code: func (idx *CfIndex) FiltersByBlockHashes(blockHashes []*chainhash.Hash,
  	filterType wire.FilterType) ([][]byte, error) {
  	return idx.entriesByBlockHashes(cfIndexKeys, filterType, blockHashes)
  }
docs: // FiltersByBlockHashes returns the serialized contents of a block's basic or
  // committed filter for a set of blocks by hash.