lnwire: add inbound fee to ChannelUpdate2

We leave a TODO that should be addressed after a discussion at the spec
meeting. For now, having the incorrect TLV type is not a problem since
this ChannelUpdate2 type is not used in production.

lnwire/channel_update_2.go

@@ -70,6 +70,11 @@ type ChannelUpdate2 struct {
 	// millionth of a satoshi.
 	FeeProportionalMillionths tlv.RecordT[tlv.TlvType18, uint32]
 
+	// InboundFee is an optional TLV record that contains the fee
+	// information for incoming HTLCs.
+	// TODO(elle): assign normal tlv type?
+	InboundFee tlv.OptionalRecordT[tlv.TlvType55555, Fee]
+
 	// Signature is used to validate the announced data and prove the
 	// ownership of node id.
 	Signature tlv.RecordT[tlv.TlvType160, Sig]
@@ -102,12 +107,13 @@ func (c *ChannelUpdate2) Decode(r io.Reader, _ uint32) error {
 	var (
 		chainHash  = tlv.ZeroRecordT[tlv.TlvType0, [32]byte]()
 		secondPeer = tlv.ZeroRecordT[tlv.TlvType8, TrueBoolean]()
+		inboundFee = tlv.ZeroRecordT[tlv.TlvType55555, Fee]()
 	)
 	typeMap, err := tlvRecords.ExtractRecords(
 		&chainHash, &c.ShortChannelID, &c.BlockHeight, &c.DisabledFlags,
 		&secondPeer, &c.CLTVExpiryDelta, &c.HTLCMinimumMsat,
 		&c.HTLCMaximumMsat, &c.FeeBaseMsat,
-		&c.FeeProportionalMillionths,
+		&c.FeeProportionalMillionths, &inboundFee,
 		&c.Signature,
 	)
 	if err != nil {
@@ -149,6 +155,11 @@ func (c *ChannelUpdate2) Decode(r io.Reader, _ uint32) error {
 		c.FeeProportionalMillionths.Val = defaultFeeProportionalMillionths //nolint:ll
 	}
 
+	// If the inbound fee was encoded, set it.
+	if _, ok := typeMap[c.InboundFee.TlvType()]; ok {
+		c.InboundFee = tlv.SomeRecordT(inboundFee)
+	}
+
 	c.ExtraSignedFields = ExtraSignedFieldsFromTypeMap(typeMap)
 
 	return nil
@@ -207,6 +218,10 @@ func (c *ChannelUpdate2) AllRecords() []tlv.Record {
 		)
 	}
 
+	c.InboundFee.WhenSome(func(r tlv.RecordT[tlv.TlvType55555, Fee]) {
+		recordProducers = append(recordProducers, &r)
+	})
+
 	recordProducers = append(recordProducers, RecordsAsProducers(
 		tlv.MapToRecords(c.ExtraSignedFields),
 	)...)

lnwire/test_message.go

@@ -569,6 +569,18 @@ func (c *ChannelUpdate2) RandTestMessage(t *rapid.T) Message {
 		ExtraSignedFields: make(map[uint64][]byte),
 	}
 
+	if rapid.Bool().Draw(t, "includeInboundFee") {
+		base := rapid.IntRange(-1000, 1000).Draw(t, "inFeeBase")
+		rate := rapid.IntRange(-1000, 1000).Draw(t, "inFeeProp")
+		fee := Fee{
+			BaseFee: int32(base),
+			FeeRate: int32(rate),
+		}
+		msg.InboundFee = tlv.SomeRecordT(
+			tlv.NewRecordT[tlv.TlvType55555](fee),
+		)
+	}
+
 	msg.Signature.Val = RandSignature(t)
 	msg.Signature.Val.ForceSchnorr()