lnwire: add additional comments to ChannelReestablish, rename fields

lnwire/channel_reestablish.go

@@ -2,37 +2,53 @@ package lnwire
 
 import "io"
 
-// ChannelReestablish is sent during node reconnection for every channel
-// established in order to synchronize the states on both sides.
+// ChannelReestablish is a message sent between peers that have an existing
+// open channel upon connection reestablishment. This message allows both sides
+// to report their local state, and their current knowledge of the state of the
+// remote commitment chain. If a deviation is detected and can be recovered
+// from, then the necessary messages will be retransmitted. If the level of
+// desynchronization if irreconcilable, then the channel will be force closed.
 type ChannelReestablish struct {
-	// ChanID serves to identify to which channel this message belongs.
+	// ChanID is the channel ID of the channel state we're attempting
+	// synchronize with the remote party.
 	ChanID ChannelID
 
-	// NextLocalCommitmentNumber is the commitment number of the next
-	// commitment signed message it expects to receive.
-	NextLocalCommitmentNumber uint64
+	// NextLocalCommitHeight is the next local commitment height of the
+	// sending party. If the height of the sender's commitment chain from
+	// the receiver's Pov is one less that this number, then the sender
+	// should re-send the *exact* same proposed commitment.
+	//
+	// In other words, the receiver should re-send their last sent
+	// commitment iff:
+	//
+	//  * NextLocalCommitHeight == remoteCommitChain.Height
+	//
+	// This covers the case of a lost commitment which was sent by the
+	// sender of this message, but never received by the receiver of this
+	// message.
+	NextLocalCommitHeight uint64
 
-	// NextRemoteRevocationNumber is the commitment number of the next
-	// revoke and ack message it expects to receive.
-	NextRemoteRevocationNumber uint64
+	// RemoteCommitTailHeight is the height of the receiving party's
+	// unrevoked commitment from the PoV of the sender of this message. If
+	// the height of the receiver's commitment is *one more* than this
+	// value, then their prior RevokeAndAck message should be
+	// retransmitted.
+	//
+	// In other words, the receiver should re-send their last sent
+	// RevokeAndAck message iff:
+	//
+	//  * localCommitChain.tail().Height == RemoteCommitTailHeight + 1
+	//
+	// This covers the case of a lost revocation, wherein the receiver of
+	// the message sent a revocation for a prior state, but the sender of
+	// the message never fully processed it.
+	RemoteCommitTailHeight uint64
 }
 
 // A compile time check to ensure ChannelReestablish implements the
 // lnwire.Message interface.
 var _ Message = (*ChannelReestablish)(nil)
 
-// Decode deserializes a serialized ChannelReestablish stored in the passed
-// io.Reader observing the specified protocol version.
-//
-// This is part of the lnwire.Message interface.
-func (a *ChannelReestablish) Decode(r io.Reader, pver uint32) error {
-	return readElements(r,
-		&a.ChanID,
-		&a.NextLocalCommitmentNumber,
-		&a.NextRemoteRevocationNumber,
-	)
-}
-
 // Encode serializes the target ChannelReestablish into the passed io.Writer
 // observing the protocol version specified.
 //
@@ -40,8 +56,20 @@ func (a *ChannelReestablish) Decode(r io.Reader, pver uint32) error {
 func (a *ChannelReestablish) Encode(w io.Writer, pver uint32) error {
 	return writeElements(w,
 		a.ChanID,
-		a.NextLocalCommitmentNumber,
-		a.NextRemoteRevocationNumber,
+		a.NextLocalCommitHeight,
+		a.RemoteCommitTailHeight,
+	)
+}
+
+// Decode deserializes a serialized ChannelReestablish stored in the passed
+// io.Reader observing the specified protocol version.
+//
+// This is part of the lnwire.Message interface.
+func (a *ChannelReestablish) Decode(r io.Reader, pver uint32) error {
+	return readElements(r,
+		&a.ChanID,
+		&a.NextLocalCommitHeight,
+		&a.RemoteCommitTailHeight,
 	)
 }
 
@@ -63,10 +91,10 @@ func (a *ChannelReestablish) MaxPayloadLength(pver uint32) uint32 {
 	// ChanID - 32 bytes
 	length += 32
 
-	// NextLocalCommitmentNumber - 8 bytes
+	// NextLocalCommitHeight - 8 bytes
 	length += 8
 
-	// NextRemoteRevocationNumber - 8 bytes
+	// RemoteCommitTailHeight - 8 bytes
 	length += 8
 
 	return length