presto-rcfile/src/main/java/io/prestosql/rcfile/binary/StringEncoding.java/StringEncoding/encodeValueInto
class StringEncoding:    @Override
    public void encodeValueInto(Block block, int position, SliceOutput output)
    {
        Slice slice = type.getSlice(block, position);
        // Note strings nested in complex structures do no use the empty string marker
        writeVInt(output, slice.length());
        output.writeBytes(slice);
    }