lnwire: let DNSAddress implement RecordProducer

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

Author: ellemouton

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)
+}

lnwire/dns_addr_test.go

@@ -1,11 +1,14 @@
 package lnwire
 
 import (
+	"bytes"
 	"fmt"
 	"strings"
 	"testing"
 
+	"github.com/lightningnetwork/lnd/tlv"
 	"github.com/stretchr/testify/require"
+	"pgregory.net/rapid"
 )
 
 // TestValidateDNSAddr tests hostname and port validation per BOLT #7.
@@ -85,3 +88,112 @@ func TestValidateDNSAddr(t *testing.T) {
 		})
 	}
 }
+
+// TestDNSAddressTLVEncoding tests the TLV encoding and decoding of DNSAddress
+// structs using the ExtraOpaqueData interface.
+func TestDNSAddressTLVEncoding(t *testing.T) {
+	t.Parallel()
+
+	testDNSAddr := DNSAddress{
+		Hostname: "lightning.example.com",
+		Port:     9000,
+	}
+
+	var extraData ExtraOpaqueData
+	require.NoError(t, extraData.PackRecords(&testDNSAddr))
+
+	var decodedDNSAddr DNSAddress
+	tlvs, err := extraData.ExtractRecords(&decodedDNSAddr)
+	require.NoError(t, err)
+
+	require.Contains(t, tlvs, tlv.Type(0))
+	require.Equal(t, testDNSAddr, decodedDNSAddr)
+}
+
+// TestDNSAddressRecord tests the TLV Record interface of DNSAddress
+// by directly encoding and decoding using the Record method.
+func TestDNSAddressRecord(t *testing.T) {
+	t.Parallel()
+
+	testDNSAddr := DNSAddress{
+		Hostname: "lightning.example.com",
+		Port:     9000,
+	}
+
+	var buf bytes.Buffer
+	record := testDNSAddr.Record()
+	require.NoError(t, record.Encode(&buf))
+
+	var decodedDNSAddr DNSAddress
+	decodedRecord := decodedDNSAddr.Record()
+	require.NoError(t, decodedRecord.Decode(&buf, uint64(buf.Len())))
+
+	require.Equal(t, testDNSAddr, decodedDNSAddr)
+}
+
+// TestDNSAddressInvalidDecoding tests error cases during TLV decoding.
+func TestDNSAddressInvalidDecoding(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name   string
+		data   []byte
+		errMsg string
+	}{
+		{
+			name:   "too short (only 1 byte)",
+			data:   []byte{0x61},
+			errMsg: "DNS address must be at least 2 bytes",
+		},
+		{
+			name:   "empty data",
+			data:   []byte{},
+			errMsg: "DNS address must be at least 2 bytes",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			var dnsAddr DNSAddress
+			record := dnsAddr.Record()
+
+			buf := bytes.NewReader(tc.data)
+			err := record.Decode(buf, uint64(len(tc.data)))
+			require.Error(t, err)
+			require.ErrorContains(t, err, tc.errMsg)
+		})
+	}
+}
+
+// TestDNSAddressProperty uses property-based testing to verify that DNSAddress
+// TLV encoding and decoding is correct for random DNSAddress values.
+func TestDNSAddressProperty(t *testing.T) {
+	t.Parallel()
+
+	scenario := func(t *rapid.T) {
+		// Generate a random valid hostname.
+		hostname := genValidHostname(t)
+
+		// Generate a random port (excluding 0 which is invalid).
+		port := rapid.Uint16Range(1, 65535).Draw(t, "port")
+
+		dnsAddr := DNSAddress{
+			Hostname: hostname,
+			Port:     port,
+		}
+
+		var buf bytes.Buffer
+		record := dnsAddr.Record()
+		err := record.Encode(&buf)
+		require.NoError(t, err)
+
+		var decodedDNSAddr DNSAddress
+		decodedRecord := decodedDNSAddr.Record()
+		err = decodedRecord.Decode(&buf, uint64(buf.Len()))
+		require.NoError(t, err)
+
+		require.Equal(t, dnsAddr, decodedDNSAddr)
+	}
+
+	rapid.Check(t, scenario)
+}

lnwire/test_message.go

@@ -1867,3 +1867,24 @@ func (c *Error) RandTestMessage(t *rapid.T) Message {
 
 	return msg
 }
+
+// genValidHostname generates a random valid hostname according to BOLT #7
+// rules.
+func genValidHostname(t *rapid.T) string {
+	// Valid characters: a-z, A-Z, 0-9, -, .
+	validChars := "abcdefghijklmnopqrstuvwxyzABCDE" +
+		"FGHIJKLMNOPQRSTUVWXYZ0123456789-."
+
+	// Generate hostname length between 1 and 255 characters.
+	length := rapid.IntRange(1, 255).Draw(t, "hostname_length")
+
+	hostname := make([]byte, length)
+	for i := 0; i < length; i++ {
+		charIndex := rapid.IntRange(0, len(validChars)-1).Draw(
+			t, fmt.Sprintf("char_%d", i),
+		)
+		hostname[i] = validChars[charIndex]
+	}
+
+	return string(hostname)
+}