private static void checkBigIntegerConversion(String ip, BigInteger bigIntegerIp) {
    InetAddress address = InetAddresses.forString(ip);
    boolean isIpv6 = address instanceof Inet6Address;
    assertThat(InetAddresses.toBigInteger(address)).isEqualTo(bigIntegerIp);
    assertThat(
            isIpv6
                ? InetAddresses.fromIPv6BigInteger(bigIntegerIp)
                : InetAddresses.fromIPv4BigInteger(bigIntegerIp))

   *     or IPv6 respectively
   */
  private static InetAddress fromBigInteger(BigInteger address, boolean isIpv6) {
    checkArgument(address.signum() >= 0, "BigInteger must be greater than or equal to 0");

    int numBytes = isIpv6 ? 16 : 4;

    byte[] addressBytes = address.toByteArray();
    byte[] targetCopyArray = new byte[numBytes];

    enableProtocol(Protocol.HTTP_2)

    val request = Request(server1.url("/"))

    server1.enqueue(refusedStream)
    server2.enqueue(bodyResponse)

    dns[server1.hostName] = listOf(ipv6, ipv4)
    socketFactory[ipv6] = server1.socketAddress
    socketFactory[ipv4] = server2.socketAddress

    client =
      client
        .newBuilder()
        .fastFallback(false)
        .apply {

   * Generate an error if the host might be a non-bracketed IPv6 literal.
   *
   * <p>URI formatting requires that IPv6 literals be surrounded by brackets, like "[2001:db8::1]".
   * Chain this call after {@link #fromString(String)} to increase the strictness of the parser, and
   * disallow IPv6 literals that don't contain these brackets.
   *
   * <p>Note that this parser identifies IPv6 literals solely based on the presence of a colon. To

    Collections.synchronizedMap(mutableMapOf())
  private val requestedHosts: MutableList<String> = Collections.synchronizedList(mutableListOf())
  private var nextAddress = 0xff000064L // 255.0.0.100 in IPv4; ::ff00:64 in IPv6.

  /** Sets the results for `hostname`.  */
  operator fun set(
    hostname: String,
    addresses: List<InetAddress>,
  ): FakeDns {
    hostAddresses[hostname] = addresses
    return this
  }

        .testEquals();
  }

  public void testRequireBracketsForIPv6() {
    // Bracketed IPv6 works fine.
    assertThat(HostAndPort.fromString("[::1]").requireBracketsForIPv6().getHost()).isEqualTo("::1");
    assertThat(HostAndPort.fromString("[::1]:80").requireBracketsForIPv6().getHost())
        .isEqualTo("::1");
    // Non-bracketed non-IPv6 works fine.

        .testEquals();
  }

  public void testRequireBracketsForIPv6() {
    // Bracketed IPv6 works fine.
    assertThat(HostAndPort.fromString("[::1]").requireBracketsForIPv6().getHost()).isEqualTo("::1");
    assertThat(HostAndPort.fromString("[::1]:80").requireBracketsForIPv6().getHost())
        .isEqualTo("::1");
    // Non-bracketed non-IPv6 works fine.

 * Prefer to alternate IP addresses from different address families, (IPv6 / IPv4), starting with IPv6.
 * Don't start a new attempt until 250 ms after the most recent attempt was started.
 * Keep whichever TCP connection succeeds first and cancel all the others.

_2022-02-01_

**This release introduces fast fallback to better support mixed IPv4+IPv6 networks.** Fast fallback
is what we're calling our implementation of Happy Eyeballs, [RFC 8305][rfc_8305]. With this
feature OkHttp will attempt both IPv6 and IPv4 connections concurrently, keeping whichever connects
first. Fast fallback gives IPv6 connections a 250 ms head start so IPv6 is preferred on networks
where it's available.

 * authentication.
 *
 * ### Host
 *
 * The host identifies the webserver that serves the URL's resource. It is either a hostname like
 * `square.com` or `localhost`, an IPv4 address like `192.168.0.1`, or an IPv6 address like `::1`.
 *
 * Usually a webserver is reachable with multiple identifiers: its IP addresses, registered
 * domain names, and even `localhost` when connecting from the server itself. Each of a web server's