text: /*-------------------------------------------------------------------------
   *
   * pgtz.c
   *	  Timezone Library Integration Functions
   *
   * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
   *
   * IDENTIFICATION
   *	  $PostgreSQL: pgsql/src/timezone/pgtz.c,v 1.63 2009/06/11 14:49:15 momjian Exp $
   *
   *-------------------------------------------------------------------------
   */
  #define NO_REDEFINE_TIMEFUNCS
  
  #include "postgres.h"
  
  #include <ctype.h>
  #include <fcntl.h>
  #include <sys/stat.h>
  #include <time.h>
  
  #include "miscadmin.h"
  #include "pgtz.h"
  #include "storage/fd.h"
  #include "tzfile.h"
  #include "utils/datetime.h"
  #include "utils/guc.h"
  #include "utils/hsearch.h"
  
  /* Current session timezone (controlled by TimeZone GUC) */
  pg_tz	   *session_timezone = NULL;
  
  /* Current log timezone (controlled by log_timezone GUC) */
  pg_tz	   *log_timezone = NULL;
  
  /* Fallback GMT timezone for last-ditch error message formatting */
  pg_tz	   *gmt_timezone = NULL;
  static pg_tz gmt_timezone_data;
  
  
  static bool scan_directory_ci(const char *dirname,
  				  const char *fname, int fnamelen,
  				  char *canonname, int canonnamelen);
  static const char *identify_system_timezone(void);
  static pg_tz *get_pg_tz_for_zone(const char *tzname);
  static pg_tz *select_default_timezone(void);
  
  
  /*
   * Return full pathname of timezone data directory
   */
  static const char *
  pg_TZDIR(void)
  {
  #ifndef SYSTEMTZDIR
  	/* normal case: timezone stuff is under our share dir */
  	static bool done_tzdir = false;
  	static char tzdir[MAXPGPATH];
  
  	if (done_tzdir)
  		return tzdir;
  
  	get_share_path(my_exec_path, tzdir);
  	strlcpy(tzdir + strlen(tzdir), "/timezone", MAXPGPATH - strlen(tzdir));
  
  	done_tzdir = true;
  	return tzdir;
  #else
  	/* we're configured to use system's timezone database */
  	return SYSTEMTZDIR;
  #endif
  }
  
  
  /*
   * Given a timezone name, open() the timezone data file.  Return the
   * file descriptor if successful, -1 if not.
   *
   * The input name is searched for case-insensitively (we assume that the
   * timezone database does not contain case-equivalent names).
   *
   * If "canonname" is not NULL, then on success the canonical spelling of the
   * given name is stored there (it is assumed to be > TZ_STRLEN_MAX bytes!).
   */
  int
  pg_open_tzfile(const char *name, char *canonname)
  {
  	const char *fname;
  	char		fullname[MAXPGPATH];
  	int			fullnamelen;
  	int			orignamelen;
  
  	/*
  	 * Loop to split the given name into directory levels; for each level,
  	 * search using scan_directory_ci().
  	 */
  	strlcpy(fullname, pg_TZDIR(), sizeof(fullname));
  	orignamelen = fullnamelen = strlen(fullname);
  	fname = name;
  	for (;;)
  	{
  		const char *slashptr;
  		int			fnamelen;
  
  		slashptr = strchr(fname, '/');
  		if (slashptr)
  			fnamelen = slashptr - fname;
  		else
  			fnamelen = strlen(fname);
  		if (fullnamelen + 1 + fnamelen >= MAXPGPATH)
  			return -1;			/* not gonna fit */
  		if (!scan_directory_ci(fullname, fname, fnamelen,
  							   fullname + fullnamelen + 1,
  							   MAXPGPATH - fullnamelen - 1))
  			return -1;
  		fullname[fullnamelen++] = '/';
  		fullnamelen += strlen(fullname + fullnamelen);
  		if (slashptr)
  			fname = slashptr + 1;
  		else
  			break;
  	}
  
  	if (canonname)
  		strlcpy(canonname, fullname + orignamelen + 1, TZ_STRLEN_MAX + 1);
  
  	return open(fullname, O_RDONLY | PG_BINARY, 0);
  }
  
  
  /*
   * Scan specified directory for a case-insensitive match to fname
   * (of length fnamelen --- fname may not be null terminated!).	If found,
   * copy the actual filename into canonname and return true.
   */
  static bool
  scan_directory_ci(const char *dirname, const char *fname, int fnamelen,
  				  char *canonname, int canonnamelen)
  {
  	bool		found = false;
  	DIR		   *dirdesc;
  	struct dirent *direntry;
  
  	dirdesc = AllocateDir(dirname);
  	if (!dirdesc)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not open directory \"%s\": %m", dirname)));
  		return false;
  	}
  
  	while ((direntry = ReadDir(dirdesc, dirname)) != NULL)
  	{
  		/*
  		 * Ignore . and .., plus any other "hidden" files.	This is a security
  		 * measure to prevent access to files outside the timezone directory.
  		 */
  		if (direntry->d_name[0] == '.')
  			continue;
  
  		if (strlen(direntry->d_name) == fnamelen &&
  			pg_strncasecmp(direntry->d_name, fname, fnamelen) == 0)
  		{
  			/* Found our match */
  			strlcpy(canonname, direntry->d_name, canonnamelen);
  			found = true;
  			break;
  		}
  	}
  
  	FreeDir(dirdesc);
  
  	return found;
  }
  
  
  /*
   * The following block of code attempts to determine which timezone in our
   * timezone database is the best match for the active system timezone.
   *
   * On most systems, we rely on trying to match the observable behavior of
   * the C library's localtime() function.  The database zone that matches
   * furthest into the past is the one to use.  Often there will be several
   * zones with identical rankings (since the zic database assigns multiple
   * names to many zones).  We break ties arbitrarily by preferring shorter,
   * then alphabetically earlier zone names.
   *
   * Win32's native knowledge about timezones appears to be too incomplete
   * and too different from the zic database for the above matching strategy
   * to be of any use. But there is just a limited number of timezones
   * available, so we can rely on a handmade mapping table instead.
   */
  
  #ifndef WIN32
  
  #define T_DAY	((time_t) (60*60*24))
  #define T_WEEK	((time_t) (60*60*24*7))
  #define T_MONTH ((time_t) (60*60*24*31))
  
  #define MAX_TEST_TIMES (52*100) /* 100 years */
  
  struct tztry
  {
  	int			n_test_times;
  	time_t		test_times[MAX_TEST_TIMES];
  };
  
  static void scan_available_timezones(char *tzdir, char *tzdirsub,
  						 struct tztry * tt,
  						 int *bestscore, char *bestzonename);
  
  
  /*
   * Get GMT offset from a system struct tm
   */
  static int
  get_timezone_offset(struct tm * tm)
  {
  #if defined(HAVE_STRUCT_TM_TM_ZONE)
  	return tm->tm_gmtoff;
  #elif defined(HAVE_INT_TIMEZONE)
  	return -TIMEZONE_GLOBAL;
  #else
  #error No way to determine TZ? Can this happen?
  #endif
  }
  
