class Net::IMAP

def fetch_internal(cmd, set, attr, mod = nil)
  case attr
  when String then
    attr = RawData.new(attr)
  when Array then
    attr = attr.map { |arg|
      arg.is_a?(String) ? RawData.new(arg) : arg
    }
  end
  synchronize do
    clear_responses("FETCH")
    if mod
      send_command(cmd, MessageSet.new(set), attr, mod)
    else
      send_command(cmd, MessageSet.new(set), attr)
    end
    clear_responses("FETCH")
  end
end