1 /* Time zone functions such as tzalloc and localtime_rz
3 Copyright 2015-2018 Free Software Foundation, Inc.
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3, or (at your option)
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License along
16 with this program; if not, see <https://www.gnu.org/licenses/>. */
18 /* Written by Paul Eggert. */
20 /* Although this module is not thread-safe, any races should be fairly
21 rare and reasonably benign. For complete thread-safety, use a C
22 library with a working timezone_t type, so that this module is not
36 #include "flexmember.h"
37 #include "time-internal.h"
40 # define SIZE_MAX ((size_t) -1)
43 /* The approximate size to use for small allocation requests. This is
44 the largest "small" request for the GNU C library malloc. */
45 enum { DEFAULT_MXFAST = 64 * sizeof (size_t) / 4 };
47 /* Minimum size of the ABBRS member of struct tm_zone. ABBRS is larger
48 only in the unlikely case where an abbreviation longer than this is
50 enum { ABBR_SIZE_MIN = DEFAULT_MXFAST - offsetof (struct tm_zone, abbrs) };
52 /* Magic cookie timezone_t value, for local time. It differs from
53 NULL and from all other timezone_t values. Only the address
54 matters; the pointer is never dereferenced. */
55 static timezone_t const local_tz = (timezone_t) 1;
57 #if HAVE_TM_ZONE || HAVE_TZNAME
59 /* Return true if the values A and B differ according to the rules for
60 tm_isdst: A and B differ if one is zero and the other positive. */
62 isdst_differ (int a, int b)
64 return !a != !b && 0 <= a && 0 <= b;
67 /* Return true if A and B are equal. */
69 equal_tm (const struct tm *a, const struct tm *b)
71 return ! ((a->tm_sec ^ b->tm_sec)
72 | (a->tm_min ^ b->tm_min)
73 | (a->tm_hour ^ b->tm_hour)
74 | (a->tm_mday ^ b->tm_mday)
75 | (a->tm_mon ^ b->tm_mon)
76 | (a->tm_year ^ b->tm_year)
77 | isdst_differ (a->tm_isdst, b->tm_isdst));
82 /* Copy to ABBRS the abbreviation at ABBR with size ABBR_SIZE (this
83 includes its trailing null byte). Append an extra null byte to
84 mark the end of ABBRS. */
86 extend_abbrs (char *abbrs, char const *abbr, size_t abbr_size)
88 memcpy (abbrs, abbr, abbr_size);
89 abbrs[abbr_size] = '\0';
92 /* Return a newly allocated time zone for NAME, or NULL on failure.
93 A null NAME stands for wall clock time (which is like unset TZ). */
95 tzalloc (char const *name)
97 size_t name_size = name ? strlen (name) + 1 : 0;
98 size_t abbr_size = name_size < ABBR_SIZE_MIN ? ABBR_SIZE_MIN : name_size + 1;
99 timezone_t tz = malloc (FLEXSIZEOF (struct tm_zone, abbrs, abbr_size));
103 #if HAVE_TZNAME && !HAVE_TM_ZONE
104 tz->tzname_copy[0] = tz->tzname_copy[1] = NULL;
106 tz->tz_is_set = !!name;
109 extend_abbrs (tz->abbrs, name, name_size);
114 /* Save into TZ any nontrivial time zone abbreviation used by TM, and
115 update *TM (if HAVE_TM_ZONE) or *TZ (if !HAVE_TM_ZONE &&
116 HAVE_TZNAME) if they use the abbreviation. Return true if
117 successful, false (setting errno) otherwise. */
119 save_abbr (timezone_t tz, struct tm *tm)
121 #if HAVE_TM_ZONE || HAVE_TZNAME
122 char const *zone = NULL;
123 char *zone_copy = (char *) "";
126 int tzname_index = -1;
134 if (! (zone && *zone) && 0 <= tm->tm_isdst)
136 tzname_index = tm->tm_isdst != 0;
