code: func (c *codecPDClient) GetRegion(ctx context.Context, key []byte) (*metapb.Region, *metapb.Peer, error) {
  	encodedKey := codec.EncodeBytes([]byte(nil), key)
  	region, peer, err := c.Client.GetRegion(ctx, encodedKey)
  	return processRegionResult(region, peer, err)
  }
docs: // GetRegion encodes the key before send requests to pd-server and decodes the
  // returned StartKey && EndKey from pd-server.