}

    @Test
    void testAddIPAddresses() throws Exception {
        InetAddress ipv4 = InetAddress.getByName("192.168.1.100");
        InetAddress ipv6 = InetAddress.getByName("2001:db8::1");

        notification.addNewIPAddress(ipv4);
        notification.addNewIPAddress(ipv6);
        notification.addOldIPAddress(ipv4);

        List<WitnessNotification.WitnessIPAddress> newAddresses = notification.getNewIPAddresses();

        assertEquals("http://127.0.0.1:8080", IpAddressUtil.buildUrl("http", ipv4, 8080, null));

        // IPv4 without port
        assertEquals("http://127.0.0.1", IpAddressUtil.buildUrl("http", ipv4, 0, ""));
        assertEquals("http://127.0.0.1", IpAddressUtil.buildUrl("http", ipv4, -1, ""));

        // IPv6 with port and path
        InetAddress ipv6 = InetAddress.getByName("::1");

internal fun reorderForHappyEyeballs(addresses: List<InetAddress>): List<InetAddress> {
  if (addresses.size < 2) {
    return addresses
  }

  val (ipv6, ipv4) = addresses.partition { it is Inet6Address }

  return if (ipv6.isEmpty() || ipv4.isEmpty()) {
    addresses
  } else {
    interleave(ipv6, ipv4)
  }

        }

        /**
         * Checks if this is an IPv4 address.
         *
         * @return true if IPv4
         */
        public boolean isIPv4() {
            return (flags & IPV4) != 0;
        }

        /**
         * Checks if this is an IPv6 address.
         *
         * @return true if IPv6
         */
        public boolean isIPv6() {

    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
  }

import java.net.InetAddress;
import java.text.ParseException;
import org.jspecify.annotations.Nullable;

/**
 * A syntactically valid host specifier, suitable for use in a URI. This may be either a numeric IP
 * address in IPv4 or IPv6 notation, or a domain name.
 *
 * <p>Because this class is intended to represent host specifiers which can reasonably be used in a

            return false;
        }
    }

    /**
     * Formats an IP address string for use in a URL.
     * IPv6 addresses are wrapped in brackets, IPv4 addresses are returned as-is.
     *
     * @param address the IP address string to format
     * @return the formatted address (IPv6 with brackets, IPv4 unchanged)
     */
    public static String formatForUrl(final String address) {
        if (address == null) {

				// Number of probes.
				// ~ cat /proc/sys/net/ipv4/tcp_keepalive_probes (defaults to 9, we reduce it to 5)
				_ = syscall.SetsockoptInt(fd, syscall.IPPROTO_TCP, syscall.TCP_KEEPCNT, 5)

				// Wait time after successful probe in seconds.
				// ~ cat /proc/sys/net/ipv4/tcp_keepalive_intvl (defaults to 75 secs, we reduce it to 15 secs)

    }
  }

  /** No SNI for literal IPv6 addresses. */
  @Test
  fun ipv6() {
    val recordedRequest = requestToHostnameViaProxy("2607:f8b0:400b:804::200e")
    assertThat(recordedRequest.url.host).isEqualTo("2607:f8b0:400b:804::200e")
    assertThat(recordedRequest.handshakeServerNames).isEmpty()
  }

  /** No SNI for literal IPv4 addresses. */
  @Test
  fun ipv4() {

  private fun decodeIpv6(input: String): ByteArray? = decodeIpv6(input, 0, input.length)

  @Test
  fun testToCanonicalHost() {
    // IPv4
    assertThat("127.0.0.1".toCanonicalHost()).isEqualTo("127.0.0.1")
    assertThat("1.2.3.4".toCanonicalHost()).isEqualTo("1.2.3.4")

    // IPv6
    assertThat("::1".toCanonicalHost()).isEqualTo("::1")
    assertThat("2001:db8::1".toCanonicalHost()).isEqualTo("2001:db8::1")