set_filename

# File lib/webrick/httpservlet/filehandler.rb, line 256
      def set_filename(req, res)
        res.filename = @root.dup
        path_info = req.path_info.scan(%r|/[^/]*|)

        path_info.unshift("")  # dummy for checking @root dir
        while base = path_info.first
          break if base == "/"
          break unless File.directory?(File.expand_path(res.filename + base))
          shift_path_info(req, res, path_info)
          call_callback(:DirectoryCallback, req, res)
        end

        if base = path_info.first
          if base == "/"
            if file = search_index_file(req, res)
              shift_path_info(req, res, path_info, file)
              call_callback(:FileCallback, req, res)
              return true
            end
            shift_path_info(req, res, path_info)
          elsif file = search_file(req, res, base)
            shift_path_info(req, res, path_info, file)
            call_callback(:FileCallback, req, res)
            return true
          else
            raise HTTPStatus::NotFound, "`#{req.path}' not found."
          end
        end

        return false
      end