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'GNU-C' -- 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 'RFC8536', was also mentioned in 'Err6435'. Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 34 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: 14 May 2022 K. Murchison 7 Fastmail 8 10 November 2021 10 The Time Zone Information Format (TZif) 11 draft-murchison-rfc8536bis-03 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 14 May 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 Simplified BSD License text 50 as described in Section 4.e of the Trust Legal Provisions and are 51 provided without warranty as described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 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 . . . . . . . . . . . . . . . 13 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 . . . . . . . . . . . 22 75 Appendix B. Example TZif Files . . . . . . . . . . . . . . . . . 25 76 B.1. Version 1 File Representing UTC (with Leap Seconds) . . . 26 77 B.2. Version 2 File Representing Pacific/Honolulu . . . . . . 31 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 . . . . . . . . . . . . . . . . . . . . . 44 82 D.1. Since rfc8536bis-02 . . . . . . . . . . . . . . . . . . . 44 83 D.2. Since rfc8536bis-01 . . . . . . . . . . . . . . . . . . . 45 84 D.3. Since rfc8536bis-00 . . . . . . . . . . . . . . . . . . . 45 85 D.4. Since RFC 8536 . . . . . . . . . . . . . . . . . . . . . 45 86 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 45 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46 89 1. Introduction 91 Time zone data typically consists of offsets from universal time 92 (UT), daylight saving transition rules, one or more local time 93 designations (acronyms or abbreviations), and optional leap-second 94 adjustments. One such format for conveying this information is 95 iCalendar [RFC5545]. It is a text-based format used by calendaring 96 and scheduling systems. 98 This document specifies the widely deployed Time Zone Information 99 Format (TZif). It is a binary format used by most UNIX systems to 100 calculate local time. This format was introduced in the 1980s and 101 has evolved since then into multiple upward-compatible versions. 102 There is a wide variety of interoperable software capable of 103 generating and reading files in this format [tz-link]. 105 This specification does not define the source of the data assembled 106 into a TZif file. One such source is the IANA-hosted time zone 107 database [RFC6557]. 109 This document obsoletes RFC 8536, providing editorial improvements, 110 new details, and errata fixes while keeping full compatibility with 111 the interchange format of RFC 8536. Additionally, a new version of 112 the format is defined. The changes from RFC 8536 are summarized in 113 Appendix C. 115 2. Conventions Used in This Document 117 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 118 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 119 "OPTIONAL" in this document are to be interpreted as described in 120 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 121 capitals, as shown here. 123 The following terms are used in this document (see "Sources for Time 124 Zone and Daylight Saving Time Data" [tz-link] for more detailed 125 information about civil timekeeping data and practice): 127 Coordinated Universal Time (UTC): The basis for civil time since 128 1960. It is approximately equal to mean solar time at the prime 129 meridian (0 degrees longitude). 131 Daylight Saving Time (DST): The time according to a location's law 132 or practice, when adjusted as necessary from standard time. The 133 adjustment may be positive or negative, and the amount of 134 adjustment may vary depending on the date and time; the TZif 135 format even allows the adjustment to be zero, although this is not 136 common practice. 138 International Atomic Time (TAI): The time standard based on atomic 139 clocks since 1972. It is equal to UTC but without leap-second 140 adjustments. 142 Leap-Second Correction (LEAPCORR): The value of TAI - UTC - 10 for 143 timestamps after the first leap second, and zero for timestamps 144 before that. The expression "TAI - UTC - 10" comes from the fact 145 that TAI - UTC was defined to be 10 just prior to the first leap 146 second in 1972, so clocks with leap seconds have a zero LEAPCORR 147 before the first leap second. 149 Local Time: Civil time for a particular location. Its offset from 150 universal time can depend on the date and time of day. 152 POSIX Epoch: 1970-01-01 00:00:00 UTC, the basis for absolute 153 timestamps in this document. 155 Standard Time: The time according to a location's law or practice, 156 unadjusted for Daylight Saving Time. 158 Time Change: A change to civil timekeeping practice. It occurs when 159 one or more of the following happen simultaneously: 161 1. a change in UT offset 163 2. a change in whether daylight saving time is in effect 165 3. a change in time zone abbreviation 167 4. a leap second (i.e., a change in LEAPCORR) 169 Time Zone Data: The Time Zone Data Distribution Service (TZDIST) 170 [RFC7808] defines "Time zone data" as "data that defines a single 171 time zone, including an identifier, UTC offset values, DST rules, 172 and other information such as time zone abbreviations." The 173 interchange format defined in this document is one such form of 174 time zone data. 176 Transition Time: The moment of occurrence of a time change that is 177 not a leap second. It is identified with a signed integer count 178 of UNIX leap time seconds since the POSIX epoch. 180 Universal Time (UT): The basis of civil time. This is the principal 181 form of the mean solar time at the prime meridian (0 degrees 182 longitude) for timestamps before UTC was introduced in 1960 and is 183 UTC for timestamps thereafter. Although UT is sometimes called 184 "UTC" or "GMT" in other sources, this specification uses the term 185 "UT" to avoid confusion with UTC or with GMT. 187 UNIX Time: The time as returned by the time() function provided by 188 the C programming language (see Section 3 of the "System 189 Interfaces" volume of [POSIX]). This is an integer number of 190 seconds since the POSIX epoch, not counting leap seconds. As an 191 extension to POSIX, negative values represent times before the 192 POSIX epoch, using UT. 194 UNIX Leap Time: UNIX time plus all preceding leap-second 195 corrections. For example, if the first leap-second record in a 196 TZif file occurs at 1972-06-30 23:59:60 UTC, the UNIX leap time 197 for the timestamp 1972-07-01 00:00:00 UTC would be 78796801, one 198 greater than the UNIX time for the same timestamp. Similarly, if 199 the second leap-second record occurs at 1972-12-31 23:59:60 UTC, 200 it accounts for the first leap second, so the UNIX leap time of 201 1972-12-31 23:59:60 UTC would be 94694401, and the UNIX leap time 202 of 1973-01-01 00:00:00 UTC would be 94694402. If a TZif file 203 specifies no leap-second records, UNIX leap time is equal to UNIX 204 time. 206 Wall Time: Another name for local time; short for "wall-clock time". 208 3. The Time Zone Information Format (TZif) 210 The Time Zone Information Format begins with a fixed 44-octet version 211 1 header (Section 3.1) containing a field that specifies the version 212 of the file's format. Readers designed for version N can read 213 version N+1 files without too much trouble; data specific to version 214 N+1 either appears after version N data so that earlier-version 215 readers can easily ignore later-version data they are not designed 216 for, or it appears as a minor extension to version N that version N 217 readers are likely to tolerate well. 219 The version 1 header is followed by a variable-length version 1 data 220 block (Section 3.2) containing four-octet (32-bit) transition times 221 and leap-second occurrences. These 32-bit values are limited to 222 representing time changes from 1901-12-13 20:45:52 through 2038-01-19 223 03:14:07 UT, and the version 1 header and data block are present only 224 for backward compatibility with obsolescent readers, as discussed in 225 Common Interoperability Issues (Appendix A). 227 Version 1 files terminate after the version 1 data block. Files from 228 versions 2 and higher extend the format by appending a second 229 44-octet version 2+ header, a variable-length version 2+ data block 230 containing eight-octet (64-bit) transition times and leap-second 231 occurrences, and a variable-length footer (Section 3.3). These 232 64-bit values can represent times approximately 292 billion years 233 into the past or future. 235 NOTE: All multi-octet integer values MUST be stored in network octet 236 order format (high-order octet first, otherwise known as big-endian), 237 with all bits significant. Signed integer values MUST be represented 238 using two's complement. 240 A TZif file is structured as follows: 242 Version 1 Versions 2+ 243 +-------------+ +-------------+ 244 | Version 1 | | Version 1 | 245 | Header | | Header | 246 +-------------+ +-------------+ 247 | Version 1 | | Version 1 | 248 | Data Block | | Data Block | 249 +-------------+ +-------------+ 250 | Version 2+ | 251 | Header | 252 +-------------+ 253 | Version 2+ | 254 | Data Block | 255 +-------------+ 256 | Footer | 257 +-------------+ 259 Figure 1: General Format of TZif Files 261 3.1. TZif Header 263 A TZif header is structured as follows (the lengths of multi-octet 264 fields are shown in parentheses): 266 +---------------+---+ 267 | magic (4) |ver| 268 +---------------+---+---------------------------------------+ 269 | [unused - reserved for future use] (15) | 270 +---------------+---------------+---------------+-----------+ 271 | isutcnt (4) | isstdcnt (4) | leapcnt (4) | 272 +---------------+---------------+---------------+ 273 | timecnt (4) | typecnt (4) | charcnt (4) | 274 +---------------+---------------+---------------+ 276 Figure 2: TZif Header 278 The fields of the header are defined as follows: 280 magic: The four-octet ASCII [RFC20] sequence "TZif" (0x54 0x5A 0x69 281 0x66), which identifies the file as utilizing the Time Zone 282 Information Format. 284 ver(sion): An octet identifying the version of the file's format. 285 The value MUST be one of the following: 287 NUL (0x00) Version 1 - The file contains only the version 1 288 header and data block. Version 1 files MUST NOT contain a 289 version 2+ header, data block, or footer. 291 '2' (0x32) Version 2 - The file MUST contain the version 1 header 292 and data block, a version 2+ header and data block, and a 293 footer. The TZ string in the footer (Section 3.3), if 294 nonempty, MUST strictly adhere to the requirements for the TZ 295 environment variable as defined in Section 8.3 of the "Base 296 Definitions" volume of [POSIX] and MUST encode the POSIX 297 portable character set as ASCII. The leap second table MUST 298 NOT be truncated at the start (Section 5.1), and MUST NOT 299 contain an expiration time. 301 '3' (0x33) Version 3 - The file MUST conform to all version 2 302 requirements, except that any TZ string in the footer 303 (Section 3.3) MAY use the TZ string extensions described below 304 (Section 3.3.1). 306 '4' (0x34) Version 4 - The file MUST conform to all version 3 307 requirements, except that the leap second table MAY be 308 truncated at the start, and MAY contain an expiration time. 310 isutcnt: A four-octet unsigned integer specifying the number of UT/ 311 local indicators contained in the data block -- MUST either be 312 zero or equal to "typecnt". 314 isstdcnt: A four-octet unsigned integer specifying the number of 315 standard/wall indicators contained in the data block -- MUST 316 either be zero or equal to "typecnt". 318 leapcnt: A four-octet unsigned integer specifying the number of 319 leap-second records contained in the data block. 321 timecnt: A four-octet unsigned integer specifying the number of 322 transition times contained in the data block. 