/**
     * 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
   * as attempting IPv6 first, can make such decisions.
   */
  @ExperimentalOkHttpApi
  enum class DnsClass(val type: Int) {
    IPV4(TYPE_A),
    IPV6(TYPE_AAAA),
  }