presto-spi/src/main/java/io/prestosql/spi/block/SingleRowBlockEncoding.java/SingleRowBlockEncoding/writeBlock
class SingleRowBlockEncoding:    @Override
    public void writeBlock(BlockEncodingSerde blockEncodingSerde, SliceOutput sliceOutput, Block block)
    {
        SingleRowBlock singleRowBlock = (SingleRowBlock) block;
        int numFields = singleRowBlock.getNumFields();
        int rowIndex = singleRowBlock.getRowIndex();
        sliceOutput.appendInt(numFields);
        for (int i = 0; i < numFields; i++) {
            blockEncodingSerde.writeBlock(sliceOutput, singleRowBlock.getRawFieldBlock(i).getRegion(rowIndex, 1));
        }
    }