channeldb: read raw htlc attempt session key

channeldb/duplicate_payments.go

@@ -53,7 +53,7 @@ type duplicateHTLCAttemptInfo struct {
 	attemptID uint64
 
 	// sessionKey is the ephemeral key used for this attempt.
-	sessionKey *btcec.PrivateKey
+	sessionKey [btcec.PrivKeyBytesLen]byte
 
 	// route is the route attempted to send the HTLC.
 	route route.Route

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

channeldb/mp_payment_test.go

@@ -0,0 +1,27 @@
+package channeldb
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestLazySessionKeyDeserialize tests that we can read htlc attempt session
+// keys that were previously serialized as a private key as raw bytes.
+func TestLazySessionKeyDeserialize(t *testing.T) {
+	var b bytes.Buffer
+
+	// Serialize as a private key.
+	err := WriteElements(&b, priv)
+	require.NoError(t, err)
+
+	// Deserialize into [btcec.PrivKeyBytesLen]byte.
+	attempt := HTLCAttemptInfo{}
+	err = ReadElements(&b, &attempt.sessionKey)
+	require.NoError(t, err)
+	require.Zero(t, b.Len())
+
+	sessionKey := attempt.SessionKey()
+	require.Equal(t, priv, sessionKey)
+}

channeldb/payment_control_test.go

@@ -37,17 +37,15 @@ func genInfo() (*PaymentCreationInfo, *HTLCAttemptInfo,
 	}
 
 	rhash := sha256.Sum256(preimage[:])
+	attempt := NewHtlcAttemptInfo(
+		0, priv, *testRoute.Copy(), time.Time{}, nil,
+	)
 	return &PaymentCreationInfo{
 		PaymentIdentifier: rhash,
 		Value:             testRoute.ReceiverAmt(),
 		CreationTime:      time.Unix(time.Now().Unix(), 0),
 		PaymentRequest:    []byte("hola"),
-		},
-		&HTLCAttemptInfo{
-			AttemptID:  0,
-			sessionKey: priv,
-			Route:      *testRoute.Copy(),
-		}, preimage, nil
+	}, attempt, preimage, nil
 }
 
 // TestPaymentControlSwitchFail checks that payment status returns to Failed

channeldb/payments_test.go

@@ -68,13 +68,10 @@ func makeFakeInfo() (*PaymentCreationInfo, *HTLCAttemptInfo) {
 		PaymentRequest: []byte(""),
 	}
 
-	a := &HTLCAttemptInfo{
-		AttemptID:   44,
-		sessionKey:  priv,
-		Route:       testRoute,
-		AttemptTime: time.Unix(100, 0),
-		Hash:        &hash,
-	}
+	a := NewHtlcAttemptInfo(
+		44, priv, testRoute, time.Unix(100, 0), &hash,
+	)
+
 	return c, a
 }