code: func (c *Cluster) GetAndCheckStoreByAddr(addr string) (*metapb.Store, error) {
  	c.RLock()
  	defer c.RUnlock()
  
  	for _, s := range c.stores {
  		if s.cancel {
  			return nil, context.Canceled
  		}
  		if s.meta.GetAddress() == addr {
  			return proto.Clone(s.meta).(*metapb.Store), nil
  		}
  	}
  	return nil, nil
  }
docs: // GetAndCheckStoreByAddr checks and returns a Store's meta by an addr