tlv+record+routing: add payload size calculation

routing/route/route_test.go

@@ -2,12 +2,20 @@ package route
 
 import (
 	"bytes"
+	"encoding/hex"
 	"testing"
 
+	"github.com/btcsuite/btcd/btcec"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/record"
 )
 
+var (
+	testPrivKeyBytes, _ = hex.DecodeString("e126f68f7eafcc8b74f54d269fe206be715000f94dac067d1c04a8ca3b2db734")
+	_, testPubKey       = btcec.PrivKeyFromBytes(btcec.S256(), testPrivKeyBytes)
+	testPubKeyBytes, _  = NewVertexFromBytes(testPubKey.SerializeCompressed())
+)
+
 // TestRouteTotalFees checks that a route reports the expected total fee.
 func TestRouteTotalFees(t *testing.T) {
 	t.Parallel()
@@ -56,7 +64,6 @@ func TestRouteTotalFees(t *testing.T) {
 	if r.TotalFees() != fee {
 		t.Fatalf("expected %v fees, got %v", fee, r.TotalFees())
 	}
-
 }
 
 var (
@@ -93,3 +100,57 @@ func TestMPPHop(t *testing.T) {
 		t.Fatalf("expected err: %v, got: %v", nil, err)
 	}
 }
+
+// TestPayloadSize tests the payload size calculation that is provided by Hop
+// structs.
+func TestPayloadSize(t *testing.T) {
+	hops := []*Hop{
+		{
+			PubKeyBytes:      testPubKeyBytes,
+			AmtToForward:     1000,
+			OutgoingTimeLock: 600000,
+			ChannelID:        3432483437438,
+			LegacyPayload:    true,
+		},
+		{
+			PubKeyBytes:      testPubKeyBytes,
+			AmtToForward:     1200,
+			OutgoingTimeLock: 700000,
+			ChannelID:        63584534844,
+		},
+		{
+			PubKeyBytes:      testPubKeyBytes,
+			AmtToForward:     1200,
+			OutgoingTimeLock: 700000,
+			MPP:              record.NewMPP(500, [32]byte{}),
+			CustomRecords: map[uint64][]byte{
+				100000:  {1, 2, 3},
+				1000000: {4, 5},
+			},
+		},
+	}
+
+	rt := Route{
+		Hops: hops,
+	}
+	path, err := rt.ToSphinxPath()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for i, onionHop := range path[:path.TrueRouteLength()] {
+		hop := hops[i]
+		var nextChan uint64
+		if i < len(hops)-1 {
+			nextChan = hops[i+1].ChannelID
+		}
+
+		expected := uint64(onionHop.HopPayload.NumBytes())
+		actual := hop.PayloadSize(nextChan)
+		if expected != actual {
+			t.Fatalf("unexpected payload size at hop %v: "+
+				"expected %v, got %v",
+				i, expected, actual)
+		}
+	}
+}