lnwire: morph HTLCSettleRequest into UpdateFufillHTLC

This commit modifies the prior HTLCSettleRequest to more closely match
the UpdateFufillHTLC defined within the specification. The only
semantic change is the move from a slice of pre-images (for “multi-sig”
LN) to a single payment preimage.

lnwire/update_fulfill_htlc.go

@@ -0,0 +1,116 @@
+package lnwire
+
+import (
+	"fmt"
+	"io"
+
+	"github.com/roasbeef/btcd/wire"
+)
+
+// UpdateFufillHTLC is sent by Alice to Bob when she wishes to settle a
+// particular HTLC referenced by its HTLCKey within a specific active channel
+// referenced by ChannelPoint.  A subsequent CommitSig message will be sent by
+// Alice to "lock-in" the removal of the specified HTLC, possible containing a
+// batch signature covering several settled HTLC's.
+type UpdateFufillHTLC struct {
+	// ChannelPoint references an active channel which holds the HTLC to be
+	// settled.
+	ChannelPoint wire.OutPoint
+
+	// ID denotes the exact HTLC stage within the receiving node's
+	// commitment transaction to be removed.
+	ID uint64
+
+	// PaymentPreimage is the R-value preimage required to fully settle an
+	// HTLC.
+	PaymentPreimage [32]byte
+}
+
+// NewUpdateFufillHTLC returns a new empty UpdateFufillHTLC.
+func NewUpdateFufillHTLC(chanPoint wire.OutPoint, id uint64,
+	preimage [32]byte) *UpdateFufillHTLC {
+
+	return &UpdateFufillHTLC{
+		ChannelPoint:    chanPoint,
+		ID:              id,
+		PaymentPreimage: preimage,
+	}
+}
+
+// A compile time check to ensure UpdateFufillHTLC implements the lnwire.Message
+// interface.
+var _ Message = (*UpdateFufillHTLC)(nil)
+
+// Decode deserializes a serialized UpdateFufillHTLC message stored in the passed
+// io.Reader observing the specified protocol version.
+//
+// This is part of the lnwire.Message interface.
+func (c *UpdateFufillHTLC) Decode(r io.Reader, pver uint32) error {
+	// ChannelPoint(8)
+	// ID(8)
+	// PaymentPreimage(32)
+	err := readElements(r,
+		&c.ChannelPoint,
+		&c.ID,
+		c.PaymentPreimage[:],
+	)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Encode serializes the target UpdateFufillHTLC into the passed io.Writer
+// observing the protocol version specified.
+//
+// This is part of the lnwire.Message interface.
+func (c *UpdateFufillHTLC) Encode(w io.Writer, pver uint32) error {
+	err := writeElements(w,
+		c.ChannelPoint,
+		c.ID,
+		c.PaymentPreimage[:],
+	)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Command returns the integer uniquely identifying this message type on the
+// wire.
+//
+// This is part of the lnwire.Message interface.
+func (c *UpdateFufillHTLC) Command() uint32 {
+	return CmdUpdateFufillHTLC
+}
+
+// MaxPayloadLength returns the maximum allowed payload size for a UpdateFufillHTLC
+// complete message observing the specified protocol version.
+//
+// This is part of the lnwire.Message interface.
+func (c *UpdateFufillHTLC) MaxPayloadLength(uint32) uint32 {
+	// 36 + 8 + (32 * 15)
+	return 524
+}
+
+// Validate performs any necessary sanity checks to ensure all fields present
+// on the UpdateFufillHTLC are valid.
+//
+// This is part of the lnwire.Message interface.
+func (c *UpdateFufillHTLC) Validate() error {
+	// We're good!
+	return nil
+}
+
+// String returns the string representation of the target UpdateFufillHTLC.
+//
+// This is part of the lnwire.Message interface.
+func (c *UpdateFufillHTLC) String() string {
+	return fmt.Sprintf("\n--- Begin UpdateFufillHTLC ---\n") +
+		fmt.Sprintf("ChannelPoint:\t%v\n", c.ChannelPoint) +
+		fmt.Sprintf("ID:\t%d\n", c.ID) +
+		fmt.Sprintf("RedemptionHashes:\t\t%x\n", c.PaymentPreimage) +
+		fmt.Sprintf("--- End UpdateFufillHTLC ---\n")
+}