router: convert Route.ToHopPayloads() to Route.ToSphinxPath()

In this commit, we update the process that we use to generate a sphinx
packet to send our onion routed HTLC. Due to recent changes in the
`sphinx` package we use, we now need to use a new PaymentPath struct. As
a result, it no longer makes sense to split up the nodes in a route and
their per hop paylods as they're now in the same struct. All tests have
been updated accordingly.

routing/pathfind_test.go

@@ -807,19 +807,22 @@ func testBasicGraphPathFindingCase(t *testing.T, graphInstance *testGraphInstanc
 	// Next, we'll assert that the "next hop" field in each route payload
 	// properly points to the channel ID that the HTLC should be forwarded
 	// along.
-	hopPayloads := route.ToHopPayloads()
-	if len(hopPayloads) != expectedHopCount {
+	sphinxPath, err := route.ToSphinxPath()
+	if err != nil {
+		t.Fatalf("unable to make sphinx path: %v", err)
+	}
+	if sphinxPath.TrueRouteLength() != expectedHopCount {
 		t.Fatalf("incorrect number of hop payloads: expected %v, got %v",
-			expectedHopCount, len(hopPayloads))
+			expectedHopCount, sphinxPath.TrueRouteLength())
 	}
 
 	// Hops should point to the next hop
 	for i := 0; i < len(expectedHops)-1; i++ {
 		var expectedHop [8]byte
 		binary.BigEndian.PutUint64(expectedHop[:], route.Hops[i+1].ChannelID)
-		if !bytes.Equal(hopPayloads[i].NextAddress[:], expectedHop[:]) {
+		if !bytes.Equal(sphinxPath[i].HopData.NextAddress[:], expectedHop[:]) {
 			t.Fatalf("first hop has incorrect next hop: expected %x, got %x",
-				expectedHop[:], hopPayloads[i].NextAddress)
+				expectedHop[:], sphinxPath[i].HopData.NextAddress)
 		}
 	}
 
@@ -827,9 +830,9 @@ func testBasicGraphPathFindingCase(t *testing.T, graphInstance *testGraphInstanc
 	// to indicate it's the exit hop.
 	var exitHop [8]byte
 	lastHopIndex := len(expectedHops) - 1
-	if !bytes.Equal(hopPayloads[lastHopIndex].NextAddress[:], exitHop[:]) {
+	if !bytes.Equal(sphinxPath[lastHopIndex].HopData.NextAddress[:], exitHop[:]) {
 		t.Fatalf("first hop has incorrect next hop: expected %x, got %x",
-			exitHop[:], hopPayloads[lastHopIndex].NextAddress)
+			exitHop[:], sphinxPath[lastHopIndex].HopData.NextAddress)
 	}
 
 	var expectedTotalFee lnwire.MilliSatoshi

routing/route/route.go

@@ -104,40 +104,6 @@ func (r *Route) HopFee(hopIndex int) lnwire.MilliSatoshi {
 	return incomingAmt - r.Hops[hopIndex].AmtToForward
 }
 
-// ToHopPayloads converts a complete route into the series of per-hop payloads
-// that is to be encoded within each HTLC using an opaque Sphinx packet.
-func (r *Route) ToHopPayloads() []sphinx.HopData {
-	hopPayloads := make([]sphinx.HopData, len(r.Hops))
-
-	// For each hop encoded within the route, we'll convert the hop struct
-	// to the matching per-hop payload struct as used by the sphinx
-	// package.
-	for i, hop := range r.Hops {
-		hopPayloads[i] = sphinx.HopData{
-			// TODO(roasbeef): properly set realm, make sphinx type
-			// an enum actually?
-			Realm:         0,
-			ForwardAmount: uint64(hop.AmtToForward),
-			OutgoingCltv:  hop.OutgoingTimeLock,
-		}
-
-		// As a base case, the next hop is set to all zeroes in order
-		// to indicate that the "last hop" as no further hops after it.
-		nextHop := uint64(0)
-
-		// If we aren't on the last hop, then we set the "next address"
-		// field to be the channel that directly follows it.
-		if i != len(r.Hops)-1 {
-			nextHop = r.Hops[i+1].ChannelID
-		}
-
-		binary.BigEndian.PutUint64(hopPayloads[i].NextAddress[:],
-			nextHop)
-	}
-
-	return hopPayloads
-}
-
 // NewRouteFromHops creates a new Route structure from the minimally required
 // information to perform the payment. It infers fee amounts and populates the
 // node, chan and prev/next hop maps.
@@ -163,3 +129,49 @@ func NewRouteFromHops(amtToSend lnwire.MilliSatoshi, timeLock uint32,
 
