* proxy server can issue an auth challenge and then close the connection.
   *
   * @return the next plan to attempt, or null if no further attempt should be made either because
   *     we've successfully connected or because no further attempts should be made.
   */
  @Throws(IOException::class)
  internal fun connectTunnel(): ConnectResult {
    val nextTunnelRequest =
      createTunnel()

    fun immutable() = commonImmutable()

    /**
     * Sets the maximum age of a cached response. If the cache response's age exceeds [maxAge], it
     * will not be used and a network request will be made.
     *
     * @param maxAge a non-negative duration. This is stored and transmitted with [TimeUnit.SECONDS]
     *     precision; finer precision will be lost.
     */
    fun maxAge(maxAge: Duration) =

     * Multiple calls to this method may be made concurrently.
     */
    @Throws(IOException::class)
    abstract fun onStream(stream: Http2Stream)

    /**
     * Notification that the connection's peer's settings may have changed to [settings].
     * Implementations should take appropriate action to handle the updated settings.
     *

    backwards-incompatible changes in forthcoming releases.
 *  Fix: Don't crash loading the public suffix database resource in obfuscated builds.
 *  Fix: Don't silently ignore calls to `EventSource.cancel()` made from
    `EventSourceListener.onOpen()`.
 *  Fix: Enforce the max intermediates constraint when using pinned certificates with Conscrypt.

  @Throws(InterruptedException::class)
  fun takeRequest(
    timeout: Long,
    unit: TimeUnit,
  ): RecordedRequest? = requestQueue.poll(timeout, unit)

  /**
   * Scripts [response] to be returned to a request made in sequence. The first request is
   * served by the first enqueued response; the second request by the second enqueued response; and
   * so on.
   *
   * @throws ClassCastException if the default dispatcher has been