictly ascending order. The number of records is specified
by the "leapcnt" field in the header. Each record has one of the by the "leapcnt" field in the header. Each record has one of the
following structures (the lengths of multi-octet fields are shown following structures (the lengths of multi-octet fields are shown
in parentheses): in parentheses):
Version 1 Data Block: Version 1 Data Block:
+---------------+---------------+
+---------------+---------------+ | occur (4) | corr (4) |
| occur (4) | corr (4) | +---------------+---------------+
+---------------+---------------+
version 2+ Data Block: version 2+ Data Block:
+---------------+---------------+---------------+
+---------------+---------------+---------------+ | occur (8) | corr (4) |
| occur (8) | corr (4) | +---------------+---------------+---------------+
+---------------+---------------+---------------+
occur(rence): A four- or eight-octet UNIX leap time value occur(rence): A four- or eight-octet UNIX leap time value
specifying the time at which a leap-second correction occurs. specifying the time at which a leap-second correction occurs or
The first value, if present, MUST be nonnegative, and each at which the leap second table expires. The first value, if
later value MUST be at least 2419199 greater than the previous present, MUST be nonnegative, and each leap second MUST occur
value. (This is 28 days' worth of seconds, minus a potential at the end of a UTC calendar month.
negative leap second.)
corr(ection): A four-octet signed integer specifying the value of corr(ection): A four-octet signed integer specifying the value of
LEAPCORR on or after the occurrence. The correction value in LEAPCORR on or after the occurrence. If "leapcnt" is zero,
the first leap-second record, if present, MUST be either one LEAPCORR is zero for all timestamps; otherwise, for timestamps
(1) or minus one (-1). The correction values in adjacent leap- before the first occurrence time, LEAPCORR is zero if the first
second records MUST differ by exactly one (1). The value of correction is one (1) or minus one (-1), and is unspecified
LEAPCORR is zero for timestamps that occur before the otherwise (which can happen only in files truncated at the
occurrence time in the first leap-second record (or for all start (Section 5.1)).
timestamps if there are no leap-second records).
The first leap second is a positive leap second if and only if
its correction is positive. Each correction after the first
MUST differ from the previous correction by either one (1) for
a positive leap second or minus one (-1) for a negative leap
second, except that if there are two or more leap-second
records the correction value of the last record MAY be the same
as the second-to-last record, with the last record indicating
the expiration time of the leap-second table.
standard/wall indicators: A series of one-octet values indicating standard/wall indicators: A series of one-octet values indicating
whether the transition times associated with local time types were whether the transition times associated with local time types were
specified as standard time or wall-clock time. Each value MUST be specified as standard time or wall-clock time. Each value MUST be
0 or 1. A value of one (1) indicates standard time. The value 0 or 1. A value of one (1) indicates standard time. The value
MUST be set to one (1) if the corresponding UT/local indicator is MUST be set to one (1) if the corresponding UT/local indicator is
set to one (1). A value of zero (0) indicates wall time. The set to one (1). A value of zero (0) indicates wall time. The
number of values is specified by the "isstdcnt" field in the number of values is specified by the "isstdcnt" field in the
header. If "isstdcnt" is zero (0), all transition times header. If "isstdcnt" is zero (0), all transition times
associated with local time types are assumed to be specified as associated with local time types are assumed to be specified as
skipping to change at page 11, line 38 skipping to change at page 11, line 44
string in the footer if present and nonempty; otherwise, it is string in the footer if present and nonempty; otherwise, it is
specified by time type 0. specified by time type 0.
A given pair of standard/wall and UT/local indicators is used to A given pair of standard/wall and UT/local indicators is used to
designate whether the corresponding transition time was specified as designate whether the corresponding transition time was specified as
UT, standard time, or wall-clock time. Note that there are only UT, standard time, or wall-clock time. Note that there are only
three combinations of the two indicators, given that the standard/ three combinations of the two indicators, given that the standard/
wall value MUST be one (1) if the UT/local value is one (1). This wall value MUST be one (1) if the UT/local value is one (1). This
information can be useful if the transition times in a TZif file need information can be useful if the transition times in a TZif file need
to be transformed into transitions appropriate for another time zone to be transformed into transitions appropriate for another time zone
(e.g. when calculating transition times for a simple POSIX TZ string (e.g. when calculating transition times for a simple POSIX-like TZ
such as "AKST9AKDT"). string such as "AKST9AKDT").
In order to eliminate unused space in a TZif file, every nonzero In order to eliminate unused space in a TZif file, every nonzero
local time type index SHOULD appear at least once in the transition local time type index SHOULD appear at least once in the transition
type array. Likewise, every octet in the time zone designations type array. Likewise, every octet in the time zone designations
array SHOULD be used by at least one time type record. array SHOULD be used by at least one time type record.
3.3. TZif Footer 3.3. TZif Footer
The TZif footer is structured as follows (the lengths of multi-octet The TZif footer is structured as follows (the lengths of multi-octet
fields are shown in parentheses): fields are shown in parentheses):
+---+--------------------+---+ +---+--------------------+---+
| NL| TZ string (0...) |NL | | NL| TZ string (0...) |NL |
+---+--------------------+---+ +---+--------------------+---+
TZif Footer Figure 4: TZif Footer
The elements of the footer are defined as follows: The elements of the footer are defined as follows:
NL: An ASCII new line character (0x0A). NL: An ASCII new line character (0x0A).
TZ string: A rule for computing local time changes after the last TZ string: A rule for computing local time changes after the last
transition time stored in the version 2+ data block. The string transition time stored in the version 2+ data block. The string
is either empty or uses the expanded format of the "TZ" is either empty or uses the expanded format of the "TZ"
environment variable as defined in Section 8.3 of the "Base environment variable as defined in Section 8.3 of the "Base
Definitions" volume of [POSIX] with ASCII encoding, possibly Definitions" volume of [POSIX] with ASCII encoding, possibly
utilizing extensions described below (Section 3.3.1) in version 3 utilizing extensions described below (Section 3.3.1) in version 3
files. If the string is empty, the corresponding information is and higher files. If the string is empty, the corresponding
not available. If the string is nonempty and one or more information is not available. If the string is nonempty and one
transitions appear in the version 2+ data, the string MUST be or more transitions appear in the version 2+ data, the string MUST
consistent with the last version 2+ transition. In other words, be consistent with the last version 2+ transition. In other
evaluating the TZ string at the time of the last transition should words, evaluating the TZ string at the time of the last transition
yield the same time type as was specified in the last transition. should yield the same time type as was specified in the last
The string MUST NOT contain NUL octets or be NUL-terminated, and transition. The string MUST NOT contain NUL octets or be
it SHOULD NOT begin with the ':' (colon) character. NUL-terminated, and it SHOULD NOT begin with the ':' (colon)
character.
The TZif footer is present only in version 2 and 3 files, as the The TZif footer is present only in version 2 and higher files, as the
obsolescent version 1 format was designed before the need for a obsolescent version 1 format was designed before the need for a
footer was apparent. footer was apparent.
3.3.1. TZ String Extensions 3.3.1. TZ String Extensions
The TZ string in a version 3 TZif file MAY use the following The TZ string in a version 3 or higher TZif file MAY use the
extensions to POSIX TZ strings. These extensions are described using following extensions to POSIX TZ strings. These extensions are
the terminology of Section 8.3 of the "Base Definitions" volume of described using the terminology of Section 8.3 of the "Base
[POSIX]. Definitions" volume of [POSIX].
o The hours part of the transition times may be signed and range * The hours part of the transition times may be signed and range
from -167 through 167 (-167 <= hh <= 167) instead of the POSIX- from -167 through 167 (-167 <= hh <= 167) instead of the POSIX-
required unsigned values from 0 through 24. required unsigned values from 0 through 24.
Example: <-03>3<-02>,M3.5.0/-2,M10.5.0/-1 Example: <-03>3<-02>,M3.5.0/-2,M10.5.0/-1
This represents a time zone that observes daylight saving time This represents a time zone that observes daylight saving time
from 22:00 on the day before March's last Sunday until 23:00 on from 22:00 on the day before March's last Sunday until 23:00 on
the day before October's last Sunday. Standard time is 3 hours the day before October's last Sunday. Standard time is 3 hours
west of UT and is abbreviated "-03"; daylight saving time is 2 west of UT and is abbreviated "-03"; daylight saving time is 2
hours west of UT and is abbreviated "-02". hours west of UT and is abbreviated "-02".
o DST is considered to be in effect all year if it starts January 1 * DST is considered to be in effect all year if it starts January 1
at 00:00 and ends December 31 at 24:00 plus the difference between at 00:00 and ends December 31 at 24:00 plus the difference between
daylight saving and standard time, leaving no room for standard daylight saving and standard time, leaving no room for standard
time in the calendar. time in the calendar.
Example: EST5EDT,0/0,J365/25 Example: EST5EDT,0/0,J365/25
This represents a time zone that observes daylight saving time This represents a time zone that observes daylight saving time
all year. It is 4 hours west of UT and is abbreviated "EDT". all year. It is 4 hours west of UT and is abbreviated "EDT".
The "EST" is ignored.
Example: XXX3EDT4,0/0,J365/23
This represents the same time zone as the previous example. It
uses a DST further west of UTC than standard time. The "XXX"
is ignored.
4. Interoperability Considerations 4. Interoperability Considerations
The following practices help ensure the interoperability of TZif The following practices help ensure the interoperability of TZif
applications. applications.
o Version 1 files are considered a legacy format and SHOULD NOT be * Version 1 files are considered a legacy format and SHOULD NOT be
generated, as they do not support transition times after the year generated, as they do not support transition times after the year
2038. 2038.
o Implementations that only understand version 1 MUST ignore any * Readers that understand only version 1 MUST ignore any data that
data that extends beyond the calculated end of the version 1 data extends beyond the calculated end of the version 1 data block.
block.
o Implementations SHOULD generate a version 3 file if TZ string * Other than version 1, writers should generate the lowest version
extensions are necessary to accurately model transition times. number needed by a file's data. For example, a writer should
Otherwise, version 2 files SHOULD be generated. generate a version 4 file only if its leap second table either
expires or is truncated at the start. Likewise, a writer not
generating a version 4 file should generate a version 3 file only
if TZ string extensions are necessary to accurately model
transition times.
o The sequence of time changes defined by the version 1 header and * To save space, writers of version 2+ files MAY output a
data block SHOULD be a contiguous sub-sequence of the time changes placeholder version 1 data block with all counts zero except that
defined by the version 2+ header and data block, and by the "typecnt" and "charcnt" are both one (1). If this is done,
footer. This guideline helps obsolescent version 1 readers agree obsolescent version-1-only readers MUST interpret these files as
with current readers about timestamps within the contiguous sub- lacking time changes and time zone abbreviations.
sequence. It also lets writers not supporting obsolescent readers
use a "timecnt" of zero in the version 1 data block to save space.
o Time zone designations SHOULD consist of at least three (3) and no * Unless the version 1 data block is a placeholder, the sequence of
timestamps defined by the version 1 header and data block SHOULD
be a contiguous sub-sequence of the timestamps defined by the
version 2+ header and data block, and by the footer. This
guideline helps obsolescent version 1 readers agree with current
readers about timestamps within the contiguous sub-sequence.
