serve.go

@@ -217,15 +217,23 @@ func (handler *dnsRequestHandler) ServeDNS(responseWriter dnsprotocol.ResponseWr
 			})
 		}
 	case dnsprotocol.TypeNS:
-		if !found {
-			goto noRecord
+		if found {
+			for _, value := range record.NS {
+				reply.Answer = append(reply.Answer, &dnsprotocol.NS{
+					Hdr: dnsprotocol.RR_Header{Name: question.Name, Rrtype: dnsprotocol.TypeNS, Class: dnsprotocol.ClassINET, Ttl: dnsTTL},
+					Ns:  normalizeName(value) + ".",
+				})
+			}
 		}
-		for _, value := range record.NS {
+		if len(reply.Answer) == 0 && normalizeName(name) == handler.service.ZoneApex() && handler.service.ZoneApex() != "" {
 			reply.Answer = append(reply.Answer, &dnsprotocol.NS{
 				Hdr: dnsprotocol.RR_Header{Name: question.Name, Rrtype: dnsprotocol.TypeNS, Class: dnsprotocol.ClassINET, Ttl: dnsTTL},
-				Ns:  normalizeName(value) + ".",
+				Ns:  normalizeName("ns."+name) + ".",
 			})
 		}
+		if len(reply.Answer) == 0 && !found {
+			goto noRecord
+		}
 	case dnsprotocol.TypePTR:
 		ip, ok := parsePTRIP(name)
 		if !ok {

service_test.go

@@ -1099,6 +1099,43 @@ func TestServiceServeAnswersSOAForDerivedZoneApexWithoutExactRecord(t *testing.T
 	}
 }
 
+func TestServiceServeAnswersNSForDerivedZoneApexWithoutExactRecord(t *testing.T) {
+	service := NewService(ServiceOptions{
+		Records: map[string]NameRecords{
+			"gateway.charon.lthn": {
+				A: []string{"10.10.10.10"},
+			},
+			"node.charon.lthn": {
+				A: []string{"10.10.10.11"},
+			},
+		},
+	})
+
+	srv, err := service.Serve("127.0.0.1", 0)
+	if err != nil {
+		t.Fatalf("expected server to start: %v", err)
+	}
+	defer func() { _ = srv.Close() }()
+
+	client := dnsprotocol.Client{}
+	request := new(dnsprotocol.Msg)
+	request.SetQuestion("charon.lthn.", dnsprotocol.TypeNS)
+	response := exchangeWithRetry(t, client, request, srv.Address())
+	if response.Rcode != dnsprotocol.RcodeSuccess {
+		t.Fatalf("expected NS query for derived apex to succeed, got %d", response.Rcode)
+	}
+	if len(response.Answer) != 1 {
+		t.Fatalf("expected one NS answer for derived apex, got %d", len(response.Answer))
+	}
+	ns, ok := response.Answer[0].(*dnsprotocol.NS)
+	if !ok {
+		t.Fatalf("expected NS answer for derived apex, got %#v", response.Answer[0])
+	}
+	if ns.Ns != "ns.charon.lthn." {
+		t.Fatalf("expected synthesized apex NS, got %q", ns.Ns)
+	}
+}
+
 func TestServiceServeReturnsNXDOMAINWhenMissing(t *testing.T) {
 	service := NewService(ServiceOptions{})