routerrpc: add TrackPayments

Add method to track all payments rather than tracking a payment by payment hash.

lnrpc/routerrpc/router.pb.gw.go

@@ -101,6 +101,34 @@ func request_Router_TrackPaymentV2_0(ctx context.Context, marshaler runtime.Mars
 
 }
 
+var (
+	filter_Router_TrackPayments_0 = &utilities.DoubleArray{Encoding: map[string]int{}, Base: []int(nil), Check: []int(nil)}
+)
+
+func request_Router_TrackPayments_0(ctx context.Context, marshaler runtime.Marshaler, client RouterClient, req *http.Request, pathParams map[string]string) (Router_TrackPaymentsClient, runtime.ServerMetadata, error) {
+	var protoReq TrackPaymentsRequest
+	var metadata runtime.ServerMetadata
+
+	if err := req.ParseForm(); err != nil {
+		return nil, metadata, status.Errorf(codes.InvalidArgument, "%v", err)
+	}
+	if err := runtime.PopulateQueryParameters(&protoReq, req.Form, filter_Router_TrackPayments_0); err != nil {
+		return nil, metadata, status.Errorf(codes.InvalidArgument, "%v", err)
+	}
+
+	stream, err := client.TrackPayments(ctx, &protoReq)
+	if err != nil {
+		return nil, metadata, err
+	}
+	header, err := stream.Header()
+	if err != nil {
+		return nil, metadata, err
+	}
+	metadata.HeaderMD = header
+	return stream, metadata, nil
+
+}
+
 func request_Router_EstimateRouteFee_0(ctx context.Context, marshaler runtime.Marshaler, client RouterClient, req *http.Request, pathParams map[string]string) (proto.Message, runtime.ServerMetadata, error) {
 	var protoReq RouteFeeRequest
 	var metadata runtime.ServerMetadata
@@ -556,6 +584,13 @@ func RegisterRouterHandlerServer(ctx context.Context, mux *runtime.ServeMux, ser
 		return
 	})
 
+	mux.Handle("GET", pattern_Router_TrackPayments_0, func(w http.ResponseWriter, req *http.Request, pathParams map[string]string) {
+		err := status.Error(codes.Unimplemented, "streaming calls are not yet supported in the in-process transport")
+		_, outboundMarshaler := runtime.MarshalerForRequest(mux, req)
+		runtime.HTTPError(ctx, mux, outboundMarshaler, w, req, err)
+		return
+	})
+
 	mux.Handle("POST", pattern_Router_EstimateRouteFee_0, func(w http.ResponseWriter, req *http.Request, pathParams map[string]string) {
 		ctx, cancel := context.WithCancel(req.Context())
 		defer cancel()
@@ -881,6 +916,26 @@ func RegisterRouterHandlerClient(ctx context.Context, mux *runtime.ServeMux, cli
 
 	})
 
+	mux.Handle("GET", pattern_Router_TrackPayments_0, func(w http.ResponseWriter, req *http.Request, pathParams map[string]string) {
+		ctx, cancel := context.WithCancel(req.Context())
+		defer cancel()
+		inboundMarshaler, outboundMarshaler := runtime.MarshalerForRequest(mux, req)
+		rctx, err := runtime.AnnotateContext(ctx, mux, req, "/routerrpc.Router/TrackPayments", runtime.WithHTTPPathPattern("/v2/router/payments"))
+		if err != nil {
+			runtime.HTTPError(ctx, mux, outboundMarshaler, w, req, err)
+			return
+		}
+		resp, md, err := request_Router_TrackPayments_0(rctx, inboundMarshaler, client, req, pathParams)
+		ctx = runtime.NewServerMetadataContext(ctx, md)
+		if err != nil {
+			runtime.HTTPError(ctx, mux, outboundMarshaler, w, req, err)
+			return
+		}
+
+		forward_Router_TrackPayments_0(ctx, mux, outboundMarshaler, w, req, func() (proto.Message, error) { return resp.Recv() }, mux.GetForwardResponseOptions()...)
+
+	})
+
 	mux.Handle("POST", pattern_Router_EstimateRouteFee_0, func(w http.ResponseWriter, req *http.Request, pathParams map[string]string) {
 		ctx, cancel := context.WithCancel(req.Context())
 		defer cancel()
@@ -1129,6 +1184,8 @@ var (
 
 	pattern_Router_TrackPaymentV2_0 = runtime.MustPattern(runtime.NewPattern(1, []int{2, 0, 2, 1, 2, 2, 1, 0, 4, 1, 5, 3}, []string{"v2", "router", "track", "payment_hash"}, ""))
 
