Ruby on Railsで任意のヘッダーを返す

コントローラーの中の適当なとこ

  def aaa
    @headers["Content-Type"] = "text/xml ;charset=utf-8";
    a = "";
    a = a + "<response>"
    a = a + "hello world"
    a = a + "</response>"
    render_text a
  end

  def bbb
    render_text "hello world"
  end

こんなかんじかな
Setting the request content type in Rails | mentalized
http://mentalized.net/journal/2005/11/14/setting_the_request_content_type_in_rails/