Merge pull request #22675 from markdroth/xds_default_route

xds: Accept either "" or "/" as the prefix for the default route.

src/core/ext/filters/client_channel/xds/xds_api.cc

@@ -1022,8 +1022,9 @@ grpc_error* RouteConfigParse(
         "No prefix field found in RouteMatch.");
   }
   const upb_strview prefix = envoy_api_v2_route_RouteMatch_prefix(match);
-  if (!upb_strview_eql(prefix, upb_strview_makez(""))) {
-    return GRPC_ERROR_CREATE_FROM_STATIC_STRING("Prefix is not empty string.");
+  if (!upb_strview_eql(prefix, upb_strview_makez("")) &&
+      !upb_strview_eql(prefix, upb_strview_makez("/"))) {
+    return GRPC_ERROR_CREATE_FROM_STATIC_STRING("Prefix is not \"\" or \"/\".");
   }
   if (!envoy_api_v2_route_Route_has_route(route)) {
     return GRPC_ERROR_CREATE_FROM_STATIC_STRING(

test/cpp/end2end/xds_end2end_test.cc

@@ -1799,6 +1799,26 @@ TEST_P(XdsResolverOnlyTest, RestartsRequestsUponReconnection) {
   EXPECT_EQ(0, std::get<1>(counts));
 }
 
+TEST_P(XdsResolverOnlyTest, DefaultRouteSpecifiesSlashPrefix) {
+  RouteConfiguration route_config =
+      balancers_[0]->ads_service()->default_route_config();
+  route_config.mutable_virtual_hosts(0)
+      ->mutable_routes(0)
+      ->mutable_match()
+      ->set_prefix("/");
+  balancers_[0]->ads_service()->SetLdsResource(
+      AdsServiceImpl::BuildListener(route_config), kDefaultResourceName);
+  SetNextResolution({});
+  SetNextResolutionForLbChannelAllBalancers();
+  AdsServiceImpl::EdsResourceArgs args({
+      {"locality0", GetBackendPorts()},
+  });
+  balancers_[0]->ads_service()->SetEdsResource(
+      AdsServiceImpl::BuildEdsResource(args), kDefaultResourceName);
+  // We need to wait for all backends to come online.
+  WaitForAllBackends();
+}
+
 class XdsResolverLoadReportingOnlyTest : public XdsEnd2endTest {
  public:
   XdsResolverLoadReportingOnlyTest() : XdsEnd2endTest(4, 1, 3) {}