func (s Server) Conn(w http.ResponseWriter, req *http.Request) *Conn {
    rwc, buf, err := w.(http.Hijacker).Hijack()
    if err != nil {
        return nil
    }
    conn, err := newServerConn(rwc, buf, req, &s.Config, s.Handshake)
    if err != nil {
        return nil
    }
    if conn == nil {
        return nil
    }
    return conn
}