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'GNU-C' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-R-TF.460' -- Possible downref: Non-RFC (?) normative reference: ref. 'POSIX' ** Obsolete normative reference: RFC 7231 (Obsoleted by RFC 9110) -- Possible downref: Non-RFC (?) normative reference: ref. 'ZIC' -- Duplicate reference: RFC8536, mentioned in 'Err6435', was also mentioned in 'Err6426'. -- Duplicate reference: RFC8536, mentioned in 'Err6757', was also mentioned in 'Err6435'. -- Duplicate reference: RFC8536, mentioned in 'RFC8536', was also mentioned in 'Err6757'. Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 36 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force (IETF) A.D. Olson 3 Internet-Draft 4 Obsoletes: 8536 (if approved) P. Eggert 5 Intended status: Standards Track UCLA 6 Expires: 13 June 2022 K. Murchison 7 Fastmail 8 10 December 2021 10 The Time Zone Information Format (TZif) 11 draft-murchison-rfc8536bis-04 13 Abstract 15 This document specifies the Time Zone Information Format (TZif) for 16 representing and exchanging time zone information, independent of any 17 particular service or protocol. Two media types for this format are 18 also defined. 20 This document replaces and obsoletes RFC 8536. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on 13 June 2022. 39 Copyright Notice 41 Copyright (c) 2021 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 46 license-info) in effect on the date of publication of this document. 47 Please review these documents carefully, as they describe your rights 48 and restrictions with respect to this document. Code Components 49 extracted from this document must include Revised BSD License text as 50 described in Section 4.e of the Trust Legal Provisions and are 51 provided without warranty as described in the Revised BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 57 3. The Time Zone Information Format (TZif) . . . . . . . . . . . 5 58 3.1. TZif Header . . . . . . . . . . . . . . . . . . . . . . . 6 59 3.2. TZif Data Block . . . . . . . . . . . . . . . . . . . . . 8 60 3.3. TZif Footer . . . . . . . . . . . . . . . . . . . . . . . 12 61 3.3.1. TZ String Extensions . . . . . . . . . . . . . . . . 13 62 4. Interoperability Considerations . . . . . . . . . . . . . . . 14 63 5. Use with the Time Zone Data Distribution Service . . . . . . 15 64 5.1. Truncating TZif Files . . . . . . . . . . . . . . . . . . 15 65 5.2. Example TZDIST Request for TZif Data . . . . . . . . . . 16 66 6. Security Considerations . . . . . . . . . . . . . . . . . . . 18 67 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18 68 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 69 8.1. application/tzif . . . . . . . . . . . . . . . . . . . . 18 70 8.2. application/tzif-leap . . . . . . . . . . . . . . . . . . 19 71 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 72 9.1. Normative References . . . . . . . . . . . . . . . . . . 21 73 9.2. Informative References . . . . . . . . . . . . . . . . . 22 74 Appendix A. Common Interoperability Issues . . . . . . . . . . . 23 75 Appendix B. Example TZif Files . . . . . . . . . . . . . . . . . 26 76 B.1. Version 1 File Representing UTC (with Leap Seconds) . . . 26 77 B.2. Version 2 File Representing Pacific/Honolulu . . . . . . 32 78 B.3. Truncated Version 3 File Representing Asia/Jerusalem . . 39 79 B.4. Truncated Version 4 File Representing America/New_York . 41 80 Appendix C. Changes from RFC 8536 . . . . . . . . . . . . . . . 44 81 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 45 82 D.1. Since rfc8536bis-03 . . . . . . . . . . . . . . . . . . . 45 83 D.2. Since rfc8536bis-02 . . . . . . . . . . . . . . . . . . . 45 84 D.3. Since rfc8536bis-01 . . . . . . . . . . . . . . . . . . . 45 85 D.4. Since rfc8536bis-00 . . . . . . . . . . . . . . . . . . . 45 86 D.5. Since RFC 8536 . . . . . . . . . . . . . . . . . . . . . 45 87 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 46 88 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46 90 1. Introduction 92 Time zone data typically consists of offsets from universal time 93 (UT), daylight saving transition rules, one or more local time 94 designations (acronyms or abbreviations), and optional leap-second 95 adjustments. One such format for conveying this information is 96 iCalendar [RFC5545]. It is a text-based format used by calendaring 97 and scheduling systems. 99 This document specifies the widely deployed Time Zone Information 100 Format (TZif). It is a binary format used by most UNIX systems to 101 calculate local time. This format was introduced in the 1980s and 102 has evolved since then into multiple upward-compatible versions. 103 There is a wide variety of interoperable software capable of 104 generating and reading files in this format [tz-link]. 106 This specification does not define the source of the data assembled 107 into a TZif file. One such source is the IANA-hosted time zone 108 database [RFC6557]. 110 This document obsoletes RFC 8536, providing editorial improvements, 111 new details, and errata fixes while keeping full compatibility with 112 the interchange format of RFC 8536. Additionally, a new version of 113 the format is defined. The changes from RFC 8536 are summarized in 114 Appendix C. 116 2. Conventions Used in This Document 118 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 119 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 120 "OPTIONAL" in this document are to be interpreted as described in 121 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 122 capitals, as shown here. 124 The following terms are used in this document (see "Sources for Time 125 Zone and Daylight Saving Time Data" [tz-link] for more detailed 126 information about civil timekeeping data and practice): 128 Coordinated Universal Time (UTC): The basis for civil time since 129 1960. It is approximately equal to mean solar time at the prime 130 meridian (0 degrees longitude). 132 Daylight Saving Time (DST): The time according to a location's law 133 or practice, when adjusted as necessary from standard time. The 134 adjustment may be positive or negative, and the amount of 135 adjustment may vary depending on the date and time; the TZif 136 format even allows the adjustment to be zero, although this is not 137 common practice. 139 International Atomic Time (TAI): The time standard based on atomic 140 clocks since 1972. It is equal to UTC but without leap-second 141 adjustments. 143 Leap-Second: A one second adjustment to keep UTC close to mean solar 144 time at the prime meridian (see [ITU-R-TF.460]). Each inserted or 145 deleted leap-second occurs at the end of a UTC month, that is, a 146 month using the Gregorian calendar and the UTC timescale. 148 Leap-Second Correction (LEAPCORR): The value of TAI - UTC - 10 for 149 timestamps after the first leap second, and zero for timestamps 150 before that. The expression "TAI - UTC - 10" comes from the fact 151 that TAI - UTC was defined to be 10 just prior to the first leap 152 second in 1972, so clocks with leap seconds have a zero LEAPCORR 153 before the first leap second. 155 Local Time: Civil time for a particular location. Its offset from 156 universal time can depend on the date and time of day. 158 POSIX Epoch: 1970-01-01 00:00:00 UTC, the basis for absolute 159 timestamps in this document. 161 Standard Time: The time according to a location's law or practice, 162 unadjusted for Daylight Saving Time. 164 Time Change: A change to civil timekeeping practice. It occurs when 165 one or more of the following happen simultaneously: 167 1. a change in UT offset 169 2. a change in whether daylight saving time is in effect 171 3. a change in time zone abbreviation 173 4. a leap second (i.e., a change in LEAPCORR) 175 Time Zone Data: The Time Zone Data Distribution Service (TZDIST) 176 [RFC7808] defines "Time zone data" as "data that defines a single 177 time zone, including an identifier, UTC offset values, DST rules, 178 and other information such as time zone abbreviations." The 179 interchange format defined in this document is one such form of 180 time zone data. 182 Transition Time: The moment of occurrence of a time change that is 183 not a leap second. It is identified with a signed integer count 184 of UNIX leap time seconds since the POSIX epoch. 186 Universal Time (UT): The basis of civil time. This is the principal 187 form of the mean solar time at the prime meridian (0 degrees 188 longitude) for timestamps before UTC was introduced in 1960 and is 189 UTC for timestamps thereafter. Although UT is sometimes called 190 "UTC" or "GMT" in other sources, this specification uses the term 191 "UT" to avoid confusion with UTC or with GMT. 193 UNIX Time: The time as returned by the time() function provided by 194 the C programming language (see Section 3 of the "System 195 Interfaces" volume of [POSIX]). This is an integer number of 196 seconds since the POSIX epoch, not counting leap seconds. As an 197 extension to POSIX, negative values represent times before the 198 POSIX epoch, using UT. 200 UNIX Leap Time: UNIX time plus all preceding leap-second 201 corrections. For example, if the first leap-second record in a 202 TZif file occurs at 1972-06-30 23:59:60 UTC, the UNIX leap time 203 for the timestamp 1972-07-01 00:00:00 UTC would be 78796801, one 204 greater than the UNIX time for the same timestamp. Similarly, if 205 the second leap-second record occurs at 1972-12-31 23:59:60 UTC, 206 it accounts for the first leap second, so the UNIX leap time of 207 1972-12-31 23:59:60 UTC would be 94694401, and the UNIX leap time 208 of 1973-01-01 00:00:00 UTC would be 94694402. If a TZif file 209 specifies no leap-second records, UNIX leap time is equal to UNIX 210 time. 212 Wall Time: Another name for local time; short for "wall-clock time". 214 3. The Time Zone Information Format (TZif) 216 The Time Zone Information Format begins with a fixed 44-octet version 217 1 header (Section 3.1) containing a field that specifies the version 218 of the file's format. Readers designed for version N can read 219 version N+1 files without too much trouble; data specific to version 220 N+1 either appears after version N data so that earlier-version 221 readers can easily ignore later-version data they are not designed 222 for, or it appears as a minor extension to version N that version N 223 readers are likely to tolerate well. 225 The version 1 header is followed by a variable-length version 1 data 226 block (Section 3.2) containing four-octet (32-bit) transition times 227 and leap-second occurrences. These 32-bit values are limited to 228 representing time changes from 1901-12-13 20:45:52 through 2038-01-19 229 03:14:07 UT, and the version 1 header and data block are present only 230 for backward compatibility with obsolescent readers, as discussed in 231 Common Interoperability Issues (Appendix A). 233 Version 1 files terminate after the version 1 data block. Files from 234 versions 2 and higher extend the format by appending a second 235 44-octet version 2+ header, a variable-length version 2+ data block 236 containing eight-octet (64-bit) transition times and leap-second 237 occurrences, and a variable-length footer (Section 3.3). These 238 64-bit values can represent times approximately 292 billion years 239 into the past or future. 241 NOTE: All multi-octet integer values MUST be stored in network octet 242 order format (high-order octet first, otherwise known as big-endian), 243 with all bits significant. Signed integer values MUST be represented 244 using two's complement. 246 A TZif file is structured as follows: 248 Version 1 Versions 2+ 249 +-------------+ +-------------+ 250 | Version 1 | | Version 1 | 251 | Header | | Header | 252 +-------------+ +-------------+ 253 | Version 1 | | Version 1 | 254 | Data Block | | Data Block | 255 +-------------+ +-------------+ 256 | Version 2+ | 257 | Header | 258 +-------------+ 259 | Version 2+ | 260 | Data Block | 261 +-------------+ 262 | Footer | 263 +-------------+ 265 Figure 1: General Format of TZif Files 267 3.1. TZif Header 269 A TZif header is structured as follows (the lengths of multi-octet 270 fields are shown in parentheses): 272 +---------------+---+ 273 | magic (4) |ver| 274 +---------------+---+---------------------------------------+ 275 | [unused - reserved for future use] (15) | 276 +---------------+---------------+---------------+-----------+ 277 | isutcnt (4) | isstdcnt (4) | leapcnt (4) | 278 +---------------+---------------+---------------+ 279 | timecnt (4) | typecnt (4) | charcnt (4) | 280 +---------------+---------------+---------------+ 281 Figure 2: TZif Header 283 The fields of the header are defined as follows: 285 magic: The four-octet ASCII [RFC20] sequence "TZif" (0x54 0x5A 0x69 286 0x66), which identifies the file as utilizing the Time Zone 287 Information Format. 