  /*
   * Convenience subroutine to convert y/m/d to time_t (NOT pg_time_t)
   */
  static time_t
  build_time_t(int year, int month, int day)
  {
  	struct tm	tm;
  
  	memset(&tm, 0, sizeof(tm));
  	tm.tm_mday = day;
  	tm.tm_mon = month - 1;
  	tm.tm_year = year - 1900;
  
  	return mktime(&tm);
  }
  
  /*
   * Does a system tm value match one we computed ourselves?
   */
  static bool
  compare_tm(struct tm * s, struct pg_tm * p)
  {
  	if (s->tm_sec != p->tm_sec ||
  		s->tm_min != p->tm_min ||
  		s->tm_hour != p->tm_hour ||
  		s->tm_mday != p->tm_mday ||
  		s->tm_mon != p->tm_mon ||
  		s->tm_year != p->tm_year ||
  		s->tm_wday != p->tm_wday ||
  		s->tm_yday != p->tm_yday ||
  		s->tm_isdst != p->tm_isdst)
  		return false;
  	return true;
  }
  
  /*
   * See how well a specific timezone setting matches the system behavior
   *
   * We score a timezone setting according to the number of test times it
   * matches.  (The test times are ordered later-to-earlier, but this routine
   * doesn't actually know that; it just scans until the first non-match.)
   *
   * We return -1 for a completely unusable setting; this is worse than the
   * score of zero for a setting that works but matches not even the first
   * test time.
   */
  static int
  score_timezone(const char *tzname, struct tztry * tt)
  {
  	int			i;
  	pg_time_t	pgtt;
  	struct tm  *systm;
  	struct pg_tm *pgtm;
  	char		cbuf[TZ_STRLEN_MAX + 1];
  	pg_tz		tz;
  
  
  	/*
  	 * Load timezone directly. Don't use pg_tzset, because we don't want all
  	 * timezones loaded in the cache at startup.
  	 */
  	if (tzload(tzname, NULL, &tz.state, TRUE) != 0)
  	{
  		if (tzname[0] == ':' || tzparse(tzname, &tz.state, FALSE) != 0)
  		{
  			return -1;			/* can't handle the TZ name at all */
  		}
  	}
  
  	/* Reject if leap seconds involved */
  	if (!tz_acceptable(&tz))
  	{
  		elog(DEBUG4, "Reject TZ \"%s\": uses leap seconds", tzname);
  		return -1;
  	}
  
  	/* Check for match at all the test times */
  	for (i = 0; i < tt->n_test_times; i++)
  	{
  		pgtt = (pg_time_t) (tt->test_times[i]);
  		pgtm = pg_localtime(&pgtt, &tz);
  		if (!pgtm)
  			return -1;			/* probably shouldn't happen */
  		systm = localtime(&(tt->test_times[i]));
  		if (!systm)
  		{
  			elog(DEBUG4, "TZ \"%s\" scores %d: at %ld %04d-%02d-%02d %02d:%02d:%02d %s, system had no data",
  				 tzname, i, (long) pgtt,
  				 pgtm->tm_year + 1900, pgtm->tm_mon + 1, pgtm->tm_mday,
  				 pgtm->tm_hour, pgtm->tm_min, pgtm->tm_sec,
  				 pgtm->tm_isdst ? "dst" : "std");
  			return i;
  		}
  		if (!compare_tm(systm, pgtm))
  		{
  			elog(DEBUG4, "TZ \"%s\" scores %d: at %ld %04d-%02d-%02d %02d:%02d:%02d %s versus %04d-%02d-%02d %02d:%02d:%02d %s",
  				 tzname, i, (long) pgtt,
  				 pgtm->tm_year + 1900, pgtm->tm_mon + 1, pgtm->tm_mday,
  				 pgtm->tm_hour, pgtm->tm_min, pgtm->tm_sec,
  				 pgtm->tm_isdst ? "dst" : "std",
  				 systm->tm_year + 1900, systm->tm_mon + 1, systm->tm_mday,
  				 systm->tm_hour, systm->tm_min, systm->tm_sec,
  				 systm->tm_isdst ? "dst" : "std");
  			return i;
  		}
  		if (systm->tm_isdst >= 0)
  		{
  			/* Check match of zone names, too */
  			if (pgtm->tm_zone == NULL)
  				return -1;		/* probably shouldn't happen */
  			memset(cbuf, 0, sizeof(cbuf));
  			strftime(cbuf, sizeof(cbuf) - 1, "%Z", systm);		/* zone abbr */
  			if (strcmp(cbuf, pgtm->tm_zone) != 0)
  			{
  				elog(DEBUG4, "TZ \"%s\" scores %d: at %ld \"%s\" versus \"%s\"",
  					 tzname, i, (long) pgtt,
  					 pgtm->tm_zone, cbuf);
  				return i;
  			}
  		}
  	}
  
  	elog(DEBUG4, "TZ \"%s\" gets max score %d", tzname, i);
  	return i;
  }
  
  
  /*
   * Try to identify a timezone name (in our terminology) that best matches the
   * observed behavior of the system timezone library.  We cannot assume that
   * the system TZ environment setting (if indeed there is one) matches our
   * terminology, so we ignore it and just look at what localtime() returns.
   */
  static const char *
  identify_system_timezone(void)
  {
  	static char resultbuf[TZ_STRLEN_MAX + 1];
  	time_t		tnow;
  	time_t		t;
  	struct tztry tt;
  	struct tm  *tm;
  	int			thisyear;
  	int			bestscore;
  	char		tmptzdir[MAXPGPATH];
  	int			std_ofs;
  	char		std_zone_name[TZ_STRLEN_MAX + 1],
  				dst_zone_name[TZ_STRLEN_MAX + 1];
  	char		cbuf[TZ_STRLEN_MAX + 1];
  
  	/* Initialize OS timezone library */
  	tzset();
  
  	/*
  	 * Set up the list of dates to be probed to see how well our timezone
  	 * matches the system zone.  We first probe January and July of the
  	 * current year; this serves to quickly eliminate the vast majority of the
  	 * TZ database entries.  If those dates match, we probe every week for 100
  	 * years backwards from the current July.  (Weekly resolution is good
  	 * enough to identify DST transition rules, since everybody switches on
  	 * Sundays.)  This is sufficient to cover most of the Unix time_t range,
  	 * and we don't want to look further than that since many systems won't
  	 * have sane TZ behavior further back anyway.  The further back the zone
  	 * matches, the better we score it.  This may seem like a rather random
  	 * way of doing things, but experience has shown that system-supplied
  	 * timezone definitions are likely to have DST behavior that is right for
  	 * the recent past and not so accurate further back. Scoring in this way
  	 * allows us to recognize zones that have some commonality with the zic
  	 * database, without insisting on exact match. (Note: we probe Thursdays,
  	 * not Sundays, to avoid triggering DST-transition bugs in localtime
  	 * itself.)
  	 */
  	tnow = time(NULL);
  	tm = localtime(&tnow);
  	if (!tm)
  		return NULL;			/* give up if localtime is broken... */
  	thisyear = tm->tm_year + 1900;
  
  	t = build_time_t(thisyear, 1, 15);
  
