Ruby on Rails and IE 8 - respond_to and HTTP accept headers

Posted: 2010-03-18

Ruby on Rails offers the ability to respond to a given request with different types depending on the URL.

For example - http://server/controller.html gives HTML where http://server/controller.pdf sends a PDF file.

However - what happens if the URL is just http://server/controller ? Well then rails will use the HTTP_ACCEPT header sent by the browser (at least in 2.3.x - haven't tested other versions).

So - when adding support for /controller.xls it seemed a little strange that all users apart from IE got the HTML page where IE8 (I suspect more but have only tested with v8) got the excel file.

The problem

The issue is in the accept header sent by IE:

  • image/gif
  • image/jpeg
  • image/pjpeg
  • application/x-ms-application
  • application/
  • application/xaml+xml
  • application/x-ms-xbap
  • application/x-shockwave-flash
  • application/
  • application/
  • application/msword
  • */*

If we change

    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @items }


    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @items }
      format.xls do
        excel = Item.get_excel

                  :type => 'application/',
                  :disposition => 'attachment',
                  :filename => excel.get_destination_filename)

then everyone will get the excel file if they request /controller.xls but IE gets the excel file also for /controller - instead of the first entry in the list - the HTML response. From the accept headers list you can see that the excel mimetype is specifically listed.

The Workaround

Most googling suggested setting the order of the respond_to elements - but here the HTML response is first.

So - as a workaround - force prefix the accept header before the call to respond_to

For this example I just grabbed the HTML part of the Safari 4 accept header and prefixed it.

  def set_accept_header
    accept = request.env["HTTP_ACCEPT"]

    request.env["HTTP_ACCEPT"] = "application/xml,application/xhtml+xml,text/html;q=0.9,#{accept}"

This can be called as a standard method call in the directly affected method or as a before_filter - depending on your needs.

Note that this is a very simplified method - it doesn't check to see what's present there or if it is IE that is the client - but for the application it was needed for its good enough ;)