findtimezone.c

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/*-------------------------------------------------------------------------
 *
 * findtimezone.c
 *    Functions for determining the default timezone to use.
 *
 * Portions Copyright (c) 1996-2013, 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 "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);

    strcpy(fullname, pg_TZDIR());
    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) != 0)
        {
            /* 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) != 0)
        {
            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 Olson 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 Olson 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 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;
}


/*
 * 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 Olson
     * 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 */
    strcpy(tmptzdir, pg_TZDIR());
    bestscore = -1;
    resultbuf[0] = '\0';
    scan_available_timezones(tmptzdir, tmptzdir + strlen(tmptzdir) + 1,
                             &tt,
                             &bestscore, resultbuf);
    if (bestscore > 0)
    {
        /* Ignore Olson'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
     * Olson 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;
}

/*
 * 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 */
                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';
    }

    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 2003 R2.
     *
     * The zones have been matched to Olson 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 */
    {
        "Argentina Standard Time", "Argentina Daylight Time",
        "America/Buenos_Aires"
    },                          /* (GMT-03:00) Buenos Aires */
    {
        "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 */
    {
        "Azerbaijan Standard Time", "Azerbaijan Daylight Time",
        "Asia/Baku"
    },                          /* (GMT+04:00) Baku */
    {
        "Azores Standard Time", "Azores Daylight Time",
        "Atlantic/Azores"
    },                          /* (GMT-01:00) Azores */
    {
        "Bangladesh Standard Time", "Bangladesh Daylight Time",
        "Asia/Dhaka"
    },                          /* (GMT+06:00) Dhaka */
    {
        "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 (other than Mexico) generally does not observe DST */
    {
        "Central America Standard Time", "Central America Daylight Time",
        "CST6"
    },                          /* (GMT-06:00) Central America */
    {
        "Central Asia Standard Time", "Central Asia Daylight Time",
        "Asia/Dhaka"
    },                          /* (GMT+06:00) Astana, Dhaka */
    {
        "Central Brazilian Standard Time", "Central Brazilian Daylight Time",
        "America/Cuiaba"
    },                          /* (GMT-04:00) Cuiaba */
    {
        "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 */
    {
        "Kamchatka Standard Time", "Kamchatka Daylight Time",
        "Asia/Kamchatka"
    },                          /* (GMT+12:00) Petropavlovsk-Kamchatsky */
    {
        "Korea Standard Time", "Korea Daylight Time",
        "Asia/Seoul"
    },                          /* (GMT+09:00) Seoul */
    {
        "Mauritius Standard Time", "Mauritius Daylight Time",
        "Indian/Mauritius"
    },                          /* (GMT+04:00) Port Louis */
    {
        "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 */
    {
        "Morocco Standard Time", "Morocco Daylight Time",
        "Africa/Casablanca"
    },                          /* (GMT) Casablanca */
    {
        "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/Novosibirsk"
    },                          /* (GMT+06:00) 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 */
    {
        "Pakistan Standard Time", "Pakistan Daylight Time",
        "Asia/Karachi"
    },                          /* (GMT+05:00) Islamabad, Karachi */
    {
        "Paraguay Standard Time", "Paraguay Daylight Time",
        "America/Asuncion"
    },                          /* (GMT-04:00) Asuncion */
    {
        "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 */
    {
        "Ulaanbaatar Standard Time", "Ulaanbaatar Daylight Time",
        "Asia/Ulaanbaatar",
    },                          /* (GMT+08:00) Ulaanbaatar */
    {
        "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 */
    {
        "Coordinated Universal Time", "Coordinated Universal Time",
        "UTC"
    },                          /* (GMT) Coordinated Universal Time */
    {
        "UTC+12", "UTC+12",
        "Etc/GMT+12"
    },                          /* (GMT+12:00) Coordinated Universal Time+12 */
    {
        "UTC-02", "UTC-02",
        "Etc/GMT-02"
    },                          /* (GMT-02:00) Coordinated Universal Time-02 */
    {
        "UTC-11", "UTC-11",
        "Etc/GMT-11"
    },                          /* (GMT-11:00) Coordinated Universal Time-11 */
    {
        "Venezuela Standard Time", "Venezuela Daylight Time",
        "America/Caracas",
    },                          /* (GMT-04:30) Caracas */
    {
        "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 */
#ifdef NOT_USED
    /* Could not find a match for this one (just a guess). Excluded for now. */
    {
        "W. Central Africa Standard Time", "W. Central Africa Daylight Time",
        "WAT"
    },                          /* (GMT+01:00) West Central Africa */
#endif
    {
        "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)
    {
#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;
}