extract_multipart_boundary

# File actionpack/lib/action_controller/request.rb, line 585
      def extract_multipart_boundary(content_type_with_parameters)
        if content_type_with_parameters =~ MULTIPART_BOUNDARY
          ['multipart/form-data', $1.dup]
        else
          extract_content_type_without_parameters(content_type_with_parameters)
        end
      end