lnwire: add OutPoint type with TLV encoding support

Add a new OutPoint type that wraps wire.OutPoint and provides TLV
encoding/decoding capabilities through the tlv.RecordProducer interface.
This enables OutPoint to be used in TLV streams of messages.

lnwire/outpoint.go

@@ -0,0 +1,53 @@
+package lnwire
+
+import (
+	"bytes"
+	"io"
+
+	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+// OutPoint describes an outpoint of a transaction via its transaction hash
+// and the outpoint index. This is a thin wrapper around the wire.OutPoint to
+// provide TLV encoding/decoding.
+type OutPoint wire.OutPoint
+
+// Record returns a TLV record that can be used to encode/decode the OutPoint.
+//
+// NOTE: this is part of the tlv.RecordProducer interface.
+func (o *OutPoint) Record() tlv.Record {
+	return tlv.MakeStaticRecord(0, o, 34, outpointEncoder, outpointDecoder)
+}
+
+// outpointEncoder is a TLV encoder for OutPoint.
+func outpointEncoder(w io.Writer, val any, _ *[8]byte) error {
+	if v, ok := val.(*OutPoint); ok {
+		buf := bytes.NewBuffer(nil)
+		err := WriteOutPoint(buf, wire.OutPoint(*v))
+		if err != nil {
+			return err
+		}
+		_, err = w.Write(buf.Bytes())
+
+		return err
+	}
+
+	return tlv.NewTypeForEncodingErr(val, "OutPoint")
+}
+
+// outpointDecoder is a TLV decoder for OutPoint.
+func outpointDecoder(r io.Reader, val any, _ *[8]byte, l uint64) error {
+	if v, ok := val.(*OutPoint); ok {
+		var o wire.OutPoint
+		if err := ReadElement(r, &o); err != nil {
+			return err
+		}
+
+		*v = OutPoint(o)
+
+		return nil
+	}
+
+	return tlv.NewTypeForDecodingErr(val, "OutPoint", l, 34)
+}