code: public int read(byte []buffer, int offset, int length)
      throws IOException
    {
      int len = _next.read(buffer, offset, length);
  
      _crc = Crc64.generate(_crc, buffer, offset, len);
  
      return len;
    }
docs: Reads a buffer from the underlying stream.
  
  @param buffer the byte array to read.
  @param offset the offset into the byte array.
  @param length the number of bytes to read.