time/tzset.c

   1 /* Copyright (C) 1991-2017 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    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <ctype.h>
  19 #include <errno.h>
  20 #include <libc-lock.h>
  21 #include <stdbool.h>
  22 #include <stddef.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <time.h>
  27
  28 #include <timezone/tzfile.h>
  29
  30 #define SECSPERDAY 86400
  31
  32 char *__tzname[2] = { (char *) "GMT", (char *) "GMT" };
  33 int __daylight = 0;
  34 long int __timezone = 0L;
  35
  36 weak_alias (__tzname, tzname)
  37 weak_alias (__daylight, daylight)
  38 weak_alias (__timezone, timezone)
  39
  40 /* This locks all the state variables in tzfile.c and this file.  */
  41 __libc_lock_define_initialized (static, tzset_lock)
  42
  43 /* This structure contains all the information about a
  44    timezone given in the POSIX standard TZ envariable.  */
  45 typedef struct
  46   {
  47     const char *name;
  48
  49     /* When to change.  */
  50     enum { J0, J1, M } type;    /* Interpretation of:  */
  51     unsigned short int m, n, d; /* Month, week, day.  */
  52     int secs;                   /* Time of day.  */
  53
  54     long int offset;            /* Seconds east of GMT (west if < 0).  */
  55
  56     /* We cache the computed time of change for a
  57        given year so we don't have to recompute it.  */
  58     time_t change;      /* When to change to this zone.  */
  59     int computed_for;   /* Year above is computed for.  */
  60   } tz_rule;
  61
  62 /* tz_rules[0] is standard, tz_rules[1] is daylight.  */
  63 static tz_rule tz_rules[2];
  64
  65
  66 static void compute_change (tz_rule *rule, int year) __THROW internal_function;
  67 static void tzset_internal (int always);
  68 \f
  69 /* List of buffers containing time zone strings. */
  70 struct tzstring_l
  71 {
  72   struct tzstring_l *next;
  73   size_t len;  /* strlen(data) - doesn't count terminating NUL! */
  74   char data[0];
  75 };
  76
  77 static struct tzstring_l *tzstring_list;
  78
  79 /* Allocate a permanent home for the first LEN characters of S.  It
  80    will never be moved or deallocated, but may share space with other
  81    strings.  Don't modify the returned string. */
  82 static char *
  83 __tzstring_len (const char *s, size_t len)
  84 {
  85   char *p;
  86   struct tzstring_l *t, *u, *new;
  87
  88   /* Walk the list and look for a match.  If this string is the same
  89      as the end of an already-allocated string, it can share space. */
  90   for (u = t = tzstring_list; t; u = t, t = t->next)
  91     if (len <= t->len)
  92       {
  93         p = &t->data[t->len - len];
  94         if (memcmp (s, p, len) == 0)
  95           return p;
  96       }
  97
  98   /* Not found; allocate a new buffer. */
  99   new = malloc (sizeof (struct tzstring_l) + len + 1);
 100   if (!new)
 101     return NULL;
 102
 103   new->next = NULL;
 104   new->len = len;
 105   memcpy (new->data, s, len);
 106   new->data[len] = '\0';
 107
 108   if (u)
 109     u->next = new;
 110   else
 111     tzstring_list = new;
 112
 113   return new->data;
 114 }
 115
 116 /* Allocate a permanent home for S.  It will never be moved or
 117    deallocated, but may share space with other strings.  Don't modify
 118    the returned string. */
 119 char *
 120 __tzstring (const char *s)
 121 {
 122   return __tzstring_len (s, strlen (s));
 123 }
 124
 125 static char *old_tz;
 126
 127 static void
 128 internal_function
 129 update_vars (void)
 130 {
 131   __daylight = tz_rules[0].offset != tz_rules[1].offset;
 132   __timezone = -tz_rules[0].offset;
 133   __tzname[0] = (char *) tz_rules[0].name;
 134   __tzname[1] = (char *) tz_rules[1].name;
 135 }
 136
 137
 138 static unsigned int
 139 compute_offset (unsigned int ss, unsigned int mm, unsigned int hh)
 140 {
 141   if (ss > 59)
 142     ss = 59;
 143   if (mm > 59)
 144     mm = 59;
 145   if (hh > 24)
 146     hh = 24;
 147   return ss + mm * 60 + hh * 60 * 60;
 148 }
 149
