reference: move leap second source into leapdb

Separate out source of leap second data into a new module in preparation
for supporting more sources such as leap-seconds.list.

leapdb.c

@@ -0,0 +1,147 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2009-2018, 2020, 2022
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * 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
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  This module provides leap second information. */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "conf.h"
+#include "leapdb.h"
+#include "logging.h"
+
+/* ================================================== */
+
+/* Name of a system timezone containing leap seconds occuring at midnight */
+static char *leap_tzname;
+
+/* ================================================== */
+
+static NTP_Leap
+get_tz_leap(time_t when, int *tai_offset)
+{
+  static time_t last_tz_leap_check;
+  static NTP_Leap tz_leap;
+  static int tz_tai_offset;
+
+  struct tm stm, *tm;
+  time_t t;
+  char *tz_env, tz_orig[128];
+
+  *tai_offset = tz_tai_offset;
+
+  /* Do this check at most twice a day */
+  when = when / (12 * 3600) * (12 * 3600);
+  if (last_tz_leap_check == when)
+      return tz_leap;
+
+  last_tz_leap_check = when;
+  tz_leap = LEAP_Normal;
+  tz_tai_offset = 0;
+
+  tm = gmtime(&when);
+  if (!tm)
+    return tz_leap;
+
+  stm = *tm;
+
+  /* Temporarily switch to the timezone containing leap seconds */
+  tz_env = getenv("TZ");
+  if (tz_env) {
+    if (strlen(tz_env) >= sizeof (tz_orig))
+      return tz_leap;
+    strcpy(tz_orig, tz_env);
+  }
+  setenv("TZ", leap_tzname, 1);
+  tzset();
+
+  /* Get the TAI-UTC offset, which started at the epoch at 10 seconds */
+  t = mktime(&stm);
+  if (t != -1)
+    tz_tai_offset = t - when + 10;
+
+  /* Set the time to 23:59:60 and see how it overflows in mktime() */
+  stm.tm_sec = 60;
+  stm.tm_min = 59;
+  stm.tm_hour = 23;
+
+  t = mktime(&stm);
+
+  if (tz_env)
+    setenv("TZ", tz_orig, 1);
+  else
+    unsetenv("TZ");
+  tzset();
+
+  if (t == -1)
+    return tz_leap;
+
+  if (stm.tm_sec == 60)
+    tz_leap = LEAP_InsertSecond;
+  else if (stm.tm_sec == 1)
+    tz_leap = LEAP_DeleteSecond;
+
+  *tai_offset = tz_tai_offset;
+
+  return tz_leap;
+}
+
+/* ================================================== */
+
+void
+LDB_Initialise(void)
+{
+  int tai_offset;
+
+  leap_tzname = CNF_GetLeapSecTimezone();
+  if (leap_tzname) {
+    /* Check that the timezone has good data for Jun 30 2012 and Dec 31 2012 */
+    if (get_tz_leap(1341014400, &tai_offset) == LEAP_InsertSecond && tai_offset == 34 &&
+        get_tz_leap(1356912000, &tai_offset) == LEAP_Normal && tai_offset == 35) {
+      LOG(LOGS_INFO, "Using %s timezone to obtain leap second data", leap_tzname);
+    } else {
+      LOG(LOGS_WARN, "Timezone %s failed leap second check, ignoring", leap_tzname);
+      leap_tzname = NULL;
+    }
+  }
+}
+
+/* ================================================== */
+
+NTP_Leap
+LDB_GetLeap(time_t when, int *tai_offset)
+{
+  *tai_offset = 0;
+  if (leap_tzname)
+    return get_tz_leap(when, tai_offset);
+  return LEAP_Normal;
+}
+
+/* ================================================== */
+
+void
+LDB_Finalise(void)
+{
+  /* Nothing to do */
+}