gistfile1.rb

# this responder allows the system to render a streaming proc
# rendering a proc was removed in Rails 3.0
ActionController::Renderers.add :csv do |proc, options|
  raise ArgumentError "CSV responder requires :filename" unless options.key? :filename
  
  filename = options[:filename]
  
  headers.merge!(
    'Cache-Control' => 'must-revalidate, post-check=0, pre-check=0',
    'Content-Disposition' => "attachment; filename=\"#{filename}\"",
    'Content-Transfer-Encoding' => 'binary'
  )
  
  self.content_type ||= Mime::CSV
  self.response_body  = proc
end