sphinx: rename incomingCltv to replayData in ProcessOnionPacket

Rename the parameter to be more generic since it is passed to the
ReplayLog and can store any auxiliary data, not just CLTV values.
Update godoc to explain usage with and without replay protection.

Author: gijswijs

sphinx.go

@@ -606,11 +606,17 @@ func WithTLVPayloadOnly() ProcessOnionOpt {
 // in the onion packet to derive the shared secret. Finally, if the MAC doesn't
 // check the packet is again rejected.
 //
-// In the case of a successful packet processing, and ProcessedPacket struct is
+// The replayData parameter is passed to the ReplayLog and can be used by
+// implementations to store auxiliary data alongside the packet hash. For
+// example, in HTLC forwarding this could be the incoming CLTV value. When using
+// NoOpReplayLog (no replay protection), this value is ignored and can be set
+// to 0.
+//
+// In the case of a successful packet processing, a ProcessedPacket struct is
 // returned which houses the newly parsed packet, along with instructions on
 // what to do next.
 func (r *Router) ProcessOnionPacket(onionPkt *OnionPacket, assocData []byte,
-	incomingCltv uint32, opts ...ProcessOnionOpt) (*ProcessedPacket,
+	replayData uint32, opts ...ProcessOnionOpt) (*ProcessedPacket,
 	error) {
 
 	cfg := &processOnionCfg{}
@@ -642,7 +648,7 @@ func (r *Router) ProcessOnionPacket(onionPkt *OnionPacket, assocData []byte,
 
 	// Atomically compare this hash prefix with the contents of the on-disk
 	// log, persisting it only if this entry was not detected as a replay.
-	if err := r.log.Put(hashPrefix, incomingCltv); err != nil {
+	if err := r.log.Put(hashPrefix, replayData); err != nil {
 		return nil, err
 	}
 
@@ -853,11 +859,17 @@ func (r *Router) BeginTxn(id []byte, nels int) *Tx {
 // in the onion packet to derive the shared secret. Finally, if the MAC doesn't
 // check the packet is again rejected.
 //
-// In the case of a successful packet processing, and ProcessedPacket struct is
+// The replayData parameter is passed to the ReplayLog and can be used by
+// implementations to store auxiliary data alongside the packet hash. For
+// example, in HTLC forwarding this could be the incoming CLTV value. When using
+// NoOpReplayLog (no replay protection), this value is ignored and can be set
+// to 0.
+//
+// In the case of a successful packet processing, a ProcessedPacket struct is
 // returned which houses the newly parsed packet, along with instructions on
 // what to do next.
 func (t *Tx) ProcessOnionPacket(seqNum uint16, onionPkt *OnionPacket,
-	assocData []byte, incomingCltv uint32, opts ...ProcessOnionOpt) error {
+	assocData []byte, replayData uint32, opts ...ProcessOnionOpt) error {
 
 	cfg := &processOnionCfg{}
 	for _, o := range opts {
@@ -891,7 +903,7 @@ func (t *Tx) ProcessOnionPacket(seqNum uint16, onionPkt *OnionPacket,
 
 	// Add the hash prefix to pending batch of shared secrets that will be
 	// written later via Commit().
-	err = t.batch.Put(seqNum, hashPrefix, incomingCltv)
+	err = t.batch.Put(seqNum, hashPrefix, replayData)
 	if err != nil {
 		return err
 	}