 150 /* Parses the time zone name at *TZP, and writes a pointer to an
 151    interned string to tz_rules[WHICHRULE].name.  On success, advances
 152    *TZP, and returns true.  Returns false otherwise.  */
 153 static bool
 154 parse_tzname (const char **tzp, int whichrule)
 155 {
 156   const char *start = *tzp;
 157   const char *p = start;
 158   while (('a' <= *p && *p <= 'z')
 159          || ('A' <= *p && *p <= 'Z'))
 160       ++p;
 161   size_t len = p - start;
 162   if (len < 3)
 163     {
 164       p = *tzp;
 165       if (__glibc_unlikely (*p++ != '<'))
 166         return false;
 167       start = p;
 168       while (('a' <= *p && *p <= 'z')
 169              || ('A' <= *p && *p <= 'Z')
 170              || ('0' <= *p && *p <= '9')
 171              || *p == '+' || *p == '-')
 172         ++p;
 173       len = p - start;
 174       if (*p++ != '>' || len < 3)
 175         return false;
 176     }
 177
 178   const char *name = __tzstring_len (start, len);
 179   if (name == NULL)
 180     return false;
 181   tz_rules[whichrule].name = name;
 182
 183   *tzp = p;
 184   return true;
 185 }
 186
 187 /* Parses the time zone offset at *TZP, and writes it to
 188    tz_rules[WHICHRULE].offset.  Returns true if the parse was
 189    successful.  */
 190 static bool
 191 parse_offset (const char **tzp, int whichrule)
 192 {
 193   const char *tz = *tzp;
 194   if (whichrule == 0
 195       && (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz))))
 196     return false;
 197
 198   long sign;
 199   if (*tz == '-' || *tz == '+')
 200     sign = *tz++ == '-' ? 1L : -1L;
 201   else
 202     sign = -1L;
 203   *tzp = tz;
 204
 205   unsigned short int hh;
 206   unsigned short mm = 0;
 207   unsigned short ss = 0;
 208   int consumed = 0;
 209   if (sscanf (tz, "%hu%n:%hu%n:%hu%n",
 210               &hh, &consumed, &mm, &consumed, &ss, &consumed) > 0)
 211     tz_rules[whichrule].offset = sign * compute_offset (ss, mm, hh);
 212   else
 213     /* Nothing could be parsed. */
 214     if (whichrule == 0)
 215       {
 216         /* Standard time defaults to offset zero.  */
 217         tz_rules[0].offset = 0;
 218         return false;
 219       }
 220       else
 221         /* DST defaults to one hour later than standard time.  */
 222         tz_rules[1].offset = tz_rules[0].offset + (60 * 60);
 223   *tzp = tz + consumed;
 224   return true;
 225 }
 226
 227 /* Parses the standard <-> DST rules at *TZP.  Updates
 228    tz_rule[WHICHRULE].  On success, advances *TZP and returns true.
 229    Otherwise, returns false.  */
 230 static bool
 231 parse_rule (const char **tzp, int whichrule)
 232 {
 233   const char *tz = *tzp;
 234   tz_rule *tzr = &tz_rules[whichrule];
 235
 236   /* Ignore comma to support string following the incorrect
 237      specification in early POSIX.1 printings.  */
 238   tz += *tz == ',';
 239
 240   /* Get the date of the change.  */
 241   if (*tz == 'J' || isdigit (*tz))
 242     {
 243       char *end;
 244       tzr->type = *tz == 'J' ? J1 : J0;
 245       if (tzr->type == J1 && !isdigit (*++tz))
 246         return false;
 247       unsigned long int d = strtoul (tz, &end, 10);
 248       if (end == tz || d > 365)
 249         return false;
 250       if (tzr->type == J1 && d == 0)
 251         return false;
 252       tzr->d = d;
 253       tz = end;
 254     }
 255   else if (*tz == 'M')
 256     {
 257       tzr->type = M;
 258       int consumed;
 259       if (sscanf (tz, "M%hu.%hu.%hu%n",
 260                   &tzr->m, &tzr->n, &tzr->d, &consumed) != 3
 261           || tzr->m < 1 || tzr->m > 12
 262           || tzr->n < 1 || tzr->n > 5 || tzr->d > 6)
 263         return false;
 264       tz += consumed;
 265     }
 266   else if (*tz == '\0')
 267     {
 268       /* Daylight time rules in the U.S. are defined in the U.S. Code,
 269          Title 15, Chapter 6, Subchapter IX - Standard Time.  These
 270          dates were established by Congress in the Energy Policy Act
 271          of 2005 [Pub. L. no. 109-58, 119 Stat 594 (2005)].
