Consistently use "superuser" instead of "super user"

[pgsql.git] / src / bin / initdb / findtimezone.c

/*-------------------------------------------------------------------------
 *
 * findtimezone.c
 *        Functions for determining the default timezone to use.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        src/bin/initdb/findtimezone.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"

#include <fcntl.h>
#include <sys/stat.h>
#include <time.h>
#include <unistd.h>

#include "pgtz.h"

/* Ideally this would be in a .h file, but it hardly seems worth the trouble */
extern const char *select_default_timezone(const char *share_path);


#ifndef SYSTEMTZDIR
static char tzdirpath[MAXPGPATH];
#endif


/*
 * Return full pathname of timezone data directory
 *
 * In this file, tzdirpath is assumed to be set up by select_default_timezone.
 */
static const char *
pg_TZDIR(void)
{
#ifndef SYSTEMTZDIR
        /* normal case: timezone stuff is under our share dir */
        return tzdirpath;
#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.
 *
 * This is simpler than the backend function of the same name because
 * we assume that the input string has the correct case already, so there
 * is no need for case-folding.  (This is obviously true if we got the file
 * name from the filesystem to start with.  The only other place it can come
 * from is the environment variable TZ, and there seems no need to allow
 * case variation in that; other programs aren't likely to.)
 *
 * If "canonname" is not NULL, then on success the canonical spelling of the
 * given name is stored there (the buffer must be > TZ_STRLEN_MAX bytes!).
 * This is redundant but kept for compatibility with the backend code.
 */
int
pg_open_tzfile(const char *name, char *canonname)
{
        char            fullname[MAXPGPATH];

        if (canonname)
                strlcpy(canonname, name, TZ_STRLEN_MAX + 1);

        strlcpy(fullname, pg_TZDIR(), sizeof(fullname));
        if (strlen(fullname) + 1 + strlen(name) >= MAXPGPATH)
                return -1;                              /* not gonna fit */
        strcat(fullname, "/");
        strcat(fullname, name);

        return open(fullname, O_RDONLY | PG_BINARY, 0);
}



/*
 * Load a timezone definition.
 * Does not verify that the timezone is acceptable!
 *
 * This corresponds to the backend's pg_tzset(), except that we only support
 * one loaded timezone at a time.
 */
static pg_tz *
pg_load_tz(const char *name)
{
        static pg_tz tz;

        if (strlen(name) > TZ_STRLEN_MAX)
                return NULL;                    /* not going to fit */

        /*
         * "GMT" is always sent to tzparse(); see comments for pg_tzset().
         */
        if (strcmp(name, "GMT") == 0)
        {
                if (!tzparse(name, &tz.state, true))
                {
                        /* This really, really should not happen ... */
                        return NULL;
                }
        }
        else if (tzload(name, NULL, &tz.state, true) != 0)
        {
                if (name[0] == ':' || !tzparse(name, &tz.state, false))
                {
                        return NULL;            /* unknown timezone */
                }
        }

        strcpy(tz.TZname, name);

        return &tz;
}


/*
 * 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 IANA database assigns multiple
 * names to many zones).  We break ties by first checking for "preferred"
 * names (such as "UTC"), and then arbitrarily by preferring shorter, then
 * alphabetically earlier zone names.  (If we did not explicitly prefer
 * "UTC", we would get the alias name "UCT" instead due to alphabetic
 * ordering.)
 *
 * Many modern systems use the IANA database, so if we can determine the
 * system's idea of which zone it is using and its behavior matches our zone
 * of the same name, we can skip the rather-expensive search through all the
 * zones in our database.  This short-circuit path also ensures that we spell
 * the zone name the same way the system setting does, even in the presence
 * of multiple aliases for the same zone.
 *
 * Win32's native knowledge about timezones appears to be too incomplete
 * and too different from the IANA 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 bool check_system_link_file(const char *linkname, struct tztry *tt,
                                                                   char *bestzonename);
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;
        tm.tm_isdst = -1;

        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 definition */
        tz = pg_load_tz(tzname);
        if (!tz)
                return -1;                              /* unrecognized zone name */

        /* Reject if leap seconds involved */
        if (!pg_tz_acceptable(tz))
        {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                fprintf(stderr, "Reject TZ \"%s\": uses leap seconds\n", tzname);
#endif
                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)
                {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                        fprintf(stderr, "TZ \"%s\" scores %d: at %ld %04d-%02d-%02d %02d:%02d:%02d %s, system had no data\n",
                                        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");
#endif
                        return i;
                }
                if (!compare_tm(systm, pgtm))
                {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                        fprintf(stderr, "TZ \"%s\" scores %d: at %ld %04d-%02d-%02d %02d:%02d:%02d %s versus %04d-%02d-%02d %02d:%02d:%02d %s\n",
                                        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");
#endif
                        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)
                        {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                                fprintf(stderr, "TZ \"%s\" scores %d: at %ld \"%s\" versus \"%s\"\n",
                                                tzname, i, (long) pgtt,
                                                pgtm->tm_zone, cbuf);
#endif
                                return i;
                        }
                }
        }

