xDS server serving status: Use a struct to allow more fields to be added in the future (#27242)

include/grpc/grpc.h

@@ -410,12 +410,18 @@ GRPCAPI void grpc_server_register_completion_queue(grpc_server* server,
                                                    grpc_completion_queue* cq,
                                                    void* reserved);
 
+// More members might be added in later, so users should take care to memset
+// this to 0 before using it.
+typedef struct {
+  grpc_status_code code;
+  const char* error_message;
+} grpc_serving_status_update;
+
 // There might be more methods added later, so users should take care to memset
 // this to 0 before using it.
 typedef struct {
   void (*on_serving_status_update)(void* user_data, const char* uri,
-                                   grpc_status_code code,
-                                   const char* error_message);
+                                   grpc_serving_status_update update);
   void* user_data;
 } grpc_server_xds_status_notifier;
 

include/grpcpp/xds_server_builder.h

@@ -28,6 +28,10 @@ namespace experimental {
 
 class XdsServerServingStatusNotifierInterface {
  public:
+  struct ServingStatusUpdate {
+    ::grpc::Status status;
+  };
+
   virtual ~XdsServerServingStatusNotifierInterface() = default;
 
   // \a uri contains the listening target associated with the notification. Note
@@ -37,7 +41,8 @@ class XdsServerServingStatusNotifierInterface {
   // The API does not provide any guarantees around duplicate updates.
   // Status::OK signifies that the server is serving, while a non-OK status
   // signifies that the server is not serving.
-  virtual void OnServingStatusUpdate(std::string uri, grpc::Status status) = 0;
+  virtual void OnServingStatusUpdate(std::string uri,
+                                     ServingStatusUpdate update) = 0;
 };
 
 class XdsServerBuilder : public ::grpc::ServerBuilder {
@@ -62,13 +67,13 @@ class XdsServerBuilder : public ::grpc::ServerBuilder {
   }
 
   static void OnServingStatusUpdate(void* user_data, const char* uri,
-                                    grpc_status_code code,
-                                    const char* error_message) {
+                                    grpc_serving_status_update update) {
     if (user_data == nullptr) return;
     XdsServerServingStatusNotifierInterface* notifier =
         static_cast<XdsServerServingStatusNotifierInterface*>(user_data);
     notifier->OnServingStatusUpdate(
-        uri, grpc::Status(static_cast<StatusCode>(code), error_message));
+        uri, {grpc::Status(static_cast<StatusCode>(update.code),
+                           update.error_message)});
   }
 
   XdsServerServingStatusNotifierInterface* notifier_ = nullptr;

src/core/ext/xds/xds_server_config_fetcher.cc

@@ -428,7 +428,7 @@ class XdsServerConfigFetcher : public grpc_server_config_fetcher {
         if (serving_status_notifier_.on_serving_status_update != nullptr) {
           serving_status_notifier_.on_serving_status_update(
               serving_status_notifier_.user_data, listening_address_.c_str(),
-              GRPC_STATUS_OK, "");
+              {GRPC_STATUS_OK, ""});
         } else {
           gpr_log(GPR_INFO,
                   "xDS Listener resource obtained; will start serving on %s",
@@ -459,7 +459,7 @@ class XdsServerConfigFetcher : public grpc_server_config_fetcher {
         if (serving_status_notifier_.on_serving_status_update != nullptr) {
           serving_status_notifier_.on_serving_status_update(
               serving_status_notifier_.user_data, listening_address_.c_str(),
-              GRPC_STATUS_UNAVAILABLE, grpc_error_std_string(error).c_str());
+              {GRPC_STATUS_UNAVAILABLE, grpc_error_std_string(error).c_str()});
         } else {
           gpr_log(
               GPR_ERROR,
@@ -486,8 +486,8 @@ class XdsServerConfigFetcher : public grpc_server_config_fetcher {
       if (serving_status_notifier_.on_serving_status_update != nullptr) {
         serving_status_notifier_.on_serving_status_update(
             serving_status_notifier_.user_data, listening_address_.c_str(),
-            static_cast<grpc_status_code>(status.raw_code()),
-            std::string(status.message()).c_str());
+            {static_cast<grpc_status_code>(status.raw_code()),
+             std::string(status.message()).c_str()});
       }
     }
 

test/cpp/end2end/xds_end2end_test.cc

@@ -2491,9 +2491,10 @@ class XdsEnd2endTest : public ::testing::TestWithParam<TestType> {
   class XdsServingStatusNotifier
       : public grpc::experimental::XdsServerServingStatusNotifierInterface {
    public:
-    void OnServingStatusUpdate(std::string uri, grpc::Status status) override {
+    void OnServingStatusUpdate(std::string uri,
+                               ServingStatusUpdate update) override {
       grpc_core::MutexLock lock(&mu_);
-      status_map[uri] = status;
+      status_map[uri] = update.status;
       cond_.Signal();
     }