[xDS] don't allocate drop config if not needed (#35326)

Closes #35326

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35326 from markdroth:xds_drop_config_cleanup cad30e861e
PiperOrigin-RevId: 591348198

src/core/ext/filters/client_channel/lb_policy/xds/xds_cluster_impl.cc

@@ -371,7 +371,7 @@ LoadBalancingPolicy::PickResult XdsClusterImplLb::Picker::Pick(
     LoadBalancingPolicy::PickArgs args) {
   // Handle EDS drops.
   const std::string* drop_category;
-  if (drop_config_->ShouldDrop(&drop_category)) {
+  if (drop_config_ != nullptr && drop_config_->ShouldDrop(&drop_category)) {
     if (drop_stats_ != nullptr) drop_stats_->AddCallDropped(*drop_category);
     return PickResult::Drop(absl::UnavailableError(
         absl::StrCat("EDS-configured drop: ", *drop_category)));
@@ -705,7 +705,7 @@ void XdsClusterImplLbConfig::JsonPostLoad(const Json& json,
   // Parse "dropCategories" field.
   {
     auto value = LoadJsonObjectField<std::vector<DropCategory>>(
-        json.object(), args, "dropCategories", errors);
+        json.object(), args, "dropCategories", errors, /*required=*/false);
     if (value.has_value()) {
       drop_config_ = MakeRefCounted<XdsEndpointResource::DropConfig>();
       for (size_t i = 0; i < value->size(); ++i) {

src/core/ext/filters/client_channel/lb_policy/xds/xds_cluster_resolver.cc

@@ -889,8 +889,14 @@ XdsClusterResolverLb::CreateChildPolicyConfigLocked() {
            Json::FromObject(std::move(xds_override_host_lb_config))},
       })};
       // Wrap it in the xds_cluster_impl policy.
-      Json::Array drop_categories;
+      Json::Object xds_cluster_impl_config = {
+          {"clusterName", Json::FromString(discovery_config.cluster_name)},
+          {"childPolicy", Json::FromArray(std::move(xds_override_host_config))},
+          {"maxConcurrentRequests",
+           Json::FromNumber(discovery_config.max_concurrent_requests)},
+      };
       if (discovery_entry.latest_update->drop_config != nullptr) {
+        Json::Array drop_categories;
         for (const auto& category :
              discovery_entry.latest_update->drop_config->drop_category_list()) {
           drop_categories.push_back(Json::FromObject({
@@ -899,14 +905,11 @@ XdsClusterResolverLb::CreateChildPolicyConfigLocked() {
                Json::FromNumber(category.parts_per_million)},
           }));
         }
+        if (!drop_categories.empty()) {
+          xds_cluster_impl_config["dropCategories"] =
+              Json::FromArray(std::move(drop_categories));
+        }
       }
-      Json::Object xds_cluster_impl_config = {
-          {"clusterName", Json::FromString(discovery_config.cluster_name)},
-          {"childPolicy", Json::FromArray(std::move(xds_override_host_config))},
-          {"dropCategories", Json::FromArray(std::move(drop_categories))},
-          {"maxConcurrentRequests",
-           Json::FromNumber(discovery_config.max_concurrent_requests)},
-      };
       if (!discovery_config.eds_service_name.empty()) {
         xds_cluster_impl_config["edsServiceName"] =
             Json::FromString(discovery_config.eds_service_name);

src/core/ext/xds/xds_endpoint.cc

@@ -142,8 +142,9 @@ std::string XdsEndpointResource::ToString() const {
     priority_strings.emplace_back(
         absl::StrCat("priority ", i, ": ", priority.ToString()));
   }
-  return absl::StrCat("priorities=[", absl::StrJoin(priority_strings, ", "),
+  return absl::StrCat(
-                      "], drop_config=", drop_config->ToString());
+      "priorities=[", absl::StrJoin(priority_strings, ", "), "], drop_config=",
+      drop_config == nullptr ? "<null>" : drop_config->ToString());
 }
 
 //
@@ -447,7 +448,6 @@ absl::StatusOr<std::shared_ptr<const XdsEndpointResource>> EdsResourceParse(
     }
   }
   // policy
-  eds_resource->drop_config = MakeRefCounted<XdsEndpointResource::DropConfig>();
   const auto* policy = envoy_config_endpoint_v3_ClusterLoadAssignment_policy(
       cluster_load_assignment);
   if (policy != nullptr) {
@@ -456,6 +456,10 @@ absl::StatusOr<std::shared_ptr<const XdsEndpointResource>> EdsResourceParse(
     const auto* const* drop_overload =
         envoy_config_endpoint_v3_ClusterLoadAssignment_Policy_drop_overloads(
             policy, &drop_size);
+    if (drop_size > 0) {
+      eds_resource->drop_config =
+          MakeRefCounted<XdsEndpointResource::DropConfig>();
+    }
     for (size_t i = 0; i < drop_size; ++i) {
       ValidationErrors::ScopedField field(
           &errors, absl::StrCat(".drop_overloads[", i, "]"));

src/core/ext/xds/xds_endpoint.h

@@ -62,6 +62,7 @@ struct XdsEndpointResource : public XdsResourceType::ResourceData {
     std::map<XdsLocalityName*, Locality, XdsLocalityName::Less> localities;
 