#ifdef DEBUG_IDENTIFY_TIMEZONE
        fprintf(stderr, "TZ \"%s\" gets max score %d\n", tzname, i);
#endif

        return i;
}

/*
 * Test whether given zone name is a perfect match to localtime() behavior
 */
static bool
perfect_timezone_match(const char *tzname, struct tztry *tt)
{
        return (score_timezone(tzname, tt) == tt->n_test_times);
}


/*
 * Try to identify a timezone name (in our terminology) that best matches the
 * observed behavior of the system localtime() function.
 */
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 IANA
         * 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;
        }

        /*
         * Try to avoid the brute-force search by seeing if we can recognize the
         * system's timezone setting directly.
         *
         * Currently we just check /etc/localtime; there are other conventions for
         * this, but that seems to be the only one used on enough platforms to be
         * worth troubling over.
         */
        if (check_system_link_file("/etc/localtime", &tt, resultbuf))
                return resultbuf;

        /* No luck, so 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 IANA's rather silly "Factory" 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')
        {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                fprintf(stderr, "could not determine system time zone\n");
#endif
                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
         * IANA 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);

#ifdef DEBUG_IDENTIFY_TIMEZONE
        fprintf(stderr, "could not recognize system time zone, using \"%s\"\n",
                        resultbuf);
#endif
        return resultbuf;
}

/*
 * Examine a system-provided symlink file to see if it tells us the timezone.
 *
 * Unfortunately, there is little standardization of how the system default
 * timezone is determined in the absence of a TZ environment setting.
 * But a common strategy is to create a symlink at a well-known place.
 * If "linkname" identifies a readable symlink, and the tail of its contents
 * matches a zone name we know, and the actual behavior of localtime() agrees
 * with what we think that zone means, then we may use that zone name.
 *
 * We insist on a perfect behavioral match, which might not happen if the
 * system has a different IANA database version than we do; but in that case
 * it seems best to fall back to the brute-force search.
 *
 * linkname is the symlink file location to probe.
 *
 * tt tells about the system timezone behavior we need to match.
 *
 * If we successfully identify a zone name, store it in *bestzonename and
 * return true; else return false.  bestzonename must be a buffer of length
 * TZ_STRLEN_MAX + 1.
 */
static bool
check_system_link_file(const char *linkname, struct tztry *tt,
                                           char *bestzonename)
{
#ifdef HAVE_READLINK
        char            link_target[MAXPGPATH];
        int                     len;
        const char *cur_name;

        /*
         * Try to read the symlink.  If not there, not a symlink, etc etc, just
         * quietly fail; the precise reason needn't concern us.
         */
        len = readlink(linkname, link_target, sizeof(link_target));
        if (len < 0 || len >= sizeof(link_target))
                return false;
        link_target[len] = '\0';

#ifdef DEBUG_IDENTIFY_TIMEZONE
        fprintf(stderr, "symbolic link \"%s\" contains \"%s\"\n",
                        linkname, link_target);
#endif

        /*
         * The symlink is probably of the form "/path/to/zones/zone/name", or
         * possibly it is a relative path.  Nobody puts their zone DB directly in
         * the root directory, so we can definitely skip the first component; but
         * after that it's trial-and-error to identify which path component begins
         * the zone name.
         */
        cur_name = link_target;
        while (*cur_name)
        {
                /* Advance to next segment of path */
                cur_name = strchr(cur_name + 1, '/');
                if (cur_name == NULL)
                        break;
                /* If there are consecutive slashes, skip all, as the kernel would */
                do
                {
                        cur_name++;
                } while (*cur_name == '/');

                /*
                 * Test remainder of path to see if it is a matching zone name.
                 * Relative paths might contain ".."; we needn't bother testing if the
                 * first component is that.  Also defend against overlength names.
                 */
                if (*cur_name && *cur_name != '.' &&
                        strlen(cur_name) <= TZ_STRLEN_MAX &&
                        perfect_timezone_match(cur_name, tt))
                {
                        /* Success! */
                        strcpy(bestzonename, cur_name);
                        return true;
                }
        }

        /* Couldn't extract a matching zone name */
        return false;
#else
        /* No symlinks?  Forget it */
        return false;
#endif
}

/*
 * Given a timezone name, determine whether it should be preferred over other
 * names which are equally good matches. The output is arbitrary but we will
 * use 0 for "neutral" default preference; larger values are more preferred.
 */
static int
zone_name_pref(const char *zonename)
{
        /*
         * Prefer UTC over alternatives such as UCT.  Also prefer Etc/UTC over
         * Etc/UCT; but UTC is preferred to Etc/UTC.
         */
        if (strcmp(zonename, "UTC") == 0)
                return 50;
        if (strcmp(zonename, "Etc/UTC") == 0)
                return 40;

        /*
         * We don't want to pick "localtime" or "posixrules", unless we can find
         * no other name for the prevailing zone.  Those aren't real zone names.
         */
        if (strcmp(zonename, "localtime") == 0 ||
                strcmp(zonename, "posixrules") == 0)
                return -50;

        return 0;
}

/*
 * 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);
        char      **names;
        char      **namep;

        names = pgfnames(tzdir);
        if (!names)
                return;

        for (namep = names; *namep; namep++)
        {
                char       *name = *namep;
                struct stat statbuf;

