loop: integrate the probe api with loop-in quote

In this commit we add a call to the new probe endpoint directly into the
loop-in quote call. Furthermore we add an option to include private
channels in the loopin swap payment request. This is also useful for when
users quote/probe directly using the client API and specify hop hints.

Author: bhandras

client.go

@@ -565,6 +565,7 @@ func (s *Client) LoopInQuote(ctx context.Context,
 
 	quote, err := s.Server.GetLoopInQuote(
 		ctx, request.Amount, s.lndServices.NodePubkey, request.LastHop,
+		request.RouteHints,
 	)
 	if err != nil {
 		return nil, err

interface.go

@@ -249,6 +249,10 @@ type LoopInQuoteRequest struct {
 	// the client has already requested a server probe for more accurate
 	// routing fee estimation.
 	LastHop *route.Vertex
+
+	// RouteHints are optional route hints to reach the destination through
+	// private channels.
+	RouteHints [][]zpay32.HopHint
 }
 
 // LoopInQuote contains estimates for the fees making up the total swap cost

loopd/swapclient_server.go

@@ -483,10 +483,29 @@ func (s *swapClientServer) GetLoopInQuote(ctx context.Context,
 		return nil, err
 	}
 
+	var lastHop *route.Vertex
+	if req.LoopInLastHop != nil {
+		lastHopVertex, err := route.NewVertexFromBytes(
+			req.LoopInLastHop,
+		)
+		if err != nil {
+			return nil, err
+		}
+
+		lastHop = &lastHopVertex
+	}
+
+	routeHints, err := unmarshallRouteHints(req.LoopInRouteHints)
+	if err != nil {
+		return nil, err
+	}
+
 	quote, err := s.impl.LoopInQuote(ctx, &loop.LoopInQuoteRequest{
 		Amount:         btcutil.Amount(req.Amt),
 		HtlcConfTarget: htlcConfTarget,
 		ExternalHtlc:   req.ExternalHtlc,
+		LastHop:        lastHop,
+		RouteHints:     routeHints,
 	})
 	if err != nil {
 		return nil, err
@@ -569,7 +588,6 @@ func (s *swapClientServer) Probe(ctx context.Context,
 		LastHop:    lastHop,
 		RouteHints: routeHints,
 	})
-
 	if err != nil {
 		return nil, err
 	}

loopin.go

@@ -82,9 +82,14 @@ func newLoopInSwap(globalCtx context.Context, cfg *swapConfig,
 
 	// Request current server loop in terms and use these to calculate the
 	// swap fee that we should subtract from the swap amount in the payment
-	// request that we send to the server.
+	// request that we send to the server. We pass nil as optional route
+	// hints as hop hint selection when generating invoices with private
+	// channels is an LND side black box feaure. Advanced users will quote
+	// directly anyway and there they have the option to add specific
+	// route hints.
 	quote, err := cfg.server.GetLoopInQuote(
 		globalCtx, request.Amount, cfg.lnd.NodePubkey, request.LastHop,
+		nil,
 	)
 	if err != nil {
 		return nil, wrapGrpcError("loop in terms", err)

looprpc/client.pb.go

@@ -575,6 +575,11 @@ message QuoteRequest {
     server.
     */
     bytes loop_in_last_hop = 5;
+
+    /*
+    Optional route hints to reach the destination through private channels.
+    */
+    repeated RouteHint loop_in_route_hints = 6;
 }
 
 message InQuoteResponse {

looprpc/client.proto

@@ -213,7 +213,7 @@ func (s *serverMock) GetLoopInTerms(ctx context.Context) (
 }
 
 func (s *serverMock) GetLoopInQuote(context.Context, btcutil.Amount,
-	route.Vertex, *route.Vertex) (*LoopInQuote, error) {
+	route.Vertex, *route.Vertex, [][]zpay32.HopHint) (*LoopInQuote, error) {
 
 	return &LoopInQuote{
 		SwapFee:   testSwapFee,

server_mock_test.go

@@ -23,7 +23,9 @@ import (
 	"github.com/lightningnetwork/lnd/tor"
 	"github.com/lightningnetwork/lnd/zpay32"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/status"
 )
 
 var (
@@ -53,7 +55,8 @@ type swapServerClient interface {
 		*LoopInTerms, error)
 
 	GetLoopInQuote(ctx context.Context, amt btcutil.Amount,
-		pubKey route.Vertex, lastHop *route.Vertex) (*LoopInQuote, error)
+		pubKey route.Vertex, lastHop *route.Vertex,
+		routeHints [][]zpay32.HopHint) (*LoopInQuote, error)
 
 	Probe(ctx context.Context, amt btcutil.Amount, target route.Vertex,
 		lastHop *route.Vertex, routeHints [][]zpay32.HopHint) error
@@ -207,8 +210,13 @@ func (s *grpcSwapServerClient) GetLoopInTerms(ctx context.Context) (
 }
 
 func (s *grpcSwapServerClient) GetLoopInQuote(ctx context.Context,
-	amt btcutil.Amount, pubKey route.Vertex, lastHop *route.Vertex) (
-	*LoopInQuote, error) {
+	amt btcutil.Amount, pubKey route.Vertex, lastHop *route.Vertex,
+	routeHints [][]zpay32.HopHint) (*LoopInQuote, error) {
+
+	err := s.Probe(ctx, amt, pubKey, lastHop, routeHints)
+	if err != nil && status.Code(err) != codes.Unavailable {
+		log.Warnf("Server probe error: %v", err)
+	}
 
 	rpcCtx, rpcCancel := context.WithTimeout(ctx, globalCallTimeout)
 	defer rpcCancel()