324 typecnt: A four-octet unsigned integer specifying the number of 325 local time type records contained in the data block -- MUST NOT be 326 zero. (Although local time type records convey no useful 327 information in files that have nonempty TZ strings but no 328 transitions, at least one such record is nevertheless required 329 because many TZif readers reject files that have zero time types.) 331 charcnt: A four-octet unsigned integer specifying the total number 332 of octets used by the set of time zone designations contained in 333 the data block - MUST NOT be zero. The count includes the 334 trailing NUL (0x00) octet at the end of the last time zone 335 designation. 337 Although the version 1 and 2+ headers have the same format, magic 338 number, and version fields, their count fields may differ, because 339 the version 1 data can be a subset of the version 2+ data. 341 3.2. TZif Data Block 343 A TZif data block consists of seven variable-length elements, each of 344 which is a series of items. The number of items in each series is 345 determined by the corresponding count field in the header. The total 346 length of each element is calculated by multiplying the number of 347 items by the size of each item. Therefore, implementations that do 348 not wish to parse or use the version 1 data block can calculate its 349 total length and skip directly to the header of the version 2+ data 350 block. 352 In the version 1 data block, time values are 32 bits (TIME_SIZE = 4 353 octets). In the version 2+ data block, present only in version 2 and 354 higher files, time values are 64 bits (TIME_SIZE = 8 octets). 356 The data block is structured as follows (the lengths of multi-octet 357 fields are shown in parentheses): 359 +---------------------------------------------------------+ 360 | transition times (timecnt x TIME_SIZE) | 361 +---------------------------------------------------------+ 362 | transition types (timecnt) | 363 +---------------------------------------------------------+ 364 | local time type records (typecnt x 6) | 365 +---------------------------------------------------------+ 366 | time zone designations (charcnt) | 367 +---------------------------------------------------------+ 368 | leap-second records (leapcnt x (TIME_SIZE + 4)) | 369 +---------------------------------------------------------+ 370 | standard/wall indicators (isstdcnt) | 371 +---------------------------------------------------------+ 372 | UT/local indicators (isutcnt) | 373 +---------------------------------------------------------+ 375 Figure 3: TZif Data Block 377 The elements of the data block are defined as follows: 379 transition times: A series of four- or eight-octet UNIX leap-time 380 values sorted in strictly ascending order. Each value is used as 381 a transition time at which the rules for computing local time may 382 change. The number of time values is specified by the "timecnt" 383 field in the header. Each time value SHOULD be at least -2**59. 384 (-2**59 is the greatest negated power of 2 that predates the Big 385 Bang, and avoiding earlier timestamps works around known TZif 386 reader bugs relating to outlandishly negative timestamps.) 388 transition types: A series of one-octet unsigned integers specifying 389 the type of local time of the corresponding transition time. 390 These values serve as zero-based indices into the array of local 391 time type records. The number of type indices is specified by the 392 "timecnt" field in the header. Each type index MUST be in the 393 range [0, "typecnt" - 1]. 395 local time type records: A series of six-octet records specifying a 396 local time type. The number of records is specified by the 397 "typecnt" field in the header. Each record has the following 398 format (the lengths of multi-octet fields are shown in 399 parentheses): 401 +---------------+---+---+ 402 | utoff (4) |dst|idx| 403 +---------------+---+---+ 405 utoff: A four-octet signed integer specifying the number of 406 seconds to be added to UT in order to determine local time. 407 The value MUST NOT be -2**31 and SHOULD be in the range 408 [-89999, 93599] (i.e., its value SHOULD be more than -25 hours 409 and less than 26 hours). Avoiding -2**31 allows 32-bit clients 410 to negate the value without overflow. Restricting it to 411 [-89999, 93599] allows easy support by implementations that 412 already support the POSIX-required range [-24:59:59, 25:59:59]. 414 (is)dst: A one-octet value indicating whether local time should 415 be considered Daylight Saving Time (DST). The value MUST be 0 416 or 1. A value of one (1) indicates that this type of time is 417 DST. A value of zero (0) indicates that this time type is 418 standard time. 420 (desig)idx: A one-octet unsigned integer specifying a zero-based 421 index into the series of time zone designation octets, thereby 422 selecting a particular designation string. Each index MUST be 423 in the range [0, "charcnt" - 1]; it designates the 424 NUL-terminated string of octets starting at position "idx" in 425 the time zone designations. (This string MAY be empty.) A NUL 426 octet MUST exist in the time zone designations at or after 427 position "idx". If the designation string is "-00", the time 428 type is a placeholder indicating that local time is 429 unspecified. 431 time zone designations: A series of octets constituting an array of 432 NUL-terminated (0x00) time zone designation strings. The total 433 number of octets is specified by the "charcnt" field in the 434 header. Note that two designations MAY overlap if one is a suffix 435 of the other. The character encoding of time zone designation 436 strings is not specified; however, see Section 4 of this document. 438 leap-second records: A series of eight- or twelve-octet records 439 specifying the corrections that need to be applied to UTC in order 440 to determine TAI. The records are sorted by the occurrence time 441 in strictly ascending order. The number of records is specified 442 by the "leapcnt" field in the header. Each record has one of the 443 following structures (the lengths of multi-octet fields are shown 444 in parentheses): 446 Version 1 Data Block: 447 +---------------+---------------+ 448 | occur (4) | corr (4) | 449 +---------------+---------------+ 451 version 2+ Data Block: 452 +---------------+---------------+---------------+ 453 | occur (8) | corr (4) | 454 +---------------+---------------+---------------+ 456 occur(rence): A four- or eight-octet UNIX leap time value 457 specifying the time at which a leap-second correction occurs or 458 at which the leap second table expires. The first value, if 459 present, MUST be nonnegative, and each leap second MUST occur 460 at the end of a UTC calendar month. 462 corr(ection): A four-octet signed integer specifying the value of 463 LEAPCORR on or after the occurrence. If "leapcnt" is zero, 464 LEAPCORR is zero for all timestamps; otherwise, for timestamps 465 before the first occurrence time, LEAPCORR is zero if the first 466 correction is one (1) or minus one (-1), and is unspecified 467 otherwise (which can happen only in files truncated at the 468 start (Section 5.1)). 470 The first leap second is a positive leap second if and only if 471 its correction is positive. Each correction after the first 472 MUST differ from the previous correction by either one (1) for 473 a positive leap second or minus one (-1) for a negative leap 474 second, except that if there are two or more leap-second 475 records the correction value of the last record MAY be the same 476 as the second-to-last record, with the last record indicating 477 the expiration time of the leap-second table. 479 standard/wall indicators: A series of one-octet values indicating 480 whether the transition times associated with local time types were 481 specified as standard time or wall-clock time. Each value MUST be 482 0 or 1. A value of one (1) indicates standard time. The value 483 MUST be set to one (1) if the corresponding UT/local indicator is 484 set to one (1). A value of zero (0) indicates wall time. The 485 number of values is specified by the "isstdcnt" field in the 486 header. If "isstdcnt" is zero (0), all transition times 487 associated with local time types are assumed to be specified as 488 wall time. 490 UT/local indicators: A series of one-octet values indicating whether 491 the transition times associated with local time types were 492 specified as UT or local time. Each value MUST be 0 or 1. A 493 value of one (1) indicates UT, and the corresponding standard/wall 494 indicator MUST also be set to one (1). A value of zero (0) 495 indicates local time. The number of values is specified by the 496 "isutcnt" field in the header. If "isutcnt" is zero (0), all 497 transition times associated with local time types are assumed to 498 be specified as local time. 500 The type corresponding to a transition time specifies local time for 501 timestamps starting at the given transition time and continuing up 502 to, but not including, the next transition time. Local time for 503 timestamps before the first transition is specified by the first time 504 type (time type 0). Local time for timestamps on or after the last 505 transition is specified by the TZ string in the footer (Section 3.3) 506 if present and nonempty; otherwise, it is unspecified. If there are 507 no transitions, local time for all timestamps is specified by the TZ 508 string in the footer if present and nonempty; otherwise, it is 509 specified by time type 0. A time type with a designation string of 510 "-00" represents an unspecified local time. 512 A given pair of standard/wall and UT/local indicators is used to 513 designate whether the corresponding transition time was specified as 514 UT, standard time, or wall-clock time. Note that there are only 515 three combinations of the two indicators, given that the standard/ 516 wall value MUST be one (1) if the UT/local value is one (1). This 517 information can be useful if the transition times in a TZif file need 518 to be transformed into transitions appropriate for another time zone 519 (e.g. when calculating transition times for a simple POSIX-like TZ 520 string such as "AKST9AKDT"). 522 In order to eliminate unused space in a TZif file, every nonzero 523 local time type index SHOULD appear at least once in the transition 524 type array. Likewise, every octet in the time zone designations 525 array SHOULD be used by at least one time type record. 527 3.3. TZif Footer 529 The TZif footer is structured as follows (the lengths of multi-octet 530 fields are shown in parentheses): 532 +---+--------------------+---+ 533 | NL| TZ string (0...) |NL | 534 +---+--------------------+---+ 536 Figure 4: TZif Footer 538 The elements of the footer are defined as follows: 540 NL: An ASCII new line character (0x0A). 542 TZ string: A rule for computing local time changes after the last 543 transition time stored in the version 2+ data block. The string 544 is either empty or uses the expanded format of the "TZ" 545 environment variable as defined in Section 8.3 of the "Base 546 Definitions" volume of [POSIX] with ASCII encoding, possibly 547 utilizing extensions described below (Section 3.3.1) in version 3 548 and higher files. If the string is empty, the corresponding 549 information is not available. If the string is nonempty and one 550 or more transitions appear in the version 2+ data, the string MUST 551 be consistent with the last version 2+ transition. In other 552 words, evaluating the TZ string at the time of the last transition 553 should yield the same time type as was specified in the last 554 transition. The string MUST NOT contain NUL octets or be 555 NUL-terminated, and it SHOULD NOT begin with the ':' (colon) 556 character. 558 The TZif footer is present only in version 2 and higher files, as the 559 obsolescent version 1 format was designed before the need for a 560 footer was apparent. 562 3.3.1. TZ String Extensions 564 The TZ string in a version 3 or higher TZif file MAY use the 565 following extensions to POSIX TZ strings. These extensions are 566 described using the terminology of Section 8.3 of the "Base 567 Definitions" volume of [POSIX]. 