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

    client =
      client
        .newBuilder()
        .fastFallback(false)
        .apply {
          retryOnConnectionFailure = false
        }.build()

    executeSynchronously(request)
      .assertFailureMatches("stream was reset: REFUSED_STREAM")

              socketReadTimeoutMillis = socketReadTimeoutMillis,
              pingIntervalMillis = pingIntervalMillis,
              retryOnConnectionFailure = retryOnConnectionFailure,
              fastFallback = fastFallback,
              address = address,
              routeDatabase = routeDatabase,
              connectionUser = user,
            ),
          ),
          taskRunner,
        )
      },
    ),
  )

  private val handshakeCertificates = localhost()

  open val fastFallback: Boolean get() = true

  private var client: OkHttpClient =
    clientTestRule
      .newClientBuilder()
      .connectionPool(ConnectionPool(connectionListener = listener))
      .fastFallback(fastFallback)
      .build()

  @BeforeEach
  fun setUp() {
    platform.assumeNotOpenJSSE()

     * wasted resources.
     *
     * Defaults to enabled, call with [fastFallback] = false to revert to 4.x behaviour.
     *
     * [rfc_6555]: https://datatracker.ietf.org/doc/html/rfc6555
     */
    fun fastFallback(fastFallback: Boolean) =
      apply {
        this.fastFallback = fastFallback
      }

    /**

  private fun newRouteSelector(
    address: Address,
    routeDatabase: RouteDatabase = this.routeDatabase,
    fastFallback: Boolean = false,
    call: RealCall = this.call,
  ): RouteSelector =
    RouteSelector(
      address = address,
      routeDatabase = routeDatabase,
      fastFallback = fastFallback,
      connectionUser = CallConnectionUser(call, ConnectionListener.NONE, newChain(call)),
    )

      socketReadTimeoutMillis = chain.readTimeoutMillis,
      pingIntervalMillis = client.pingIntervalMillis,
      retryOnConnectionFailure = client.retryOnConnectionFailure,
      fastFallback = client.fastFallback,
      address = address,
      routeDatabase = client.routeDatabase,
      connectionUser =
        CallConnectionUser(
          call,
          client.connectionPool.delegate.connectionListener,

          fastFallback = client.fastFallback,
          address = client.address(request.url),
          connectionUser = CallConnectionUser(this, connectionPool.connectionListener, chain),
          routeDatabase = client.routeDatabase,
        )
      this.exchangeFinder =
        when {
          client.fastFallback -> FastFallbackExchangeFinder(routePlanner, client.taskRunner)

      newRouteSelector =
        RouteSelector(
          address = address,
          routeDatabase = routeDatabase,
          connectionUser = connectionUser,
          fastFallback = fastFallback,
        )
      routeSelector = newRouteSelector
    }

    // List available IP addresses for the current proxy. This may block in Dns.lookup().

 */
class RouteSelector(
  private val address: Address,
  private val routeDatabase: RouteDatabase,
  private val connectionUser: ConnectionUser,
  private val fastFallback: Boolean,
) {
  // State for negotiating the next proxy to use.
  private var proxies = emptyList<Proxy>()
  private var nextProxyIndex: Int = 0

  // State for negotiating the next socket address to use.

        .newClientBuilder()
        .eventListenerFactory(clientTestRule.wrap(listener))
        .connectTimeout(60, TimeUnit.SECONDS) // Deliberately exacerbate slow fallbacks.
        .dns { dnsResults }
        .fastFallback(true)
        .build()
    url =
      serverIpv4
        .url("/")
        .newBuilder()
        .host("localhost")
        .build()
  }

  @AfterEach
  internal fun tearDown() {