code: func (c *Cluster) GetRegionByID(regionID uint64) (*metapb.Region, *metapb.Peer) {
  	c.RLock()
  	defer c.RUnlock()
  
  	for _, r := range c.regions {
  		if r.Meta.GetId() == regionID {
  			return proto.Clone(r.Meta).(*metapb.Region), proto.Clone(r.leaderPeer()).(*metapb.Peer)
  		}
  	}
  	return nil, nil
  }
docs: // GetRegionByID returns the Region and its leader whose ID is regionID.