569 * The hours part of the transition times may be signed and range 570 from -167 through 167 (-167 <= hh <= 167) instead of the POSIX- 571 required unsigned values from 0 through 24. 573 Example: <-03>3<-02>,M3.5.0/-2,M10.5.0/-1 574 This represents a time zone that observes daylight saving time 575 from 22:00 on the day before March's last Sunday until 23:00 on 576 the day before October's last Sunday. Standard time is 3 hours 577 west of UT and is abbreviated "-03"; daylight saving time is 2 578 hours west of UT and is abbreviated "-02". 580 * DST is considered to be in effect all year if it starts January 1 581 at 00:00 and ends December 31 at 24:00 plus the difference between 582 daylight saving and standard time, leaving no room for standard 583 time in the calendar. 585 Example: EST5EDT,0/0,J365/25 586 This represents a time zone that observes daylight saving time 587 all year. It is 4 hours west of UT and is abbreviated "EDT". 588 The "EST" is ignored. 590 Example: XXX3EDT4,0/0,J365/23 591 This represents the same time zone as the previous example. It 592 uses a DST further west of UTC than standard time. The "XXX" 593 is ignored. 595 4. Interoperability Considerations 597 The following practices help ensure the interoperability of TZif 598 applications. 600 * Version 1 files are considered a legacy format and SHOULD NOT be 601 generated, as they do not support transition times after the year 602 2038. 604 * Readers that understand only version 1 MUST ignore any data that 605 extends beyond the calculated end of the version 1 data block. 607 * Other than version 1, writers should generate the lowest version 608 number needed by a file's data. For example, a writer should 609 generate a version 4 file only if its leap second table either 610 expires or is truncated at the start. Likewise, a writer not 611 generating a version 4 file should generate a version 3 file only 612 if TZ string extensions are necessary to accurately model 613 transition times. 615 * To save space, writers of version 2+ files MAY output a 616 placeholder version 1 data block with all counts zero except that 617 "typecnt" and "charcnt" are both one (1). If this is done, 618 obsolescent version-1-only readers MUST interpret these files as 619 lacking time changes and time zone abbreviations. 621 * Unless the version 1 data block is a placeholder, the sequence of 622 timestamps defined by the version 1 header and data block SHOULD 623 be a contiguous sub-sequence of the timestamps defined by the 624 version 2+ header and data block, and by the footer. This 625 guideline helps obsolescent version 1 readers agree with current 626 readers about timestamps within the contiguous sub-sequence. 628 * When a TZif file contains a leap second table expiration time, 629 TZif readers SHOULD either refuse to process post-expiration 630 timestamps, or process them as if the expiration time did not 631 exist (possibly with an error indication). 633 * Time zone designations SHOULD consist of at least three (3) and no 634 more than six (6) ASCII characters from the set of alphanumerics, 635 '-', and '+'. This is for compatibility with POSIX requirements 636 for time zone abbreviations. 638 * When reading a version 2 or higher file, readers SHOULD ignore the 639 version 1 header and data block except for the purpose of skipping 640 over them. 642 * Readers SHOULD calculate the total lengths of the headers and data 643 blocks and check that they all fit within the actual file size, as 644 part of a validity check for the file. 646 * When a TZif file is used in a MIME message entity, it SHOULD be 647 indicated by one of the following media types: 649 - "application/tzif-leap" (Section 8.2) to indicate that leap- 650 second records are included in the TZif data as necessary (none 651 are necessary if the file is truncated to a range that precedes 652 the first leap second). 654 - "application/tzif" (Section 8.1) to indicate that leap-second 655 records are not included in the TZif data; "leapcnt" in the 656 header(s) MUST be zero (0). 658 * Common interoperability issues and possible workarounds are 659 described in Appendix A. 661 5. Use with the Time Zone Data Distribution Service 663 The Time Zone Data Distribution Service (TZDIST) [RFC7808] is a 664 service that allows reliable, secure, and fast delivery of time zone 665 data and leap-second rules to client systems such as calendaring and 666 scheduling applications or operating systems. 668 A TZDIST service MAY supply time zone data to clients in the Time 669 Zone Information Format. Such a service MUST indicate that it 670 supports this format by including the media type "application/tzif" 671 (Section 8.1) in its "capabilities" response (see Section 5.1 of 672 [RFC7808]). A TZDIST service MAY also include the media type 673 "application/tzif-leap" (Section 8.2) in its "capabilities" response 674 if it is able to generate TZif files containing leap-second records. 675 A TZDIST service MUST NOT advertise the "application/tzif-leap" media 676 type without also advertising "application/tzif". 678 TZDIST clients MUST use the HTTP "Accept" [RFC7231] header field to 679 indicate their preference to receive data in the "application/tzif" 680 and/or "application/tzif-leap" formats. 682 5.1. Truncating TZif Files 684 As described in Section 3.9 of [RFC7808], a TZDIST service MAY 685 truncate time zone transition data. A truncated TZif file is valid 686 from its first and up to, but not including, its last version 2+ 687 transition time, if present. 689 When truncating the start of a TZif file, the service MUST supply in 690 the version 2+ data a first transition time that is the start point 691 of the truncation range. As with untruncated TZif files, time type 0 692 indicates local time immediately before the start point, and the time 693 type of the first transition indicates local time thereafter. Time 694 type 0 SHOULD be a placeholder indicating that local time is 695 unspecified. 697 When truncating the start of a TZif file containing leap-second 698 records, the service MUST keep all leap-second records governing 699 timestamps within the truncation range, even if the first such record 700 precedes the start point of the truncation range. If the truncated 701 leap second table is nonempty, its first record MUST have a positive 702 correction if and only if it represents a positive leap second. 704 When truncating the end of a TZif file, the service MUST supply in 705 the version 2+ data a last transition time that is the end point of 706 the truncation range and MUST supply an empty TZ string. As with 707 untruncated TZif files with empty TZ strings, a truncated TZif file 708 does not indicate local time after the last transition. To this end, 709 the time type of the last transition SHOULD be a placeholder 710 indicating that local time is unspecified. 712 All represented information that falls inside the truncation range 713 MUST be the same as that represented by a corresponding untruncated 714 TZif file. 716 TZDIST clients SHOULD NOT use a truncated TZif file (as described 717 above) to interpret timestamps outside the truncation time range. 719 5.2. Example TZDIST Request for TZif Data 721 In this example, the client checks the server for the available 722 formats and then requests that the time zone with a specific time 723 zone identifier be returned in Time Zone Information Format. 725 Note that this example presumes that the time zone context path has 726 been discovered (see [RFC7808], Section 4.2.1) to be "/tzdist". 728 >> Request << 730 GET /tzdist/capabilities HTTP/1.1 731 Host: tz.example.com 733 >> Response << 735 HTTP/1.1 200 OK 736 Date: Fri, 01 Jun 2018 14:52:23 GMT 737 Content-Type: application/json 738 Content-Length: xxxx 740 { 741 "version": 1, 743 "info": { 744 "primary-source": "IANA:2018e", 745 "formats": [ 746 "text/calendar", 747 "application/tzif", 748 "application/tzif-leap" 749 ], 750 ... 751 }, 752 ... 753 } 755 >> Request << 757 GET /tzdist/zones/America%2FNew_York HTTP/1.1 758 Host: tz.example.com 759 Accept: application/tzif 761 >> Response << 763 HTTP/1.1 200 OK 764 Date: Fri, 01 Jun 2018 14:52:24 GMT 765 Content-Type: application/tzif 766 Content-Length: xxxx 767 ETag: "123456789-000-111" 769 TZif2...[binary data without leap-second records]... 770 EST5EDT,M3.2.0,M11.1.0 772 6. Security Considerations 774 The Time Zone Information Format contains no executable code, and it 775 does not define any extensible areas that could be used to store such 776 code. 778 TZif contains counted arrays of data elements. All counts should be 779 checked when processing TZif objects, to guard against references 780 past the end of the object. 782 TZif provides no confidentiality or integrity protection. Time zone 783 information is normally public and does not call for confidentiality 784 protection. Since time zone information is used in many critical 785 applications, integrity protection may be required and must be 786 provided externally. 788 7. Privacy Considerations 790 The Time Zone Information Format contains publicly available data, 791 and it does not define any extensible areas that could be used to 792 store private data. 794 As discussed in Section 9 of [RFC7808], transmission of time zone 795 data over an insecure communications channel could leak the past, 796 current, or future location of a device or user. As such, TZif data 797 transmitted over a public communications channel MUST be protected 798 with a confidentiality layer such as that provided by Transport Layer 799 Security (TLS) [RFC8446]. 801 8. IANA Considerations 803 This document defines two media types [RFC6838] for the exchange of 804 data utilizing the Time Zone Information Format. 806 8.1. application/tzif 808 Type name: 809 application 811 Subtype name: 812 tzif 814 Required parameters: 815 none 817 Optional parameters: 818 none 820 Encoding considerations: 821 binary 823 Security considerations: 824 See Section 6 of RFC XXXX. 826 Interoperability considerations: 827 See Section 4 of RFC XXXX. 829 Published specification: 830 This specification. 832 Applications that use this media type: 833 This media type is designed for widespread use by applications 834 that need to use or exchange time zone information, such as the 835 Time Zone Information Compiler (zic) [ZIC] and the GNU C Library 836 [GNU-C]. The Time Zone Distribution Service [RFC7808] can 837 directly use this media type. 839 Fragment identifier considerations: 840 N/A 842 Additional information: 843 Magic number(s): The first 4 octets are 0x54, 0x5A, 0x69, 0x66 845 File extensions(s): N/A 847 Macintosh file type code(s): N/A 849 Person & email address to contact for further information: 850 Time Zone Database mailing list 852 Intended usage: 853 COMMON 855 Restrictions on usage: 856 N/A 858 Author: 859 See the "Authors' Addresses" section of RFC XXXX. 861 Change controller: 862 IETF 864 8.2. application/tzif-leap 866 Type name: 867 application 869 Subtype name: 870 tzif-leap 872 Required parameters: 873 none 875 Optional parameters: 876 none 878 Encoding considerations: 879 binary 881 Security considerations: 882 See Section 6 of RFC XXXX. 884 Interoperability considerations: 885 See Section 4 of RFC XXXX. 887 Published specification: 888 This specification. 890 Applications that use this media type: 891 This media type is designed for widespread use by applications 892 that need to use or exchange time zone information, such as the 893 Time Zone Information Compiler (zic) [ZIC] and the GNU C Library 894 [GNU-C]. The Time Zone Distribution Service [RFC7808] can 895 directly use this media type. 897 Fragment identifier considerations: 898 N/A 900 Additional information: 901 Magic number(s): The first 4 octets are 0x54, 0x5A, 0x69, 0x66 903 File extensions(s): N/A 905 Macintosh file type code(s): N/A 907 Person & email address to contact for further information: 908 Time Zone Database mailing list 910 Intended usage: 911 COMMON 913 Restrictions on usage: 914 N/A 916 Author: 917 See the "Authors' Addresses" section of RFC XXXX. 919 Change controller: 920 IETF 922 9. References 924 9.1. Normative References 926 [GNU-C] "The GNU C Library (glibc)", 927 . 