137 zone = tzname[tzname_index];
141 /* No need to replace null zones, or zones within the struct tm. */
142 if (!zone || ((char *) tm <= zone && zone < (char *) (tm + 1)))
147 zone_copy = tz->abbrs;
149 while (strcmp (zone_copy, zone) != 0)
151 if (! (*zone_copy || (zone_copy == tz->abbrs && tz->tz_is_set)))
153 size_t zone_size = strlen (zone) + 1;
154 size_t zone_used = zone_copy - tz->abbrs;
155 if (SIZE_MAX - zone_used < zone_size)
160 if (zone_used + zone_size < ABBR_SIZE_MIN)
161 extend_abbrs (zone_copy, zone, zone_size);
164 tz = tz->next = tzalloc (zone);
168 zone_copy = tz->abbrs;
173 zone_copy += strlen (zone_copy) + 1;
174 if (!*zone_copy && tz->next)
177 zone_copy = tz->abbrs;
182 /* Replace the zone name so that its lifetime matches that of TZ. */
184 tm->tm_zone = zone_copy;
186 if (0 <= tzname_index)
187 tz->tzname_copy[tzname_index] = zone_copy;
194 /* Free a time zone. */
196 tzfree (timezone_t tz)
201 timezone_t next = tz->next;
207 /* Get and set the TZ environment variable. These functions can be
208 overridden by programs like Emacs that manage their own environment. */
214 return getenv ("TZ");
220 setenv_TZ (char const *tz)
222 return tz ? setenv ("TZ", tz, 1) : unsetenv ("TZ");
226 /* Change the environment to match the specified timezone_t value.
227 Return true if successful, false (setting errno) otherwise. */
229 change_env (timezone_t tz)
231 if (setenv_TZ (tz->tz_is_set ? tz->abbrs : NULL) != 0)
237 /* Temporarily set the time zone to TZ, which must not be null.
238 Return LOCAL_TZ if the time zone setting is already correct.
239 Otherwise return a newly allocated time zone representing the old
240 setting, or NULL (setting errno) on failure. */
242 set_tz (timezone_t tz)
244 char *env_tz = getenv_TZ ();
246 ? tz->tz_is_set && strcmp (tz->abbrs, env_tz) == 0
251 timezone_t old_tz = tzalloc (env_tz);
254 if (! change_env (tz))
256 int saved_errno = errno;
265 /* Restore an old setting returned by set_tz. It must not be null.
266 Return true (preserving errno) if successful, false (setting errno)
269 revert_tz (timezone_t tz)
275 int saved_errno = errno;
276 bool ok = change_env (tz);
285 /* Use time zone TZ to compute localtime_r (T, TM). */
287 localtime_rz (timezone_t tz, time_t const *t, struct tm *tm)
289 #ifdef HAVE_LOCALTIME_INFLOOP_BUG
290 /* The -67768038400665599 comes from:
291 https://lists.gnu.org/r/bug-gnulib/2017-07/msg00142.html
292 On affected platforms the greatest POSIX-compatible time_t value
293 that could return nonnull is 67768036191766798 (when
294 TZ="XXX24:59:59" it resolves to the year 2**31 - 1 + 1900, on
295 12-31 at 23:59:59), so test for that too while we're in the
297 if (! (-67768038400665599 <= *t && *t <= 67768036191766798))
305 return gmtime_r (t, tm);
308 timezone_t old_tz = set_tz (tz);
311 bool abbr_saved = localtime_r (t, tm) && save_abbr (tz, tm);
312 if (revert_tz (old_tz) && abbr_saved)
319 /* Use time zone TZ to compute mktime (TM). */
321 mktime_z (timezone_t tz, struct tm *tm)
327 timezone_t old_tz = set_tz (tz);
330 time_t t = mktime (tm);
331 #if HAVE_TM_ZONE || HAVE_TZNAME
335 || (localtime_r (&t, &tm_1) && equal_tm (tm, &tm_1)))
336 && !save_abbr (tz, tm))
339 if (revert_tz (old_tz))