* When a TZif file contains a leap second table expiration time,
TZif readers SHOULD either refuse to process post-expiration
timestamps, or process them as if the expiration time did not
exist (possibly with an error indication).
* Time zone designations SHOULD consist of at least three (3) and no
more than six (6) ASCII characters from the set of alphanumerics, more than six (6) ASCII characters from the set of alphanumerics,
'-', and '+'. This is for compatibility with POSIX requirements '-', and '+'. This is for compatibility with POSIX requirements
for time zone abbreviations. for time zone abbreviations.
o When reading a version 2 or 3 file, implementations SHOULD ignore * When reading a version 2 or higher file, readers SHOULD ignore the
the version 1 header and data block except for the purpose of version 1 header and data block except for the purpose of skipping
skipping over them. over them.
o Implementations SHOULD calculate the total lengths of the headers * Readers SHOULD calculate the total lengths of the headers and data
and data blocks and check that they all fit within the actual file blocks and check that they all fit within the actual file size, as
size, as part of a validity check for the file. part of a validity check for the file.
o When a TZif file is used in a MIME message entity, it SHOULD be * When a TZif file is used in a MIME message entity, it SHOULD be
indicated by one of the following media types: indicated by one of the following media types:
* "application/tzif-leap" (Section 8.2) to indicate that leap- - "application/tzif-leap" (Section 8.2) to indicate that leap-
second records are included in the TZif data as necessary (none second records are included in the TZif data as necessary (none
are necessary if the file is truncated to a range that precedes are necessary if the file is truncated to a range that precedes
the first leap second). the first leap second).
* "application/tzif" (Section 8.1) to indicate that leap-second - "application/tzif" (Section 8.1) to indicate that leap-second
records are not included in the TZif data; "leapcnt" in the records are not included in the TZif data; "leapcnt" in the
header(s) MUST be zero (0). header(s) MUST be zero (0).
o Common interoperability issues and possible workarounds are * Common interoperability issues and possible workarounds are
described in Appendix A. described in Appendix A.
5. Use with the Time Zone Data Distribution Service 5. Use with the Time Zone Data Distribution Service
The Time Zone Data Distribution Service (TZDIST) [RFC7808] is a The Time Zone Data Distribution Service (TZDIST) [RFC7808] is a
service that allows reliable, secure, and fast delivery of time zone service that allows reliable, secure, and fast delivery of time zone
data and leap-second rules to client systems such as calendaring and data and leap-second rules to client systems such as calendaring and
scheduling applications or operating systems. scheduling applications or operating systems.
A TZDIST service MAY supply time zone data to clients in the Time A TZDIST service MAY supply time zone data to clients in the Time
skipping to change at page 15, line 22 skipping to change at page 15, line 32
truncate time zone transition data. A truncated TZif file is valid truncate time zone transition data. A truncated TZif file is valid
from its first and up to, but not including, its last version 2+ from its first and up to, but not including, its last version 2+
transition time, if present. transition time, if present.
When truncating the start of a TZif file, the service MUST supply in When truncating the start of a TZif file, the service MUST supply in
the version 2+ data a first transition time that is the start point the version 2+ data a first transition time that is the start point
of the truncation range. As with untruncated TZif files, time type 0 of the truncation range. As with untruncated TZif files, time type 0
indicates local time immediately before the start point, and the time indicates local time immediately before the start point, and the time
type of the first transition indicates local time thereafter. type of the first transition indicates local time thereafter.
When truncating the start of a TZif file containing leap-second
records, the service MUST keep all leap-second records governing
timestamps within the truncation range, even if the first such record
precedes the start point of the truncation range. If the truncated
leap second table is nonempty, its first record MUST have a positive
correction if and only if it represents a positive leap second.
When truncating the end of a TZif file, the service MUST supply in When truncating the end of a TZif file, the service MUST supply in
the version 2+ data a last transition time that is the end point of the version 2+ data a last transition time that is the end point of
the truncation range and MUST supply an empty TZ string. As with the truncation range and MUST supply an empty TZ string. As with
untruncated TZif files with empty TZ strings, a truncated TZif file untruncated TZif files with empty TZ strings, a truncated TZif file
does not indicate local time after the last transition. does not indicate local time after the last transition.
All represented information that falls inside the truncation range All represented information that falls inside the truncation range
MUST be the same as that represented by a corresponding untruncated MUST be the same as that represented by a corresponding untruncated
TZif file. TZif file.
skipping to change at page 16, line 17 skipping to change at page 17, line 14
>> Request << >> Request <<
GET /tzdist/capabilities HTTP/1.1 GET /tzdist/capabilities HTTP/1.1
Host: tz.example.com Host: tz.example.com
>> Response << >> Response <<
HTTP/1.1 200 OK HTTP/1.1 200 OK
Date: Fri, 01 Jun 2018 14:52:23 GMT Date: Fri, 01 Jun 2018 14:52:23 GMT
Content-Type: application/json; charset="utf-8" Content-Type: application/json
Content-Length: xxxx Content-Length: xxxx
{ {
"version": 1, "version": 1,
"info": { "info": {
"primary-source": "IANA:2018e", "primary-source": "IANA:2018e",
"formats": [ "formats": [
"text/calendar", "text/calendar",
"application/tzif", "application/tzif",
skipping to change at page 17, line 41 skipping to change at page 18, line 41
with a confidentiality layer such as that provided by Transport Layer with a confidentiality layer such as that provided by Transport Layer
Security (TLS) [RFC8446]. Security (TLS) [RFC8446].
8. IANA Considerations 8. IANA Considerations
This document defines two media types [RFC6838] for the exchange of This document defines two media types [RFC6838] for the exchange of
data utilizing the Time Zone Information Format. data utilizing the Time Zone Information Format.
8.1. application/tzif 8.1. application/tzif
Type name: application Type name:
application
Subtype name: tzif Subtype name:
tzif
Required parameters: none Required parameters:
none
Optional parameters: none Optional parameters:
none
Encoding considerations: binary Encoding considerations:
binary
Security considerations: See Section 6 of RFC 8536. Security considerations:
See Section 6 of RFC XXXX.
Interoperability considerations: See Section 4 of RFC 8536. Interoperability considerations:
See Section 4 of RFC XXXX.
Published specification: This specification. Published specification:
This specification.
Applications that use this media type: This media type is designed Applications that use this media type:
for widespread use by applications that need to use or exchange This media type is designed for widespread use by applications
time zone information, such as the Time Zone Information Compiler that need to use or exchange time zone information, such as the
(zic) [ZIC] and the GNU C Library [GNU-C]. The Time Zone Time Zone Information Compiler (zic) [ZIC] and the GNU C Library
Distribution Service [RFC7808] can directly use this media type. [GNU-C]. The Time Zone Distribution Service [RFC7808] can
directly use this media type.
Fragment identifier considerations: N/A Fragment identifier considerations:
N/A
Additional information: Additional information:
Magic number(s): The first 4 octets are 0x54, 0x5A, 0x69, 0x66 Magic number(s): The first 4 octets are 0x54, 0x5A, 0x69, 0x66
File extensions(s): N/A File extensions(s): N/A
Macintosh file type code(s): N/A Macintosh file type code(s): N/A
Person & email address to contact for further information: Person & email address to contact for further information:
Time Zone Database mailing list <tz@iana.org> Time Zone Database mailing list <tz@iana.org>
Intended usage: COMMON Intended usage:
COMMON
Restrictions on usage: N/A Restrictions on usage:
N/A
Author: See the "Authors' Addresses" section of RFC 8536. Author:
See the "Authors' Addresses" section of RFC XXXX.
Change controller: IETF Change controller:
IETF
8.2. application/tzif-leap 8.2. application/tzif-leap
Type name: application Type name:
application
Subtype name: tzif-leap Subtype name:
tzif-leap
Required parameters: none Required parameters:
none
Optional parameters: none Optional parameters:
none
Encoding considerations: binary Encoding considerations:
binary
Security considerations: See Section 6 of RFC 8536. Security considerations:
See Section 6 of RFC XXXX.
Interoperability considerations: See Section 4 of RFC 8536. Interoperability considerations:
See Section 4 of RFC XXXX.
Published specification: This specification. Published specification:
This specification.
Applications that use this media type: This media type is designed Applications that use this media type:
for widespread use by applications that need to use or exchange This media type is designed for widespread use by applications
time zone information, such as the Time Zone Information Compiler that need to use or exchange time zone information, such as the
(zic) [ZIC] and the GNU C Library [GNU-C]. The Time Zone Time Zone Information Compiler (zic) [ZIC] and the GNU C Library
Distribution Service [RFC7808] can directly use this media type. [GNU-C]. The Time Zone Distribution Service [RFC7808] can
directly use this media type.
Fragment identifier considerations: N/A Fragment identifier considerations:
N/A
Additional information: Additional information:
Magic number(s): The first 4 octets are 0x54, 0x5A, 0x69, 0x66 Magic number(s): The first 4 octets are 0x54, 0x5A, 0x69, 0x66
File extensions(s): N/A File extensions(s): N/A
Macintosh file type code(s): N/A Macintosh file type code(s): N/A
Person & email address to contact for further information: Person & email address to contact for further information:
Time Zone Database mailing list <tz@iana.org> Time Zone Database mailing list <tz@iana.org>
Intended usage: COMMON Intended usage:
COMMON
Restrictions on usage: N/A Restrictions on usage:
N/A
Author: See the "Authors' Addresses" section of RFC 8536. Author:
See the "Authors' Addresses" section of RFC XXXX.
Change controller: IETF Change controller:
IETF
9. References 9. References
9.1. Normative References 9.1. Normative References
[GNU-C] "The GNU C Library (glibc)", [GNU-C] "The GNU C Library (glibc)",
<https://www.gnu.org/software/libc/>. <https://www.gnu.org/software/libc/>.
