code: func (t *Transport) PeerConn(id uint64) (*grpc.ClientConn, error) {
  	t.mu.Lock()
  	defer t.mu.Unlock()
  	p, ok := t.peers[id]
  	if !ok {
  		return nil, ErrIsNotFound
  	}
  	p.mu.Lock()
  	active := p.active
  	p.mu.Unlock()
  	if !active {
  		return nil, errors.New("peer is inactive")
  	}
  	return p.conn(), nil
  }
docs: // PeerConn returns raw grpc connection to peer.