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Diffstat (limited to 'lib/time_rz.c')
| -rw-r--r-- | lib/time_rz.c | 321 |
1 files changed, 321 insertions, 0 deletions
diff --git a/lib/time_rz.c b/lib/time_rz.c new file mode 100644 index 000000000..612093bbc --- /dev/null +++ b/lib/time_rz.c @@ -0,0 +1,321 @@ +/* Time zone functions such as tzalloc and localtime_rz + + Copyright 2015-2016 Free Software Foundation, Inc. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2, or (at your option) + any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License along + with this program; if not, see <http://www.gnu.org/licenses/>. */ + +/* Written by Paul Eggert. */ + +/* Although this module is not thread-safe, any races should be fairly + rare and reasonably benign. For complete thread-safety, use a C + library with a working timezone_t type, so that this module is not + needed. */ + +#include <config.h> + +#include <time.h> + +#include <errno.h> +#include <stdbool.h> +#include <stddef.h> +#include <stdlib.h> +#include <string.h> + +#include "time-internal.h" + +#if !HAVE_TZSET +static void tzset (void) { } +#endif + +/* The approximate size to use for small allocation requests. This is + the largest "small" request for the GNU C library malloc. */ +enum { DEFAULT_MXFAST = 64 * sizeof (size_t) / 4 }; + +/* Minimum size of the ABBRS member of struct abbr. ABBRS is larger + only in the unlikely case where an abbreviation longer than this is + used. */ +enum { ABBR_SIZE_MIN = DEFAULT_MXFAST - offsetof (struct tm_zone, abbrs) }; + +/* Magic cookie timezone_t value, for local time. It differs from + NULL and from all other timezone_t values. Only the address + matters; the pointer is never dereferenced. */ +static timezone_t const local_tz = (timezone_t) 1; + +#if HAVE_TM_ZONE || HAVE_TZNAME + +/* Return true if the values A and B differ according to the rules for + tm_isdst: A and B differ if one is zero and the other positive. */ +static bool +isdst_differ (int a, int b) +{ + return !a != !b && 0 <= a && 0 <= b; +} + +/* Return true if A and B are equal. */ +static int +equal_tm (const struct tm *a, const struct tm *b) +{ + return ! ((a->tm_sec ^ b->tm_sec) + | (a->tm_min ^ b->tm_min) + | (a->tm_hour ^ b->tm_hour) + | (a->tm_mday ^ b->tm_mday) + | (a->tm_mon ^ b->tm_mon) + | (a->tm_year ^ b->tm_year) + | isdst_differ (a->tm_isdst, b->tm_isdst)); +} + +#endif + +/* Copy to ABBRS the abbreviation at ABBR with size ABBR_SIZE (this + includes its trailing null byte). Append an extra null byte to + mark the end of ABBRS. */ +static void +extend_abbrs (char *abbrs, char const *abbr, size_t abbr_size) +{ + memcpy (abbrs, abbr, abbr_size); + abbrs[abbr_size] = '\0'; +} + +/* Return a newly allocated time zone for NAME, or NULL on failure. + A null NAME stands for wall clock time (which is like unset TZ). */ +timezone_t +tzalloc (char const *name) +{ + size_t name_size = name ? strlen (name) + 1 : 0; + size_t abbr_size = name_size < ABBR_SIZE_MIN ? ABBR_SIZE_MIN : name_size + 1; + timezone_t tz = malloc (offsetof (struct tm_zone, abbrs) + abbr_size); + if (tz) + { + tz->next = NULL; +#if HAVE_TZNAME && !HAVE_TM_ZONE + tz->tzname_copy[0] = tz->tzname_copy[1] = NULL; +#endif + tz->tz_is_set = !!name; + tz->abbrs[0] = '\0'; + if (name) + extend_abbrs (tz->abbrs, name, name_size); + } + return tz; +} + +/* Save into TZ any nontrivial time zone abbreviation used by TM, and + update *TM (if HAVE_TM_ZONE) or *TZ (if !HAVE_TM_ZONE && + HAVE_TZNAME) if they use the abbreviation. Return true if + successful, false (setting errno) otherwise. */ +static bool +save_abbr (timezone_t tz, struct tm *tm) +{ +#if HAVE_TM_ZONE || HAVE_TZNAME + char const *zone = NULL; + char *zone_copy = (char *) ""; + +# if HAVE_TZNAME + int tzname_index = -1; +# endif + +# if HAVE_TM_ZONE + zone = tm->tm_zone; +# endif + +# if HAVE_TZNAME + if (! (zone && *zone) && 0 <= tm->tm_isdst) + { + tzname_index = tm->tm_isdst != 0; + zone = tzname[tzname_index]; + } +# endif + + /* No need to replace null zones, or zones within the struct tm. */ + if (!zone || ((char *) tm <= zone && zone < (char *) (tm + 1))) + return true; + + if (*zone) + { + zone_copy = tz->abbrs; + + while (strcmp (zone_copy, zone) != 0) + { + if (! (*zone_copy || (zone_copy == tz->abbrs && tz->tz_is_set))) + { + size_t zone_size = strlen (zone) + 1; + if (zone_size < tz->abbrs + ABBR_SIZE_MIN - zone_copy) + extend_abbrs (zone_copy, zone, zone_size); + else + { + tz = tz->next = tzalloc (zone); + if (!tz) + return false; + tz->tz_is_set = 0; + zone_copy = tz->abbrs; + } + break; + } + + zone_copy += strlen (zone_copy) + 1; + if (!*zone_copy && tz->next) + { + tz = tz->next; + zone_copy = tz->abbrs; + } + } + } + + /* Replace the zone name so that its lifetime matches that of TZ. */ +# if HAVE_TM_ZONE + tm->tm_zone = zone_copy; +# else + if (0 <= tzname_index) + tz->tzname_copy[tzname_index] = zone_copy; +# endif +#endif + + return true; +} + +/* Free a time zone. */ +void +tzfree (timezone_t tz) +{ + if (tz != local_tz) + while (tz) + { + timezone_t next = tz->next; + free (tz); + tz = next; + } +} + +/* Get and set the TZ environment variable. These functions can be + overridden by programs like Emacs that manage their own environment. */ + +#ifndef getenv_TZ +static char * +getenv_TZ (void) +{ + return getenv ("TZ"); +} +#endif + +#ifndef setenv_TZ +static int +setenv_TZ (char const *tz) +{ + return tz ? setenv ("TZ", tz, 1) : unsetenv ("TZ"); +} +#endif + +/* Change the environment to match the specified timezone_t value. + Return true if successful, false (setting errno) otherwise. */ +static bool +change_env (timezone_t tz) +{ + if (setenv_TZ (tz->tz_is_set ? tz->abbrs : NULL) != 0) + return false; + tzset (); + return true; +} + +/* Temporarily set the time zone to TZ, which must not be null. + Return LOCAL_TZ if the time zone setting is already correct. + Otherwise return a newly allocated time zone representing the old + setting, or NULL (setting errno) on failure. */ +static timezone_t +set_tz (timezone_t tz) +{ + char *env_tz = getenv_TZ (); + if (env_tz + ? tz->tz_is_set && strcmp (tz->abbrs, env_tz) == 0 + : !tz->tz_is_set) + return local_tz; + else + { + timezone_t old_tz = tzalloc (env_tz); + if (!old_tz) + return old_tz; + if (! change_env (tz)) + { + int saved_errno = errno; + tzfree (old_tz); + errno = saved_errno; + return NULL; + } + return old_tz; + } +} + +/* Restore an old setting returned by set_tz. It must not be null. + Return true (preserving errno) if successful, false (setting errno) + otherwise. */ +static bool +revert_tz (timezone_t tz) +{ + if (tz == local_tz) + return true; + else + { + int saved_errno = errno; + bool ok = change_env (tz); + if (!ok) + saved_errno = errno; + tzfree (tz); + errno = saved_errno; + return ok; + } +} + +/* Use time zone TZ to compute localtime_r (T, TM). */ +struct tm * +localtime_rz (timezone_t tz, time_t const *t, struct tm *tm) +{ + if (!tz) + return gmtime_r (t, tm); + else + { + timezone_t old_tz = set_tz (tz); + if (old_tz) + { + bool abbr_saved = localtime_r (t, tm) && save_abbr (tz, tm); + if (revert_tz (old_tz) && abbr_saved) + return tm; + } + return NULL; + } +} + +/* Use time zone TZ to compute mktime (TM). */ +time_t +mktime_z (timezone_t tz, struct tm *tm) +{ + if (!tz) + return timegm (tm); + else + { + timezone_t old_tz = set_tz (tz); + if (old_tz) + { + time_t t = mktime (tm); +#if HAVE_TM_ZONE || HAVE_TZNAME + time_t badtime = -1; + struct tm tm_1; + if ((t != badtime + || (localtime_r (&t, &tm_1) && equal_tm (tm, &tm_1))) + && !save_abbr (tz, tm)) + t = badtime; +#endif + if (revert_tz (old_tz)) + return t; + } + return -1; + } +} |