code: func (b *ByteBuf) ReadUInt64() (uint64, error) {
  	if b.Readable() < 8 {
  		return 0, io.ErrShortBuffer
  	}
  
  	b.readerIndex += 8
  	return Byte2UInt64(b.buf[b.readerIndex-8 : b.readerIndex]), nil
  }
docs: // ReadUInt64 get uint64 value from buf