time/tzset.c

   1 /* Copyright (C) 1991-2015 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
  29 #define NOID
  30 #include <timezone/tzfile.h>
  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
  44 #define min(a, b)       ((a) < (b) ? (a) : (b))
  45 #define max(a, b)       ((a) > (b) ? (a) : (b))
  46 #define sign(x)         ((x) < 0 ? -1 : 1)
  47
  48
  49 /* This structure contains all the information about a
  50    timezone given in the POSIX standard TZ envariable.  */
  51 typedef struct
  52   {
  53     const char *name;
  54
  55     /* When to change.  */
  56     enum { J0, J1, M } type;    /* Interpretation of:  */
  57     unsigned short int m, n, d; /* Month, week, day.  */
  58     int secs;                   /* Time of day.  */
  59
  60     long int offset;            /* Seconds east of GMT (west if < 0).  */
  61
  62     /* We cache the computed time of change for a
  63        given year so we don't have to recompute it.  */
  64     time_t change;      /* When to change to this zone.  */
  65     int computed_for;   /* Year above is computed for.  */
  66   } tz_rule;
  67
  68 /* tz_rules[0] is standard, tz_rules[1] is daylight.  */
  69 static tz_rule tz_rules[2];
  70
  71
  72 static void compute_change (tz_rule *rule, int year) __THROW internal_function;
  73 static void tzset_internal (int always, int explicit)
  74      __THROW internal_function;
  75 \f
  76 /* List of buffers containing time zone strings. */
  77 struct tzstring_l
  78 {
  79   struct tzstring_l *next;
  80   size_t len;  /* strlen(data) - doesn't count terminating NUL! */
  81   char data[0];
  82 };
  83
  84 static struct tzstring_l *tzstring_list;
  85
  86 /* Allocate a permanent home for the first LEN characters of S.  It
  87    will never be moved or deallocated, but may share space with other
  88    strings.  Don't modify the returned string. */
  89 static char *
  90 __tzstring_len (const char *s, size_t len)
  91 {
  92   char *p;
  93   struct tzstring_l *t, *u, *new;
  94
  95   /* Walk the list and look for a match.  If this string is the same
  96      as the end of an already-allocated string, it can share space. */
  97   for (u = t = tzstring_list; t; u = t, t = t->next)
  98     if (len <= t->len)
  99       {
 100         p = &t->data[t->len - len];
 101         if (memcmp (s, p, len) == 0)
 102           return p;
 103       }
 104
 105   /* Not found; allocate a new buffer. */
 106   new = malloc (sizeof (struct tzstring_l) + len + 1);
 107   if (!new)
 108     return NULL;
 109
 110   new->next = NULL;
 111   new->len = len;
 112   memcpy (new->data, s, len);
 113   new->data[len] = '\0';
 114
 115   if (u)
 116     u->next = new;
 117   else
 118     tzstring_list = new;
 119
 120   return new->data;
 121 }
 122
 123 /* Allocate a permanent home for S.  It will never be moved or
 124    deallocated, but may share space with other strings.  Don't modify
 125    the returned string. */
 126 char *
 127 __tzstring (const char *s)
 128 {
 129   return __tzstring_len (s, strlen (s));
 130 }
 131 \f
 132 /* Maximum length of a timezone name.  tzset_internal keeps this up to date
 133    (never decreasing it) when ! __use_tzfile.
