diff -r d45cfe9072cd sys/src/cmd/upas/imap4d/date.c
--- a/sys/src/cmd/upas/imap4d/date.c	Sat May 30 13:03:05 2020 +0200
+++ b/sys/src/cmd/upas/imap4d/date.c	Sat May 30 19:08:04 2020 -0700
@@ -1,142 +1,10 @@
 #include "imap4d.h"
 
-static char *wdayname[] = {
-	"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
-};
-
-static char *monname[] = {
-	"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
-};
-
-/*
- * zone	: [A-Za-z][A-Za-z][A-Za-z]	some time zone names
- *	| [A-IK-Z]			military time; rfc1123 says the rfc822 spec is wrong.
- *	| "UT"				universal time
- *	| [+-][0-9][0-9][0-9][0-9]
- * zones is the rfc-822 list of time zone names
- */
-static Namedint zones[] =
-{
-	{"A",	-1 * 3600},
-	{"B",	-2 * 3600},
-	{"C",	-3 * 3600},
-	{"CDT", -5 * 3600},
-	{"CST", -6 * 3600},
-	{"D",	-4 * 3600},
-	{"E",	-5 * 3600},
-	{"EDT", -4 * 3600},
-	{"EST", -5 * 3600},
-	{"F",	-6 * 3600},
-	{"G",	-7 * 3600},
-	{"GMT", 0},
-	{"H",	-8 * 3600},
-	{"I",	-9 * 3600},
-	{"K",	-10 * 3600},
-	{"L",	-11 * 3600},
-	{"M",	-12 * 3600},
-	{"MDT", -6 * 3600},
-	{"MST", -7 * 3600},
-	{"N",	+1 * 3600},
-	{"O",	+2 * 3600},
-	{"P",	+3 * 3600},
-	{"PDT", -7 * 3600},
-	{"PST", -8 * 3600},
-	{"Q",	+4 * 3600},
-	{"R",	+5 * 3600},
-	{"S",	+6 * 3600},
-	{"T",	+7 * 3600},
-	{"U",	+8 * 3600},
-	{"UT",	0},
-	{"V",	+9 * 3600},
-	{"W",	+10 * 3600},
-	{"X",	+11 * 3600},
-	{"Y",	+12 * 3600},
-	{"Z",	0},
-};
-
-static void
-zone2tm(Tm *tm, char *s)
-{
-	int i;
-	Tm aux, *atm;
-
-	if(*s == '+' || *s == '-'){
-		i = strtol(s, &s, 10);
-		tm->tzoff = (i/100)*3600 + i%100;
-		strncpy(tm->zone, "", 4);
-		return;
-	}
-
-	/*
-	 * look it up in the standard rfc822 table
-	 */
-	strncpy(tm->zone, s, 3);
-	tm->zone[3] = 0;
-	tm->tzoff = 0;
-	for(i = 0; i < nelem(zones); i++){
-		if(cistrcmp(zones[i].name, s) == 0){
-			tm->tzoff = zones[i].v;
-			return;
-		}
-	}
-
-	/*
-	 * one last try: look it up in the current local timezone
-	 * probe a couple of times to get daylight/standard time change.
-	 */
-	aux = *tm;
-	memset(aux.zone, 0, 4);
-	aux.hour--;
-	for(i = 0; i < 2; i++){
-		atm = localtime(tm2sec(&aux));
-		if(cistrcmp(tm->zone, atm->zone) == 0){
-			tm->tzoff = atm->tzoff;
-			return;
-		}
-		aux.hour++;
-	}
-
-	strncpy(tm->zone, "GMT", 4);
-	tm->tzoff = 0;
-}
-
-/*
- * hh[:mm[:ss]]
- */
-static void
-time2tm(Tm *tm, char *s)
-{
-	tm->hour = strtoul(s, &s, 10);
-	if(*s++ != ':')
-		return;
-	tm->min = strtoul(s, &s, 10);
-	if(*s++ != ':')
-		return;
-	tm->sec = strtoul(s, &s, 10);
-}
-
-static int
-dateindex(char *d, char **tab, int n)
-{
-	int i;
-
-	for(i = 0; i < n; i++)
-		if(cistrcmp(d, tab[i]) == 0)
-			return i;
-	return -1;
-}
-
 int
 imap4date(Tm *tm, char *date)
 {
-	char *flds[4];
-
-	if(getfields(date, flds, 3, 0, "-") != 3)
+	if(tmparse(tm, "DD-MM-YYYY", date, nil) == nil)
 		return 0;
-
-	tm->mday = strtol(flds[0], nil, 10);
-	tm->mon = dateindex(flds[1], monname, 12);
-	tm->year = strtol(flds[2], nil, 10) - 1900;
 	return 1;
 }
 
