fix: DNS NCACHE TTL and OPT RRs (#2900)

* Fix: DNS NCACHE TTL and OPT RRs

1. DNS NCACHE was not correctly implemented.
2. OPT RRs must not be cached or forwarded.

Closes #2889.

dns/resolver.go

@@ -195,7 +195,11 @@ func (r *Resolver) exchangeWithoutCache(ctx context.Context, m *D.Msg) (msg *D.M
 			msg := result.(*D.Msg)
 
 			if cache {
-				putMsgToCache(r.lruCache, q.String(), 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
+				})
+				putMsgToCache(r.lruCache, q.String(), q, msg)
 			}
 		}()