code: func (h *HandshakeLayer) sendAlert(err Alert) error {
  	tmp := make([]byte, 2)
  	tmp[0] = AlertLevelError
  	tmp[1] = byte(err)
  	h.conn.WriteRecord(&TLSPlaintext{
  		contentType: RecordTypeAlert,
  		fragment:    tmp},
  	)
  
  	// closeNotify is a special case in that it isn't an error:
  	if err != AlertCloseNotify {
  		return &net.OpError{Op: "local error", Err: err}
  	}
  	return nil
  }
docs: // sendAlert sends a TLS alert message.