# File lib/sup/mbox/ssh-file.rb, line 121
  def size
    if @file_size.nil? || (Time.now - @last_size_check) > SIZE_CHECK_INTERVAL
      @last_size_check = Time.now
      @file_size = do_remote("wc -c #@fn").split.first.to_i
    end
    @file_size
  end