time/tzset.c

   1 /* Copyright (C) 1991-2018 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;
  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 update_vars (void)
 129 {
 130   __daylight = tz_rules[0].offset != tz_rules[1].offset;
 131   __timezone = -tz_rules[0].offset;
 132   __tzname[0] = (char *) tz_rules[0].name;
 133   __tzname[1] = (char *) tz_rules[1].name;
 134 }
 135
 136
 137 static unsigned int
 138 compute_offset (unsigned int ss, unsigned int mm, unsigned int hh)
 139 {
 140   if (ss > 59)
 141     ss = 59;
 142   if (mm > 59)
 143     mm = 59;
 144   if (hh > 24)
 145     hh = 24;
 146   return ss + mm * 60 + hh * 60 * 60;
 147 }
 148
 149 /* Parses the time zone name at *TZP, and writes a pointer to an
 150    interned string to tz_rules[WHICHRULE].name.  On success, advances
 151    *TZP, and returns true.  Returns false otherwise.  */
 152 static bool
 153 parse_tzname (const char **tzp, int whichrule)
 154 {
 155   const char *start = *tzp;
 156   const char *p = start;
 157   while (('a' <= *p && *p <= 'z')
 158          || ('A' <= *p && *p <= 'Z'))
 159       ++p;
 160   size_t len = p - start;
 161   if (len < 3)
 162     {
 163       p = *tzp;
 164       if (__glibc_unlikely (*p++ != '<'))
 165         return false;
 166       start = p;
 167       while (('a' <= *p && *p <= 'z')
 168              || ('A' <= *p && *p <= 'Z')
 169              || ('0' <= *p && *p <= '9')
 170              || *p == '+' || *p == '-')
 171         ++p;
 172       len = p - start;
 173       if (*p++ != '>' || len < 3)
 174         return false;
 175     }
 176
 177   const char *name = __tzstring_len (start, len);
 178   if (name == NULL)
 179     return false;
 180   tz_rules[whichrule].name = name;
 181
 182   *tzp = p;
 183   return true;
 184 }
 185
 186 /* Parses the time zone offset at *TZP, and writes it to
 187    tz_rules[WHICHRULE].offset.  Returns true if the parse was
 188    successful.  */
 189 static bool
 190 parse_offset (const char **tzp, int whichrule)
 191 {
 192   const char *tz = *tzp;
 193   if (whichrule == 0
 194       && (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz))))
 195     return false;
 196
 197   long sign;
 198   if (*tz == '-' || *tz == '+')
 199     sign = *tz++ == '-' ? 1L : -1L;
 200   else
 201     sign = -1L;
 202   *tzp = tz;
 203
 204   unsigned short int hh;
 205   unsigned short mm = 0;
 206   unsigned short ss = 0;
 207   int consumed = 0;
 208   if (sscanf (tz, "%hu%n:%hu%n:%hu%n",
 209               &hh, &consumed, &mm, &consumed, &ss, &consumed) > 0)
 210     tz_rules[whichrule].offset = sign * compute_offset (ss, mm, hh);
 211   else
 212     /* Nothing could be parsed. */
 213     if (whichrule == 0)
 214       {
 215         /* Standard time defaults to offset zero.  */
 216         tz_rules[0].offset = 0;
 217         return false;
 218       }
 219       else
 220         /* DST defaults to one hour later than standard time.  */
 221         tz_rules[1].offset = tz_rules[0].offset + (60 * 60);
 222   *tzp = tz + consumed;
 223   return true;
 224 }
 225
 226 /* Parses the standard <-> DST rules at *TZP.  Updates
 227    tz_rule[WHICHRULE].  On success, advances *TZP and returns true.
