code: func RandomBuf(size int) []byte {
  	buf := make([]byte, size)
  	for i := 0; i < size; i++ {
  		buf[i] = byte(rand.Intn(127))
  		if buf[i] == 0 || buf[i] == byte('$') {
  			buf[i]++
  		}
  	}
  	return buf
  }
docs: // RandomBuf generates a random string using ASCII characters but avoid separator character.
  // See https://github.com/mysql/mysql-server/blob/5.7/mysys_ssl/crypt_genhash_impl.cc#L435