findtimezone.c File Reference

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

Include dependency graph for findtimezone.c:

Go to the source code of this file.

Data Structures
struct	tztry

Macros
#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 */

Functions
const char *	select_default_timezone (const char *share_path)
static const char *	pg_TZDIR (void)
int	pg_open_tzfile (const char *name, char *canonname)
static pg_tz *	pg_load_tz (const char *name)
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)
static int	get_timezone_offset (struct tm *tm)
static time_t	build_time_t (int year, int month, int day)
static bool	compare_tm (struct tm *s, struct pg_tm *p)
static int	score_timezone (const char *tzname, struct tztry *tt)
static bool	perfect_timezone_match (const char *tzname, struct tztry *tt)
static const char *	identify_system_timezone (void)
static int	zone_name_pref (const char *zonename)
static bool	validate_zone (const char *tzname)

Variables
static char	tzdirpath [MAXPGPATH]

Macro Definition Documentation

MAX_TEST_TIMES

#define MAX_TEST_TIMES   (52*100) /* 100 years */

Definition at line 143 of file findtimezone.c.

T_DAY

#define T_DAY   ((time_t) (60*60*24))

Definition at line 139 of file findtimezone.c.

T_MONTH

#define T_MONTH   ((time_t) (60*60*24*31))

Definition at line 141 of file findtimezone.c.

T_WEEK

#define T_WEEK   ((time_t) (60*60*24*7))

Definition at line 140 of file findtimezone.c.

Function Documentation

build_time_t()

static time_t build_time_t ( int  year, int  month, int  day  )

static

Definition at line 177 of file findtimezone.c.

{
    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);
}

References fb(), tm, pg_tm::tm_isdst, pg_tm::tm_mday, pg_tm::tm_mon, and pg_tm::tm_year.

Referenced by identify_system_timezone().

check_system_link_file()

static bool check_system_link_file ( const char *  linkname, struct tztry *  tt, char *  bestzonename  )

static

Definition at line 531 of file findtimezone.c.

{
#ifdef HAVE_READLINK
    char        link_target[MAXPGPATH];
    ssize_t     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
}

References fb(), fprintf, len, MAXPGPATH, perfect_timezone_match(), readlink, and TZ_STRLEN_MAX.

Referenced by identify_system_timezone().

compare_tm()

static bool compare_tm ( struct tm *  s, struct pg_tm *  p  )

static

Definition at line 194 of file findtimezone.c.

{
    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;
}

References pg_tm::tm_hour, pg_tm::tm_isdst, pg_tm::tm_mday, pg_tm::tm_min, pg_tm::tm_mon, pg_tm::tm_sec, pg_tm::tm_wday, pg_tm::tm_yday, and pg_tm::tm_year.

Referenced by score_timezone().

get_timezone_offset()

static int get_timezone_offset ( struct tm *  tm )

static

Definition at line 162 of file findtimezone.c.

{
#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
}

References TIMEZONE_GLOBAL, tm, and pg_tm::tm_gmtoff.

Referenced by identify_system_timezone().

identify_system_timezone()

static const char * identify_system_timezone ( void  )

static

Definition at line 318 of file findtimezone.c.

{
    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;
}

References build_time_t(), check_system_link_file(), fb(), fprintf, get_timezone_offset(), MAX_TEST_TIMES, MAXPGPATH, pg_TZDIR(), scan_available_timezones(), score_timezone(), snprintf, strlcpy(), T_DAY, T_MONTH, T_WEEK, tm, pg_tm::tm_isdst, pg_tm::tm_year, and TZ_STRLEN_MAX.

Referenced by select_default_timezone().

perfect_timezone_match()

static bool perfect_timezone_match ( const char *  tzname, struct tztry *  tt  )

static

Definition at line 307 of file findtimezone.c.

{
    return (score_timezone(tzname, tt) == tt->n_test_times);
}

References fb(), and score_timezone().

Referenced by check_system_link_file().

pg_load_tz()

static pg_tz * pg_load_tz ( const char *  name )

static

Definition at line 91 of file findtimezone.c.

{
    static pg_tz tz;
 
    if (strlen(name) > TZ_STRLEN_MAX)
        return NULL;            /* not going to fit */
 
    /*
     * Let the IANA tzdb code interpret the time zone name.
     */
    if (!pg_tzload(name, NULL, &tz.state))
        return NULL;            /* unknown timezone */
 
    strcpy(tz.TZname, name);
 
    return &tz;
}

References fb(), name, pg_tzload(), pg_tz::state, TZ_STRLEN_MAX, and pg_tz::TZname.

Referenced by score_timezone(), and validate_zone().

pg_open_tzfile()

int pg_open_tzfile	(	const char *	name,
		char *	canonname
	)

Definition at line 65 of file findtimezone.c.

{
    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);
}

References fb(), MAXPGPATH, name, PG_BINARY, pg_TZDIR(), strlcpy(), and TZ_STRLEN_MAX.

Referenced by tzloadbody().

pg_TZDIR()

static const char * pg_TZDIR ( void  )

static

Definition at line 37 of file findtimezone.c.

{
#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
}

References fb(), and tzdirpath.

Referenced by identify_system_timezone(), and pg_open_tzfile().

scan_available_timezones()

static void scan_available_timezones ( char *  tzdir, char *  tzdirsub, struct tztry *  tt, int *  bestscore, char *  bestzonename  )

static

Definition at line 644 of file findtimezone.c.

{
    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\": %m\n",
                    tzdir);
#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);
}

References fb(), fprintf, MAXPGPATH, name, pgfnames(), pgfnames_cleanup(), S_ISDIR, scan_available_timezones(), score_timezone(), snprintf, stat, strlcpy(), TZ_STRLEN_MAX, and zone_name_pref().

Referenced by identify_system_timezone(), and scan_available_timezones().

score_timezone()

static int score_timezone ( const char *  tzname, struct tztry *  tt  )

static

Definition at line 221 of file findtimezone.c.

{
    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;
}

References compare_tm(), fb(), fprintf, i, pg_load_tz(), pg_localtime(), pg_tz_acceptable(), tm, and TZ_STRLEN_MAX.

Referenced by identify_system_timezone(), perfect_timezone_match(), and scan_available_timezones().

select_default_timezone()

const char * select_default_timezone ( const char *  share_path )

extern

Definition at line 1744 of file findtimezone.c.

{
    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;
}

References fb(), identify_system_timezone(), share_path, snprintf, tzdirpath, and validate_zone().

Referenced by test_config_settings().

validate_zone()

static bool validate_zone ( const char *  tzname )

static

Definition at line 1715 of file findtimezone.c.

{
    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;
}

References fb(), pg_load_tz(), and pg_tz_acceptable().

Referenced by select_default_timezone().

zone_name_pref()

static int zone_name_pref ( const char *  zonename )

static

Definition at line 602 of file findtimezone.c.

{
    /*
     * 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;
}

References fb().

Referenced by scan_available_timezones().

Variable Documentation

tzdirpath

char tzdirpath[MAXPGPATH]

static

Definition at line 27 of file findtimezone.c.

Referenced by pg_TZDIR(), and select_default_timezone().