     # continue looping
        end while need_retry
      end
    end

    #
    # Logging
    #

    private

    def LOG_off
      @save_debug_out = @debug_output
      @debug_output = nil
    end

    def LOG_on
      @debug_output = @save_debug_out
    end

    def LOG(msg)
      return unless @debug_output
      @debug_output << msg + "\n"
    end
  end


  class InternetMessageIO < BufferedIO   #:nodoc: internal use only
    def initialize(*, **)
      super
      @wbuf = nil
    end

    #
    # Read
    #

    def each_message_chunk
      LOG 'reading message...'
      LOG_off()
      read_bytes = 0
      while (line = readuntil("\r\n")) != ".\r\n"
        read_bytes += line.size
        yield line.delete_prefix('.')
      end
      LOG_on()
      LOG "read message (#{read_bytes} bytes)"
    end

    # *library private* (cannot handle 'break')
    def each_list_item
      while (str = readuntil("\r\n")) != ".\r\n"
        yield str.chop
      end
    end

    def write_message_0(src)
      prev = @written_bytes
      each_crlf_line(src) do |line|
        write0 dot_stuff(line)
      end
      @written_bytes - prev
    end

    #
    # Write
    #

    def write_message(src)
      LOG "writing message from #{src.class}"
      LOG_off()
      len = writing {
     