code: func (lc *LightChain) GetHeaderByNumberOdr(ctx context.Context, number uint64) (*types.Header, error) {
  	if header := lc.hc.GetHeaderByNumber(number); header != nil {
  		return header, nil
  	}
  	return GetHeaderByNumber(ctx, lc.odr, number)
  }
docs: // GetHeaderByNumberOdr retrieves a block header from the database or network
  // by number, caching it (associated with its hash) if found.