lnwallet: add noop updateType to paymendDescriptor

We add a new update type to the payment descriptor to describe this new
type of htlc. We also add the isAdd helper as the two HTLC add types are
almost identical except for the settling part.

Author: GeorgeTsagk

lnwallet/payment_descriptor.go

@@ -42,6 +42,12 @@ const (
 	// FeeUpdate is an update type sent by the channel initiator that
 	// updates the fee rate used when signing the commitment transaction.
 	FeeUpdate
+
+	// NoopAdd is an update type that adds a new HTLC entry into the log.
+	// This differs from the normal Add type, in that when settled the
+	// balance will go back to the sender, rather than be credited for the
+	// receiver.
+	NoopAdd
 )
 
 // String returns a human readable string that uniquely identifies the target
@@ -58,6 +64,8 @@ func (u updateType) String() string {
 		return "Settle"
 	case FeeUpdate:
 		return "FeeUpdate"
+	case NoopAdd:
+		return "NoopAdd"
 	default:
 		return "<unknown type>"
 	}
@@ -238,7 +246,7 @@ type paymentDescriptor struct {
 func (pd *paymentDescriptor) toLogUpdate() channeldb.LogUpdate {
 	var msg lnwire.Message
 	switch pd.EntryType {
-	case Add:
+	case Add, NoopAdd:
 		msg = &lnwire.UpdateAddHTLC{
 			ChanID:        pd.ChanID,
 			ID:            pd.HtlcIndex,
@@ -290,7 +298,7 @@ func (pd *paymentDescriptor) setCommitHeight(
 	whoseCommitChain lntypes.ChannelParty, nextHeight uint64) {
 
 	switch pd.EntryType {
-	case Add:
+	case Add, NoopAdd:
 		pd.addCommitHeights.SetForParty(
 			whoseCommitChain, nextHeight,
 		)
@@ -311,3 +319,8 @@ func (pd *paymentDescriptor) setCommitHeight(
 		)
 	}
 }
+
+// isAdd returns true if the paymentDescriptor is of type Add.
+func (pd *paymentDescriptor) isAdd() bool {
+	return pd.EntryType == Add || pd.EntryType == NoopAdd
+}