929 [POSIX] IEEE, "Standard for Information Technology--Portable 930 Operating System Interface (POSIX(R)) Base Specifications, 931 Issue 7", IEEE 1003.1-2017, 932 DOI 10.1109/IEEESTD.2018.8277153, 31 January 2018, 933 . 935 [RFC20] Cerf, V., "ASCII format for network interchange", STD 80, 936 RFC 20, DOI 10.17487/RFC0020, October 1969, 937 . 939 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 940 Requirement Levels", BCP 14, RFC 2119, 941 DOI 10.17487/RFC2119, March 1997, 942 . 944 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 945 Specifications and Registration Procedures", BCP 13, 946 RFC 6838, DOI 10.17487/RFC6838, January 2013, 947 . 949 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 950 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 951 DOI 10.17487/RFC7231, June 2014, 952 . 954 [RFC7808] Douglass, M. and C. Daboo, "Time Zone Data Distribution 955 Service", RFC 7808, DOI 10.17487/RFC7808, March 2016, 956 . 958 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 959 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 960 May 2017, . 962 [ZIC] Kerrisk, M., "ZIC(8)", man-pages release 4.16, 25 February 963 2010, . 965 9.2. Informative References 967 [EGGERT-TZ] 968 "History for tz", March 2021, 969 . 971 [Err6426] RFC Errata, "Erratum ID 6426", RFC 8536, 972 . 974 [Err6435] RFC Errata, "Erratum ID 6435", RFC 8536, 975 . 977 [RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and 978 Scheduling Core Object Specification (iCalendar)", 979 RFC 5545, DOI 10.17487/RFC5545, September 2009, 980 . 982 [RFC6557] Lear, E. and P. Eggert, "Procedures for Maintaining the 983 Time Zone Database", BCP 175, RFC 6557, 984 DOI 10.17487/RFC6557, February 2012, 985 . 987 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 988 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 989 . 991 [RFC8536] Olson, A., Eggert, P., and K. Murchison, "The Time Zone 992 Information Format (TZif)", RFC 8536, 993 DOI 10.17487/RFC8536, February 2019, 994 . 996 [tz-link] Eggert, P. and A.D. Olson, "Sources for Time Zone and 997 Daylight Saving Time Data", 2018, 998 . 1000 Appendix A. Common Interoperability Issues 1002 This section documents common problems in implementing this 1003 specification. Most of these are problems in generating TZif files 1004 for use by readers conforming to predecessors of this specification 1005 [EGGERT-TZ]. The goals of this section are: 1007 1. to help TZif writers output files that avoid common pitfalls in 1008 older or buggy TZif readers, 1010 2. to help TZif readers avoid common pitfalls when reading files 1011 generated by future TZif writers, and 1013 3. to help any future specification authors see what sort of 1014 problems arise when the TZif format is changed. 1016 When new versions of the TZif format have been defined, a design goal 1017 has been that a reader can successfully use a TZif file even if the 1018 file is of a later TZif version than what the reader was designed 1019 for. When complete compatibility was not achieved, an attempt was 1020 made to limit glitches to rarely used timestamps and allow simple 1021 partial workarounds in writers designed to generate new-version data 1022 useful even for older-version readers. This section attempts to 1023 document these compatibility issues and workarounds, as well as 1024 documenting other common bugs in readers. 1026 Interoperability problems with TZif include the following: 1028 * Some readers examine only version 1 data. As a partial 1029 workaround, a writer can output as much version 1 data as 1030 possible. However, a reader should ignore version 1 data and use 1031 version 2+ data, even if the reader's native timestamps have only 1032 32 bits. 1034 * Some readers designed for version 2 might mishandle timestamps 1035 after a version 3 or higher file's last transition, because they 1036 cannot parse extensions to POSIX in the TZ-like string. As a 1037 partial workaround, a writer can output more transitions than 1038 necessary, so that only far-future timestamps are mishandled by 1039 version 2 readers. 1041 * Some readers designed for version 2 do not support permanent 1042 daylight saving time with transitions after 24:00 -- e.g., a TZ 1043 string "EST5EDT,0/0,J365/25" denoting permanent Eastern Daylight 1044 Time (-04). As a workaround, a writer can substitute standard 1045 time for two time zones east, e.g., "XXX3EDT4,0/0,J365/23" for a 1046 time zone with a never-used standard time (XXX, -03) and negative 1047 daylight saving time (EDT, -04) all year. Alternatively, as a 1048 partial workaround a writer can substitute standard time for the 1049 next time zone east -- e.g., "AST4" for permanent Atlantic 1050 Standard Time (-04). 1052 * Some readers designed for version 2 or 3, and that require strict 1053 conformance to RFC 8536, reject version 4 files whose leap second 1054 tables are truncated at the start or that end in expiration times. 1056 * Some readers ignore the footer and instead predict future 1057 timestamps from the time type of the last transition. As a 1058 partial workaround, a writer can output more transitions than 1059 necessary. 1061 * Some readers do not use time type 0 for timestamps before the 1062 first transition, in that they infer a time type using a heuristic 1063 that does not always select time type 0. As a partial workaround, 1064 a writer can output a dummy (no-op) first transition at an early 1065 time. 1067 * Some readers mishandle timestamps before the first transition that 1068 has a timestamp not less than -2**31. Readers that support only 1069 32-bit timestamps are likely to be more prone to this problem, for 1070 example, when they process 64-bit transitions, only some of which 1071 are representable in 32 bits. As a partial workaround, a writer 1072 can output a dummy transition at timestamp -2**31. 1074 * Some readers mishandle a transition if its timestamp has the 1075 minimum possible signed 64-bit value. Timestamps less than -2**59 1076 are not recommended. 1078 * Some readers mishandle POSIX-style TZ strings that contain "<" or 1079 ">". As a partial workaround, a writer can avoid using '<' or '>' 1080 for time zone abbreviations containing only alphabetic characters. 1082 * Many readers mishandle time zone abbreviations that contain non- 1083 ASCII characters. These characters are not recommended. 1085 * Some readers may mishandle time zone abbreviations that contain 1086 fewer than 3 or more than 6 characters, or that contain ASCII 1087 characters other than alphanumerics, '-', and '+'. These 1088 abbreviations are not recommended. 1090 * This specification does not dictate how readers should deal with 1091 timestamps when local time is unspecified. Common practice is for 1092 readers to report UT with designation string "-00". A reader 1093 could return an error indication instead. 1095 * Some readers mishandle TZif files that specify daylight saving 1096 time UT offsets that are less than the UT offsets for the 1097 corresponding standard time. These readers do not support 1098 locations like Ireland, which uses the equivalent of the POSIX TZ 1099 string "IST-1GMT0,M10.5.0,M3.5.0/1", observing standard time (IST, 1100 +01) in summer and daylight saving time (GMT, +00) in winter. As 1101 a partial workaround, a writer can output data for the equivalent 1102 of the POSIX TZ string "GMT0IST,M3.5.0/1,M10.5.0", thus swapping 1103 standard and daylight saving time. Although this workaround 1104 misidentifies which part of the year uses daylight saving time, it 1105 records UT offsets and time zone abbreviations correctly. 1107 * Some readers generate ambiguous timestamps for positive leap 1108 seconds that occur when the UTC offset is not a multiple of 60 1109 seconds. For example, in a timezone with UTC offset +01:23:45 and 1110 with a positive leap second 78796801 (1972-06-30 23:59:60 UTC), 1111 some readers will map both 78796800 and 78796801 to 01:23:45 local 1112 time the next day instead of mapping the latter to 01:23:46, and 1113 they will map 78796815 to 01:23:59 instead of to 01:23:60. This 1114 has not yet been a practical problem, since no civil authority has 1115 observed such UTC offsets since leap seconds were introduced in 1116 1972. 1118 Some interoperability problems are reader bugs that are listed here 1119 mostly as warnings to developers of readers. 1121 * Some readers do not support negative timestamps. Developers of 1122 distributed applications should keep this in mind if they need to 1123 deal with pre-1970 data. 1125 * Some readers mishandle timestamps before the first transition that 1126 has a nonnegative timestamp. Readers that do not support negative 1127 timestamps are likely to be more prone to this problem. 1129 * Some readers mishandle time zone abbreviations like "-08" that 1130 contain '+', '-', or digits. 1132 * Some readers mishandle UT offsets that are out of the traditional 1133 range of -12 through +12 hours and so do not support locations 1134 like Kiritimati that are outside this range. 1136 * Some readers mishandle UT offsets in the range [-3599, -1] seconds 1137 from UT, because they integer-divide the offset by 3600 to get 0 1138 and then display the hour part as "+00". 1140 * Some readers mishandle UT offsets that are not a multiple of one 1141 hour, 15 minutes, or 1 minute. 1143 Appendix B. Example TZif Files 1145 The following sections contain annotated hexadecimal dumps of example 1146 TZif files. 1148 Note that these examples should only be considered informative. 1149 Although the example data entries are current as of the publication 1150 date of this document, the data will likely change in the future as 1151 leap seconds are added and changes are made to civil time. 1153 B.1. Version 1 File Representing UTC (with Leap Seconds) 1155 +========+=============+==================+========================+ 1156 | File | Hexadecimal | Record Name / | Field Value | 1157 | Offset | Octets | Field Name | | 1158 +========+=============+==================+========================+ 1159 | 000 | 54 5a 69 66 | magic | "TZif" | 1160 +--------+-------------+------------------+------------------------+ 1161 | 004 | 00 | version | 0 (1) | 1162 +--------+-------------+------------------+------------------------+ 1163 | 005 | 00 00 00 00 | | | 1164 | | 00 00 00 00 | | | 1165 | | 00 00 00 00 | | | 1166 | | 00 00 00 | | | 1167 +--------+-------------+------------------+------------------------+ 1168 | 020 | 00 00 00 01 | isutcnt | 1 | 1169 +--------+-------------+------------------+------------------------+ 1170 | 024 | 00 00 00 01 | isstdcnt | 1 | 1171 +--------+-------------+------------------+------------------------+ 1172 | 028 | 00 00 00 1b | leapcnt | 27 | 1173 +--------+-------------+------------------+------------------------+ 1174 | 032 | 00 00 00 00 | timecnt | 0 | 1175 +--------+-------------+------------------+------------------------+ 1176 | 036 | 00 00 00 01 | typecnt | 1 | 1177 +--------+-------------+------------------+------------------------+ 1178 | 040 | 00 00 00 04 | charcnt | 4 | 1179 +--------+-------------+------------------+------------------------+ 1180 +--------+-------------+------------------+------------------------+ 1181 | | | localtimetype[0] | | 1182 +--------+-------------+------------------+------------------------+ 1183 | 044 | 00 00 00 00 | utoff | 0 (+00:00) | 1184 +--------+-------------+------------------+------------------------+ 1185 | 048 | 00 | isdst | 0 (no) | 1186 +--------+-------------+------------------+------------------------+ 1187 | 049 | 00 | desigidx | 0 | 1188 +--------+-------------+------------------+------------------------+ 1189 +--------+-------------+------------------+------------------------+ 1190 | 050 | 55 54 43 00 | designations[0] | "UTC" | 