lib/time_rz.c

   1 /* Time zone functions such as tzalloc and localtime_rz
   2
   3    Copyright 2015-2024 Free Software Foundation, Inc.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation, either version 3 of the
   8    License, or (at your option) any later version.
   9
  10    This file 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 Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Paul Eggert.  */
  19
  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
  23    needed.  */
  24
  25 #include <config.h>
  26
  27 /* Specification.  */
  28 #include <time.h>
  29
  30 #if NEED_TIMEZONE_NULL_SUPPORT          /* Android API level >= 35 */
  31
  32 struct tm *
  33 localtime_rz (timezone_t tz, time_t const *t, struct tm *tm)
  34 # undef localtime_rz
  35 {
  36   if (!tz)
  37     return gmtime_r (t, tm);
  38   else
  39     return localtime_rz (tz, t, tm);
  40 }
  41
  42 time_t
  43 mktime_z (timezone_t tz, struct tm *tm)
  44 # undef mktime_z
  45 {
  46   if (!tz)
  47     return timegm (tm);
  48   else
  49     return mktime_z (tz, tm);
  50 }
  51
  52 #else
  53
  54 # include <errno.h>
  55 # include <stddef.h>
  56 # include <stdlib.h>
  57 # include <string.h>
  58
  59 # include "flexmember.h"
  60 # include "idx.h"
  61 # include "time-internal.h"
  62
  63 /* The approximate size to use for small allocation requests.  This is
  64    the largest "small" request for the GNU C library malloc.  */
  65 enum { DEFAULT_MXFAST = 64 * sizeof (size_t) / 4 };
  66
  67 /* Minimum size of the ABBRS member of struct tm_zone.  ABBRS is larger
  68    only in the unlikely case where an abbreviation longer than this is
  69    used.  */
  70 enum { ABBR_SIZE_MIN = DEFAULT_MXFAST - offsetof (struct tm_zone, abbrs) };
  71
  72 /* Copy to ABBRS the abbreviation at ABBR with size ABBR_SIZE (this
  73    includes its trailing null byte).  Append an extra null byte to
  74    mark the end of ABBRS.  */
  75 static void
  76 extend_abbrs (char *abbrs, char const *abbr, size_t abbr_size)
  77 {
  78   memcpy (abbrs, abbr, abbr_size);
  79   abbrs[abbr_size] = '\0';
  80 }
  81
  82 /* Return a newly allocated time zone for NAME, or NULL on failure.
  83    A null NAME stands for wall clock time (which is like unset TZ).  */
  84 timezone_t
  85 tzalloc (char const *name)
  86 {
  87   size_t name_size = name ? strlen (name) + 1 : 0;
  88   size_t abbr_size = name_size < ABBR_SIZE_MIN ? ABBR_SIZE_MIN : name_size + 1;
  89   timezone_t tz = malloc (FLEXSIZEOF (struct tm_zone, abbrs, abbr_size));
  90   if (tz)
  91     {
  92       tz->next = NULL;
  93       tz->tz_is_set = !!name;
  94       tz->abbrs[0] = '\0';
  95       if (name)
  96         extend_abbrs (tz->abbrs, name, name_size);
  97     }
  98   return tz;
  99 }
 100
 101 /* If HAVE_STRUCT_TM_TM_ZONE, save into TZ any nontrivial time zone
 102    abbreviation used by TM, and update *TM to contain the saved abbreviation.
 103    Return true if successful, false (setting errno) otherwise.  */
 104 static bool
 105 save_abbr (timezone_t tz, struct tm *tm)
 106 {
 107 # if HAVE_STRUCT_TM_TM_ZONE
 108   char const *zone = tm->tm_zone;
 109   char *zone_copy = (char *) "";
 110
 111   /* No need to replace null zones, or zones within the struct tm.  */
 112   if (!zone || ((char *) tm <= zone && zone < (char *) (tm + 1)))
 113     return true;
 114
 115   if (*zone)
 116     {
 117       zone_copy = tz->abbrs;
 118
 119       while (strcmp (zone_copy, zone) != 0)
 120         {
 121           if (! (*zone_copy || (zone_copy == tz->abbrs && tz->tz_is_set)))
 122             {
 123               idx_t zone_size = strlen (zone) + 1;
 124               if (zone_size < tz->abbrs + ABBR_SIZE_MIN - zone_copy)
 125                 extend_abbrs (zone_copy, zone, zone_size);
 126               else
 127                 {
 128                   tz = tz->next = tzalloc (zone);
 129                   if (!tz)
 130                     return false;
 131                   tz->tz_is_set = 0;
 132                   zone_copy = tz->abbrs;
 133                 }
 134               break;
 135             }
 136
 137           zone_copy += strlen (zone_copy) + 1;
 138           if (!*zone_copy && tz->next)
 139             {
 140               tz = tz->next;
 141               zone_copy = tz->abbrs;
 142             }
 143         }
 144     }
 145
 146   /* Replace the zone name so that its lifetime matches that of TZ.  */
 147   tm->tm_zone = zone_copy;
 148 # endif
 149
 150   return true;
 151 }
 152
 153 /* Free a time zone.  */
 154 void
 155 tzfree (timezone_t tz)
 156 {
 157   if (tz != local_tz)
 158     while (tz)
 159       {
 160         timezone_t next = tz->next;
 161         free (tz);
 162         tz = next;
 163       }
 164 }
 165
 166 /* Get and set the TZ environment variable.  These functions can be
 167    overridden by programs like Emacs that manage their own environment.  */
 168
 169 # ifndef getenv_TZ
 170 static char *
 171 getenv_TZ (void)
 172 {
 173   return getenv ("TZ");
 174 }
 175 # endif
 176
 177 # ifndef setenv_TZ
 178 static int
 179 setenv_TZ (char const *tz)
 180 {
 181   return tz ? setenv ("TZ", tz, 1) : unsetenv ("TZ");
 182 }
 183 # endif
 184
 185 /* Change the environment to match the specified timezone_t value.