 228    Otherwise, returns false.  */
 229 static bool
 230 parse_rule (const char **tzp, int whichrule)
 231 {
 232   const char *tz = *tzp;
 233   tz_rule *tzr = &tz_rules[whichrule];
 234
 235   /* Ignore comma to support string following the incorrect
 236      specification in early POSIX.1 printings.  */
 237   tz += *tz == ',';
 238
 239   /* Get the date of the change.  */
 240   if (*tz == 'J' || isdigit (*tz))
 241     {
 242       char *end;
 243       tzr->type = *tz == 'J' ? J1 : J0;
 244       if (tzr->type == J1 && !isdigit (*++tz))
 245         return false;
 246       unsigned long int d = strtoul (tz, &end, 10);
 247       if (end == tz || d > 365)
 248         return false;
 249       if (tzr->type == J1 && d == 0)
 250         return false;
 251       tzr->d = d;
 252       tz = end;
 253     }
 254   else if (*tz == 'M')
 255     {
 256       tzr->type = M;
 257       int consumed;
 258       if (sscanf (tz, "M%hu.%hu.%hu%n",
 259                   &tzr->m, &tzr->n, &tzr->d, &consumed) != 3
 260           || tzr->m < 1 || tzr->m > 12
 261           || tzr->n < 1 || tzr->n > 5 || tzr->d > 6)
 262         return false;
 263       tz += consumed;
 264     }
 265   else if (*tz == '\0')
 266     {
 267       /* Daylight time rules in the U.S. are defined in the U.S. Code,
 268          Title 15, Chapter 6, Subchapter IX - Standard Time.  These
 269          dates were established by Congress in the Energy Policy Act
 270          of 2005 [Pub. L. no. 109-58, 119 Stat 594 (2005)].
 271          Below is the equivalent of "M3.2.0,M11.1.0" [/2 not needed
 272          since 2:00AM is the default].  */
 273       tzr->type = M;
 274       if (tzr == &tz_rules[0])
 275         {
 276           tzr->m = 3;
 277           tzr->n = 2;
 278           tzr->d = 0;
 279         }
 280       else
 281         {
 282           tzr->m = 11;
 283           tzr->n = 1;
 284           tzr->d = 0;
 285         }
 286     }
 287   else
 288     return false;
 289
 290   if (*tz != '\0' && *tz != '/' && *tz != ',')
 291     return false;
 292   else if (*tz == '/')
 293     {
 294       /* Get the time of day of the change.  */
 295       int negative;
 296       ++tz;
 297       if (*tz == '\0')
 298         return false;
 299       negative = *tz == '-';
 300       tz += negative;
 301       /* Default to 2:00 AM.  */
 302       unsigned short hh = 2;
 303       unsigned short mm = 0;
 304       unsigned short ss = 0;
 305       int consumed = 0;
 306       sscanf (tz, "%hu%n:%hu%n:%hu%n",
 307               &hh, &consumed, &mm, &consumed, &ss, &consumed);;
 308       tz += consumed;
 309       tzr->secs = (negative ? -1 : 1) * ((hh * 60 * 60) + (mm * 60) + ss);
 310     }
 311   else
 312     /* Default to 2:00 AM.  */
 313     tzr->secs = 2 * 60 * 60;
 314
 315   tzr->computed_for = -1;
 316   *tzp = tz;
 317   return true;
 318 }
 319
 320 /* Parse the POSIX TZ-style string.  */
 321 void
 322 __tzset_parse_tz (const char *tz)
 323 {
 324   /* Clear out old state and reset to unnamed UTC.  */
 325   memset (tz_rules, '\0', sizeof tz_rules);
 326   tz_rules[0].name = tz_rules[1].name = "";
 327
 328   /* Get the standard timezone name.  */
 329   if (parse_tzname (&tz, 0) && parse_offset (&tz, 0))
 330     {
 331       /* Get the DST timezone name (if any).  */
 332       if (*tz != '\0')
 333         {
 334           if (parse_tzname (&tz, 1))
 335             {
 336               parse_offset (&tz, 1);
 337               if (*tz == '\0' || (tz[0] == ',' && tz[1] == '\0'))
 338                 {
 339                   /* There is no rule.  See if there is a default rule
 340                      file.  */
 341                   __tzfile_default (tz_rules[0].name, tz_rules[1].name,
 342                                     tz_rules[0].offset, tz_rules[1].offset);
 343                   if (__use_tzfile)
 344                     {
 345                       free (old_tz);
 346                       old_tz = NULL;
 347                       return;
 348                     }
 349                 }
 350             }
 351           /* Figure out the standard <-> DST rules.  */
 352           if (parse_rule (&tz, 0))
 353             parse_rule (&tz, 1);
 354         }
 355       else
 356         {
 357           /* There is no DST.  */
 358           tz_rules[1].name = tz_rules[0].name;
 359           tz_rules[1].offset = tz_rules[0].offset;
 360         }
 361     }
 362
 363   update_vars ();
 364 }
 365
 366 /* Interpret the TZ envariable.  */
 367 static void
 368 tzset_internal (int always)
 369 {
 370   static int is_initialized;
 371   const char *tz;
 372
 373   if (is_initialized && !always)
 374     return;
 375   is_initialized = 1;
 376
 377   /* Examine the TZ environment variable.  */
 378   tz = getenv ("TZ");
 379   if (tz && *tz == '\0')
 380     /* User specified the empty string; use UTC explicitly.  */
 381     tz = "Universal";
 382
 383   /* A leading colon means "implementation defined syntax".