+	pattern_Router_TrackPayments_0 = runtime.MustPattern(runtime.NewPattern(1, []int{2, 0, 2, 1, 2, 2}, []string{"v2", "router", "payments"}, ""))
+
 	pattern_Router_EstimateRouteFee_0 = runtime.MustPattern(runtime.NewPattern(1, []int{2, 0, 2, 1, 2, 2, 2, 3}, []string{"v2", "router", "route", "estimatefee"}, ""))
 
 	pattern_Router_SendToRouteV2_0 = runtime.MustPattern(runtime.NewPattern(1, []int{2, 0, 2, 1, 2, 2, 2, 3}, []string{"v2", "router", "route", "send"}, ""))
@@ -1159,6 +1216,8 @@ var (
 
 	forward_Router_TrackPaymentV2_0 = runtime.ForwardResponseStream
 
+	forward_Router_TrackPayments_0 = runtime.ForwardResponseStream
+
 	forward_Router_EstimateRouteFee_0 = runtime.ForwardResponseMessage
 
 	forward_Router_SendToRouteV2_0 = runtime.ForwardResponseMessage

lnrpc/routerrpc/router.pb.json.go

@@ -107,6 +107,48 @@ func RegisterRouterJSONCallbacks(registry map[string]func(ctx context.Context,
 		}()
 	}
 
+	registry["routerrpc.Router.TrackPayments"] = func(ctx context.Context,
+		conn *grpc.ClientConn, reqJSON string, callback func(string, error)) {
+
+		req := &TrackPaymentsRequest{}
+		err := marshaler.Unmarshal([]byte(reqJSON), req)
+		if err != nil {
+			callback("", err)
+			return
+		}
+
+		client := NewRouterClient(conn)
+		stream, err := client.TrackPayments(ctx, req)
+		if err != nil {
+			callback("", err)
+			return
+		}
+
+		go func() {
+			for {
+				select {
+				case <-stream.Context().Done():
+					callback("", stream.Context().Err())
+					return
+				default:
+				}
+
+				resp, err := stream.Recv()
+				if err != nil {
+					callback("", err)
+					return
+				}
+
+				respBytes, err := marshaler.Marshal(resp)
+				if err != nil {
+					callback("", err)
+					return
+				}
+				callback(string(respBytes), nil)
+			}
+		}()
+	}
+
 	registry["routerrpc.Router.EstimateRouteFee"] = func(ctx context.Context,
 		conn *grpc.ClientConn, reqJSON string, callback func(string, error)) {
 

lnrpc/routerrpc/router.proto

@@ -22,6 +22,16 @@ service Router {
     */
     rpc TrackPaymentV2 (TrackPaymentRequest) returns (stream lnrpc.Payment);
 
+    /*
+    TrackPayments returns an update stream for every payment that is not in a
+    terminal state. Note that if payments are in-flight while starting a new
+    subscription, the start of the payment stream could produce out-of-order
+    and/or duplicate events. In order to get updates for every in-flight
+    payment attempt make sure to subscribe to this method before initiating any
+    payments.
+    */
+    rpc TrackPayments (TrackPaymentsRequest) returns (stream lnrpc.Payment);
+
     /*
     EstimateRouteFee allows callers to obtain a lower bound w.r.t how much it
     may cost to send an HTLC to the target end destination.
@@ -303,6 +313,14 @@ message TrackPaymentRequest {
     bool no_inflight_updates = 2;
 }
 
