-cat >"$tempfile" <<EOF
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:Berlin RAW Confetti
-BEGIN:VEVENT
-UID:$uid
-DTSTAMP:TZID=${tzid}:${tstamp}
-DTSTART:
-DURATION:
-RRULE:
-SUMMARY:
-COMMENT:
-END:VEVENT
-END:VCARD
-EOF
-
-echo -n "Location: ?p=courses&edit=$course\n\n"
+if tempfile="$(SLOCK "$coursefile")"; then
+ cat >"$tempfile" <<-EOF
+ BEGIN:VCALENDAR
+ VERSION:2.0
+ PRODID:Berlin RAW Confetti
+ BEGIN:VEVENT
+ UID:$uid
+ DTSTAMP:TZID=${tzid}:${tstamp}
+ DTSTART:TZID=${tzid}:${tstamp}
+ DURATION:
+ RRULE:
+ SUMMARY:
+ COMMENT:
+ END:VEVENT
+ END:VCARD
+ EOF
+ REDIRECT "${_BASE}/courses/?e=${course}"
+else
+ SET_COOKIE session message="EDITLOCK"
+ REDIRECT "${_BASE}/courses/"
+fi