protocol::http::request::request request;
protocol::http::request::parser parser(expr);

if (!parser.parse(request))
    ; // TODO: throw

const auto &header = request.header_;
if (header.connection == "Upgrade")
{
    if (header.upgrade == "websocket")
    {
        std::cout << "Key: " << header.sec_websocket.key << std::endl;
        std::cout << "Version: " << header.sec_websocket.version << std::endl;
        std::cout << "Protocol:";
        for (auto &protocol : header.sec_websocket.protocol)
            std::cout << " " << protocol;
        std::cout << std::endl;
    }
}