 	return route, nil
 }
+
+// ToSphinxPath converts a complete route into a sphinx PaymentPath that
+// contains the per-hop paylods used to encoding the HTLC routing data for each
+// hop in the route.
+func (r *Route) ToSphinxPath() (*sphinx.PaymentPath, error) {
+	var path sphinx.PaymentPath
+
+	// For each hop encoded within the route, we'll convert the hop struct
+	// to an OnionHop with matching per-hop payload within the path as used
+	// by the sphinx package.
+	for i, hop := range r.Hops {
+		pub, err := btcec.ParsePubKey(
+			hop.PubKeyBytes[:], btcec.S256(),
+		)
+		if err != nil {
+			return nil, err
+		}
+
+		path[i] = sphinx.OnionHop{
+			NodePub: *pub,
+			HopData: sphinx.HopData{
+				// TODO(roasbeef): properly set realm, make
+				// sphinx type an enum actually?
+				Realm:         [1]byte{0},
+				ForwardAmount: uint64(hop.AmtToForward),
+				OutgoingCltv:  hop.OutgoingTimeLock,
+			},
+		}
+
+		// As a base case, the next hop is set to all zeroes in order
+		// to indicate that the "last hop" as no further hops after it.
+		nextHop := uint64(0)
+
+		// If we aren't on the last hop, then we set the "next address"
+		// field to be the channel that directly follows it.
+		if i != len(r.Hops)-1 {
+			nextHop = r.Hops[i+1].ChannelID
+		}
+
+		binary.BigEndian.PutUint64(
+			path[i].HopData.NextAddress[:], nextHop,
+		)
+	}
+
+	return &path, nil
+}

routing/router.go

@@ -1467,30 +1467,25 @@ func generateSphinxPacket(rt *route.Route, paymentHash []byte) ([]byte,
 		return nil, nil, route.ErrNoRouteHopsProvided
 	}
 
-	// First obtain all the public keys along the route which are contained
-	// in each hop.
-	nodes := make([]*btcec.PublicKey, len(rt.Hops))
-	for i, hop := range rt.Hops {
-		pub, err := btcec.ParsePubKey(hop.PubKeyBytes[:],
-			btcec.S256())
+	// Now that we know we have an actual route, we'll map the route into a
+	// sphinx payument path which includes per-hop paylods for each hop
+	// that give each node within the route the necessary information
+	// (fees, CLTV value, etc) to properly forward the payment.
+	sphinxPath, err := rt.ToSphinxPath()
 	if err != nil {
 		return nil, nil, err
 	}
 
-		nodes[i] = pub
-	}
-
-	// Next we generate the per-hop payload which gives each node within
-	// the route the necessary information (fees, CLTV value, etc) to
-	// properly forward the payment.
-	hopPayloads := rt.ToHopPayloads()
-
 	log.Tracef("Constructed per-hop payloads for payment_hash=%x: %v",
 		paymentHash[:], newLogClosure(func() string {
-			return spew.Sdump(hopPayloads)
+			return spew.Sdump(sphinxPath[:sphinxPath.TrueRouteLength()])
 		}),
 	)
 
+	// Generate a new random session key to ensure that we don't trigger
+	// any replay.
+	//
+	// TODO(roasbeef): add more sources of randomness?
 	sessionKey, err := btcec.NewPrivateKey(btcec.S256())
 	if err != nil {
 		return nil, nil, err
@@ -1499,7 +1494,7 @@ func generateSphinxPacket(rt *route.Route, paymentHash []byte) ([]byte,
 	// Next generate the onion routing packet which allows us to perform
 	// privacy preserving source routing across the network.
 	sphinxPacket, err := sphinx.NewOnionPacket(
-		nodes, sessionKey, hopPayloads, paymentHash,
+		sphinxPath, sessionKey, paymentHash,
 	)
 	if err != nil {
 		return nil, nil, err
@@ -1523,7 +1518,7 @@ func generateSphinxPacket(rt *route.Route, paymentHash []byte) ([]byte,
 
 	return onionBlob.Bytes(), &sphinx.Circuit{
 		SessionKey:  sessionKey,
-		PaymentPath: nodes,
+		PaymentPath: sphinxPath.NodeKeys(),
 	}, nil
 }