[POSIX] IEEE, "Standard for Information Technology--Portable [POSIX] IEEE, "Standard for Information Technology--Portable
Operating System Interface (POSIX(R)) Base Operating System Interface (POSIX(R)) Base Specifications,
Specifications, Issue 7", IEEE 1003.1-2017, Issue 7", IEEE 1003.1-2017,
DOI 10.1109/IEEESTD.2018.8277153, January 2018, DOI 10.1109/IEEESTD.2018.8277153, 31 January 2018,
<http://pubs.opengroup.org/onlinepubs/9699919799/>. <https://pubs.opengroup.org/onlinepubs/9699919799/>.
[RFC20] Cerf, V., "ASCII format for network interchange", STD 80, [RFC20] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969, RFC 20, DOI 10.17487/RFC0020, October 1969,
<https://www.rfc-editor.org/info/rfc20>. <https://www.rfc-editor.org/info/rfc20>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013, RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>. <https://www.rfc-editor.org/info/rfc6838>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Transfer Protocol (HTTP/1.1): Semantics and Content", Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
RFC 7231, DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
[RFC7808] Douglass, M. and C. Daboo, "Time Zone Data Distribution [RFC7808] Douglass, M. and C. Daboo, "Time Zone Data Distribution
Service", RFC 7808, DOI 10.17487/RFC7808, March 2016, Service", RFC 7808, DOI 10.17487/RFC7808, March 2016,
<https://www.rfc-editor.org/info/rfc7808>. <https://www.rfc-editor.org/info/rfc7808>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[ZIC] Kerrisk, M., "ZIC(8)", man-pages release 4.16, February [ZIC] Kerrisk, M., "ZIC(8)", man-pages release 4.16, 25 February
2010, <http://man7.org/linux/man-pages/man8/zic.8.html>. 2010, <http://man7.org/linux/man-pages/man8/zic.8.html>.
9.2. Informative References 9.2. Informative References
[EGGERT-TZ] "History for tz", October 2018, [EGGERT-TZ]
<https://github.com/eggert/tz/commits/master/tzfile.5>. "History for tz", March 2021,
<https://github.com/eggert/tz/commits/main/tzfile.5>.
[RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and [Err6426] RFC Errata, "Erratum ID 6426", RFC 8536,
Scheduling Core Object Specification (iCalendar)", <https://www.rfc-editor.org/errata/eid6426>.
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 [Err6435] RFC Errata, "Erratum ID 6435", RFC 8536,
Time Zone Database", BCP 175, RFC 6557, <https://www.rfc-editor.org/errata/eid6435>.
DOI 10.17487/RFC6557, February 2012,
<https://www.rfc-editor.org/info/rfc6557>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) [RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and
Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, Scheduling Core Object Specification (iCalendar)",
August 2018, <https://www.rfc-editor.org/info/rfc8446>. RFC 5545, DOI 10.17487/RFC5545, September 2009,
<https://www.rfc-editor.org/info/rfc5545>.
[tz-link] Eggert, P. and A. Olson, "Sources for Time Zone and [RFC6557] Lear, E. and P. Eggert, "Procedures for Maintaining the
Daylight Saving Time Data", 2018, Time Zone Database", BCP 175, RFC 6557,
<https://www.iana.org/time-zones/repository/ DOI 10.17487/RFC6557, February 2012,
tz-link.html>. <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>.
[RFC8536] Olson, A., Eggert, P., and K. Murchison, "The Time Zone
Information Format (TZif)", RFC 8536,
DOI 10.17487/RFC8536, February 2019,
<https://www.rfc-editor.org/info/rfc8536>.
[tz-link] Eggert, P. and A.D. 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 Appendix A. Common Interoperability Issues
This section documents common problems in implementing this This section documents common problems in implementing this
specification. Most of these are problems in generating TZif files specification. Most of these are problems in generating TZif files
for use by readers conforming to predecessors of this specification for use by readers conforming to predecessors of this specification
[EGGERT-TZ]. The goals of this section are: [EGGERT-TZ]. The goals of this section are:
1. to help TZif writers output files that avoid common pitfalls in 1. to help TZif writers output files that avoid common pitfalls in
older or buggy TZif readers, older or buggy TZif readers,
skipping to change at page 21, line 33 skipping to change at page 23, line 20
file is of a later TZif version than what the reader was designed file is of a later TZif version than what the reader was designed
for. When complete compatibility was not achieved, an attempt was for. When complete compatibility was not achieved, an attempt was
made to limit glitches to rarely used timestamps and allow simple made to limit glitches to rarely used timestamps and allow simple
partial workarounds in writers designed to generate new-version data partial workarounds in writers designed to generate new-version data
useful even for older-version readers. This section attempts to useful even for older-version readers. This section attempts to
document these compatibility issues and workarounds, as well as document these compatibility issues and workarounds, as well as
documenting other common bugs in readers. documenting other common bugs in readers.
Interoperability problems with TZif include the following: Interoperability problems with TZif include the following:
o Some readers examine only version 1 data. As a partial * Some readers examine only version 1 data. As a partial
workaround, a writer can output as much version 1 data as workaround, a writer can output as much version 1 data as
possible. However, a reader should ignore version 1 data and use possible. However, a reader should ignore version 1 data and use
version 2+ data, even if the reader's native timestamps have only version 2+ data, even if the reader's native timestamps have only
32 bits. 32 bits.
o Some readers designed for version 2 might mishandle timestamps * Some readers designed for version 2 might mishandle timestamps
after a version 3 file's last transition, because they cannot after a version 3 or higher file's last transition, because they
parse extensions to POSIX in the TZ-like string. As a partial cannot parse extensions to POSIX in the TZ-like string. As a
workaround, a writer can output more transitions than necessary, partial workaround, a writer can output more transitions than
so that only far-future timestamps are mishandled by version 2 necessary, so that only far-future timestamps are mishandled by
readers. version 2 readers.
o Some readers designed for version 2 do not support permanent * Some readers designed for version 2 do not support permanent
daylight saving time -- e.g., a TZ string "EST5EDT,0/0,J365/25" daylight saving time with transitions after 24:00 -- e.g., a TZ
denoting permanent Eastern Daylight Time (-04). As a partial string "EST5EDT,0/0,J365/25" denoting permanent Eastern Daylight
workaround, a writer can substitute standard time for the next Time (-04). As a workaround, a writer can substitute standard
time zone east -- e.g., "AST4" for permanent Atlantic Standard time for two time zones east, e.g., "XXX3EDT4,0/0,J365/23" for a
Time (-04). time zone with a never-used standard time (XXX, -03) and negative
daylight saving time (EDT, -04) all year. Alternatively, 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 * Some readers designed for version 2 or 3, and that require strict
conformance to RFC 8536, reject version 4 files whose leap second
tables are truncated at the start or that end in expiration times.
* Some readers ignore the footer and instead predict future
timestamps from the time type of the last transition. As a timestamps from the time type of the last transition. As a
partial workaround, a writer can output more transitions than partial workaround, a writer can output more transitions than
necessary. necessary.
o Some readers do not use time type 0 for timestamps before the * Some readers do not use time type 0 for timestamps before the
first transition, in that they infer a time type using a heuristic first transition, in that they infer a time type using a heuristic
that does not always select time type 0. As a partial workaround, 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 a writer can output a dummy (no-op) first transition at an early
time. time.
o Some readers mishandle timestamps before the first transition that * Some readers mishandle timestamps before the first transition that
has a timestamp not less than -2**31. Readers that support only 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 32-bit timestamps are likely to be more prone to this problem, for
example, when they process 64-bit transitions, only some of which example, when they process 64-bit transitions, only some of which
are representable in 32 bits. As a partial workaround, a writer are representable in 32 bits. As a partial workaround, a writer
can output a dummy transition at timestamp -2**31. can output a dummy transition at timestamp -2**31.
o Some readers mishandle a transition if its timestamp has the * Some readers mishandle a transition if its timestamp has the
minimum possible signed 64-bit value. Timestamps less than -2**59 minimum possible signed 64-bit value. Timestamps less than -2**59
are not recommended. are not recommended.
o Some readers mishandle POSIX-style TZ strings that contain "<" or * Some readers mishandle POSIX-style TZ strings that contain "<" or
">". As a partial workaround, a writer can avoid using '<' or '>' ">". As a partial workaround, a writer can avoid using '<' or '>'
for time zone abbreviations containing only alphabetic characters. for time zone abbreviations containing only alphabetic characters.
o Many readers mishandle time zone abbreviations that contain non- * Many readers mishandle time zone abbreviations that contain non-
ASCII characters. These characters are not recommended. ASCII characters. These characters are not recommended.
o Some readers may mishandle time zone abbreviations that contain * Some readers may mishandle time zone abbreviations that contain
fewer than 3 or more than 6 characters, or that contain ASCII fewer than 3 or more than 6 characters, or that contain ASCII
characters other than alphanumerics, '-', and '+'. These characters other than alphanumerics, '-', and '+'. These
abbreviations are not recommended. abbreviations are not recommended.
o Some readers mishandle TZif files that specify daylight saving * Some readers mishandle TZif files that specify daylight saving
time UT offsets that are less than the UT offsets for the time UT offsets that are less than the UT offsets for the
corresponding standard time. These readers do not support corresponding standard time. These readers do not support
locations like Ireland, which uses the equivalent of the POSIX TZ 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, 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 +01) in summer and daylight saving time (GMT, +00) in winter. As
a partial workaround, a writer can output data for the equivalent 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 of the POSIX TZ string "GMT0IST,M3.5.0/1,M10.5.0", thus swapping
standard and daylight saving time. Although this workaround standard and daylight saving time. Although this workaround
misidentifies which part of the year uses daylight saving time, it misidentifies which part of the year uses daylight saving time, it
records UT offsets and time zone abbreviations correctly. records UT offsets and time zone abbreviations correctly.
* Some readers generate ambiguous timestamps for positive leap
seconds that occur when the UTC offset is not a multiple of 60
seconds. For example, in a timezone with UTC offset +01:23:45 and
with a positive leap second 78796801 (1972-06-30 23:59:60 UTC),
some readers will map both 78796800 and 78796801 to 01:23:45 local
time the next day instead of mapping the latter to 01:23:46, and
they will map 78796815 to 01:23:59 instead of to 01:23:60. This
has not yet been a practical problem, since no civil authority has
observed such UTC offsets since leap seconds were introduced in
1972.
