time/tzset.c

   1 /* Copyright (C) 1991-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <ctype.h>
  19 #include <libc-lock.h>
  20 #include <stdbool.h>
  21 #include <stddef.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <time.h>
  26
  27 #include <timezone/tzfile.h>
  28
  29 #define SECSPERDAY ((__time64_t) 86400)
  30
  31 char *__tzname[2] = { (char *) "GMT", (char *) "GMT" };
  32 int __daylight = 0;
  33 long int __timezone = 0L;
  34
  35 weak_alias (__tzname, tzname)
  36 weak_alias (__daylight, daylight)
  37 weak_alias (__timezone, timezone)
  38
  39 /* This locks all the state variables in tzfile.c and this file.  */
  40 __libc_lock_define_initialized (static, tzset_lock)
  41
  42 /* This structure contains all the information about a
  43    timezone given in the POSIX standard TZ envariable.  */
  44 typedef struct
  45   {
  46     const char *name;
  47
  48     /* When to change.  */
  49     enum { J0, J1, M } type;    /* Interpretation of:  */
  50     unsigned short int m, n, d; /* Month, week, day.  */
  51     int secs;                   /* Time of day.  */
  52
  53     int offset;                 /* Seconds east of GMT (west if < 0).  */
  54
  55     /* We cache the computed time of change for a
  56        given year so we don't have to recompute it.  */
  57     __time64_t change;  /* When to change to this zone.  */
  58     int computed_for;   /* Year above is computed for.  */
  59   } tz_rule;
  60
  61 /* tz_rules[0] is standard, tz_rules[1] is daylight.  */
  62 static tz_rule tz_rules[2];
  63
  64
  65 static void compute_change (tz_rule *rule, int year) __THROW;
  66 static void tzset_internal (int always);
  67 \f
  68 /* List of buffers containing time zone strings. */
  69 struct tzstring_l
  70 {
  71   struct tzstring_l *next;
  72   size_t len;  /* strlen(data) - doesn't count terminating NUL! */
  73   char data[0];
  74 };
  75
  76 static struct tzstring_l *tzstring_list;
  77
  78 /* Allocate a permanent home for the first LEN characters of S.  It
  79    will never be moved or deallocated, but may share space with other
  80    strings.  Don't modify the returned string. */
  81 static char *
  82 __tzstring_len (const char *s, size_t len)
  83 {
  84   char *p;
  85   struct tzstring_l *t, *u, *new;
  86
  87   /* Walk the list and look for a match.  If this string is the same
  88      as the end of an already-allocated string, it can share space. */
  89   for (u = t = tzstring_list; t; u = t, t = t->next)
  90     if (len <= t->len)
  91       {
  92         p = &t->data[t->len - len];
  93         if (memcmp (s, p, len) == 0)
  94           return p;
  95       }
  96
  97   /* Not found; allocate a new buffer. */
  98   new = malloc (sizeof (struct tzstring_l) + len + 1);
  99   if (!new)
 100     return NULL;
 101
 102   new->next = NULL;
 103   new->len = len;
 104   memcpy (new->data, s, len);
 105   new->data[len] = '\0';
 106
 107   if (u)
 108     u->next = new;
 109   else
 110     tzstring_list = new;
 111
 112   return new->data;
 113 }
 114
 115 /* Allocate a permanent home for S.  It will never be moved or
 116    deallocated, but may share space with other strings.  Don't modify
 117    the returned string. */
 118 char *
 119 __tzstring (const char *s)
 120 {
 121   return __tzstring_len (s, strlen (s));
 122 }
 123
 124 static char *old_tz;
 125
 126 static void
 127 update_vars (void)
 128 {
 129   __daylight = tz_rules[0].offset != tz_rules[1].offset;
 130   __timezone = -tz_rules[0].offset;
 131   __tzname[0] = (char *) tz_rules[0].name;
 132   __tzname[1] = (char *) tz_rules[1].name;
 133 }
 134
 135
 136 static unsigned int
 137 compute_offset (unsigned int ss, unsigned int mm, unsigned int hh)
 138 {
 139   if (ss > 59)
 140     ss = 59;
 141   if (mm > 59)
 142     mm = 59;
 143   if (hh > 24)
 144     hh = 24;
 145   return ss + mm * 60 + hh * 60 * 60;
 146 }
 147
 148 /* Parses the time zone abbreviation at *TZP, and writes a pointer to an
