/*
* 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[MAX_PG_PATH];
int std_ofs;
char std_zone_name[TZ_STRLEN_MAX + 1];
char dst_zone_name[TZ_STRLEN_MAX + 1];
char cbuf[TZ_STRLEN_MAX + 1];
/* Initialize OS timezone library */
tzset();
/*
* Set up the list of dates to be probed to see how well our timezone
* matches the system zone. We first probe January and July of the
* current year; this serves to quickly eliminate the vast majority of the
* TZ database entries. If those dates match, we probe every week for 100
* years backwards from the current July. (Weekly resolution is good
* enough to identify DST transition rules, since everybody switches on
* Sundays.) This is sufficient to cover most of the Unix time_t range,
* and we don't want to look further than that since many systems won't
* have sane TZ behavior further back anyway. The further back the zone
* matches, the better we score it. This may seem like a rather random
* way of doing things, but experience has shown that system-supplied
* timezone definitions are likely to have DST behavior that is right for
* the recent past and not so accurate further back. Scoring in this way
* allows us to recognize zones that have some commonality with the zic
* database, without insisting on exact match. (Note: we probe Thursdays,
* not Sundays, to avoid triggering DST-transition bugs in localtime
* itself.)
*/
tnow = time(NULL);
tm = localtime(&tnow);
if (!tm)
return NULL; /* give up if localtime is broken... */
thisyear = tm->tm_year + 1900;
t = build_time_t(thisyear, 1, 15);
/*
* Round back to GMT midnight Thursday. This depends on the knowledge
* that the time_t origin is Thu Jan 01 1970. (With a different origin
* we'd be probing some other day of the week, but it wouldn't matter
* anyway unless localtime() had DST-transition bugs.)
*/
t -= (t % T_WEEK);
tt.n_test_times = 0;
tt.test_times[tt.n_test_times++] = t;
t = build_time_t(thisyear, 7, 15);
t -= (t % T_WEEK);
tt.test_times[tt.n_test_times++] = t;
while (tt.n_test_times < MAX_TEST_TIMES) {
t -= T_WEEK;
tt.test_times[tt.n_test_times++] = t;
}
/* Search for the best-matching timezone file */
strcpy(tmptzdir, pg_TZDIR());
bestscore = -1;
resultbuf[0] = '\0';
scan_available_timezones(tmptzdir, tmptzdir + strlen(tmptzdir) + 1, &tt, &bestscore, resultbuf);
if (bestscore > 0) {
/* Ignore zic's rather silly "Factory" time zone; use GMT instead */
if (strcmp(resultbuf, "Factory") == 0)
return NULL;
return resultbuf;
}
/*
* Couldn't find a match in the database, so next we try constructed zone
* names (like "PST8PDT").
*
* First we need to determine the names of the local standard and daylight
* zones. The idea here is to scan forward from today until we have seen
* both zones, if both are in use.
*/
memset(std_zone_name, 0, sizeof(std_zone_name));
memset(dst_zone_name, 0, sizeof(dst_zone_name));
std_ofs = 0;
tnow = time(NULL);
/*
* Round back to a GMT midnight so results don't depend on local time of
* day
*/
tnow -= (tnow % T_DAY);
/*
* We have to look a little further ahead than one year, in case today is
* just past a DST boundary that falls earlier in the year than the next
* similar boundary. Arbitrarily scan up to 14 months.
