tree data UPDATE do not call tzset() (#2367)

* utests - call tzset after setenv TZ

unit-tests can fail if run in an env where TZ is already set.
This is because utest.h setup calls setenv("TZ"), but does not call
tzset() immediately after that.

This causes tzname, timezone, and daylight global variables to by out of
sync from the newly set environment value of "TZ".

To fix this, explicitly call tzset().

It's unlikely that a program would call setenv("TZ") during it's
lifetime, and this should ideally only happen in a test env.

* avoid tz_set calls in ly_time functions.

It does not seem necessary to call `ly_tzset_once()` from
`ly_time_time2str()` or `ly_time_tz_offset_at()`.

If the user changes TZ env variable, they must explicitly call `tzset()`
to update the global variables `tzname`, `timezone` and `daylight`

Author: irfanHaslanded

src/tree_data_common.c

@@ -1620,30 +1620,12 @@ ly_time_tz_offset(void)
     return ly_time_tz_offset_at(time(NULL));
 }
 
-/**
- * @brief Call tzset() if not already called by this process.
- */
-static void
-ly_tzset_once(void)
-{
-    static int ly_tzset_called = 0;
-
-    if (ly_tzset_called) {
-        return;
-    }
-    tzset();
-    ly_tzset_called = 1;
-}
-
 LIBYANG_API_DEF int
 ly_time_tz_offset_at(time_t time)
 {
     struct tm tm_local, tm_utc;
     int result = 0;
 
-    /* init timezone */
-    ly_tzset_once();
-
     /* get local and UTC time */
     localtime_r(&time, &tm_local);
     gmtime_r(&time, &tm_utc);
@@ -1791,9 +1773,6 @@ ly_time_time2str(time_t time, const char *fractions_s, char **str)
 
     LY_CHECK_ARG_RET(NULL, str, LY_EINVAL);
 
-    /* init timezone */
-    ly_tzset_once();
-
     /* convert */
     if (!localtime_r(&time, &tm)) {
         return LY_ESYS;

tests/utests/utests.h

@@ -1326,6 +1326,8 @@ utest_setup(void **state)
 
     /* set CET */
     setenv("TZ", "CET+02:00", 1);
+    /* call tzset explicitly, to update the tzname, timezone and daylight global variables */
+    tzset();
 
     return 0;
 }