code: func (d *Dialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
  	conn, err := d.dial(ctx, network, address)
  	if err != nil {
  		return nil, err
  	}
  
  	closable := &closableConn{Conn: conn}
  
  	// Start tracking the connection
  	d.mu.Lock()
  	d.conns[closable] = struct{}{}
  	d.mu.Unlock()
  
  	// When the connection is closed, remove it from the map. This will
  	// be no-op if the connection isn't in the map, e.g. if CloseAll()
  	// is called.
  	closable.onClose = func() {
  		d.mu.Lock()
  		delete(d.conns, closable)
  		d.mu.Unlock()
  	}
  
  	return closable, nil
  }
docs: // DialContext creates a new tracked connection.