Fix redundant string copy of PlaceholderGroup (#18236)

Signed-off-by: Nxaxys <zheng.guan@zilliz.com>

internal/core/src/query/Plan.cpp

@@ -21,12 +21,19 @@
 
 namespace milvus::query {
 
+// deprecated
 std::unique_ptr<PlaceholderGroup>
-ParsePlaceholderGroup(const Plan* plan, const std::string& blob) {
+ParsePlaceholderGroup(const Plan* plan, const std::string& placeholder_group_blob) {
+    return ParsePlaceholderGroup(plan, reinterpret_cast<const uint8_t*>(placeholder_group_blob.c_str()),
+                                 placeholder_group_blob.size());
+}
+
+std::unique_ptr<PlaceholderGroup>
+ParsePlaceholderGroup(const Plan* plan, const uint8_t* blob, const int64_t blob_len) {
     namespace ser = milvus::proto::common;
     auto result = std::make_unique<PlaceholderGroup>();
     ser::PlaceholderGroup ph_group;
-    auto ok = ph_group.ParseFromString(blob);
+    auto ok = ph_group.ParseFromArray(blob, blob_len);
     Assert(ok);
     for (auto& info : ph_group.placeholders()) {
         Placeholder element;

internal/core/src/query/Plan.h

@@ -34,6 +34,10 @@ CreatePlan(const Schema& schema, const std::string& dsl);
 std::unique_ptr<Plan>
 CreateSearchPlanByExpr(const Schema& schema, const void* serialized_expr_plan, const int64_t size);
 
+std::unique_ptr<PlaceholderGroup>
+ParsePlaceholderGroup(const Plan* plan, const uint8_t* blob, const int64_t blob_len);
+
+// deprecated
 std::unique_ptr<PlaceholderGroup>
 ParsePlaceholderGroup(const Plan* plan, const std::string& placeholder_group_blob);
 

internal/core/src/segcore/plan_c.cpp

@@ -77,11 +77,10 @@ ParsePlaceholderGroup(CSearchPlan c_plan,
                       const void* placeholder_group_blob,
                       const int64_t blob_size,
                       CPlaceholderGroup* res_placeholder_group) {
-    std::string blob_str((char*)placeholder_group_blob, blob_size);
     auto plan = (milvus::query::Plan*)c_plan;
 
     try {
-        auto res = milvus::query::ParsePlaceholderGroup(plan, blob_str);
+        auto res = milvus::query::ParsePlaceholderGroup(plan, (const uint8_t*)(placeholder_group_blob), blob_size);
 
         auto status = CStatus();
         status.error_code = Success;