code: public int read(long pos) {
      if (pos >= size) {
        return -1;
      }
  
      byte[] block = blocks[blockIndex(pos)];
      int off = offsetInBlock(pos);
      return UnsignedBytes.toInt(block[off]);
    }
docs: Reads the byte at position {@code pos} in this file as an unsigned integer in the range 0-255.
  If {@code pos} is greater than or equal to the size of this file, returns -1 instead.