* Don't start a new attempt until 250 ms after the most recent attempt was started.
 * Keep whichever TCP connection succeeds first and cancel all the others.
 * Race TCP only. Only attempt a TLS handshake on the winning TCP connection.

 *
 * All event methods must execute fast, without external locking, cannot throw exceptions,
 * attempt to mutate the event parameters, or be reentrant back into the client.
 * Any IO - writing to files or network should be done asynchronously.
 */
@ExperimentalOkHttpApi
abstract class ConnectionListener {
  /**
   * Invoked as soon as a call causes a connection to be started.

   *
   * The [dispatcher][OkHttpClient.dispatcher] defines when the request will run: usually
   * immediately unless there are several other requests currently being executed.
   *
   * This client will later call back `responseCallback` with either an HTTP response or a failure
   * exception.
   *
   * @throws IllegalStateException when the call has already been executed.
   */
  fun enqueue(responseCallback: Callback)

Calls are executed in one of two ways:

 * **Synchronous:** your thread blocks until the response is readable.
 * **Asynchronous:** you enqueue the request on any thread, and get [called back](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-callback/) on another thread when the response is readable.

our best to right the wrong.

Although this list cannot be exhaustive, we explicitly honor diversity in age, culture, ethnicity,
gender identity or expression, language, national origin, political beliefs, profession, race,
religion, sexual orientation, socioeconomic status, and technical ability. We will not tolerate
discrimination based on any of the protected characteristics above, including participants with
disabilities.

Reporting Issues

 * Fix: Ensure `null` is never returned from a connection's `getHeaderFields()`.
 * Fix: Persist proper `Content-Encoding` header to cache for GZip responses.
 * Fix: Eliminate rare race condition in SPDY streams that would prevent connection reuse.
 * Fix: Change HTTP date formats to UTC to conform to RFC2616 section 3.3.
 * Fix: Support SPDY header blocks with trailing bytes.

    settings1[Settings.MAX_CONCURRENT_STREAMS] = maxConcurrentStreams
    peer.sendFrame().settings(settings1)
    peer.acceptFrame() // ACK
    peer.sendFrame().ping(false, 2, 0)
    peer.acceptFrame() // PING
    peer.play()

    // Play it back.
    val connection =
      Http2Connection.Builder(true, TaskRunner.INSTANCE)
        .socket(peer.openSocket())

    assertThat(TimeUnit.NANOSECONDS.toMillis(elapsedUntilPong3).toDouble())
      .isCloseTo(1500.0, 250.0)

    // The client pinged the server 3 times, and it has ponged back 3 times.
    assertThat(webSocket.sentPingCount()).isEqualTo(3)
    assertThat(server.receivedPingCount()).isEqualTo(3)
    assertThat(webSocket.receivedPongCount()).isEqualTo(3)

  }

  /**
   * Ignored due to incompatibilities between Android and Java on how non-ASCII subject alt names
   * are parsed. Android fails to parse these, which means we fall back to the CN. The RI does parse
   * them, so the CN is unused.
   */
  @Test fun verifyNonAsciiSubjectAlt() {
    // Expecting actual:
    //  ["bar.com", "花子.co.jp"]
    // to contain exactly (and in same order):

    client.processNextFrame()
    taskFaker.runTasks()
    server.webSocket!!.pong("pong 3".encodeUtf8())
    client.processNextFrame()

    // After 500ms the client automatically pings and the server pongs back.
    taskFaker.advanceUntil(ns(500L))
    server.processNextFrame() // Ping.
    client.processNextFrame() // Pong.

    // After 1000ms the client will attempt a ping 2, but we don't process it. That'll cause the