routing+lnd: provide payment premiere as response to SendPayment

htlcswitch.go

@@ -26,6 +26,10 @@ const (
 	htlcQueueSize = 50
 )
 
+var (
+	zeroBytes [32]byte
+)
+
 // link represents an active channel capable of forwarding HTLCs. Each
 // active channel registered with the htlc switch creates a new link which will
 // be used for forwarding outgoing HTLCs. The link also has additional
@@ -60,6 +64,8 @@ type htlcPacket struct {
 	payHash [32]byte
 	amt     btcutil.Amount
 
+	preImage chan [32]byte
+
 	err chan error
 }
 
@@ -125,9 +131,9 @@ type htlcSwitch struct {
 	interfaceMtx sync.RWMutex
 	interfaces   map[chainhash.Hash][]*link
 
-	// onionIndex is an index used to properly forward a message
-	// to the next hop within a Sphinx circuit. Within the sphinx packets,
-	// the "next-hop" destination is encoded as the hash160 of the node's
+	// onionIndex is an index used to properly forward a message to the
+	// next hop within a Sphinx circuit. Within the sphinx packets, the
+	// "next-hop" destination is encoded as the hash160 of the node's
 	// public key serialized in compressed format.
 	onionMtx   sync.RWMutex
 	onionIndex map[[ripemd160.Size]byte][]*link
@@ -145,11 +151,11 @@ type htlcSwitch struct {
 	// the RPC system.
 	outgoingPayments chan *htlcPacket
 
-	// htlcPlex is the channel which all connected links use to
-	// coordinate the setup/teardown of Sphinx (onion routing) payment
-	// circuits. Active links forward any add/settle messages over this
-	// channel each state transition, sending new adds/settles which are
-	// fully locked in.
+	// htlcPlex is the channel which all connected links use to coordinate
+	// the setup/teardown of Sphinx (onion routing) payment circuits.
+	// Active links forward any add/settle messages over this channel each
+	// state transition, sending new adds/settles which are fully locked
+	// in.
 	htlcPlex chan *htlcPacket
 
 	// TODO(roasbeef): sampler to log sat/sec and tx/sec
@@ -206,12 +212,13 @@ func (h *htlcSwitch) Stop() error {
 // In the event that the interface has insufficient capacity for the payment,
 // an error is returned. Additionally, if the interface cannot be found, an
 // alternative error is returned.
-func (h *htlcSwitch) SendHTLC(htlcPkt *htlcPacket) error {
+func (h *htlcSwitch) SendHTLC(htlcPkt *htlcPacket) ([32]byte, error) {
 	htlcPkt.err = make(chan error, 1)
+	htlcPkt.preImage = make(chan [32]byte, 1)
 
 	h.outgoingPayments <- htlcPkt
 
-	return <-htlcPkt.err
+	return <-htlcPkt.preImage, <-htlcPkt.err
 }
 
 // htlcForwarder is responsible for optimally forwarding (and possibly
@@ -243,6 +250,7 @@ out:
 				err := fmt.Errorf("Unable to locate link %x",
 					dest[:])
 				hswcLog.Errorf(err.Error())
+				htlcPkt.preImage <- zeroBytes
 				htlcPkt.err <- err
 				continue
 			}
@@ -277,6 +285,7 @@ out:
 			}
 
 			hswcLog.Errorf("Unable to send payment, insufficient capacity")
+			htlcPkt.preImage <- zeroBytes
 			htlcPkt.err <- fmt.Errorf("Insufficient capacity")
 		case pkt := <-h.htlcPlex:
 			// TODO(roasbeef): properly account with cleared vs settled
@@ -373,8 +382,9 @@ out:
 				// continue propagating the HTLC across the
 				// network.
 				circuit.clear.linkChan <- &htlcPacket{
-					msg: wireMsg,
-					err: make(chan error, 1),
+					msg:      wireMsg,
+					preImage: make(chan [32]byte, 1),
+					err:      make(chan error, 1),
 				}
 
 				// Reduce the available bandwidth for the link

peer.go

@@ -1055,7 +1055,8 @@ type pendingPayment struct {
 	htlc  *lnwire.UpdateAddHTLC
 	index uint64
 
-	err chan error
+	preImage chan [32]byte
+	err      chan error
 }
 
 // commitmentState is the volatile+persistent state of an active channel's
@@ -1314,9 +1315,10 @@ func (p *peer) handleDownStreamPkt(state *commitmentState, pkt *htlcPacket) {
 		p.queueMsg(htlc, nil)
 
 		state.pendingBatch = append(state.pendingBatch, &pendingPayment{
-			htlc:  htlc,
-			index: index,
-			err:   pkt.err,
+			htlc:     htlc,
+			index:    index,
+			preImage: pkt.preImage,
+			err:      pkt.err,
 		})
 
 	case *lnwire.UpdateFufillHTLC:
@@ -1565,15 +1567,17 @@ func (p *peer) handleUpstreamMsg(state *commitmentState, msg lnwire.Message) {
 			if p, ok := state.clearedHTCLs[parentIndex]; ok {
 				switch htlc.EntryType {
 				// If the HTLC was settled successfully, then
-				// we return a nil error back to the possible
-				// caller.
+				// we return a nil error as well as the payment
+				// preimage back to the possible caller.
 				case lnwallet.Settle:
+					p.preImage <- htlc.RPreimage
 					p.err <- nil
 
