presto-orc/src/main/java/io/prestosql/orc/metadata/OrcMetadataWriter.java/OrcMetadataWriter/toUserMetadata
class OrcMetadataWriter:    private static UserMetadataItem toUserMetadata(Entry<String, Slice> entry)
    {
        return OrcProto.UserMetadataItem.newBuilder()
                .setName(entry.getKey())
                .setValue(ByteString.copyFrom(entry.getValue().getBytes()))
                .build();
    }