return headersQueue.removeFirst()
      }
      throw errorException ?: StreamResetException(errorCode!!)
    }
  }

  /**
   * Returns the trailers if they're immediately available.
   */
  @Throws(IOException::class)
  fun peekTrailers(): Headers? {
    withLock {
      if (source.finished && source.receiveBuffer.exhausted() && source.readBuffer.exhausted()) {

  /**
   * Add a shutdown hook to wait for thread completion in the given {@link ExecutorService service}.
   * This is useful if the given service uses daemon threads, and we want to keep the JVM from
   * exiting immediately on shutdown, instead giving these daemon threads a chance to terminate
   * normally.
   *
   * @param service ExecutorService which uses daemon threads

 *
 * @author Isaac Shum
 * @since 1.0
 */
@GwtCompatible
public final class Callables {
  private Callables() {}

  /** Creates a {@code Callable} which immediately returns a preset value each time it is called. */
  public static <T extends @Nullable Object> Callable<T> returning(@ParametricNullness T value) {
    return () -> value;
  }

  /**

  private val random: Random,
  private val pingIntervalMillis: Long,
  /**
   * For clients this is initially null, and will be assigned to the agreed-upon extensions. For
   * servers, it should be the agreed-upon extensions immediately.
   */
  private var extensions: WebSocketExtensions?,
  /** If compression is negotiated, outbound messages of this size and larger will be compressed. */
  private var minimumDeflateSize: Long,

                        "cannot immediately follow // TESTSETUP: $test")
                }
                if (previousTest != null && previousTest.testTearDown) {
                    throw new InvalidUserDataException("// TEST[continued] " +
                        "cannot immediately follow // TEARDOWN: $test")
                }
            } else {

   *
   * @param eventClass a class to assert that the returned event is an instance of, or null to
   *     take any event class.
   * @param elapsedMs the time in milliseconds elapsed since the immediately-preceding event, or
   *     -1L to take any duration.
   */
  fun takeEvent(
    eventClass: Class<out ConnectionEvent>? = null,
    elapsedMs: Long = -1L,
  ): ConnectionEvent {

   * detect if followups need to do a full connection-finding process including DNS resolution, and
   * certificate pin checks.
   */
  fun sameHostAndPort(url: HttpUrl): Boolean

  /**
   * A plan holds either an immediately-usable connection, or one that must be connected first.
   * These steps are split so callers can call [connectTcp] on a background thread if attempting
   * multiple plans concurrently.
   */
  interface Plan {

    this.maxSize = maxSize;
  }

  /**
   * Creates and returns a new evicting queue that will hold up to {@code maxSize} elements.
   *
   * <p>When {@code maxSize} is zero, elements will be evicted immediately after being added to the
   * queue.
   */
  public static <E> EvictingQueue<E> create(int maxSize) {
    return new EvictingQueue<>(maxSize);
  }

  /**

   *
   * @param eventClass a class to assert that the returned event is an instance of, or null to
   *     take any event class.
   * @param elapsedMs the time in milliseconds elapsed since the immediately-preceding event, or
   *     -1L to take any duration.
   */
  fun takeEvent(
    eventClass: Class<out CallEvent>? = null,
    elapsedMs: Long = -1L,
  ): CallEvent {
    val result = eventSequence.remove()

        assertTrue(errorHandler.shouldFallbackToTcp(hardwareError), "Hardware errors should suggest TCP fallback");
        assertFalse(errorHandler.shouldFallbackToTcp(timeoutError), "Timeout errors should not immediately suggest TCP fallback");

        // Test error classification using public API
        assertNotNull(errorHandler, "Error handler should handle network errors");

        // Test fallback logic which is public