                /* Ignore . and .., plus any other "hidden" files */
                if (name[0] == '.')
                        continue;

                snprintf(tzdir + tzdir_orig_len, MAXPGPATH - tzdir_orig_len,
                                 "/%s", name);

                if (stat(tzdir, &statbuf) != 0)
                {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                        fprintf(stderr, "could not stat \"%s\": %s\n",
                                        tzdir, strerror(errno));
#endif
                        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 */
                                int                     namepref = (zone_name_pref(tzdirsub) -
                                                                                zone_name_pref(bestzonename));

                                if (namepref > 0 ||
                                        (namepref == 0 &&
                                         (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';
        }

        pgfnames_cleanup(names);
}
#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 7, Windows 10, and Windows Server 2019.
         *
         * The zones have been matched to IANA timezones by looking at the cities
         * listed in the win32 display name (in the comment here) in most cases.
         */
        {
                /* (UTC+04:30) Kabul */
                "Afghanistan Standard Time", "Afghanistan Daylight Time",
                "Asia/Kabul"
        },
        {
                /* (UTC-09:00) Alaska */
                "Alaskan Standard Time", "Alaskan Daylight Time",
                "US/Alaska"
        },
        {
                /* (UTC-10:00) Aleutian Islands */
                "Aleutian Standard Time", "Aleutian Daylight Time",
                "US/Aleutan"
        },
        {
                /* (UTC+07:00) Barnaul, Gorno-Altaysk */
                "Altai Standard Time", "Altai Daylight Time",
                "Asia/Barnaul"
        },
        {
                /* (UTC+03:00) Kuwait, Riyadh */
                "Arab Standard Time", "Arab Daylight Time",
                "Asia/Kuwait"
        },
        {
                /* (UTC+04:00) Abu Dhabi, Muscat */
                "Arabian Standard Time", "Arabian Daylight Time",
                "Asia/Muscat"
        },
        {
                /* (UTC+03:00) Baghdad */
                "Arabic Standard Time", "Arabic Daylight Time",
                "Asia/Baghdad"
        },
        {
                /* (UTC-03:00) City of Buenos Aires */
                "Argentina Standard Time", "Argentina Daylight Time",
                "America/Buenos_Aires"
        },
        {
                /* (UTC+04:00) Baku, Tbilisi, Yerevan */
                "Armenian Standard Time", "Armenian Daylight Time",
                "Asia/Yerevan"
        },
        {
                /* (UTC+04:00) Astrakhan, Ulyanovsk */
                "Astrakhan Standard Time", "Astrakhan Daylight Time",
                "Europe/Astrakhan"
        },
        {
                /* (UTC-04:00) Atlantic Time (Canada) */
                "Atlantic Standard Time", "Atlantic Daylight Time",
                "Canada/Atlantic"
        },
        {
                /* (UTC+09:30) Darwin */
                "AUS Central Standard Time", "AUS Central Daylight Time",
                "Australia/Darwin"
        },
        {
                /* (UTC+08:45) Eucla */
                "Aus Central W. Standard Time", "Aus Central W. Daylight Time",
                "Australia/Eucla"
        },
        {
                /* (UTC+10:00) Canberra, Melbourne, Sydney */
                "AUS Eastern Standard Time", "AUS Eastern Daylight Time",
                "Australia/Canberra"
        },
        {
                /* (UTC+04:00) Baku */
                "Azerbaijan Standard Time", "Azerbaijan Daylight Time",
                "Asia/Baku"
        },
        {
                /* (UTC-01:00) Azores */
                "Azores Standard Time", "Azores Daylight Time",
                "Atlantic/Azores"
        },
        {
                /* (UTC-03:00) Salvador */
                "Bahia Standard Time", "Bahia Daylight Time",
                "America/Salvador"
        },
        {
                /* (UTC+06:00) Dhaka */
                "Bangladesh Standard Time", "Bangladesh Daylight Time",
                "Asia/Dhaka"
        },
        {
                /* (UTC+11:00) Bougainville Island */
                "Bougainville Standard Time", "Bougainville Daylight Time",
                "Pacific/Bougainville"
        },
        {
                /* (UTC+03:00) Minsk */
                "Belarus Standard Time", "Belarus Daylight Time",
                "Europe/Minsk"
        },
        {
                /* (UTC-01:00) Cabo Verde Is. */
                "Cabo Verde Standard Time", "Cabo Verde Daylight Time",
                "Atlantic/Cape_Verde"
        },
        {
                /* (UTC+12:45) Chatham Islands */
                "Chatham Islands Standard Time", "Chatham Islands Daylight Time",
                "Pacific/Chatham"
        },
        {
                /* (UTC-06:00) Saskatchewan */
                "Canada Central Standard Time", "Canada Central Daylight Time",
                "Canada/Saskatchewan"
        },
        {
                /* (UTC-01:00) Cape Verde Is. */
                "Cape Verde Standard Time", "Cape Verde Daylight Time",
                "Atlantic/Cape_Verde"
        },
        {
                /* (UTC+04:00) Yerevan */
                "Caucasus Standard Time", "Caucasus Daylight Time",