 149    interned string to tz_rules[WHICHRULE].name.  On success, advances
 150    *TZP, and returns true.  Returns false otherwise.  */
 151 static bool
 152 parse_tzname (const char **tzp, int whichrule)
 153 {
 154   const char *start = *tzp;
 155   const char *p = start;
 156   while (('a' <= *p && *p <= 'z')
 157          || ('A' <= *p && *p <= 'Z'))
 158       ++p;
 159   size_t len = p - start;
 160   if (len < 3)
 161     {
 162       p = *tzp;
 163       if (__glibc_unlikely (*p++ != '<'))
 164         return false;
 165       start = p;
 166       while (('a' <= *p && *p <= 'z')
 167              || ('A' <= *p && *p <= 'Z')
 168              || ('0' <= *p && *p <= '9')
 169              || *p == '+' || *p == '-')
 170         ++p;
 171       len = p - start;
 172       if (*p++ != '>' || len < 3)
 173         return false;
 174     }
 175
 176   const char *name = __tzstring_len (start, len);
 177   if (name == NULL)
 178     return false;
 179   tz_rules[whichrule].name = name;
 180
 181   *tzp = p;
 182   return true;
 183 }
 184
 185 /* Parses the time zone offset at *TZP, and writes it to
 186    tz_rules[WHICHRULE].offset.  Returns true if the parse was
 187    successful.  */
 188 static bool
 189 parse_offset (const char **tzp, int whichrule)
 190 {
 191   const char *tz = *tzp;
 192   if (whichrule == 0
 193       && (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz))))
 194     return false;
 195
 196   int sign;
 197   if (*tz == '-' || *tz == '+')
 198     sign = *tz++ == '-' ? 1 : -1;
 199   else
 200     sign = -1;
 201   *tzp = tz;
 202
 203   unsigned short int hh;
 204   unsigned short mm = 0;
 205   unsigned short ss = 0;
 206   int consumed = 0;
 207   if (sscanf (tz, "%hu%n:%hu%n:%hu%n",
 208               &hh, &consumed, &mm, &consumed, &ss, &consumed) > 0)
 209     tz_rules[whichrule].offset = sign * compute_offset (ss, mm, hh);
 210   else
 211     /* Nothing could be parsed. */
 212     if (whichrule == 0)
 213       {
 214         /* Standard time defaults to offset zero.  */
 215         tz_rules[0].offset = 0;
 216         return false;
 217       }
 218       else
 219         /* DST defaults to one hour later than standard time.  */
 220         tz_rules[1].offset = tz_rules[0].offset + (60 * 60);
 221   *tzp = tz + consumed;
 222   return true;
 223 }
 224
 225 /* Parses the standard <-> DST rules at *TZP.  Updates
 226    tz_rule[WHICHRULE].  On success, advances *TZP and returns true.
 227    Otherwise, returns false.  */
 228 static bool
 229 parse_rule (const char **tzp, int whichrule)
 230 {
 231   const char *tz = *tzp;
 232   tz_rule *tzr = &tz_rules[whichrule];
 233
 234   /* Ignore comma to support string following the incorrect
 235      specification in early POSIX.1 printings.  */
 236   tz += *tz == ',';
 237
 238   /* Get the date of the change.  */
 239   if (*tz == 'J' || isdigit (*tz))
 240     {
 241       char *end;
 242       tzr->type = *tz == 'J' ? J1 : J0;
 243       if (tzr->type == J1 && !isdigit (*++tz))
 244         return false;
 245       unsigned long int d = strtoul (tz, &end, 10);
 246       if (end == tz || d > 365)
 247         return false;
 248       if (tzr->type == J1 && d == 0)
 249         return false;
 250       tzr->d = d;
 251       tz = end;
 252     }
 253   else if (*tz == 'M')
 254     {
 255       tzr->type = M;
 256       int consumed;
 257       if (sscanf (tz, "M%hu.%hu.%hu%n",
 258                   &tzr->m, &tzr->n, &tzr->d, &consumed) != 3
 259           || tzr->m < 1 || tzr->m > 12
 260           || tzr->n < 1 || tzr->n > 5 || tzr->d > 6)
 261         return false;
 262       tz += consumed;
 263     }
 264   else if (*tz == '\0')
 265     {
 266       /* Daylight time rules in the U.S. are defined in the U.S. Code,
 267          Title 15, Chapter 6, Subchapter IX - Standard Time.  These
 268          dates were established by Congress in the Energy Policy Act
 269          of 2005 [Pub. L. no. 109-58, 119 Stat 594 (2005)].