  	/*
  	 * Round back to GMT midnight Thursday.  This depends on the knowledge
  	 * that the time_t origin is Thu Jan 01 1970.  (With a different origin
  	 * we'd be probing some other day of the week, but it wouldn't matter
  	 * anyway unless localtime() had DST-transition bugs.)
  	 */
  	t -= (t % T_WEEK);
  
  	tt.n_test_times = 0;
  	tt.test_times[tt.n_test_times++] = t;
  
  	t = build_time_t(thisyear, 7, 15);
  	t -= (t % T_WEEK);
  
  	tt.test_times[tt.n_test_times++] = t;
  
  	while (tt.n_test_times < MAX_TEST_TIMES)
  	{
  		t -= T_WEEK;
  		tt.test_times[tt.n_test_times++] = t;
  	}
  
  	/* Search for the best-matching timezone file */
  	strlcpy(tmptzdir, pg_TZDIR(), sizeof(tmptzdir));
  	bestscore = -1;
  	resultbuf[0] = '\0';
  	scan_available_timezones(tmptzdir, tmptzdir + strlen(tmptzdir) + 1,
  							 &tt,
  							 &bestscore, resultbuf);
  	if (bestscore > 0)
  	{
  		/* Ignore zic's rather silly "Factory" time zone; use GMT instead */
  		if (strcmp(resultbuf, "Factory") == 0)
  			return NULL;
  		return resultbuf;
  	}
  
  	/*
  	 * Couldn't find a match in the database, so next we try constructed zone
  	 * names (like "PST8PDT").
  	 *
  	 * First we need to determine the names of the local standard and daylight
  	 * zones.  The idea here is to scan forward from today until we have seen
  	 * both zones, if both are in use.
  	 */
  	memset(std_zone_name, 0, sizeof(std_zone_name));
  	memset(dst_zone_name, 0, sizeof(dst_zone_name));
  	std_ofs = 0;
  
  	tnow = time(NULL);
  
  	/*
  	 * Round back to a GMT midnight so results don't depend on local time of
  	 * day
  	 */
  	tnow -= (tnow % T_DAY);
  
  	/*
  	 * We have to look a little further ahead than one year, in case today is
  	 * just past a DST boundary that falls earlier in the year than the next
  	 * similar boundary.  Arbitrarily scan up to 14 months.
  	 */
  	for (t = tnow; t <= tnow + T_MONTH * 14; t += T_MONTH)
  	{
  		tm = localtime(&t);
  		if (!tm)
  			continue;
  		if (tm->tm_isdst < 0)
  			continue;
  		if (tm->tm_isdst == 0 && std_zone_name[0] == '\0')
  		{
  			/* found STD zone */
  			memset(cbuf, 0, sizeof(cbuf));
  			strftime(cbuf, sizeof(cbuf) - 1, "%Z", tm); /* zone abbr */
  			strcpy(std_zone_name, cbuf);
  			std_ofs = get_timezone_offset(tm);
  		}
  		if (tm->tm_isdst > 0 && dst_zone_name[0] == '\0')
  		{
  			/* found DST zone */
  			memset(cbuf, 0, sizeof(cbuf));
  			strftime(cbuf, sizeof(cbuf) - 1, "%Z", tm); /* zone abbr */
  			strcpy(dst_zone_name, cbuf);
  		}
  		/* Done if found both */
  		if (std_zone_name[0] && dst_zone_name[0])
  			break;
  	}
  
  	/* We should have found a STD zone name by now... */
  	if (std_zone_name[0] == '\0')
  	{
  		ereport(LOG,
  				(errmsg("could not determine system time zone, defaulting to \"%s\"", "GMT"),
  		errhint("You can specify the correct timezone in postgresql.conf.")));
  		return NULL;			/* go to GMT */
  	}
  
  	/* If we found DST then try STD<ofs>DST */
  	if (dst_zone_name[0] != '\0')
  	{
  		snprintf(resultbuf, sizeof(resultbuf), "%s%d%s",
  				 std_zone_name, -std_ofs / 3600, dst_zone_name);
  		if (score_timezone(resultbuf, &tt) > 0)
  			return resultbuf;
  	}
  
  	/* Try just the STD timezone (works for GMT at least) */
  	strcpy(resultbuf, std_zone_name);
  	if (score_timezone(resultbuf, &tt) > 0)
  		return resultbuf;
  
  	/* Try STD<ofs> */
  	snprintf(resultbuf, sizeof(resultbuf), "%s%d",
  			 std_zone_name, -std_ofs / 3600);
  	if (score_timezone(resultbuf, &tt) > 0)
  		return resultbuf;
  
  	/*
  	 * Did not find the timezone.  Fallback to use a GMT zone.	Note that the
  	 * zic timezone database names the GMT-offset zones in POSIX style: plus
  	 * is west of Greenwich.  It's unfortunate that this is opposite of SQL
  	 * conventions.  Should we therefore change the names? Probably not...
  	 */
  	snprintf(resultbuf, sizeof(resultbuf), "Etc/GMT%s%d",
  			 (-std_ofs > 0) ? "+" : "", -std_ofs / 3600);
  
  	ereport(LOG,
  		 (errmsg("could not recognize system timezone, defaulting to \"%s\"",
  				 resultbuf),
  	   errhint("You can specify the correct timezone in postgresql.conf.")));
  	return resultbuf;
  }
  
  /*
   * Recursively scan the timezone database looking for the best match to
   * the system timezone behavior.
   *
   * tzdir points to a buffer of size MAXPGPATH.	On entry, it holds the
   * pathname of a directory containing TZ files.  We internally modify it
   * to hold pathnames of sub-directories and files, but must restore it
   * to its original contents before exit.
   *
   * tzdirsub points to the part of tzdir that represents the subfile name
   * (ie, tzdir + the original directory name length, plus one for the
   * first added '/').
   *
   * tt tells about the system timezone behavior we need to match.
   *
   * *bestscore and *bestzonename on entry hold the best score found so far
   * and the name of the best zone.  We overwrite them if we find a better
   * score.  bestzonename must be a buffer of length TZ_STRLEN_MAX + 1.
   */
  static void
  scan_available_timezones(char *tzdir, char *tzdirsub, struct tztry * tt,
  						 int *bestscore, char *bestzonename)
  {
  	int			tzdir_orig_len = strlen(tzdir);
  	DIR		   *dirdesc;
  	struct dirent *direntry;
  	
  	dirdesc = AllocateDir(tzdir);
  	if (!dirdesc)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not open directory \"%s\": %m", tzdir)));
  		return;
  	}
  
  	while ((direntry = ReadDir(dirdesc, tzdir)) != NULL)
  	{
  		struct stat statbuf;
  
