    # File lib/rack/file.rb, line 36
        def _call(env)
          unless ALLOWED_VERBS.include? env[REQUEST_METHOD]
            return fail(405, "Method Not Allowed", {'Allow' => ALLOW_HEADER})
          end

          path_info = Utils.unescape(env[PATH_INFO])
          clean_path_info = Utils.clean_path_info(path_info)

          @path = F.join(@root, clean_path_info)

          available = begin
            F.file?(@path) && F.readable?(@path)
          rescue SystemCallError
            false
          end

          if available
            serving(env)
          else
            fail(404, "File not found: #{path_info}")
          end
        end