1 files changed, 57 insertions, 0 deletions
diff --git a/internal/dns/rr_opt.go b/internal/dns/rr_opt.go
new file mode 100644
index 0000000..77bc1ee
--- /dev/null
+++ b/internal/dns/rr_opt.go
@@ -0,0 +1,57 @@
+package dns
+
+import "fmt"
+
+// https://datatracker.ietf.org/doc/html/rfc6891#section-4.1
+type Option struct {
+	Code uint16
+	Data []byte
+}
+
+type OPT struct {
+	// https://datatracker.ietf.org/doc/html/rfc6891#section-4.3
+	UDPSize  uint16
+	ExtRCode uint8
+	Version  uint8
+	DO       bool
+	Z        uint16
+	Options  []Option
+}
+
+func (o *OPT) Type() uint16 { return TypeOPT }
+
+func (o *OPT) Pack(p *packer) error {
+	for _, opt := range o.Options {
+		p.writeUint16(opt.Code)
+		p.writeUint16(uint16(len(opt.Data)))
+		p.buf = append(p.buf, opt.Data...)
+	}
+	return nil
+}
+
+func (o *OPT) Unpack(u *unpacker, length uint16) error {
+	end := u.off + int(length)
+	for u.off < end {
+		code, err := u.readUint16()
+		if err != nil {
+			return err
+		}
+		optLen, err := u.readUint16()
+		if err != nil {
+			return err
+		}
+		if u.off+int(optLen) > end {
+			return fmt.Errorf("dns: opt data overflow")
+		}
+		o.Options = append(o.Options, Option{
+			Code: code,
+			Data: append([]byte(nil), u.buf[u.off:u.off+int(optLen)]...),
+		})
+		u.off += int(optLen)
+	}
+	return nil
+}
+
+func (o *OPT) String() string {
+	return fmt.Sprintf("OPT udpsize=%d extrcode=%d version=%d do=%t", o.UDPSize, o.ExtRCode, o.Version, o.DO)
+}