  		/* Ignore . and .., plus any other "hidden" files */
  		if (direntry->d_name[0] == '.')
  			continue;
  
  	    /* Odd... On snow leopard, I got back a "/" as a subdir, which causes infinite recursion */
  		if (direntry->d_name[0] == '/' && direntry->d_name[1]== '\0')
  			continue;
  
  		snprintf(tzdir + tzdir_orig_len, MAXPGPATH - tzdir_orig_len,
  				 "/%s", direntry->d_name);
  
  		if (stat(tzdir, &statbuf) != 0)
  		{
  			ereport(LOG,
  					(errcode_for_file_access(),
  					 errmsg("could not stat \"%s\": %m", tzdir)));
  			tzdir[tzdir_orig_len] = '\0';
  			continue;
  		}
  
  		if (S_ISDIR(statbuf.st_mode))
  		{
  			/* Recurse into subdirectory */
  			scan_available_timezones(tzdir, tzdirsub, tt,
  									 bestscore, bestzonename);
  		}
  		else
  		{
  			/* Load and test this file */
  			int			score = score_timezone(tzdirsub, tt);
  
  			if (score > *bestscore)
  			{
  				*bestscore = score;
  				strlcpy(bestzonename, tzdirsub, TZ_STRLEN_MAX + 1);
  			}
  			else if (score == *bestscore)
  			{
  				/* Consider how to break a tie */
  				if (strlen(tzdirsub) < strlen(bestzonename) ||
  					(strlen(tzdirsub) == strlen(bestzonename) &&
  					 strcmp(tzdirsub, bestzonename) < 0))
  					strlcpy(bestzonename, tzdirsub, TZ_STRLEN_MAX + 1);
  			}
  		}
  
  		/* Restore tzdir */
  		tzdir[tzdir_orig_len] = '\0';
  	}
  
  	FreeDir(dirdesc);
  }
  #else							/* WIN32 */
  
  static const struct
  {
  	const char *stdname;		/* Windows name of standard timezone */
  	const char *dstname;		/* Windows name of daylight timezone */
  	const char *pgtzname;		/* Name of pgsql timezone to map to */
  }	win32_tzmap[] =
  
