[Store] metric: add response struct

mooncake-store/include/master_client.h

@@ -180,11 +180,10 @@ class MasterClient {
     /**
      * @brief Pings master to check its availability
      * @param client_id The uuid of the client
-     * @return tl::expected<std::pair<ViewVersionId, ClientStatus>, ErrorCode>
+     * @return tl::expected<PingResponse, ErrorCode>
      * containing view version and client status
      */
-    [[nodiscard]] tl::expected<std::pair<ViewVersionId, ClientStatus>,
-                               ErrorCode>
+    [[nodiscard]] tl::expected<PingResponse, ErrorCode>
     Ping(const UUID& client_id);
 
    private:

mooncake-store/include/master_service.h

@@ -231,13 +231,12 @@ class MasterService {
     /**
      * @brief Heartbeat from client
      * @param client_id The uuid of the client
-     * @param[out] view_version The view version of the master
-     * @param[out] client_status The status of the client from the master
+     * @return PingResponse containing view version and client status
      * @return ErrorCode::OK on success, ErrorCode::INTERNAL_ERROR if the client
      *         ping queue is full
      */
     auto Ping(const UUID& client_id)
-        -> tl::expected<std::pair<ViewVersionId, ClientStatus>, ErrorCode>;
+        -> tl::expected<PingResponse, ErrorCode>;
 
     /**
      * @brief Get the master service cluster ID to use as subdirectory name

mooncake-store/include/rpc_service.h

@@ -80,7 +80,7 @@ class WrappedMasterService {
 
     tl::expected<std::string, ErrorCode> GetFsdir();
 
-    tl::expected<std::pair<ViewVersionId, ClientStatus>, ErrorCode> Ping(
+    tl::expected<PingResponse, ErrorCode> Ping(
         const UUID& client_id);
 
    private:

mooncake-store/include/types.h

@@ -466,7 +466,6 @@ enum class ClientStatus {
     NEED_REMOUNT,   // Ping ttl expired, or the first time connect to master, so
                     // need to remount
 };
-YLT_REFL(ClientStatus);
 
 /**
  * @brief Stream operator for ClientStatus
@@ -483,6 +482,25 @@ inline std::ostream& operator<<(std::ostream& os,
     return os;
 }
 
+/**
+ * @brief Response structure for Ping operation
+ */
+struct PingResponse {
+    ViewVersionId view_version_id;
+    ClientStatus client_status;
+
+    PingResponse() = default;
+    PingResponse(ViewVersionId view_version, ClientStatus status)
+        : view_version_id(view_version), client_status(status) {}
+
+    friend std::ostream& operator<<(std::ostream& os,
+                                    const PingResponse& response) noexcept {
+        return os << "PingResponse: { view_version_id: " << response.view_version_id
+                  << ", client_status: " << response.client_status << " }";
+    }
+};
+YLT_REFL(PingResponse, view_version_id, client_status);
+
 enum class BufferAllocatorType {
     CACHELIB = 0,  // CachelibBufferAllocator
     OFFSET = 1,    // OffsetBufferAllocator

mooncake-store/src/master_client.cpp

@@ -554,7 +554,7 @@ tl::expected<void, ErrorCode> MasterClient::UnmountSegment(
     return result;
 }
 
-tl::expected<std::pair<ViewVersionId, ClientStatus>, ErrorCode>
+tl::expected<PingResponse, ErrorCode>
 MasterClient::Ping(const UUID& client_id) {
     ScopedVLogTimer timer(1, "MasterClient::Ping");
     timer.LogRequest("client_id=", client_id);
@@ -569,8 +569,7 @@ MasterClient::Ping(const UUID& client_id) {
     auto request_result =
         client->send_request<&WrappedMasterService::Ping>(client_id);
     auto result = coro::syncAwait(
-        [&]() -> coro::Lazy<tl::expected<std::pair<ViewVersionId, ClientStatus>,
-                                         ErrorCode>> {
+        [&]() -> coro::Lazy<tl::expected<PingResponse, ErrorCode>> {
             auto result = co_await co_await request_result;
             if (!result) {
                 LOG(ERROR) << "Failed to ping master: " << result.error().msg;

mooncake-store/src/master_service.cpp

@@ -583,7 +583,7 @@ size_t MasterService::GetKeyCount() const {
 }
 
 auto MasterService::Ping(const UUID& client_id)
-    -> tl::expected<std::pair<ViewVersionId, ClientStatus>, ErrorCode> {
+    -> tl::expected<PingResponse, ErrorCode> {
     if (!enable_ha_) {
         LOG(ERROR) << "Ping is only available in HA mode";
         return tl::make_unexpected(ErrorCode::UNAVAILABLE_IN_CURRENT_MODE);
@@ -604,7 +604,7 @@ auto MasterService::Ping(const UUID& client_id)
                    << ", error=client_ping_queue_full";
         return tl::make_unexpected(ErrorCode::INTERNAL_ERROR);
     }
-    return std::make_pair(view_version_, client_status);
+    return PingResponse(view_version_, client_status);
 }
 
 tl::expected<std::string, ErrorCode> MasterService::GetFsdir() const {

mooncake-store/src/rpc_service.cpp

@@ -450,7 +450,7 @@ tl::expected<std::string, ErrorCode> WrappedMasterService::GetFsdir() {
     return result;
 }
 
-tl::expected<std::pair<ViewVersionId, ClientStatus>, ErrorCode>
+tl::expected<PingResponse, ErrorCode>
 WrappedMasterService::Ping(const UUID& client_id) {
     ScopedVLogTimer timer(1, "Ping");
     timer.LogRequest("client_id=", client_id);