code: func (nc *Conn) Buffered() (int, error) {
  	nc.mu.RLock()
  	defer nc.mu.RUnlock()
  	if nc.isClosed() || nc.bw == nil {
  		return -1, ErrConnectionClosed
  	}
  	return nc.bw.Buffered(), nil
  }
docs: // Buffered will return the number of bytes buffered to be sent to the server.
  // FIXME(dlc) take into account disconnected state.