return EventSource.Factory { request, listener ->
      val actualRequest =
        if (request.header("Accept") == null) {
          request.newBuilder().addHeader("Accept", "text/event-stream").build()
        } else {
          request
        }

      RealEventSource(actualRequest, listener).apply {
        connect(callFactory)
      }
    }
  }

  @JvmStatic

     * 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();
    }

    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
  }

    val request =
      Request.Builder()
        .url(server.url("/"))
        .build()
    val response = client.newCall(request).execute()
    processResponse(response, listener)
    listener.assertOpen()
    listener.assertEvent(null, null, "hey")
    listener.assertClose()
  }

  @Test
  fun cancelShortCircuits() {
    server.enqueue(
      MockResponse.Builder()
        .body(
          """
          |data: hey

  private val name: String,
) : WebSocketListener() {
  private val events = LinkedBlockingQueue<Any>()
  private var delegate: WebSocketListener? = null

  /** Sets a delegate for handling the next callback to this listener. Cleared after invoked.  */
  fun setNextEventDelegate(delegate: WebSocketListener?) {
    this.delegate = delegate
  }

  override fun onOpen(
    webSocket: WebSocket,
    response: Response,
  ) {