 384      We ignore the colon and always use the same algorithm:
 385      try a data file, and if none exists parse the 1003.1 syntax.  */
 386   if (tz && *tz == ':')
 387     ++tz;
 388
 389   /* Check whether the value changed since the last run.  */
 390   if (old_tz != NULL && tz != NULL && strcmp (tz, old_tz) == 0)
 391     /* No change, simply return.  */
 392     return;
 393
 394   if (tz == NULL)
 395     /* No user specification; use the site-wide default.  */
 396     tz = TZDEFAULT;
 397
 398   tz_rules[0].name = NULL;
 399   tz_rules[1].name = NULL;
 400
 401   /* Save the value of `tz'.  */
 402   free (old_tz);
 403   old_tz = tz ? __strdup (tz) : NULL;
 404
 405   /* Try to read a data file.  */
 406   __tzfile_read (tz, 0, NULL);
 407   if (__use_tzfile)
 408     return;
 409
 410   /* No data file found.  Default to UTC if nothing specified.  */
 411
 412   if (tz == NULL || *tz == '\0'
 413       || (TZDEFAULT != NULL && strcmp (tz, TZDEFAULT) == 0))
 414     {
 415       memset (tz_rules, '\0', sizeof tz_rules);
 416       tz_rules[0].name = tz_rules[1].name = "UTC";
 417       if (J0 != 0)
 418         tz_rules[0].type = tz_rules[1].type = J0;
 419       tz_rules[0].change = tz_rules[1].change = (time_t) -1;
 420       update_vars ();
 421       return;
 422     }
 423
 424   __tzset_parse_tz (tz);
 425 }
 426 \f
 427 /* Figure out the exact time (as a time_t) in YEAR
 428    when the change described by RULE will occur and
 429    put it in RULE->change, saving YEAR in RULE->computed_for.  */
 430 static void
 431 compute_change (tz_rule *rule, int year)
 432 {
 433   time_t t;
 434
 435   if (year != -1 && rule->computed_for == year)
 436     /* Operations on times in 2 BC will be slower.  Oh well.  */
 437     return;
 438
 439   /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
 440   if (year > 1970)
 441     t = ((year - 1970) * 365
 442          + /* Compute the number of leapdays between 1970 and YEAR
 443               (exclusive).  There is a leapday every 4th year ...  */
 444          + ((year - 1) / 4 - 1970 / 4)
 445          /* ... except every 100th year ... */
 446          - ((year - 1) / 100 - 1970 / 100)
 447          /* ... but still every 400th year.  */
 448          + ((year - 1) / 400 - 1970 / 400)) * SECSPERDAY;
 449   else
 450     t = 0;
 451
 452   switch (rule->type)
 453     {
 454     case J1:
 455       /* Jn - Julian day, 1 == January 1, 60 == March 1 even in leap years.
 456          In non-leap years, or if the day number is 59 or less, just
 457          add SECSPERDAY times the day number-1 to the time of
 458          January 1, midnight, to get the day.  */
 459       t += (rule->d - 1) * SECSPERDAY;
 460       if (rule->d >= 60 && __isleap (year))
 461         t += SECSPERDAY;
 462       break;
 463
 464     case J0:
 465       /* n - Day of year.
 466          Just add SECSPERDAY times the day number to the time of Jan 1st.  */
 467       t += rule->d * SECSPERDAY;
 468       break;
 469
 470     case M:
 471       /* Mm.n.d - Nth "Dth day" of month M.  */
 472       {
 473         unsigned int i;
 474         int d, m1, yy0, yy1, yy2, dow;
 475         const unsigned short int *myday =
 476           &__mon_yday[__isleap (year)][rule->m];
 477
 478         /* First add SECSPERDAY for each day in months before M.  */
 479         t += myday[-1] * SECSPERDAY;
 480
 481         /* Use Zeller's Congruence to get day-of-week of first day of month. */
 482         m1 = (rule->m + 9) % 12 + 1;
 483         yy0 = (rule->m <= 2) ? (year - 1) : year;
 484         yy1 = yy0 / 100;
 485         yy2 = yy0 % 100;
 486         dow = ((26 * m1 - 2) / 10 + 1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
 487         if (dow < 0)
 488           dow += 7;
 489
 490         /* DOW is the day-of-week of the first day of the month.  Get the
 491            day-of-month (zero-origin) of the first DOW day of the month.  */
 492         d = rule->d - dow;
 493         if (d < 0)
 494           d += 7;
 495         for (i = 1; i < rule->n; ++i)
 496           {
 497             if (d + 7 >= (int) myday[0] - myday[-1])
 498               break;
 499             d += 7;
 500           }
 501
 502         /* D is the day-of-month (zero-origin) of the day we want.  */
 503         t += d * SECSPERDAY;
 504       }
 505       break;
 506     }
 507
 508   /* T is now the Epoch-relative time of 0:00:00 GMT on the day we want.
