# File lib/docker/util.rb, line 145
  def create_relative_dir_tar(directory, output)
    Gem::Package::TarWriter.new(output) do |tar|
      files = glob_all_files(File.join(directory, "**/*"))
      remove_ignored_files!(directory, files)

      files.each do |prefixed_file_name|
        stat = File.stat(prefixed_file_name)
        next unless stat.file?

        unprefixed_file_name = prefixed_file_name[directory.length..-1]
        add_file_to_tar(
          tar, unprefixed_file_name, stat.mode, stat.size, stat.mtime
        ) do |tar_file|
          IO.copy_stream(File.open(prefixed_file_name, 'rb'), tar_file)
        end
      end
    end
  end