fix: incorrect OPT RR filter order (#2634)

Author: woaihsw

dns/util.go

@@ -64,6 +64,13 @@ func putMsgToCache(c dnsCache, q D.Question, msg *D.Msg) {
 		return
 	}
 
+	msg = msg.Copy() // never modify the original msg
+
+	// OPT RRs MUST NOT be cached, forwarded, or stored in or loaded from master files.
+	msg.Extra = lo.Filter(msg.Extra, func(rr D.RR, index int) bool {
+		return rr.Header().Rrtype != D.TypeOPT
+	})
+
 	var ttl uint32
 	if msg.Rcode == D.RcodeServerFailure {
 		// [...] a resolver MAY cache a server failure response.
@@ -76,13 +83,6 @@ func putMsgToCache(c dnsCache, q D.Question, msg *D.Msg) {
 		return
 	}
 
-	msg = msg.Copy() // never modify the original msg
-
-	// OPT RRs MUST NOT be cached, forwarded, or stored in or loaded from master files.
-	msg.Extra = lo.Filter(msg.Extra, func(rr D.RR, index int) bool {
-		return rr.Header().Rrtype != D.TypeOPT
-	})
-
 	c.SetWithExpire(q.String(), msg, time.Now().Add(time.Duration(ttl)*time.Second))
 }