                "Asia/Baku"
        },
        {
                /* (UTC+09:30) Adelaide */
                "Cen. Australia Standard Time", "Cen. Australia Daylight Time",
                "Australia/Adelaide"
        },
        /* Central America (other than Mexico) generally does not observe DST */
        {
                /* (UTC-06:00) Central America */
                "Central America Standard Time", "Central America Daylight Time",
                "CST6"
        },
        {
                /* (UTC+06:00) Astana */
                "Central Asia Standard Time", "Central Asia Daylight Time",
                "Asia/Dhaka"
        },
        {
                /* (UTC-04:00) Cuiaba */
                "Central Brazilian Standard Time", "Central Brazilian Daylight Time",
                "America/Cuiaba"
        },
        {
                /* (UTC+01:00) Belgrade, Bratislava, Budapest, Ljubljana, Prague */
                "Central Europe Standard Time", "Central Europe Daylight Time",
                "Europe/Belgrade"
        },
        {
                /* (UTC+01:00) Sarajevo, Skopje, Warsaw, Zagreb */
                "Central European Standard Time", "Central European Daylight Time",
                "Europe/Sarajevo"
        },
        {
                /* (UTC+11:00) Solomon Is., New Caledonia */
                "Central Pacific Standard Time", "Central Pacific Daylight Time",
                "Pacific/Noumea"
        },
        {
                /* (UTC-06:00) Central Time (US & Canada) */
                "Central Standard Time", "Central Daylight Time",
                "US/Central"
        },
        {
                /* (UTC-06:00) Guadalajara, Mexico City, Monterrey */
                "Central Standard Time (Mexico)", "Central Daylight Time (Mexico)",
                "America/Mexico_City"
        },
        {
                /* (UTC+08:00) Beijing, Chongqing, Hong Kong, Urumqi */
                "China Standard Time", "China Daylight Time",
                "Asia/Hong_Kong"
        },
        {
                /* (UTC-05:00) Havana */
                "Cuba Standard Time", "Cuba Daylight Time",
                "America/Havana"
        },
        {
                /* (UTC-12:00) International Date Line West */
                "Dateline Standard Time", "Dateline Daylight Time",
                "Etc/UTC+12"
        },
        {
                /* (UTC+03:00) Nairobi */
                "E. Africa Standard Time", "E. Africa Daylight Time",
                "Africa/Nairobi"
        },
        {
                /* (UTC+10:00) Brisbane */
                "E. Australia Standard Time", "E. Australia Daylight Time",
                "Australia/Brisbane"
        },
        {
                /* (UTC+02:00) Chisinau */
                "E. Europe Standard Time", "E. Europe Daylight Time",
                "Europe/Bucharest"
        },
        {
                /* (UTC-03:00) Brasilia */
                "E. South America Standard Time", "E. South America Daylight Time",
                "America/Araguaina"
        },
        {
                /* (UTC-05:00) Eastern Time (US & Canada) */
                "Eastern Standard Time", "Eastern Daylight Time",
                "US/Eastern"
        },
        {
                /* (UTC-05:00) Chetumal */
                "Eastern Standard Time (Mexico)", "Eastern Daylight Time (Mexico)",
                "America/Mexico_City"
        },
        {
                /* (UTC-06:00) Easter Island */
                "Easter Island Standard Time", "Easter Island Daylight Time",
                "Pacific/Easter"
        },
        {
                /* (UTC+02:00) Cairo */
                "Egypt Standard Time", "Egypt Daylight Time",
                "Africa/Cairo"
        },
        {
                /* (UTC+05:00) Ekaterinburg */
                "Ekaterinburg Standard Time (RTZ 4)", "Ekaterinburg Daylight Time",
                "Asia/Yekaterinburg"
        },
        {
                /* (UTC+12:00) Fiji */
                "Fiji Standard Time", "Fiji Daylight Time",
                "Pacific/Fiji"
        },
        {
                /* (UTC+02:00) Helsinki, Kyiv, Riga, Sofia, Tallinn, Vilnius */
                "FLE Standard Time", "FLE Daylight Time",
                "Europe/Helsinki"
        },
        {
                /* (UTC+04:00) Tbilisi */
                "Georgian Standard Time", "Georgian Daylight Time",
                "Asia/Tbilisi"
        },
        {
                /* (UTC+00:00) Dublin, Edinburgh, Lisbon, London */
                "GMT Standard Time", "GMT Daylight Time",
                "Europe/London"
        },
        {
                /* (UTC-03:00) Greenland */
                "Greenland Standard Time", "Greenland Daylight Time",
                "America/Godthab"
        },
        {
                /* (UTC+00:00) Monrovia, Reykjavik */
                "Greenwich Standard Time", "Greenwich Daylight Time",
                "Africa/Casablanca"
        },
        {
                /* (UTC+02:00) Athens, Bucharest */
                "GTB Standard Time", "GTB Daylight Time",
                "Europe/Athens"
        },
        {
                /* (UTC-05:00) Haiti */
                "Haiti Standard Time", "Haiti Daylight Time",
                "US/Eastern"
        },
        {
                /* (UTC-10:00) Hawaii */
                "Hawaiian Standard Time", "Hawaiian Daylight Time",
                "US/Hawaii"
        },
        {
                /* (UTC+05:30) Chennai, Kolkata, Mumbai, New Delhi */
                "India Standard Time", "India Daylight Time",
                "Asia/Calcutta"
