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/* Work around platform bugs in localtime.
Copyright (C) 2017-2024 Free Software Foundation, Inc.
This file 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 2.1 of the
License, or (at your option) any later version.
This file 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 <https://www.gnu.org/licenses/>. */
#include <config.h>
/* Specification. */
#include <time.h>
#include <stdlib.h>
#include <string.h>
#if defined _WIN32 && ! defined __CYGWIN__
# include <wchar.h>
#endif
#undef localtime
struct tm *
rpl_localtime (const time_t *tp)
{
#if defined _WIN32 && ! defined __CYGWIN__
/* Rectify the value of the environment variable TZ.
There are four possible kinds of such values:
- Traditional US time zone names, e.g. "PST8PDT". Syntax: see
<https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/tzset>
- Time zone names based on geography, that contain one or more
slashes, e.g. "Europe/Moscow".
- Time zone names based on geography, without slashes, e.g.
"Singapore".
- Time zone names that contain explicit DST rules. Syntax: see
<https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03>
The Microsoft CRT understands only the first kind. It produces incorrect
results if the value of TZ is of the other kinds.
But in a Cygwin environment, /etc/profile.d/tzset.sh sets TZ to a value
of the second kind for most geographies, or of the first kind in a few
other geographies. If it is of the second kind, neutralize it. For the
Microsoft CRT, an absent or empty TZ means the time zone that the user
has set in the Windows Control Panel.
If the value of TZ is of the third or fourth kind -- Cygwin programs
understand these syntaxes as well --, it does not matter whether we
neutralize it or not, since these values occur only when a Cygwin user
has set TZ explicitly; this case is 1. rare and 2. under the user's
responsibility. */
const char *tz = getenv ("TZ");
if (tz != NULL && strchr (tz, '/') != NULL)
{
/* Neutralize it, in a way that is multithread-safe.
(If we were to use _putenv ("TZ="), it would free the memory allocated
for the environment variable "TZ", and thus other threads that are
using the previously fetched value of getenv ("TZ") could crash.) */
char **env = _environ;
wchar_t **wenv = _wenviron;
if (env != NULL)
for (char **ep = env; *ep != NULL; ep++)
{
char *s = *ep;
if (s[0] == 'T' && s[1] == 'Z' && s[2] == '=')
s[0] = '$';
}
if (wenv != NULL)
for (wchar_t **wep = wenv; *wep != NULL; wep++)
{
wchar_t *ws = *wep;
if (ws[0] == L'T' && ws[1] == L'Z' && ws[2] == L'=')
ws[0] = L'$';
}
}
#endif
return localtime (tp);
}
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