 509      Just add the time of day and local offset from GMT, and we're done.  */
 510
 511   rule->change = t - rule->offset + rule->secs;
 512   rule->computed_for = year;
 513 }
 514
 515
 516 /* Figure out the correct timezone for TM and set `__tzname',
 517    `__timezone', and `__daylight' accordingly.  */
 518 void
 519 __tz_compute (time_t timer, struct tm *tm, int use_localtime)
 520 {
 521   compute_change (&tz_rules[0], 1900 + tm->tm_year);
 522   compute_change (&tz_rules[1], 1900 + tm->tm_year);
 523
 524   if (use_localtime)
 525     {
 526       int isdst;
 527
 528       /* We have to distinguish between northern and southern
 529          hemisphere.  For the latter the daylight saving time
 530          ends in the next year.  */
 531       if (__builtin_expect (tz_rules[0].change
 532                             > tz_rules[1].change, 0))
 533         isdst = (timer < tz_rules[1].change
 534                  || timer >= tz_rules[0].change);
 535       else
 536         isdst = (timer >= tz_rules[0].change
 537                  && timer < tz_rules[1].change);
 538       tm->tm_isdst = isdst;
 539       tm->tm_zone = __tzname[isdst];
 540       tm->tm_gmtoff = tz_rules[isdst].offset;
 541     }
 542 }
 543 \f
 544 /* Reinterpret the TZ environment variable and set `tzname'.  */
 545 #undef tzset
 546
 547 void
 548 __tzset (void)
 549 {
 550   __libc_lock_lock (tzset_lock);
 551
 552   tzset_internal (1);
 553
 554   if (!__use_tzfile)
 555     {
 556       /* Set `tzname'.  */
 557       __tzname[0] = (char *) tz_rules[0].name;
 558       __tzname[1] = (char *) tz_rules[1].name;
 559     }
 560
 561   __libc_lock_unlock (tzset_lock);
 562 }
 563 weak_alias (__tzset, tzset)
 564 \f
 565 /* Return the `struct tm' representation of *TIMER in the local timezone.
 566    Use local time if USE_LOCALTIME is nonzero, UTC otherwise.  */
 567 struct tm *
 568 __tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
 569 {
 570   long int leap_correction;
 571   int leap_extra_secs;
 572
 573   if (timer == NULL)
 574     {
 575       __set_errno (EINVAL);
 576       return NULL;
 577     }
 578
 579   __libc_lock_lock (tzset_lock);
 580
 581   /* Update internal database according to current TZ setting.
 582      POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
 583      This is a good idea since this allows at least a bit more parallelism.  */
 584   tzset_internal (tp == &_tmbuf && use_localtime);
 585
 586   if (__use_tzfile)
 587     __tzfile_compute (*timer, use_localtime, &leap_correction,
 588                       &leap_extra_secs, tp);
 589   else
 590     {
 591       if (! __offtime (timer, 0, tp))
 592         tp = NULL;
 593       else
 594         __tz_compute (*timer, tp, use_localtime);
 595       leap_correction = 0L;
 596       leap_extra_secs = 0;
 597     }
 598
 599   __libc_lock_unlock (tzset_lock);
 600
 601   if (tp)
 602     {
 603       if (! use_localtime)
 604         {
 605           tp->tm_isdst = 0;
 606           tp->tm_zone = "GMT";
 607           tp->tm_gmtoff = 0L;
 608         }
 609
 610       if (__offtime (timer, tp->tm_gmtoff - leap_correction, tp))
 611         tp->tm_sec += leap_extra_secs;
 612       else
 613         tp = NULL;
 614     }
 615
 616   return tp;
 617 }
 618
 619
 620 libc_freeres_fn (free_mem)
 621 {
 622   while (tzstring_list != NULL)
 623     {
 624       struct tzstring_l *old = tzstring_list;
 625
 626       tzstring_list = tzstring_list->next;
 627       free (old);
 628     }
 629   free (old_tz);
 630   old_tz = NULL;
 631 }