class Net::InternetMessageIO

def write_message_by_block(&block)
  LOG 'writing message from block'
  LOG_off()
  len = writing {
    using_each_crlf_line {
      begin
        block.call(WriteAdapter.new(self.method(:write_message_0)))
      rescue LocalJumpError
        # allow `break' from writer block
      end
    }
  }
  LOG_on()
  LOG "wrote #{len} bytes"
  len
end