+message TrackPaymentsRequest {
+    /*
+    If set, only the final payment updates are streamed back. Intermediate
+    updates that show which htlcs are still in flight are suppressed.
+    */
+    bool no_inflight_updates = 1;
+}
+
 message RouteFeeRequest {
     /*
     The destination once wishes to obtain a routing fee quote to.

lnrpc/routerrpc/router.swagger.json

@@ -250,6 +250,47 @@
         ]
       }
     },
+    "/v2/router/payments": {
+      "get": {
+        "summary": "TrackPayments returns an update stream for every payment that is not in a\nterminal state. Note that if payments are in-flight while starting a new\nsubscription, the start of the payment stream could produce out-of-order\nand/or duplicate events. In order to get updates for every in-flight\npayment attempt make sure to subscribe to this method before initiating any\npayments.",
+        "operationId": "Router_TrackPayments",
+        "responses": {
+          "200": {
+            "description": "A successful response.(streaming responses)",
+            "schema": {
+              "type": "object",
+              "properties": {
+                "result": {
+                  "$ref": "#/definitions/lnrpcPayment"
+                },
+                "error": {
+                  "$ref": "#/definitions/rpcStatus"
+                }
+              },
+              "title": "Stream result of lnrpcPayment"
+            }
+          },
+          "default": {
+            "description": "An unexpected error response.",
+            "schema": {
+              "$ref": "#/definitions/rpcStatus"
+            }
+          }
+        },
+        "parameters": [
+          {
+            "name": "no_inflight_updates",
+            "description": "If set, only the final payment updates are streamed back. Intermediate\nupdates that show which htlcs are still in flight are suppressed.",
+            "in": "query",
+            "required": false,
+            "type": "boolean"
+          }
+        ],
+        "tags": [
+          "Router"
+        ]
+      }
+    },
     "/v2/router/route": {
       "post": {
         "summary": "BuildRoute builds a fully specified route based on a list of hop public\nkeys. It retrieves the relevant channel policies from the graph in order to\ncalculate the correct fees and time locks.",

lnrpc/routerrpc/router.yaml

@@ -8,6 +8,8 @@ http:
       body: "*"
     - selector: routerrpc.Router.TrackPaymentV2
       get: "/v2/router/track/{payment_hash}"
+    - selector: routerrpc.Router.TrackPayments
+      get: "/v2/router/payments"
     - selector: routerrpc.Router.EstimateRouteFee
       post: "/v2/router/route/estimatefee"
       body: "*"

lnrpc/routerrpc/router_grpc.pb.go

@@ -26,6 +26,13 @@ type RouterClient interface {
 	// TrackPaymentV2 returns an update stream for the payment identified by the
 	// payment hash.
 	TrackPaymentV2(ctx context.Context, in *TrackPaymentRequest, opts ...grpc.CallOption) (Router_TrackPaymentV2Client, error)
+	// TrackPayments returns an update stream for every payment that is not in a
+	// terminal state. Note that if payments are in-flight while starting a new
+	// subscription, the start of the payment stream could produce out-of-order
+	// and/or duplicate events. In order to get updates for every in-flight
+	// payment attempt make sure to subscribe to this method before initiating any
+	// payments.
+	TrackPayments(ctx context.Context, in *TrackPaymentsRequest, opts ...grpc.CallOption) (Router_TrackPaymentsClient, error)
 	// EstimateRouteFee allows callers to obtain a lower bound w.r.t how much it
 	// may cost to send an HTLC to the target end destination.
 	EstimateRouteFee(ctx context.Context, in *RouteFeeRequest, opts ...grpc.CallOption) (*RouteFeeResponse, error)
@@ -165,6 +172,38 @@ func (x *routerTrackPaymentV2Client) Recv() (*lnrpc.Payment, error) {
 	return m, nil
 }
 
