channeldb/payments: make payment status helper methods

This commit splits FetchPaymentStatus and
UpdatePaymentStatus, such that they each invoke
helper methods that can be composed into different
db txns. This enables us to improve performance on
send/receive, as we can remove the exclusive lock
from the control tower, and allow concurrent calls
to utilize Batch more effectively.

channeldb/payments.go

@@ -191,33 +191,33 @@ func (db *DB) DeleteAllPayments() error {
 // local database.
 func (db *DB) UpdatePaymentStatus(paymentHash [32]byte, status PaymentStatus) error {
 	return db.Batch(func(tx *bolt.Tx) error {
-		paymentStatuses, err := tx.CreateBucketIfNotExists(paymentStatusBucket)
+		return UpdatePaymentStatusTx(tx, paymentHash, status)
-		if err != nil {
-			return err
-		}
-
-		return paymentStatuses.Put(paymentHash[:], status.Bytes())
 	})
 }
 
+// UpdatePaymentStatusTx is a helper method that sets the payment status for
+// outgoing/finished payments in the local database. This method accepts a
+// boltdb transaction such that the operation can be composed into other
+// database transactions.
+func UpdatePaymentStatusTx(tx *bolt.Tx,
+	paymentHash [32]byte, status PaymentStatus) error {
+
+	paymentStatuses, err := tx.CreateBucketIfNotExists(paymentStatusBucket)
+	if err != nil {
+		return err
+	}
+
+	return paymentStatuses.Put(paymentHash[:], status.Bytes())
+}
+
 // FetchPaymentStatus returns the payment status for outgoing payment.
 // If status of the payment isn't found, it will default to "StatusGrounded".
 func (db *DB) FetchPaymentStatus(paymentHash [32]byte) (PaymentStatus, error) {
-	// The default status for all payments that aren't recorded in database.
+	var paymentStatus = StatusGrounded
-	paymentStatus := StatusGrounded
-
 	err := db.View(func(tx *bolt.Tx) error {
-		bucket := tx.Bucket(paymentStatusBucket)
+		var err error
-		if bucket == nil {
+		paymentStatus, err = FetchPaymentStatusTx(tx, paymentHash)
-			return nil
+		return err
-		}
-
-		paymentStatusBytes := bucket.Get(paymentHash[:])
-		if paymentStatusBytes == nil {
-			return nil
-		}
-
-		return paymentStatus.FromBytes(paymentStatusBytes)
 	})
 	if err != nil {
 		return StatusGrounded, err
@@ -226,6 +226,29 @@ func (db *DB) FetchPaymentStatus(paymentHash [32]byte) (PaymentStatus, error) {
 	return paymentStatus, nil
 }
 
+// FetchPaymentStatusTx is a helper method that returns the payment status for
+// outgoing payment.  If status of the payment isn't found, it will default to
+// "StatusGrounded". It accepts the boltdb transactions such that this method
+// can be composed into other atomic operations.
+func FetchPaymentStatusTx(tx *bolt.Tx, paymentHash [32]byte) (PaymentStatus, error) {
+	// The default status for all payments that aren't recorded in database.
+	var paymentStatus = StatusGrounded
+
+	bucket := tx.Bucket(paymentStatusBucket)
+	if bucket == nil {
+		return paymentStatus, nil
+	}
+
+	paymentStatusBytes := bucket.Get(paymentHash[:])
+	if paymentStatusBytes == nil {
+		return paymentStatus, nil
+	}
+
+	paymentStatus.FromBytes(paymentStatusBytes)
+
+	return paymentStatus, nil
+}
+
 func serializeOutgoingPayment(w io.Writer, p *OutgoingPayment) error {
 	var scratch [8]byte