 186    Return true if successful, false (setting errno) otherwise.  */
 187 static bool
 188 change_env (timezone_t tz)
 189 {
 190   if (setenv_TZ (tz->tz_is_set ? tz->abbrs : NULL) != 0)
 191     return false;
 192   tzset ();
 193   return true;
 194 }
 195
 196 /* Temporarily set the time zone to TZ, which must not be null.
 197    Return LOCAL_TZ if the time zone setting is already correct.
 198    Otherwise return a newly allocated time zone representing the old
 199    setting, or NULL (setting errno) on failure.  */
 200 timezone_t
 201 set_tz (timezone_t tz)
 202 {
 203   char *env_tz = getenv_TZ ();
 204   if (env_tz
 205       ? tz->tz_is_set && strcmp (tz->abbrs, env_tz) == 0
 206       : !tz->tz_is_set)
 207     return local_tz;
 208   else
 209     {
 210       timezone_t old_tz = tzalloc (env_tz);
 211       if (!old_tz)
 212         return old_tz;
 213       if (! change_env (tz))
 214         {
 215           int saved_errno = errno;
 216           tzfree (old_tz);
 217           errno = saved_errno;
 218           return NULL;
 219         }
 220       return old_tz;
 221     }
 222 }
 223
 224 /* Restore an old setting returned by set_tz.  It must not be null.
 225    Return true (preserving errno) if successful, false (setting errno)
 226    otherwise.  */
 227 bool
 228 revert_tz (timezone_t tz)
 229 {
 230   if (tz == local_tz)
 231     return true;
 232   else
 233     {
 234       int saved_errno = errno;
 235       bool ok = change_env (tz);
 236       if (!ok)
 237         saved_errno = errno;
 238       tzfree (tz);
 239       errno = saved_errno;
 240       return ok;
 241     }
 242 }
 243
 244 /* Use time zone TZ to compute localtime_r (T, TM).  */
 245 struct tm *
 246 localtime_rz (timezone_t tz, time_t const *t, struct tm *tm)
 247 {
 248 # ifdef HAVE_LOCALTIME_INFLOOP_BUG
 249   /* The -67768038400665599 comes from:
 250      https://lists.gnu.org/r/bug-gnulib/2017-07/msg00142.html
 251      On affected platforms the greatest POSIX-compatible time_t value
 252      that could return nonnull is 67768036191766798 (when
 253      TZ="XXX24:59:59" it resolves to the year 2**31 - 1 + 1900, on
 254      12-31 at 23:59:59), so test for that too while we're in the
 255      neighborhood.  */
 256   if (! (-67768038400665599 <= *t && *t <= 67768036191766798))
 257     {
 258       errno = EOVERFLOW;
 259       return NULL;
 260     }
 261 # endif
 262
 263   if (!tz)
 264     return gmtime_r (t, tm);
 265   else
 266     {
 267       timezone_t old_tz = set_tz (tz);
 268       if (old_tz)
 269         {
 270           bool abbr_saved = localtime_r (t, tm) && save_abbr (tz, tm);
 271           if (revert_tz (old_tz) && abbr_saved)
 272             return tm;
 273         }
 274       return NULL;
 275     }
 276 }
 277
 278 /* Use time zone TZ to compute mktime (TM).  */
 279 time_t
 280 mktime_z (timezone_t tz, struct tm *tm)
 281 {
 282   if (!tz)
 283     return timegm (tm);
 284   else
 285     {
 286       timezone_t old_tz = set_tz (tz);
 287       if (old_tz)
 288         {
 289           struct tm tm_1;
 290           tm_1.tm_sec = tm->tm_sec;
 291           tm_1.tm_min = tm->tm_min;
 292           tm_1.tm_hour = tm->tm_hour;
 293           tm_1.tm_mday = tm->tm_mday;
 294           tm_1.tm_mon = tm->tm_mon;
 295           tm_1.tm_year = tm->tm_year;
 296           tm_1.tm_yday = -1;
 297           tm_1.tm_isdst = tm->tm_isdst;
 298           time_t t = mktime (&tm_1);
 299           bool ok = 0 <= tm_1.tm_yday;
 300           ok = ok && save_abbr (tz, &tm_1);
 301           if (revert_tz (old_tz) && ok)
 302             {
 303               *tm = tm_1;
 304               return t;
 305             }
 306         }
 307       return -1;
 308     }
 309 }
 310
 311 #endif