  {
  	/*
  	 * This list was built from the contents of the registry at
  	 * HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time
  	 * Zones on Windows XP Professional SP2
  	 *
  	 * The zones have been matched to zic timezones by looking at the cities
  	 * listed in the win32 display name (in the comment here) in most cases.
  	 */
  	{
  		"Afghanistan Standard Time", "Afghanistan Daylight Time",
  		"Asia/Kabul"
  	},							/* (GMT+04:30) Kabul */
  	{
  		"Alaskan Standard Time", "Alaskan Daylight Time",
  		"US/Alaska"
  	},							/* (GMT-09:00) Alaska */
  	{
  		"Arab Standard Time", "Arab Daylight Time",
  		"Asia/Kuwait"
  	},							/* (GMT+03:00) Kuwait, Riyadh */
  	{
  		"Arabian Standard Time", "Arabian Daylight Time",
  		"Asia/Muscat"
  	},							/* (GMT+04:00) Abu Dhabi, Muscat */
  	{
  		"Arabic Standard Time", "Arabic Daylight Time",
  		"Asia/Baghdad"
  	},							/* (GMT+03:00) Baghdad */
  	{
  		"Armenian Standard Time", "Armenian Daylight Time",
  		"Asia/Yerevan"
  	},							/* (GMT+04:00) Yerevan */
  	{
  		"Atlantic Standard Time", "Atlantic Daylight Time",
  		"Canada/Atlantic"
  	},							/* (GMT-04:00) Atlantic Time (Canada) */
  	{
  		"AUS Central Standard Time", "AUS Central Daylight Time",
  		"Australia/Darwin"
  	},							/* (GMT+09:30) Darwin */
  	{
  		"AUS Eastern Standard Time", "AUS Eastern Daylight Time",
  		"Australia/Canberra"
  	},							/* (GMT+10:00) Canberra, Melbourne, Sydney */
  	{
  		"Azores Standard Time", "Azores Daylight Time",
  		"Atlantic/Azores"
  	},							/* (GMT-01:00) Azores */
  	{
  		"Canada Central Standard Time", "Canada Central Daylight Time",
  		"Canada/Saskatchewan"
  	},							/* (GMT-06:00) Saskatchewan */
  	{
  		"Cape Verde Standard Time", "Cape Verde Daylight Time",
  		"Atlantic/Cape_Verde"
  	},							/* (GMT-01:00) Cape Verde Is. */
  	{
  		"Caucasus Standard Time", "Caucasus Daylight Time",
  		"Asia/Baku"
  	},							/* (GMT+04:00) Baku, Tbilisi, Yerevan */
  	{
  		"Cen. Australia Standard Time", "Cen. Australia Daylight Time",
  		"Australia/Adelaide"
  	},							/* (GMT+09:30) Adelaide */
  	{
  		"Central America Standard Time", "Central America Daylight Time",
  		"CST6CDT"
  	},							/* (GMT-06:00) Central America */
  	{
  		"Central Asia Standard Time", "Central Asia Daylight Time",
  		"Asia/Dhaka"
  	},							/* (GMT+06:00) Astana, Dhaka */
  	{
  		"Central Europe Standard Time", "Central Europe Daylight Time",
  		"Europe/Belgrade"
  	},							/* (GMT+01:00) Belgrade, Bratislava, Budapest,
  								 * Ljubljana, Prague */
  	{
  		"Central European Standard Time", "Central European Daylight Time",
  		"Europe/Sarajevo"
  	},							/* (GMT+01:00) Sarajevo, Skopje, Warsaw,
  								 * Zagreb */
  	{
  		"Central Pacific Standard Time", "Central Pacific Daylight Time",
  		"Pacific/Noumea"
  	},							/* (GMT+11:00) Magadan, Solomon Is., New
  								 * Caledonia */
  	{
  		"Central Standard Time", "Central Daylight Time",
  		"US/Central"
  	},							/* (GMT-06:00) Central Time (US & Canada) */
  	{
  		"Central Standard Time (Mexico)", "Central Daylight Time (Mexico)",
  		"America/Mexico_City"
  	},							/* (GMT-06:00) Guadalajara, Mexico City,
  								 * Monterrey - New */
  	{
  		"China Standard Time", "China Daylight Time",
  		"Asia/Hong_Kong"
  	},							/* (GMT+08:00) Beijing, Chongqing, Hong Kong,
  								 * Urumqi */
  	{
  		"Dateline Standard Time", "Dateline Daylight Time",
  		"Etc/GMT+12"
  	},							/* (GMT-12:00) International Date Line West */
  	{
  		"E. Africa Standard Time", "E. Africa Daylight Time",
  		"Africa/Nairobi"
  	},							/* (GMT+03:00) Nairobi */
  	{
  		"E. Australia Standard Time", "E. Australia Daylight Time",
  		"Australia/Brisbane"
  	},							/* (GMT+10:00) Brisbane */
  	{
  		"E. Europe Standard Time", "E. Europe Daylight Time",
  		"Europe/Bucharest"
  	},							/* (GMT+02:00) Bucharest */
  	{
  		"E. South America Standard Time", "E. South America Daylight Time",
  		"America/Araguaina"
  	},							/* (GMT-03:00) Brasilia */
  	{
  		"Eastern Standard Time", "Eastern Daylight Time",
  		"US/Eastern"
  	},							/* (GMT-05:00) Eastern Time (US & Canada) */
  	{
  		"Egypt Standard Time", "Egypt Daylight Time",
  		"Africa/Cairo"
  	},							/* (GMT+02:00) Cairo */
  	{
  		"Ekaterinburg Standard Time", "Ekaterinburg Daylight Time",
  		"Asia/Yekaterinburg"
  	},							/* (GMT+05:00) Ekaterinburg */
  	{
  		"Fiji Standard Time", "Fiji Daylight Time",
  		"Pacific/Fiji"
  	},							/* (GMT+12:00) Fiji, Kamchatka, Marshall Is. */
  	{
  		"FLE Standard Time", "FLE Daylight Time",
  		"Europe/Helsinki"
  	},							/* (GMT+02:00) Helsinki, Kyiv, Riga, Sofia,
  								 * Tallinn, Vilnius */
  	{
  		"Georgian Standard Time", "Georgian Daylight Time",
  		"Asia/Tbilisi"
  	},							/* (GMT+03:00) Tbilisi */
  	{
  		"GMT Standard Time", "GMT Daylight Time",
  		"Europe/London"
  	},							/* (GMT) Greenwich Mean Time : Dublin,
  								 * Edinburgh, Lisbon, London */
  	{
  		"Greenland Standard Time", "Greenland Daylight Time",
  		"America/Godthab"
  	},							/* (GMT-03:00) Greenland */
  	{
  		"Greenwich Standard Time", "Greenwich Daylight Time",
  		"Africa/Casablanca"
  	},							/* (GMT) Casablanca, Monrovia */
  	{
  		"GTB Standard Time", "GTB Daylight Time",
  		"Europe/Athens"
  	},							/* (GMT+02:00) Athens, Istanbul, Minsk */
  	{
  		"Hawaiian Standard Time", "Hawaiian Daylight Time",
  		"US/Hawaii"
  	},							/* (GMT-10:00) Hawaii */
  	{
  		"India Standard Time", "India Daylight Time",
  		"Asia/Calcutta"
  	},							/* (GMT+05:30) Chennai, Kolkata, Mumbai, New
  								 * Delhi */
  	{
  		"Iran Standard Time", "Iran Daylight Time",
  		"Asia/Tehran"
  	},							/* (GMT+03:30) Tehran */
  	{
  		"Jerusalem Standard Time", "Jerusalem Daylight Time",
  		"Asia/Jerusalem"
  	},							/* (GMT+02:00) Jerusalem */
  	{
  		"Jordan Standard Time", "Jordan Daylight Time",
  		"Asia/Amman"
  	},							/* (GMT+02:00) Amman */
  	{
  		"Korea Standard Time", "Korea Daylight Time",
  		"Asia/Seoul"
  	},							/* (GMT+09:00) Seoul */
  	{
  		"Mexico Standard Time", "Mexico Daylight Time",
  		"America/Mexico_City"
  	},							/* (GMT-06:00) Guadalajara, Mexico City,
  								 * Monterrey */
  	{
  		"Mexico Standard Time 2", "Mexico Daylight Time 2",
  		"America/Chihuahua"
  	},							/* (GMT-07:00) Chihuahua, La Paz, Mazatlan */
  	{
  		"Mid-Atlantic Standard Time", "Mid-Atlantic Daylight Time",
  		"Atlantic/South_Georgia"
  	},							/* (GMT-02:00) Mid-Atlantic */
  	{
  		"Middle East Standard Time", "Middle East Daylight Time",
  		"Asia/Beirut"
  	},							/* (GMT+02:00) Beirut */
  	{
  		"Montevideo Standard Time", "Montevideo Daylight Time",
  		"America/Montevideo"
  	},							/* (GMT-03:00) Montevideo */
  	{
  		"Mountain Standard Time", "Mountain Daylight Time",
  		"US/Mountain"
  	},							/* (GMT-07:00) Mountain Time (US & Canada) */
  	{
  		"Mountain Standard Time (Mexico)", "Mountain Daylight Time (Mexico)",
  		"America/Chihuahua"
  	},							/* (GMT-07:00) Chihuahua, La Paz, Mazatlan -
  								 * New */
  	{
  		"Myanmar Standard Time", "Myanmar Daylight Time",
  		"Asia/Rangoon"
  	},							/* (GMT+06:30) Rangoon */
  	{
  		"N. Central Asia Standard Time", "N. Central Asia Daylight Time",
  		"Asia/Almaty"
  	},							/* (GMT+06:00) Almaty, Novosibirsk */
  	{
  		"Namibia Standard Time", "Namibia Daylight Time",
  		"Africa/Windhoek"
  	},							/* (GMT+02:00) Windhoek */
  	{
  		"Nepal Standard Time", "Nepal Daylight Time",
  		"Asia/Katmandu"
  	},							/* (GMT+05:45) Kathmandu */
  	{
  		"New Zealand Standard Time", "New Zealand Daylight Time",
  		"Pacific/Auckland"
  	},							/* (GMT+12:00) Auckland, Wellington */
  	{
  		"Newfoundland Standard Time", "Newfoundland Daylight Time",
  		"Canada/Newfoundland"
  	},							/* (GMT-03:30) Newfoundland */
  	{
  		"North Asia East Standard Time", "North Asia East Daylight Time",
  		"Asia/Irkutsk"
  	},							/* (GMT+08:00) Irkutsk, Ulaan Bataar */
  	{
  		"North Asia Standard Time", "North Asia Daylight Time",
  		"Asia/Krasnoyarsk"
  	},							/* (GMT+07:00) Krasnoyarsk */
  	{
  		"Pacific SA Standard Time", "Pacific SA Daylight Time",
  		"America/Santiago"
  	},							/* (GMT-04:00) Santiago */
  	{
  		"Pacific Standard Time", "Pacific Daylight Time",
  		"US/Pacific"
  	},							/* (GMT-08:00) Pacific Time (US & Canada);
  								 * Tijuana */
  	{
  		"Pacific Standard Time (Mexico)", "Pacific Daylight Time (Mexico)",
  		"America/Tijuana"
  	},							/* (GMT-08:00) Tijuana, Baja California */
  	{
  		"Romance Standard Time", "Romance Daylight Time",
  		"Europe/Brussels"
  	},							/* (GMT+01:00) Brussels, Copenhagen, Madrid,
  								 * Paris */
  	{
  		"Russian Standard Time", "Russian Daylight Time",
  		"Europe/Moscow"
  	},							/* (GMT+03:00) Moscow, St. Petersburg,
  								 * Volgograd */
  	{
  		"SA Eastern Standard Time", "SA Eastern Daylight Time",
  		"America/Buenos_Aires"
  	},							/* (GMT-03:00) Buenos Aires, Georgetown */
  	{
  		"SA Pacific Standard Time", "SA Pacific Daylight Time",
  		"America/Bogota"
  	},							/* (GMT-05:00) Bogota, Lima, Quito */
  	{
  		"SA Western Standard Time", "SA Western Daylight Time",
  		"America/Caracas"
  	},							/* (GMT-04:00) Caracas, La Paz */
  	{
  		"Samoa Standard Time", "Samoa Daylight Time",
  		"Pacific/Midway"
  	},							/* (GMT-11:00) Midway Island, Samoa */
  	{
  		"SE Asia Standard Time", "SE Asia Daylight Time",
  		"Asia/Bangkok"
  	},							/* (GMT+07:00) Bangkok, Hanoi, Jakarta */
  	{
  		"Malay Peninsula Standard Time", "Malay Peninsula Daylight Time",
  		"Asia/Kuala_Lumpur"
  	},							/* (GMT+08:00) Kuala Lumpur, Singapore */
  	{
  		"South Africa Standard Time", "South Africa Daylight Time",
  		"Africa/Harare"
  	},							/* (GMT+02:00) Harare, Pretoria */
  	{
  		"Sri Lanka Standard Time", "Sri Lanka Daylight Time",
  		"Asia/Colombo"
  	},							/* (GMT+06:00) Sri Jayawardenepura */
  	{
  		"Taipei Standard Time", "Taipei Daylight Time",
  		"Asia/Taipei"
  	},							/* (GMT+08:00) Taipei */
  	{
  		"Tasmania Standard Time", "Tasmania Daylight Time",
  		"Australia/Hobart"
  	},							/* (GMT+10:00) Hobart */
  	{
  		"Tokyo Standard Time", "Tokyo Daylight Time",
  		"Asia/Tokyo"
  	},							/* (GMT+09:00) Osaka, Sapporo, Tokyo */
  	{
  		"Tonga Standard Time", "Tonga Daylight Time",
  		"Pacific/Tongatapu"
  	},							/* (GMT+13:00) Nuku'alofa */
  	{
  		"US Eastern Standard Time", "US Eastern Daylight Time",
  		"US/Eastern"
  	},							/* (GMT-05:00) Indiana (East) */
  	{
  		"US Mountain Standard Time", "US Mountain Daylight Time",
  		"US/Arizona"
  	},							/* (GMT-07:00) Arizona */
  	{
  		"Vladivostok Standard Time", "Vladivostok Daylight Time",
  		"Asia/Vladivostok"
  	},							/* (GMT+10:00) Vladivostok */
  	{
  		"W. Australia Standard Time", "W. Australia Daylight Time",
  		"Australia/Perth"
  	},							/* (GMT+08:00) Perth */
  /*	{"W. Central Africa Standard Time", "W. Central Africa Daylight Time",
  	 *	 *	 *	 *	 *	 *	 *	 *	""}, Could not find a match for this one. Excluded for now. *//* (
  	 * G MT+01:00) West Central Africa */
  	{
  		"W. Europe Standard Time", "W. Europe Daylight Time",
  		"CET"
  	},							/* (GMT+01:00) Amsterdam, Berlin, Bern, Rome,
  								 * Stockholm, Vienna */
  	{
  		"West Asia Standard Time", "West Asia Daylight Time",
  		"Asia/Karachi"
  	},							/* (GMT+05:00) Islamabad, Karachi, Tashkent */
  	{
  		"West Pacific Standard Time", "West Pacific Daylight Time",
  		"Pacific/Guam"
  	},							/* (GMT+10:00) Guam, Port Moresby */
  	{
  		"Yakutsk Standard Time", "Yakutsk Daylight Time",
  		"Asia/Yakutsk"
  	},							/* (GMT+09:00) Yakutsk */
  	{
  		NULL, NULL, NULL
  	}
  };
  
