* header, or they may decline the challenge by returning null. In this case the unauthenticated
 * response will be returned to the caller that triggered it.
 *
 * Implementations should check if the initial request already included an attempt to
 * authenticate. If so it is likely that further attempts will not be useful and the authenticator
 * should give up.
 *

     * ## The buffer
     *
     * In this case the bytes are immediately copied into [sink] and the number of bytes copied is
     * returned.
     *
     * If upstream would be selected but another thread is already reading upstream this will
     * block until that read completes. It is possible to time out while waiting for that.
     */
    @Throws(IOException::class)
    override fun read(
      sink: Buffer,

  fun request(): Request

  /**
   * Immediately and violently release resources held by this event source. This does nothing if
   * the event source has already been closed or canceled.
   */
  fun cancel()

  fun interface Factory {
    /**
     * Creates a new event source and immediately returns it. Creating an event source initiates an

  override fun cancel() {
    if (canceled) return // Already canceled.

    canceled = true
    exchange?.cancel()
    for (plan in plansToCancel) {
      plan.cancel()
    }

    eventListener.canceled(this)
  }

  override fun isCanceled(): Boolean = canceled

  override fun execute(): Response {
    check(executed.compareAndSet(false, true)) { "Already Executed" }

    timeout.enter()

            route: Route?,
            response: Response,
          ): Request? {
            if (response.request.header("Authorization") != null) {
              return null // Give up, we've already attempted to authenticate.
            }

            println("Authenticating for response: $response")
            println("Challenges: ${response.challenges()}")

      if (logHeaders) {
        val headers = request.headers

        if (requestBody != null) {
          // Request body headers are only present when installed as a network interceptor. When not
          // already present, force them to be included (if available) so their values are known.
          requestBody.contentType()?.let {
            if (headers["Content-Type"] == null) {
              logger.log("Content-Type: $it")

            FailedPlan(e)
          }
        }
        else -> return null // Nothing further to try.
      }

    // Already connected. Return it immediately.
    if (plan.isReady) return ConnectResult(plan)

    // Already failed? Return it immediately.
    if (plan is FailedPlan) return plan.result

    // Connect TCP asynchronously.
    tcpConnectsInFlight += plan

   * exception.
   *
   * @throws IllegalStateException when the call has already been executed.
   */
  fun enqueue(responseCallback: Callback)

  /** Cancels the request, if possible. Requests that are already complete cannot be canceled. */
  fun cancel()

  /**
   * Returns true if this call has been either [executed][execute] or [enqueued][enqueue]. It is an

    // If the task is already scheduled, take the earlier of the two times.
    val existingIndex = futureTasks.indexOf(task)
    if (existingIndex != -1) {
      if (task.nextExecuteNanoTime <= executeNanoTime) {
        taskRunner.logger.taskLog(task, this) { "already scheduled" }
        return false
      }
      futureTasks.removeAt(existingIndex) // Already scheduled later: reschedule below!
    }

    }
  }

  /**
   * Returns an immediately-executable task for the calling thread to execute, sleeping as necessary
   * until one is ready. If there are no ready queues, or if other threads have everything under
   * control this will return null. If there is more than a single task ready to execute immediately
   * this will start another thread to handle that work.
   */
  fun awaitTaskToRun(): Task? {
    lock.assertHeld()