Method is_socket_open

examples/server/httplib.h:7886–7889

inline int ClientImpl::port() const { return port_; }

inline size_t ClientImpl::is_socket_open() const {
  std::lock_guard<std::mutex> guard(socket_mutex_);
  return socket_.is_open();
}

inline socket_t ClientImpl::socket() const { return socket_.sock; }