289 ver(sion): An octet identifying the version of the file's format. 290 The value MUST be one of the following: 292 NUL (0x00) Version 1 - The file contains only the version 1 293 header and data block. Version 1 files MUST NOT contain a 294 version 2+ header, data block, or footer. 296 '2' (0x32) Version 2 - The file MUST contain the version 1 header 297 and data block, a version 2+ header and data block, and a 298 footer. The TZ string in the footer (Section 3.3), if 299 nonempty, MUST strictly adhere to the requirements for the TZ 300 environment variable as defined in Section 8.3 of the "Base 301 Definitions" volume of [POSIX] and MUST encode the POSIX 302 portable character set as ASCII. The leap second table MUST 303 NOT be truncated at the start (Section 5.1), and MUST NOT 304 contain an expiration time. 306 '3' (0x33) Version 3 - The file MUST conform to all version 2 307 requirements, except that any TZ string in the footer 308 (Section 3.3) MAY use the TZ string extensions described below 309 (Section 3.3.1). 311 '4' (0x34) Version 4 - The file MUST conform to all version 3 312 requirements, except that the leap second table MAY be 313 truncated at the start, and MAY contain an expiration time. 315 isutcnt: A four-octet unsigned integer specifying the number of UT/ 316 local indicators contained in the data block -- MUST either be 317 zero or equal to "typecnt". 319 isstdcnt: A four-octet unsigned integer specifying the number of 320 standard/wall indicators contained in the data block -- MUST 321 either be zero or equal to "typecnt". 323 leapcnt: A four-octet unsigned integer specifying the number of 324 leap-second records contained in the data block. 326 timecnt: A four-octet unsigned integer specifying the number of 327 transition times contained in the data block. 329 typecnt: A four-octet unsigned integer specifying the number of 330 local time type records contained in the data block -- MUST NOT be 331 zero. (Although local time type records convey no useful 332 information in files that have nonempty TZ strings but no 333 transitions, at least one such record is nevertheless required 334 because many TZif readers reject files that have zero time types.) 336 charcnt: A four-octet unsigned integer specifying the total number 337 of octets used by the set of time zone designations contained in 338 the data block - MUST NOT be zero. The count includes the 339 trailing NUL (0x00) octet at the end of the last time zone 340 designation. 342 Although the version 1 and 2+ headers have the same format, magic 343 number, and version fields, their count fields may differ, because 344 the version 1 data can be a subset of the version 2+ data. 346 3.2. TZif Data Block 348 A TZif data block consists of seven variable-length elements, each of 349 which is a series of items. The number of items in each series is 350 determined by the corresponding count field in the header. The total 351 length of each element is calculated by multiplying the number of 352 items by the size of each item. Therefore, implementations that do 353 not wish to parse or use the version 1 data block can calculate its 354 total length and skip directly to the header of the version 2+ data 355 block. 357 In the version 1 data block, time values are 32 bits (TIME_SIZE = 4 358 octets). In the version 2+ data block, present only in version 2 and 359 higher files, time values are 64 bits (TIME_SIZE = 8 octets). 361 The data block is structured as follows (the lengths of multi-octet 362 fields are shown in parentheses): 364 +---------------------------------------------------------+ 365 | transition times (timecnt x TIME_SIZE) | 366 +---------------------------------------------------------+ 367 | transition types (timecnt) | 368 +---------------------------------------------------------+ 369 | local time type records (typecnt x 6) | 370 +---------------------------------------------------------+ 371 | time zone designations (charcnt) | 372 +---------------------------------------------------------+ 373 | leap-second records (leapcnt x (TIME_SIZE + 4)) | 374 +---------------------------------------------------------+ 375 | standard/wall indicators (isstdcnt) | 376 +---------------------------------------------------------+ 377 | UT/local indicators (isutcnt) | 378 +---------------------------------------------------------+ 380 Figure 3: TZif Data Block 382 The elements of the data block are defined as follows: 384 transition times: A series of four- or eight-octet UNIX leap-time 385 values sorted in strictly ascending order. Each value is used as 386 a transition time at which the rules for computing local time may 387 change. The number of time values is specified by the "timecnt" 388 field in the header. Each time value SHOULD be at least -2**59. 389 (-2**59 is the greatest negated power of 2 that predates the Big 390 Bang, and avoiding earlier timestamps works around known TZif 391 reader bugs relating to outlandishly negative timestamps.) 393 transition types: A series of one-octet unsigned integers specifying 394 the type of local time of the corresponding transition time. 395 These values serve as zero-based indices into the array of local 396 time type records. The number of type indices is specified by the 397 "timecnt" field in the header. Each type index MUST be in the 398 range [0, "typecnt" - 1]. 400 local time type records: A series of six-octet records specifying a 401 local time type. The number of records is specified by the 402 "typecnt" field in the header. Each record has the following 403 format (the lengths of multi-octet fields are shown in 404 parentheses): 406 +---------------+---+---+ 407 | utoff (4) |dst|idx| 408 +---------------+---+---+ 410 utoff: A four-octet signed integer specifying the number of 411 seconds to be added to UT in order to determine local time. 412 The value MUST NOT be -2**31 and SHOULD be in the range 413 [-89999, 93599] (i.e., its value SHOULD be more than -25 hours 414 and less than 26 hours). Avoiding -2**31 allows 32-bit clients 415 to negate the value without overflow. Restricting it to 416 [-89999, 93599] allows easy support by implementations that 417 already support the POSIX-required range [-24:59:59, 25:59:59]. 419 (is)dst: A one-octet value indicating whether local time should 420 be considered Daylight Saving Time (DST). The value MUST be 0 421 or 1. A value of one (1) indicates that this type of time is 422 DST. A value of zero (0) indicates that this time type is 423 standard time. 425 (desig)idx: A one-octet unsigned integer specifying a zero-based 426 index into the series of time zone designation octets, thereby 427 selecting a particular designation string. Each index MUST be 428 in the range [0, "charcnt" - 1]; it designates the 429 NUL-terminated string of octets starting at position "idx" in 430 the time zone designations. (This string MAY be empty.) A NUL 431 octet MUST exist in the time zone designations at or after 432 position "idx". If the designation string is "-00", the time 433 type is a placeholder indicating that local time is 434 unspecified. 436 time zone designations: A series of octets constituting an array of 437 NUL-terminated (0x00) time zone designation strings. The total 438 number of octets is specified by the "charcnt" field in the 439 header. Note that two designations MAY overlap if one is a suffix 440 of the other. The character encoding of time zone designation 441 strings is not specified; however, see Section 4 of this document. 443 leap-second records: A series of eight- or twelve-octet records 444 specifying the corrections that need to be applied to UTC in order 445 to determine TAI. The records are sorted by the occurrence time 446 in strictly ascending order. The number of records is specified 447 by the "leapcnt" field in the header. Each record has one of the 448 following structures (the lengths of multi-octet fields are shown 449 in parentheses): 451 Version 1 Data Block: 452 +---------------+---------------+ 453 | occur (4) | corr (4) | 454 +---------------+---------------+ 456 version 2+ Data Block: 457 +---------------+---------------+---------------+ 458 | occur (8) | corr (4) | 459 +---------------+---------------+---------------+ 461 occur(rence): A four- or eight-octet UNIX leap time value 462 specifying the time at which a leap-second correction occurs or 463 at which the leap second table expires. The first value, if 464 present, MUST be nonnegative, and each leap second MUST occur 465 at the end of a UTC month. 467 corr(ection): A four-octet signed integer specifying the value of 468 LEAPCORR on or after the occurrence. If "leapcnt" is zero, 469 LEAPCORR is zero for all timestamps; otherwise, for timestamps 470 before the first occurrence time, LEAPCORR is zero if the first 471 correction is one (1) or minus one (-1), and is unspecified 472 otherwise (which can happen only in files truncated at the 473 start (Section 5.1)). 475 The first leap second is a positive leap second if and only if 476 its correction is positive. Each correction after the first 477 MUST differ from the previous correction by either one (1) for 478 a positive leap second or minus one (-1) for a negative leap 479 second, except that if there are two or more leap-second 480 records the correction value of the last record MAY be the same 481 as the second-to-last record, with the last record indicating 482 the expiration time of the leap-second table. 484 standard/wall indicators: A series of one-octet values indicating 485 whether the transition times associated with local time types were 486 specified as standard time or wall-clock time. Each value MUST be 487 0 or 1. A value of one (1) indicates standard time. The value 488 MUST be set to one (1) if the corresponding UT/local indicator is 489 set to one (1). A value of zero (0) indicates wall time. The 490 number of values is specified by the "isstdcnt" field in the 491 header. If "isstdcnt" is zero (0), all transition times 492 associated with local time types are assumed to be specified as 493 wall time. 495 UT/local indicators: A series of one-octet values indicating whether 496 the transition times associated with local time types were 497 specified as UT or local time. Each value MUST be 0 or 1. A 498 value of one (1) indicates UT, and the corresponding standard/wall 499 indicator MUST also be set to one (1). A value of zero (0) 500 indicates local time. The number of values is specified by the 501 "isutcnt" field in the header. If "isutcnt" is zero (0), all 502 transition times associated with local time types are assumed to 503 be specified as local time. 505 The type corresponding to a transition time specifies local time for 506 timestamps starting at the given transition time and continuing up 507 to, but not including, the next transition time. Local time for 508 timestamps before the first transition is specified by the first time 509 type (time type 0). Local time for timestamps on or after the last 510 transition is specified by the TZ string in the footer (Section 3.3) 511 if present and nonempty; otherwise, it is unspecified. If there are 512 no transitions, local time for all timestamps is specified by the TZ 513 string in the footer if present and nonempty; otherwise, it is 514 specified by time type 0. A time type with a designation string of 515 "-00" represents an unspecified local time. 517 A given pair of standard/wall and UT/local indicators is used to 518 designate whether the corresponding transition time was specified as 519 UT, standard time, or wall-clock time. Note that there are only 520 three combinations of the two indicators, given that the standard/ 521 wall value MUST be one (1) if the UT/local value is one (1). This 522 information can be useful if the transition times in a TZif file need 523 to be transformed into transitions appropriate for another time zone 524 (e.g. when calculating transition times for a simple POSIX-like TZ 525 string such as "AKST9AKDT"). 