request_parameters_list

# File actionpack/lib/action_dispatch/http/request.rb, line 442
    def request_parameters_list
      # We don't use Rack's parse result, but we must call it so Rack
      # can populate the rack.request.* keys we need.
      rack_post = rack_request.POST

      if form_pairs = get_header("rack.request.form_pairs")
        # Multipart
        form_pairs
      elsif form_vars = get_header("rack.request.form_vars")
        # URL-encoded
        ActionDispatch::QueryParser.each_pair(form_vars)
      elsif rack_post && !rack_post.empty?
        # It was multipart, but Rack did not preserve a pair list
        # (probably too old). Flat parameter list is not available.
        nil
      else
        # No request body, or not a format Rack knows
        []
      end
    end