lnwire+channeldb: parse inbound fees

In this commit, the tlv extension of a channel update message is parsed.
If an inbound fee schedule is encountered, it is reported in the
graph rpc calls.

lnwire/typed_fee.go

@@ -0,0 +1,60 @@
+package lnwire
+
+import (
+	"io"
+
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+const (
+	FeeRecordType tlv.Type = 55555
+)
+
+// Fee represents a fee schedule.
+type Fee struct {
+	BaseFee int32
+	FeeRate int32
+}
+
+// Record returns a TLV record that can be used to encode/decode the fee
+// type from a given TLV stream.
+func (l *Fee) Record() tlv.Record {
+	return tlv.MakeStaticRecord(
+		FeeRecordType, l, 8, feeEncoder, feeDecoder, //nolint:gomnd
+	)
+}
+
+// feeEncoder is a custom TLV encoder for the fee record.
+func feeEncoder(w io.Writer, val interface{}, buf *[8]byte) error {
+	v, ok := val.(*Fee)
+	if !ok {
+		return tlv.NewTypeForEncodingErr(val, "lnwire.Fee")
+	}
+
+	if err := tlv.EUint32T(w, uint32(v.BaseFee), buf); err != nil {
+		return err
+	}
+
+	return tlv.EUint32T(w, uint32(v.FeeRate), buf)
+}
+
+// feeDecoder is a custom TLV decoder for the fee record.
+func feeDecoder(r io.Reader, val interface{}, buf *[8]byte, l uint64) error {
+	v, ok := val.(*Fee)
+	if !ok {
+		return tlv.NewTypeForDecodingErr(val, "lnwire.Fee", l, 8)
+	}
+
+	var baseFee, feeRate uint32
+	if err := tlv.DUint32(r, &baseFee, buf, 4); err != nil { //nolint: gomnd,lll
+		return err
+	}
+	if err := tlv.DUint32(r, &feeRate, buf, 4); err != nil { //nolint: gomnd,lll
+		return err
+	}
+
+	v.FeeRate = int32(feeRate)
+	v.BaseFee = int32(baseFee)
+
+	return nil
+}