527 In order to eliminate unused space in a TZif file, every nonzero 528 local time type index SHOULD appear at least once in the transition 529 type array. Likewise, every octet in the time zone designations 530 array SHOULD be used by at least one time type record. 532 3.3. TZif Footer 534 The TZif footer is structured as follows (the lengths of multi-octet 535 fields are shown in parentheses): 537 +---+--------------------+---+ 538 | NL| TZ string (0...) |NL | 539 +---+--------------------+---+ 541 Figure 4: TZif Footer 543 The elements of the footer are defined as follows: 545 NL: An ASCII new line character (0x0A). 547 TZ string: A rule for computing local time changes after the last 548 transition time stored in the version 2+ data block. The string 549 is either empty or uses the expanded format of the "TZ" 550 environment variable as defined in Section 8.3 of the "Base 551 Definitions" volume of [POSIX] with ASCII encoding, possibly 552 utilizing extensions described below (Section 3.3.1) in version 3 553 and higher files. If the string is empty, the corresponding 554 information is not available. If the string is nonempty and one 555 or more transitions appear in the version 2+ data, the string MUST 556 be consistent with the last version 2+ transition. In other 557 words, evaluating the TZ string at the time of the last transition 558 should yield the same time type as was specified in the last 559 transition. The string MUST NOT contain NUL octets or be 560 NUL-terminated, and it SHOULD NOT begin with the ':' (colon) 561 character. 563 The TZif footer is present only in version 2 and higher files, as the 564 obsolescent version 1 format was designed before the need for a 565 footer was apparent. 567 3.3.1. TZ String Extensions 569 The TZ string in a version 3 or higher TZif file MAY use the 570 following extensions to POSIX TZ strings. These extensions are 571 described using the terminology of Section 8.3 of the "Base 572 Definitions" volume of [POSIX]. 574 * The hours part of the transition times may be signed and range 575 from -167 through 167 (-167 <= hh <= 167) instead of the POSIX- 576 required unsigned values from 0 through 24. 578 Example: <-03>3<-02>,M3.5.0/-2,M10.5.0/-1 579 This represents a time zone that observes daylight saving time 580 from 22:00 on the day before March's last Sunday until 23:00 on 581 the day before October's last Sunday. Standard time is 3 hours 582 west of UT and is abbreviated "-03"; daylight saving time is 2 583 hours west of UT and is abbreviated "-02". 585 * DST is considered to be in effect all year if it starts January 1 586 at 00:00 and ends December 31 at 24:00 plus the difference between 587 daylight saving and standard time, leaving no room for standard 588 time in the calendar. 590 Example: EST5EDT,0/0,J365/25 591 This represents a time zone that observes daylight saving time 592 all year. It is 4 hours west of UT and is abbreviated "EDT". 593 The "EST" is ignored. 595 Example: XXX3EDT4,0/0,J365/23 596 This represents the same time zone as the previous example. It 597 uses a DST further west of UTC than standard time. The "XXX" 598 is ignored. 600 4. Interoperability Considerations 602 The following practices help ensure the interoperability of TZif 603 applications. 605 * Version 1 files are considered a legacy format and SHOULD NOT be 606 generated, as they do not support transition times after the year 607 2038. 609 * Readers that understand only version 1 MUST ignore any data that 610 extends beyond the calculated end of the version 1 data block. 612 * Other than version 1, writers should generate the lowest version 613 number needed by a file's data. For example, a writer should 614 generate a version 4 file only if its leap second table either 615 expires or is truncated at the start. Likewise, a writer not 616 generating a version 4 file should generate a version 3 file only 617 if TZ string extensions are necessary to accurately model 618 transition times. 620 * To save space, writers of version 2+ files MAY output a 621 placeholder version 1 data block with all counts zero except that 622 "typecnt" and "charcnt" are both one (1). If this is done, 623 obsolescent version-1-only readers MUST interpret these files as 624 lacking time changes and time zone abbreviations. 626 * Unless the version 1 data block is a placeholder, the sequence of 627 timestamps defined by the version 1 header and data block SHOULD 628 be a contiguous sub-sequence of the timestamps defined by the 629 version 2+ header and data block, and by the footer. This 630 guideline helps obsolescent version 1 readers agree with current 631 readers about timestamps within the contiguous sub-sequence. 633 * When a TZif file contains a leap second table expiration time, 634 TZif readers SHOULD either refuse to process post-expiration 635 timestamps, or process them as if the expiration time did not 636 exist (possibly with an error indication). 638 * Time zone designations SHOULD consist of at least three (3) and no 639 more than six (6) ASCII characters from the set of alphanumerics, 640 '-', and '+'. This is for compatibility with POSIX requirements 641 for time zone abbreviations. 643 * When reading a version 2 or higher file, readers SHOULD ignore the 644 version 1 header and data block except for the purpose of skipping 645 over them. 647 * Readers SHOULD calculate the total lengths of the headers and data 648 blocks and check that they all fit within the actual file size, as 649 part of a validity check for the file. 651 * When a TZif file is used in a MIME message entity, it SHOULD be 652 indicated by one of the following media types: 654 - "application/tzif-leap" (Section 8.2) to indicate that leap- 655 second records are included in the TZif data as necessary (none 656 are necessary if the file is truncated to a range that precedes 657 the first leap second). 659 - "application/tzif" (Section 8.1) to indicate that leap-second 660 records are not included in the TZif data; "leapcnt" in the 661 header(s) MUST be zero (0). 663 * Common interoperability issues and possible workarounds are 664 described in Appendix A. 666 5. Use with the Time Zone Data Distribution Service 668 The Time Zone Data Distribution Service (TZDIST) [RFC7808] is a 669 service that allows reliable, secure, and fast delivery of time zone 670 data and leap-second rules to client systems such as calendaring and 671 scheduling applications or operating systems. 673 A TZDIST service MAY supply time zone data to clients in the Time 674 Zone Information Format. Such a service MUST indicate that it 675 supports this format by including the media type "application/tzif" 676 (Section 8.1) in its "capabilities" response (see Section 5.1 of 677 [RFC7808]). A TZDIST service MAY also include the media type 678 "application/tzif-leap" (Section 8.2) in its "capabilities" response 679 if it is able to generate TZif files containing leap-second records. 680 A TZDIST service MUST NOT advertise the "application/tzif-leap" media 681 type without also advertising "application/tzif". 683 TZDIST clients MUST use the HTTP "Accept" [RFC7231] header field to 684 indicate their preference to receive data in the "application/tzif" 685 and/or "application/tzif-leap" formats. 687 5.1. Truncating TZif Files 689 As described in Section 3.9 of [RFC7808], a TZDIST service MAY 690 truncate time zone transition data. A truncated TZif file is valid 691 from its first and up to, but not including, its last version 2+ 692 transition time, if present. 694 When truncating the start of a TZif file, the service MUST supply in 695 the version 2+ data a first transition time that is the start point 696 of the truncation range. As with untruncated TZif files, time type 0 697 indicates local time immediately before the start point, and the time 698 type of the first transition indicates local time thereafter. Time 699 type 0 SHOULD be a placeholder indicating that local time is 700 unspecified. 702 When truncating the start of a TZif file containing leap-second 703 records, the service MUST keep all leap-second records governing 704 timestamps within the truncation range, even if the first such record 705 precedes the start point of the truncation range. If the truncated 706 leap second table is nonempty, its first record MUST have a positive 707 correction if and only if it represents a positive leap second. 709 When truncating the end of a TZif file, the service MUST supply in 710 the version 2+ data a last transition time that is the end point of 711 the truncation range and MUST supply an empty TZ string. As with 712 untruncated TZif files with empty TZ strings, a truncated TZif file 713 does not indicate local time after the last transition. To this end, 714 the time type of the last transition SHOULD be a placeholder 715 indicating that local time is unspecified. 717 All represented information that falls inside the truncation range 718 MUST be the same as that represented by a corresponding untruncated 719 TZif file. 721 TZDIST clients SHOULD NOT use a truncated TZif file (as described 722 above) to interpret timestamps outside the truncation time range. 724 5.2. Example TZDIST Request for TZif Data 726 In this example, the client checks the server for the available 727 formats and then requests that the time zone with a specific time 728 zone identifier be returned in Time Zone Information Format. 730 Note that this example presumes that the time zone context path has 731 been discovered (see [RFC7808], Section 4.2.1) to be "/tzdist". 733 >> Request << 735 GET /tzdist/capabilities HTTP/1.1 736 Host: tz.example.com 738 >> Response << 740 HTTP/1.1 200 OK 741 Date: Fri, 01 Jun 2018 14:52:23 GMT 742 Content-Type: application/json 743 Content-Length: xxxx 745 { 746 "version": 1, 748 "info": { 749 "primary-source": "IANA:2018e", 750 "formats": [ 751 "text/calendar", 752 "application/tzif", 753 "application/tzif-leap" 754 ], 755 ... 756 }, 757 ... 758 } 760 >> Request << 762 GET /tzdist/zones/America%2FNew_York HTTP/1.1 763 Host: tz.example.com 764 Accept: application/tzif 766 >> Response << 768 HTTP/1.1 200 OK 769 Date: Fri, 01 Jun 2018 14:52:24 GMT 770 Content-Type: application/tzif 771 Content-Length: xxxx 772 ETag: "123456789-000-111" 774 TZif2...[binary data without leap-second records]... 775 EST5EDT,M3.2.0,M11.1.0 777 6. Security Considerations 779 The Time Zone Information Format contains no executable code, and it 780 does not define any extensible areas that could be used to store such 781 code. 783 TZif contains counted arrays of data elements. All counts should be 784 checked when processing TZif objects, to guard against references 785 past the end of the object. 787 TZif provides no confidentiality or integrity protection. Time zone 788 information is normally public and does not call for confidentiality 789 protection. Since time zone information is used in many critical 790 applications, integrity protection may be required and must be 791 provided externally. 793 7. Privacy Considerations 795 The Time Zone Information Format contains publicly available data, 796 and it does not define any extensible areas that could be used to 797 store private data. 799 As discussed in Section 9 of [RFC7808], transmission of time zone 800 data over an insecure communications channel could leak the past, 801 current, or future location of a device or user. As such, TZif data 802 transmitted over a public communications channel MUST be protected 803 with a confidentiality layer such as that provided by Transport Layer 804 Security (TLS) [RFC8446]. 806 8. IANA Considerations 808 This document defines two media types [RFC6838] for the exchange of 809 data utilizing the Time Zone Information Format. 811 8.1. application/tzif 813 Type name: 814 application 816 Subtype name: 817 tzif 819 Required parameters: 820 none 822 Optional parameters: 823 none 825 Encoding considerations: 826 binary 828 Security considerations: 829 See Section 6 of RFC XXXX. 831 Interoperability considerations: 832 See Section 4 of RFC XXXX. 834 Published specification: 835 This specification. 