 270          Below is the equivalent of "M3.2.0,M11.1.0" [/2 not needed
 271          since 2:00AM is the default].  */
 272       tzr->type = M;
 273       if (tzr == &tz_rules[0])
 274         {
 275           tzr->m = 3;
 276           tzr->n = 2;
 277           tzr->d = 0;
 278         }
 279       else
 280         {
 281           tzr->m = 11;
 282           tzr->n = 1;
 283           tzr->d = 0;
 284         }
 285     }
 286   else
 287     return false;
 288
 289   if (*tz != '\0' && *tz != '/' && *tz != ',')
 290     return false;
 291   else if (*tz == '/')
 292     {
 293       /* Get the time of day of the change.  */
 294       int negative;
 295       ++tz;
 296       if (*tz == '\0')
 297         return false;
 298       negative = *tz == '-';
 299       tz += negative;
 300       /* Default to 2:00 AM.  */
 301       unsigned short hh = 2;
 302       unsigned short mm = 0;
 303       unsigned short ss = 0;
 304       int consumed = 0;
 305       sscanf (tz, "%hu%n:%hu%n:%hu%n",
 306               &hh, &consumed, &mm, &consumed, &ss, &consumed);;
 307       tz += consumed;
 308       tzr->secs = (negative ? -1 : 1) * ((hh * 60 * 60) + (mm * 60) + ss);
 309     }
 310   else
 311     /* Default to 2:00 AM.  */
 312     tzr->secs = 2 * 60 * 60;
 313
 314   tzr->computed_for = -1;
 315   *tzp = tz;
 316   return true;
 317 }
 318
 319 /* Parse the POSIX TZ-style string.  */
 320 void
 321 __tzset_parse_tz (const char *tz)
 322 {
 323   /* Clear out old state and reset to unnamed UTC.  */
 324   memset (tz_rules, '\0', sizeof tz_rules);
 325   tz_rules[0].name = tz_rules[1].name = "";
 326
 327   /* Get the standard time zone abbreviations.  */
 328   if (parse_tzname (&tz, 0) && parse_offset (&tz, 0))
 329     {
 330       /* Get the DST time zone abbreviation (if any).  */
 331       if (*tz != '\0')
 332         {
 333           if (parse_tzname (&tz, 1))
 334             {
 335               parse_offset (&tz, 1);
 336               if (*tz == '\0' || (tz[0] == ',' && tz[1] == '\0'))
 337                 {
 338                   /* There is no rule.  See if there is a default rule
 339                      file.  */
 340                   __tzfile_default (tz_rules[0].name, tz_rules[1].name,
 341                                     tz_rules[0].offset, tz_rules[1].offset);
 342                   if (__use_tzfile)
 343                     {
 344                       free (old_tz);
 345                       old_tz = NULL;
 346                       return;
 347                     }
 348                 }
 349             }
 350           /* Figure out the standard <-> DST rules.  */
 351           if (parse_rule (&tz, 0))
 352             parse_rule (&tz, 1);
 353         }
 354       else
 355         {
 356           /* There is no DST.  */
 357           tz_rules[1].name = tz_rules[0].name;
 358           tz_rules[1].offset = tz_rules[0].offset;
 359         }
 360     }
 361
 362   update_vars ();
 363 }
 364
 365 /* Interpret the TZ envariable.  */
 366 static void
 367 tzset_internal (int always)
 368 {
 369   static int is_initialized;
 370   const char *tz;
 371
 372   if (is_initialized && !always)
 373     return;
 374   is_initialized = 1;
 375
 376   /* Examine the TZ environment variable.  */
 377   tz = getenv ("TZ");
 378   if (tz && *tz == '\0')
 379     /* User specified the empty string; use UTC explicitly.  */
 380     tz = "Universal";
 381
 382   /* A leading colon means "implementation defined syntax".
