def cmd_size(param)
      send_unauthorised and return unless logged_in?
      send_param_required and return if param.nil?

      @driver.bytes(build_path(param)) do |bytes|
        if bytes
          send_response "213 #{bytes}"
        else
          send_response "450 file not available"
        end
      end
    end
def cmd_size(param)
      send_unauthorised and return unless logged_in?
      send_param_required and return if param.nil?

      @driver.bytes(build_path(param)) do |bytes|
        if bytes
          send_response "213 #{bytes}"
        else
          send_response "450 file not available"
        end
      end
    end
return the size of a file in bytes