  static const char *
  identify_system_timezone(void)
  {
  	int			i;
  	char		tzname[128];
  	char		localtzname[256];
  	time_t		t = time(NULL);
  	struct tm  *tm = localtime(&t);
  	HKEY		rootKey;
  	int			idx;
  
  	if (!tm)
  	{
  		ereport(WARNING,
  				(errmsg_internal("could not determine current date/time: localtime failed")));
  		return NULL;
  	}
  
  	memset(tzname, 0, sizeof(tzname));
  	strftime(tzname, sizeof(tzname) - 1, "%Z", tm);
  
  	for (i = 0; win32_tzmap[i].stdname != NULL; i++)
  	{
  		if (strcmp(tzname, win32_tzmap[i].stdname) == 0 ||
  			strcmp(tzname, win32_tzmap[i].dstname) == 0)
  		{
  			elog(DEBUG4, "TZ \"%s\" matches Windows timezone \"%s\"",
  				 win32_tzmap[i].pgtzname, tzname);
  			return win32_tzmap[i].pgtzname;
  		}
  	}
  
  	/*
  	 * Localized Windows versions return localized names for the timezone.
  	 * Scan the registry to find the English name, and then try matching
  	 * against our table again.
  	 */
  	memset(localtzname, 0, sizeof(localtzname));
  	if (RegOpenKeyEx(HKEY_LOCAL_MACHINE,
  			   "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones",
  					 0,
  					 KEY_READ,
  					 &rootKey) != ERROR_SUCCESS)
  	{
  		ereport(WARNING,
  				(errmsg_internal("could not open registry key to identify Windows timezone: %i", (int) GetLastError())));
  		return NULL;
  	}
  
  	for (idx = 0;; idx++)
  	{
  		char		keyname[256];
  		char		zonename[256];
  		DWORD		namesize;
  		FILETIME	lastwrite;
  		HKEY		key;
  		LONG		r;
  
  		memset(keyname, 0, sizeof(keyname));
  		namesize = sizeof(keyname);
  		if ((r = RegEnumKeyEx(rootKey,
  							  idx,
  							  keyname,
  							  &namesize,
  							  NULL,
  							  NULL,
  							  NULL,
  							  &lastwrite)) != ERROR_SUCCESS)
  		{
  			if (r == ERROR_NO_MORE_ITEMS)
  				break;
  			ereport(WARNING,
  					(errmsg_internal("could not enumerate registry subkeys to identify Windows timezone: %i", (int) r)));
  			break;
  		}
  
  		if ((r = RegOpenKeyEx(rootKey, keyname, 0, KEY_READ, &key)) != ERROR_SUCCESS)
  		{
  			ereport(WARNING,
  					(errmsg_internal("could not open registry subkey to identify Windows timezone: %i", (int) r)));
  			break;
  		}
  
