impl(pubsub): add default message batch impl (#12676)

Author: alevenberg

google/cloud/pubsub/CMakeLists.txt

@@ -75,6 +75,7 @@ add_library(
     internal/flow_controlled_publisher_connection.h
     internal/flow_controlled_publisher_tracing_connection.cc
     internal/flow_controlled_publisher_tracing_connection.h
+    internal/noop_message_batch.h
     internal/ordering_key_publisher_connection.cc
     internal/ordering_key_publisher_connection.h
     internal/publisher_auth_decorator.cc

google/cloud/pubsub/google_cloud_cpp_pubsub.bzl

@@ -38,6 +38,7 @@ google_cloud_cpp_pubsub_hdrs = [
     "internal/extend_leases_with_retry.h",
     "internal/flow_controlled_publisher_connection.h",
     "internal/flow_controlled_publisher_tracing_connection.h",
+    "internal/noop_message_batch.h",
     "internal/ordering_key_publisher_connection.h",
     "internal/publisher_auth_decorator.h",
     "internal/publisher_logging_decorator.h",

google/cloud/pubsub/internal/noop_message_batch.h

@@ -0,0 +1,46 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_PUBSUB_INTERNAL_NOOP_MESSAGE_BATCH_H
+#define GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_PUBSUB_INTERNAL_NOOP_MESSAGE_BATCH_H
+
+#include "google/cloud/pubsub/internal/message_batch.h"
+
+namespace google {
+namespace cloud {
+namespace pubsub_internal {
+GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN
+
+/**
+ * A no-op implementation of `MessageBatch`
+ */
+class NoOpMessageBatch : public MessageBatch {
+ public:
+  NoOpMessageBatch() = default;
+
+  ~NoOpMessageBatch() override = default;
+
+  void SaveMessage(pubsub::Message m) override{};
+
+  void Flush() override{};
+
+  void FlushCallback() override{};
+};
+
+GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
+}  // namespace pubsub_internal
+}  // namespace cloud
+}  // namespace google
+
+#endif  // GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_PUBSUB_INTERNAL_NOOP_MESSAGE_BATCH_H