routing: query bandwidth hints before each payment attempt

Previously the bandwidth hints were only queried once per payment. This
did not allow for concurrent payments changing channel balances.

routing/payment_session.go

@@ -33,7 +33,7 @@ type PaymentSession interface {
 type paymentSession struct {
 	additionalEdges map[route.Vertex][]*channeldb.ChannelEdgePolicy
 
-	bandwidthHints map[uint64]lnwire.MilliSatoshi
+	getBandwidthHints func() (map[uint64]lnwire.MilliSatoshi, error)
 
 	sessionSource *SessionSource
 
@@ -97,11 +97,22 @@ func (p *paymentSession) RequestRoute(payment *LightningPayment,
 		CltvLimit:         cltvLimit,
 	}
 
+	// We'll also obtain a set of bandwidthHints from the lower layer for
+	// each of our outbound channels. This will allow the path finding to
+	// skip any links that aren't active or just don't have enough bandwidth
+	// to carry the payment. New bandwidth hints are queried for every new
+	// path finding attempt, because concurrent payments may change
+	// balances.
+	bandwidthHints, err := p.getBandwidthHints()
+	if err != nil {
+		return nil, err
+	}
+
 	path, err := p.pathFinder(
 		&graphParams{
 			graph:           ss.Graph,
 			additionalEdges: p.additionalEdges,
-			bandwidthHints:  p.bandwidthHints,
+			bandwidthHints:  bandwidthHints,
 		},
 		restrictions, &ss.PathFindingConfig,
 		ss.SelfNode.PubKeyBytes, payment.Target,

routing/payment_session_source.go

@@ -97,26 +97,22 @@ func (m *SessionSource) NewPaymentSession(routeHints [][]zpay32.HopHint,
 		}
 	}
 
-	// We'll also obtain a set of bandwidthHints from the lower layer for
-	// each of our outbound channels. This will allow the path finding to
-	// skip any links that aren't active or just don't have enough
-	// bandwidth to carry the payment.
 	sourceNode, err := m.Graph.SourceNode()
 	if err != nil {
 		return nil, err
 	}
-	bandwidthHints, err := generateBandwidthHints(
-		sourceNode, m.QueryBandwidth,
-	)
-	if err != nil {
-		return nil, err
+
+	getBandwidthHints := func() (map[uint64]lnwire.MilliSatoshi,
+		error) {
+
+		return generateBandwidthHints(sourceNode, m.QueryBandwidth)
 	}
 
 	return &paymentSession{
-		additionalEdges: edges,
-		bandwidthHints:  bandwidthHints,
-		sessionSource:   m,
-		pathFinder:      findPath,
+		additionalEdges:   edges,
+		getBandwidthHints: getBandwidthHints,
+		sessionSource:     m,
+		pathFinder:        findPath,
 	}, nil
 }
 

routing/payment_session_test.go

@@ -41,6 +41,11 @@ func TestRequestRoute(t *testing.T) {
 	}
 
 	session := &paymentSession{
+		getBandwidthHints: func() (map[uint64]lnwire.MilliSatoshi,
+			error) {
+
+			return nil, nil
+		},
 		sessionSource: sessionSource,
 		pathFinder:    findPath,
 	}