837 Applications that use this media type: 838 This media type is designed for widespread use by applications 839 that need to use or exchange time zone information, such as the 840 Time Zone Information Compiler (zic) [ZIC] and the GNU C Library 841 [GNU-C]. The Time Zone Distribution Service [RFC7808] can 842 directly use this media type. 844 Fragment identifier considerations: 845 N/A 847 Additional information: 848 Magic number(s): The first 4 octets are 0x54, 0x5A, 0x69, 0x66 850 File extensions(s): N/A 852 Macintosh file type code(s): N/A 854 Person & email address to contact for further information: 855 Time Zone Database mailing list 857 Intended usage: 858 COMMON 860 Restrictions on usage: 861 N/A 863 Author: 864 See the "Authors' Addresses" section of RFC XXXX. 866 Change controller: 867 IETF 869 8.2. application/tzif-leap 871 Type name: 872 application 874 Subtype name: 875 tzif-leap 877 Required parameters: 878 none 880 Optional parameters: 881 none 883 Encoding considerations: 884 binary 886 Security considerations: 887 See Section 6 of RFC XXXX. 889 Interoperability considerations: 890 See Section 4 of RFC XXXX. 892 Published specification: 893 This specification. 895 Applications that use this media type: 896 This media type is designed for widespread use by applications 897 that need to use or exchange time zone information, such as the 898 Time Zone Information Compiler (zic) [ZIC] and the GNU C Library 899 [GNU-C]. The Time Zone Distribution Service [RFC7808] can 900 directly use this media type. 902 Fragment identifier considerations: 903 N/A 905 Additional information: 906 Magic number(s): The first 4 octets are 0x54, 0x5A, 0x69, 0x66 908 File extensions(s): N/A 910 Macintosh file type code(s): N/A 912 Person & email address to contact for further information: 913 Time Zone Database mailing list 915 Intended usage: 916 COMMON 918 Restrictions on usage: 919 N/A 921 Author: 922 See the "Authors' Addresses" section of RFC XXXX. 924 Change controller: 925 IETF 927 9. References 929 9.1. Normative References 931 [GNU-C] "The GNU C Library (glibc)", 932 . 934 [ITU-R-TF.460] 935 International Telecommunications Union, "Standard- 936 frequency and time-signal emissions", ITU-R Recommendation 937 TF.460, February 2002, 938 . 940 [POSIX] IEEE, "Standard for Information Technology--Portable 941 Operating System Interface (POSIX(R)) Base Specifications, 942 Issue 7", IEEE 1003.1-2017, 943 DOI 10.1109/IEEESTD.2018.8277153, 31 January 2018, 944 . 946 [RFC20] Cerf, V., "ASCII format for network interchange", STD 80, 947 RFC 20, DOI 10.17487/RFC0020, October 1969, 948 . 950 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 951 Requirement Levels", BCP 14, RFC 2119, 952 DOI 10.17487/RFC2119, March 1997, 953 . 955 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 956 Specifications and Registration Procedures", BCP 13, 957 RFC 6838, DOI 10.17487/RFC6838, January 2013, 958 . 960 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 961 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 962 DOI 10.17487/RFC7231, June 2014, 963 . 965 [RFC7808] Douglass, M. and C. Daboo, "Time Zone Data Distribution 966 Service", RFC 7808, DOI 10.17487/RFC7808, March 2016, 967 . 969 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 970 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 971 May 2017, . 973 [ZIC] Kerrisk, M., "ZIC(8)", man-pages release 4.16, 25 February 974 2010, . 976 9.2. Informative References 978 [EGGERT-TZ] 979 "History for tz", March 2021, 980 . 982 [Err6426] RFC Errata, "Erratum ID 6426", RFC 8536, 983 . 985 [Err6435] RFC Errata, "Erratum ID 6435", RFC 8536, 986 . 988 [Err6757] RFC Errata, "Erratum ID 6757", RFC 8536, 989 . 991 [RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and 992 Scheduling Core Object Specification (iCalendar)", 993 RFC 5545, DOI 10.17487/RFC5545, September 2009, 994 . 996 [RFC6557] Lear, E. and P. Eggert, "Procedures for Maintaining the 997 Time Zone Database", BCP 175, RFC 6557, 998 DOI 10.17487/RFC6557, February 2012, 999 . 1001 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 1002 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 1003 . 1005 [RFC8536] Olson, A., Eggert, P., and K. Murchison, "The Time Zone 1006 Information Format (TZif)", RFC 8536, 1007 DOI 10.17487/RFC8536, February 2019, 1008 . 1010 [tz-link] Eggert, P. and A.D. Olson, "Sources for Time Zone and 1011 Daylight Saving Time Data", 2018, 1012 . 1014 Appendix A. Common Interoperability Issues 1016 This section documents common problems in implementing this 1017 specification. Most of these are problems in generating TZif files 1018 for use by readers conforming to predecessors of this specification 1019 [EGGERT-TZ]. The goals of this section are: 1021 1. to help TZif writers output files that avoid common pitfalls in 1022 older or buggy TZif readers, 1024 2. to help TZif readers avoid common pitfalls when reading files 1025 generated by future TZif writers, and 1027 3. to help any future specification authors see what sort of 1028 problems arise when the TZif format is changed. 1030 When new versions of the TZif format have been defined, a design goal 1031 has been that a reader can successfully use a TZif file even if the 1032 file is of a later TZif version than what the reader was designed 1033 for. When complete compatibility was not achieved, an attempt was 1034 made to limit glitches to rarely used timestamps and allow simple 1035 partial workarounds in writers designed to generate new-version data 1036 useful even for older-version readers. This section attempts to 1037 document these compatibility issues and workarounds, as well as 1038 documenting other common bugs in readers. 1040 Interoperability problems with TZif include the following: 1042 * Some readers examine only version 1 data. As a partial 1043 workaround, a writer can output as much version 1 data as 1044 possible. However, a reader should ignore version 1 data and use 1045 version 2+ data, even if the reader's native timestamps have only 1046 32 bits. 1048 * Some readers designed for version 2 might mishandle timestamps 1049 after a version 3 or higher file's last transition, because they 1050 cannot parse extensions to POSIX in the TZ-like string. As a 1051 partial workaround, a writer can output more transitions than 1052 necessary, so that only far-future timestamps are mishandled by 1053 version 2 readers. 1055 * Some readers designed for version 2 do not support permanent 1056 daylight saving time with transitions after 24:00 -- e.g., a TZ 1057 string "EST5EDT,0/0,J365/25" denoting permanent Eastern Daylight 1058 Time (-04). As a workaround, a writer can substitute standard 1059 time for two time zones east, e.g., "XXX3EDT4,0/0,J365/23" for a 1060 time zone with a never-used standard time (XXX, -03) and negative 1061 daylight saving time (EDT, -04) all year. Alternatively, as a 1062 partial workaround a writer can substitute standard time for the 1063 next time zone east -- e.g., "AST4" for permanent Atlantic 1064 Standard Time (-04). 1066 * Some readers designed for version 2 or 3, and that require strict 1067 conformance to RFC 8536, reject version 4 files whose leap second 1068 tables are truncated at the start or that end in expiration times. 1070 * Some readers ignore the footer and instead predict future 1071 timestamps from the time type of the last transition. As a 1072 partial workaround, a writer can output more transitions than 1073 necessary. 1075 * Some readers do not use time type 0 for timestamps before the 1076 first transition, in that they infer a time type using a heuristic 1077 that does not always select time type 0. As a partial workaround, 1078 a writer can output a dummy (no-op) first transition at an early 1079 time. 1081 * Some readers mishandle timestamps before the first transition that 1082 has a timestamp not less than -2**31. Readers that support only 1083 32-bit timestamps are likely to be more prone to this problem, for 1084 example, when they process 64-bit transitions, only some of which 1085 are representable in 32 bits. As a partial workaround, a writer 1086 can output a dummy transition at timestamp -2**31. 1088 * Some readers mishandle a transition if its timestamp has the 1089 minimum possible signed 64-bit value. Timestamps less than -2**59 1090 are not recommended. 1092 * Some readers mishandle POSIX-style TZ strings that contain "<" or 1093 ">". As a partial workaround, a writer can avoid using '<' or '>' 1094 for time zone abbreviations containing only alphabetic characters. 1096 * Many readers mishandle time zone abbreviations that contain non- 1097 ASCII characters. These characters are not recommended. 1099 * Some readers may mishandle time zone abbreviations that contain 1100 fewer than 3 or more than 6 characters, or that contain ASCII 1101 characters other than alphanumerics, '-', and '+'. These 1102 abbreviations are not recommended. 1104 * This specification does not dictate how readers should deal with 1105 timestamps when local time is unspecified. Common practice is for 1106 readers to report UT with designation string "-00". A reader 1107 could return an error indication instead. 1109 * Some readers mishandle TZif files that specify daylight saving 1110 time UT offsets that are less than the UT offsets for the 1111 corresponding standard time. These readers do not support 1112 locations like Ireland, which uses the equivalent of the POSIX TZ 1113 string "IST-1GMT0,M10.5.0,M3.5.0/1", observing standard time (IST, 1114 +01) in summer and daylight saving time (GMT, +00) in winter. As 1115 a partial workaround, a writer can output data for the equivalent 1116 of the POSIX TZ string "GMT0IST,M3.5.0/1,M10.5.0", thus swapping 1117 standard and daylight saving time. Although this workaround 1118 misidentifies which part of the year uses daylight saving time, it 1119 records UT offsets and time zone abbreviations correctly. 1121 * Some readers generate ambiguous timestamps for positive leap 1122 seconds that occur when the UTC offset is not a multiple of 60 1123 seconds. For example, in a timezone with UTC offset +01:23:45 and 1124 with a positive leap second 78796801 (1972-06-30 23:59:60 UTC), 1125 some readers will map both 78796800 and 78796801 to 01:23:45 local 1126 time the next day instead of mapping the latter to 01:23:46, and 1127 they will map 78796815 to 01:23:59 instead of to 01:23:60. This 1128 has not yet been a practical problem, since no civil authority has 1129 observed such UTC offsets since leap seconds were introduced in 1130 1972. 1132 Some interoperability problems are reader bugs that are listed here 1133 mostly as warnings to developers of readers. 1135 * Some readers do not support negative timestamps. Developers of 1136 distributed applications should keep this in mind if they need to 1137 deal with pre-1970 data. 1139 * Some readers mishandle timestamps before the first transition that 1140 has a nonnegative timestamp. Readers that do not support negative 1141 timestamps are likely to be more prone to this problem. 1143 * Some readers mishandle time zone abbreviations like "-08" that 1144 contain '+', '-', or digits. 1146 * Some readers mishandle UT offsets that are out of the traditional 1147 range of -12 through +12 hours and so do not support locations 1148 like Kiritimati that are outside this range. 1150 * Some readers mishandle UT offsets in the range [-3599, -1] seconds 1151 from UT, because they integer-divide the offset by 3600 to get 0 1152 and then display the hour part as "+00". 1154 * Some readers mishandle UT offsets that are not a multiple of one 1155 hour, 15 minutes, or 1 minute. 1157 Appendix B. Example TZif Files 1159 The following sections contain annotated hexadecimal dumps of example 1160 TZif files. 1162 Note that these examples should only be considered informative. 