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djgpp: Set TZ=UTC to convert UTC timestamp to time_t

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Since djgpp has neither a timezone variable or timegm(), this horrible
method must be used.  It is the only one I could find that produces
accurate results, and is recommended as portable alternative to
timegm() by the GNU libc manual.  Reference:

https://www.gnu.org/software/libc/manual/html_node/Broken_002ddown-Time.html#index-timegm

Now, a much nicer alternative solution could be:

    timestamp_local = mktime(timestamp_tm);
    timestamp_utc = timestamp_local + timestamp_tm->tm_gmtoff
                                    - (timestamp_tm->tm_isdst ? 3600 : 0);

This works due to the fact that mktime() populates the tm_gmtoff and
tm_isdst fields in the source timestamp.  It is accurate everywhere in
the world, *except* on Lord Howe Island, Australia, where a 30 minute
DST offset is used.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19274)
This commit is contained in:
J.W. Jagersma 2022-09-26 20:35:46 +02:00 committed by Tomas Mraz
parent 8ae74c5bc0
commit cffb65f2ff
1 changed files with 29 additions and 6 deletions
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35
crypto/asn1/a_time.c
View File

@ -605,7 +605,9 @@ time_t ossl_asn1_string_to_time_t(const char *asn1_string)
{
ASN1_TIME *timestamp_asn1 = NULL;
struct tm *timestamp_tm = NULL;
#ifndef USE_TIMEGM
#if defined(__DJGPP__)
char *tz = NULL;
#elif !defined(USE_TIMEGM)
time_t timestamp_local;
#endif
time_t timestamp_utc;
@ -627,17 +629,38 @@ time_t ossl_asn1_string_to_time_t(const char *asn1_string)
ASN1_TIME_free(timestamp_asn1);
return -1;
}
ASN1_TIME_free(timestamp_asn1);
#ifdef USE_TIMEGM
#if defined(__DJGPP__)
/*
* This is NOT thread-safe. Do not use this method for platforms other
* than djgpp.
*/
tz = getenv("TZ");
if (tz != NULL) {
tz = OPENSSL_strdup(tz);
if (tz == NULL) {
OPENSSL_free(timestamp_tm);
return -1;
}
}
setenv("TZ", "UTC", 1);
timestamp_utc = mktime(timestamp_tm);
if (tz != NULL) {
setenv("TZ", tz, 1);
OPENSSL_free(tz);
} else {
unsetenv("TZ");
}
#elif defined(USE_TIMEGM)
timestamp_utc = timegm(timestamp_tm);
OPENSSL_free(timestamp_tm);
#else
timestamp_local = mktime(timestamp_tm);
OPENSSL_free(timestamp_tm);
timestamp_utc = timestamp_local - timezone;
#endif
OPENSSL_free(timestamp_tm);
ASN1_TIME_free(timestamp_asn1);
return timestamp_utc;
}