1 /* Copyright (C) 1991-2023 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
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
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
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
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 }