1163 Although the example data entries are current as of the publication 1164 date of this document, the data will likely change in the future as 1165 leap seconds are added and changes are made to civil time. 1167 B.1. Version 1 File Representing UTC (with Leap Seconds) 1169 +========+=============+==================+========================+ 1170 | File | Hexadecimal | Record Name / | Field Value | 1171 | Offset | Octets | Field Name | | 1172 +========+=============+==================+========================+ 1173 | 000 | 54 5a 69 66 | magic | "TZif" | 1174 +--------+-------------+------------------+------------------------+ 1175 | 004 | 00 | version | 0 (1) | 1176 +--------+-------------+------------------+------------------------+ 1177 | 005 | 00 00 00 00 | | | 1178 | | 00 00 00 00 | | | 1179 | | 00 00 00 00 | | | 1180 | | 00 00 00 | | | 1181 +--------+-------------+------------------+------------------------+ 1182 | 020 | 00 00 00 01 | isutcnt | 1 | 1183 +--------+-------------+------------------+------------------------+ 1184 | 024 | 00 00 00 01 | isstdcnt | 1 | 1185 +--------+-------------+------------------+------------------------+ 1186 | 028 | 00 00 00 1b | leapcnt | 27 | 1187 +--------+-------------+------------------+------------------------+ 1188 | 032 | 00 00 00 00 | timecnt | 0 | 1189 +--------+-------------+------------------+------------------------+ 1190 | 036 | 00 00 00 01 | typecnt | 1 | 1191 +--------+-------------+------------------+------------------------+ 1192 | 040 | 00 00 00 04 | charcnt | 4 | 1193 +--------+-------------+------------------+------------------------+ 1194 +--------+-------------+------------------+------------------------+ 1195 | | | localtimetype[0] | | 1196 +--------+-------------+------------------+------------------------+ 1197 | 044 | 00 00 00 00 | utoff | 0 (+00:00) | 1198 +--------+-------------+------------------+------------------------+ 1199 | 048 | 00 | isdst | 0 (no) | 1200 +--------+-------------+------------------+------------------------+ 1201 | 049 | 00 | desigidx | 0 | 1202 +--------+-------------+------------------+------------------------+ 1203 +--------+-------------+------------------+------------------------+ 1204 | 050 | 55 54 43 00 | designations[0] | "UTC" | 1205 +--------+-------------+------------------+------------------------+ 1206 +--------+-------------+------------------+------------------------+ 1207 | | | leapsecond[0] | | 1208 +--------+-------------+------------------+------------------------+ 1209 | 054 | 04 b2 58 00 | occurrence | 78796800 | 1210 | | | | (1972-06-30T23:59:60Z) | 1211 +--------+-------------+------------------+------------------------+ 1212 | 058 | 00 00 00 01 | correction | 1 | 1213 +--------+-------------+------------------+------------------------+ 1214 +--------+-------------+------------------+------------------------+ 1215 | | | leapsecond[1] | | 1216 +--------+-------------+------------------+------------------------+ 1217 | 062 | 05 a4 ec 01 | occurrence | 94694401 | 1218 | | | | (1972-12-31T23:59:60Z) | 1219 +--------+-------------+------------------+------------------------+ 1220 | 066 | 00 00 00 02 | correction | 2 | 1221 +--------+-------------+------------------+------------------------+ 1222 +--------+-------------+------------------+------------------------+ 1223 | | | leapsecond[2] | | 1224 +--------+-------------+------------------+------------------------+ 1225 | 070 | 07 86 1f 82 | occurrence | 126230402 | 1226 | | | | (1973-12-31T23:59:60Z) | 1227 +--------+-------------+------------------+------------------------+ 1228 | 074 | 00 00 00 03 | correction | 3 | 1229 +--------+-------------+------------------+------------------------+ 1230 +--------+-------------+------------------+------------------------+ 1231 | | | leapsecond[3] | | 1232 +--------+-------------+------------------+------------------------+ 1233 | 078 | 09 67 53 03 | occurrence | 157766403 | 1234 | | | | (1974-12-31T23:59:60Z) | 1235 +--------+-------------+------------------+------------------------+ 1236 | 082 | 00 00 00 04 | correction | 4 | 1237 +--------+-------------+------------------+------------------------+ 1238 +--------+-------------+------------------+------------------------+ 1239 | | | leapsecond[4] | | 1240 +--------+-------------+------------------+------------------------+ 1241 | 086 | 0b 48 86 84 | occurrence | 189302404 | 1242 | | | | (1975-12-31T23:59:60Z) | 1243 +--------+-------------+------------------+------------------------+ 1244 | 090 | 00 00 00 05 | correction | 5 | 1245 +--------+-------------+------------------+------------------------+ 1246 +--------+-------------+------------------+------------------------+ 1247 | | | leapsecond[5] | | 1248 +--------+-------------+------------------+------------------------+ 1249 | 094 | 0d 2b 0b 85 | occurrence | 220924805 | 1250 | | | | (1976-12-31T23:59:60Z) | 1251 +--------+-------------+------------------+------------------------+ 1252 | 098 | 00 00 00 06 | correction | 6 | 1253 +--------+-------------+------------------+------------------------+ 1254 +--------+-------------+------------------+------------------------+ 1255 | | | leapsecond[6] | | 1256 +--------+-------------+------------------+------------------------+ 1257 | 102 | 0f 0c 3f 06 | occurrence | 252460806 | 1258 | | | | (1977-12-31T23:59:60Z) | 1259 +--------+-------------+------------------+------------------------+ 1260 | 106 | 00 00 00 07 | correction | 7 | 1261 +--------+-------------+------------------+------------------------+ 1262 +--------+-------------+------------------+------------------------+ 1263 | | | leapsecond[7] | | 1264 +--------+-------------+------------------+------------------------+ 1265 | 110 | 10 ed 72 87 | occurrence | 283996807 | 1266 | | | | (1978-12-31T23:59:60Z) | 1267 +--------+-------------+------------------+------------------------+ 1268 | 114 | 00 00 00 08 | correction | 8 | 1269 +--------+-------------+------------------+------------------------+ 1270 +--------+-------------+------------------+------------------------+ 1271 | | | leapsecond[8] | | 1272 +--------+-------------+------------------+------------------------+ 1273 | 118 | 12 ce a6 08 | occurrence | 315532808 | 1274 | | | | (1979-12-31T23:59:60Z) | 1275 +--------+-------------+------------------+------------------------+ 1276 | 122 | 00 00 00 09 | correction | 9 | 1277 +--------+-------------+------------------+------------------------+ 1278 +--------+-------------+------------------+------------------------+ 1279 | | | leapsecond[9] | | 1280 +--------+-------------+------------------+------------------------+ 1281 | 126 | 15 9f ca 89 | occurrence | 362793609 | 1282 | | | | (1981-06-30T23:59:60Z) | 1283 +--------+-------------+------------------+------------------------+ 1284 | 130 | 00 00 00 0a | correction | 10 | 1285 +--------+-------------+------------------+------------------------+ 1286 +--------+-------------+------------------+------------------------+ 1287 | | | leapsecond[10] | | 1288 +--------+-------------+------------------+------------------------+ 1289 | 134 | 17 80 fe 0a | occurrence | 394329610 | 1290 | | | | (1982-06-30T23:59:60Z) | 1291 +--------+-------------+------------------+------------------------+ 1292 | 138 | 00 00 00 0b | correction | 11 | 1293 +--------+-------------+------------------+------------------------+ 1294 +--------+-------------+------------------+------------------------+ 1295 | | | leapsecond[11] | | 1296 +--------+-------------+------------------+------------------------+ 1297 | 142 | 19 62 31 8b | occurrence | 425865611 | 1298 | | | | (1983-06-30T23:59:60Z) | 1299 +--------+-------------+------------------+------------------------+ 1300 | 146 | 00 00 00 0c | correction | 12 | 1301 +--------+-------------+------------------+------------------------+ 1302 +--------+-------------+------------------+------------------------+ 1303 | | | leapsecond[12] | | 1304 +--------+-------------+------------------+------------------------+ 1305 | 150 | 1d 25 ea 0c | occurrence | 489024012 | 1306 | | | | (1985-06-30T23:59:60Z) | 1307 +--------+-------------+------------------+------------------------+ 1308 | 154 | 00 00 00 0d | correction | 13 | 1309 +--------+-------------+------------------+------------------------+ 1310 +--------+-------------+------------------+------------------------+ 1311 | | | leapsecond[13] | | 1312 +--------+-------------+------------------+------------------------+ 1313 | 158 | 21 da e5 0d | occurrence | 567993613 | 1314 | | | | (1987-12-31T23:59:60Z) | 1315 +--------+-------------+------------------+------------------------+ 1316 | 162 | 00 00 00 0e | correction | 14 | 1317 +--------+-------------+------------------+------------------------+ 1318 +--------+-------------+------------------+------------------------+ 1319 | | | leapsecond[14] | | 1320 +--------+-------------+------------------+------------------------+ 1321 | 166 | 25 9e 9d 8e | occurrence | 631152014 | 1322 | | | | (1989-12-31T23:59:60Z) | 1323 +--------+-------------+------------------+------------------------+ 1324 | 170 | 00 00 00 0f | correction | 15 | 1325 +--------+-------------+------------------+------------------------+ 1326 +--------+-------------+------------------+------------------------+ 1327 | | | leapsecond[15] | | 1328 +--------+-------------+------------------+------------------------+ 1329 | 174 | 27 7f d1 0f | occurrence | 662688015 | 1330 | | | | (1990-12-31T23:59:60Z) | 1331 +--------+-------------+------------------+------------------------+ 1332 | 178 | 00 00 00 10 | correction | 16 | 1333 +--------+-------------+------------------+------------------------+ 1334 +--------+-------------+------------------+------------------------+ 1335 | | | leapsecond[16] | | 1336 +--------+-------------+------------------+------------------------+ 1337 | 182 | 2a 50 f5 90 | occurrence | 709948816 | 1338 | | | | (1992-06-30T23:59:60Z) | 1339 +--------+-------------+------------------+------------------------+ 1340 | 186 | 00 00 00 11 | correction | 17 | 1341 +--------+-------------+------------------+------------------------+ 1342 +--------+-------------+------------------+------------------------+ 1343 | | | leapsecond[17] | | 1344 +--------+-------------+------------------+------------------------+ 1345 | 190 | 2c 32 29 11 | occurrence | 741484817 | 1346 | | | | (1993-06-30T23:59:60Z) | 1347 +--------+-------------+------------------+------------------------+ 1348 | 194 | 00 00 00 12 | correction | 18 | 1349 +--------+-------------+------------------+------------------------+ 1350 +--------+-------------+------------------+------------------------+ 1351 | | | leapsecond[18] | | 1352 +--------+-------------+------------------+------------------------+ 1353 | 198 | 2e 13 5c 92 | occurrence | 773020818 | 1354 | | | | (1994-06-30T23:59:60Z) | 1355 +--------+-------------+------------------+------------------------+ 1356 | 202 | 00 00 00 13 | correction | 19 | 1357 +--------+-------------+------------------+------------------------+ 1358 +--------+-------------+------------------+------------------------+ 1359 | | | leapsecond[19] | | 1360 +--------+-------------+------------------+------------------------+ 1361 | 206 | 30 e7 24 13 | occurrence | 820454419 | 1362 | | | | (1995-12-31T23:59:60Z) | 1363 +--------+-------------+------------------+------------------------+ 1364 | 210 | 00 00 00 14 | correction | 20 | 1365 +--------+-------------+------------------+------------------------+ 1366 +--------+-------------+------------------+------------------------+ 1367 | | | leapsecond[20] | | 1368 +--------+-------------+------------------+------------------------+ 1369 | 214 | 33 b8 48 94 | occurrence | 867715220 | 1370 | | | | (1997-06-30T23:59:60Z) | 1371 +--------+-------------+------------------+------------------------+ 1372 | 218 | 00 00 00 15 | correction | 21 | 1373 +--------+-------------+------------------+------------------------+ 1374 +--------+-------------+------------------+------------------------+ 1375 | | | leapsecond[21] | | 1376 +--------+-------------+------------------+------------------------+ 1377 | 222 | 36 8c 10 15 | occurrence | 915148821 | 1378 | | | | (1998-12-31T23:59:60Z) | 1379 +--------+-------------+------------------+------------------------+ 1380 | 226 | 00 00 00 16 | correction | 22 | 1381 +--------+-------------+------------------+------------------------+ 1382 +--------+-------------+------------------+------------------------+ 1383 | | | leapsecond[22] | | 1384 +--------+-------------+------------------+------------------------+ 1385 | 230 | 43 b7 1b 96 | occurrence | 1136073622 | 1386 | | | | (2005-12-31T23:59:60Z) | 1387 +--------+-------------+------------------+------------------------+ 1388 | 234 | 00 00 00 17 | correction | 23 | 1389 +--------+-------------+------------------+------------------------+ 1390 +--------+-------------+------------------+------------------------+ 1391 | | | leapsecond[23] | | 1392 +--------+-------------+------------------+------------------------+ 1393 | 238 | 49 5c 07 97 | occurrence | 1230768023 | 1394 | | | | (2008-12-31T23:59:60Z) | 1395 +--------+-------------+------------------+------------------------+ 1396 | 242 | 00 00 00 18 | correction | 24 | 1397 +--------+-------------+------------------+------------------------+ 1398 +--------+-------------+------------------+------------------------+ 1399 | | | leapsecond[24] | | 1400 +--------+-------------+------------------+------------------------+ 1401 | 246 | 4f ef 93 18 | occurrence | 1341100824 | 1402 | | | | (2012-06-30T23:59:60Z) | 1403 +--------+-------------+------------------+------------------------+ 1404 | 250 | 00 00 00 19 | correction | 25 | 1405 +--------+-------------+------------------+------------------------+ 1406 +--------+-------------+------------------+------------------------+ 1407 | | | leapsecond[25] | | 1408 +--------+-------------+------------------+------------------------+ 1409 | 254 | 55 93 2d 99 | occurrence | 1435708825 | 1410 | | | | (2015-06-30T23:59:60Z) | 1411 +--------+-------------+------------------+------------------------+ 1412 | 258 | 00 00 00 1a | correction | 26 | 1413 +--------+-------------+------------------+------------------------+ 1414 +--------+-------------+------------------+------------------------+ 1415 | | | leapsecond[26] | | 1416 +--------+-------------+------------------+------------------------+ 1417 | 262 | 58 68 46 9a | occurrence | 1483228826 | 1418 | | | | (2016-12-31T23:59:60Z) | 1419 +--------+-------------+------------------+------------------------+ 1420 | 266 | 00 00 00 1b | correction | 27 | 1421 +--------+-------------+------------------+------------------------+ 1422 +--------+-------------+------------------+------------------------+ 1423 | 270 | 00 | standard/wall[0] | 0 (wall) | 1424 +--------+-------------+------------------+------------------------+ 1425 +--------+-------------+------------------+------------------------+ 1426 | 271 | 00 | UT/local[0] | 0 (local) | 1427 +--------+-------------+------------------+------------------------+ 1429 Table 1 1431 To determine TAI corresponding to 2000-01-01T00:00:00Z 1432 (UNIX time = 946684800), the following procedure would be followed: 1434 1. Find the latest leap-second occurrence prior to the time of 1435 interest (leapsecond[21]) and note the correction value 1436 (LEAPCORR = 22). 1438 2. Add LEAPCORR + 10 to the time of interest to yield TAI of 1439 2000-01-01T00:00:32. 1441 B.2. Version 2 File Representing Pacific/Honolulu 1443 +========+=============+==================+========================+ 1444 | File | Hexadecimal | Record Name / | Field Value | 1445 | Offset | Octets | Field Name | | 1446 +========+=============+==================+========================+ 1447 | 000 | 54 5a 69 66 | magic | "TZif" | 1448 +--------+-------------+------------------+------------------------+ 1449 | 004 | 32 | version | '2' (2) | 1450 +--------+-------------+------------------+------------------------+ 1451 | 005 | 00 00 00 00 | | | 1452 | | 00 00 00 00 | | | 1453 | | 00 00 00 00 | | | 1454 | | 00 00 00 | | | 1455 +--------+-------------+------------------+------------------------+ 1456 | 020 | 00 00 00 06 | isutcnt | 6 | 1457 +--------+-------------+------------------+------------------------+ 1458 | 024 | 00 00 00 06 | isstdcnt | 6 | 1459 +--------+-------------+------------------+------------------------+ 1460 | 028 | 00 00 00 00 | leapcnt | 0 | 1461 +--------+-------------+------------------+------------------------+ 1462 | 032 | 00 00 00 07 | timecnt | 7 | 1463 +--------+-------------+------------------+------------------------+ 1464 | 036 | 00 00 00 06 | typecnt | 6 | 1465 +--------+-------------+------------------+------------------------+ 1466 | 040 | 00 00 00 14 | charcnt | 20 | 1467 +--------+-------------+------------------+------------------------+ 1468 +--------+-------------+------------------+------------------------+ 1469 | 044 | 80 00 00 00 | trans time[0] | -2147483648 | 1470 | | | | (1901-12-13T20:45:52Z) | 1471 +--------+-------------+------------------+------------------------+ 1472 | 048 | bb 05 43 48 | trans time[1] | -1157283000 | 1473 | | | | (1933-04-30T12:30:00Z) | 1474 +--------+-------------+------------------+------------------------+ 1475 | 052 | bb 21 71 58 | trans time[2] | -1155436200 | 1476 | | | | (1933-05-21T21:30:00Z) | 1477 +--------+-------------+------------------+------------------------+ 1478 | 056 | cb 89 3d c8 | trans time[3] | -880198200 | 1479 | | | | (1942-02-09T12:30:00Z) | 1480 +--------+-------------+------------------+------------------------+ 1481 | 060 | d2 23 f4 70 | trans time[4] | -769395600 | 1482 | | | | (1945-08-14T23:00:00Z) | 1483 +--------+-------------+------------------+------------------------+ 1484 | 064 | d2 61 49 38 | trans time[5] | -765376200 | 1485 | | | | (1945-09-30T11:30:00Z) | 1486 +--------+-------------+------------------+------------------------+ 1487 | 068 | d5 8d 73 48 | trans time[6] | -712150200 | 1488 | | | | (1947-06-08T12:30:00Z) | 1489 +--------+-------------+------------------+------------------------+ 1490 +--------+-------------+------------------+------------------------+ 1491 | 072 | 01 | trans type[0] | 1 | 1492 +--------+-------------+------------------+------------------------+ 1493 | 073 | 02 | trans type[1] | 2 | 1494 +--------+-------------+------------------+------------------------+ 1495 | 074 | 01 | trans type[2] | 1 | 1496 +--------+-------------+------------------+------------------------+ 1497 | 075 | 03 | trans type[3] | 3 | 1498 +--------+-------------+------------------+------------------------+ 1499 | 076 | 04 | trans type[4] | 4 | 1500 +--------+-------------+------------------+------------------------+ 1501 | 077 | 01 | trans type[5] | 1 | 1502 +--------+-------------+------------------+------------------------+ 1503 | 078 | 05 | trans type[6] | 5 | 1504 +--------+-------------+------------------+------------------------+ 1505 +--------+-------------+------------------+------------------------+ 1506 | | | localtimetype[0] | | 1507 +--------+-------------+------------------+------------------------+ 1508 | 079 | ff ff 6c 02 | utoff | -37886 (-10:21:26) | 1509 +--------+-------------+------------------+------------------------+ 1510 | 083 | 00 | isdst | 0 (no) | 1511 +--------+-------------+------------------+------------------------+ 1512 | 084 | 00 | desigidx | 0 | 1513 +--------+-------------+------------------+------------------------+ 1514 +--------+-------------+------------------+------------------------+ 1515 | | | localtimetype[1] | | 1516 +--------+-------------+------------------+------------------------+ 1517 | 085 | ff ff 6c 58 | utoff | -37800 (-10:30) | 1518 +--------+-------------+------------------+------------------------+ 1519 | 089 | 00 | isdst | 0 (no) | 1520 +--------+-------------+------------------+------------------------+ 1521 | 090 | 04 | desigidx | 4 | 1522 +--------+-------------+------------------+------------------------+ 1523 +--------+-------------+------------------+------------------------+ 1524 | | | localtimetype[2] | | 1525 +--------+-------------+------------------+------------------------+ 1526 | 091 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1527 +--------+-------------+------------------+------------------------+ 1528 | 095 | 01 | isdst | 1 (yes) | 1529 +--------+-------------+------------------+------------------------+ 1530 | 096 | 08 | desigidx | 8 | 1531 +--------+-------------+------------------+------------------------+ 1532 +--------+-------------+------------------+------------------------+ 1533 | | | localtimetype[3] | | 1534 +--------+-------------+------------------+------------------------+ 1535 | 097 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1536 +--------+-------------+------------------+------------------------+ 1537 | 101 | 01 | isdst | 1 (yes) | 1538 +--------+-------------+------------------+------------------------+ 1539 | 102 | 0c | desigidx | 12 | 1540 +--------+-------------+------------------+------------------------+ 1541 +--------+-------------+------------------+------------------------+ 1542 | | | localtimetype[4] | | 1543 +--------+-------------+------------------+------------------------+ 1544 | 103 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1545 +--------+-------------+------------------+------------------------+ 1546 | 107 | 01 | isdst | 1 (yes) | 1547 +--------+-------------+------------------+------------------------+ 1548 | 108 | 10 | desigidx | 16 | 1549 +--------+-------------+------------------+------------------------+ 1550 +--------+-------------+------------------+------------------------+ 1551 | | | localtimetype[5] | | 1552 +--------+-------------+------------------+------------------------+ 1553 | 109 | ff ff 73 60 | utoff | -36000 (-10:00) | 1554 +--------+-------------+------------------+------------------------+ 1555 | 113 | 00 | isdst | 0 (no) | 1556 +--------+-------------+------------------+------------------------+ 1557 | 114 | 04 | desigidx | 4 | 1558 +--------+-------------+------------------+------------------------+ 1559 +--------+-------------+------------------+------------------------+ 1560 | 115 | 4c 4d 54 00 | designations[0] | "LMT" | 1561 +--------+-------------+------------------+------------------------+ 1562 | 119 | 48 53 54 00 | designations[4] | "HST" | 1563 +--------+-------------+------------------+------------------------+ 1564 | 123 | 48 44 54 00 | designations[8] | "HDT" | 1565 +--------+-------------+------------------+------------------------+ 1566 | 127 | 48 57 54 00 | designations[12] | "HWT" | 1567 +--------+-------------+------------------+------------------------+ 1568 | 131 | 48 50 54 00 | designations[16] | "HPT" | 1569 +--------+-------------+------------------+------------------------+ 1570 +--------+-------------+------------------+------------------------+ 1571 | 135 | 00 | standard/wall[0] | 0 (wall) | 1572 +--------+-------------+------------------+------------------------+ 1573 | 136 | 00 | standard/wall[1] | 0 (wall) | 1574 +--------+-------------+------------------+------------------------+ 1575 | 137 | 00 | standard/wall[2] | 0 (wall) | 1576 +--------+-------------+------------------+------------------------+ 1577 | 138 | 00 | standard/wall[3] | 0 (wall) | 1578 +--------+-------------+------------------+------------------------+ 1579 | 139 | 01 | standard/wall[4] | 1 (standard) | 1580 +--------+-------------+------------------+------------------------+ 1581 | 140 | 00 | standard/wall[5] | 0 (wall) | 1582 +--------+-------------+------------------+------------------------+ 1583 +--------+-------------+------------------+------------------------+ 1584 | 141 | 00 | UT/local[0] | 0 (local) | 1585 +--------+-------------+------------------+------------------------+ 1586 | 142 | 00 | UT/local[1] | 0 (local) | 1587 +--------+-------------+------------------+------------------------+ 1588 | 143 | 00 | UT/local[2] | 0 (local) | 1589 +--------+-------------+------------------+------------------------+ 1590 | 144 | 00 | UT/local[3] | 0 (local) | 1591 +--------+-------------+------------------+------------------------+ 1592 | 145 | 01 | UT/local[4] | 1 (UT) | 1593 +--------+-------------+------------------+------------------------+ 1594 | 146 | 00 | UT/local[5] | 0 (local) | 1595 +--------+-------------+------------------+------------------------+ 1596 +--------+-------------+------------------+------------------------+ 1597 | 147 | 54 5a 69 66 | magic | "TZif" | 1598 +--------+-------------+------------------+------------------------+ 1599 | 151 | 32 | version | '2' (2) | 1600 +--------+-------------+------------------+------------------------+ 1601 | 152 | 00 00 00 00 | | | 1602 | | 00 00 00 00 | | | 1603 | | 00 00 00 00 | | | 1604 | | 00 00 00 | | | 1605 +--------+-------------+------------------+------------------------+ 1606 | 167 | 00 00 00 06 | isutcnt | 6 | 1607 +--------+-------------+------------------+------------------------+ 1608 | 171 | 00 00 00 06 | isstdcnt | 6 | 1609 +--------+-------------+------------------+------------------------+ 1610 | 175 | 00 00 00 00 | leapcnt | 0 | 1611 +--------+-------------+------------------+------------------------+ 1612 | 179 | 00 00 00 07 | timecnt | 7 | 1613 +--------+-------------+------------------+------------------------+ 1614 | 183 | 00 00 00 06 | typecnt | 6 | 1615 +--------+-------------+------------------+------------------------+ 1616 | 187 | 00 00 00 14 | charcnt | 20 | 1617 +--------+-------------+------------------+------------------------+ 1618 +--------+-------------+------------------+------------------------+ 