        },
        {
                /* (UTC+03:30) Tehran */
                "Iran Standard Time", "Iran Daylight Time",
                "Asia/Tehran"
        },
        {
                /* (UTC+02:00) Jerusalem */
                "Jerusalem Standard Time", "Jerusalem Daylight Time",
                "Asia/Jerusalem"
        },
        {
                /* (UTC+02:00) Amman */
                "Jordan Standard Time", "Jordan Daylight Time",
                "Asia/Amman"
        },
        {
                /* (UTC+12:00) Petropavlovsk-Kamchatsky - Old */
                "Kamchatka Standard Time", "Kamchatka Daylight Time",
                "Asia/Kamchatka"
        },
        {
                /* (UTC+09:00) Seoul */
                "Korea Standard Time", "Korea Daylight Time",
                "Asia/Seoul"
        },
        {
                /* (UTC+02:00) Tripoli */
                "Libya Standard Time", "Libya Daylight Time",
                "Africa/Tripoli"
        },
        {
                /* (UTC+14:00) Kiritimati Island */
                "Line Islands Standard Time", "Line Islands Daylight Time",
                "Pacific/Kiritimati"
        },
        {
                /* (UTC+10:30) Lord Howe Island */
                "Lord Howe Standard Time", "Lord Howe Daylight Time",
                "Australia/Lord_Howe"
        },
        {
                /* (UTC+11:00) Magadan */
                "Magadan Standard Time", "Magadan Daylight Time",
                "Asia/Magadan"
        },
        {
                /* (UTC-03:00) Punta Arenas */
                "Magallanes Standard Time", "Magallanes Daylight Time",
                "America/Punta_Arenas"
        },
        {
                /* (UTC-09:30) Marquesas Islands */
                "Marquesas Standard Time", "Marquesas Daylight Time",
                "Pacific/Marquesas"
        },
        {
                /* (UTC+04:00) Port Louis */
                "Mauritius Standard Time", "Mauritius Daylight Time",
                "Indian/Mauritius"
        },
        {
                /* (UTC-06:00) Guadalajara, Mexico City, Monterrey */
                "Mexico Standard Time", "Mexico Daylight Time",
                "America/Mexico_City"
        },
        {
                /* (UTC-07:00) Chihuahua, La Paz, Mazatlan */
                "Mexico Standard Time 2", "Mexico Daylight Time 2",
                "America/Chihuahua"
        },
        {
                /* (UTC-02:00) Mid-Atlantic - Old */
                "Mid-Atlantic Standard Time", "Mid-Atlantic Daylight Time",
                "Atlantic/South_Georgia"
        },
        {
                /* (UTC+02:00) Beirut */
                "Middle East Standard Time", "Middle East Daylight Time",
                "Asia/Beirut"
        },
        {
                /* (UTC-03:00) Montevideo */
                "Montevideo Standard Time", "Montevideo Daylight Time",
                "America/Montevideo"
        },
        {
                /* (UTC+01:00) Casablanca */
                "Morocco Standard Time", "Morocco Daylight Time",
                "Africa/Casablanca"
        },
        {
                /* (UTC-07:00) Mountain Time (US & Canada) */
                "Mountain Standard Time", "Mountain Daylight Time",
                "US/Mountain"
        },
        {
                /* (UTC-07:00) Chihuahua, La Paz, Mazatlan */
                "Mountain Standard Time (Mexico)", "Mountain Daylight Time (Mexico)",
                "America/Chihuahua"
        },
        {
                /* (UTC+06:30) Yangon (Rangoon) */
                "Myanmar Standard Time", "Myanmar Daylight Time",
                "Asia/Rangoon"
        },
        {
                /* (UTC+06:00) Novosibirsk (RTZ 5) */
                "N. Central Asia Standard Time", "N. Central Asia Daylight Time",
                "Asia/Novosibirsk"
        },
        {
                /* (UTC+02:00) Windhoek */
                "Namibia Standard Time", "Namibia Daylight Time",
                "Africa/Windhoek"
        },
        {
                /* (UTC+05:45) Kathmandu */
                "Nepal Standard Time", "Nepal Daylight Time",
                "Asia/Katmandu"
        },
        {
                /* (UTC+12:00) Auckland, Wellington */
                "New Zealand Standard Time", "New Zealand Daylight Time",
                "Pacific/Auckland"
        },
        {
                /* (UTC-03:30) Newfoundland */
                "Newfoundland Standard Time", "Newfoundland Daylight Time",
                "Canada/Newfoundland"
        },
        {
                /* (UTC+11:00) Norfolk Island */
                "Norfolk Standard Time", "Norfolk Daylight Time",
                "Pacific/Norfolk"
        },
        {
                /* (UTC+08:00) Irkutsk, Ulaan Bataar */
                "North Asia East Standard Time", "North Asia East Daylight Time",
                "Asia/Irkutsk"
        },
        {
                /* (UTC+07:00) Krasnoyarsk */
                "North Asia Standard Time", "North Asia Daylight Time",
                "Asia/Krasnoyarsk"
        },
        {
                /* (UTC+09:00) Pyongyang */
                "North Korea Standard Time", "North Korea Daylight Time",
                "Asia/Pyongyang"
        },
        {
                /* (UTC+07:00) Novosibirsk */
                "Novosibirsk Standard Time", "Novosibirsk Daylight Time",
                "Asia/Novosibirsk"
        },
        {
                /* (UTC+06:00) Omsk */
                "Omsk Standard Time", "Omsk Daylight Time",
                "Asia/Omsk"
        },
        {
