multi: partition lnwire.ChanUpdateFlag into ChannelFlags and MessageFlags

In this commit:

* we partition lnwire.ChanUpdateFlag into two (ChanUpdateChanFlags and
ChanUpdateMsgFlags), from a uint16 to a pair of uint8's

* we rename the ChannelUpdate.Flags to ChannelFlags and add an
additional MessageFlags field, which will be used to indicate the
presence of the optional field HtlcMaximumMsat within the ChannelUpdate.

* we partition ChannelEdgePolicy.Flags into message and channel flags.
This change corresponds to the partitioning of the ChannelUpdate's Flags
field into MessageFlags and ChannelFlags.

Co-authored-by: Johan T. Halseth <johanth@gmail.com>

lnwire/channel_update.go

@@ -8,16 +8,20 @@ import (
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 )
 
-// ChanUpdateFlag is a bitfield that signals various options concerning a
+// ChanUpdateMsgFlags is a bitfield that signals whether optional fields are
+// present in the ChannelUpdate.
+type ChanUpdateMsgFlags uint8
+
+// ChanUpdateChanFlags is a bitfield that signals various options concerning a
 // particular channel edge. Each bit is to be examined in order to determine
 // how the ChannelUpdate message is to be interpreted.
-type ChanUpdateFlag uint16
+type ChanUpdateChanFlags uint8
 
 const (
 	// ChanUpdateDirection indicates the direction of a channel update. If
 	// this bit is set to 0 if Node1 (the node with the "smaller" Node ID)
 	// is updating the channel, and to 1 otherwise.
-	ChanUpdateDirection ChanUpdateFlag = 1 << iota
+	ChanUpdateDirection ChanUpdateChanFlags = 1 << iota
 
 	// ChanUpdateDisabled is a bit that indicates if the channel edge
 	// selected by the ChanUpdateDirection bit is to be treated as being
@@ -48,13 +52,18 @@ type ChannelUpdate struct {
 	// the last-received.
 	Timestamp uint32
 
-	// Flags is a bitfield that describes additional meta-data concerning
-	// how the update is to be interpreted. Currently, the
+	// MessageFlags is a bitfield that describes whether optional fields
+	// are present in this update. Currently, the least-significant bit
+	// must be set to 1 if the optional field MaxHtlc is present.
+	MessageFlags ChanUpdateMsgFlags
+
+	// ChannelFlags is a bitfield that describes additional meta-data
+	// concerning how the update is to be interpreted. Currently, the
 	// least-significant bit must be set to 0 if the creating node
 	// corresponds to the first node in the previously sent channel
 	// announcement and 1 otherwise. If the second bit is set, then the
 	// channel is set to be disabled.
-	Flags ChanUpdateFlag
+	ChannelFlags ChanUpdateChanFlags
 
 	// TimeLockDelta is the minimum number of blocks this node requires to
 	// be added to the expiry of HTLCs. This is a security parameter
@@ -98,7 +107,8 @@ func (a *ChannelUpdate) Decode(r io.Reader, pver uint32) error {
 		a.ChainHash[:],
 		&a.ShortChannelID,
 		&a.Timestamp,
-		&a.Flags,
+		&a.MessageFlags,
+		&a.ChannelFlags,
 		&a.TimeLockDelta,
 		&a.HtlcMinimumMsat,
 		&a.BaseFee,
@@ -133,7 +143,8 @@ func (a *ChannelUpdate) Encode(w io.Writer, pver uint32) error {
 		a.ChainHash[:],
 		a.ShortChannelID,
 		a.Timestamp,
-		a.Flags,
+		a.MessageFlags,
+		a.ChannelFlags,
 		a.TimeLockDelta,
 		a.HtlcMinimumMsat,
 		a.BaseFee,
@@ -168,7 +179,8 @@ func (a *ChannelUpdate) DataToSign() ([]byte, error) {
 		a.ChainHash[:],
 		a.ShortChannelID,
 		a.Timestamp,
-		a.Flags,
+		a.MessageFlags,
+		a.ChannelFlags,
 		a.TimeLockDelta,
 		a.HtlcMinimumMsat,
 		a.BaseFee,

lnwire/lnwire.go

@@ -105,9 +105,15 @@ func WriteElement(w io.Writer, element interface{}) error {
 		if _, err := w.Write(b[:]); err != nil {
 			return err
 		}
-	case ChanUpdateFlag:
-		var b [2]byte
-		binary.BigEndian.PutUint16(b[:], uint16(e))
+	case ChanUpdateMsgFlags:
+		var b [1]byte
+		b[0] = uint8(e)
+		if _, err := w.Write(b[:]); err != nil {
+			return err
+		}
+	case ChanUpdateChanFlags:
+		var b [1]byte
+		b[0] = uint8(e)
 		if _, err := w.Write(b[:]); err != nil {
 			return err
 		}
@@ -470,12 +476,18 @@ func ReadElement(r io.Reader, element interface{}) error {
 			return err
 		}
 		*e = binary.BigEndian.Uint16(b[:])
-	case *ChanUpdateFlag:
-		var b [2]byte
-		if _, err := io.ReadFull(r, b[:]); err != nil {
+	case *ChanUpdateMsgFlags:
+		var b [1]uint8
+		if _, err := r.Read(b[:]); err != nil {
 			return err
 		}
-		*e = ChanUpdateFlag(binary.BigEndian.Uint16(b[:]))
+		*e = ChanUpdateMsgFlags(b[0])
+	case *ChanUpdateChanFlags:
+		var b [1]uint8
+		if _, err := r.Read(b[:]); err != nil {
+			return err
+		}
+		*e = ChanUpdateChanFlags(b[0])
 	case *ErrorCode:
 		var b [2]byte
 		if _, err := io.ReadFull(r, b[:]); err != nil {

lnwire/lnwire_test.go

@@ -608,7 +608,8 @@ func TestLightningWireProtocol(t *testing.T) {
 			req := ChannelUpdate{
 				ShortChannelID:  NewShortChanIDFromInt(uint64(r.Int63())),
 				Timestamp:       uint32(r.Int31()),
-				Flags:           ChanUpdateFlag(r.Int31()),
+				MessageFlags:    ChanUpdateMsgFlags(r.Int31()),
+				ChannelFlags:    ChanUpdateChanFlags(r.Int31()),
 				TimeLockDelta:   uint16(r.Int31()),
 				HtlcMinimumMsat: MilliSatoshi(r.Int63()),
 				BaseFee:         uint32(r.Int31()),

lnwire/onion_error_test.go

@@ -20,7 +20,8 @@ var (
 		Signature:      sig,
 		ShortChannelID: NewShortChanIDFromInt(1),
 		Timestamp:      1,
-		Flags:          1,
+		MessageFlags:   0,
+		ChannelFlags:   1,
 	}
 )