  		memset(zonename, 0, sizeof(zonename));
  		namesize = sizeof(zonename);
  		if ((r = RegQueryValueEx(key, "Std", NULL, NULL, zonename, &namesize)) != ERROR_SUCCESS)
  		{
  			ereport(WARNING,
  					(errmsg_internal("could not query value for 'std' to identify Windows timezone: %i", (int) r)));
  			RegCloseKey(key);
  			break;
  		}
  		if (strcmp(tzname, zonename) == 0)
  		{
  			/* Matched zone */
  			strcpy(localtzname, keyname);
  			RegCloseKey(key);
  			break;
  		}
  		memset(zonename, 0, sizeof(zonename));
  		namesize = sizeof(zonename);
  		if ((r = RegQueryValueEx(key, "Dlt", NULL, NULL, zonename, &namesize)) != ERROR_SUCCESS)
  		{
  			ereport(WARNING,
  					(errmsg_internal("could not query value for 'dlt' to identify Windows timezone: %i", (int) r)));
  			RegCloseKey(key);
  			break;
  		}
  		if (strcmp(tzname, zonename) == 0)
  		{
  			/* Matched DST zone */
  			strcpy(localtzname, keyname);
  			RegCloseKey(key);
  			break;
  		}
  
  		RegCloseKey(key);
  	}
  
  	RegCloseKey(rootKey);
  
  	if (localtzname[0])
  	{
  		/* Found a localized name, so scan for that one too */
  		for (i = 0; win32_tzmap[i].stdname != NULL; i++)
  		{
  			if (strcmp(localtzname, win32_tzmap[i].stdname) == 0 ||
  				strcmp(localtzname, win32_tzmap[i].dstname) == 0)
  			{
  				elog(DEBUG4, "TZ \"%s\" matches localized Windows timezone \"%s\" (\"%s\")",
  					 win32_tzmap[i].pgtzname, tzname, localtzname);
  				return win32_tzmap[i].pgtzname;
  			}
  		}
  	}
  
  	ereport(WARNING,
  			(errmsg("could not find a match for Windows timezone \"%s\"",
  					tzname)));
  	return NULL;
  }
  #endif   /* WIN32 */
  
  
  
  /*
   * We keep loaded timezones in a hashtable so we don't have to
   * load and parse the TZ definition file every time one is selected.
   * Because we want timezone names to be found case-insensitively,
   * the hash key is the uppercased name of the zone.
   */
  typedef struct
  {
  	/* tznameupper contains the all-upper-case name of the timezone */
  	char		tznameupper[TZ_STRLEN_MAX + 1];
  	pg_tz		tz;
  } pg_tz_cache;
  
  static HTAB *timezone_cache = NULL;
  
  
  static bool
  init_timezone_hashtable(void)
  {
  	HASHCTL		hash_ctl;
  
  	MemSet(&hash_ctl, 0, sizeof(hash_ctl));
  
  	hash_ctl.keysize = TZ_STRLEN_MAX + 1;
  	hash_ctl.entrysize = sizeof(pg_tz_cache);
  
  	timezone_cache = hash_create("Timezones",
  								 4,
  								 &hash_ctl,
  								 HASH_ELEM);
  	if (!timezone_cache)
  		return false;
  
  	return true;
  }
  
  /*
   * Load a timezone from file or from cache.
   * Does not verify that the timezone is acceptable!
   */
  struct pg_tz *
  pg_tzset(const char *name)
  {
  	pg_tz_cache *tzp;
  	struct state tzstate;
  	char		uppername[TZ_STRLEN_MAX + 1];
  	char		canonname[TZ_STRLEN_MAX + 1];
  	char	   *p;
  
  	if (strlen(name) > TZ_STRLEN_MAX)
  		return NULL;			/* not going to fit */
  
  	if (!timezone_cache)
  		if (!init_timezone_hashtable())
  			return NULL;
  
  	/*
  	 * Upcase the given name to perform a case-insensitive hashtable search.
  	 * (We could alternatively downcase it, but we prefer upcase so that we
  	 * can get consistently upcased results from tzparse() in case the name is
  	 * a POSIX-style timezone spec.)
  	 */
  	p = uppername;
  	while (*name)
  		*p++ = pg_toupper((unsigned char) *name++);
  	*p = '\0';
  
  	tzp = (pg_tz_cache *) hash_search(timezone_cache,
  									  uppername,
  									  HASH_FIND,
  									  NULL);
  	if (tzp)
  	{
  		/* Timezone found in cache, nothing more to do */
  		return &tzp->tz;
  	}
  
  	if (tzload(uppername, canonname, &tzstate, TRUE) != 0)
  	{
  		if (uppername[0] == ':' || tzparse(uppername, &tzstate, FALSE) != 0)
  		{
  			/* Unknown timezone. Fail our call instead of loading GMT! */
  			return NULL;
  		}
  		/* For POSIX timezone specs, use uppercase name as canonical */
  		strcpy(canonname, uppername);
  	}
  
  	/* Save timezone in the cache */
  	tzp = (pg_tz_cache *) hash_search(timezone_cache,
  									  uppername,
  									  HASH_ENTER,
  									  NULL);
  
  	/* hash_search already copied uppername into the hash key */
  	strcpy(tzp->tz.TZname, canonname);
  	memcpy(&tzp->tz.state, &tzstate, sizeof(tzstate));
  
  	return &tzp->tz;
  }
  
  
  /*
   * Check whether timezone is acceptable.
   *
   * What we are doing here is checking for leap-second-aware timekeeping.
   * We need to reject such TZ settings because they'll wreak havoc with our
   * date/time arithmetic.
   *
   * NB: this must NOT ereport(ERROR).  The caller must get control back so that
   * it can restore the old value of TZ if we don't like the new one.
   */
  bool
  tz_acceptable(pg_tz *tz)
  {
  	struct pg_tm *tt;
  	pg_time_t	time2000;
  
  	/*
  	 * To detect leap-second timekeeping, run pg_localtime for what should be
  	 * GMT midnight, 2000-01-01.  Insist that the tm_sec value be zero; any
  	 * other result has to be due to leap seconds.
  	 */
  	time2000 = (POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY;
  	tt = pg_localtime(&time2000, tz);
  	if (!tt || tt->tm_sec != 0)
  		return false;
  
  	return true;
  }
  
  
  /*
   * Get a pg_tz struct for the given timezone name.	Returns NULL if name
   * is invalid or not an "acceptable" zone.
   */
  static pg_tz *
  get_pg_tz_for_zone(const char *tzname)
  {
  	pg_tz	   *tz;
  
  	if (!tzname || !tzname[0])
  		return NULL;
  
  	tz = pg_tzset(tzname);
  	if (!tz)
  		return NULL;
  
  	if (!tz_acceptable(tz))
  		return NULL;
  
  	return tz;
  }
  
  /*
   * Identify a suitable default timezone setting based on the environment.
   *
   * We first look to the TZ environment variable.  If not found or not
   * recognized by our own code, we see if we can identify the timezone
   * from the behavior of the system timezone library.  When all else fails,
   * fall back to GMT.
   */
  static pg_tz *
  select_default_timezone(void)
  {
  	pg_tz	   *def_tz;
  
  	def_tz = get_pg_tz_for_zone(getenv("TZ"));
  	if (def_tz)
  		return def_tz;
  
  	def_tz = get_pg_tz_for_zone(identify_system_timezone());
  	if (def_tz)
  		return def_tz;
  
  	def_tz = get_pg_tz_for_zone("GMT");
  	if (def_tz)
  		return def_tz;
  
  	ereport(FATAL,
  			(errmsg("could not select a suitable default timezone"),
  			 errdetail("It appears that your GMT time zone uses leap seconds. PostgreSQL does not support leap seconds.")));
  	return NULL;				/* keep compiler quiet */
  }
  
