lnwire: add SingleFundingComplete to single funder

This commit adds the SingleFundingComplete message to the single funder
channel workflow. This is the 3rd message sent in the workflow,
traveling from Alice to Bob once Alice is able to construct the final
commitment transaction.

lnwire/single_funding_complete.go

@@ -0,0 +1,124 @@
+package lnwire
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+
+	"github.com/roasbeef/btcd/btcec"
+	"github.com/roasbeef/btcd/wire"
+)
+
+// SingleFundingComplete is the message Alice sends to Bob once she is able to
+// fully assemble the funding transaction, and both versions of the commitment
+// transaction. The purpose of this message is to present Bob with the items
+// required for him to generate a signature for Alice's version of the
+// commitment transaction.
+type SingleFundingComplete struct {
+	// ChannelID serves to uniquely identify the future channel created by
+	// the initiated single funder workflow.
+	ChannelID uint64
+
+	// FundingOutPoint is the outpoint (txid:index) of the funding
+	// transaction. With this value, Bob will be able to generate a
+	// signature for Alice's version of the commitment transaction.
+	FundingOutPoint wire.OutPoint
+
+	// CommitmentSignature is Alice's signature for Bob's version of the
+	// commitment transaction.
+	CommitmentSignature *btcec.Signature
+}
+
+// Decode deserializes the serialized SingleFundingComplete stored in the passed
+// io.Reader into the target SingleFundingComplete using the deserialization
+// rules defined by the passed protocol version.
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingComplete) Decode(r io.Reader, pver uint32) error {
+	// ChannelID (8)
+	// FundingOutPoint (36)
+	// Commitment Signature (73)
+	err := readElements(r,
+		&s.ChannelID,
+		&s.FundingOutPoint,
+		&s.CommitmentSignature)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Encode serializes the target SingleFundingComplete 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 *SingleFundingComplete) Encode(w io.Writer, pver uint32) error {
+	// ChannelID (8)
+	// FundingOutPoint (36)
+	// Commitment Signature (73)
+	err := writeElements(w,
+		s.ChannelID,
+		s.FundingOutPoint,
+		s.CommitmentSignature)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// NewSingleFundingComplete creates, and returns a new empty
+// SingleFundingResponse.
+func NewSingleFundingComplete() *SingleFundingComplete {
+	return &SingleFundingComplete{}
+}
+
+// Command returns the uint32 code which uniquely identifies this message as a
+// SingleFundingRequest on the wire.
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingComplete) Command() uint32 {
+	return CmdSingleFundingComplete
+}
+
+// MaxPayloadLength returns the maximum allowed payload length for a
+// SingleFundingComplete. This is calculated by summing the max length of all
+// the fields within a SingleFundingResponse. To enforce a maximum
+// DeliveryPkScript size, the size of a P2PKH public key script is used.
+// Therefore, the final breakdown is: 8 + 36 + 73 = 117
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingComplete) MaxPayloadLength(uint32) uint32 {
+	return 117
+}
+
+// Validate examines each populated field within the SingleFundingComplete for
+// field sanity.
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingComplete) Validate() error {
+	var zeroHash [32]byte
+	if bytes.Equal(zeroHash[:], s.FundingOutPoint.Hash[:]) {
+		return fmt.Errorf("funding outpoint hash must be non-zero")
+	}
+
+	if s.CommitmentSignature == nil {
+		return fmt.Errorf("commitment signature must be non-nil")
+	}
+
+	// We're good!
+	return nil
+}
+
+// String returns the string representation of the SingleFundingResponse.
+//
+// This is part of the lnwire.Message interface.
+func (s *SingleFundingComplete) String() string {
+	return fmt.Sprintf("\n--- Begin SingleFundingComplete ---\n") +
+		fmt.Sprintf("ChannelID:\t\t\t%d\n", s.ChannelID) +
+		fmt.Sprintf("FundingOutPoint:\t\t\t%x\n", s.FundingOutPoint) +
+		fmt.Sprintf("CommitmentSignature\t\t\t\t%x\n", s.CommitmentSignature) +
+		fmt.Sprintf("--- End SingleFundingComplete ---\n")
+}