code: protected final void initSrcBuffer(int sizeBytes) {
          ChannelOptions config = channel.options();
          src = (S) newByteBuffer(sizeBytes, config.getOption(DIRECT_BUF));
      }
docs: Initializes the src buffer. Should only be called by InboundHandler
  implementations that have a ByteBuffer as source.
  
  @param sizeBytes the size of the srcBuffer in bytes.