channeldb: read raw htlc attempt session key

channeldb/mp_payment.go

@@ -21,8 +21,10 @@ type HTLCAttemptInfo struct {
 	// AttemptID is the unique ID used for this attempt.
 	AttemptID uint64
 
-	// sessionKey is the ephemeral key used for this attempt.
-	sessionKey *btcec.PrivateKey
+	// sessionKey is the raw bytes ephemeral key used for this attempt.
+	// These bytes are lazily read off disk to save ourselves the expensive
+	// EC operations used by btcec.PrivKeyFromBytes.
+	sessionKey [btcec.PrivKeyBytesLen]byte
 
 	// Route is the route attempted to send the HTLC.
 	Route route.Route
@@ -43,18 +45,23 @@ func NewHtlcAttemptInfo(attemptID uint64, sessionKey *btcec.PrivateKey,
 	route route.Route, attemptTime time.Time,
 	hash *lntypes.Hash) *HTLCAttemptInfo {
 
+	var scratch [btcec.PrivKeyBytesLen]byte
+	copy(scratch[:], sessionKey.Serialize())
+
 	return &HTLCAttemptInfo{
 		AttemptID:   attemptID,
-		sessionKey:  sessionKey,
+		sessionKey:  scratch,
 		Route:       route,
 		AttemptTime: attemptTime,
 		Hash:        hash,
 	}
 }
 
-// SessionKey returns the ephemeral key used for a htlc attempt.
+// SessionKey returns the ephemeral key used for a htlc attempt. This function
+// performs expensive ec-ops to obtain the session key.
 func (h *HTLCAttemptInfo) SessionKey() *btcec.PrivateKey {
-	return h.sessionKey
+	priv, _ := btcec.PrivKeyFromBytes(btcec.S256(), h.sessionKey[:])
+	return priv
 }
 
 // HTLCAttempt contains information about a specific HTLC attempt for a given