code: func (t *Transport) PeerAddr(id uint64) (string, error) {
  	t.mu.Lock()
  	defer t.mu.Unlock()
  	p, ok := t.peers[id]
  	if !ok {
  		return "", ErrIsNotFound
  	}
  	return p.address(), nil
  }
docs: // PeerAddr returns address of peer with id.