Add DNS resource NSEC helper

lns_package_test.go

@@ -730,6 +730,11 @@ func TestPackageResourceAliases(t *testing.T) {
 		t.Fatal("resource aliases should expose record type helpers from pkg/dns")
 	}
 
+	nsec := resource.ToNSEC("Example")
+	if nsec.Name != "Example." || nsec.NextDomain != "example\x00." || nsec.TTL != DEFAULT_TTL {
+		t.Fatalf("Resource.ToNSEC returned %+v", nsec)
+	}
+
 	encoded, err := resource.Encode()
 	if err != nil {
 		t.Fatalf("Resource.Encode returned error: %v", err)

pkg/dns/resource.go

@@ -247,6 +247,30 @@ func (r *Resource) GetHasDS() bool {
 	return r.HasDS()
 }
 
+// ToNSEC constructs the reference NSEC helper output for the resource.
+//
+// The bitmap selection matches the JS reference helper:
+// - NS-capable resources use TYPE_MAP_NS
+// - TXT-only resources use TYPE_MAP_TXT
+// - everything else falls back to TYPE_MAP_EMPTY
+func (r *Resource) ToNSEC(name string) NSECRecord {
+	typeMap := TYPE_MAP_EMPTY
+	if r != nil {
+		if r.HasNS() {
+			typeMap = TYPE_MAP_NS
+		} else if r.HasType(HSTypeTXT) {
+			typeMap = TYPE_MAP_TXT
+		}
+	}
+
+	return Create(name, NextName(name), typeMap)
+}
+
+// GetToNSEC is an alias for ToNSEC.
+func (r *Resource) GetToNSEC(name string) NSECRecord {
+	return r.ToNSEC(name)
+}
+
 // Encode serializes the resource payload in the reference binary format.
 func (r *Resource) Encode() ([]byte, error) {
 	if r == nil {

pkg/dns/resource_test.go

@@ -242,6 +242,67 @@ func TestResourceTypeHelpers(t *testing.T) {
 	}
 }
 
+func TestResourceToNSEC(t *testing.T) {
+	cases := []struct {
+		name   string
+		record []ResourceRecord
+		want   []byte
+	}{
+		{
+			name: "empty",
+			want: TYPE_MAP_EMPTY,
+		},
+		{
+			name: "txt",
+			record: []ResourceRecord{
+				TXTRecord{Entries: []string{"txt"}},
+			},
+			want: TYPE_MAP_TXT,
+		},
+		{
+			name: "ns",
+			record: []ResourceRecord{
+				TXTRecord{Entries: []string{"txt"}},
+				NSRecord{NS: "ns1.example."},
+			},
+			want: TYPE_MAP_NS,
+		},
+	}
+
+	for _, tc := range cases {
+		resource := NewResource()
+		resource.Records = append(resource.Records, tc.record...)
+
+		rr := resource.ToNSEC("Example")
+		if rr.Name != "Example." {
+			t.Fatalf("%s: ToNSEC name = %q, want %q", tc.name, rr.Name, "Example.")
+		}
+
+		if rr.NextDomain != "example\x00." {
+			t.Fatalf("%s: ToNSEC next domain = %q, want %q", tc.name, rr.NextDomain, "example\x00.")
+		}
+
+		if rr.TTL != DEFAULT_TTL {
+			t.Fatalf("%s: ToNSEC TTL = %d, want %d", tc.name, rr.TTL, DEFAULT_TTL)
+		}
+
+		if !bytes.Equal(rr.TypeBitmap, tc.want) {
+			t.Fatalf("%s: ToNSEC bitmap = %x, want %x", tc.name, rr.TypeBitmap, tc.want)
+		}
+
+		alias := resource.GetToNSEC("Example")
+		if alias.Name != rr.Name || alias.NextDomain != rr.NextDomain || alias.TTL != rr.TTL {
+			t.Fatalf("%s: GetToNSEC should alias ToNSEC, got %+v want %+v", tc.name, alias, rr)
+		}
+	}
+
+	var nilResource *Resource
+	rr := nilResource.ToNSEC("Example")
+	if !bytes.Equal(rr.TypeBitmap, TYPE_MAP_EMPTY) {
+		t.Fatalf("nil resource ToNSEC bitmap = %x, want %x", rr.TypeBitmap, TYPE_MAP_EMPTY)
+	}
+}
+
 func TestResourceDecodeStopsAtUnknownType(t *testing.T) {
 	resource := NewResource()
 	resource.Records = []ResourceRecord{TXTRecord{Entries: []string{"known"}}}