 134    tzfile.c keeps it up to date when __use_tzfile.  */
 135 size_t __tzname_cur_max;
 136
 137 long int
 138 __tzname_max (void)
 139 {
 140   __libc_lock_lock (tzset_lock);
 141
 142   tzset_internal (0, 0);
 143
 144   __libc_lock_unlock (tzset_lock);
 145
 146   return __tzname_cur_max;
 147 }
 148 \f
 149 static char *old_tz;
 150
 151 static void
 152 internal_function
 153 update_vars (void)
 154 {
 155   __daylight = tz_rules[0].offset != tz_rules[1].offset;
 156   __timezone = -tz_rules[0].offset;
 157   __tzname[0] = (char *) tz_rules[0].name;
 158   __tzname[1] = (char *) tz_rules[1].name;
 159
 160   /* Keep __tzname_cur_max up to date.  */
 161   size_t len0 = strlen (__tzname[0]);
 162   size_t len1 = strlen (__tzname[1]);
 163   if (len0 > __tzname_cur_max)
 164     __tzname_cur_max = len0;
 165   if (len1 > __tzname_cur_max)
 166     __tzname_cur_max = len1;
 167 }
 168
 169
 170 static unsigned int
 171 __attribute_noinline__
 172 compute_offset (unsigned int ss, unsigned int mm, unsigned int hh)
 173 {
 174   return min (ss, 59) + min (mm, 59) * 60 + min (hh, 24) * 60 * 60;
 175 }
 176
 177 /* Parses the time zone name at *TZP, and writes a pointer to an
 178    interned string to tz_rules[WHICHRULE].name.  On success, advances
 179    *TZP, and returns true.  Returns false otherwise.  */
 180 static bool
 181 parse_tzname (const char **tzp, int whichrule)
 182 {
 183   const char *start = *tzp;
 184   const char *p = start;
 185   while (('a' <= *p && *p <= 'z')
 186          || ('A' <= *p && *p <= 'Z'))
 187       ++p;
 188   size_t len = p - start;
 189   if (len < 3)
 190     {
 191       p = *tzp;
 192       if (__glibc_unlikely (*p++ != '<'))
 193         return false;
 194       start = p;
 195       while (('a' <= *p && *p <= 'z')
 196              || ('A' <= *p && *p <= 'Z')
 197              || ('0' <= *p && *p <= '9')
 198              || *p == '+' || *p == '-')
 199         ++p;
 200       len = p - start;
 201       if (*p++ != '>' || len < 3)
 202         return false;
 203     }
 204
 205   const char *name = __tzstring_len (start, len);
 206   if (name == NULL)
 207     return false;
 208   tz_rules[whichrule].name = name;
 209
 210   *tzp = p;
 211   return true;
 212 }
 213
 214 /* Parses the time zone offset at *TZP, and writes it to
 215    tz_rules[WHICHRULE].offset.  Returns true if the parse was
 216    successful.  */
 217 static bool
 218 parse_offset (const char **tzp, int whichrule)
 219 {
 220   const char *tz = *tzp;
 221   if (whichrule == 0
 222       && (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz))))
 223     return false;
 224
 225   long sign;
 226   if (*tz == '-' || *tz == '+')
 227     sign = *tz++ == '-' ? 1L : -1L;
 228   else
 229     sign = -1L;
 230   *tzp = tz;
 231
 232   unsigned short int hh;
 233   unsigned short mm = 0;
 234   unsigned short ss = 0;
 235   int consumed = 0;
 236   if (sscanf (tz, "%hu%n:%hu%n:%hu%n",
 237               &hh, &consumed, &mm, &consumed, &ss, &consumed) > 0)
 238     tz_rules[whichrule].offset = sign * compute_offset (ss, mm, hh);
 239   else
 240     /* Nothing could be parsed. */
 241     if (whichrule == 0)
 242       {
 243         /* Standard time defaults to offset zero.  */
 244         tz_rules[0].offset = 0;
 245         return false;
 246       }
 247       else
 248         /* DST defaults to one hour later than standard time.  */
 249         tz_rules[1].offset = tz_rules[0].offset + (60 * 60);
 250   *tzp = tz + consumed;
 251   return true;
 252 }
 253
 254 /* Parses the standard <-> DST rules at *TZP.  Updates
 255    tz_rule[WHICHRULE].  On success, advances *TZP and returns true.
 256    Otherwise, returns false.  */
 257 static bool
 258 parse_rule (const char **tzp, int whichrule)
 259 {
 260   const char *tz = *tzp;
 261   tz_rule *tzr = &tz_rules[whichrule];
 262
 263   /* Ignore comma to support string following the incorrect
 264      specification in early POSIX.1 printings.  */
 265   tz += *tz == ',';
 266
 267   /* Get the date of the change.  */
 268   if (*tz == 'J' || isdigit (*tz))
 269     {
 270       char *end;
 271       tzr->type = *tz == 'J' ? J1 : J0;
 272       if (tzr->type == J1 && !isdigit (*++tz))
 273         return false;
 274       unsigned long int d = strtoul (tz, &end, 10);
 275       if (end == tz || d > 365)
 276         return false;
 277       if (tzr->type == J1 && d == 0)
 278         return false;
 279       tzr->d = d;
 280       tz = end;
 281     }
 282   else if (*tz == 'M')
 283     {
 284       tzr->type = M;
 285       int consumed;
 286       if (sscanf (tz, "M%hu.%hu.%hu%n",
 287                   &tzr->m, &tzr->n, &tzr->d, &consumed) != 3
 288           || tzr->m < 1 || tzr->m > 12
 289           || tzr->n < 1 || tzr->n > 5 || tzr->d > 6)
 290         return false;
 291       tz += consumed;
 292     }
 293   else if (*tz == '\0')
 294     {
 295       /* Daylight time rules in the U.S. are defined in the U.S. Code,
 296          Title 15, Chapter 6, Subchapter IX - Standard Time.  These
 297          dates were established by Congress in the Energy Policy Act
 298          of 2005 [Pub. L. no. 109-58, 119 Stat 594 (2005)].
