#include <cstdint>
#include <iostream>
#include <variant>

enum class TransportTypeID : uint32_t
{
    Error    = 0,
    End      = 1,
    Request  = 2,
    Response = 3,
    Stream   = 4
};

template < TransportTypeID ID, typename T = void >
struct TransportType
{
    static constexpr uint32_t typeID = static_cast< uint32_t >( ID );
    T                         data;
};

template < TransportTypeID ID >
struct TransportType< ID, void >
{
    static constexpr uint32_t typeID = static_cast< uint32_t >( ID );
};

template < TransportTypeID ID, typename T >
struct Transmission
{
    uint64_t               length;
    uint64_t               id;
    TransportType< ID, T > data;
};

namespace management
{
enum class RequestID : uint32_t
{
    Identify = 0,
    Connect  = 1
};

struct Identify
{
    static constexpr uint32_t typeID =
        static_cast< uint32_t >( RequestID::Identify );

    struct Request
    {
        uint32_t protocol_version;
    };

    struct Response
    {
        uint32_t    protocol_version;
        std::string id;
        uint32_t    service_protocol_version;
    };
};

struct Connect
{
    static constexpr uint32_t typeID =
        static_cast< uint32_t >( RequestID::Connect );

    struct Request
    {
        uint32_t protocol_version;
        uint32_t connection_id;
        uint32_t rpc_interval_timeout_ms;
    };

    struct Response
    {
        uint32_t connection_id;
        uint16_t port;
    };
};

} // namespace management


int
main()
{
    Transmission< TransportTypeID::Request, management::Identify > a;
}