 				// Otherwise, the HTLC failed, so we propagate
 				// the error back to the potential caller.
 				case lnwallet.Fail:
 					errMsg := state.cancelReasons[parentIndex]
+					p.preImage <- [32]byte{}
 					p.err <- errors.New(errMsg.String())
 				}
 

routing/router.go

@@ -82,7 +82,7 @@ type Config struct {
 	// denoted by its public key. A non-nil error is to be returned if the
 	// payment was unsuccessful.
 	SendToSwitch func(firstHop *btcec.PublicKey,
-		htlcAdd *lnwire.UpdateAddHTLC) error
+		htlcAdd *lnwire.UpdateAddHTLC) ([32]byte, error)
 }
 
 // ChannelRouter is the layer 3 router within the Lightning stack. Below the
@@ -1105,14 +1105,20 @@ type LightningPayment struct {
 // payment is successful, or all candidates routes have been attempted and
 // resulted in a failed payment. If the payment succeeds, then a non-nil Route
 // will be returned which describes the path the successful payment traversed
-// within the network to reach the destination.
-func (r *ChannelRouter) SendPayment(payment *LightningPayment) (*Route, error) {
+// within the network to reach the destination. Additionally, the payment
+// preimage will also be returned.
+func (r *ChannelRouter) SendPayment(payment *LightningPayment) ([32]byte, *Route, error) {
+	var (
+		err      error
+		preImage [32]byte
+	)
+
 	// Query the graph for a potential path to the destination node that
 	// can support our payment amount. If a path is ultimately unavailable,
 	// then an error will be returned.
 	route, err := r.FindRoute(payment.Target, payment.Amount)
 	if err != nil {
-		return nil, err
+		return preImage, nil, err
 	}
 	log.Tracef("Selected route for payment: %#v", route)
 
@@ -1120,7 +1126,7 @@ func (r *ChannelRouter) SendPayment(payment *LightningPayment) (*Route, error) {
 	// htlcAdd message that we send directly to the switch.
 	sphinxPacket, err := generateSphinxPacket(route, payment.PaymentHash[:])
 	if err != nil {
-		return nil, err
+		return preImage, nil, err
 	}
 
 	// Craft an HTLC packet to send to the layer 2 switch. The metadata
@@ -1135,11 +1141,12 @@ func (r *ChannelRouter) SendPayment(payment *LightningPayment) (*Route, error) {
 	// Attempt to send this payment through the network to complete the
 	// payment. If this attempt fails, then we'll bail our early.
 	firstHop := route.Hops[0].Channel.Node.PubKey
-	if err := r.cfg.SendToSwitch(firstHop, htlcAdd); err != nil {
-		return nil, err
+	preImage, err = r.cfg.SendToSwitch(firstHop, htlcAdd)
+	if err != nil {
+		return preImage, nil, err
 	}
 
-	return route, nil
+	return preImage, route, nil
 }
 
 // TopologyClient...

rpcserver.go

@@ -965,7 +965,7 @@ func (r *rpcServer) SendPayment(paymentStream lnrpc.Lightning_SendPaymentServer)
 					Amount:      amt,
 					PaymentHash: rHash,
 				}
-				route, err := r.server.chanRouter.SendPayment(payment)
+				preImage, route, err := r.server.chanRouter.SendPayment(payment)
 				if err != nil {
 					errChan <- err
 					return
@@ -978,9 +978,9 @@ func (r *rpcServer) SendPayment(paymentStream lnrpc.Lightning_SendPaymentServer)
 					return
 				}
 
-				// TODO(roasbeef): tack on payment hash also?
 				err = paymentStream.Send(&lnrpc.SendResponse{
-					PaymentRoute: marshalRoute(route),
+					PaymentPreimage: preImage[:],
+					PaymentRoute:    marshalRoute(route),
 				})
 				if err != nil {
 					errChan <- err
@@ -1047,7 +1047,7 @@ func (r *rpcServer) SendPaymentSync(ctx context.Context,
 	// Finally, send a payment request to the channel router. If the
 	// payment succeeds, then the returned route will be that was used
 	// successfully within the payment.
-	route, err := r.server.chanRouter.SendPayment(&routing.LightningPayment{
+	preImage, route, err := r.server.chanRouter.SendPayment(&routing.LightningPayment{
 		Target:      destPub,
 		Amount:      amt,
 		PaymentHash: rHash,
@@ -1063,7 +1063,8 @@ func (r *rpcServer) SendPaymentSync(ctx context.Context,
 	}
 
 	return &lnrpc.SendResponse{
-		PaymentRoute: marshalRoute(route),
+		PaymentPreimage: preImage[:],
+		PaymentRoute:    marshalRoute(route),
 	}, nil
 }
 

server.go

@@ -179,7 +179,7 @@ func newServer(listenAddrs []string, notifier chainntnfs.ChainNotifier,
 		Broadcast:    s.broadcastMessage,
 		SendMessages: s.sendToPeer,
 		SendToSwitch: func(firstHop *btcec.PublicKey,
-			htlcAdd *lnwire.UpdateAddHTLC) error {
+			htlcAdd *lnwire.UpdateAddHTLC) ([32]byte, error) {
 
 			firstHopPub := firstHop.SerializeCompressed()
 			destInterface := chainhash.Hash(fastsha256.Sum256(firstHopPub))