libfetch: allow obsolete date format in http timestamps

RFC2616 §3.3.1 requires compliant client to accept the two
obsolete formats in addition to the Internet standard format.

Based on patch by John Hallam <sw@j.hallam.dk>

(cherry picked from commit 908efa92)

libfetch/http.c

@@ -482,8 +482,15 @@ http_parse_mtime(const char *p, time_t *mtime)
 
 	locale = strdupa(setlocale(LC_TIME, NULL));
 	setlocale(LC_TIME, "C");
+	/* RFC2616 §3.3.1 requires compliant client to accept the Internet
+	 * standard, and the two obsolete, date formats:
+	 *  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
+	 *  Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
+	 *  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
+	 */
 	r = strptime(p, "%a, %d %b %Y %H:%M:%S GMT", &tm);
-	/* XXX should add support for date-2 and date-3 */
+	if (!r) r = strptime(p, "%A, %d-%b-%y %H:%M:%S GMT", &tm);
+	if (!r) r = strptime(p, "%a %b %d %H:%M:%S %Y", &tm);
 	setlocale(LC_TIME, locale);
 	if (r == NULL)
 		return (-1);