 299          Below is the equivalent of "M3.2.0,M11.1.0" [/2 not needed
 300          since 2:00AM is the default].  */
 301       tzr->type = M;
 302       if (tzr == &tz_rules[0])
 303         {
 304           tzr->m = 3;
 305           tzr->n = 2;
 306           tzr->d = 0;
 307         }
 308       else
 309         {
 310           tzr->m = 11;
 311           tzr->n = 1;
 312           tzr->d = 0;
 313         }
 314     }
 315   else
 316     return false;
 317
 318   if (*tz != '\0' && *tz != '/' && *tz != ',')
 319     return false;
 320   else if (*tz == '/')
 321     {
 322       /* Get the time of day of the change.  */
 323       int negative;
 324       ++tz;
 325       if (*tz == '\0')
 326         return false;
 327       negative = *tz == '-';
 328       tz += negative;
 329       /* Default to 2:00 AM.  */
 330       unsigned short hh = 2;
 331       unsigned short mm = 0;
 332       unsigned short ss = 0;
 333       int consumed = 0;
 334       sscanf (tz, "%hu%n:%hu%n:%hu%n",
 335               &hh, &consumed, &mm, &consumed, &ss, &consumed);;
 336       tz += consumed;
 337       tzr->secs = (negative ? -1 : 1) * ((hh * 60 * 60) + (mm * 60) + ss);
 338     }
 339   else
 340     /* Default to 2:00 AM.  */
 341     tzr->secs = 2 * 60 * 60;
 342
 343   tzr->computed_for = -1;
 344   *tzp = tz;
 345   return true;
 346 }
 347
 348 /* Parse the POSIX TZ-style string.  */
 349 void
 350 __tzset_parse_tz (const char *tz)
 351 {
 352   /* Clear out old state and reset to unnamed UTC.  */
 353   memset (tz_rules, '\0', sizeof tz_rules);
 354   tz_rules[0].name = tz_rules[1].name = "";
 355
 356   /* Get the standard timezone name.  */
 357   if (parse_tzname (&tz, 0) && parse_offset (&tz, 0))
 358     {
 359       /* Get the DST timezone name (if any).  */
 360       if (*tz != '\0')
 361         {
 362           if (parse_tzname (&tz, 1))
 363             {
 364               parse_offset (&tz, 1);
 365               if (*tz == '\0' || (tz[0] == ',' && tz[1] == '\0'))
 366                 {
 367                   /* There is no rule.  See if there is a default rule
 368                      file.  */
 369                   __tzfile_default (tz_rules[0].name, tz_rules[1].name,
 370                                     tz_rules[0].offset, tz_rules[1].offset);
 371                   if (__use_tzfile)
 372                     {
 373                       free (old_tz);
 374                       old_tz = NULL;
 375                       return;
 376                     }
 377                 }
 378             }
 379           /* Figure out the standard <-> DST rules.  */
 380           if (parse_rule (&tz, 0))
 381             parse_rule (&tz, 1);
 382         }
 383       else
 384         {
 385           /* There is no DST.  */
 386           tz_rules[1].name = tz_rules[0].name;
 387           tz_rules[1].offset = tz_rules[0].offset;
 388         }
 389     }
 390
 391   update_vars ();
 392 }
 393
 394 /* Interpret the TZ envariable.  */
 395 static void
 396 internal_function
 397 tzset_internal (always, explicit)
 398      int always;
 399      int explicit;
 400 {
 401   static int is_initialized;
 402   const char *tz;
 403
 404   if (is_initialized && !always)
 405     return;
 406   is_initialized = 1;
 407
 408   /* Examine the TZ environment variable.  */
 409   tz = getenv ("TZ");
 410   if (tz == NULL && !explicit)
 411     /* Use the site-wide default.  This is a file name which means we
 412        would not see changes to the file if we compare only the file
 413        name for change.  We want to notice file changes if tzset() has
 414        been called explicitly.  Leave TZ as NULL in this case.  */
 415     tz = TZDEFAULT;
 416   if (tz && *tz == '\0')
 417     /* User specified the empty string; use UTC explicitly.  */
 418     tz = "Universal";
 419
 420   /* A leading colon means "implementation defined syntax".