 272          Below is the equivalent of "M3.2.0,M11.1.0" [/2 not needed
 273          since 2:00AM is the default].  */
 274       tzr->type = M;
 275       if (tzr == &tz_rules[0])
 276         {
 277           tzr->m = 3;
 278           tzr->n = 2;
 279           tzr->d = 0;
 280         }
 281       else
 282         {
 283           tzr->m = 11;
 284           tzr->n = 1;
 285           tzr->d = 0;
 286         }
 287     }
 288   else
 289     return false;
 290
 291   if (*tz != '\0' && *tz != '/' && *tz != ',')
 292     return false;
 293   else if (*tz == '/')
 294     {
 295       /* Get the time of day of the change.  */
 296       int negative;
 297       ++tz;
 298       if (*tz == '\0')
 299         return false;
 300       negative = *tz == '-';
 301       tz += negative;
 302       /* Default to 2:00 AM.  */
 303       unsigned short hh = 2;
 304       unsigned short mm = 0;
 305       unsigned short ss = 0;
 306       int consumed = 0;
 307       sscanf (tz, "%hu%n:%hu%n:%hu%n",
 308               &hh, &consumed, &mm, &consumed, &ss, &consumed);;
 309       tz += consumed;
 310       tzr->secs = (negative ? -1 : 1) * ((hh * 60 * 60) + (mm * 60) + ss);
 311     }
 312   else
 313     /* Default to 2:00 AM.  */
 314     tzr->secs = 2 * 60 * 60;
 315
 316   tzr->computed_for = -1;
 317   *tzp = tz;
 318   return true;
 319 }
 320
 321 /* Parse the POSIX TZ-style string.  */
 322 void
 323 __tzset_parse_tz (const char *tz)
 324 {
 325   /* Clear out old state and reset to unnamed UTC.  */
 326   memset (tz_rules, '\0', sizeof tz_rules);
 327   tz_rules[0].name = tz_rules[1].name = "";
 328
 329   /* Get the standard timezone name.  */
 330   if (parse_tzname (&tz, 0) && parse_offset (&tz, 0))
 331     {
 332       /* Get the DST timezone name (if any).  */
 333       if (*tz != '\0')
 334         {
 335           if (parse_tzname (&tz, 1))
 336             {
 337               parse_offset (&tz, 1);
 338               if (*tz == '\0' || (tz[0] == ',' && tz[1] == '\0'))
 339                 {
 340                   /* There is no rule.  See if there is a default rule
 341                      file.  */
 342                   __tzfile_default (tz_rules[0].name, tz_rules[1].name,
 343                                     tz_rules[0].offset, tz_rules[1].offset);
 344                   if (__use_tzfile)
 345                     {
 346                       free (old_tz);
 347                       old_tz = NULL;
 348                       return;
 349                     }
 350                 }
 351             }
 352           /* Figure out the standard <-> DST rules.  */
 353           if (parse_rule (&tz, 0))
 354             parse_rule (&tz, 1);
 355         }
 356       else
 357         {
 358           /* There is no DST.  */
 359           tz_rules[1].name = tz_rules[0].name;
 360           tz_rules[1].offset = tz_rules[0].offset;
 361         }
 362     }
 363
 364   update_vars ();
 365 }
 366
 367 /* Interpret the TZ envariable.  */
 368 static void
 369 tzset_internal (int always)
 370 {
 371   static int is_initialized;
 372   const char *tz;
 373
 374   if (is_initialized && !always)
 375     return;
 376   is_initialized = 1;
 377
 378   /* Examine the TZ environment variable.  */
 379   tz = getenv ("TZ");
 380   if (tz && *tz == '\0')
 381     /* User specified the empty string; use UTC explicitly.  */
 382     tz = "Universal";
 383
 384   /* A leading colon means "implementation defined syntax".
