# File lib/docker/util.rb, line 122
  def create_tar(hash = {})
    output = StringIO.new
    Gem::Package::TarWriter.new(output) do |tar|
      hash.each do |file_name, file_details|
        permissions = file_details.is_a?(Hash) ? file_details[:permissions] : 0640
        tar.add_file(file_name, permissions) do |tar_file|
          content = file_details.is_a?(Hash) ? file_details[:content] : file_details
          tar_file.write(content)
        end
      end
    end
    output.tap(&:rewind).string
  end