code: func (cli *Client) DialHijack(ctx context.Context, url, proto string, meta map[string][]string) (net.Conn, error) {
  	req, err := http.NewRequest("POST", url, nil)
  	if err != nil {
  		return nil, err
  	}
  	req = cli.addHeaders(req, meta)
  
  	return cli.setupHijackConn(ctx, req, proto)
  }
docs: // DialHijack returns a hijacked connection with negotiated protocol proto.