code: func (b *ByteBuf) PeekInt(offset int) (int, error) {
  	if b.Readable() < 4+offset {
  		return 0, io.ErrShortBuffer
  	}
  
  	start := b.readerIndex + offset
  	return Byte2Int(b.buf[start : start+4]), nil
  }
docs: // PeekInt get int value from buf based on currently read index, after read, read index not modifed