 383      We ignore the colon and always use the same algorithm:
 384      try a data file, and if none exists parse the 1003.1 syntax.  */
 385   if (tz && *tz == ':')
 386     ++tz;
 387
 388   /* Check whether the value changed since the last run.  */
 389   if (old_tz != NULL && tz != NULL && strcmp (tz, old_tz) == 0)
 390     /* No change, simply return.  */
 391     return;
 392
 393   if (tz == NULL)
 394     /* No user specification; use the site-wide default.  */
 395     tz = TZDEFAULT;
 396
 397   tz_rules[0].name = NULL;
 398   tz_rules[1].name = NULL;
 399
 400   /* Save the value of `tz'.  */
 401   free (old_tz);
 402   old_tz = tz ? __strdup (tz) : NULL;
 403
 404   /* Try to read a data file.  */
 405   __tzfile_read (tz, 0, NULL);
 406   if (__use_tzfile)
 407     return;
 408
 409   /* No data file found.  Default to UTC if nothing specified.  */
 410
 411   if (tz == NULL || *tz == '\0'
 412       || (TZDEFAULT != NULL && strcmp (tz, TZDEFAULT) == 0))
 413     {
 414       memset (tz_rules, '\0', sizeof tz_rules);
 415       tz_rules[0].name = tz_rules[1].name = "UTC";
 416       if (J0 != 0)
 417         tz_rules[0].type = tz_rules[1].type = J0;
 418       tz_rules[0].change = tz_rules[1].change = -1;
 419       update_vars ();
 420       return;
 421     }
 422
 423   __tzset_parse_tz (tz);
 424 }
 425 \f
 426 /* Figure out the exact time (as a __time64_t) in YEAR
 427    when the change described by RULE will occur and
 428    put it in RULE->change, saving YEAR in RULE->computed_for.  */
 429 static void
 430 compute_change (tz_rule *rule, int year)
 431 {
 432   __time64_t t;
 433
 434   if (year != -1 && rule->computed_for == year)
 435     /* Operations on times in 2 BC will be slower.  Oh well.  */
 436     return;
 437
 438   /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
 439   if (year > 1970)
 440     t = ((year - 1970) * 365
 441          + /* Compute the number of leapdays between 1970 and YEAR
 442               (exclusive).  There is a leapday every 4th year ...  */
 443          + ((year - 1) / 4 - 1970 / 4)
 444          /* ... except every 100th year ... */
 445          - ((year - 1) / 100 - 1970 / 100)
 446          /* ... but still every 400th year.  */
 447          + ((year - 1) / 400 - 1970 / 400)) * SECSPERDAY;
 448   else
 449     t = 0;
 450
 451   switch (rule->type)
 452     {
 453     case J1:
 454       /* Jn - Julian day, 1 == January 1, 60 == March 1 even in leap years.
 455          In non-leap years, or if the day number is 59 or less, just
 456          add SECSPERDAY times the day number-1 to the time of
 457          January 1, midnight, to get the day.  */
 458       t += (rule->d - 1) * SECSPERDAY;
 459       if (rule->d >= 60 && __isleap (year))
 460         t += SECSPERDAY;
 461       break;
 462
 463     case J0:
 464       /* n - Day of year.
 465          Just add SECSPERDAY times the day number to the time of Jan 1st.  */
 466       t += rule->d * SECSPERDAY;
 467       break;
 468
 469     case M:
 470       /* Mm.n.d - Nth "Dth day" of month M.  */
 471       {
 472         unsigned int i;
 473         int d, m1, yy0, yy1, yy2, dow;
 474         const unsigned short int *myday =
 475           &__mon_yday[__isleap (year)][rule->m];
 476
 477         /* First add SECSPERDAY for each day in months before M.  */
 478         t += myday[-1] * SECSPERDAY;
 479
 480         /* Use Zeller's Congruence to get day-of-week of first day of month. */
 481         m1 = (rule->m + 9) % 12 + 1;
 482         yy0 = (rule->m <= 2) ? (year - 1) : year;
 483         yy1 = yy0 / 100;
 484         yy2 = yy0 % 100;
 485         dow = ((26 * m1 - 2) / 10 + 1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
 486         if (dow < 0)
 487           dow += 7;
 488
 489         /* DOW is the day-of-week of the first day of the month.  Get the
 490            day-of-month (zero-origin) of the first DOW day of the month.  */
 491         d = rule->d - dow;
 492         if (d < 0)
 493           d += 7;
 494         for (i = 1; i < rule->n; ++i)
 495           {
 496             if (d + 7 >= (int) myday[0] - myday[-1])
 497               break;
 498             d += 7;
 499           }
 500
 501         /* D is the day-of-month (zero-origin) of the day we want.  */
 502         t += d * SECSPERDAY;
 503       }
 504       break;
 505     }
 506
 507   /* T is now the Epoch-relative time of 0:00:00 GMT on the day we want.
