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#pragma once 
 
#include <grpc++/impl/codegen/byte_buffer.h> 
#include <grpc++/impl/codegen/proto_utils.h> 
 
#include <variant> 
 
namespace NGrpc { 
 
/** 
 * Universal response that owns underlying message or buffer. 
 */ 
template <typename TMsg> 
class TUniversalResponse: public TAtomicRefCount<TUniversalResponse<TMsg>>, public TMoveOnly {
    friend class grpc::SerializationTraits<TUniversalResponse<TMsg>>; 
 
public: 
    explicit TUniversalResponse(NProtoBuf::Message* msg) noexcept 
        : Data_{TMsg{}} 
    { 
        std::get<TMsg>(Data_).Swap(static_cast<TMsg*>(msg)); 
    } 
 
    explicit TUniversalResponse(grpc::ByteBuffer* buffer) noexcept 
        : Data_{grpc::ByteBuffer{}} 
    { 
        std::get<grpc::ByteBuffer>(Data_).Swap(buffer); 
    } 
 
private: 
    std::variant<TMsg, grpc::ByteBuffer> Data_; 
}; 
 
/** 
 * Universal response that only keeps reference to underlying message or buffer. 
 */ 
template <typename TMsg> 
class TUniversalResponseRef: private TMoveOnly { 
    friend class grpc::SerializationTraits<TUniversalResponseRef<TMsg>>; 
 
public: 
    explicit TUniversalResponseRef(const NProtoBuf::Message* msg) 
        : Data_{msg} 
    { 
    } 
 
    explicit TUniversalResponseRef(const grpc::ByteBuffer* buffer) 
        : Data_{buffer} 
    { 
    } 
 
private: 
    std::variant<const NProtoBuf::Message*, const grpc::ByteBuffer*> Data_; 
}; 
 
} // namespace NGrpc 
 
namespace grpc { 
 
template <typename TMsg> 
class SerializationTraits<NGrpc::TUniversalResponse<TMsg>> { 
public: 
    static Status Serialize( 
            const NGrpc::TUniversalResponse<TMsg>& resp, 
            ByteBuffer* buffer, 
            bool* ownBuffer) 
    { 
        return std::visit([&](const auto& data) { 
            using T = std::decay_t<decltype(data)>; 
            return SerializationTraits<T>::Serialize(data, buffer, ownBuffer); 
        }, resp.Data_); 
    } 
}; 
 
template <typename TMsg> 
class SerializationTraits<NGrpc::TUniversalResponseRef<TMsg>> { 
public: 
    static Status Serialize( 
        const NGrpc::TUniversalResponseRef<TMsg>& resp, 
        ByteBuffer* buffer, 
        bool* ownBuffer) 
    { 
        return std::visit([&](const auto* data) { 
            using T = std::decay_t<std::remove_pointer_t<decltype(data)>>; 
            return SerializationTraits<T>::Serialize(*data, buffer, ownBuffer); 
        }, resp.Data_); 
    } 
}; 
 
} // namespace grpc