lnwire: add SingleFundingOpenProof message

The SFOP is the final message sent during the single funding channel
negotiation protocol. Once Alice sends the SFOP message to Bob, Bob
will then commit resources to watching and updating the newly created
channel with Alice.

lnwire/single_funding_open_proof.go

@@ -0,0 +1,103 @@
+package lnwire
+
+import (
+	"fmt"
+	"io"
+)
+
+// SingleFundingOpenProof is the message sent by the channel initiator to the
+// responder after the previously constructed funding transaction has achieved
+// a sufficient number of confirmations. It is the initiator's duty to present
+// a proof of an open channel to the responder. Otherwise, responding node may
+// be vulernable to a resource exhasution attack wherein the a requesting node
+// repeatedly negotiates funding transactions which are never broadcast. If the
+// responding node commits resources to watch the chain for each funding
+// transaction, then this attack is very cheap for the initiator.
+type SingleFundingOpenProof struct {
+	// ChannelID serves to uniquely identify the future channel created by
+	// the initiated single funder workflow.
+	ChannelID uint64
+
+	// SpvProof is an merkle proof of the inclusion of the funding
+	// transaction within a block.
+	// TODO(roasbeef): spec out format for SPV proof, only of single tx so
+	// can be compact
+	SpvProof []byte
+}
+
+// Decode deserializes the serialized SingleFundingOpenProof stored in the
+// passed io.Reader into the target SingleFundingOpenProof using the
+// deserialization rules defined by the passed protocol version.
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingOpenProof) Decode(r io.Reader, pver uint32) error {
+	// ChannelID (8)
+	// SpvProof (?)
+	err := readElements(r,
+		&s.ChannelID,
+		&s.SpvProof)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// NewSingleFundingSignComplete creates a new empty SingleFundingOpenProof
+// message.
+func NewSingleFundingOpenProof() *SingleFundingOpenProof {
+	return &SingleFundingOpenProof{}
+}
+
+// Encode serializes the target SingleFundingOpenProof into the passed
+// io.Writer implementation. Serialization will observe the rules defined by
+// the passed protocol version.
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingOpenProof) Encode(w io.Writer, pver uint32) error {
+	err := writeElements(w,
+		s.ChannelID,
+		s.SpvProof)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Command returns the uint32 code which uniquely identifies this message as a
+// SingleFundingSignComplete on the wire.
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingOpenProof) Command() uint32 {
+	return CmdSingleFundingOpenProof
+}
+
+// MaxPayloadLength returns the maximum allowed payload length for a
+// SingleFundingComplete. This is calculated by summing the max length of all
+// the fields within a SingleFundingOpenProof.
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingOpenProof) MaxPayloadLength(uint32) uint32 {
+	// 8 +
+	return 81
+}
+
+// Validate examines each populated field within the SingleFundingOpenProof for
+// field sanity.
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingOpenProof) Validate() error {
+	// We're good!
+	return nil
+}
+
+// String returns the string representation of the SingleFundingOpenProof.
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingOpenProof) String() string {
+	return fmt.Sprintf("\n--- Begin FundingSignComplete ---\n") +
+		fmt.Sprintf("ChannelID:\t\t%d\n", s.ChannelID) +
+		fmt.Sprintf("SpvProof\t\t%s\n", s.SpvProof) +
+		fmt.Sprintf("--- End FundingSignComplete ---\n")
+}