* asynchronous process to connect the socket. Once that succeeds or fails, `listener` will be
     * notified. The caller must cancel the returned event source when it is no longer in use.
     */
    fun newEventSource(
      request: Request,
      listener: EventSourceListener,
    ): EventSource
  }

![Events Diagram](../assets/images/******@****.***)

Here’s a [sample event listener](https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/okhttp3/recipes/PrintEventsNonConcurrent.java) that prints each event with a timestamp.

```java
class PrintingEventListener extends EventListener {

  @RegisterExtension
  @JvmField
  var clientTestRule = OkHttpClientTestRule()

  private val listener = RecordingEventListener()
  private val handshakeCertificates = platform.localhostHandshakeCertificates()

  private var client =
    clientTestRule.newClientBuilder()
      .eventListenerFactory(clientTestRule.wrap(listener))
      .build()

  private lateinit var server: MockWebServer

  @BeforeEach

    }
  }

  /** See https://api.slack.com/rtm. */
  public WebSocket rtm(HttpUrl url, WebSocketListener listener) {
    return httpClient.newWebSocket(new Request.Builder()
        .url(url)
        .build(), listener);
  }

  static final class SlackJsonAdapters {
    @ToJson String urlToJson(HttpUrl httpUrl) {
      return httpUrl.toString();
    }

  private var protocol: Protocol?,
  private var source: BufferedSource?,
  private var sink: BufferedSink?,
  private val pingIntervalMillis: Int,
  internal val connectionListener: ConnectionListener,
) : Http2Connection.Listener(), Connection, ExchangeCodec.Carrier {
  private var http2Connection: Http2Connection? = null

  internal val lock: ReentrantLock = ReentrantLock()

  // These properties are guarded by [lock].

  /**

   * [requestBodyOpen], [responseBodyOpen], and [expectMoreExchanges].
   *
   * This will release the connection if it is still held.
   *
   * It will also notify the listener that the call completed; either successfully or
   * unsuccessfully.
   *
   * If the call was canceled or timed out, this will wrap [e] in an exception that provides that

    }
    responseBody.close()
    assertEquals(if (connectionType == H2) 1 else 0, client.connectionPool.connectionCount())

    cancelLatch.await()

    val events = listener.eventSequence.filter { isConnectionEvent(it) }.map { it.name }
    listener.clearAllEvents()

    assertThat(events).startsWith("CallStart", "ConnectStart", "ConnectEnd", "ConnectionAcquired")
    if (cancelMode == CANCEL) {

    val x = findTests(listOf(testSelector))

    x.find { it is ClassBasedTestDescriptor && it.testClass == SampleTest::class.java }
  }

  @Test
  fun testTreeListener() {
    val listener = treeListener()

    assertNotNull(listener)
  }

import okio.source

/** A basic HTTP/2 server that serves the contents of a local directory.  */
class Http2Server(
  private val baseDirectory: File,
  private val sslSocketFactory: SSLSocketFactory,
) : Http2Connection.Listener() {
  private fun run() {
    val serverSocket = ServerSocket(8888)
    serverSocket.reuseAddress = true
    while (true) {
      var socket: Socket? = null
      try {
        socket = serverSocket.accept()

     * asynchronous process to connect the socket. Once that succeeds or fails, `listener` will be
     * notified. The caller must either close or cancel the returned web socket when it is no longer
     * in use.
     */
    fun newWebSocket(
      request: Request,
      listener: WebSocketListener,
    ): WebSocket
  }