code: func (o *ioOutput) Flush() error {
  	if w, ok := o.writer.(flushWriter); ok {
  		return w.Flush()
  	}
  	if w, ok := o.writer.(syncWriter); ok {
  		return w.Sync()
  	}
  	return nil
  }
docs: // Flushes all logs that have been buffered for writing to this output.