  
  /*
   * Pre-initialize timezone library
   *
   * This is called before GUC variable initialization begins.  Its purpose
   * is to ensure that elog.c has a pgtz variable available to format timestamps
   * with, in case log_line_prefix is set to a value requiring that.	We cannot
   * set log_timezone yet.
   */
  void
  pg_timezone_pre_initialize(void)
  {
  	/*
  	 * We can't use tzload() because we may not know where PGSHAREDIR is (in
  	 * particular this is true in an EXEC_BACKEND subprocess). Since this
  	 * timezone variable will only be used for emergency fallback purposes, it
  	 * seems OK to just use the "lastditch" case provided by tzparse().
  	 */
  	if (tzparse("GMT", &gmt_timezone_data.state, TRUE) != 0)
  		elog(FATAL, "could not initialize GMT timezone");
  	strcpy(gmt_timezone_data.TZname, "GMT");
  	gmt_timezone = &gmt_timezone_data;
  }
  
  /*
   * Initialize timezone library
   *
   * This is called after initial loading of postgresql.conf.  If no TimeZone
   * setting was found therein, we try to derive one from the environment.
   * Likewise for log_timezone.
   */
  void
  pg_timezone_initialize(void)
  {
  	pg_tz	   *def_tz = NULL;
  
  	/* Do we need to try to figure the session timezone? */
  	if (pg_strcasecmp(GetConfigOption("timezone"), "UNKNOWN") == 0)
  	{
  		/* Select setting */
  		def_tz = select_default_timezone();
  		session_timezone = def_tz;
  		/* Tell GUC about the value. Will redundantly call pg_tzset() */
  		SetConfigOption("timezone", pg_get_timezone_name(def_tz),
  						PGC_POSTMASTER, PGC_S_ARGV);
  	}
  
  	/* What about the log timezone? */
  	if (pg_strcasecmp(GetConfigOption("log_timezone"), "UNKNOWN") == 0)
  	{
  		/* Select setting, but don't duplicate work */
  		if (!def_tz)
  			def_tz = select_default_timezone();
  		log_timezone = def_tz;
  		/* Tell GUC about the value. Will redundantly call pg_tzset() */
  		SetConfigOption("log_timezone", pg_get_timezone_name(def_tz),
  						PGC_POSTMASTER, PGC_S_ARGV);
  	}
  }
  
  
  /*
   * Functions to enumerate available timezones
   *
   * Note that pg_tzenumerate_next() will return a pointer into the pg_tzenum
   * structure, so the data is only valid up to the next call.
   *
   * All data is allocated using palloc in the current context.
   */
  #define MAX_TZDIR_DEPTH 10
  
  struct pg_tzenum
  {
  	int			baselen;
  	int			depth;
  	DIR		   *dirdesc[MAX_TZDIR_DEPTH];
  	char	   *dirname[MAX_TZDIR_DEPTH];
  	struct pg_tz tz;
  };
  
  /* typedef pg_tzenum is declared in pgtime.h */
  
  pg_tzenum *
  pg_tzenumerate_start(void)
  {
  	pg_tzenum  *ret = (pg_tzenum *) palloc0(sizeof(pg_tzenum));
  	char	   *startdir = pstrdup(pg_TZDIR());
  
  	ret->baselen = strlen(startdir) + 1;
  	ret->depth = 0;
  	ret->dirname[0] = startdir;
  	ret->dirdesc[0] = AllocateDir(startdir);
  	if (!ret->dirdesc[0])
  		ereport(ERROR,
  				(errcode_for_file_access(),
  				 errmsg("could not open directory \"%s\": %m", startdir)));
  	return ret;
  }
  
  void
  pg_tzenumerate_end(pg_tzenum *dir)
  {
  	while (dir->depth >= 0)
  	{
  		FreeDir(dir->dirdesc[dir->depth]);
  		pfree(dir->dirname[dir->depth]);
  		dir->depth--;
  	}
  	pfree(dir);
  }
  
  pg_tz *
  pg_tzenumerate_next(pg_tzenum *dir)
  {
  	while (dir->depth >= 0)
  	{
  		struct dirent *direntry;
  		char		fullname[MAXPGPATH];
  		struct stat statbuf;
  
  		direntry = ReadDir(dir->dirdesc[dir->depth], dir->dirname[dir->depth]);
  
  		if (!direntry)
  		{
  			/* End of this directory */
  			FreeDir(dir->dirdesc[dir->depth]);
  			pfree(dir->dirname[dir->depth]);
  			dir->depth--;
  			continue;
  		}
  
  		if (direntry->d_name[0] == '.')
  			continue;
  
  		snprintf(fullname, MAXPGPATH, "%s/%s",
  				 dir->dirname[dir->depth], direntry->d_name);
  		if (stat(fullname, &statbuf) != 0)
  			ereport(ERROR,
  					(errcode_for_file_access(),
  					 errmsg("could not stat \"%s\": %m", fullname)));
  
  		if (S_ISDIR(statbuf.st_mode))
  		{
  			/* Step into the subdirectory */
  			if (dir->depth >= MAX_TZDIR_DEPTH - 1)
  				ereport(ERROR,
  						(errmsg("timezone directory stack overflow")));
  			dir->depth++;
  			dir->dirname[dir->depth] = pstrdup(fullname);
  			dir->dirdesc[dir->depth] = AllocateDir(fullname);
  			if (!dir->dirdesc[dir->depth])
  				ereport(ERROR,
  						(errcode_for_file_access(),
  						 errmsg("could not open directory \"%s\": %m",
  								fullname)));
  
  			/* Start over reading in the new directory */
  			continue;
  		}
  
  		/*
  		 * Load this timezone using tzload() not pg_tzset(), so we don't fill
  		 * the cache
  		 */
  		if (tzload(fullname + dir->baselen, dir->tz.TZname, &dir->tz.state,
  				   TRUE) != 0)
  		{
  			/* Zone could not be loaded, ignore it */
  			continue;
  		}
  
  		if (!tz_acceptable(&dir->tz))
  		{
  			/* Ignore leap-second zones */
  			continue;
  		}
  
  		/* Timezone loaded OK. */
  		return &dir->tz;
  	}
  
  	/* Nothing more found */
  	return NULL;
  }
  