From: Tomas Korbar <tkorbar@redhat.com>
Subject: [PATCH] Fix UTC offset calculation using tm_gmtoff

The UTC offset was derived via mktime(gmtime()) with a manual +1 hour
DST adjustment.  That breaks with modern tzdata (e.g. America/Vancouver
in tzdata >= 2026b, Europe/Dublin negative DST).  Use tm_gmtoff from
localtime() instead, matching s-nail commit 60ed19eed5.

The sendout.c change is identical to a patch proposed by Mason Loring
Bliss (RHEL-232782).  head.c and imap.c are updated with the same
tm_gmtoff approach.

Reported-by: Mason Loring Bliss <mason@blisses.org>
Resolves: RHEL-232782
---
 sendout.c |  6 ++----
 head.c    |  7 +------
 imap.c    | 17 +++++------------
 3 files changed, 8 insertions(+), 22 deletions(-)

--- a/sendout.c
+++ b/sendout.c
@@ -1149,13 +1149,11 @@
 	int tzdiff, tzdiff_hour, tzdiff_min;
 
 	time(&t);
-	tzdiff = t - mktime(gmtime(&t));
+	tmptr = localtime(&t);
+	tzdiff = tmptr->tm_gmtoff;
 	tzdiff_hour = (int)(tzdiff / 60);
 	tzdiff_min = tzdiff_hour % 60;
 	tzdiff_hour /= 60;
-	tmptr = localtime(&t);
-	if (tmptr->tm_isdst > 0)
-		tzdiff_hour++;
 	return fprintf(fo, "%s: %s, %02d %s %04d %02d:%02d:%02d %+05d\n",
 			field,
 			weekday_names[tmptr->tm_wday],
--- a/head.c
+++ b/head.c
@@ -1081,7 +1081,6 @@
 	char	*fp, *xp;
 	time_t	t;
 	int	i, year, month, day, hour, minute, second;
-	int	tzdiff;
 	struct tm	*tmptr;
 
 	for (fp = from; *fp && *fp != '\n'; fp++);
@@ -1116,11 +1115,8 @@
 	if ((t = combinetime(year, month, day, hour, minute, second)) ==
 			(time_t)-1)
 		goto invalid;
-	tzdiff = t - mktime(gmtime(&t));
 	tmptr = localtime(&t);
-	if (tmptr->tm_isdst > 0)
-		tzdiff += 3600;
-	t -= tzdiff;
+	t += tmptr->tm_gmtoff;
 	return t;
 invalid:
 	time(&t);
--- a/imap.c
+++ b/imap.c
@@ -3508,7 +3508,7 @@
 imap_read_date(const char *cp)
 {
 	time_t	t;
-	int	year, month, day, i, tzdiff;
+	int	year, month, day, i;
 	struct tm	*tmptr;
 	char	*xp, *yp;
 
@@ -3532,11 +3532,8 @@
 		return -1;
 	if ((t = combinetime(year, month, day, 0, 0, 0)) == (time_t)-1)
 		return -1;
-	tzdiff = t - mktime(gmtime(&t));
 	tmptr = localtime(&t);
-	if (tmptr->tm_isdst > 0)
-		tzdiff += 3600;
-	t -= tzdiff;
+	t += tmptr->tm_gmtoff;
 	return t;
 }
 
@@ -3547,13 +3544,11 @@
 	struct tm	*tmptr;
 	int	tzdiff, tzdiff_hour, tzdiff_min;
 
-	tzdiff = t - mktime(gmtime(&t));
+	tmptr = localtime(&t);
+	tzdiff = tmptr->tm_gmtoff;
 	tzdiff_hour = (int)(tzdiff / 60);
 	tzdiff_min = tzdiff_hour % 60;
 	tzdiff_hour /= 60;
-	tmptr = localtime(&t);
-	if (tmptr->tm_isdst > 0)
-		tzdiff_hour++;
 	snprintf(s, sizeof s, "\"%02d-%s-%04d %02d:%02d:%02d %+03d%02d\"",
 			tmptr->tm_mday,
 			month_names[tmptr->tm_mon],