Add gRPC service for wal_history and backend framework

- Implement gRPC service to provide wal_history information
- Add extensible backend framework for gRPC services
- Add unit tests for wal_history_service_impl
- Refactor test base to support backend/service factory injection
- Update documentation to reflect gRPC service and backend framework for wal_history

Author: umegane

docs/internal/wal_sync_impl_design.md

@@ -3,6 +3,7 @@ file(GLOB SOURCES
         "limestone/replication/*.cpp"
         "limestone/partitioned_cursor/*.cpp"
         "limestone/grpc/service/*.cpp"
+        "limestone/grpc/backend/*.cpp"
         "limestone/grpc/client/*.cpp"
         "limestone/wal_sync/*.cpp"
 )

src/CMakeLists.txt

@@ -4,19 +4,22 @@ This directory contains the gRPC implementation for limestone datastore.
 
 ## Directory Structure
 
+
 ```
 src/limestone/grpc/
 ├── README.md           # This file (directory overview and conventions)
 ├── proto/              # Protocol Buffer definitions
 ├── service/            # gRPC service implementations
+├── backend/            # gRPC service backend implementations (service logic backend, abstraction for datastore access, etc.)
 └── client/             # gRPC client implementations
 ```
 
 ## Naming Conventions
 
-### C++ Namespaces & Protocol Buffer Package
+### C++ Namespaces
 
 - `limestone::grpc::service` - gRPC service implementations
+- `limestone::grpc::backend` - gRPC backend implementations
 - `limestone::grpc::client` - gRPC client implementations
 - `limestone::grpc::proto` - Protocol Buffer generated code
 
@@ -59,6 +62,22 @@ namespace limestone::grpc::client {
 5. **Documentation**: Include English comments for all public interfaces
 6. **Testing**: Create corresponding test files for each implementation
 
+
+## Message Versioning
+
+Some gRPC request/response messages include a `version` field for future compatibility.
+The version value to use for each message is defined as a constant in `grpc/message_versions.h`.
+Both client and service must check and set the version accordingly.
+
+Example:
+
+```cpp
+#include "grpc/message_versions.h"
+request.set_version(list_wal_history_message_version);
+```
+
+The initial version number for each message is 1.
+
 ## Build Integration
 
 The gRPC components are integrated into the main limestone build system through CMake.

src/limestone/grpc/README.md

@@ -0,0 +1,15 @@
+#include "backend_shared_impl.h"
+namespace limestone::grpc::backend {
+
+using limestone::internal::wal_history;    
+
+
+backend_shared_impl::backend_shared_impl(const boost::filesystem::path& log_dir)
+    : log_dir_(log_dir) {}
+
+std::vector<wal_history::record> backend_shared_impl::list_wal_history() {
+    wal_history wal_history_(log_dir_);
+    return wal_history_.list();
+}
+
+} // namespace limestone::grpc::backend

src/limestone/grpc/backend/backend_shared_impl.cpp

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <vector>
+#include "wal_sync/wal_history.h"
+
+namespace limestone::grpc::backend {
+
+class backend_shared_impl {
+public:
+    explicit backend_shared_impl(const boost::filesystem::path& log_dir);
+    virtual ~backend_shared_impl() = default;
+
+    // Shared logic for listing WAL history
+    std::vector<limestone::internal::wal_history::record> list_wal_history();
+
+private:
+    boost::filesystem::path log_dir_;
+};
+
+} // namespace limestone::grpc::backend

src/limestone/grpc/backend/backend_shared_impl.h

@@ -0,0 +1,34 @@
+
+/*
+ * Copyright 2022-2025 Project Tsurugi.
+ *
+ * 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
+ *
+ *     http://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.
+ */ 
+#include "grpc_service_backend.h"
+#include "inproc_backend.h"
+#include "standalone_backend.h"
+
+
+namespace limestone::grpc::backend {
+
+using limestone::api::datastore;    
+
+std::unique_ptr<grpc_service_backend> grpc_service_backend::create_inproc(datastore& store, const boost::filesystem::path& log_dir) {
+	return std::make_unique<inproc_backend>(store, log_dir);
+}
+
+std::unique_ptr<grpc_service_backend> grpc_service_backend::create_standalone(const boost::filesystem::path& log_dir) {
+	return std::make_unique<standalone_backend>(log_dir);
+}
+
+} // namespace limestone::grpc::backend

