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

/** Reuse a connection from the pool. */
internal class ReusePlan(
  val connection: RealConnection,
) : RoutePlanner.Plan {
  override val isReady = true

  override fun connectTcp() = error("already connected")

  override fun connectTlsEtc() = error("already connected")

  override fun handleSuccess() = connection

  override fun cancel() = error("unexpected cancel")

   * be transmitted before the close message is sent but subsequent calls to [send] will return
   * false and their messages will not be enqueued.
   *
   * This returns true if a graceful shutdown was initiated by this call. It returns false if
   * a graceful shutdown was already underway or if the web socket is already closed or canceled.
   *

        return map.containsKey(o);
    }

    /**
     * Adds the specified element to this set if it is not already present.
     *
     * @param o
     *            element to be added to this set.
     * @return true if the set did not already contain the specified
     *         element.
     */
    @Override
    public boolean add(final E o) {

  /**
   * Adds {@code node} if it is not already present.
   *
   * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
   *
   * @return {@code true} if the graph was modified as a result of this call
   */
  @CanIgnoreReturnValue
  boolean addNode(N node);

  /**
   * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present, and sets

  /**
   * Adds {@code node} if it is not already present.
   *
   * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
   *
   * @return {@code true} if the graph was modified as a result of this call
   */
  @CanIgnoreReturnValue
  boolean addNode(N node);

  /**
   * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present.
   *

      "Cannot call source()/target() on a EndpointPair from an undirected graph. Consider calling "
          + "adjacentNode(node) if you already have a node, or nodeU()/nodeV() if you don't.";
  static final String EDGE_ALREADY_EXISTS = "Edge %s already exists in the graph.";
  static final String ENDPOINTS_MISMATCH =
      "Mismatch: endpoints' ordering is not compatible with directionality of the graph";

    // 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!
    }

  - Fixing or improving documentation.
  - Improvements to Maven configuration.

Guidelines for any code contributions:

  1. Any significant changes should be accompanied by tests. The project already
     has good test coverage, so look at some existing tests if you're unsure
     how to go about it.
  2. All contributions must be licensed Apache 2.0 and all files must have a