presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/storage/OrcStorageManager.java/OrcStorageManager/getOrcFileMetadata
class OrcStorageManager:    private static Optional<OrcFileMetadata> getOrcFileMetadata(OrcReader reader)
    {
        return Optional.ofNullable(reader.getFooter().getUserMetadata().get(OrcFileMetadata.KEY))
                .map(slice -> METADATA_CODEC.fromJson(slice.getBytes()));
    }