Discards the bytes between the 0th index and {@code readerIndex}.
It moves the bytes between {@code readerIndex} and {@code writerIndex}
to the 0th index, and sets {@code readerIndex} and {@code writerIndex}
to {@code 0} and {@code oldWriterIndex - oldReaderIndex} respectively.
<p>
Please refer to the class documentation for more detailed explanation.
Discards the bytes between the 0th index and {@code readerIndex}. It moves the bytes between {@code readerIndex} and {@code writerIndex} to the 0th index, and sets {@code readerIndex} and {@code writerIndex} to {@code 0} and {@code oldWriterIndex - oldReaderIndex} respectively. <p> Please refer to the class documentation for more detailed explanation.