1191 +--------+-------------+------------------+------------------------+ 1192 +--------+-------------+------------------+------------------------+ 1193 | | | leapsecond[0] | | 1194 +--------+-------------+------------------+------------------------+ 1195 | 054 | 04 b2 58 00 | occurrence | 78796800 | 1196 | | | | (1972-06-30T23:59:60Z) | 1197 +--------+-------------+------------------+------------------------+ 1198 | 058 | 00 00 00 01 | correction | 1 | 1199 +--------+-------------+------------------+------------------------+ 1200 +--------+-------------+------------------+------------------------+ 1201 | | | leapsecond[1] | | 1202 +--------+-------------+------------------+------------------------+ 1203 | 062 | 05 a4 ec 01 | occurrence | 94694401 | 1204 | | | | (1972-12-31T23:59:60Z) | 1205 +--------+-------------+------------------+------------------------+ 1206 | 066 | 00 00 00 02 | correction | 2 | 1207 +--------+-------------+------------------+------------------------+ 1208 +--------+-------------+------------------+------------------------+ 1209 | | | leapsecond[2] | | 1210 +--------+-------------+------------------+------------------------+ 1211 | 070 | 07 86 1f 82 | occurrence | 126230402 | 1212 | | | | (1973-12-31T23:59:60Z) | 1213 +--------+-------------+------------------+------------------------+ 1214 | 074 | 00 00 00 03 | correction | 3 | 1215 +--------+-------------+------------------+------------------------+ 1216 +--------+-------------+------------------+------------------------+ 1217 | | | leapsecond[3] | | 1218 +--------+-------------+------------------+------------------------+ 1219 | 078 | 09 67 53 03 | occurrence | 157766403 | 1220 | | | | (1974-12-31T23:59:60Z) | 1221 +--------+-------------+------------------+------------------------+ 1222 | 082 | 00 00 00 04 | correction | 4 | 1223 +--------+-------------+------------------+------------------------+ 1224 +--------+-------------+------------------+------------------------+ 1225 | | | leapsecond[4] | | 1226 +--------+-------------+------------------+------------------------+ 1227 | 086 | 0b 48 86 84 | occurrence | 189302404 | 1228 | | | | (1975-12-31T23:59:60Z) | 1229 +--------+-------------+------------------+------------------------+ 1230 | 090 | 00 00 00 05 | correction | 5 | 1231 +--------+-------------+------------------+------------------------+ 1232 +--------+-------------+------------------+------------------------+ 1233 | | | leapsecond[5] | | 1234 +--------+-------------+------------------+------------------------+ 1235 | 094 | 0d 2b 0b 85 | occurrence | 220924805 | 1236 | | | | (1976-12-31T23:59:60Z) | 1237 +--------+-------------+------------------+------------------------+ 1238 | 098 | 00 00 00 06 | correction | 6 | 1239 +--------+-------------+------------------+------------------------+ 1240 +--------+-------------+------------------+------------------------+ 1241 | | | leapsecond[6] | | 1242 +--------+-------------+------------------+------------------------+ 1243 | 102 | 0f 0c 3f 06 | occurrence | 252460806 | 1244 | | | | (1977-12-31T23:59:60Z) | 1245 +--------+-------------+------------------+------------------------+ 1246 | 106 | 00 00 00 07 | correction | 7 | 1247 +--------+-------------+------------------+------------------------+ 1248 +--------+-------------+------------------+------------------------+ 1249 | | | leapsecond[7] | | 1250 +--------+-------------+------------------+------------------------+ 1251 | 110 | 10 ed 72 87 | occurrence | 283996807 | 1252 | | | | (1978-12-31T23:59:60Z) | 1253 +--------+-------------+------------------+------------------------+ 1254 | 114 | 00 00 00 08 | correction | 8 | 1255 +--------+-------------+------------------+------------------------+ 1256 +--------+-------------+------------------+------------------------+ 1257 | | | leapsecond[8] | | 1258 +--------+-------------+------------------+------------------------+ 1259 | 118 | 12 ce a6 08 | occurrence | 315532808 | 1260 | | | | (1979-12-31T23:59:60Z) | 1261 +--------+-------------+------------------+------------------------+ 1262 | 122 | 00 00 00 09 | correction | 9 | 1263 +--------+-------------+------------------+------------------------+ 1264 +--------+-------------+------------------+------------------------+ 1265 | | | leapsecond[9] | | 1266 +--------+-------------+------------------+------------------------+ 1267 | 126 | 15 9f ca 89 | occurrence | 362793609 | 1268 | | | | (1981-06-30T23:59:60Z) | 1269 +--------+-------------+------------------+------------------------+ 1270 | 130 | 00 00 00 0a | correction | 10 | 1271 +--------+-------------+------------------+------------------------+ 1272 +--------+-------------+------------------+------------------------+ 1273 | | | leapsecond[10] | | 1274 +--------+-------------+------------------+------------------------+ 1275 | 134 | 17 80 fe 0a | occurrence | 394329610 | 1276 | | | | (1982-06-30T23:59:60Z) | 1277 +--------+-------------+------------------+------------------------+ 1278 | 138 | 00 00 00 0b | correction | 11 | 1279 +--------+-------------+------------------+------------------------+ 1280 +--------+-------------+------------------+------------------------+ 1281 | | | leapsecond[11] | | 1282 +--------+-------------+------------------+------------------------+ 1283 | 142 | 19 62 31 8b | occurrence | 425865611 | 1284 | | | | (1983-06-30T23:59:60Z) | 1285 +--------+-------------+------------------+------------------------+ 1286 | 146 | 00 00 00 0c | correction | 12 | 1287 +--------+-------------+------------------+------------------------+ 1288 +--------+-------------+------------------+------------------------+ 1289 | | | leapsecond[12] | | 1290 +--------+-------------+------------------+------------------------+ 1291 | 150 | 1d 25 ea 0c | occurrence | 489024012 | 1292 | | | | (1985-06-30T23:59:60Z) | 1293 +--------+-------------+------------------+------------------------+ 1294 | 154 | 00 00 00 0d | correction | 13 | 1295 +--------+-------------+------------------+------------------------+ 1296 +--------+-------------+------------------+------------------------+ 1297 | | | leapsecond[13] | | 1298 +--------+-------------+------------------+------------------------+ 1299 | 158 | 21 da e5 0d | occurrence | 567993613 | 1300 | | | | (1987-12-31T23:59:60Z) | 1301 +--------+-------------+------------------+------------------------+ 1302 | 162 | 00 00 00 0e | correction | 14 | 1303 +--------+-------------+------------------+------------------------+ 1304 +--------+-------------+------------------+------------------------+ 1305 | | | leapsecond[14] | | 1306 +--------+-------------+------------------+------------------------+ 1307 | 166 | 25 9e 9d 8e | occurrence | 631152014 | 1308 | | | | (1989-12-31T23:59:60Z) | 1309 +--------+-------------+------------------+------------------------+ 1310 | 170 | 00 00 00 0f | correction | 15 | 1311 +--------+-------------+------------------+------------------------+ 1312 +--------+-------------+------------------+------------------------+ 1313 | | | leapsecond[15] | | 1314 +--------+-------------+------------------+------------------------+ 1315 | 174 | 27 7f d1 0f | occurrence | 662688015 | 1316 | | | | (1990-12-31T23:59:60Z) | 1317 +--------+-------------+------------------+------------------------+ 1318 | 178 | 00 00 00 10 | correction | 16 | 1319 +--------+-------------+------------------+------------------------+ 1320 +--------+-------------+------------------+------------------------+ 1321 | | | leapsecond[16] | | 1322 +--------+-------------+------------------+------------------------+ 1323 | 182 | 2a 50 f5 90 | occurrence | 709948816 | 1324 | | | | (1992-06-30T23:59:60Z) | 1325 +--------+-------------+------------------+------------------------+ 1326 | 186 | 00 00 00 11 | correction | 17 | 1327 +--------+-------------+------------------+------------------------+ 1328 +--------+-------------+------------------+------------------------+ 1329 | | | leapsecond[17] | | 1330 +--------+-------------+------------------+------------------------+ 1331 | 190 | 2c 32 29 11 | occurrence | 741484817 | 1332 | | | | (1993-06-30T23:59:60Z) | 1333 +--------+-------------+------------------+------------------------+ 1334 | 194 | 00 00 00 12 | correction | 18 | 1335 +--------+-------------+------------------+------------------------+ 1336 +--------+-------------+------------------+------------------------+ 1337 | | | leapsecond[18] | | 1338 +--------+-------------+------------------+------------------------+ 1339 | 198 | 2e 13 5c 92 | occurrence | 773020818 | 1340 | | | | (1994-06-30T23:59:60Z) | 1341 +--------+-------------+------------------+------------------------+ 1342 | 202 | 00 00 00 13 | correction | 19 | 1343 +--------+-------------+------------------+------------------------+ 1344 +--------+-------------+------------------+------------------------+ 1345 | | | leapsecond[19] | | 1346 +--------+-------------+------------------+------------------------+ 1347 | 206 | 30 e7 24 13 | occurrence | 820454419 | 1348 | | | | (1995-12-31T23:59:60Z) | 1349 +--------+-------------+------------------+------------------------+ 1350 | 210 | 00 00 00 14 | correction | 20 | 1351 +--------+-------------+------------------+------------------------+ 1352 +--------+-------------+------------------+------------------------+ 1353 | | | leapsecond[20] | | 1354 +--------+-------------+------------------+------------------------+ 1355 | 214 | 33 b8 48 94 | occurrence | 867715220 | 1356 | | | | (1997-06-30T23:59:60Z) | 1357 +--------+-------------+------------------+------------------------+ 1358 | 218 | 00 00 00 15 | correction | 21 | 1359 +--------+-------------+------------------+------------------------+ 1360 +--------+-------------+------------------+------------------------+ 1361 | | | leapsecond[21] | | 1362 +--------+-------------+------------------+------------------------+ 1363 | 222 | 36 8c 10 15 | occurrence | 915148821 | 1364 | | | | (1998-12-31T23:59:60Z) | 1365 +--------+-------------+------------------+------------------------+ 1366 | 226 | 00 00 00 16 | correction | 22 | 1367 +--------+-------------+------------------+------------------------+ 1368 +--------+-------------+------------------+------------------------+ 1369 | | | leapsecond[22] | | 1370 +--------+-------------+------------------+------------------------+ 1371 | 230 | 43 b7 1b 96 | occurrence | 1136073622 | 1372 | | | | (2005-12-31T23:59:60Z) | 1373 +--------+-------------+------------------+------------------------+ 1374 | 234 | 00 00 00 17 | correction | 23 | 1375 +--------+-------------+------------------+------------------------+ 1376 +--------+-------------+------------------+------------------------+ 1377 | | | leapsecond[23] | | 1378 +--------+-------------+------------------+------------------------+ 1379 | 238 | 49 5c 07 97 | occurrence | 1230768023 | 1380 | | | | (2008-12-31T23:59:60Z) | 1381 +--------+-------------+------------------+------------------------+ 1382 | 242 | 00 00 00 18 | correction | 24 | 1383 +--------+-------------+------------------+------------------------+ 1384 +--------+-------------+------------------+------------------------+ 1385 | | | leapsecond[24] | | 1386 +--------+-------------+------------------+------------------------+ 1387 | 246 | 4f ef 93 18 | occurrence | 1341100824 | 1388 | | | | (2012-06-30T23:59:60Z) | 1389 +--------+-------------+------------------+------------------------+ 1390 | 250 | 00 00 00 19 | correction | 25 | 1391 +--------+-------------+------------------+------------------------+ 1392 +--------+-------------+------------------+------------------------+ 1393 | | | leapsecond[25] | | 1394 +--------+-------------+------------------+------------------------+ 1395 | 254 | 55 93 2d 99 | occurrence | 1435708825 | 1396 | | | | (2015-06-30T23:59:60Z) | 1397 +--------+-------------+------------------+------------------------+ 1398 | 258 | 00 00 00 1a | correction | 26 | 1399 +--------+-------------+------------------+------------------------+ 1400 +--------+-------------+------------------+------------------------+ 1401 | | | leapsecond[26] | | 1402 +--------+-------------+------------------+------------------------+ 1403 | 262 | 58 68 46 9a | occurrence | 1483228826 | 1404 | | | | (2016-12-31T23:59:60Z) | 1405 +--------+-------------+------------------+------------------------+ 1406 | 266 | 00 00 00 1b | correction | 27 | 1407 +--------+-------------+------------------+------------------------+ 1408 +--------+-------------+------------------+------------------------+ 1409 | 270 | 00 | standard/wall[0] | 0 (wall) | 1410 +--------+-------------+------------------+------------------------+ 1411 +--------+-------------+------------------+------------------------+ 1412 | 271 | 00 | UT/local[0] | 0 (local) | 1413 +--------+-------------+------------------+------------------------+ 1415 Table 1 1417 To determine TAI corresponding to 2000-01-01T00:00:00Z 1418 (UNIX time = 946684800), the following procedure would be followed: 1420 1. Find the latest leap-second occurrence prior to the time of 1421 interest (leapsecond[21]) and note the correction value 1422 (LEAPCORR = 22). 