Rails respond_to rendering wrong format in IE

I ran into an interesting issue today where a client viewing my Rails site would go to a link; and instead of seeing the html view rendered, it was skipping right to an alternate format in the respond_to block.

Clicking a link going to /orders, was instead taking them to /orders.xls, which I have in a respond_to block like so:

  def orders
    @orders = Order.all
    respond_to do |format|
      format.html # new.html.erb
      format.xls   # new.xls.erb
    end
  end

The client in question was using Internet Explorer. This provided a major clue.
It turns out that IE will send an HTTP_ACCEPT header listing all the stuff it can accept in the browser, and thus, because it can accept .xls files, it requests that format.

I’m experiencing this in a Rails 2.3.8 app, but documentation at railsguides.info states this behavior was changed in Rails 2.2. Perhaps an older plugin is switching it back on, I’ll have to investigate.

In any case, adding this line to application.rb solves the problem:

config.action_controller.use_accept_header = false

This causes it to behave as expected, where it uses the file extension alone to determine the format when there is a question which format to use.

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