+func (c *routerClient) TrackPayments(ctx context.Context, in *TrackPaymentsRequest, opts ...grpc.CallOption) (Router_TrackPaymentsClient, error) {
+	stream, err := c.cc.NewStream(ctx, &Router_ServiceDesc.Streams[2], "/routerrpc.Router/TrackPayments", opts...)
+	if err != nil {
+		return nil, err
+	}
+	x := &routerTrackPaymentsClient{stream}
+	if err := x.ClientStream.SendMsg(in); err != nil {
+		return nil, err
+	}
+	if err := x.ClientStream.CloseSend(); err != nil {
+		return nil, err
+	}
+	return x, nil
+}
+
+type Router_TrackPaymentsClient interface {
+	Recv() (*lnrpc.Payment, error)
+	grpc.ClientStream
+}
+
+type routerTrackPaymentsClient struct {
+	grpc.ClientStream
+}
+
+func (x *routerTrackPaymentsClient) Recv() (*lnrpc.Payment, error) {
+	m := new(lnrpc.Payment)
+	if err := x.ClientStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
 func (c *routerClient) EstimateRouteFee(ctx context.Context, in *RouteFeeRequest, opts ...grpc.CallOption) (*RouteFeeResponse, error) {
 	out := new(RouteFeeResponse)
 	err := c.cc.Invoke(ctx, "/routerrpc.Router/EstimateRouteFee", in, out, opts...)
@@ -257,7 +296,7 @@ func (c *routerClient) BuildRoute(ctx context.Context, in *BuildRouteRequest, op
 }
 
 func (c *routerClient) SubscribeHtlcEvents(ctx context.Context, in *SubscribeHtlcEventsRequest, opts ...grpc.CallOption) (Router_SubscribeHtlcEventsClient, error) {
-	stream, err := c.cc.NewStream(ctx, &Router_ServiceDesc.Streams[2], "/routerrpc.Router/SubscribeHtlcEvents", opts...)
+	stream, err := c.cc.NewStream(ctx, &Router_ServiceDesc.Streams[3], "/routerrpc.Router/SubscribeHtlcEvents", opts...)
 	if err != nil {
 		return nil, err
 	}
@@ -290,7 +329,7 @@ func (x *routerSubscribeHtlcEventsClient) Recv() (*HtlcEvent, error) {
 
 // Deprecated: Do not use.
 func (c *routerClient) SendPayment(ctx context.Context, in *SendPaymentRequest, opts ...grpc.CallOption) (Router_SendPaymentClient, error) {
-	stream, err := c.cc.NewStream(ctx, &Router_ServiceDesc.Streams[3], "/routerrpc.Router/SendPayment", opts...)
+	stream, err := c.cc.NewStream(ctx, &Router_ServiceDesc.Streams[4], "/routerrpc.Router/SendPayment", opts...)
 	if err != nil {
 		return nil, err
 	}
@@ -323,7 +362,7 @@ func (x *routerSendPaymentClient) Recv() (*PaymentStatus, error) {
 
 // Deprecated: Do not use.
 func (c *routerClient) TrackPayment(ctx context.Context, in *TrackPaymentRequest, opts ...grpc.CallOption) (Router_TrackPaymentClient, error) {
-	stream, err := c.cc.NewStream(ctx, &Router_ServiceDesc.Streams[4], "/routerrpc.Router/TrackPayment", opts...)
+	stream, err := c.cc.NewStream(ctx, &Router_ServiceDesc.Streams[5], "/routerrpc.Router/TrackPayment", opts...)
 	if err != nil {
 		return nil, err
 	}
@@ -355,7 +394,7 @@ func (x *routerTrackPaymentClient) Recv() (*PaymentStatus, error) {
 }
 