Some interoperability problems are reader bugs that are listed here Some interoperability problems are reader bugs that are listed here
mostly as warnings to developers of readers. mostly as warnings to developers of readers.
o Some readers do not support negative timestamps. Developers of * Some readers do not support negative timestamps. Developers of
distributed applications should keep this in mind if they need to distributed applications should keep this in mind if they need to
deal with pre-1970 data. deal with pre-1970 data.
o Some readers mishandle timestamps before the first transition that * Some readers mishandle timestamps before the first transition that
has a nonnegative timestamp. Readers that do not support negative has a nonnegative timestamp. Readers that do not support negative
timestamps are likely to be more prone to this problem. timestamps are likely to be more prone to this problem.
o Some readers mishandle time zone abbreviations like "-08" that * Some readers mishandle time zone abbreviations like "-08" that
contain '+', '-', or digits. contain '+', '-', or digits.
o Some readers mishandle UT offsets that are out of the traditional * Some readers mishandle UT offsets that are out of the traditional
range of -12 through +12 hours and so do not support locations range of -12 through +12 hours and so do not support locations
like Kiritimati that are outside this range. like Kiritimati that are outside this range.
o Some readers mishandle UT offsets in the range [-3599, -1] seconds * Some readers mishandle UT offsets in the range [-3599, -1] seconds
from UT, because they integer-divide the offset by 3600 to get 0 from UT, because they integer-divide the offset by 3600 to get 0
and then display the hour part as "+00". and then display the hour part as "+00".
o Some readers mishandle UT offsets that are not a multiple of one * Some readers mishandle UT offsets that are not a multiple of one
hour, 15 minutes, or 1 minute. hour, 15 minutes, or 1 minute.
Appendix B. Example TZif Files Appendix B. Example TZif Files
The following sections contain annotated hexadecimal dumps of example The following sections contain annotated hexadecimal dumps of example
TZif files. TZif files.
Note that these examples should only be considered informative. Note that these examples should only be considered informative.
Although the example data entries are current as of the publication Although the example data entries are current as of the publication
date of this document, the data will likely change in the future as date of this document, the data will likely change in the future as
leap seconds are added and changes are made to civil time. leap seconds are added and changes are made to civil time.
B.1. Version 1 File Representing UTC (with Leap Seconds) B.1. Version 1 File Representing UTC (with Leap Seconds)
+-------+---------------+------------------+------------------------+ +========+=============+==================+========================+
| File | Data Octets | Record Name / | Field Value | | File | Hexadecimal | Record Name / | Field Value |
| Offset| (hexadecimal) | Field Name | | | Offset | Octets | Field Name | |
+-------+---------------+------------------+------------------------+ +========+=============+==================+========================+
| 000 | 54 5a 69 66 | magic | "TZif" | | 000 | 54 5a 69 66 | magic | "TZif" |
| 004 | 00 | version | 0 (1) | +--------+-------------+------------------+------------------------+
| 005 | 00 00 00 00 | | | | 004 | 00 | version | 0 (1) |
| | 00 00 00 00 | | | +--------+-------------+------------------+------------------------+
| | 00 00 00 00 | | | | 005 | 00 00 00 00 | | |
| | 00 00 00 | | | | | 00 00 00 00 | | |
| 020 | 00 00 00 01 | isutccnt | 1 | | | 00 00 00 00 | | |
| 024 | 00 00 00 01 | isstdcnt | 1 | | | 00 00 00 | | |
| 028 | 00 00 00 1b | isleapcnt | 27 | +--------+-------------+------------------+------------------------+
| 032 | 00 00 00 00 | timecnt | 0 | | 020 | 00 00 00 01 | isutcnt | 1 |
| 036 | 00 00 00 01 | typecnt | 1 | +--------+-------------+------------------+------------------------+
| 040 | 00 00 00 04 | charcnt | 4 | | 024 | 00 00 00 01 | isstdcnt | 1 |
| | | | | +--------+-------------+------------------+------------------------+
| | | localtimetype[0] | | | 028 | 00 00 00 1b | leapcnt | 27 |
| 044 | 00 00 00 00 | utcoff | 00:00 | +--------+-------------+------------------+------------------------+
| 048 | 00 | isdst | 0 (no) | | 032 | 00 00 00 00 | timecnt | 0 |
| 049 | 00 | desigidx | 0 | +--------+-------------+------------------+------------------------+
| | | | | | 036 | 00 00 00 01 | typecnt | 1 |
| 050 | 55 54 43 00 | designations[0] | "UTC" | +--------+-------------+------------------+------------------------+
| | | | | | 040 | 00 00 00 04 | charcnt | 4 |
| | | leapsecond[0] | | +--------+-------------+------------------+------------------------+
| 054 | 04 b2 58 00 | occurrence | 78796800 | +--------+-------------+------------------+------------------------+
| | | | (1972-06-30T23:59:60Z) | | | | localtimetype[0] | |
| 058 | 00 00 00 01 | correction | 1 | +--------+-------------+------------------+------------------------+
| | | | | | 044 | 00 00 00 00 | utoff | 0 (+00:00) |
| | | leapsecond[1] | | +--------+-------------+------------------+------------------------+
| 062 | 05 a4 ec 01 | occurrence | 94694401 | | 048 | 00 | isdst | 0 (no) |
| | | | (1972-12-31T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 066 | 00 00 00 02 | correction | 2 | | 049 | 00 | desigidx | 0 |
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[2] | | +--------+-------------+------------------+------------------------+
| 070 | 07 86 1f 82 | occurrence | 126230402 | | 050 | 55 54 43 00 | designations[0] | "UTC" |
| | | | (1973-12-31T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 074 | 00 00 00 03 | correction | 3 | +--------+-------------+------------------+------------------------+
| | | | | | | | leapsecond[0] | |
| | | leapsecond[3] | | +--------+-------------+------------------+------------------------+
| 078 | 09 67 53 03 | occurrence | 157766403 | | 054 | 04 b2 58 00 | occurrence | 78796800 |
| | | | (1974-12-31T23:59:60Z) | | | | | (1972-06-30T23:59:60Z) |
| 082 | 00 00 00 04 | correction | 4 | +--------+-------------+------------------+------------------------+
| | | | | | 058 | 00 00 00 01 | correction | 1 |
| | | leapsecond[4] | | +--------+-------------+------------------+------------------------+
| 086 | 0b 48 86 84 | occurrence | 189302404 | +--------+-------------+------------------+------------------------+
| | | | (1975-12-31T23:59:60Z) | | | | leapsecond[1] | |
| 090 | 00 00 00 05 | correction | 5 | +--------+-------------+------------------+------------------------+
| | | | | | 062 | 05 a4 ec 01 | occurrence | 94694401 |
| | | leapsecond[5] | | | | | | (1972-12-31T23:59:60Z) |
| 094 | 0d 2b 0b 85 | occurrence | 220924805 | +--------+-------------+------------------+------------------------+
| | | | (1976-12-31T23:59:60Z) | | 066 | 00 00 00 02 | correction | 2 |
| 098 | 00 00 00 06 | correction | 6 | +--------+-------------+------------------+------------------------+
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[6] | | | | | leapsecond[2] | |
| 102 | 0f 0c 3f 06 | occurrence | 252460806 | +--------+-------------+------------------+------------------------+
| | | | (1977-12-31T23:59:60Z) | | 070 | 07 86 1f 82 | occurrence | 126230402 |
| 106 | 00 00 00 07 | correction | 7 | | | | | (1973-12-31T23:59:60Z) |
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[7] | | | 074 | 00 00 00 03 | correction | 3 |
| 110 | 10 ed 72 87 | occurrence | 283996807 | +--------+-------------+------------------+------------------------+
| | | | (1978-12-31T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 114 | 00 00 00 08 | correction | 8 | | | | leapsecond[3] | |
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[8] | | | 078 | 09 67 53 03 | occurrence | 157766403 |
| 118 | 12 ce a6 08 | occurrence | 315532808 | | | | | (1974-12-31T23:59:60Z) |
| | | | (1979-12-31T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 122 | 00 00 00 09 | correction | 9 | | 082 | 00 00 00 04 | correction | 4 |
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[9] | | +--------+-------------+------------------+------------------------+
| 126 | 15 9f ca 89 | occurrence | 362793609 | | | | leapsecond[4] | |
| | | | (1981-06-30T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 130 | 00 00 00 0a | correction | 10 | | 086 | 0b 48 86 84 | occurrence | 189302404 |
| | | | | | | | | (1975-12-31T23:59:60Z) |
| | | leapsecond[10] | | +--------+-------------+------------------+------------------------+
| 134 | 17 80 fe 0a | occurrence | 394329610 | | 090 | 00 00 00 05 | correction | 5 |
| | | | (1982-06-30T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 138 | 00 00 00 0b | correction | 11 | +--------+-------------+------------------+------------------------+
| | | | | | | | leapsecond[5] | |
| | | leapsecond[11] | | +--------+-------------+------------------+------------------------+
| 142 | 19 62 31 8b | occurrence | 425865611 | | 094 | 0d 2b 0b 85 | occurrence | 220924805 |
| | | | (1983-06-30T23:59:60Z) | | | | | (1976-12-31T23:59:60Z) |
| 146 | 00 00 00 0c | correction | 12 | +--------+-------------+------------------+------------------------+
| | | | | | 098 | 00 00 00 06 | correction | 6 |
