routing/payment_lifecycle: move requesting route out of createNewPaymentAttempt

To prepare for having more than one payment attempt in flight at the
same time, we decouple fetching the next route from crafting the payment
attempt.

routing/payment_lifecycle.go

@@ -51,7 +51,72 @@ func (p *paymentLifecycle) resumePayment() ([32]byte, *route.Route, error) {
 		// If this payment had no existing payment attempt, we create
 		// and send one now.
 		if p.attempt == nil {
-			firstHop, htlcAdd, err := p.createNewPaymentAttempt()
+			// Before we attempt this next payment, we'll check to see if either
+			// we've gone past the payment attempt timeout, or the router is
+			// exiting. In either case, we'll stop this payment attempt short. If a
+			// timeout is not applicable, timeoutChan will be nil.
+			select {
+			case <-p.timeoutChan:
+				// Mark the payment as failed because of the
+				// timeout.
+				err := p.router.cfg.Control.Fail(
+					p.paymentHash, channeldb.FailureReasonTimeout,
+				)
+				if err != nil {
+					return [32]byte{}, nil, err
+				}
+
+				errStr := fmt.Sprintf("payment attempt not completed " +
+					"before timeout")
+
+				return [32]byte{}, nil, newErr(ErrPaymentAttemptTimeout, errStr)
+
+			// The payment will be resumed from the current state
+			// after restart.
+			case <-p.router.quit:
+				return [32]byte{}, nil, ErrRouterShuttingDown
+
+			// Fall through if we haven't hit our time limit or are
+			// exiting.
+			default:
+			}
+
+			// Create a new payment attempt from the given payment session.
+			rt, err := p.paySession.RequestRoute(
+				p.totalAmount, p.feeLimit, 0, uint32(p.currentHeight),
+			)
+			if err != nil {
+				log.Warnf("Failed to find route for payment %x: %v",
+					p.paymentHash, err)
+
+				// Convert error to payment-level failure.
+				failure := errorToPaymentFailure(err)
+
+				// If we're unable to successfully make a payment using
+				// any of the routes we've found, then mark the payment
+				// as permanently failed.
+				saveErr := p.router.cfg.Control.Fail(
+					p.paymentHash, failure,
+				)
+				if saveErr != nil {
+					return [32]byte{}, nil, saveErr
+				}
+
+				// If there was an error already recorded for this
+				// payment, we'll return that.
+				if p.lastError != nil {
+					return [32]byte{}, nil, errNoRoute{lastError: p.lastError}
+				}
+
+				// Terminal state, return.
+				return [32]byte{}, nil, err
+			}
+
+			// Using the route received from the payment session,
+			// create a new shard to send.
+			firstHop, htlcAdd, err := p.createNewPaymentAttempt(
+				rt,
+			)
 			if err != nil {
 				return [32]byte{}, nil, err
 			}
@@ -234,71 +299,9 @@ func errorToPaymentFailure(err error) channeldb.FailureReason {
 
 // createNewPaymentAttempt creates and stores a new payment attempt to the
 // database.
-func (p *paymentLifecycle) createNewPaymentAttempt() (lnwire.ShortChannelID,
+func (p *paymentLifecycle) createNewPaymentAttempt(rt *route.Route) (lnwire.ShortChannelID,
 	*lnwire.UpdateAddHTLC, error) {
 
-	// Before we attempt this next payment, we'll check to see if either
-	// we've gone past the payment attempt timeout, or the router is
-	// exiting. In either case, we'll stop this payment attempt short. If a
-	// timeout is not applicable, timeoutChan will be nil.
-	select {
-	case <-p.timeoutChan:
-		// Mark the payment as failed because of the
-		// timeout.
-		err := p.router.cfg.Control.Fail(
-			p.paymentHash, channeldb.FailureReasonTimeout,
-		)
-		if err != nil {
-			return lnwire.ShortChannelID{}, nil, err
-		}
-
-		errStr := fmt.Sprintf("payment attempt not completed " +
-			"before timeout")
-
-		return lnwire.ShortChannelID{}, nil,
-			newErr(ErrPaymentAttemptTimeout, errStr)
-
-	case <-p.router.quit:
-		// The payment will be resumed from the current state
-		// after restart.
-		return lnwire.ShortChannelID{}, nil, ErrRouterShuttingDown
-
-	default:
-		// Fall through if we haven't hit our time limit, or
-		// are expiring.
-	}
-
-	// Create a new payment attempt from the given payment session.
-	rt, err := p.paySession.RequestRoute(
-		p.totalAmount, p.feeLimit, 0, uint32(p.currentHeight),
-	)
-	if err != nil {
-		log.Warnf("Failed to find route for payment %x: %v",
-			p.paymentHash, err)
-
-		// Convert error to payment-level failure.
-		failure := errorToPaymentFailure(err)
-
-		// If we're unable to successfully make a payment using
-		// any of the routes we've found, then mark the payment
-		// as permanently failed.
-		saveErr := p.router.cfg.Control.Fail(
-			p.paymentHash, failure,
-		)
-		if saveErr != nil {
-			return lnwire.ShortChannelID{}, nil, saveErr
-		}
-
-		// If there was an error already recorded for this
-		// payment, we'll return that.
-		if p.lastError != nil {
-			return lnwire.ShortChannelID{}, nil,
-				errNoRoute{lastError: p.lastError}
-		}
-		// Terminal state, return.
-		return lnwire.ShortChannelID{}, nil, err
-	}
-
 	// Generate a new key to be used for this attempt.
 	sessionKey, err := generateNewSessionKey()
 	if err != nil {