 385      We ignore the colon and always use the same algorithm:
 386      try a data file, and if none exists parse the 1003.1 syntax.  */
 387   if (tz && *tz == ':')
 388     ++tz;
 389
 390   /* Check whether the value changed since the last run.  */
 391   if (old_tz != NULL && tz != NULL && strcmp (tz, old_tz) == 0)
 392     /* No change, simply return.  */
 393     return;
 394
 395   if (tz == NULL)
 396     /* No user specification; use the site-wide default.  */
 397     tz = TZDEFAULT;
 398
 399   tz_rules[0].name = NULL;
 400   tz_rules[1].name = NULL;
 401
 402   /* Save the value of `tz'.  */
 403   free (old_tz);
 404   old_tz = tz ? __strdup (tz) : NULL;
 405
 406   /* Try to read a data file.  */
 407   __tzfile_read (tz, 0, NULL);
 408   if (__use_tzfile)
 409     return;
 410
 411   /* No data file found.  Default to UTC if nothing specified.  */
 412
 413   if (tz == NULL || *tz == '\0'
 414       || (TZDEFAULT != NULL && strcmp (tz, TZDEFAULT) == 0))
 415     {
 416       memset (tz_rules, '\0', sizeof tz_rules);
 417       tz_rules[0].name = tz_rules[1].name = "UTC";
 418       if (J0 != 0)
 419         tz_rules[0].type = tz_rules[1].type = J0;
 420       tz_rules[0].change = tz_rules[1].change = (time_t) -1;
 421       update_vars ();
 422       return;
 423     }
 424
 425   __tzset_parse_tz (tz);
 426 }
 427 \f
 428 /* Figure out the exact time (as a time_t) in YEAR
 429    when the change described by RULE will occur and
 430    put it in RULE->change, saving YEAR in RULE->computed_for.  */
 431 static void
 432 internal_function
 433 compute_change (tz_rule *rule, int year)
 434 {
 435   time_t t;
 436
 437   if (year != -1 && rule->computed_for == year)
 438     /* Operations on times in 2 BC will be slower.  Oh well.  */
 439     return;
 440
 441   /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
 442   if (year > 1970)
 443     t = ((year - 1970) * 365
 444          + /* Compute the number of leapdays between 1970 and YEAR
 445               (exclusive).  There is a leapday every 4th year ...  */
 446          + ((year - 1) / 4 - 1970 / 4)
 447          /* ... except every 100th year ... */
 448          - ((year - 1) / 100 - 1970 / 100)
 449          /* ... but still every 400th year.  */
 450          + ((year - 1) / 400 - 1970 / 400)) * SECSPERDAY;
 451   else
 452     t = 0;
 453
 454   switch (rule->type)
 455     {
 456     case J1:
 457       /* Jn - Julian day, 1 == January 1, 60 == March 1 even in leap years.
 458          In non-leap years, or if the day number is 59 or less, just
 459          add SECSPERDAY times the day number-1 to the time of
 460          January 1, midnight, to get the day.  */
 461       t += (rule->d - 1) * SECSPERDAY;
 462       if (rule->d >= 60 && __isleap (year))
 463         t += SECSPERDAY;
 464       break;
 465
 466     case J0:
 467       /* n - Day of year.
 468          Just add SECSPERDAY times the day number to the time of Jan 1st.  */
 469       t += rule->d * SECSPERDAY;
 470       break;
 471
 472     case M:
 473       /* Mm.n.d - Nth "Dth day" of month M.  */
 474       {
 475         unsigned int i;
 476         int d, m1, yy0, yy1, yy2, dow;
 477         const unsigned short int *myday =
 478           &__mon_yday[__isleap (year)][rule->m];
 479
 480         /* First add SECSPERDAY for each day in months before M.  */
 481         t += myday[-1] * SECSPERDAY;
 482
 483         /* Use Zeller's Congruence to get day-of-week of first day of month. */
 484         m1 = (rule->m + 9) % 12 + 1;
 485         yy0 = (rule->m <= 2) ? (year - 1) : year;
 486         yy1 = yy0 / 100;
 487         yy2 = yy0 % 100;
 488         dow = ((26 * m1 - 2) / 10 + 1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
 489         if (dow < 0)
 490           dow += 7;
 491
 492         /* DOW is the day-of-week of the first day of the month.  Get the
 493            day-of-month (zero-origin) of the first DOW day of the month.  */
 494         d = rule->d - dow;
 495         if (d < 0)
 496           d += 7;
 497         for (i = 1; i < rule->n; ++i)
 498           {
 499             if (d + 7 >= (int) myday[0] - myday[-1])
 500               break;
 501             d += 7;
 502           }
 503
 504         /* D is the day-of-month (zero-origin) of the day we want.  */
 505         t += d * SECSPERDAY;
 506       }
 507       break;
 508     }
 509
 510   /* T is now the Epoch-relative time of 0:00:00 GMT on the day we want.
