lnrpc+lnrpc/routerrpc: add a new TLV record field to the Hop proto

In this commit, we add a new field to the Hop proto to allow callers to
be able to specify TLV records for the SendToRoute call, and also to be
able to display TLV records that were used during regular path finding.

We also update SendPayment to support dest TLV records.

rpcserver.go

@@ -17,6 +17,7 @@ import (
 
 	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
 	"github.com/lightningnetwork/lnd/routing/route"
+	"github.com/lightningnetwork/lnd/tlv"
 	"github.com/lightningnetwork/lnd/watchtower"
 
 	"github.com/btcsuite/btcd/blockchain"
@@ -2926,6 +2927,8 @@ type rpcPaymentIntent struct {
 	outgoingChannelID *uint64
 	payReq            []byte
 
+	destTLV []tlv.Record
+
 	route *route.Route
 }
 
@@ -2968,6 +2971,16 @@ func extractPaymentIntent(rpcPayReq *rpcPaymentRequest) (rpcPaymentIntent, error
 		payIntent.cltvLimit = &rpcPayReq.CltvLimit
 	}
 
+	if len(rpcPayReq.DestTlv) != 0 {
+		var err error
+		payIntent.destTLV, err = tlv.MapToRecords(
+			rpcPayReq.DestTlv,
+		)
+		if err != nil {
+			return payIntent, err
+		}
+	}
+
 	// If the payment request field isn't blank, then the details of the
 	// invoice are encoded entirely within the encoded payReq.  So we'll
 	// attempt to decode it, populating the payment accordingly.
@@ -3123,6 +3136,7 @@ func (r *rpcServer) dispatchPaymentIntent(
 			OutgoingChannelID: payIntent.outgoingChannelID,
 			PaymentRequest:    payIntent.payReq,
 			PayAttemptTimeout: routing.DefaultPayAttemptTimeout,
+			FinalDestRecords:  payIntent.destTLV,
 		}
 
 		preImage, route, routerErr = r.server.chanRouter.SendPayment(
@@ -3293,10 +3307,16 @@ func (r *rpcServer) sendPayment(stream *paymentStream) error {
 					return
 				}
 
-				marshalledRouted := r.routerBackend.
-					MarshallRoute(resp.Route)
+				backend := r.routerBackend
+				marshalledRouted, err := backend.MarshallRoute(
+					resp.Route,
+				)
+				if err != nil {
+					errChan <- err
+					return
+				}
 
-				err := stream.send(&lnrpc.SendResponse{
+				err = stream.send(&lnrpc.SendResponse{
 					PaymentHash:     payIntent.rHash[:],
 					PaymentPreimage: resp.Preimage[:],
 					PaymentRoute:    marshalledRouted,
@@ -3375,10 +3395,15 @@ func (r *rpcServer) sendPaymentSync(ctx context.Context,
 		}, nil
 	}
 
+	rpcRoute, err := r.routerBackend.MarshallRoute(resp.Route)
+	if err != nil {
+		return nil, err
+	}
+
 	return &lnrpc.SendResponse{
 		PaymentHash:     payIntent.rHash[:],
 		PaymentPreimage: resp.Preimage[:],
-		PaymentRoute:    r.routerBackend.MarshallRoute(resp.Route),
+		PaymentRoute:    rpcRoute,
 	}, nil
 }