                /* (UTC-04:00) Santiago */
                "Pacific SA Standard Time", "Pacific SA Daylight Time",
                "America/Santiago"
        },
        {
                /* (UTC-08:00) Pacific Time (US & Canada) */
                "Pacific Standard Time", "Pacific Daylight Time",
                "US/Pacific"
        },
        {
                /* (UTC-08:00) Baja California */
                "Pacific Standard Time (Mexico)", "Pacific Daylight Time (Mexico)",
                "America/Tijuana"
        },
        {
                /* (UTC+05:00) Islamabad, Karachi */
                "Pakistan Standard Time", "Pakistan Daylight Time",
                "Asia/Karachi"
        },
        {
                /* (UTC-04:00) Asuncion */
                "Paraguay Standard Time", "Paraguay Daylight Time",
                "America/Asuncion"
        },
        {
                /* (UTC+05:00) Qyzylorda */
                "Qyzylorda Standard Time", "Qyzylorda Daylight Time",
                "Asia/Qyzylorda"
        },
        {
                /* (UTC+01:00) Brussels, Copenhagen, Madrid, Paris */
                "Romance Standard Time", "Romance Daylight Time",
                "Europe/Brussels"
        },
        {
                /* (UTC+02:00) Kaliningrad */
                "Russia TZ 1 Standard Time", "Russia TZ 1 Daylight Time",
                "Europe/Kaliningrad"
        },
        {
                /* (UTC+03:00) Moscow, St. Petersburg */
                "Russia TZ 2 Standard Time", "Russia TZ 2 Daylight Time",
                "Europe/Moscow"
        },
        {
                /* (UTC+04:00) Izhevsk, Samara */
                "Russia TZ 3 Standard Time", "Russia TZ 3 Daylight Time",
                "Europe/Samara"
        },
        {
                /* (UTC+05:00) Ekaterinburg */
                "Russia TZ 4 Standard Time", "Russia TZ 4 Daylight Time",
                "Asia/Yekaterinburg"
        },
        {
                /* (UTC+06:00) Novosibirsk (RTZ 5) */
                "Russia TZ 5 Standard Time", "Russia TZ 5 Daylight Time",
                "Asia/Novosibirsk"
        },
        {
                /* (UTC+07:00) Krasnoyarsk */
                "Russia TZ 6 Standard Time", "Russia TZ 6 Daylight Time",
                "Asia/Krasnoyarsk"
        },
        {
                /* (UTC+08:00) Irkutsk */
                "Russia TZ 7 Standard Time", "Russia TZ 7 Daylight Time",
                "Asia/Irkutsk"
        },
        {
                /* (UTC+09:00) Yakutsk */
                "Russia TZ 8 Standard Time", "Russia TZ 8 Daylight Time",
                "Asia/Yakutsk"
        },
        {
                /* (UTC+10:00) Vladivostok */
                "Russia TZ 9 Standard Time", "Russia TZ 9 Daylight Time",
                "Asia/Vladivostok"
        },
        {
                /* (UTC+11:00) Chokurdakh */
                "Russia TZ 10 Standard Time", "Russia TZ 10 Daylight Time",
                "Asia/Magadan"
        },
        {
                /* (UTC+12:00) Anadyr, Petropavlovsk-Kamchatsky */
                "Russia TZ 11 Standard Time", "Russia TZ 11 Daylight Time",
                "Asia/Anadyr"
        },
        {
                /* (UTC+03:00) Moscow, St. Petersburg, Volgograd */
                "Russian Standard Time", "Russian Daylight Time",
                "Europe/Moscow"
        },
        {
                /* (UTC-03:00) Cayenne, Fortaleza */
                "SA Eastern Standard Time", "SA Eastern Daylight Time",
                "America/Buenos_Aires"
        },
        {
                /* (UTC-05:00) Bogota, Lima, Quito, Rio Branco */
                "SA Pacific Standard Time", "SA Pacific Daylight Time",
                "America/Bogota"
        },
        {
                /* (UTC-04:00) Georgetown, La Paz, Manaus, San Juan */
                "SA Western Standard Time", "SA Western Daylight Time",
                "America/Caracas"
        },
        {
                /* (UTC-03:00) Saint Pierre and Miquelon */
                "Saint Pierre Standard Time", "Saint Pierre Daylight Time",
                "America/Miquelon"
        },
        {
                /* (UTC+13:00) Samoa */
                "Samoa Standard Time", "Samoa Daylight Time",
                "Pacific/Samoa"
        },
        {
                /* (UTC+00:00) Sao Tome */
                "Sao Tome Standard Time", "Sao Tome Daylight Time",
                "Africa/Sao_Tome"
        },
        {
                /* (UTC+04:00) Saratov */
                "Saratov Standard Time", "Saratov Daylight Time",
                "Europe/Saratov"
        },
        {
                /* (UTC+07:00) Bangkok, Hanoi, Jakarta */
                "SE Asia Standard Time", "SE Asia Daylight Time",
                "Asia/Bangkok"
        },
        {
                /* (UTC+08:00) Kuala Lumpur, Singapore */
                "Malay Peninsula Standard Time", "Malay Peninsula Daylight Time",
                "Asia/Kuala_Lumpur"
        },
        {
                /* (UTC+11:00) Sakhalin */
                "Sakhalin Standard Time", "Sakhalin Daylight Time",
                "Asia/Sakhalin"
        },
        {
                /* (UTC+02:00) Harare, Pretoria */
                "South Africa Standard Time", "South Africa Daylight Time",
                "Africa/Harare"
        },
        {
                /* (UTC+05:30) Sri Jayawardenepura */
                "Sri Lanka Standard Time", "Sri Lanka Daylight Time",
                "Asia/Colombo"
        },
        {
                /* (UTC+02:00) Khartoum */
                "Sudan Standard Time", "Sudan Daylight Time",