 508      Just add the time of day and local offset from GMT, and we're done.  */
 509
 510   rule->change = t - rule->offset + rule->secs;
 511   rule->computed_for = year;
 512 }
 513
 514
 515 /* Figure out the correct timezone for TM and set `__tzname',
 516    `__timezone', and `__daylight' accordingly.  */
 517 void
 518 __tz_compute (__time64_t timer, struct tm *tm, int use_localtime)
 519 {
 520   compute_change (&tz_rules[0], 1900 + tm->tm_year);
 521   compute_change (&tz_rules[1], 1900 + tm->tm_year);
 522
 523   if (use_localtime)
 524     {
 525       int isdst;
 526
 527       /* We have to distinguish between northern and southern
 528          hemisphere.  For the latter the daylight saving time
 529          ends in the next year.  */
 530       if (__builtin_expect (tz_rules[0].change
 531                             > tz_rules[1].change, 0))
 532         isdst = (timer < tz_rules[1].change
 533                  || timer >= tz_rules[0].change);
 534       else
 535         isdst = (timer >= tz_rules[0].change
 536                  && timer < tz_rules[1].change);
 537       tm->tm_isdst = isdst;
 538       tm->tm_zone = __tzname[isdst];
 539       tm->tm_gmtoff = tz_rules[isdst].offset;
 540     }
 541 }
 542 \f
 543 /* Reinterpret the TZ environment variable and set `tzname'.  */
 544 #undef tzset
 545
 546 void
 547 __tzset (void)
 548 {
 549   __libc_lock_lock (tzset_lock);
 550
 551   tzset_internal (1);
 552
 553   if (!__use_tzfile)
 554     {
 555       /* Set `tzname'.  */
 556       __tzname[0] = (char *) tz_rules[0].name;
 557       __tzname[1] = (char *) tz_rules[1].name;
 558     }
 559
 560   __libc_lock_unlock (tzset_lock);
 561 }
 562 weak_alias (__tzset, tzset)
 563 \f
 564 /* Return the `struct tm' representation of TIMER in the local timezone.
 565    Use local time if USE_LOCALTIME is nonzero, UTC otherwise.  */
 566 struct tm *
 567 __tz_convert (__time64_t timer, int use_localtime, struct tm *tp)
 568 {
 569   long int leap_correction;
 570   int leap_extra_secs;
 571
 572   __libc_lock_lock (tzset_lock);
 573
 574   /* Update internal database according to current TZ setting.
 575      POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
 576      This is a good idea since this allows at least a bit more parallelism.  */
 577   tzset_internal (tp == &_tmbuf && use_localtime);
 578
 579   if (__use_tzfile)
 580     __tzfile_compute (timer, use_localtime, &leap_correction,
 581                       &leap_extra_secs, tp);
 582   else
 583     {
 584       if (! __offtime (timer, 0, tp))
 585         tp = NULL;
 586       else
 587         __tz_compute (timer, tp, use_localtime);
 588       leap_correction = 0L;
 589       leap_extra_secs = 0;
 590     }
 591
 592   __libc_lock_unlock (tzset_lock);
 593
 594   if (tp)
 595     {
 596       if (! use_localtime)
 597         {
 598           tp->tm_isdst = 0;
 599           tp->tm_zone = "GMT";
 600           tp->tm_gmtoff = 0L;
 601         }
 602
 603       if (__offtime (timer, tp->tm_gmtoff - leap_correction, tp))
 604         tp->tm_sec += leap_extra_secs;
 605       else
 606         tp = NULL;
 607     }
 608
 609   return tp;
 610 }
 611
 612
 613 void
 614 __libc_tzset_freemem (void)
 615 {
 616   while (tzstring_list != NULL)
 617     {
 618       struct tzstring_l *old = tzstring_list;
 619
 620       tzstring_list = tzstring_list->next;
 621       free (old);
 622     }
 623   free (old_tz);
 624   old_tz = NULL;
 625 }