| | | leapsecond[12] | | +--------+-------------+------------------+------------------------+
| 150 | 1d 25 ea 0c | occurrence | 489024012 | +--------+-------------+------------------+------------------------+
| | | | (1985-06-30T23:59:60Z) | | | | leapsecond[6] | |
| 154 | 00 00 00 0d | correction | 13 | +--------+-------------+------------------+------------------------+
| | | | | | 102 | 0f 0c 3f 06 | occurrence | 252460806 |
| | | leapsecond[13] | | | | | | (1977-12-31T23:59:60Z) |
| 158 | 21 da e5 0d | occurrence | 567993613 | +--------+-------------+------------------+------------------------+
| | | | (1987-12-31T23:59:60Z) | | 106 | 00 00 00 07 | correction | 7 |
| 162 | 00 00 00 0e | correction | 14 | +--------+-------------+------------------+------------------------+
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[14] | | | | | leapsecond[7] | |
| 166 | 25 9e 9d 8e | occurrence | 631152014 | +--------+-------------+------------------+------------------------+
| | | | (1989-12-31T23:59:60Z) | | 110 | 10 ed 72 87 | occurrence | 283996807 |
| 170 | 00 00 00 0f | correction | 15 | | | | | (1978-12-31T23:59:60Z) |
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[15] | | | 114 | 00 00 00 08 | correction | 8 |
| 174 | 27 7f d1 0f | occurrence | 662688015 | +--------+-------------+------------------+------------------------+
| | | | (1990-12-31T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 178 | 00 00 00 10 | correction | 16 | | | | leapsecond[8] | |
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[16] | | | 118 | 12 ce a6 08 | occurrence | 315532808 |
| 182 | 2a 50 f5 90 | occurrence | 709948816 | | | | | (1979-12-31T23:59:60Z) |
| | | | (1992-06-30T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 186 | 00 00 00 11 | correction | 17 | | 122 | 00 00 00 09 | correction | 9 |
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[17] | | +--------+-------------+------------------+------------------------+
| 190 | 2c 32 29 11 | occurrence | 741484817 | | | | leapsecond[9] | |
| | | | (1993-06-30T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 194 | 00 00 00 12 | correction | 18 | | 126 | 15 9f ca 89 | occurrence | 362793609 |
| | | | | | | | | (1981-06-30T23:59:60Z) |
| | | leapsecond[18] | | +--------+-------------+------------------+------------------------+
| 198 | 2e 13 5c 92 | occurrence | 773020818 | | 130 | 00 00 00 0a | correction | 10 |
| | | | (1994-06-30T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 202 | 00 00 00 13 | correction | 19 | +--------+-------------+------------------+------------------------+
| | | | | | | | leapsecond[10] | |
| | | leapsecond[19] | | +--------+-------------+------------------+------------------------+
| 206 | 30 e7 24 13 | occurrence | 820454419 | | 134 | 17 80 fe 0a | occurrence | 394329610 |
| | | | (1995-12-31T23:59:60Z) | | | | | (1982-06-30T23:59:60Z) |
| 210 | 00 00 00 14 | correction | 20 | +--------+-------------+------------------+------------------------+
| | | | | | 138 | 00 00 00 0b | correction | 11 |
| | | leapsecond[20] | | +--------+-------------+------------------+------------------------+
| 214 | 33 b8 48 94 | occurrence | 867715220 | +--------+-------------+------------------+------------------------+
| | | | (1997-06-30T23:59:60Z) | | | | leapsecond[11] | |
| 218 | 00 00 00 15 | correction | 21 | +--------+-------------+------------------+------------------------+
| | | | | | 142 | 19 62 31 8b | occurrence | 425865611 |
| | | leapsecond[21] | | | | | | (1983-06-30T23:59:60Z) |
| 222 | 36 8c 10 15 | occurrence | 915148821 | +--------+-------------+------------------+------------------------+
| | | | (1998-12-31T23:59:60Z) | | 146 | 00 00 00 0c | correction | 12 |
| 226 | 00 00 00 16 | correction | 22 | +--------+-------------+------------------+------------------------+
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[22] | | | | | leapsecond[12] | |
| 230 | 43 b7 1b 96 | occurrence | 1136073622 | +--------+-------------+------------------+------------------------+
| | | | (2005-12-31T23:59:60Z) | | 150 | 1d 25 ea 0c | occurrence | 489024012 |
| 234 | 00 00 00 17 | correction | 23 | | | | | (1985-06-30T23:59:60Z) |
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[23] | | | 154 | 00 00 00 0d | correction | 13 |
| 238 | 49 5c 07 97 | occurrence | 1230768023 | +--------+-------------+------------------+------------------------+
| | | | (2008-12-31T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 242 | 00 00 00 18 | correction | 24 | | | | leapsecond[13] | |
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[24] | | | 158 | 21 da e5 0d | occurrence | 567993613 |
| 246 | 4f ef 93 18 | occurrence | 1341100824 | | | | | (1987-12-31T23:59:60Z) |
| | | | (2012-06-30T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 250 | 00 00 00 19 | correction | 25 | | 162 | 00 00 00 0e | correction | 14 |
| | | | | +--------+-------------+------------------+------------------------+
| | | leapsecond[25] | | +--------+-------------+------------------+------------------------+
| 254 | 55 93 2d 99 | occurrence | 1435708825 | | | | leapsecond[14] | |
| | | | (2015-06-30T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 258 | 00 00 00 1a | correction | 26 | | 166 | 25 9e 9d 8e | occurrence | 631152014 |
| | | | | | | | | (1989-12-31T23:59:60Z) |
| | | leapsecond[26] | | +--------+-------------+------------------+------------------------+
| 262 | 58 68 46 9a | occurrence | 1483228826 | | 170 | 00 00 00 0f | correction | 15 |
| | | | (2016-12-31T23:59:60Z) | +--------+-------------+------------------+------------------------+
| 266 | 00 00 00 1b | correction | 27 | +--------+-------------+------------------+------------------------+
| | | | | | | | leapsecond[15] | |
| 270 | 00 | UT/local[0] | 0 (local) | +--------+-------------+------------------+------------------------+
| | | | | | 174 | 27 7f d1 0f | occurrence | 662688015 |
| 271 | 00 | standard/wall[0] | 0 (wall) | | | | | (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 | standard/wall[0] | 0 (wall) |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 271 | 00 | UT/local[0] | 0 (local) |
+--------+-------------+------------------+------------------------+
Table 1
To determine TAI corresponding to 2000-01-01T00:00:00Z To determine TAI corresponding to 2000-01-01T00:00:00Z
(UNIX time = 946684800), the following procedure would be followed: (UNIX time = 946684800), the following procedure would be followed:
1. Find the latest leap-second occurrence prior to the time of 1. Find the latest leap-second occurrence prior to the time of
interest (leapsecond[21]) and note the correction value interest (leapsecond[21]) and note the correction value
(LEAPCORR = 22). (LEAPCORR = 22).
2. Add LEAPCORR + 10 to the time of interest to yield TAI of 2. Add LEAPCORR + 10 to the time of interest to yield TAI of
2000-01-01T00:00:32. 2000-01-01T00:00:32.
B.2. Version 2 File Representing Pacific/Honolulu B.2. Version 2 File Representing Pacific/Honolulu
+--------+--------------+------------------+------------------------+ +========+=============+==================+========================+
| File | Hexadecimal | Record Name / | Field Value | | File | Hexadecimal | Record Name / | Field Value |
| Offset | Octets | Field Name | | | Offset | Octets | Field Name | |
+--------+--------------+------------------+------------------------+ +========+=============+==================+========================+
| 000 | 54 5a 69 66 | magic | "TZif" | | 000 | 54 5a 69 66 | magic | "TZif" |
| 004 | 32 | version | '2' (2) | +--------+-------------+------------------+------------------------+
| 005 | 00 00 00 00 | | | | 004 | 32 | version | '2' (2) |
| | 00 00 00 00 | | | +--------+-------------+------------------+------------------------+
| | 00 00 00 00 | | | | 005 | 00 00 00 00 | | |
| | 00 00 00 | | | | | 00 00 00 00 | | |
| 020 | 00 00 00 06 | isutccnt | 6 | | | 00 00 00 00 | | |
| 024 | 00 00 00 06 | isstdcnt | 6 | | | 00 00 00 | | |
| 028 | 00 00 00 00 | isleapcnt | 0 | +--------+-------------+------------------+------------------------+
| 032 | 00 00 00 07 | timecnt | 7 | | 020 | 00 00 00 06 | isutcnt | 6 |
| 036 | 00 00 00 06 | typecnt | 6 | +--------+-------------+------------------+------------------------+
| 040 | 00 00 00 14 | charcnt | 20 | | 024 | 00 00 00 06 | isstdcnt | 6 |
| | | | | +--------+-------------+------------------+------------------------+
| 044 | 80 00 00 00 | trans time[0] | -2147483648 | | 028 | 00 00 00 00 | leapcnt | 0 |
| | | | (1901-12-13T20:45:52Z) | +--------+-------------+------------------+------------------------+
| 048 | bb 05 43 48 | trans time[1] | -1157283000 | | 032 | 00 00 00 07 | timecnt | 7 |
| | | | (1933-04-30T12:30:00Z) | +--------+-------------+------------------+------------------------+
| 052 | bb 21 71 58 | trans time[2] | -1155436200 | | 036 | 00 00 00 06 | typecnt | 6 |
| | | | (1933-05-21T21:30:00Z) | +--------+-------------+------------------+------------------------+
| 056 | cb 89 3d c8 | trans time[3] | -880198200 | | 040 | 00 00 00 14 | charcnt | 20 |
| | | | (1942-02-09T12:30:00Z) | +--------+-------------+------------------+------------------------+
| 060 | d2 23 f4 70 | trans time[4] | -769395600 | +--------+-------------+------------------+------------------------+
| | | | (1945-08-14T23:00:00Z) | | 044 | 80 00 00 00 | trans time[0] | -2147483648 |
| 064 | d2 61 49 38 | trans time[5] | -765376200 | | | | | (1901-12-13T20:45:52Z) |