                "Africa/Khartoum"
        },
        {
                /* (UTC+02:00) Damascus */
                "Syria Standard Time", "Syria Daylight Time",
                "Asia/Damascus"
        },
        {
                /* (UTC+08:00) Taipei */
                "Taipei Standard Time", "Taipei Daylight Time",
                "Asia/Taipei"
        },
        {
                /* (UTC+10:00) Hobart */
                "Tasmania Standard Time", "Tasmania Daylight Time",
                "Australia/Hobart"
        },
        {
                /* (UTC-03:00) Araguaina */
                "Tocantins Standard Time", "Tocantins Daylight Time",
                "America/Araguaina"
        },
        {
                /* (UTC+09:00) Osaka, Sapporo, Tokyo */
                "Tokyo Standard Time", "Tokyo Daylight Time",
                "Asia/Tokyo"
        },
        {
                /* (UTC+13:00) Nuku'alofa */
                "Tonga Standard Time", "Tonga Daylight Time",
                "Pacific/Tongatapu"
        },
        {
                /* (UTC+07:00) Tomsk */
                "Tomsk Standard Time", "Tomsk Daylight Time",
                "Asia/Tomsk"
        },
        {
                /* (UTC+09:00) Chita */
                "Transbaikal Standard Time", "Transbaikal Daylight Time",
                "Asia/Chita"
        },
        {
                /* (UTC+03:00) Istanbul */
                "Turkey Standard Time", "Turkey Daylight Time",
                "Europe/Istanbul"
        },
        {
                /* (UTC-05:00) Turks and Caicos */
                "Turks and Caicos Standard Time", "Turks and Caicos Daylight Time",
                "America/Grand_Turk"
        },
        {
                /* (UTC+08:00) Ulaanbaatar */
                "Ulaanbaatar Standard Time", "Ulaanbaatar Daylight Time",
                "Asia/Ulaanbaatar",
        },
        {
                /* (UTC-05:00) Indiana (East) */
                "US Eastern Standard Time", "US Eastern Daylight Time",
                "US/Eastern"
        },
        {
                /* (UTC-07:00) Arizona */
                "US Mountain Standard Time", "US Mountain Daylight Time",
                "US/Arizona"
        },
        {
                /* (UTC) Coordinated Universal Time */
                "Coordinated Universal Time", "Coordinated Universal Time",
                "UTC"
        },
        {
                /* (UTC+12:00) Coordinated Universal Time+12 */
                "UTC+12", "UTC+12",
                "Etc/GMT+12"
        },
        {
                /* (UTC+13:00) Coordinated Universal Time+13 */
                "UTC+13", "UTC+13",
                "Etc/GMT+13"
        },
        {
                /* (UTC-02:00) Coordinated Universal Time-02 */
                "UTC-02", "UTC-02",
                "Etc/GMT-02"
        },
        {
                /* (UTC-08:00) Coordinated Universal Time-08 */
                "UTC-08", "UTC-08",
                "Etc/GMT-08"
        },
        {
                /* (UTC-09:00) Coordinated Universal Time-09 */
                "UTC-09", "UTC-09",
                "Etc/GMT-09"
        },
        {
                /* (UTC-11:00) Coordinated Universal Time-11 */
                "UTC-11", "UTC-11",
                "Etc/GMT-11"
        },
        {
                /* (UTC-04:00) Caracas */
                "Venezuela Standard Time", "Venezuela Daylight Time",
                "America/Caracas",
        },
        {
                /* (UTC+10:00) Vladivostok (RTZ 9) */
                "Vladivostok Standard Time", "Vladivostok Daylight Time",
                "Asia/Vladivostok"
        },
        {
                /* (UTC+04:00) Volgograd */
                "Volgograd Standard Time", "Volgograd Daylight Time",
                "Europe/Volgograd"
        },
        {
                /* (UTC+08:00) Perth */
                "W. Australia Standard Time", "W. Australia Daylight Time",
                "Australia/Perth"
        },
#ifdef NOT_USED
        /* Could not find a match for this one (just a guess). Excluded for now. */
        {
                /* (UTC+01:00) West Central Africa */
                "W. Central Africa Standard Time", "W. Central Africa Daylight Time",
                "WAT"
        },
#endif
        {
                /* (UTC+01:00) Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna */
                "W. Europe Standard Time", "W. Europe Daylight Time",
                "CET"
        },
        {
                /* (UTC+07:00) Hovd */
                "W. Mongolia Standard Time", "W. Mongolia Daylight Time",
                "Asia/Hovd"
        },
        {
                /* (UTC+05:00) Ashgabat, Tashkent */
                "West Asia Standard Time", "West Asia Daylight Time",
                "Asia/Karachi"
        },
        {
                /* (UTC+02:00) Gaza, Hebron */
                "West Bank Gaza Standard Time", "West Bank Gaza Daylight Time",
                "Asia/Gaza"
        },
        {
                /* (UTC+10:00) Guam, Port Moresby */
                "West Pacific Standard Time", "West Pacific Daylight Time",
                "Pacific/Guam"
        },
        {
                /* (UTC+09:00) Yakutsk */
                "Yakutsk Standard Time", "Yakutsk Daylight Time",
                "Asia/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)
        {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                fprintf(stderr, "could not identify system time zone: localtime() failed\n");
#endif
                return NULL;                    /* go to GMT */
        }