 511      Just add the time of day and local offset from GMT, and we're done.  */
 512
 513   rule->change = t - rule->offset + rule->secs;
 514   rule->computed_for = year;
 515 }
 516
 517
 518 /* Figure out the correct timezone for TM and set `__tzname',
 519    `__timezone', and `__daylight' accordingly.  */
 520 void
 521 internal_function
 522 __tz_compute (time_t timer, struct tm *tm, int use_localtime)
 523 {
 524   compute_change (&tz_rules[0], 1900 + tm->tm_year);
 525   compute_change (&tz_rules[1], 1900 + tm->tm_year);
 526
 527   if (use_localtime)
 528     {
 529       int isdst;
 530
 531       /* We have to distinguish between northern and southern
 532          hemisphere.  For the latter the daylight saving time
 533          ends in the next year.  */
 534       if (__builtin_expect (tz_rules[0].change
 535                             > tz_rules[1].change, 0))
 536         isdst = (timer < tz_rules[1].change
 537                  || timer >= tz_rules[0].change);
 538       else
 539         isdst = (timer >= tz_rules[0].change
 540                  && timer < tz_rules[1].change);
 541       tm->tm_isdst = isdst;
 542       tm->tm_zone = __tzname[isdst];
 543       tm->tm_gmtoff = tz_rules[isdst].offset;
 544     }
 545 }
 546 \f
 547 /* Reinterpret the TZ environment variable and set `tzname'.  */
 548 #undef tzset
 549
 550 void
 551 __tzset (void)
 552 {
 553   __libc_lock_lock (tzset_lock);
 554
 555   tzset_internal (1);
 556
 557   if (!__use_tzfile)
 558     {
 559       /* Set `tzname'.  */
 560       __tzname[0] = (char *) tz_rules[0].name;
 561       __tzname[1] = (char *) tz_rules[1].name;
 562     }
 563
 564   __libc_lock_unlock (tzset_lock);
 565 }
 566 weak_alias (__tzset, tzset)
 567 \f
 568 /* Return the `struct tm' representation of *TIMER in the local timezone.
 569    Use local time if USE_LOCALTIME is nonzero, UTC otherwise.  */
 570 struct tm *
 571 __tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
 572 {
 573   long int leap_correction;
 574   int leap_extra_secs;
 575
 576   if (timer == NULL)
 577     {
 578       __set_errno (EINVAL);
 579       return NULL;
 580     }
 581
 582   __libc_lock_lock (tzset_lock);
 583
 584   /* Update internal database according to current TZ setting.
 585      POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
 586      This is a good idea since this allows at least a bit more parallelism.  */
 587   tzset_internal (tp == &_tmbuf && use_localtime);
 588
 589   if (__use_tzfile)
 590     __tzfile_compute (*timer, use_localtime, &leap_correction,
 591                       &leap_extra_secs, tp);
 592   else
 593     {
 594       if (! __offtime (timer, 0, tp))
 595         tp = NULL;
 596       else
 597         __tz_compute (*timer, tp, use_localtime);
 598       leap_correction = 0L;
 599       leap_extra_secs = 0;
 600     }
 601
 602   __libc_lock_unlock (tzset_lock);
 603
 604   if (tp)
 605     {
 606       if (! use_localtime)
 607         {
 608           tp->tm_isdst = 0;
 609           tp->tm_zone = "GMT";
 610           tp->tm_gmtoff = 0L;
 611         }
 612
 613       if (__offtime (timer, tp->tm_gmtoff - leap_correction, tp))
 614         tp->tm_sec += leap_extra_secs;
 615       else
 616         tp = NULL;
 617     }
 618
 619   return tp;
 620 }
 621
 622
 623 libc_freeres_fn (free_mem)
 624 {
 625   while (tzstring_list != NULL)
 626     {
 627       struct tzstring_l *old = tzstring_list;
 628
 629       tzstring_list = tzstring_list->next;
 630       free (old);
 631     }
 632   free (old_tz);
 633   old_tz = NULL;
 634 }