@@ -146,29 +14,11 @@
 ulong
 imap4datetime(char *date)
 {
-	char *flds[4], *sflds[4];
-	ulong t;
 	Tm tm;
 
-	if(getfields(date, flds, 4, 0, " ") != 3)
+	if(tmparse(&tm, "DD-MM-YYYY hh:mm:ss ?ZZZ", date, nil) == nil)
 		return ~0;
-
-	if(!imap4date(&tm, flds[0]))
-		return ~0;
-
-	if(getfields(flds[1], sflds, 3, 0, ":") != 3)
-		return ~0;
-
-	tm.hour = strtol(sflds[0], nil, 10);
-	tm.min = strtol(sflds[1], nil, 10);
-	tm.sec = strtol(sflds[2], nil, 10);
-
-	strcpy(tm.zone, "GMT");
-	tm.yday = 0;
-	t = tm2sec(&tm);
-	zone2tm(&tm, flds[2]);
-	t -= tm.tzoff;
-	return t;
+	return tm.abs;
 }
 
 /*
@@ -181,85 +31,16 @@
 Tm*
 date2tm(Tm *tm, char *date)
 {
-	char *flds[7], *s, dstr[64];
-	int n;
-	Tm gmt, *atm;
+	char **f, *fmts[] = {
+		"?W ?DD ?MMM ?YYYY hh:mm:ss ?Z",
+		"?W, ?DD ?MMM ?YYYY hh:mm:ss ?Z",
+		"?W, ?DD ?MMM hh:mm:ss ?Z ?YYYY",
+		"?MMM hh:mm:ss ?Z ?YYYY",
+		nil
+	};
+	for(f = fmts; *f != nil; f++)
+		if(tmparse(tm, *f, date, nil) != nil)
+			return tm;
+	return nil;
+}
 
-	/*
-	 * default date is Thu Jan  1 00:00:00 GMT 1970
-	 */
-	tm->wday = 4;
-	tm->mday = 1;
-	tm->mon = 1;
-	tm->hour = 0;
-	tm->min = 0;
-	tm->sec = 0;
-	tm->year = 70;
-	strcpy(tm->zone, "GMT");
-	tm->tzoff = 0;
-
-	strncpy(dstr, date, sizeof dstr);
-	dstr[sizeof dstr - 1] = 0;
-	n = tokenize(dstr, flds, 7);
-	if(n != 6 && n != 5)
-		return nil;
-
-	if(n == 5){
-		for(n = 5; n >= 1; n--)
-			flds[n] = flds[n - 1];
-		n = 5;
-	}else{
-		/*
-		 * Wday[,]
-		 */
-		s = strchr(flds[0], ',');
-		if(s != nil)
-			*s = 0;
-		tm->wday = dateindex(flds[0], wdayname, 7);
-		if(tm->wday < 0)
-			return nil;
-	}
-
-	/*
-	 * check for the two major formats:
-	 * Month first or day first
-	 */
-	tm->mon = dateindex(flds[1], monname, 12);
-	if(tm->mon >= 0){
-		tm->mday = strtoul(flds[2], nil, 10);
-		time2tm(tm, flds[3]);
-		zone2tm(tm, flds[4]);
-		tm->year = strtoul(flds[5], nil, 10);
-		if(strlen(flds[5]) > 2)
-			tm->year -= 1900;
-	}else{
-		tm->mday = strtoul(flds[1], nil, 10);
-		tm->mon = dateindex(flds[2], monname, 12);
-		if(tm->mon < 0)
-			return nil;
-		tm->year = strtoul(flds[3], nil, 10);
-		if(strlen(flds[3]) > 2)
-			tm->year -= 1900;
-		time2tm(tm, flds[4]);
-		zone2tm(tm, flds[5]);
-	}
-
-	if(n == 5){
-		gmt = *tm;
-		strncpy(gmt.zone, "", 4);
-		gmt.tzoff = 0;
-		atm = gmtime(tm2sec(&gmt));
-		tm->wday = atm->wday;
-	}else{
-		/*
-		 * Wday[,]
-		 */
-		s = strchr(flds[0], ',');
-		if(s != nil)
-			*s = 0;
-		tm->wday = dateindex(flds[0], wdayname, 7);
-		if(tm->wday < 0)
-			return nil;
-	}
-	return tm;
-}