class Net::InternetMessageIO

def using_each_crlf_line
  @wbuf = ''.b
  yield
  if not @wbuf.empty?   # unterminated last line
    write0 dot_stuff(@wbuf.chomp) + "\r\n"
  elsif @written_bytes == 0   # empty src
    write0 "\r\n"
  end
  write0 ".\r\n"
  @wbuf = nil
end