 421      We ignore the colon and always use the same algorithm:
 422      try a data file, and if none exists parse the 1003.1 syntax.  */
 423   if (tz && *tz == ':')
 424     ++tz;
 425
 426   /* Check whether the value changed since the last run.  */
 427   if (old_tz != NULL && tz != NULL && strcmp (tz, old_tz) == 0)
 428     /* No change, simply return.  */
 429     return;
 430
 431   if (tz == NULL)
 432     /* No user specification; use the site-wide default.  */
 433     tz = TZDEFAULT;
 434
 435   tz_rules[0].name = NULL;
 436   tz_rules[1].name = NULL;
 437
 438   /* Save the value of `tz'.  */
 439   free (old_tz);
 440   old_tz = tz ? __strdup (tz) : NULL;
 441
 442   /* Try to read a data file.  */
 443   __tzfile_read (tz, 0, NULL);
 444   if (__use_tzfile)
 445     return;
 446
 447   /* No data file found.  Default to UTC if nothing specified.  */
 448
 449   if (tz == NULL || *tz == '\0'
 450       || (TZDEFAULT != NULL && strcmp (tz, TZDEFAULT) == 0))
 451     {
 452       memset (tz_rules, '\0', sizeof tz_rules);
 453       tz_rules[0].name = tz_rules[1].name = "UTC";
 454       if (J0 != 0)
 455         tz_rules[0].type = tz_rules[1].type = J0;
 456       tz_rules[0].change = tz_rules[1].change = (time_t) -1;
 457       update_vars ();
 458       return;
 459     }
 460
 461   __tzset_parse_tz (tz);
 462 }
 463 \f
 464 /* Figure out the exact time (as a time_t) in YEAR
 465    when the change described by RULE will occur and
 466    put it in RULE->change, saving YEAR in RULE->computed_for.  */
 467 static void
 468 internal_function
 469 compute_change (rule, year)
 470      tz_rule *rule;
 471      int year;
 472 {
 473   time_t t;
 474
 475   if (year != -1 && rule->computed_for == year)
 476     /* Operations on times in 2 BC will be slower.  Oh well.  */
 477     return;
 478
 479   /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
 480   if (year > 1970)
 481     t = ((year - 1970) * 365
 482          + /* Compute the number of leapdays between 1970 and YEAR
 483               (exclusive).  There is a leapday every 4th year ...  */
 484          + ((year - 1) / 4 - 1970 / 4)
 485          /* ... except every 100th year ... */
 486          - ((year - 1) / 100 - 1970 / 100)
 487          /* ... but still every 400th year.  */
 488          + ((year - 1) / 400 - 1970 / 400)) * SECSPERDAY;
 489   else
 490     t = 0;
 491
 492   switch (rule->type)
 493     {
 494     case J1:
 495       /* Jn - Julian day, 1 == January 1, 60 == March 1 even in leap years.
 496          In non-leap years, or if the day number is 59 or less, just
 497          add SECSPERDAY times the day number-1 to the time of
 498          January 1, midnight, to get the day.  */
 499       t += (rule->d - 1) * SECSPERDAY;
 500       if (rule->d >= 60 && __isleap (year))
 501         t += SECSPERDAY;
 502       break;
 503
 504     case J0:
 505       /* n - Day of year.
 506          Just add SECSPERDAY times the day number to the time of Jan 1st.  */
 507       t += rule->d * SECSPERDAY;
 508       break;
 509
 510     case M:
 511       /* Mm.n.d - Nth "Dth day" of month M.  */
 512       {
 513         unsigned int i;
 514         int d, m1, yy0, yy1, yy2, dow;
 515         const unsigned short int *myday =
 516           &__mon_yday[__isleap (year)][rule->m];
 517
 518         /* First add SECSPERDAY for each day in months before M.  */
 519         t += myday[-1] * SECSPERDAY;
 520
 521         /* Use Zeller's Congruence to get day-of-week of first day of month. */
 522         m1 = (rule->m + 9) % 12 + 1;
 523         yy0 = (rule->m <= 2) ? (year - 1) : year;
 524         yy1 = yy0 / 100;
 525         yy2 = yy0 % 100;
 526         dow = ((26 * m1 - 2) / 10 + 1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
 527         if (dow < 0)
 528           dow += 7;
 529
 530         /* DOW is the day-of-week of the first day of the month.  Get the
 531            day-of-month (zero-origin) of the first DOW day of the month.  */
 532         d = rule->d - dow;
 533         if (d < 0)
 534           d += 7;
 535         for (i = 1; i < rule->n; ++i)
 536           {
 537             if (d + 7 >= (int) myday[0] - myday[-1])
 538               break;
 539             d += 7;
 540           }
 541
 542         /* D is the day-of-month (zero-origin) of the day we want.  */
 543         t += d * SECSPERDAY;
 544       }
 545       break;
 546     }
 547
 548   /* T is now the Epoch-relative time of 0:00:00 GMT on the day we want.
