* May be an empty list indicating that the host is unreachable.
     */
    fun onResponse(
      hostname: String,
      addresses: List<InetAddress>,
    )

    /**
     * Returns an error for the DNS query.
     */
    fun onFailure(
      hostname: String,
      e: IOException,
    )
  }

  /**
   * Class of DNS addresses, such that clients that treat these differently, such