     bool operator==(const Priority& other) const;
+    bool operator!=(const Priority& other) const { return !(*this == other); }
     std::string ToString() const;
   };
   using PriorityList = std::vector<Priority>;
@@ -121,7 +122,10 @@ struct XdsEndpointResource : public XdsResourceType::ResourceData {
   RefCountedPtr<DropConfig> drop_config;
 
   bool operator==(const XdsEndpointResource& other) const {
-    return priorities == other.priorities && *drop_config == *other.drop_config;
+    if (priorities != other.priorities) return false;
+    if (drop_config == nullptr) return other.drop_config == nullptr;
+    if (other.drop_config == nullptr) return false;
+    return *drop_config == *other.drop_config;
   }
   std::string ToString() const;
 };

test/core/xds/xds_endpoint_resource_type_test.cc

@@ -167,8 +167,7 @@ TEST_F(XdsEndpointTest, MinimumValidConfig) {
                                 .Set(GRPC_ARG_ADDRESS_WEIGHT, 1)
                                 .Set(GRPC_ARG_XDS_HEALTH_STATUS,
                                      XdsHealthStatus::HealthStatus::kUnknown));
-  ASSERT_NE(resource.drop_config, nullptr);
+  EXPECT_EQ(resource.drop_config, nullptr);
-  EXPECT_TRUE(resource.drop_config->drop_category_list().empty());
 }
 
 TEST_F(XdsEndpointTest, EndpointWeight) {
@@ -214,8 +213,7 @@ TEST_F(XdsEndpointTest, EndpointWeight) {
                                 .Set(GRPC_ARG_ADDRESS_WEIGHT, 3)
                                 .Set(GRPC_ARG_XDS_HEALTH_STATUS,
                                      XdsHealthStatus::HealthStatus::kUnknown));
-  ASSERT_NE(resource.drop_config, nullptr);
+  EXPECT_EQ(resource.drop_config, nullptr);
-  EXPECT_TRUE(resource.drop_config->drop_category_list().empty());
 }
 
 TEST_F(XdsEndpointTest, IgnoresLocalityWithNoWeight) {
@@ -263,8 +261,7 @@ TEST_F(XdsEndpointTest, IgnoresLocalityWithNoWeight) {
                                 .Set(GRPC_ARG_ADDRESS_WEIGHT, 1)
                                 .Set(GRPC_ARG_XDS_HEALTH_STATUS,
                                      XdsHealthStatus::HealthStatus::kUnknown));
-  ASSERT_NE(resource.drop_config, nullptr);
+  EXPECT_EQ(resource.drop_config, nullptr);
-  EXPECT_TRUE(resource.drop_config->drop_category_list().empty());
 }
 
 TEST_F(XdsEndpointTest, IgnoresLocalityWithZeroWeight) {
@@ -313,8 +310,7 @@ TEST_F(XdsEndpointTest, IgnoresLocalityWithZeroWeight) {
                                 .Set(GRPC_ARG_ADDRESS_WEIGHT, 1)
                                 .Set(GRPC_ARG_XDS_HEALTH_STATUS,
                                      XdsHealthStatus::HealthStatus::kUnknown));
-  ASSERT_NE(resource.drop_config, nullptr);
+  EXPECT_EQ(resource.drop_config, nullptr);
-  EXPECT_TRUE(resource.drop_config->drop_category_list().empty());
 }
 
 TEST_F(XdsEndpointTest, LocalityWithNoEndpoints) {
@@ -346,8 +342,7 @@ TEST_F(XdsEndpointTest, LocalityWithNoEndpoints) {
   EXPECT_EQ(p.first->sub_zone(), "mysubzone");
   EXPECT_EQ(p.second.lb_weight, 1);
   EXPECT_EQ(p.second.endpoints.size(), 0);
-  ASSERT_NE(resource.drop_config, nullptr);
+  EXPECT_EQ(resource.drop_config, nullptr);
-  EXPECT_TRUE(resource.drop_config->drop_category_list().empty());
 }
 
 TEST_F(XdsEndpointTest, NoLocality) {
@@ -544,8 +539,7 @@ TEST_F(XdsEndpointTest, MultipleAddressesPerEndpoint) {
                                  .Set(GRPC_ARG_ADDRESS_WEIGHT, 1)
                                  .Set(GRPC_ARG_XDS_HEALTH_STATUS,
                                       XdsHealthStatus::HealthStatus::kUnknown));
-  ASSERT_NE(resource.drop_config, nullptr);
+  EXPECT_EQ(resource.drop_config, nullptr);
-  EXPECT_TRUE(resource.drop_config->drop_category_list().empty());
 }
 
 TEST_F(XdsEndpointTest, AdditionalAddressesMissingAddress) {
@@ -735,8 +729,7 @@ TEST_F(XdsEndpointTest, IgnoresMultipleAddressesPerEndpointWhenNotEnabled) {
                                  .Set(GRPC_ARG_ADDRESS_WEIGHT, 1)
                                  .Set(GRPC_ARG_XDS_HEALTH_STATUS,
                                       XdsHealthStatus::HealthStatus::kUnknown));
-  ASSERT_NE(resource.drop_config, nullptr);
+  EXPECT_EQ(resource.drop_config, nullptr);
-  EXPECT_TRUE(resource.drop_config->drop_category_list().empty());
 }
 
 TEST_F(XdsEndpointTest, MissingEndpoint) {