 549      Just add the time of day and local offset from GMT, and we're done.  */
 550
 551   rule->change = t - rule->offset + rule->secs;
 552   rule->computed_for = year;
 553 }
 554
 555
 556 /* Figure out the correct timezone for TM and set `__tzname',
 557    `__timezone', and `__daylight' accordingly.  */
 558 void
 559 internal_function
 560 __tz_compute (timer, tm, use_localtime)
 561      time_t timer;
 562      struct tm *tm;
 563      int use_localtime;
 564 {
 565   compute_change (&tz_rules[0], 1900 + tm->tm_year);
 566   compute_change (&tz_rules[1], 1900 + tm->tm_year);
 567
 568   if (use_localtime)
 569     {
 570       int isdst;
 571
 572       /* We have to distinguish between northern and southern
 573          hemisphere.  For the latter the daylight saving time
 574          ends in the next year.  */
 575       if (__builtin_expect (tz_rules[0].change
 576                             > tz_rules[1].change, 0))
 577         isdst = (timer < tz_rules[1].change
 578                  || timer >= tz_rules[0].change);
 579       else
 580         isdst = (timer >= tz_rules[0].change
 581                  && timer < tz_rules[1].change);
 582       tm->tm_isdst = isdst;
 583       tm->tm_zone = __tzname[isdst];
 584       tm->tm_gmtoff = tz_rules[isdst].offset;
 585     }
 586 }
 587 \f
 588 /* Reinterpret the TZ environment variable and set `tzname'.  */
 589 #undef tzset
 590
 591 void
 592 __tzset (void)
 593 {
 594   __libc_lock_lock (tzset_lock);
 595
 596   tzset_internal (1, 1);
 597
 598   if (!__use_tzfile)
 599     {
 600       /* Set `tzname'.  */
 601       __tzname[0] = (char *) tz_rules[0].name;
 602       __tzname[1] = (char *) tz_rules[1].name;
 603     }
 604
 605   __libc_lock_unlock (tzset_lock);
 606 }
 607 weak_alias (__tzset, tzset)
 608 \f
 609 /* Return the `struct tm' representation of *TIMER in the local timezone.
 610    Use local time if USE_LOCALTIME is nonzero, UTC otherwise.  */
 611 struct tm *
 612 __tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
 613 {
 614   long int leap_correction;
 615   int leap_extra_secs;
 616
 617   if (timer == NULL)
 618     {
 619       __set_errno (EINVAL);
 620       return NULL;
 621     }
 622
 623   __libc_lock_lock (tzset_lock);
 624
 625   /* Update internal database according to current TZ setting.
 626      POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
 627      This is a good idea since this allows at least a bit more parallelism.  */
 628   tzset_internal (tp == &_tmbuf && use_localtime, 1);
 629
 630   if (__use_tzfile)
 631     __tzfile_compute (*timer, use_localtime, &leap_correction,
 632                       &leap_extra_secs, tp);
 633   else
 634     {
 635       if (! __offtime (timer, 0, tp))
 636         tp = NULL;
 637       else
 638         __tz_compute (*timer, tp, use_localtime);
 639       leap_correction = 0L;
 640       leap_extra_secs = 0;
 641     }
 642
 643   __libc_lock_unlock (tzset_lock);
 644
 645   if (tp)
 646     {
 647       if (! use_localtime)
 648         {
 649           tp->tm_isdst = 0;
 650           tp->tm_zone = "GMT";
 651           tp->tm_gmtoff = 0L;
 652         }
 653
 654       if (__offtime (timer, tp->tm_gmtoff - leap_correction, tp))
 655         tp->tm_sec += leap_extra_secs;
 656       else
 657         tp = NULL;
 658     }
 659
 660   return tp;
 661 }
 662
 663
 664 libc_freeres_fn (free_mem)
 665 {
 666   while (tzstring_list != NULL)
 667     {
 668       struct tzstring_l *old = tzstring_list;
 669
 670       tzstring_list = tzstring_list->next;
 671       free (old);
 672     }
 673   free (old_tz);
 674   old_tz = NULL;
 675 }