fix(store): validate client HA backend availability

Author: Lin-z-w

mooncake-store/src/client_service.cpp

@@ -241,6 +241,11 @@ tl::expected<std::optional<ha::HABackendSpec>, ErrorCode> ParseHABackendSpec(
         return tl::make_unexpected(ErrorCode::INVALID_PARAMS);
     }
 
+    auto availability = ha::ValidateHABackendAvailability(backend_type.value());
+    if (availability != ErrorCode::OK) {
+        return tl::make_unexpected(availability);
+    }
+
     return std::optional<ha::HABackendSpec>{ha::HABackendSpec{
         .type = backend_type.value(),
         .connstring = master_server_entry.substr(delimiter_pos + 3),

mooncake-store/tests/ha/leadership/ha_backend_availability_test.cpp

@@ -1,8 +1,13 @@
 #include "ha/ha_types.h"
 
 #include <gtest/gtest.h>
+#include <ylt/util/tl/expected.hpp>
 
 namespace mooncake {
+
+tl::expected<std::optional<ha::HABackendSpec>, ErrorCode> ParseHABackendSpec(
+    const std::string& master_server_entry);
+
 namespace ha {
 namespace {
 
@@ -36,6 +41,13 @@ TEST(HABackendAvailabilityTest, K8sLeaseIsRejectedUntilCoordinatorExists) {
               ValidateHABackendAvailability(HABackendType::K8S));
 }
 
+TEST(HABackendAvailabilityTest,
+     ClientSpecParsingRejectsUnavailableBackendBeforeCoordinatorCreation) {
+    auto spec = ParseHABackendSpec("k8s://default/master");
+    ASSERT_FALSE(spec.has_value());
+    EXPECT_EQ(ErrorCode::UNAVAILABLE_IN_CURRENT_MODE, spec.error());
+}
+
 }  // namespace
 }  // namespace ha
 }  // namespace mooncake