 func (c *routerClient) HtlcInterceptor(ctx context.Context, opts ...grpc.CallOption) (Router_HtlcInterceptorClient, error) {
-	stream, err := c.cc.NewStream(ctx, &Router_ServiceDesc.Streams[5], "/routerrpc.Router/HtlcInterceptor", opts...)
+	stream, err := c.cc.NewStream(ctx, &Router_ServiceDesc.Streams[6], "/routerrpc.Router/HtlcInterceptor", opts...)
 	if err != nil {
 		return nil, err
 	}
@@ -405,6 +444,13 @@ type RouterServer interface {
 	// TrackPaymentV2 returns an update stream for the payment identified by the
 	// payment hash.
 	TrackPaymentV2(*TrackPaymentRequest, Router_TrackPaymentV2Server) error
+	// TrackPayments returns an update stream for every payment that is not in a
+	// terminal state. Note that if payments are in-flight while starting a new
+	// subscription, the start of the payment stream could produce out-of-order
+	// and/or duplicate events. In order to get updates for every in-flight
+	// payment attempt make sure to subscribe to this method before initiating any
+	// payments.
+	TrackPayments(*TrackPaymentsRequest, Router_TrackPaymentsServer) error
 	// EstimateRouteFee allows callers to obtain a lower bound w.r.t how much it
 	// may cost to send an HTLC to the target end destination.
 	EstimateRouteFee(context.Context, *RouteFeeRequest) (*RouteFeeResponse, error)
@@ -483,6 +529,9 @@ func (UnimplementedRouterServer) SendPaymentV2(*SendPaymentRequest, Router_SendP
 func (UnimplementedRouterServer) TrackPaymentV2(*TrackPaymentRequest, Router_TrackPaymentV2Server) error {
 	return status.Errorf(codes.Unimplemented, "method TrackPaymentV2 not implemented")
 }
+func (UnimplementedRouterServer) TrackPayments(*TrackPaymentsRequest, Router_TrackPaymentsServer) error {
+	return status.Errorf(codes.Unimplemented, "method TrackPayments not implemented")
+}
 func (UnimplementedRouterServer) EstimateRouteFee(context.Context, *RouteFeeRequest) (*RouteFeeResponse, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method EstimateRouteFee not implemented")
 }
@@ -583,6 +632,27 @@ func (x *routerTrackPaymentV2Server) Send(m *lnrpc.Payment) error {
 	return x.ServerStream.SendMsg(m)
 }
 
+func _Router_TrackPayments_Handler(srv interface{}, stream grpc.ServerStream) error {
+	m := new(TrackPaymentsRequest)
+	if err := stream.RecvMsg(m); err != nil {
+		return err
+	}
+	return srv.(RouterServer).TrackPayments(m, &routerTrackPaymentsServer{stream})
+}
+
+type Router_TrackPaymentsServer interface {
+	Send(*lnrpc.Payment) error
+	grpc.ServerStream
+}
+
+type routerTrackPaymentsServer struct {
+	grpc.ServerStream
+}
+
+func (x *routerTrackPaymentsServer) Send(m *lnrpc.Payment) error {
+	return x.ServerStream.SendMsg(m)
+}
+
 func _Router_EstimateRouteFee_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
 	in := new(RouteFeeRequest)
 	if err := dec(in); err != nil {
@@ -933,6 +1003,11 @@ var Router_ServiceDesc = grpc.ServiceDesc{
 			Handler:       _Router_TrackPaymentV2_Handler,
 			ServerStreams: true,
 		},
+		{
+			StreamName:    "TrackPayments",
+			Handler:       _Router_TrackPayments_Handler,
+			ServerStreams: true,
+		},
 		{
 			StreamName:    "SubscribeHtlcEvents",
 			Handler:       _Router_SubscribeHtlcEvents_Handler,

lnrpc/routerrpc/router_server.go

@@ -72,6 +72,10 @@ var (
 			Entity: "offchain",
 			Action: "read",
 		}},
+		"/routerrpc.Router/TrackPayments": {{
+			Entity: "offchain",
+			Action: "read",
+		}},
 		"/routerrpc.Router/EstimateRouteFee": {{
 			Entity: "offchain",
 			Action: "read",
@@ -737,19 +741,62 @@ func (s *Server) trackPayment(identifier lntypes.Hash,
 	router := s.cfg.RouterBackend
 
