lnwire: let DNSAddress implement RecordProducer

In preparation for using this type as a TLV record, we let it implement
the RecordProducer interface.

lnwire/dns_addr.go

@@ -1,10 +1,14 @@
 package lnwire
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
+	"io"
 	"net"
 	"strconv"
+
+	"github.com/lightningnetwork/lnd/tlv"
 )
 
 var (
@@ -86,3 +90,70 @@ func ValidateDNSAddr(hostname string, port uint16) error {
 
 	return nil
 }
+
+// Record returns a TLV record that can be used to encode/decode the DNSAddress.
+//
+// NOTE: this is part of the tlv.RecordProducer interface.
+func (d *DNSAddress) Record() tlv.Record {
+	sizeFunc := func() uint64 {
+		// Hostname length + 2 bytes for port.
+		return uint64(len(d.Hostname) + 2)
+	}
+
+	return tlv.MakeDynamicRecord(
+		0, d, sizeFunc, dnsAddressEncoder, dnsAddressDecoder,
+	)
+}
+
+// dnsAddressEncoder is a TLV encoder for DNSAddress.
+func dnsAddressEncoder(w io.Writer, val any, _ *[8]byte) error {
+	if v, ok := val.(*DNSAddress); ok {
+		var buf bytes.Buffer
+
+		// Write the hostname as raw bytes (no length prefix for TLV).
+		if _, err := buf.WriteString(v.Hostname); err != nil {
+			return err
+		}
+
+		// Write the port as 2 bytes.
+		err := WriteUint16(&buf, v.Port)
+		if err != nil {
+			return err
+		}
+
+		_, err = w.Write(buf.Bytes())
+
+		return err
+	}
+
+	return tlv.NewTypeForEncodingErr(val, "DNSAddress")
+}
+
+// dnsAddressDecoder is a TLV decoder for DNSAddress.
+func dnsAddressDecoder(r io.Reader, val any, _ *[8]byte,
+	l uint64) error {
+
+	if v, ok := val.(*DNSAddress); ok {
+		if l < 2 {
+			return fmt.Errorf("DNS address must be at least 2 " +
+				"bytes")
+		}
+
+		// Read hostname (all bytes except last 2).
+		hostnameLen := l - 2
+		hostnameBytes := make([]byte, hostnameLen)
+		if _, err := io.ReadFull(r, hostnameBytes); err != nil {
+			return err
+		}
+		v.Hostname = string(hostnameBytes)
+
+		// Read port (last 2 bytes).
+		if err := ReadElement(r, &v.Port); err != nil {
+			return err
+		}
+
+		return ValidateDNSAddr(v.Hostname, v.Port)
+	}
+
+	return tlv.NewTypeForDecodingErr(val, "DNSAddress", l, 0)
+}