class Zip::FileSystem::ZipFsDir

def foreach(directory_name)
  unless @file.stat(directory_name).directory?
    raise Errno::ENOTDIR, directory_name
  end
  path = @file.expand_path(directory_name)
  path << '/' unless path.end_with?('/')
  path = Regexp.escape(path)
  subdir_entry_regex = Regexp.new("^#{path}([^/]+)$")
  @mapped_zip.each do |filename|
    match = subdir_entry_regex.match(filename)
    yield(match[1]) unless match.nil?
  end
end