 	// Subscribe to the outcome of this payment.
-	subscription, err := router.Tower.SubscribePayment(
-		identifier,
-	)
+	subscription, err := router.Tower.SubscribePayment(identifier)
+
 	switch {
 	case err == channeldb.ErrPaymentNotInitiated:
 		return status.Error(codes.NotFound, err.Error())
 	case err != nil:
 		return err
 	}
+
+	// Stream updates to the client.
+	err = s.trackPaymentStream(
+		stream.Context(), subscription, noInflightUpdates, stream.Send,
+	)
+
+	if errors.Is(err, context.Canceled) {
+		log.Debugf("Payment stream %v canceled", identifier)
+	}
+
+	return err
+}
+
+// TrackPayments returns a stream of payment state updates.
+func (s *Server) TrackPayments(request *TrackPaymentsRequest,
+	stream Router_TrackPaymentsServer) error {
+
+	log.Debug("TrackPayments called")
+
+	router := s.cfg.RouterBackend
+
+	// Subscribe to payments.
+	subscription, err := router.Tower.SubscribeAllPayments()
+	if err != nil {
+		return err
+	}
+
+	// Stream updates to the client.
+	err = s.trackPaymentStream(
+		stream.Context(), subscription, request.NoInflightUpdates,
+		stream.Send,
+	)
+
+	if errors.Is(err, context.Canceled) {
+		log.Debugf("TrackPayments payment stream canceled.")
+	}
+
+	return err
+}
+
+// trackPaymentStream streams payment updates to the client.
+func (s *Server) trackPaymentStream(context context.Context,
+	subscription *routing.ControlTowerSubscriber, noInflightUpdates bool,
+	send func(*lnrpc.Payment) error) error {
+
 	defer subscription.Close()
 
-	// Stream updates back to the client. The first update is always the
-	// current state of the payment.
+	// Stream updates back to the client.
 	for {
 		select {
 		case item, ok := <-subscription.Updates:
@@ -766,13 +813,15 @@ func (s *Server) trackPayment(identifier lntypes.Hash,
 				continue
 			}
 
-			rpcPayment, err := router.MarshallPayment(result)
+			rpcPayment, err := s.cfg.RouterBackend.MarshallPayment(
+				result,
+			)
 			if err != nil {
 				return err
 			}
 
 			// Send event to the client.
-			err = stream.Send(rpcPayment)
+			err = send(rpcPayment)
 			if err != nil {
 				return err
 			}
@@ -780,9 +829,8 @@ func (s *Server) trackPayment(identifier lntypes.Hash,
 		case <-s.quit:
 			return errServerShuttingDown
 
-		case <-stream.Context().Done():
-			log.Debugf("Payment status stream %v canceled", identifier)
-			return stream.Context().Err()
+		case <-context.Done():
+			return context.Err()
 		}
 	}
 }