| | | | (1945-09-30T11:30:00Z) | +--------+-------------+------------------+------------------------+
| 068 | d5 8d 73 48 | trans time[6] | -712150200 | | 048 | bb 05 43 48 | trans time[1] | -1157283000 |
| | | | (1947-06-08T12:30:00Z) | | | | | (1933-04-30T12:30:00Z) |
| | | | | +--------+-------------+------------------+------------------------+
| 072 | 01 | trans type[0] | 1 | | 052 | bb 21 71 58 | trans time[2] | -1155436200 |
| 073 | 02 | trans type[1] | 2 | | | | | (1933-05-21T21:30:00Z) |
| 074 | 01 | trans type[2] | 1 | +--------+-------------+------------------+------------------------+
| 075 | 03 | trans type[3] | 3 | | 056 | cb 89 3d c8 | trans time[3] | -880198200 |
| 076 | 04 | trans type[4] | 4 | | | | | (1942-02-09T12:30:00Z) |
| 077 | 01 | trans type[5] | 1 | +--------+-------------+------------------+------------------------+
| 078 | 05 | trans type[6] | 5 | | 060 | d2 23 f4 70 | trans time[4] | -769395600 |
| | | | | | | | | (1945-08-14T23:00:00Z) |
| | | localtimetype[0] | | +--------+-------------+------------------+------------------------+
| 079 | ff ff 6c 02 | utcoff | -37886 (-10:21:26) | | 064 | d2 61 49 38 | trans time[5] | -765376200 |
| 083 | 00 | isdst | 0 (no) | | | | | (1945-09-30T11:30:00Z) |
| 084 | 00 | desigidx | 0 | +--------+-------------+------------------+------------------------+
| | | | | | 068 | d5 8d 73 48 | trans time[6] | -712150200 |
| | | localtimetype[1] | | | | | | (1947-06-08T12:30:00Z) |
| 085 | ff ff 6c 58 | utcoff | -37800 (-10:30) | +--------+-------------+------------------+------------------------+
| 089 | 00 | isdst | 0 (no) | +--------+-------------+------------------+------------------------+
| 090 | 04 | desigidx | 4 | | 072 | 01 | trans type[0] | 1 |
| | | | | +--------+-------------+------------------+------------------------+
| | | localtimetype[2] | | | 073 | 02 | trans type[1] | 2 |
| 091 | ff ff 7a 68 | utcoff | -34200 (-09:30) | +--------+-------------+------------------+------------------------+
| 095 | 01 | isdst | 1 (yes) | | 074 | 01 | trans type[2] | 1 |
| 096 | 08 | desigidx | 8 | +--------+-------------+------------------+------------------------+
| | | | | | 075 | 03 | trans type[3] | 3 |
| | | localtimetype[3] | | +--------+-------------+------------------+------------------------+
| 097 | ff ff 7a 68 | utcoff | -34200 (-09:30) | | 076 | 04 | trans type[4] | 4 |
| 101 | 01 | isdst | 1 (yes) | +--------+-------------+------------------+------------------------+
| 102 | 0c | desigidx | 12 | | 077 | 01 | trans type[5] | 1 |
| | | | | +--------+-------------+------------------+------------------------+
| | | localtimetype[4] | | | 078 | 05 | trans type[6] | 5 |
| 103 | ff ff 7a 68 | utcoff | -34200 (-09:30) | +--------+-------------+------------------+------------------------+
| 107 | 01 | isdst | 1 (yes) | +--------+-------------+------------------+------------------------+
| 108 | 10 | desigidx | 16 | | | | localtimetype[0] | |
| | | | | +--------+-------------+------------------+------------------------+
| | | localtimetype[5] | | | 079 | ff ff 6c 02 | utoff | -37886 (-10:21:26) |
| 109 | ff ff 73 60 | utcoff | -36000 (-10:00) | +--------+-------------+------------------+------------------------+
| 113 | 00 | isdst | 0 (no) | | 083 | 00 | isdst | 0 (no) |
| 114 | 04 | desigidx | 4 | +--------+-------------+------------------+------------------------+
| | | | | | 084 | 00 | desigidx | 0 |
| 115 | 4c 4d 54 00 | designations[0] | "LMT" | +--------+-------------+------------------+------------------------+
| 119 | 48 53 54 00 | designations[4] | "HST" | +--------+-------------+------------------+------------------------+
| 123 | 48 44 54 00 | designations[8] | "HDT" | | | | localtimetype[1] | |
| 127 | 48 57 54 00 | designations[12] | "HWT" | +--------+-------------+------------------+------------------------+
| 131 | 48 50 54 00 | designations[16] | "HPT" | | 085 | ff ff 6c 58 | utoff | -37800 (-10:30) |
| | | | | +--------+-------------+------------------+------------------------+
| 135 | 00 | UT/local[0] | 1 (UT) | | 089 | 00 | isdst | 0 (no) |
| 136 | 00 | UT/local[1] | 0 (local) | +--------+-------------+------------------+------------------------+
| 137 | 00 | UT/local[2] | 0 (local) | | 090 | 04 | desigidx | 4 |
| 138 | 00 | UT/local[3] | 0 (local) | +--------+-------------+------------------+------------------------+
| 139 | 01 | UT/local[4] | 1 (UT) | +--------+-------------+------------------+------------------------+
| 140 | 00 | UT/local[5] | 0 (local) | | | | localtimetype[2] | |
| | | | | +--------+-------------+------------------+------------------------+
| 141 | 00 | standard/wall[0] | 1 (standard) | | 091 | ff ff 7a 68 | utoff | -34200 (-09:30) |
| 142 | 00 | standard/wall[1] | 0 (wall) | +--------+-------------+------------------+------------------------+
| 143 | 00 | standard/wall[2] | 0 (wall) | | 095 | 01 | isdst | 1 (yes) |
| 144 | 00 | standard/wall[3] | 0 (wall) | +--------+-------------+------------------+------------------------+
| 145 | 01 | standard/wall[4] | 1 (standard) | | 096 | 08 | desigidx | 8 |
| 146 | 00 | standard/wall[5] | 0 (wall) | +--------+-------------+------------------+------------------------+
| | | | | +--------+-------------+------------------+------------------------+
| 147 | 54 5a 69 66 | magic | "TZif" | | | | localtimetype[3] | |
| 151 | 32 | version | '2' (2) | +--------+-------------+------------------+------------------------+
| 152 | 00 00 00 00 | | | | 097 | ff ff 7a 68 | utoff | -34200 (-09:30) |
| | 00 00 00 00 | | | +--------+-------------+------------------+------------------------+
| | 00 00 00 00 | | | | 101 | 01 | isdst | 1 (yes) |
| | 00 00 00 | | | +--------+-------------+------------------+------------------------+
| 167 | 00 00 00 06 | isutccnt | 6 | | 102 | 0c | desigidx | 12 |
| 171 | 00 00 00 06 | isstdcnt | 6 | +--------+-------------+------------------+------------------------+
| 175 | 00 00 00 00 | isleapcnt | 0 | +--------+-------------+------------------+------------------------+
| 179 | 00 00 00 07 | timecnt | 7 | | | | localtimetype[4] | |
| 183 | 00 00 00 06 | typecnt | 6 | +--------+-------------+------------------+------------------------+
| 187 | 00 00 00 14 | charcnt | 20 | | 103 | ff ff 7a 68 | utoff | -34200 (-09:30) |
| | | | | +--------+-------------+------------------+------------------------+
| 191 | ff ff ff ff | trans time[0] | -2334101314 | | 107 | 01 | isdst | 1 (yes) |
| | 74 e0 70 be | | (1896-01-13T22:31:26Z) | +--------+-------------+------------------+------------------------+
| 199 | ff ff ff ff | trans time[1] | -1157283000 | | 108 | 10 | desigidx | 16 |
| | 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) | | | | localtimetype[5] | |
| 215 | ff ff ff ff | trans time[3] | -880198200 | +--------+-------------+------------------+------------------------+
| | cb 89 3d c8 | | (1942-02-09T12:30:00Z) | | 109 | ff ff 73 60 | utoff | -36000 (-10:00) |
| 223 | ff ff ff ff | trans time[4] | -769395600 | +--------+-------------+------------------+------------------------+
| | d2 23 f4 70 | | (1945-08-14T23:00:00Z) | | 113 | 00 | isdst | 0 (no) |
| 231 | ff ff ff ff | trans time[5] | -765376200 | +--------+-------------+------------------+------------------------+
| | d2 61 49 38 | | (1945-09-30T11:30:00Z) | | 114 | 04 | desigidx | 4 |
| 239 | ff ff ff ff | trans time[6] | -712150200 | +--------+-------------+------------------+------------------------+
| | d5 8d 73 48 | | (1947-06-08T12:30:00Z) | +--------+-------------+------------------+------------------------+
| | | | | | 115 | 4c 4d 54 00 | designations[0] | "LMT" |
| 247 | 01 | trans type[0] | 1 | +--------+-------------+------------------+------------------------+
| 248 | 02 | trans type[1] | 2 | | 119 | 48 53 54 00 | designations[4] | "HST" |
| 249 | 01 | trans type[2] | 1 | +--------+-------------+------------------+------------------------+
| 250 | 03 | trans type[3] | 3 | | 123 | 48 44 54 00 | designations[8] | "HDT" |
| 251 | 04 | trans type[4] | 4 | +--------+-------------+------------------+------------------------+
| 252 | 01 | trans type[5] | 1 | | 127 | 48 57 54 00 | designations[12] | "HWT" |
| 253 | 05 | trans type[6] | 5 | +--------+-------------+------------------+------------------------+
| | | | | | 131 | 48 50 54 00 | designations[16] | "HPT" |
| | | localtimetype[0] | | +--------+-------------+------------------+------------------------+
| 254 | ff ff 6c 02 | utcoff | -37886 (-10:21:26) | +--------+-------------+------------------+------------------------+
| 258 | 00 | isdst | 0 (no) | | 135 | 00 | standard/wall[0] | 0 (wall) |
| 259 | 00 | desigidx | 0 | +--------+-------------+------------------+------------------------+
| | | | | | 136 | 00 | standard/wall[1] | 0 (wall) |
| | | localtimetype[1] | | +--------+-------------+------------------+------------------------+
| 260 | ff ff 6c 58 | utcoff | -37800 (-10:30) | | 137 | 00 | standard/wall[2] | 0 (wall) |
| 264 | 00 | isdst | 0 (no) | +--------+-------------+------------------+------------------------+
| 265 | 04 | desigidx | 4 | | 138 | 00 | standard/wall[3] | 0 (wall) |
| | | | | +--------+-------------+------------------+------------------------+
| | | localtimetype[2] | | | 139 | 01 | standard/wall[4] | 1 (standard) |
| 266 | ff ff 7a 68 | utcoff | -34200 (-09:30) | +--------+-------------+------------------+------------------------+
| 270 | 01 | isdst | 1 (yes) | | 140 | 00 | standard/wall[5] | 0 (wall) |
