channeldb+routing: move control tower interface to routing

This commit creates an empty shall for control tower in the routing
package. It is a preparation for adding event notification.

routing/control_tower.go

@@ -0,0 +1,94 @@
+package routing
+
+import (
+	"github.com/lightningnetwork/lnd/channeldb"
+
+	"github.com/lightningnetwork/lnd/lntypes"
+)
+
+// ControlTower tracks all outgoing payments made, whose primary purpose is to
+// prevent duplicate payments to the same payment hash. In production, a
+// persistent implementation is preferred so that tracking can survive across
+// restarts. Payments are transitioned through various payment states, and the
+// ControlTower interface provides access to driving the state transitions.
+type ControlTower interface {
+	// InitPayment atomically moves the payment into the InFlight state.
+	// This method checks that no suceeded payment exist for this payment
+	// hash.
+	InitPayment(lntypes.Hash, *channeldb.PaymentCreationInfo) error
+
+	// RegisterAttempt atomically records the provided PaymentAttemptInfo.
+	RegisterAttempt(lntypes.Hash, *channeldb.PaymentAttemptInfo) error
+
+	// Success transitions a payment into the Succeeded state. After
+	// invoking this method, InitPayment should always return an error to
+	// prevent us from making duplicate payments to the same payment hash.
+	// The provided preimage is atomically saved to the DB for record
+	// keeping.
+	Success(lntypes.Hash, lntypes.Preimage) error
+
+	// Fail transitions a payment into the Failed state, and records the
+	// reason the payment failed. After invoking this method, InitPayment
+	// should return nil on its next call for this payment hash, allowing
+	// the switch to make a subsequent payment.
+	Fail(lntypes.Hash, channeldb.FailureReason) error
+
+	// FetchInFlightPayments returns all payments with status InFlight.
+	FetchInFlightPayments() ([]*channeldb.InFlightPayment, error)
+}
+
+// controlTower is persistent implementation of ControlTower to restrict
+// double payment sending.
+type controlTower struct {
+	db *channeldb.PaymentControl
+}
+
+// NewControlTower creates a new instance of the controlTower.
+func NewControlTower(db *channeldb.PaymentControl) ControlTower {
+	return &controlTower{
+		db: db,
+	}
+}
+
+// InitPayment checks or records the given PaymentCreationInfo with the DB,
+// making sure it does not already exist as an in-flight payment. Then this
+// method returns successfully, the payment is guranteeed to be in the InFlight
+// state.
+func (p *controlTower) InitPayment(paymentHash lntypes.Hash,
+	info *channeldb.PaymentCreationInfo) error {
+
+	return p.db.InitPayment(paymentHash, info)
+}
+
+// RegisterAttempt atomically records the provided PaymentAttemptInfo to the
+// DB.
+func (p *controlTower) RegisterAttempt(paymentHash lntypes.Hash,
+	attempt *channeldb.PaymentAttemptInfo) error {
+
+	return p.db.RegisterAttempt(paymentHash, attempt)
+}
+
+// Success transitions a payment into the Succeeded state. After invoking this
+// method, InitPayment should always return an error to prevent us from making
+// duplicate payments to the same payment hash. The provided preimage is
+// atomically saved to the DB for record keeping.
+func (p *controlTower) Success(paymentHash lntypes.Hash,
+	preimage lntypes.Preimage) error {
+
+	return p.db.Success(paymentHash, preimage)
+}
+
+// Fail transitions a payment into the Failed state, and records the reason the
+// payment failed. After invoking this method, InitPayment should return nil on
+// its next call for this payment hash, allowing the switch to make a
+// subsequent payment.
+func (p *controlTower) Fail(paymentHash lntypes.Hash,
+	reason channeldb.FailureReason) error {
+
+	return p.db.Fail(paymentHash, reason)
+}
+
+// FetchInFlightPayments returns all payments with status InFlight.
+func (p *controlTower) FetchInFlightPayments() ([]*channeldb.InFlightPayment, error) {
+	return p.db.FetchInFlightPayments()
+}