lnwire: channels are now identified by outpoint

This commit modifies most of the wire messages to uniquely identify any
*active* channels by their funding output. This allows the wire
protocol to support funding transactions which open several channels in
parallel.

Any pending channels created by partial completion of the funding
workflow are to be identified by a uint64 initialized by both sides as
follows: the initiator of the connection starts from 0, while the
listening node starts from (1 << 63). These pending channel identifiers
are expected to be monotonically increasing with each new funding
workflow between two nodes. This identifier is volatile w.r.t to each
connection initiation.

lnwire/close_request.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"github.com/roasbeef/btcd/btcec"
+	"github.com/roasbeef/btcd/wire"
 	"github.com/roasbeef/btcutil"
 
 	"io"
@@ -20,8 +21,8 @@ import (
 // both sides are able to arrive at an identical closure transaction as they
 // know the order of the inputs/outputs.
 type CloseRequest struct {
-	// ChannelID serves to identify which channel is to be closed.
-	ChannelID uint64
+	// ChannelPoint serves to identify which channel is to be closed.
+	ChannelPoint *wire.OutPoint
 
 	// RequesterCloseSig is the signature of the requester for the fully
 	// assembled closing transaction.
@@ -30,20 +31,34 @@ type CloseRequest struct {
 	// Fee is the required fee-per-KB the closing transaction must have.
 	// It is recommended that a "sufficient" fee be paid in order to achieve
 	// timely channel closure.
+	// TODO(roasbeef): if initiator always pays fees, then no longer needed.
 	Fee btcutil.Amount
 }
 
+// NewCloseRequest creates a new CloseRequest.
+func NewCloseRequest(cp *wire.OutPoint, sig *btcec.Signature) *CloseRequest {
+	// TODO(roasbeef): update once fees aren't hardcoded
+	return &CloseRequest{
+		ChannelPoint:      cp,
+		RequesterCloseSig: sig,
+	}
+}
+
+// A compile time check to ensure CloseRequest implements the lnwire.Message
+// interface.
+var _ Message = (*CloseRequest)(nil)
+
 // Decode deserializes a serialized CloseRequest stored in the passed io.Reader
 // observing the specified protocol version.
 //
 // This is part of the lnwire.Message interface.
 func (c *CloseRequest) Decode(r io.Reader, pver uint32) error {
-	// ChannelID (8)
+	// ChannelPoint (8)
 	// RequesterCloseSig (73)
 	// 	First byte length then sig
 	// Fee (8)
 	err := readElements(r,
-		&c.ChannelID,
+		&c.ChannelPoint,
 		&c.RequesterCloseSig,
 		&c.Fee)
 	if err != nil {
@@ -53,15 +68,6 @@ func (c *CloseRequest) Decode(r io.Reader, pver uint32) error {
 	return nil
 }
 
-// NewCloseRequest creates a new CloseRequest.
-func NewCloseRequest() *CloseRequest {
-	return &CloseRequest{}
-}
-
-// A compile time check to ensure CloseRequest implements the lnwire.Message
-// interface.
-var _ Message = (*CloseRequest)(nil)
-
 // Encode serializes the target CloseRequest into the passed io.Writer observing
 // the protocol version specified.
 //
@@ -71,7 +77,7 @@ func (c *CloseRequest) Encode(w io.Writer, pver uint32) error {
 	// RequesterCloseSig
 	// Fee
 	err := writeElements(w,
-		c.ChannelID,
+		c.ChannelPoint,
 		c.RequesterCloseSig,
 		c.Fee)
 	if err != nil {
@@ -94,8 +100,8 @@ func (c *CloseRequest) Command() uint32 {
 //
 // This is part of the lnwire.Message interface.
 func (c *CloseRequest) MaxPayloadLength(pver uint32) uint32 {
-	// 8 + 73 + 8
-	return 89
+	// 36 + 73 + 8
+	return 117
 }
 
 // Validate performs any necessary sanity checks to ensure all fields present
@@ -122,7 +128,7 @@ func (c *CloseRequest) String() string {
 	}
 
 	return fmt.Sprintf("\n--- Begin CloseRequest ---\n") +
-		fmt.Sprintf("ChannelID:\t\t%d\n", c.ChannelID) +
+		fmt.Sprintf("ChannelPoint:\t\t%d\n", c.ChannelPoint) +
 		fmt.Sprintf("CloseSig\t\t%x\n", serializedSig) +
 		fmt.Sprintf("Fee:\t\t\t%d\n", c.Fee) +
 		fmt.Sprintf("--- End CloseRequest ---\n")