* on the same [call] to process the next event.
 *
 * By forcing the list of listeners to change after every event, we can detect if buggy code caches
 * a stale [EventListener] in a field or local variable.
 */
class EventListenerRelay(
  val call: Call,
  val eventRecorder: EventRecorder,
) {
  private val eventListenerAdapter =
    EventListenerAdapter()
      .apply {

                final long numOfDeleted = searchEngineClient.deleteByQuery(index, queryBuilder);
                logger.info("[{}] Deleted {} stale documents.", dataConfig.getName(), numOfDeleted);
            } catch (final Exception e) {
                logger.error("[{}] Failed to delete stale documents.", dataConfig.getName(), e);
            }
        }

        /**
         * Checks if the crawling thread has finished execution.

 *   // The resource was cached! Show it.
 * } else {
 *   // The resource was not cached.
 * }
 * ```
 *
 * This technique works even better in situations where a stale response is better than no response.
 * To permit stale cached responses, use the `max-stale` directive with the maximum staleness in
 * seconds:
 *
 * ```java
 * Request request = new Request.Builder()
 *     .cacheControl(new CacheControl.Builder()

 * [okhttp-spring-boot](https://github.com/freefair/okhttp-spring-boot): Spring Boot starters for OkHttp
 * [okhttp-staleiferror-interceptor](https://github.com/PeelTechnologies/okhttp-staleiferror-interceptor/): serve stale responses when the server isn’t reachable.
 * [okhttp-stats](https://github.com/flipkart-incubator/okhttp-stats): Get stats like average network speed.

   *
   * This method returns false unless it is overridden by a subclass.
   *
   * By default OkHttp will attempt to retransmit request bodies when the original request fails
   * due to any of:
   *
   *  * A stale connection. The request was made on a reused connection and that reused connection
   *    has since been closed by the server.
   *  * A client timeout (HTTP 408).

   * implementation; otherwise refreshes will be performed during unrelated cache read and write
   * operations.
   *
   * <p>Currently automatic refreshes are performed when the first stale request for an entry
   * occurs. The request triggering refresh will make a synchronous call to {@link
   * CacheLoader#reload}
   * to obtain a future of the new value. If the returned future is already complete, it is returned

  // TODO GET preferred order - with tests to confirm this
  // 1. successful fresh cached GET response
  // 2. unsuccessful (404, 500) fresh cached GET response
  // 3. successful network response
  // 4. successful stale cached GET response
  // 5. unsuccessful response
  @Test
  fun usesCache() {
    val cache = Cache(cacheFs, "cache".toPath(), (100 * 1024).toLong())

                final long deletedDocCount = deleteOldDocuments(searchEngineClient, docList);
                if (logger.isDebugEnabled()) {
                    logger.debug("Deleted {} stale documents", deletedDocCount);
                }
                final BulkResponse response =
                        searchEngineClient.addAll(fessConfig.getIndexDocumentUpdateIndex(), docList, (doc, builder) -> {

        .header("Cache-Control", "max-stale=180")
        .build()
    val response = client.newCall(request).execute()
    assertThat(response.body.string()).isEqualTo("A")
    assertThat(response.header("Warning")).isEqualTo(
      "110 HttpURLConnection \"Response is stale\"",
    )
  }

  @Test
  fun requestMaxStaleDirectiveWithNoValue() {
    // Add a stale response to the cache.
    server.enqueue(

   * implementation; otherwise refreshes will be performed during unrelated cache read and write
   * operations.
   *
   * <p>Currently automatic refreshes are performed when the first stale request for an entry
   * occurs. The request triggering refresh will make a synchronous call to {@link
   * CacheLoader#reload}
   * to obtain a future of the new value. If the returned future is already complete, it is returned