src/limestone/grpc/backend/grpc_service_backend.cpp

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2022-2025 Project Tsurugi.
+ *
+ * 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
+ *
+ *     http://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.
+ */ 
+#pragma once
+#include <memory>
+#include <string>
+#include <boost/filesystem.hpp>
+#include "limestone/api/datastore.h"
+#include "wal_sync/wal_history.h"
+
+namespace limestone::grpc::backend {
+
+using limestone::internal::wal_history;
+
+// Pure interface for gRPC backends.
+// Implementations: inproc_backend, standalone_backend.
+class grpc_service_backend {
+public:
+    virtual ~grpc_service_backend() = default;
+
+    // Factory helpers (unchanged)
+    [[nodiscard]] static std::unique_ptr<grpc_service_backend> create_inproc(limestone::api::datastore& store, const boost::filesystem::path& log_dir);
+    [[nodiscard]] static std::unique_ptr<grpc_service_backend> create_standalone(const boost::filesystem::path& log_dir);
+    
+    // Returns the list of WAL history records.
+    [[nodiscard]] virtual std::vector<wal_history::record> list_wal_history() = 0;
+
+    // Returns the log directory path (for debugging purposes)
+    [[nodiscard]] virtual boost::filesystem::path get_log_dir() const noexcept = 0;
+protected:
+    grpc_service_backend() = default;
+};
+
+} // namespace limestone::grpc::backend

src/limestone/grpc/backend/grpc_service_backend.h

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2022-2025 Project Tsurugi.
+ *
+ * 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
+ *
+ *     http://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.
+ */ 
+#include "inproc_backend.h"
+
+namespace limestone::grpc::backend {
+
+
+inproc_backend::inproc_backend(limestone::api::datastore& ds, const boost::filesystem::path& log_dir)
+	: datastore_(ds), log_dir_(log_dir), backend_shared_impl_(log_dir)
+{
+}
+
+std::vector<wal_history::record> inproc_backend::list_wal_history() {
+	return backend_shared_impl_.list_wal_history();
+}
+
+boost::filesystem::path inproc_backend::get_log_dir() const noexcept {
+	return log_dir_;
+}
+
+} // namespace limestone::grpc::backend

src/limestone/grpc/backend/inproc_backend.cpp

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2022-2025 Project Tsurugi.
+ *
+ * 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
+ *
+ *     http://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.
+ */ 
+#pragma once
+
+#include <vector>
+#include "grpc_service_backend.h"
+#include "backend_shared_impl.h"
+namespace limestone::grpc::backend {
+
+class inproc_backend : public grpc_service_backend {
+public:
+    inproc_backend(limestone::api::datastore& ds, const boost::filesystem::path& log_dir);
+    ~inproc_backend() override = default;
+
+    std::vector<wal_history::record> list_wal_history() override;
+    boost::filesystem::path get_log_dir() const noexcept override;
+private:
+    limestone::api::datastore& datastore_;
+    boost::filesystem::path log_dir_;
+    backend_shared_impl backend_shared_impl_;
+};
+
+} // namespace limestone::grpc::backend
+// Move file to src/limestone/grpc/service/backend/inproc_backend.h

src/limestone/grpc/backend/inproc_backend.h

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2022-2025 Project Tsurugi.
+ *
+ * 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
+ *
+ *     http://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.
+ */ 
+#include "standalone_backend.h"
+
+namespace limestone::grpc::backend {
+
+standalone_backend::standalone_backend(const boost::filesystem::path& log_dir)
+	: log_dir_(log_dir), backend_shared_impl_(log_dir)
+{
+}
+
+std::vector<wal_history::record> standalone_backend::list_wal_history() {
+	return backend_shared_impl_.list_wal_history();
+}
+
+boost::filesystem::path standalone_backend::get_log_dir() const noexcept {
+	return log_dir_;
+}
+
+} // namespace limestone::grpc::backend