1424 2. Add LEAPCORR + 10 to the time of interest to yield TAI of 1425 2000-01-01T00:00:32. 1427 B.2. Version 2 File Representing Pacific/Honolulu 1429 +========+=============+==================+========================+ 1430 | File | Hexadecimal | Record Name / | Field Value | 1431 | Offset | Octets | Field Name | | 1432 +========+=============+==================+========================+ 1433 | 000 | 54 5a 69 66 | magic | "TZif" | 1434 +--------+-------------+------------------+------------------------+ 1435 | 004 | 32 | version | '2' (2) | 1436 +--------+-------------+------------------+------------------------+ 1437 | 005 | 00 00 00 00 | | | 1438 | | 00 00 00 00 | | | 1439 | | 00 00 00 00 | | | 1440 | | 00 00 00 | | | 1441 +--------+-------------+------------------+------------------------+ 1442 | 020 | 00 00 00 06 | isutcnt | 6 | 1443 +--------+-------------+------------------+------------------------+ 1444 | 024 | 00 00 00 06 | isstdcnt | 6 | 1445 +--------+-------------+------------------+------------------------+ 1446 | 028 | 00 00 00 00 | leapcnt | 0 | 1447 +--------+-------------+------------------+------------------------+ 1448 | 032 | 00 00 00 07 | timecnt | 7 | 1449 +--------+-------------+------------------+------------------------+ 1450 | 036 | 00 00 00 06 | typecnt | 6 | 1451 +--------+-------------+------------------+------------------------+ 1452 | 040 | 00 00 00 14 | charcnt | 20 | 1453 +--------+-------------+------------------+------------------------+ 1454 +--------+-------------+------------------+------------------------+ 1455 | 044 | 80 00 00 00 | trans time[0] | -2147483648 | 1456 | | | | (1901-12-13T20:45:52Z) | 1457 +--------+-------------+------------------+------------------------+ 1458 | 048 | bb 05 43 48 | trans time[1] | -1157283000 | 1459 | | | | (1933-04-30T12:30:00Z) | 1460 +--------+-------------+------------------+------------------------+ 1461 | 052 | bb 21 71 58 | trans time[2] | -1155436200 | 1462 | | | | (1933-05-21T21:30:00Z) | 1463 +--------+-------------+------------------+------------------------+ 1464 | 056 | cb 89 3d c8 | trans time[3] | -880198200 | 1465 | | | | (1942-02-09T12:30:00Z) | 1466 +--------+-------------+------------------+------------------------+ 1467 | 060 | d2 23 f4 70 | trans time[4] | -769395600 | 1468 | | | | (1945-08-14T23:00:00Z) | 1469 +--------+-------------+------------------+------------------------+ 1470 | 064 | d2 61 49 38 | trans time[5] | -765376200 | 1471 | | | | (1945-09-30T11:30:00Z) | 1472 +--------+-------------+------------------+------------------------+ 1473 | 068 | d5 8d 73 48 | trans time[6] | -712150200 | 1474 | | | | (1947-06-08T12:30:00Z) | 1475 +--------+-------------+------------------+------------------------+ 1476 +--------+-------------+------------------+------------------------+ 1477 | 072 | 01 | trans type[0] | 1 | 1478 +--------+-------------+------------------+------------------------+ 1479 | 073 | 02 | trans type[1] | 2 | 1480 +--------+-------------+------------------+------------------------+ 1481 | 074 | 01 | trans type[2] | 1 | 1482 +--------+-------------+------------------+------------------------+ 1483 | 075 | 03 | trans type[3] | 3 | 1484 +--------+-------------+------------------+------------------------+ 1485 | 076 | 04 | trans type[4] | 4 | 1486 +--------+-------------+------------------+------------------------+ 1487 | 077 | 01 | trans type[5] | 1 | 1488 +--------+-------------+------------------+------------------------+ 1489 | 078 | 05 | trans type[6] | 5 | 1490 +--------+-------------+------------------+------------------------+ 1491 +--------+-------------+------------------+------------------------+ 1492 | | | localtimetype[0] | | 1493 +--------+-------------+------------------+------------------------+ 1494 | 079 | ff ff 6c 02 | utoff | -37886 (-10:21:26) | 1495 +--------+-------------+------------------+------------------------+ 1496 | 083 | 00 | isdst | 0 (no) | 1497 +--------+-------------+------------------+------------------------+ 1498 | 084 | 00 | desigidx | 0 | 1499 +--------+-------------+------------------+------------------------+ 1500 +--------+-------------+------------------+------------------------+ 1501 | | | localtimetype[1] | | 1502 +--------+-------------+------------------+------------------------+ 1503 | 085 | ff ff 6c 58 | utoff | -37800 (-10:30) | 1504 +--------+-------------+------------------+------------------------+ 1505 | 089 | 00 | isdst | 0 (no) | 1506 +--------+-------------+------------------+------------------------+ 1507 | 090 | 04 | desigidx | 4 | 1508 +--------+-------------+------------------+------------------------+ 1509 +--------+-------------+------------------+------------------------+ 1510 | | | localtimetype[2] | | 1511 +--------+-------------+------------------+------------------------+ 1512 | 091 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1513 +--------+-------------+------------------+------------------------+ 1514 | 095 | 01 | isdst | 1 (yes) | 1515 +--------+-------------+------------------+------------------------+ 1516 | 096 | 08 | desigidx | 8 | 1517 +--------+-------------+------------------+------------------------+ 1518 +--------+-------------+------------------+------------------------+ 1519 | | | localtimetype[3] | | 1520 +--------+-------------+------------------+------------------------+ 1521 | 097 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1522 +--------+-------------+------------------+------------------------+ 1523 | 101 | 01 | isdst | 1 (yes) | 1524 +--------+-------------+------------------+------------------------+ 1525 | 102 | 0c | desigidx | 12 | 1526 +--------+-------------+------------------+------------------------+ 1527 +--------+-------------+------------------+------------------------+ 1528 | | | localtimetype[4] | | 1529 +--------+-------------+------------------+------------------------+ 1530 | 103 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1531 +--------+-------------+------------------+------------------------+ 1532 | 107 | 01 | isdst | 1 (yes) | 1533 +--------+-------------+------------------+------------------------+ 1534 | 108 | 10 | desigidx | 16 | 1535 +--------+-------------+------------------+------------------------+ 1536 +--------+-------------+------------------+------------------------+ 1537 | | | localtimetype[5] | | 1538 +--------+-------------+------------------+------------------------+ 1539 | 109 | ff ff 73 60 | utoff | -36000 (-10:00) | 1540 +--------+-------------+------------------+------------------------+ 1541 | 113 | 00 | isdst | 0 (no) | 1542 +--------+-------------+------------------+------------------------+ 1543 | 114 | 04 | desigidx | 4 | 1544 +--------+-------------+------------------+------------------------+ 1545 +--------+-------------+------------------+------------------------+ 1546 | 115 | 4c 4d 54 00 | designations[0] | "LMT" | 1547 +--------+-------------+------------------+------------------------+ 1548 | 119 | 48 53 54 00 | designations[4] | "HST" | 1549 +--------+-------------+------------------+------------------------+ 1550 | 123 | 48 44 54 00 | designations[8] | "HDT" | 1551 +--------+-------------+------------------+------------------------+ 1552 | 127 | 48 57 54 00 | designations[12] | "HWT" | 1553 +--------+-------------+------------------+------------------------+ 1554 | 131 | 48 50 54 00 | designations[16] | "HPT" | 1555 +--------+-------------+------------------+------------------------+ 1556 +--------+-------------+------------------+------------------------+ 1557 | 135 | 00 | standard/wall[0] | 0 (wall) | 1558 +--------+-------------+------------------+------------------------+ 1559 | 136 | 00 | standard/wall[1] | 0 (wall) | 1560 +--------+-------------+------------------+------------------------+ 1561 | 137 | 00 | standard/wall[2] | 0 (wall) | 1562 +--------+-------------+------------------+------------------------+ 1563 | 138 | 00 | standard/wall[3] | 0 (wall) | 1564 +--------+-------------+------------------+------------------------+ 1565 | 139 | 01 | standard/wall[4] | 1 (standard) | 1566 +--------+-------------+------------------+------------------------+ 1567 | 140 | 00 | standard/wall[5] | 0 (wall) | 1568 +--------+-------------+------------------+------------------------+ 1569 +--------+-------------+------------------+------------------------+ 1570 | 141 | 00 | UT/local[0] | 0 (local) | 1571 +--------+-------------+------------------+------------------------+ 1572 | 142 | 00 | UT/local[1] | 0 (local) | 1573 +--------+-------------+------------------+------------------------+ 1574 | 143 | 00 | UT/local[2] | 0 (local) | 1575 +--------+-------------+------------------+------------------------+ 1576 | 144 | 00 | UT/local[3] | 0 (local) | 1577 +--------+-------------+------------------+------------------------+ 1578 | 145 | 01 | UT/local[4] | 1 (UT) | 1579 +--------+-------------+------------------+------------------------+ 1580 | 146 | 00 | UT/local[5] | 0 (local) | 1581 +--------+-------------+------------------+------------------------+ 1582 +--------+-------------+------------------+------------------------+ 1583 | 147 | 54 5a 69 66 | magic | "TZif" | 1584 +--------+-------------+------------------+------------------------+ 1585 | 151 | 32 | version | '2' (2) | 1586 +--------+-------------+------------------+------------------------+ 1587 | 152 | 00 00 00 00 | | | 1588 | | 00 00 00 00 | | | 1589 | | 00 00 00 00 | | | 1590 | | 00 00 00 | | | 1591 +--------+-------------+------------------+------------------------+ 1592 | 167 | 00 00 00 06 | isutcnt | 6 | 1593 +--------+-------------+------------------+------------------------+ 1594 | 171 | 00 00 00 06 | isstdcnt | 6 | 1595 +--------+-------------+------------------+------------------------+ 1596 | 175 | 00 00 00 00 | leapcnt | 0 | 1597 +--------+-------------+------------------+------------------------+ 1598 | 179 | 00 00 00 07 | timecnt | 7 | 1599 +--------+-------------+------------------+------------------------+ 1600 | 183 | 00 00 00 06 | typecnt | 6 | 1601 +--------+-------------+------------------+------------------------+ 1602 | 187 | 00 00 00 14 | charcnt | 20 | 1603 +--------+-------------+------------------+------------------------+ 1604 +--------+-------------+------------------+------------------------+ 1605 | 191 | ff ff ff ff | trans time[0] | -2334101314 | 1606 | | 74 e0 70 be | | (1896-01-13T22:31:26Z) | 1607 +--------+-------------+------------------+------------------------+ 1608 | 199 | ff ff ff ff | trans time[1] | -1157283000 | 1609 | | bb 05 43 48 | | (1933-04-30T12:30:00Z) | 1610 +--------+-------------+------------------+------------------------+ 1611 | 207 | ff ff ff ff | trans time[2] | -1155436200 | 1612 | | bb 21 71 58 | | (1933-05-21T21:30:00Z) | 1613 +--------+-------------+------------------+------------------------+ 1614 | 215 | ff ff ff ff | trans time[3] | -880198200 | 1615 | | cb 89 3d c8 | | (1942-02-09T12:30:00Z) | 1616 +--------+-------------+------------------+------------------------+ 1617 | 223 | ff ff ff ff | trans time[4] | -769395600 | 1618 | | d2 23 f4 70 | | (1945-08-14T23:00:00Z) | 1619 +--------+-------------+------------------+------------------------+ 1620 | 231 | ff ff ff ff | trans time[5] | -765376200 | 1621 | | d2 61 49 38 | | (1945-09-30T11:30:00Z) | 1622 +--------+-------------+------------------+------------------------+ 1623 | 239 | ff ff ff ff | trans time[6] | -712150200 | 1624 | | d5 8d 73 48 | | (1947-06-08T12:30:00Z) | 1625 +--------+-------------+------------------+------------------------+ 1626 +--------+-------------+------------------+------------------------+ 1627 | 247 | 01 | trans type[0] | 1 | 1628 +--------+-------------+------------------+------------------------+ 1629 | 248 | 02 | trans type[1] | 2 | 1630 +--------+-------------+------------------+------------------------+ 1631 | 249 | 01 | trans type[2] | 1 | 1632 +--------+-------------+------------------+------------------------+ 1633 | 250 | 03 | trans type[3] | 3 | 1634 +--------+-------------+------------------+------------------------+ 1635 | 251 | 04 | trans type[4] | 4 | 1636 +--------+-------------+------------------+------------------------+ 1637 | 252 | 01 | trans type[5] | 1 | 1638 +--------+-------------+------------------+------------------------+ 1639 | 253 | 05 | trans type[6] | 5 | 1640 +--------+-------------+------------------+------------------------+ 1641 +--------+-------------+------------------+------------------------+ 1642 | | | localtimetype[0] | | 1643 +--------+-------------+------------------+------------------------+ 1644 | 254 | ff ff 6c 02 | utoff | -37886 (-10:21:26) | 1645 +--------+-------------+------------------+------------------------+ 1646 | 258 | 00 | isdst | 0 (no) | 1647 +--------+-------------+------------------+------------------------+ 1648 | 259 | 00 | desigidx | 0 | 1649 +--------+-------------+------------------+------------------------+ 1650 +--------+-------------+------------------+------------------------+ 1651 | | | localtimetype[1] | | 1652 +--------+-------------+------------------+------------------------+ 1653 | 260 | ff ff 6c 58 | utoff | -37800 (-10:30) | 1654 +--------+-------------+------------------+------------------------+ 1655 | 264 | 00 | isdst | 0 (no) | 1656 +--------+-------------+------------------+------------------------+ 1657 | 265 | 04 | desigidx | 4 | 1658 +--------+-------------+------------------+------------------------+ 1659 +--------+-------------+------------------+------------------------+ 1660 | | | localtimetype[2] | | 1661 +--------+-------------+------------------+------------------------+ 1662 | 266 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1663 +--------+-------------+------------------+------------------------+ 1664 | 270 | 01 | isdst | 1 (yes) | 1665 +--------+-------------+------------------+------------------------+ 1666 | 271 | 08 | desigidx | 8 | 1667 +--------+-------------+------------------+------------------------+ 1668 +--------+-------------+------------------+------------------------+ 1669 | | | localtimetype[3] | | 1670 +--------+-------------+------------------+------------------------+ 1671 | 272 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1672 +--------+-------------+------------------+------------------------+ 1673 | 276 | 01 | isdst | 1 (yes) | 1674 +--------+-------------+------------------+------------------------+ 1675 | 277 | 0c | desigidx | 12 | 1676 +--------+-------------+------------------+------------------------+ 1677 +--------+-------------+------------------+------------------------+ 1678 | | | localtimetype[4] | | 1679 +--------+-------------+------------------+------------------------+ 1680 | 278 | ff ff 7a 68 | utoff | -34200 (-09:30) | 1681 +--------+-------------+------------------+------------------------+ 1682 | 282 | 01 | isdst | 1 (yes) | 1683 +--------+-------------+------------------+------------------------+ 1684 | 283 | 10 | desigidx | 16 | 1685 +--------+-------------+------------------+------------------------+ 1686 +--------+-------------+------------------+------------------------+ 1687 | | | localtimetype[5] | | 1688 +--------+-------------+------------------+------------------------+ 1689 | 284 | ff ff 73 60 | utoff | -36000 (-10:00) | 1690 +--------+-------------+------------------+------------------------+ 1691 | 288 | 00 | isdst | 0 (no) | 1692 +--------+-------------+------------------+------------------------+ 1693 | 289 | 04 | desigidx | 4 | 1694 +--------+-------------+------------------+------------------------+ 1695 +--------+-------------+------------------+------------------------+ 1696 | 290 | 4c 4d 54 00 | designations[0] | "LMT" | 1697 +--------+-------------+------------------+------------------------+ 1698 | 294 | 48 53 54 00 | designations[4] | "HST" | 1699 +--------+-------------+------------------+------------------------+ 1700 | 298 | 48 44 54 00 | designations[8] | "HDT" | 1701 +--------+-------------+------------------+------------------------+ 1702 | 302 | 48 57 54 00 | designations[12] | "HWT" | 1703 +--------+-------------+------------------+------------------------+ 1704 | 306 | 48 50 54 00 | designations[16] | "HPT" | 1705 +--------+-------------+------------------+------------------------+ 1706 +--------+-------------+------------------+------------------------+ 1707 | 310 | 00 | standard/wall[0] | 0 (wall) | 1708 +--------+-------------+------------------+------------------------+ 1709 | 311 | 00 | standard/wall[1] | 0 (wall) | 1710 +--------+-------------+------------------+------------------------+ 1711 | 312 | 00 | standard/wall[2] | 0 (wall) | 1712 +--------+-------------+------------------+------------------------+ 1713 | 313 | 00 | standard/wall[3] | 0 (wall) | 1714 +--------+-------------+------------------+------------------------+ 1715 | 314 | 01 | standard/wall[4] | 1 (standard) | 1716 +--------+-------------+------------------+------------------------+ 1717 | 315 | 00 | standard/wall[5] | 0 (wall) | 1718 +--------+-------------+------------------+------------------------+ 1719 +--------+-------------+------------------+------------------------+ 1720 | 316 | 00 | UT/local[0] | 0 (local) | 1721 +--------+-------------+------------------+------------------------+ 1722 | 317 | 00 | UT/local[1] | 0 (local) | 1723 +--------+-------------+------------------+------------------------+ 1724 | 318 | 00 | UT/local[2] | 0 (local) | 1725 +--------+-------------+------------------+------------------------+ 1726 | 319 | 00 | UT/local[3] | 0 (local) | 1727 +--------+-------------+------------------+------------------------+ 1728 | 320 | 01 | UT/local[4] | 1 (UT) | 1729 +--------+-------------+------------------+------------------------+ 1730 | 321 | 00 | UT/local[5] | 0 (local) | 1731 +--------+-------------+------------------+------------------------+ 1732 +--------+-------------+------------------+------------------------+ 1733 | 322 | 0a | NL | '\n' | 1734 +--------+-------------+------------------+------------------------+ 1735 | 323 | 48 53 54 31 | TZ string | "HST10" | 1736 | | 30 | | | 1737 +--------+-------------+------------------+------------------------+ 1738 | 328 | 0a | NL | '\n' | 1739 +--------+-------------+------------------+------------------------+ 1741 Table 2 1743 To determine the local time in this time zone corresponding to 1744 1933-05-04T12:00:00Z (UNIX time = -1156939200), the following 1745 procedure would be followed: 1747 1. Find the latest time transition prior to the time of interest 1748 (trans time[1]). 1750 2. Reference the corresponding transition type (trans type[1]) to 1751 determine the local time type index (2). 1753 3. Reference the corresponding local time type (localtimetype[2]) to 1754 determine the offset from UTC (-09:30), the daylight saving 1755 indicator (1 = yes), and the index into the time zone designation 1756 strings (8). 1758 4. Look up the corresponding time zone designation string 1759 (designations[8] = "HDT"). 1761 5. Add the UTC offset to the time of interest to yield a local 1762 daylight saving time of 1933-05-04T02:30:00-09:30 (HDT). 1764 To determine the local time in this time zone corresponding to 1765 2019-01-01T00:00:00Z (UNIX time = 1546300800), the following 1766 procedure would be followed: 1768 1. Find the latest time transition prior to the time of interest 1769 (there is no such transition). 1771 2. Look up the TZ string in the footer ("HST10"), which indicates 1772 that the time zone designation is "HST" year-round, and the 1773 offset to UTC is 10:00. 1775 3. Subtract the UTC offset from the time of interest to yield a 1776 standard local time of 2018-12-31T14:00:00-10:00 (HST). 1778 B.3. Truncated Version 3 File Representing Asia/Jerusalem 1780 The following TZif file has been truncated to start on 1781 2038-01-01T00:00:00Z. 1783 In this example: 1785 * The start time value can not be represented using 32 bits, so the 1786 version 1 header contains only the required minimum data, which 1787 will be ignored by readers. 1789 * The version 3 header leverages the fact that by specifying 1790 'isutcnt' and 'isstdcnt' as zero, all transition times associated 1791 with local time types are assumed to be specified as local wall- 1792 clock time (see the definitions of UT/local indicators and 1793 standard/wall indicators in Section 3.2). 1795 * The TZ string value has been line-wrapped for presentation 1796 purposes only. 1798 +========+=============+==================+========================+ 1799 | File | Hexadecimal | Record Name / | Field Value | 1800 | Offset | Octets | Field Name | | 1801 +========+=============+==================+========================+ 1802 | 000 | 54 5a 69 66 | magic | "TZif" | 1803 +--------+-------------+------------------+------------------------+ 1804 | 004 | 33 | version | '3' (3) | 1805 +--------+-------------+------------------+------------------------+ 1806 | 005 | 00 00 00 00 | | | 1807 | | 00 00 00 00 | | | 1808 | | 00 00 00 00 | | | 1809 | | 00 00 00 | | | 1810 +--------+-------------+------------------+------------------------+ 1811 | 020 | 00 00 00 00 | isutcnt | 0 | 1812 +--------+-------------+------------------+------------------------+ 1813 | 024 | 00 00 00 00 | isstdcnt | 0 | 1814 +--------+-------------+------------------+------------------------+ 1815 | 028 | 00 00 00 00 | leapcnt | 0 | 1816 +--------+-------------+------------------+------------------------+ 1817 | 032 | 00 00 00 00 | timecnt | 0 | 1818 +--------+-------------+------------------+------------------------+ 1819 | 036 | 00 00 00 01 | typecnt | 1 | 1820 +--------+-------------+------------------+------------------------+ 1821 | 040 | 00 00 00 01 | charcnt | 1 | 1822 +--------+-------------+------------------+------------------------+ 1823 +--------+-------------+------------------+------------------------+ 1824 | | | localtimetype[0] | | 1825 +--------+-------------+------------------+------------------------+ 1826 | 044 | 00 00 00 00 | utoff | 0 (+00:00) | 1827 +--------+-------------+------------------+------------------------+ 1828 | 048 | 00 | isdst | 0 (no) | 1829 +--------+-------------+------------------+------------------------+ 1830 | 049 | 00 | desigidx | 0 | 1831 +--------+-------------+------------------+------------------------+ 1832 +--------+-------------+------------------+------------------------+ 1833 | 050 | 00 | designations[0] | "" | 1834 +--------+-------------+------------------+------------------------+ 1835 +--------+-------------+------------------+------------------------+ 1836 | 051 | 54 5a 69 66 | magic | "TZif" | 1837 +--------+-------------+------------------+------------------------+ 1838 | 055 | 33 | version | '3' (3) | 1839 +--------+-------------+------------------+------------------------+ 1840 | 056 | 00 00 00 00 | | | 1841 | | 00 00 00 00 | | | 1842 | | 00 00 00 00 | | | 1843 | | 00 00 00 | | | 1844 +--------+-------------+------------------+------------------------+ 1845 | 071 | 00 00 00 00 | isutcnt | 0 | 1846 +--------+-------------+------------------+------------------------+ 1847 | 075 | 00 00 00 00 | isstdcnt | 0 | 1848 +--------+-------------+------------------+------------------------+ 1849 | 079 | 00 00 00 00 | leapcnt | 0 | 1850 +--------+-------------+------------------+------------------------+ 1851 | 083 | 00 00 00 01 | timecnt | 1 | 1852 +--------+-------------+------------------+------------------------+ 1853 | 087 | 00 00 00 01 | typecnt | 1 | 1854 +--------+-------------+------------------+------------------------+ 1855 | 091 | 00 00 00 04 | charcnt | 4 | 1856 +--------+-------------+------------------+------------------------+ 1857 +--------+-------------+------------------+------------------------+ 1858 | 095 | 00 00 00 00 | trans time[0] | 2145916800 | 1859 | | 7f e8 17 80 | | (2038-01-01T00:00:00Z) | 1860 +--------+-------------+------------------+------------------------+ 1861 +--------+-------------+------------------+------------------------+ 1862 | 103 | 00 | trans type[0] | 0 | 1863 +--------+-------------+------------------+------------------------+ 1864 +--------+-------------+------------------+------------------------+ 1865 | | | localtimetype[0] | | 1866 +--------+-------------+------------------+------------------------+ 1867 | 104 | 00 00 1c 20 | utoff | 7200 (+02:00) | 1868 +--------+-------------+------------------+------------------------+ 1869 | 108 | 00 | isdst | 0 (no) | 1870 +--------+-------------+------------------+------------------------+ 1871 | 109 | 00 | desigidx | 0 | 1872 +--------+-------------+------------------+------------------------+ 1873 +--------+-------------+------------------+------------------------+ 1874 | 110 | 49 53 54 00 | designations[0] | "IST" | 1875 +--------+-------------+------------------+------------------------+ 1876 +--------+-------------+------------------+------------------------+ 1877 | 114 | 0a | NL | '\n' | 1878 +--------+-------------+------------------+------------------------+ 1879 | 115 | 49 53 54 2d | TZ string | "IST-2IDT, | 1880 | | 32 49 44 54 | | M3.4.4/26,M10.5.0" | 1881 | | 2c 4d 33 2e | | | 1882 | | 34 2e 34 2f | | | 1883 | | 32 36 2c 4d | | | 1884 | | 31 30 2e 35 | | | 1885 | | 2e 30 | | | 1886 +--------+-------------+------------------+------------------------+ 1887 | 141 | 0a | NL | '\n' | 1888 +--------+-------------+------------------+------------------------+ 1890 Table 3 1892 B.4. Truncated Version 4 File Representing America/New_York 1894 The following TZif file has been truncated to start on 1895 2022-01-01T00:00:00Z. 1897 In this example: 1899 * The version 1 header contains only the required minimum data, 1900 which will be ignored by readers. 1902 * The version 4 header leverages the fact that by specifying 1903 'isutcnt' and 'isstdcnt' as zero, all transition times associated 1904 with local time types are assumed to be specified as local wall- 1905 clock time (see the definitions of UT/local indicators and 1906 standard/wall indicators in Section 3.2). 1908 * The first leap second occurrence is the most recent one prior to 1909 the truncation time. 1911 * The last leap second correction matches the second-to-last leap 1912 second correction, indicating the expiration time of the leap 1913 second table. 1915 * The TZ string value has been line-wrapped for presentation 1916 purposes only. 1918 +========+=============+==================+========================+ 1919 | File | Hexadecimal | Record Name / | Field Value | 1920 | Offset | Octets | Field Name | | 1921 +========+=============+==================+========================+ 1922 | 000 | 54 5a 69 66 | magic | "TZif" | 1923 +--------+-------------+------------------+------------------------+ 1924 | 004 | 34 | version | '4' (4) | 1925 +--------+-------------+------------------+------------------------+ 1926 | 005 | 00 00 00 00 | | | 1927 | | 00 00 00 00 | | | 1928 | | 00 00 00 00 | | | 1929 | | 00 00 00 | | | 1930 +--------+-------------+------------------+------------------------+ 1931 | 020 | 00 00 00 00 | isutcnt | 0 | 1932 +--------+-------------+------------------+------------------------+ 1933 | 024 | 00 00 00 00 | isstdcnt | 0 | 1934 +--------+-------------+------------------+------------------------+ 1935 | 028 | 00 00 00 00 | leapcnt | 0 | 1936 +--------+-------------+------------------+------------------------+ 1937 | 032 | 00 00 00 00 | timecnt | 0 | 1938 +--------+-------------+------------------+------------------------+ 1939 | 036 | 00 00 00 01 | typecnt | 1 | 1940 +--------+-------------+------------------+------------------------+ 1941 | 040 | 00 00 00 01 | charcnt | 1 | 1942 +--------+-------------+------------------+------------------------+ 1943 +--------+-------------+------------------+------------------------+ 1944 | | | localtimetype[0] | | 1945 +--------+-------------+------------------+------------------------+ 1946 | 044 | 00 00 00 00 | utoff | 0 (+00:00) | 1947 +--------+-------------+------------------+------------------------+ 1948 | 048 | 00 | isdst | 0 (no) | 1949 +--------+-------------+------------------+------------------------+ 1950 | 049 | 00 | desigidx | 0 | 1951 +--------+-------------+------------------+------------------------+ 1952 +--------+-------------+------------------+------------------------+ 1953 | 050 | 00 | designations[0] | "" | 1954 +--------+-------------+------------------+------------------------+ 1955 +--------+-------------+------------------+------------------------+ 1956 | 051 | 54 5a 69 66 | magic | "TZif" | 1957 +--------+-------------+------------------+------------------------+ 1958 | 055 | 34 | version | '4' (4) | 1959 +--------+-------------+------------------+------------------------+ 1960 | 056 | 00 00 00 00 | | | 1961 | | 00 00 00 00 | | | 1962 | | 00 00 00 00 | | | 1963 | | 00 00 00 | | | 1964 +--------+-------------+------------------+------------------------+ 1965 | 071 | 00 00 00 00 | isutcnt | 0 | 1966 +--------+-------------+------------------+------------------------+ 1967 | 075 | 00 00 00 00 | isstdcnt | 0 | 1968 +--------+-------------+------------------+------------------------+ 1969 | 079 | 00 00 00 02 | leapcnt | 2 | 1970 +--------+-------------+------------------+------------------------+ 1971 | 083 | 00 00 00 01 | timecnt | 1 | 1972 +--------+-------------+------------------+------------------------+ 1973 | 087 | 00 00 00 01 | typecnt | 1 | 1974 +--------+-------------+------------------+------------------------+ 1975 | 091 | 00 00 00 04 | charcnt | 4 | 1976 +--------+-------------+------------------+------------------------+ 1977 +--------+-------------+------------------+------------------------+ 1978 | 095 | 00 00 00 00 | trans time[0] | 1640995227 | 1979 | | 61 cf 99 9b | | (2022-01-01T00:00:00Z) | 1980 +--------+-------------+------------------+------------------------+ 1981 +--------+-------------+------------------+------------------------+ 1982 | 103 | 00 | trans type[0] | 0 | 1983 +--------+-------------+------------------+------------------------+ 1984 +--------+-------------+------------------+------------------------+ 1985 | | | localtimetype[0] | | 1986 +--------+-------------+------------------+------------------------+ 1987 | 104 | ff ff b9 b0 | utoff | -18000 (-05:00) | 1988 +--------+-------------+------------------+------------------------+ 1989 | 108 | 00 | isdst | 0 (no) | 1990 +--------+-------------+------------------+------------------------+ 1991 | 109 | 00 | desigidx | 0 | 1992 +--------+-------------+------------------+------------------------+ 1993 +--------+-------------+------------------+------------------------+ 1994 | 110 | 45 53 54 00 | designations[0] | "EST" | 1995 +--------+-------------+------------------+------------------------+ 1996 +--------+-------------+------------------+------------------------+ 1997 | | | leapsecond[0] | | 1998 +--------+-------------+------------------+------------------------+ 1999 | 114 | 00 00 00 00 | occurrence | 1483228826 | 2000 | | 58 68 46 9a | | (2016-12-31T23:59:60Z) | 2001 +--------+-------------+------------------+------------------------+ 2002 | 122 | 00 00 00 1b | correction | 27 | 2003 +--------+-------------+------------------+------------------------+ 2004 +--------+-------------+------------------+------------------------+ 2005 | | | leapsecond[1] | | 2006 +--------+-------------+------------------+------------------------+ 2007 | 126 | 00 00 00 00 | occurrence | 1656374427 | 2008 | | 62 ba 44 9b | | (2022-06-28T00:00:00Z) | 2009 +--------+-------------+------------------+------------------------+ 2010 | 134 | 00 00 00 1b | correction | 27 | 2011 +--------+-------------+------------------+------------------------+ 2012 +--------+-------------+------------------+------------------------+ 2013 | 138 | 0a | NL | '\n' | 2014 +--------+-------------+------------------+------------------------+ 2015 | 139 | 45 53 54 35 | TZ string | "EST5EDT, | 2016 | | 45 44 54 2c | | M3.2.0,M11.1.0" | 2017 | | 4d 33 2e 32 | | | 2018 | | 2e 30 2c 4d | | | 2019 | | 31 31 2e 31 | | | 2020 | | 2e 30 | | | 2021 +--------+-------------+------------------+------------------------+ 2022 | 161 | 0a | NL | '\n' | 2023 +--------+-------------+------------------+------------------------+ 2025 Table 4 2027 Appendix C. Changes from RFC 8536 2029 * Added specification of the version 4 format and the optional leap 2030 second table truncation and expiration, along with an example and 2031 relevant interoperability considerations. 2033 * Documented the longstanding practice that UT with designation 2034 string "-00" denotes unspecified local time. Added recommendation 2035 that this designation string should be used for timestamps 2036 excluded by TZif file truncation. 2038 * Applied erratum [Err6435]. 2040 * Addressed erratum [Err6426] and several other errors in the 2041 examples. 2043 * Clarified the all-year daylight saving time TZ string 2044 (Section 3.3.1) example and added a similar example with negative 2045 DST. 2047 * Added informational notes to Appendix B.3. 2049 * Miscellaneous editorial changes. 2051 Appendix D. Change Log 2053 This section is to be removed by RFC Editor before publication. 2055 D.1. Since rfc8536bis-02 2057 * Documented "-00" as meaning unspecified local time. 2059 * Recommended that "-00" be used for timestamps that are unspecified 2060 due to TZif file truncation. 2062 D.2. Since rfc8536bis-01 2064 * Converted source from xml2rfc v2 to v3. 2066 * Properly line-wrapped long TZ string values in examples (with no 2067 added space). 2069 * No other substantive changes. 2071 D.3. Since rfc8536bis-00 2073 * Added specification of the version 4 format and the optional leap 2074 second table truncation and expiration, along with an example and 2075 relevant interoperability considerations. 2077 * Specified column widths in example tables. 2079 * Noted that long TZ string values in examples are line-wrapped for 2080 presentation purposes only. 2082 D.4. Since RFC 8536 2084 * Applied erratum [Err6435]. 2086 * Addressed erratum [Err6426] and several other errors in the 2087 examples. 2089 * Clarified the all-year daylight saving time TZ string 2090 (Section 3.3.1) example and added a similar example with negative 2091 DST. 2093 * Added informational notes to Appendix B.3. 2095 * Miscellaneous editorial changes. 2097 * Added text obsoleting [RFC8536]. 2099 * Added Changes from RFC 8536 (Appendix C). 2101 * Added Tim Parenti as a contributor. 2103 Acknowledgments 2105 The authors would like to thank the following individuals for 2106 contributing their ideas and support for writing this specification: 2107 Michael Douglass, Ned Freed, Guy Harris, Eliot Lear, Alexey Melnikov, 2108 and Tim Parenti. 2110 Authors' Addresses 2112 Arthur David Olson 2114 Email: arthurdavidolson@gmail.com 2116 Paul Eggert 2117 University of California, Los Angeles 2119 Email: eggert@cs.ucla.edu 2121 Kenneth Murchison 2122 Fastmail US LLC 2124 Email: murch@fastmailteam.com