| 271 | 08 | desigidx | 8 | +--------+-------------+------------------+------------------------+
| | | | | +--------+-------------+------------------+------------------------+
| | | localtimetype[3] | | | 141 | 00 | UT/local[0] | 0 (local) |
| 272 | ff ff 7a 68 | utcoff | -34200 (-09:30) | +--------+-------------+------------------+------------------------+
| 276 | 01 | isdst | 1 (yes) | | 142 | 00 | UT/local[1] | 0 (local) |
| 277 | 0c | desigidx | 12 | +--------+-------------+------------------+------------------------+
| | | | | | 143 | 00 | UT/local[2] | 0 (local) |
| | | localtimetype[4] | | +--------+-------------+------------------+------------------------+
| 278 | ff ff 7a 68 | utcoff | -34200 (-09:30) | | 144 | 00 | UT/local[3] | 0 (local) |
| 282 | 01 | isdst | 1 (yes) | +--------+-------------+------------------+------------------------+
| 283 | 10 | desigidx | 16 | | 145 | 01 | UT/local[4] | 1 (UT) |
| | | | | +--------+-------------+------------------+------------------------+
| | | localtimetype[5] | | | 146 | 00 | UT/local[5] | 0 (local) |
| 284 | ff ff 73 60 | utcoff | -36000 (-10:00) | +--------+-------------+------------------+------------------------+
| 288 | 00 | isdst | 0 (no) | +--------+-------------+------------------+------------------------+
| 289 | 04 | desigidx | 4 | | 147 | 54 5a 69 66 | magic | "TZif" |
| | | | | +--------+-------------+------------------+------------------------+
| 290 | 4c 4d 54 00 | designations[0] | "LMT" | | 151 | 32 | version | '2' (2) |
| 294 | 48 53 54 00 | designations[4] | "HST" | +--------+-------------+------------------+------------------------+
| 298 | 48 44 54 00 | designations[8] | "HDT" | | 152 | 00 00 00 00 | | |
| 302 | 48 57 54 00 | designations[12] | "HWT" | | | 00 00 00 00 | | |
| 306 | 48 50 54 00 | designations[16] | "HPT" | | | 00 00 00 00 | | |
| | | | | | | 00 00 00 | | |
| 310 | 00 | UT/local[0] | 0 (local) | +--------+-------------+------------------+------------------------+
| 311 | 00 | UT/local[1] | 0 (local) | | 167 | 00 00 00 06 | isutcnt | 6 |
| 312 | 00 | UT/local[2] | 0 (local) | +--------+-------------+------------------+------------------------+
| 313 | 00 | UT/local[3] | 0 (local) | | 171 | 00 00 00 06 | isstdcnt | 6 |
| 314 | 01 | UT/local[4] | 1 (UT) | +--------+-------------+------------------+------------------------+
| 315 | 00 | UT/local[5] | 0 (local) | | 175 | 00 00 00 00 | leapcnt | 0 |
| | | | | +--------+-------------+------------------+------------------------+
| 316 | 00 | standard/wall[0] | 0 (wall) | | 179 | 00 00 00 07 | timecnt | 7 |
| 317 | 00 | standard/wall[1] | 0 (wall) | +--------+-------------+------------------+------------------------+
| 318 | 00 | standard/wall[2] | 0 (wall) | | 183 | 00 00 00 06 | typecnt | 6 |
| 319 | 00 | standard/wall[3] | 0 (wall) | +--------+-------------+------------------+------------------------+
| 320 | 01 | standard/wall[4] | 1 (standard) | | 187 | 00 00 00 14 | charcnt | 20 |
| 321 | 00 | standard/wall[5] | 0 (wall) | +--------+-------------+------------------+------------------------+
| | | | | +--------+-------------+------------------+------------------------+
| 322 | 0a | NL | '\n' | | 191 | ff ff ff ff | trans time[0] | -2334101314 |
| 323 | 48 53 54 31 | TZ string | "HST10" | | | 74 e0 70 be | | (1896-01-13T22:31:26Z) |
| | 30 | | | +--------+-------------+------------------+------------------------+
| 328 | 0a | NL | '\n' | | 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 | utoff | -37886 (-10:21:26) |
+--------+-------------+------------------+------------------------+
| 258 | 00 | isdst | 0 (no) |
+--------+-------------+------------------+------------------------+
| 259 | 00 | desigidx | 0 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| | | localtimetype[1] | |
+--------+-------------+------------------+------------------------+
| 260 | ff ff 6c 58 | utoff | -37800 (-10:30) |
+--------+-------------+------------------+------------------------+
| 264 | 00 | isdst | 0 (no) |
+--------+-------------+------------------+------------------------+
| 265 | 04 | desigidx | 4 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| | | localtimetype[2] | |
+--------+-------------+------------------+------------------------+
| 266 | ff ff 7a 68 | utoff | -34200 (-09:30) |
+--------+-------------+------------------+------------------------+
| 270 | 01 | isdst | 1 (yes) |
+--------+-------------+------------------+------------------------+
| 271 | 08 | desigidx | 8 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| | | localtimetype[3] | |
+--------+-------------+------------------+------------------------+
| 272 | ff ff 7a 68 | utoff | -34200 (-09:30) |
+--------+-------------+------------------+------------------------+
| 276 | 01 | isdst | 1 (yes) |
+--------+-------------+------------------+------------------------+
| 277 | 0c | desigidx | 12 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| | | localtimetype[4] | |
+--------+-------------+------------------+------------------------+
| 278 | ff ff 7a 68 | utoff | -34200 (-09:30) |
+--------+-------------+------------------+------------------------+
| 282 | 01 | isdst | 1 (yes) |
+--------+-------------+------------------+------------------------+
| 283 | 10 | desigidx | 16 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| | | localtimetype[5] | |
+--------+-------------+------------------+------------------------+
| 284 | ff ff 73 60 | utoff | -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 | standard/wall[0] | 0 (wall) |
+--------+-------------+------------------+------------------------+
| 311 | 00 | standard/wall[1] | 0 (wall) |
+--------+-------------+------------------+------------------------+
| 312 | 00 | standard/wall[2] | 0 (wall) |
+--------+-------------+------------------+------------------------+
| 313 | 00 | standard/wall[3] | 0 (wall) |
+--------+-------------+------------------+------------------------+
| 314 | 01 | standard/wall[4] | 1 (standard) |
+--------+-------------+------------------+------------------------+
| 315 | 00 | standard/wall[5] | 0 (wall) |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 316 | 00 | UT/local[0] | 0 (local) |
+--------+-------------+------------------+------------------------+
| 317 | 00 | UT/local[1] | 0 (local) |
+--------+-------------+------------------+------------------------+
| 318 | 00 | UT/local[2] | 0 (local) |
+--------+-------------+------------------+------------------------+
| 319 | 00 | UT/local[3] | 0 (local) |
+--------+-------------+------------------+------------------------+
| 320 | 01 | UT/local[4] | 1 (UT) |
+--------+-------------+------------------+------------------------+
| 321 | 00 | UT/local[5] | 0 (local) |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 322 | 0a | NL | '\n' |
+--------+-------------+------------------+------------------------+
| 323 | 48 53 54 31 | TZ string | "HST10" |
| | 30 | | |
+--------+-------------+------------------+------------------------+
| 328 | 0a | NL | '\n' |
+--------+-------------+------------------+------------------------+
Table 2
To determine the local time in this time zone corresponding to To determine the local time in this time zone corresponding to
1933-05-04T12:00:00Z (UNIX time = -1156939200), the following 1933-05-04T12:00:00Z (UNIX time = -1156939200), the following
procedure would be followed: procedure would be followed:
1. Find the latest time transition prior to the time of interest 1. Find the latest time transition prior to the time of interest
(trans time[1]). (trans time[1]).
2. Reference the corresponding transition type (trans type[1]) to 2. Reference the corresponding transition type (trans type[1]) to
determine the local time type index (2). determine the local time type index (2).
skipping to change at page 33, line 10 skipping to change at page 38, line 49
offset to UTC is 10:00. offset to UTC is 10:00.
3. Subtract the UTC offset from the time of interest to yield a 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). standard local time of 2018-12-31T14:00:00-10:00 (HST).
B.3. Truncated Version 3 File Representing Asia/Jerusalem B.3. Truncated Version 3 File Representing Asia/Jerusalem
The following TZif file has been truncated to start on The following TZif file has been truncated to start on
2038-01-01T00:00:00Z. 2038-01-01T00:00:00Z.
+--------+--------------+------------------+------------------------+ In this example:
| File | Hexadecimal | Record Name / | Field Value |
| Offset | Octets | Field Name | | * The start time value can not be represented using 32 bits, so the
+--------+--------------+------------------+------------------------+ version 1 header contains only the required minimum data, which
| 000 | 54 5a 69 66 | magic | "TZif" | will be ignored by readers.
| 004 | 33 | version | '3' (3) |
| 005 | 00 00 00 00 | | | * The version 3 header leverages the fact that by specifying
| | 00 00 00 00 | | | 'isutcnt' and 'isstdcnt' as zero, all transition times associated
| | 00 00 00 00 | | | with local time types are assumed to be specified as local wall-
| | 00 00 00 | | | clock time (see the definitions of UT/local indicators and
| 020 | 00 00 00 00 | isutccnt | 0 | standard/wall indicators in Section 3.2).
| 024 | 00 00 00 00 | isstdcnt | 0 |
| 028 | 00 00 00 00 | isleapcnt | 0 | * The TZ string value has been line-wrapped for presentation
| 032 | 00 00 00 00 | timecnt | 0 | purposes only.