*/
for (t = tnow; t <= tnow + T_MONTH * 14; t += T_MONTH) {
tm = localtime(&t);
if (!tm)
continue;
if (tm->tm_isdst < 0)
continue;
if (tm->tm_isdst == 0 && std_zone_name[0] == '\0') {
/* found STD zone */
memset(cbuf, 0, sizeof(cbuf));
strftime(cbuf, sizeof(cbuf) - 1, "%Z", tm); /* zone abbr */
strcpy(std_zone_name, cbuf);
std_ofs = get_timezone_offset(tm);
}
if (tm->tm_isdst > 0 && dst_zone_name[0] == '\0') {
/* found DST zone */
memset(cbuf, 0, sizeof(cbuf));
strftime(cbuf, sizeof(cbuf) - 1, "%Z", tm); /* zone abbr */
strcpy(dst_zone_name, cbuf);
}
/* Done if found both */
if (std_zone_name[0] && dst_zone_name[0])
break;
}
/* We should have found a STD zone name by now... */
if (std_zone_name[0] == '\0') {
ereport(LOG, (
errmsg("could not determine system time zone"),
errdetail("The PostgreSQL time zone will be set to \"%s\".", "GMT"),
errhint("You can specify the correct timezone in postgresql.conf.")));
return NULL; /* go to GMT */
}
/* If we found DST then try STD<ofs>DST */
if (dst_zone_name[0] != '\0') {
snprintf(resultbuf, sizeof(resultbuf), "%s%d%s", std_zone_name, -std_ofs / 3600, dst_zone_name);
if (score_timezone(resultbuf, &tt) > 0)
return resultbuf;
}
/* Try just the STD timezone (works for GMT at least) */
strcpy(resultbuf, std_zone_name);
if (score_timezone(resultbuf, &tt) > 0)
return resultbuf;
/* Try STD<ofs> */
snprintf(resultbuf, sizeof(resultbuf), "%s%d", std_zone_name, -std_ofs / 3600);
if (score_timezone(resultbuf, &tt) > 0)
return resultbuf;
/*
* Did not find the timezone. Fallback to use a GMT zone. Note that the
* zic timezone database names the GMT-offset zones in POSIX style: plus
* is west of Greenwich. It's unfortunate that this is opposite of SQL
* conventions. Should we therefore change the names? Probably not...
*/
snprintf(resultbuf, sizeof(resultbuf), "Etc/GMT%s%d", (-std_ofs > 0) ? "+" : "", -std_ofs / 3600);
ereport(LOG, (
errmsg("could not recognize system time zone"),
errdetail("The PostgreSQL time zone will be set to \"%s\".", resultbuf),
errhint("You can specify the correct timezone in postgresql.conf.")));
return resultbuf;
}
/*
* Recursively scan the timezone database looking for the best match to
* the system timezone behavior.
*
* tzdir points to a buffer of size MAX_PG_PATH. On entry, it holds the
* pathname of a directory containing TZ files. We internally modify it
* to hold pathnames of sub-directories and files, but must restore it
* to its original contents before exit.
*
* tzdirsub points to the part of tzdir that represents the subfile name
* (ie, tzdir + the original directory name length, plus one for the
* first added '/').
*
* tt tells about the system timezone behavior we need to match.
*
* *bestscore and *bestzonename on entry hold the best score found so far
* and the name of the best zone. We overwrite them if we find a better
* score. bestzonename must be a buffer of length TZ_STRLEN_MAX + 1.
*/
static void
scan_available_timezones(
char *tzdir,
char *tzdirsub,
struct tztry* tt,
int *bestscore,
char *bestzonename)
{
int tzdir_orig_len = strlen(tzdir);
DIR* dirdesc;
struct dirent *direntry;
dirdesc = alloc_dir(tzdir);
if (!dirdesc) {
ereport(LOG, (
errcode_file_access(),
errmsg("could not open directory \"%s\": %m", tzdir)));
return;
}
while ((direntry = read_dir(dirdesc, tzdir)) != NULL) {
struct stat statbuf;
/* Ignore . and .., plus any other "hidden" files */
if (direntry->d_name[0] == '.')
continue;
snprintf(tzdir + tzdir_orig_len, MAX_PG_PATH - tzdir_orig_len, "/%s", direntry->d_name);
if (stat(tzdir, &statbuf) != 0) {
ereport(LOG, (
errcode_file_access(),
errmsg("could not stat \"%s\": %m", tzdir)));
tzdir[tzdir_orig_len] = '\0';
continue;
}
if (S_ISDIR(statbuf.st_mode)) {
/* Recurse into subdirectory */
scan_available_timezones(tzdir, tzdirsub, tt, bestscore, bestzonename);
} else {
/* Load and test this file */
int score = score_timezone(tzdirsub, tt);
if (score > *bestscore) {
*bestscore = score;
strlcpy(bestzonename, tzdirsub, TZ_STRLEN_MAX + 1);
} else if (score == *bestscore) {
/* Consider how to break a tie */
if (strlen(tzdirsub) < strlen(bestzonename)
|| (strlen(tzdirsub) == strlen(bestzonename)
&& strcmp(tzdirsub, bestzonename) < 0))
strlcpy(bestzonename, tzdirsub, TZ_STRLEN_MAX + 1);
}
}
/* Restore tzdir */
tzdir[tzdir_orig_len] = '\0';
}
free_dir(dirdesc);
}
/*
* 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);
}