lnrpc/routerrpc/router_server_test.go

@@ -0,0 +1,169 @@
+package routerrpc
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/lnrpc"
+	"github.com/lightningnetwork/lnd/queue"
+	"github.com/lightningnetwork/lnd/routing"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc"
+)
+
+func makeStreamMock() *StreamMock {
+	return &StreamMock{
+		ctx:            context.Background(),
+		sentFromServer: make(chan *lnrpc.Payment, 10),
+	}
+}
+
+type StreamMock struct {
+	grpc.ServerStream
+	ctx            context.Context
+	sentFromServer chan *lnrpc.Payment
+}
+
+func makeControlTowerMock() *ControlTowerMock {
+	towerMock := &ControlTowerMock{
+		queue: queue.NewConcurrentQueue(20),
+	}
+	towerMock.queue.Start()
+
+	return towerMock
+}
+
+type ControlTowerMock struct {
+	queue *queue.ConcurrentQueue
+	routing.ControlTower
+}
+
+func (t *ControlTowerMock) SubscribeAllPayments() (
+	*routing.ControlTowerSubscriber, error) {
+
+	return &routing.ControlTowerSubscriber{
+		Updates: t.queue.ChanOut(),
+	}, nil
+}
+
+func (m *StreamMock) Context() context.Context {
+	return m.ctx
+}
+
+func (m *StreamMock) Send(p *lnrpc.Payment) error {
+	m.sentFromServer <- p
+	return nil
+}
+
+// TestTrackPaymentsInflightUpdate tests whether all updates from the control
+// tower are propagated to the client.
+func TestTrackPaymentsInflightUpdates(t *testing.T) {
+	// Setup mocks and request.
+	request := &TrackPaymentsRequest{
+		NoInflightUpdates: false,
+	}
+	towerMock := makeControlTowerMock()
+	stream := makeStreamMock()
+	server := &Server{
+		cfg: &Config{
+			RouterBackend: &RouterBackend{
+				Tower: towerMock,
+			},
+		},
+	}
+
+	// Listen to payment updates in a goroutine.
+	go func() {
+		err := server.TrackPayments(request, stream)
+		require.NoError(t, err)
+	}()
+
+	// Enqueue some payment updates on the mock.
+	towerMock.queue.ChanIn() <- &channeldb.MPPayment{
+		Info:   &channeldb.PaymentCreationInfo{},
+		Status: channeldb.StatusInFlight,
+	}
+	towerMock.queue.ChanIn() <- &channeldb.MPPayment{
+		Info:   &channeldb.PaymentCreationInfo{},
+		Status: channeldb.StatusSucceeded,
+	}
+
+	// Wait until there's 2 updates or the deadline is exceeded.
+	deadline := time.Now().Add(1 * time.Second)
+	for {
+		if len(stream.sentFromServer) == 2 {
+			break
+		}
+
+		if time.Now().After(deadline) {
+			require.FailNow(t, "deadline exceeded.")
+		}
+	}
+
+	// Both updates should be sent to the client.
+	require.Len(t, stream.sentFromServer, 2)
+
+	// The updates should be in the right order.
+	payment := <-stream.sentFromServer
+	require.Equal(t, lnrpc.Payment_IN_FLIGHT, payment.Status)
+	payment = <-stream.sentFromServer
+	require.Equal(t, lnrpc.Payment_SUCCEEDED, payment.Status)
+}
+
+// TestTrackPaymentsInflightUpdate tests whether only final updates from the
+// control tower are propagated to the client when noInflightUpdates = true.
+func TestTrackPaymentsNoInflightUpdates(t *testing.T) {
+	// Setup mocks and request.
+	request := &TrackPaymentsRequest{
+		NoInflightUpdates: true,
+	}
+	towerMock := &ControlTowerMock{
+		queue: queue.NewConcurrentQueue(20),
+	}
+	towerMock.queue.Start()
+	stream := makeStreamMock()
+	server := &Server{
+		cfg: &Config{
+			RouterBackend: &RouterBackend{
+				Tower: towerMock,
+			},
+		},
+	}
+
+	// Listen to payment updates in a goroutine.
+	go func() {
+		err := server.TrackPayments(request, stream)
+		require.NoError(t, err)
+	}()
+
+	// Enqueue some payment updates on the mock.
+	towerMock.queue.ChanIn() <- &channeldb.MPPayment{
+		Info:   &channeldb.PaymentCreationInfo{},
+		Status: channeldb.StatusInFlight,
+	}
+	towerMock.queue.ChanIn() <- &channeldb.MPPayment{
+		Info:   &channeldb.PaymentCreationInfo{},
+		Status: channeldb.StatusSucceeded,
+	}
+
+	// Wait until there's 1 update or the deadline is exceeded.
+	deadline := time.Now().Add(1 * time.Second)
+	for {
+		if len(stream.sentFromServer) == 1 {
+			break
+		}
+
+		if time.Now().After(deadline) {
+			require.FailNow(t, "deadline exceeded.")
+		}
+	}
+
+	// Only 1 update should be sent to the client.
+	require.Len(t, stream.sentFromServer, 1)
+
+	// Only the final states should be sent to the client.
+	payment := <-stream.sentFromServer
+	require.Equal(t, lnrpc.Payment_SUCCEEDED, payment.Status)
+}