| 036 | 00 00 00 00 | typecnt | 0 |
| 040 | 00 00 00 00 | charcnt | 0 | +========+=============+==================+========================+
| | | | | | File | Hexadecimal | Record Name / | Field Value |
| 044 | 54 5a 69 66 | magic | "TZif" | | Offset | Octets | Field Name | |
| 048 | 33 | version | '3' (3) | +========+=============+==================+========================+
| 049 | 00 00 00 00 | | | | 000 | 54 5a 69 66 | magic | "TZif" |
| | 00 00 00 00 | | | +--------+-------------+------------------+------------------------+
| | 00 00 00 00 | | | | 004 | 33 | version | '3' (3) |
| | 00 00 00 | | | +--------+-------------+------------------+------------------------+
| 064 | 00 00 00 03 | isutccnt | 1 | | 005 | 00 00 00 00 | | |
| 068 | 00 00 00 03 | isstdcnt | 1 | | | 00 00 00 00 | | |
| 072 | 00 00 00 00 | isleapcnt | 0 | | | 00 00 00 00 | | |
| 076 | 00 00 00 03 | timecnt | 1 | | | 00 00 00 | | |
| 080 | 00 00 00 03 | typecnt | 1 | +--------+-------------+------------------+------------------------+
| 084 | 00 00 00 08 | charcnt | 4 | | 020 | 00 00 00 00 | isutcnt | 0 |
| | | | | +--------+-------------+------------------+------------------------+
| 088 | 00 00 00 00 | trans time[0] | 2145916800 | | 024 | 00 00 00 00 | isstdcnt | 0 |
| | 7f e8 17 80 | | (2038-01-01T00:00:00Z) | +--------+-------------+------------------+------------------------+
| | | | | | 028 | 00 00 00 00 | leapcnt | 0 |
| 096 | 00 | trans type[0] | 0 | +--------+-------------+------------------+------------------------+
| | | | | | 032 | 00 00 00 00 | timecnt | 0 |
| | | localtimetype[0] | | +--------+-------------+------------------+------------------------+
| 097 | 00 00 1c 20 | utcoff | 7200 (+02:00) | | 036 | 00 00 00 01 | typecnt | 1 |
| 101 | 00 | isdst | 0 (no) | +--------+-------------+------------------+------------------------+
| 102 | 00 | desigidx | 0 | | 040 | 00 00 00 01 | charcnt | 1 |
| | | | | +--------+-------------+------------------+------------------------+
| 103 | 49 53 54 00 | designations[0] | "IST" | +--------+-------------+------------------+------------------------+
| | | | | | | | localtimetype[0] | |
| 107 | 01 | UT/local[0] | 1 (UT) | +--------+-------------+------------------+------------------------+
| | | | | | 044 | 00 00 00 00 | utoff | 0 (+00:00) |
| 108 | 01 | standard/wall[0] | 1 (standard) | +--------+-------------+------------------+------------------------+
| | | | | | 048 | 00 | isdst | 0 (no) |
| 109 | 0a | NL | '\n' | +--------+-------------+------------------+------------------------+
| 110 | 49 53 54 2d | TZ string | "IST-2IDT, | | 049 | 00 | desigidx | 0 |
| | 32 49 44 54 | | M3.4.4/26,M10.5.0" | +--------+-------------+------------------+------------------------+
| | 2c 4d 33 2e | | | +--------+-------------+------------------+------------------------+
| | 34 2e 34 2f | | | | 050 | 00 | designations[0] | "" |
| | 32 36 2c 4d | | | +--------+-------------+------------------+------------------------+
| | 31 30 2e 35 | | | +--------+-------------+------------------+------------------------+
| | 2e 30 | | | | 051 | 54 5a 69 66 | magic | "TZif" |
| 136 | 0a | NL | '\n' | +--------+-------------+------------------+------------------------+
+--------+--------------+------------------+------------------------+ | 055 | 33 | version | '3' (3) |
+--------+-------------+------------------+------------------------+
| 056 | 00 00 00 00 | | |
| | 00 00 00 00 | | |
| | 00 00 00 00 | | |
| | 00 00 00 | | |
+--------+-------------+------------------+------------------------+
| 071 | 00 00 00 00 | isutcnt | 0 |
+--------+-------------+------------------+------------------------+
| 075 | 00 00 00 00 | isstdcnt | 0 |
+--------+-------------+------------------+------------------------+
| 079 | 00 00 00 00 | leapcnt | 0 |
+--------+-------------+------------------+------------------------+
| 083 | 00 00 00 01 | timecnt | 1 |
+--------+-------------+------------------+------------------------+
| 087 | 00 00 00 01 | typecnt | 1 |
+--------+-------------+------------------+------------------------+
| 091 | 00 00 00 04 | charcnt | 4 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 095 | 00 00 00 00 | trans time[0] | 2145916800 |
| | 7f e8 17 80 | | (2038-01-01T00:00:00Z) |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 103 | 00 | trans type[0] | 0 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| | | localtimetype[0] | |
+--------+-------------+------------------+------------------------+
| 104 | 00 00 1c 20 | utoff | 7200 (+02:00) |
+--------+-------------+------------------+------------------------+
| 108 | 00 | isdst | 0 (no) |
+--------+-------------+------------------+------------------------+
| 109 | 00 | desigidx | 0 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 110 | 49 53 54 00 | designations[0] | "IST" |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 114 | 0a | NL | '\n' |
+--------+-------------+------------------+------------------------+
| 115 | 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 | | |
+--------+-------------+------------------+------------------------+
| 141 | 0a | NL | '\n' |
+--------+-------------+------------------+------------------------+
Table 3
B.4. Truncated Version 4 File Representing America/New_York
The following TZif file has been truncated to start on
2022-01-01T00:00:00Z.
In this example:
* The version 1 header contains only the required minimum data,
which will be ignored by readers.
* The version 4 header leverages the fact that by specifying
'isutcnt' and 'isstdcnt' as zero, all transition times associated
with local time types are assumed to be specified as local wall-
clock time (see the definitions of UT/local indicators and
standard/wall indicators in Section 3.2).
* The first leap second occurrence is the most recent one prior to
the truncation time.
* The last leap second correction matches the second-to-last leap
second correction, indicating the expiration time of the leap
second table.
* The TZ string value has been line-wrapped for presentation
purposes only.
+========+=============+==================+========================+
| File | Hexadecimal | Record Name / | Field Value |
| Offset | Octets | Field Name | |
+========+=============+==================+========================+
| 000 | 54 5a 69 66 | magic | "TZif" |
+--------+-------------+------------------+------------------------+
| 004 | 34 | version | '4' (4) |
+--------+-------------+------------------+------------------------+
| 005 | 00 00 00 00 | | |
| | 00 00 00 00 | | |
| | 00 00 00 00 | | |
| | 00 00 00 | | |
+--------+-------------+------------------+------------------------+
| 020 | 00 00 00 00 | isutcnt | 0 |
+--------+-------------+------------------+------------------------+
| 024 | 00 00 00 00 | isstdcnt | 0 |
+--------+-------------+------------------+------------------------+
| 028 | 00 00 00 00 | leapcnt | 0 |
+--------+-------------+------------------+------------------------+
| 032 | 00 00 00 00 | timecnt | 0 |
+--------+-------------+------------------+------------------------+
| 036 | 00 00 00 01 | typecnt | 1 |
+--------+-------------+------------------+------------------------+
| 040 | 00 00 00 01 | charcnt | 1 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| | | localtimetype[0] | |
+--------+-------------+------------------+------------------------+
| 044 | 00 00 00 00 | utoff | 0 (+00:00) |
+--------+-------------+------------------+------------------------+
| 048 | 00 | isdst | 0 (no) |
+--------+-------------+------------------+------------------------+
| 049 | 00 | desigidx | 0 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 050 | 00 | designations[0] | "" |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 051 | 54 5a 69 66 | magic | "TZif" |
+--------+-------------+------------------+------------------------+
| 055 | 34 | version | '4' (4) |
+--------+-------------+------------------+------------------------+
| 056 | 00 00 00 00 | | |
| | 00 00 00 00 | | |
| | 00 00 00 00 | | |
| | 00 00 00 | | |
+--------+-------------+------------------+------------------------+
| 071 | 00 00 00 00 | isutcnt | 0 |
+--------+-------------+------------------+------------------------+
| 075 | 00 00 00 00 | isstdcnt | 0 |
+--------+-------------+------------------+------------------------+
| 079 | 00 00 00 02 | leapcnt | 2 |
+--------+-------------+------------------+------------------------+
| 083 | 00 00 00 01 | timecnt | 1 |
+--------+-------------+------------------+------------------------+
| 087 | 00 00 00 01 | typecnt | 1 |
+--------+-------------+------------------+------------------------+
| 091 | 00 00 00 04 | charcnt | 4 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 095 | 00 00 00 00 | trans time[0] | 1640995227 |
| | 61 cf 99 9b | | (2022-01-01T00:00:00Z) |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 103 | 00 | trans type[0] | 0 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| | | localtimetype[0] | |
+--------+-------------+------------------+------------------------+
| 104 | ff ff b9 b0 | utoff | -18000 (-05:00) |
+--------+-------------+------------------+------------------------+
| 108 | 00 | isdst | 0 (no) |
+--------+-------------+------------------+------------------------+
| 109 | 00 | desigidx | 0 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 110 | 45 53 54 00 | designations[0] | "EST" |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| | | leapsecond[0] | |
+--------+-------------+------------------+------------------------+
| 114 | 00 00 00 00 | occurrence | 1483228826 |
| | 58 68 46 9a | | (2016-12-31T23:59:60Z) |
+--------+-------------+------------------+------------------------+
| 122 | 00 00 00 1b | correction | 27 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| | | leapsecond[1] | |
+--------+-------------+------------------+------------------------+
| 126 | 00 00 00 00 | occurrence | 1656374427 |
| | 62 ba 44 9b | | (2022-06-28T00:00:00Z) |
+--------+-------------+------------------+------------------------+
| 134 | 00 00 00 1b | correction | 27 |
+--------+-------------+------------------+------------------------+
+--------+-------------+------------------+------------------------+
| 138 | 0a | NL | '\n' |
+--------+-------------+------------------+------------------------+
| 139 | 45 53 54 35 | TZ string | "EST5EDT, |
| | 45 44 54 2c | | M3.2.0,M11.1.0" |
| | 4d 33 2e 32 | | |
| | 2e 30 2c 4d | | |
| | 31 31 2e 31 | | |
| | 2e 30 | | |
+--------+-------------+------------------+------------------------+
| 161 | 0a | NL | '\n' |
+--------+-------------+------------------+------------------------+
Table 4
Appendix C. Changes from RFC 8536
* Added specification of the version 4 format and the optional leap
second table truncation and expiration, along with an example and
relevant interoperability considerations.
* Applied erratum [Err6435].
* Addressed erratum [Err6426] and several other errors in the
examples.
* Clarified the all-year daylight saving time TZ string
(Section 3.3.1) example and added a similar example with negative
DST.
* Added informational notes to Appendix B.3.
* Miscellaneous editorial changes.
Appendix D. Change Log
This section is to be removed by RFC Editor before publication.
D.1. Since rfc8536bis-01
* Converted source from xml2rfc v2 to v3.
* Properly line-wrapped long TZ string values in examples (with no
added space).
* No other substantive changes.
D.2. Since rfc8536bis-00
* Added specification of the version 4 format and the optional leap
second table truncation and expiration, along with an example and
relevant interoperability considerations.
* Specified column widths in example tables.
* Noted that long TZ string values in examples are line-wrapped for
presentation purposes only.
D.3. Since RFC 8536
* Applied erratum [Err6435].
* Addressed erratum [Err6426] and several other errors in the
examples.
* Clarified the all-year daylight saving time TZ string
(Section 3.3.1) example and added a similar example with negative
DST.
* Added informational notes to Appendix B.3.
* Miscellaneous editorial changes.
* Added text obsoleting [RFC8536].
* Added Changes from RFC 8536 (Appendix C).
* Added Tim Parenti as a contributor.
Acknowledgments Acknowledgments
The authors would like to thank the following individuals for The authors would like to thank the following individuals for
contributing their ideas and support for writing this specification: contributing their ideas and support for writing this specification:
Michael Douglass, Ned Freed, Guy Harris, Eliot Lear, and Alexey Michael Douglass, Ned Freed, Guy Harris, Eliot Lear, Alexey Melnikov,
Melnikov. and Tim Parenti.
Authors' Addresses Authors' Addresses
Arthur David Olson Arthur David Olson
Email: arthurdavidolson@gmail.com Email: arthurdavidolson@gmail.com
Paul Eggert Paul Eggert
University of California, Los Angeles University of California, Los Angeles
Email: eggert@cs.ucla.edu Email: eggert@cs.ucla.edu
Kenneth Murchison Kenneth Murchison
FastMail US LLC Fastmail US LLC
Email: murch@fastmailteam.com Email: murch@fastmailteam.com
 End of changes. 113 change blocks. 
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