        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)
                {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                        fprintf(stderr, "TZ \"%s\" matches system time zone \"%s\"\n",
                                        win32_tzmap[i].pgtzname, tzname);
#endif
                        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)
        {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                fprintf(stderr, "could not open registry key to identify system time zone: error code %lu\n",
                                GetLastError());
#endif
                return NULL;                    /* go to GMT */
        }

        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;
#ifdef DEBUG_IDENTIFY_TIMEZONE
                        fprintf(stderr, "could not enumerate registry subkeys to identify system time zone: %d\n",
                                        (int) r);
#endif
                        break;
                }

                if ((r = RegOpenKeyEx(rootKey, keyname, 0, KEY_READ, &key)) != ERROR_SUCCESS)
                {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                        fprintf(stderr, "could not open registry subkey to identify system time zone: %d\n",
                                        (int) r);
#endif
                        break;
                }

                memset(zonename, 0, sizeof(zonename));
                namesize = sizeof(zonename);
                if ((r = RegQueryValueEx(key, "Std", NULL, NULL, (unsigned char *) zonename, &namesize)) != ERROR_SUCCESS)
                {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                        fprintf(stderr, "could not query value for key \"std\" to identify system time zone \"%s\": %d\n",
                                        keyname, (int) r);
#endif
                        RegCloseKey(key);
                        continue;                       /* Proceed to look at the next timezone */
                }
                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, (unsigned char *) zonename, &namesize)) != ERROR_SUCCESS)
                {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                        fprintf(stderr, "could not query value for key \"dlt\" to identify system time zone \"%s\": %d\n",
                                        keyname, (int) r);
#endif
                        RegCloseKey(key);
                        continue;                       /* Proceed to look at the next timezone */
                }
                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)
                        {
#ifdef DEBUG_IDENTIFY_TIMEZONE
                                fprintf(stderr, "TZ \"%s\" matches localized system time zone \"%s\" (\"%s\")\n",
                                                win32_tzmap[i].pgtzname, tzname, localtzname);
#endif
                                return win32_tzmap[i].pgtzname;
                        }
                }
        }

#ifdef DEBUG_IDENTIFY_TIMEZONE
        fprintf(stderr, "could not find a match for system time zone \"%s\"\n",
                        tzname);
#endif
        return NULL;                            /* go to GMT */
}
#endif                                                  /* WIN32 */


/*
 * Return true if the given zone name is valid and is an "acceptable" zone.
 */
static bool
validate_zone(const char *tzname)
{
        pg_tz      *tz;

        if (!tzname || !tzname[0])
                return false;

        tz = pg_load_tz(tzname);
        if (!tz)
                return false;

        if (!pg_tz_acceptable(tz))
                return false;

        return true;
}

/*
 * Identify a suitable default timezone setting based on the environment.
 *
 * The installation share_path must be passed in, as that is the default
 * location for the timezone database directory.
 *
 * 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,
 * return NULL, indicating that we should default to GMT.
 */
const char *
select_default_timezone(const char *share_path)
{
        const char *tzname;

        /* Initialize timezone directory path, if needed */
#ifndef SYSTEMTZDIR
        snprintf(tzdirpath, sizeof(tzdirpath), "%s/timezone", share_path);
#endif

        /* Check TZ environment variable */
        tzname = getenv("TZ");
        if (validate_zone(tzname))
                return tzname;

        /* Nope, so try to identify the system timezone */
        tzname = identify_system_timezone();
        if (validate_zone(tzname))
                return tzname;

        return NULL;
}