routing/pathfind: ensure final hop supports payment addrs

This commit adds an optional PaymentAddr field to the RestrictParams, so
that we can verify the final hop can support it before doing an
expensive round of pathfindig.

routing/pathfind_test.go

@@ -1532,6 +1532,71 @@ func TestMissingFeatureDep(t *testing.T) {
 	assertExpectedPath(t, ctx.testGraphInstance.aliasMap, path, "conner")
 }
 
+// TestDestPaymentAddr asserts that we properly detect when we can send a
+// payment address to a receiver, and also that we fallback to the receiver's
+// node announcement if we don't have an invoice features.
+func TestDestPaymentAddr(t *testing.T) {
+	t.Parallel()
+
+	testChannels := []*testChannel{
+		symmetricTestChannel("roasbeef", "luoji", 100000,
+			&testChannelPolicy{
+				Expiry:  144,
+				FeeRate: 400,
+				MinHTLC: 1,
+				MaxHTLC: 100000000,
+			},
+		),
+	}
+
+	ctx := newPathFindingTestContext(t, testChannels, "roasbeef")
+	defer ctx.cleanup()
+
+	sourceNode, err := ctx.graphParams.graph.SourceNode()
+	if err != nil {
+		t.Fatalf("unable to fetch source node: %v", err)
+
+	}
+
+	find := func(r *RestrictParams,
+		target route.Vertex) ([]*channeldb.ChannelEdgePolicy, error) {
+
+		return findPath(
+			&graphParams{
+				graph: ctx.graphParams.graph,
+			},
+			r, testPathFindingConfig,
+			sourceNode.PubKeyBytes, target, 100,
+		)
+	}
+
+	luoji := ctx.testGraphInstance.aliasMap["luoji"]
+
+	restrictions := *noRestrictions
+
+	// Add payment address w/o any invoice features.
+	restrictions.PaymentAddr = &[32]byte{1}
+
+	// Add empty destination features. This should cause us to fail, since
+	// this overrides anything in the graph.
+	restrictions.DestFeatures = lnwire.EmptyFeatureVector()
+
+	_, err = find(&restrictions, luoji)
+	if err != errNoPaymentAddr {
+		t.Fatalf("path shouldn't have been found: %v", err)
+	}
+
+	// Now, set the TLV and payment address features for the destination. We
+	// should succeed in finding a path to luoji.
+	restrictions.DestFeatures = tlvPayAddrFeatures
+
+	path, err := find(&restrictions, luoji)
+	if err != nil {
+		t.Fatalf("path should have been found: %v", err)
+	}
+	assertExpectedPath(t, ctx.testGraphInstance.aliasMap, path, "luoji")
+}
+
 func TestPathInsufficientCapacity(t *testing.T) {
 	t.Parallel()