lnwire: add update_fail_malformed_htlc message

In this commit BOLT#4 specification message have been added to the
lnwire package. This messsage is needed in order to notify payment
sender that forwarding node unable to parse the onion blob.

lnwire/lnwire.go

@@ -180,7 +180,10 @@ func writeElement(w io.Writer, element interface{}) error {
 		if _, err := w.Write(e[:]); err != nil {
 			return err
 		}
-
+	case FailCode:
+		if err := writeElement(w, uint16(e)); err != nil {
+			return err
+		}
 	case ShortChannelID:
 		// Check that field fit in 3 bytes and write the blockHeight
 		if e.BlockHeight > ((1 << 24) - 1) {
@@ -440,6 +443,10 @@ func readElement(r io.Reader, element interface{}) error {
 			Hash:  *hash,
 			Index: uint32(index),
 		}
+	case *FailCode:
+		if err := readElement(r, (*uint16)(e)); err != nil {
+			return err
+		}
 
 	case *ChannelID:
 		if _, err := io.ReadFull(r, e[:]); err != nil {

lnwire/lnwire_test.go

@@ -529,6 +529,13 @@ func TestLightningWireProtocol(t *testing.T) {
 				return mainScenario(&m)
 			},
 		},
+		{
+
+			msgType: MsgUpdateFailMalformedHTLC,
+			scenario: func(m UpdateFailMalformedHTLC) bool {
+				return mainScenario(&m)
+			},
+		},
 		{
 			msgType: MsgChannelAnnouncement,
 			scenario: func(m ChannelAnnouncement) bool {

lnwire/message.go

@@ -39,6 +39,7 @@ const (
 	MsgUpdateFailHTLC                        = 131
 	MsgCommitSig                             = 132
 	MsgRevokeAndAck                          = 133
+	MsgUpdateFailMalformedHTLC               = 135
 	MsgUpdateFee                             = 137
 	MsgChannelAnnouncement                   = 256
 	MsgNodeAnnouncement                      = 257
@@ -75,6 +76,8 @@ func (t MessageType) String() string {
 		return "CommitSig"
 	case MsgRevokeAndAck:
 		return "RevokeAndAck"
+	case MsgUpdateFailMalformedHTLC:
+		return "UpdateFailMalformedHTLC"
 	case MsgError:
 		return "Error"
 	case MsgChannelAnnouncement:
@@ -161,6 +164,8 @@ func makeEmptyMessage(msgType MessageType) (Message, error) {
 		msg = &RevokeAndAck{}
 	case MsgUpdateFee:
 		msg = &UpdateFee{}
+	case MsgUpdateFailMalformedHTLC:
+		msg = &UpdateFailMalformedHTLC{}
 	case MsgError:
 		msg = &Error{}
 	case MsgChannelAnnouncement:

lnwire/update_fail_malformed_htlc.go

@@ -0,0 +1,74 @@
+package lnwire
+
+import (
+	"crypto/sha256"
+	"io"
+)
+
+// UpdateFailMalformedHTLC is sent by either the payment forwarder or by payment
+// receiver to the payment sender in order to notify it that the onion blob
+// can't be parsed. For that reason we send this message instead of obfuscate
+// the onion failure.
+type UpdateFailMalformedHTLC struct {
+	// ChanID is the particular active channel that this
+	// UpdateFailMalformedHTLC is bound to.
+	ChanID ChannelID
+
+	// ID references which HTLC on the remote node's commitment transaction
+	// has timed out.
+	ID uint64
+
+	// ShaOnionBlob hash of the onion blob on which can't be parsed by the
+	// node in the payment path.
+	ShaOnionBlob [sha256.Size]byte
+
+	// FailureCode the exact reason why onion blob haven't been parsed.
+	FailureCode FailCode
+}
+
+// A compile time check to ensure UpdateFailMalformedHTLC implements the lnwire.Message
+// interface.
+var _ Message = (*UpdateFailMalformedHTLC)(nil)
+
+// Decode deserializes a serialized UpdateFailMalformedHTLC message stored in the passed
+// io.Reader observing the specified protocol version.
+//
+// This is part of the lnwire.Message interface.
+func (c *UpdateFailMalformedHTLC) Decode(r io.Reader, pver uint32) error {
+	return readElements(r,
+		&c.ChanID,
+		&c.ID,
+		c.ShaOnionBlob[:],
+		&c.FailureCode,
+	)
+}
+
+// Encode serializes the target UpdateFailMalformedHTLC into the passed io.Writer observing
+// the protocol version specified.
+//
+// This is part of the lnwire.Message interface.
+func (c *UpdateFailMalformedHTLC) Encode(w io.Writer, pver uint32) error {
+	return writeElements(w,
+		c.ChanID,
+		c.ID,
+		c.ShaOnionBlob[:],
+		c.FailureCode,
+	)
+}
+
+// MsgType returns the integer uniquely identifying this message type on the
+// wire.
+//
+// This is part of the lnwire.Message interface.
+func (c *UpdateFailMalformedHTLC) MsgType() MessageType {
+	return MsgUpdateFailMalformedHTLC
+}
+
+// MaxPayloadLength returns the maximum allowed payload size for a UpdateFailMalformedHTLC
+// complete message observing the specified protocol version.
+//
+// This is part of the lnwire.Message interface.
+func (c *UpdateFailMalformedHTLC) MaxPayloadLength(uint32) uint32 {
+	// 32 +  8 + 32 + 2
+	return 74
+}