1619 | 191 | ff ff ff ff | trans time[0] | -2334101314 | 1620 | | 74 e0 70 be | | (1896-01-13T22:31:26Z) | 1621 +--------+-------------+------------------+------------------------+ 1622 | 199 | ff ff ff ff | trans time[1] | -1157283000 | 1623 | | bb 05 43 48 | | (1933-04-30T12:30:00Z) | 1624 +--------+-------------+------------------+------------------------+ 1625 | 207 | ff ff ff ff | trans time[2] | -1155436200 | 1626 | | bb 21 71 58 | | (1933-05-21T21:30:00Z) | 1627 +--------+-------------+------------------+------------------------+ 1628 | 215 | ff ff ff ff | trans time[3] | -880198200 | 1629 | | cb 89 3d c8 | | (1942-02-09T12:30:00Z) | 1630 +--------+-------------+------------------+------------------------+ 1631 | 223 | ff ff ff ff | trans time[4] | -769395600 | 1632 | | d2 23 f4 70 | | (1945-08-14T23:00:00Z) | 1633 +--------+-------------+------------------+------------------------+ 1634 | 231 | ff ff ff ff | trans time[5] | -765376200 | 1635 | | d2 61 49 38 | | (1945-09-30T11:30:00Z) | 1636 +--------+-------------+------------------+------------------------+ 1637 | 239 | ff ff ff ff | trans time[6] | -712150200 | 1638 | | d5 8d 73 48 | | (1947-06-08T12:30:00Z) | 1639 +--------+-------------+------------------+------------------------+ 1640 +--------+-------------+------------------+------------------------+ 1641 | 247 | 01 | trans type[0] | 1 | 1642 +--------+-------------+------------------+------------------------+ 1643 | 248 | 02 | trans type[1] | 2 | 1644 +--------+-------------+------------------+------------------------+ 1645 | 249 | 01 | trans type[2] | 1 | 1646 +--------+-------------+------------------+------------------------+ 1647 | 250 | 03 | trans type[3] | 3 | 1648 +--------+-------------+------------------+------------------------+ 1649 | 251 | 04 | trans type[4] | 4 | 1650 +--------+-------------+------------------+------------------------+ 1651 | 252 | 01 | trans type[5] | 1 | 1652 +--------+-------------+------------------+------------------------+ 1653 | 253 | 05 | trans type[6] | 5 | 1654 +--------+-------------+------------------+------------------------+ 1655 +--------+-------------+------------------+------------------------+ 1656 | | | localtimetype[0] | | 1657 +--------+-------------+------------------+------------------------+ 1658 | 254 | ff ff 6c 02 | utoff | -37886 (-10:21:26) | 1659 +--------+-------------+------------------+------------------------+ 1660 | 258 | 00 | isdst | 0 (no) | 1661 +--------+-------------+------------------+------------------------+ 1662 | 259 | 00 | desigidx | 0 | 1663 +--------+-------------+------------------+------------------------+ 1664 +--------+-------------+------------------+------------------------+ 1665 | | | localtimetype[1] | | 1666 +--------+-------------+------------------+------------------------+ 1667 | 260 | ff ff 6c 58 | utoff | -37800 (-10:30) | 1668 +--------+-------------+------------------+------------------------+ 1669 | 264 | 00 | isdst | 0 (no) | 1670 +--------+-------------+------------------+------------------------+ 1671 | 265 | 04 | desigidx | 4 | 1672 +--------+-------------+------------------+------------------------+ 1673 +--------+-------------+------------------+------------------------+ 1674 | | | localtimetype[2] | | 1675 +--------+-------------+------------------+------------------------+ 1676 | 266 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1677 +--------+-------------+------------------+------------------------+ 1678 | 270 | 01 | isdst | 1 (yes) | 1679 +--------+-------------+------------------+------------------------+ 1680 | 271 | 08 | desigidx | 8 | 1681 +--------+-------------+------------------+------------------------+ 1682 +--------+-------------+------------------+------------------------+ 1683 | | | localtimetype[3] | | 1684 +--------+-------------+------------------+------------------------+ 1685 | 272 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1686 +--------+-------------+------------------+------------------------+ 1687 | 276 | 01 | isdst | 1 (yes) | 1688 +--------+-------------+------------------+------------------------+ 1689 | 277 | 0c | desigidx | 12 | 1690 +--------+-------------+------------------+------------------------+ 1691 +--------+-------------+------------------+------------------------+ 1692 | | | localtimetype[4] | | 1693 +--------+-------------+------------------+------------------------+ 1694 | 278 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1695 +--------+-------------+------------------+------------------------+ 1696 | 282 | 01 | isdst | 1 (yes) | 1697 +--------+-------------+------------------+------------------------+ 1698 | 283 | 10 | desigidx | 16 | 1699 +--------+-------------+------------------+------------------------+ 1700 +--------+-------------+------------------+------------------------+ 1701 | | | localtimetype[5] | | 1702 +--------+-------------+------------------+------------------------+ 1703 | 284 | ff ff 73 60 | utoff | -36000 (-10:00) | 1704 +--------+-------------+------------------+------------------------+ 1705 | 288 | 00 | isdst | 0 (no) | 1706 +--------+-------------+------------------+------------------------+ 1707 | 289 | 04 | desigidx | 4 | 1708 +--------+-------------+------------------+------------------------+ 1709 +--------+-------------+------------------+------------------------+ 1710 | 290 | 4c 4d 54 00 | designations[0] | "LMT" | 1711 +--------+-------------+------------------+------------------------+ 1712 | 294 | 48 53 54 00 | designations[4] | "HST" | 1713 +--------+-------------+------------------+------------------------+ 1714 | 298 | 48 44 54 00 | designations[8] | "HDT" | 1715 +--------+-------------+------------------+------------------------+ 1716 | 302 | 48 57 54 00 | designations[12] | "HWT" | 1717 +--------+-------------+------------------+------------------------+ 1718 | 306 | 48 50 54 00 | designations[16] | "HPT" | 1719 +--------+-------------+------------------+------------------------+ 1720 +--------+-------------+------------------+------------------------+ 1721 | 310 | 00 | standard/wall[0] | 0 (wall) | 1722 +--------+-------------+------------------+------------------------+ 1723 | 311 | 00 | standard/wall[1] | 0 (wall) | 1724 +--------+-------------+------------------+------------------------+ 1725 | 312 | 00 | standard/wall[2] | 0 (wall) | 1726 +--------+-------------+------------------+------------------------+ 1727 | 313 | 00 | standard/wall[3] | 0 (wall) | 1728 +--------+-------------+------------------+------------------------+ 1729 | 314 | 01 | standard/wall[4] | 1 (standard) | 1730 +--------+-------------+------------------+------------------------+ 1731 | 315 | 00 | standard/wall[5] | 0 (wall) | 1732 +--------+-------------+------------------+------------------------+ 1733 +--------+-------------+------------------+------------------------+ 1734 | 316 | 00 | UT/local[0] | 0 (local) | 1735 +--------+-------------+------------------+------------------------+ 1736 | 317 | 00 | UT/local[1] | 0 (local) | 1737 +--------+-------------+------------------+------------------------+ 1738 | 318 | 00 | UT/local[2] | 0 (local) | 1739 +--------+-------------+------------------+------------------------+ 1740 | 319 | 00 | UT/local[3] | 0 (local) | 1741 +--------+-------------+------------------+------------------------+ 1742 | 320 | 01 | UT/local[4] | 1 (UT) | 1743 +--------+-------------+------------------+------------------------+ 1744 | 321 | 00 | UT/local[5] | 0 (local) | 1745 +--------+-------------+------------------+------------------------+ 1746 +--------+-------------+------------------+------------------------+ 1747 | 322 | 0a | NL | '\n' | 1748 +--------+-------------+------------------+------------------------+ 1749 | 323 | 48 53 54 31 | TZ string | "HST10" | 1750 | | 30 | | | 1751 +--------+-------------+------------------+------------------------+ 1752 | 328 | 0a | NL | '\n' | 1753 +--------+-------------+------------------+------------------------+ 1755 Table 2 1757 To determine the local time in this time zone corresponding to 1758 1933-05-04T12:00:00Z (UNIX time = -1156939200), the following 1759 procedure would be followed: 1761 1. Find the latest time transition prior to the time of interest 1762 (trans time[1]). 1764 2. Reference the corresponding transition type (trans type[1]) to 1765 determine the local time type index (2). 1767 3. Reference the corresponding local time type (localtimetype[2]) to 1768 determine the offset from UTC (-09:30), the daylight saving 1769 indicator (1 = yes), and the index into the time zone designation 1770 strings (8). 1772 4. Look up the corresponding time zone designation string 1773 (designations[8] = "HDT"). 1775 5. Add the UTC offset to the time of interest to yield a local 1776 daylight saving time of 1933-05-04T02:30:00-09:30 (HDT). 1778 To determine the local time in this time zone corresponding to 1779 2019-01-01T00:00:00Z (UNIX time = 1546300800), the following 1780 procedure would be followed: 1782 1. Find the latest time transition prior to the time of interest 1783 (there is no such transition). 1785 2. Look up the TZ string in the footer ("HST10"), which indicates 1786 that the time zone designation is "HST" year-round, and the 1787 offset to UTC is 10:00. 1789 3. Subtract the UTC offset from the time of interest to yield a 1790 standard local time of 2018-12-31T14:00:00-10:00 (HST). 1792 B.3. Truncated Version 3 File Representing Asia/Jerusalem 1794 The following TZif file has been truncated to start on 1795 2038-01-01T00:00:00Z. 1797 In this example: 1799 * The start time value can not be represented using 32 bits, so the 1800 version 1 header contains only the required minimum data, which 1801 will be ignored by readers. 1803 * The version 3 header leverages the fact that by specifying 1804 'isutcnt' and 'isstdcnt' as zero, all transition times associated 1805 with local time types are assumed to be specified as local wall- 1806 clock time (see the definitions of UT/local indicators and 1807 standard/wall indicators in Section 3.2). 1809 * The TZ string value has been line-wrapped for presentation 1810 purposes only. 1812 +========+=============+==================+========================+ 1813 | File | Hexadecimal | Record Name / | Field Value | 1814 | Offset | Octets | Field Name | | 1815 +========+=============+==================+========================+ 1816 | 000 | 54 5a 69 66 | magic | "TZif" | 1817 +--------+-------------+------------------+------------------------+ 1818 | 004 | 33 | version | '3' (3) | 1819 +--------+-------------+------------------+------------------------+ 1820 | 005 | 00 00 00 00 | | | 1821 | | 00 00 00 00 | | | 1822 | | 00 00 00 00 | | | 1823 | | 00 00 00 | | | 1824 +--------+-------------+------------------+------------------------+ 1825 | 020 | 00 00 00 00 | isutcnt | 0 | 1826 +--------+-------------+------------------+------------------------+ 1827 | 024 | 00 00 00 00 | isstdcnt | 0 | 1828 +--------+-------------+------------------+------------------------+ 1829 | 028 | 00 00 00 00 | leapcnt | 0 | 1830 +--------+-------------+------------------+------------------------+ 1831 | 032 | 00 00 00 00 | timecnt | 0 | 1832 +--------+-------------+------------------+------------------------+ 1833 | 036 | 00 00 00 01 | typecnt | 1 | 1834 +--------+-------------+------------------+------------------------+ 1835 | 040 | 00 00 00 01 | charcnt | 1 | 1836 +--------+-------------+------------------+------------------------+ 1837 +--------+-------------+------------------+------------------------+ 1838 | | | localtimetype[0] | | 1839 +--------+-------------+------------------+------------------------+ 1840 | 044 | 00 00 00 00 | utoff | 0 (+00:00) | 1841 +--------+-------------+------------------+------------------------+ 1842 | 048 | 00 | isdst | 0 (no) | 1843 +--------+-------------+------------------+------------------------+ 1844 | 049 | 00 | desigidx | 0 | 1845 +--------+-------------+------------------+------------------------+ 1846 +--------+-------------+------------------+------------------------+ 1847 | 050 | 00 | designations[0] | "" | 1848 +--------+-------------+------------------+------------------------+ 1849 +--------+-------------+------------------+------------------------+ 1850 | 051 | 54 5a 69 66 | magic | "TZif" | 1851 +--------+-------------+------------------+------------------------+ 1852 | 055 | 33 | version | '3' (3) | 1853 +--------+-------------+------------------+------------------------+ 1854 | 056 | 00 00 00 00 | | | 1855 | | 00 00 00 00 | | | 1856 | | 00 00 00 00 | | | 1857 | | 00 00 00 | | | 1858 +--------+-------------+------------------+------------------------+ 1859 | 071 | 00 00 00 00 | isutcnt | 0 | 1860 +--------+-------------+------------------+------------------------+ 1861 | 075 | 00 00 00 00 | isstdcnt | 0 | 1862 +--------+-------------+------------------+------------------------+ 1863 | 079 | 00 00 00 00 | leapcnt | 0 | 1864 +--------+-------------+------------------+------------------------+ 1865 | 083 | 00 00 00 01 | timecnt | 1 | 1866 +--------+-------------+------------------+------------------------+ 1867 | 087 | 00 00 00 01 | typecnt | 1 | 1868 +--------+-------------+------------------+------------------------+ 1869 | 091 | 00 00 00 04 | charcnt | 4 | 1870 +--------+-------------+------------------+------------------------+ 1871 +--------+-------------+------------------+------------------------+ 1872 | 095 | 00 00 00 00 | trans time[0] | 2145916800 | 1873 | | 7f e8 17 80 | | (2038-01-01T00:00:00Z) | 1874 +--------+-------------+------------------+------------------------+ 1875 +--------+-------------+------------------+------------------------+ 1876 | 103 | 00 | trans type[0] | 0 | 1877 +--------+-------------+------------------+------------------------+ 1878 +--------+-------------+------------------+------------------------+ 1879 | | | localtimetype[0] | | 1880 +--------+-------------+------------------+------------------------+ 1881 | 104 | 00 00 1c 20 | utoff | 7200 (+02:00) | 1882 +--------+-------------+------------------+------------------------+ 1883 | 108 | 00 | isdst | 0 (no) | 1884 +--------+-------------+------------------+------------------------+ 1885 | 109 | 00 | desigidx | 0 | 1886 +--------+-------------+------------------+------------------------+ 1887 +--------+-------------+------------------+------------------------+ 1888 | 110 | 49 53 54 00 | designations[0] | "IST" | 1889 +--------+-------------+------------------+------------------------+ 1890 +--------+-------------+------------------+------------------------+ 1891 | 114 | 0a | NL | '\n' | 1892 +--------+-------------+------------------+------------------------+ 1893 | 115 | 49 53 54 2d | TZ string | "IST-2IDT, | 1894 | | 32 49 44 54 | | M3.4.4/26,M10.5.0" | 1895 | | 2c 4d 33 2e | | | 1896 | | 34 2e 34 2f | | | 1897 | | 32 36 2c 4d | | | 1898 | | 31 30 2e 35 | | | 1899 | | 2e 30 | | | 1900 +--------+-------------+------------------+------------------------+ 1901 | 141 | 0a | NL | '\n' | 1902 +--------+-------------+------------------+------------------------+ 1904 Table 3 1906 B.4. Truncated Version 4 File Representing America/New_York 1908 The following TZif file has been truncated to start on 1909 2022-01-01T00:00:00Z. 1911 In this example: 1913 * The version 1 header contains only the required minimum data, 1914 which will be ignored by readers. 1916 * The version 4 header leverages the fact that by specifying 1917 'isutcnt' and 'isstdcnt' as zero, all transition times associated 1918 with local time types are assumed to be specified as local wall- 1919 clock time (see the definitions of UT/local indicators and 1920 standard/wall indicators in Section 3.2). 1922 * The first leap second occurrence is the most recent one prior to 1923 the truncation time. 1925 * The last leap second correction matches the second-to-last leap 1926 second correction, indicating the expiration time of the leap 1927 second table. 1929 * The TZ string value has been line-wrapped for presentation 1930 purposes only. 1932 +========+=============+==================+========================+ 1933 | File | Hexadecimal | Record Name / | Field Value | 1934 | Offset | Octets | Field Name | | 1935 +========+=============+==================+========================+ 1936 | 000 | 54 5a 69 66 | magic | "TZif" | 1937 +--------+-------------+------------------+------------------------+ 1938 | 004 | 34 | version | '4' (4) | 1939 +--------+-------------+------------------+------------------------+ 1940 | 005 | 00 00 00 00 | | | 1941 | | 00 00 00 00 | | | 1942 | | 00 00 00 00 | | | 1943 | | 00 00 00 | | | 1944 +--------+-------------+------------------+------------------------+ 1945 | 020 | 00 00 00 00 | isutcnt | 0 | 1946 +--------+-------------+------------------+------------------------+ 1947 | 024 | 00 00 00 00 | isstdcnt | 0 | 1948 +--------+-------------+------------------+------------------------+ 1949 | 028 | 00 00 00 00 | leapcnt | 0 | 1950 +--------+-------------+------------------+------------------------+ 1951 | 032 | 00 00 00 00 | timecnt | 0 | 1952 +--------+-------------+------------------+------------------------+ 1953 | 036 | 00 00 00 01 | typecnt | 1 | 1954 +--------+-------------+------------------+------------------------+ 1955 | 040 | 00 00 00 01 | charcnt | 1 | 1956 +--------+-------------+------------------+------------------------+ 1957 +--------+-------------+------------------+------------------------+ 1958 | | | localtimetype[0] | | 1959 +--------+-------------+------------------+------------------------+ 1960 | 044 | 00 00 00 00 | utoff | 0 (+00:00) | 1961 +--------+-------------+------------------+------------------------+ 1962 | 048 | 00 | isdst | 0 (no) | 1963 +--------+-------------+------------------+------------------------+ 1964 | 049 | 00 | desigidx | 0 | 1965 +--------+-------------+------------------+------------------------+ 1966 +--------+-------------+------------------+------------------------+ 1967 | 050 | 00 | designations[0] | "" | 1968 +--------+-------------+------------------+------------------------+ 1969 +--------+-------------+------------------+------------------------+ 1970 | 051 | 54 5a 69 66 | magic | "TZif" | 1971 +--------+-------------+------------------+------------------------+ 1972 | 055 | 34 | version | '4' (4) | 1973 +--------+-------------+------------------+------------------------+ 1974 | 056 | 00 00 00 00 | | | 1975 | | 00 00 00 00 | | | 1976 | | 00 00 00 00 | | | 1977 | | 00 00 00 | | | 1978 +--------+-------------+------------------+------------------------+ 1979 | 071 | 00 00 00 00 | isutcnt | 0 | 1980 +--------+-------------+------------------+------------------------+ 1981 | 075 | 00 00 00 00 | isstdcnt | 0 | 1982 +--------+-------------+------------------+------------------------+ 1983 | 079 | 00 00 00 02 | leapcnt | 2 | 1984 +--------+-------------+------------------+------------------------+ 1985 | 083 | 00 00 00 01 | timecnt | 1 | 1986 +--------+-------------+------------------+------------------------+ 1987 | 087 | 00 00 00 01 | typecnt | 1 | 1988 +--------+-------------+------------------+------------------------+ 1989 | 091 | 00 00 00 04 | charcnt | 4 | 1990 +--------+-------------+------------------+------------------------+ 1991 +--------+-------------+------------------+------------------------+ 1992 | 095 | 00 00 00 00 | trans time[0] | 1640995227 | 1993 | | 61 cf 99 9b | | (2022-01-01T00:00:00Z) | 1994 +--------+-------------+------------------+------------------------+ 1995 +--------+-------------+------------------+------------------------+ 1996 | 103 | 00 | trans type[0] | 0 | 1997 +--------+-------------+------------------+------------------------+ 1998 +--------+-------------+------------------+------------------------+ 1999 | | | localtimetype[0] | | 2000 +--------+-------------+------------------+------------------------+ 2001 | 104 | ff ff b9 b0 | utoff | -18000 (-05:00) | 2002 +--------+-------------+------------------+------------------------+ 2003 | 108 | 00 | isdst | 0 (no) | 2004 +--------+-------------+------------------+------------------------+ 2005 | 109 | 00 | desigidx | 0 | 2006 +--------+-------------+------------------+------------------------+ 2007 +--------+-------------+------------------+------------------------+ 2008 | 110 | 45 53 54 00 | designations[0] | "EST" | 2009 +--------+-------------+------------------+------------------------+ 2010 +--------+-------------+------------------+------------------------+ 2011 | | | leapsecond[0] | | 2012 +--------+-------------+------------------+------------------------+ 2013 | 114 | 00 00 00 00 | occurrence | 1483228826 | 2014 | | 58 68 46 9a | | (2016-12-31T23:59:60Z) | 2015 +--------+-------------+------------------+------------------------+ 2016 | 122 | 00 00 00 1b | correction | 27 | 2017 +--------+-------------+------------------+------------------------+ 2018 +--------+-------------+------------------+------------------------+ 2019 | | | leapsecond[1] | | 2020 +--------+-------------+------------------+------------------------+ 2021 | 126 | 00 00 00 00 | occurrence | 1656374427 | 2022 | | 62 ba 44 9b | | (2022-06-28T00:00:00Z) | 2023 +--------+-------------+------------------+------------------------+ 2024 | 134 | 00 00 00 1b | correction | 27 | 2025 +--------+-------------+------------------+------------------------+ 2026 +--------+-------------+------------------+------------------------+ 2027 | 138 | 0a | NL | '\n' | 2028 +--------+-------------+------------------+------------------------+ 2029 | 139 | 45 53 54 35 | TZ string | "EST5EDT, | 2030 | | 45 44 54 2c | | M3.2.0,M11.1.0" | 2031 | | 4d 33 2e 32 | | | 2032 | | 2e 30 2c 4d | | | 2033 | | 31 31 2e 31 | | | 2034 | | 2e 30 | | | 2035 +--------+-------------+------------------+------------------------+ 2036 | 161 | 0a | NL | '\n' | 2037 +--------+-------------+------------------+------------------------+ 2039 Table 4 2041 Appendix C. Changes from RFC 8536 2043 * Added specification of the version 4 format and the optional leap 2044 second table truncation and expiration, along with an example and 2045 relevant interoperability considerations. 2047 * Documented the longstanding practice that UT with designation 2048 string "-00" denotes unspecified local time. Added recommendation 2049 that this designation string should be used for timestamps 2050 excluded by TZif file truncation. 2052 * Applied erratum [Err6435]. 2054 * Addressed errata [Err6426] and [Err6757] as well as several other 2055 errors in the examples. 2057 * Clarified the all-year daylight saving time TZ string 2058 (Section 3.3.1) example and added a similar example with negative 2059 DST. 2061 * Added informational notes to Appendix B.3. 2063 * Miscellaneous editorial changes. 2065 Appendix D. Change Log 2067 This section is to be removed by RFC Editor before publication. 2069 D.1. Since rfc8536bis-03 2071 * Noted that erratum [Err6757] has been addressed. 2073 * Added a definition of Leap-Second, including UTC month. 2075 D.2. Since rfc8536bis-02 2077 * Documented "-00" as meaning unspecified local time. 2079 * Recommended that "-00" be used for timestamps that are unspecified 2080 due to TZif file truncation. 2082 D.3. Since rfc8536bis-01 2084 * Converted source from xml2rfc v2 to v3. 2086 * Properly line-wrapped long TZ string values in examples (with no 2087 added space). 2089 * No other substantive changes. 2091 D.4. Since rfc8536bis-00 2093 * Added specification of the version 4 format and the optional leap 2094 second table truncation and expiration, along with an example and 2095 relevant interoperability considerations. 2097 * Specified column widths in example tables. 2099 * Noted that long TZ string values in examples are line-wrapped for 2100 presentation purposes only. 2102 D.5. Since RFC 8536 2104 * Applied erratum [Err6435]. 2106 * Addressed erratum [Err6426] and several other errors in the 2107 examples. 2109 * Clarified the all-year daylight saving time TZ string 2110 (Section 3.3.1) example and added a similar example with negative 2111 DST. 2113 * Added informational notes to Appendix B.3. 2115 * Miscellaneous editorial changes. 2117 * Added text obsoleting [RFC8536]. 2119 * Added Changes from RFC 8536 (Appendix C). 2121 * Added Tim Parenti as a contributor. 2123 Acknowledgments 2125 The authors would like to thank the following individuals for 2126 contributing their ideas and support for writing this specification: 2127 Michael Douglass, Ned Freed, Guy Harris, Eliot Lear, Alexey Melnikov, 2128 and Tim Parenti. 2130 Authors' Addresses 2132 Arthur David Olson 2134 Email: arthurdavidolson@gmail.com 2136 Paul Eggert 2137 University of California, Los Angeles 2139 Email: eggert@cs.ucla.edu 2141 Kenneth Murchison 2142 Fastmail US LLC 2144 Email: murch@fastmailteam.com