code: func (cli *Client) Dialer() func(context.Context) (net.Conn, error) {
  	return func(ctx context.Context) (net.Conn, error) {
  		if transport, ok := cli.client.Transport.(*http.Transport); ok {
  			if transport.DialContext != nil && transport.TLSClientConfig == nil {
  				return transport.DialContext(ctx, cli.proto, cli.addr)
  			}
  		}
  		return fallbackDial(cli.proto, cli.addr, resolveTLSConfig(cli.client.Transport))
  	}
  }
docs: // Dialer returns a dialer for a raw stream connection, with HTTP/1.1 header, that can be used for proxying the daemon connection.
  // Used by `docker dial-stdio` (docker/cli#889).