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

![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 {

     * 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
  }

  @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

  // These properties are guarded by this.

  /**

   * [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

    server.processNextFrame()
    client.listener.assertClosing(1000, "Hello!")
    server.listener.assertClosing(1000, "Hi!")
    client.webSocket!!.finishReader()
    server.webSocket!!.finishReader()
    client.listener.assertClosed(1000, "Hello!")
    server.listener.assertClosed(1000, "Hi!")
    taskFaker.runTasks()
    assertThat(client.closed).isTrue()

    // In the process we made one successful connection attempt.
    assertThat(listener.recordedEventTypes().filter { it == "ConnectStart" }).hasSize(2)
    assertThat(listener.recordedEventTypes().filter { it == "ConnectFailed" }).hasSize(1)
    assertThat(listener.recordedEventTypes().filter { it == "ConnectEnd" }).hasSize(1)
  }

  @Test
  fun reachesIpv6WhenIpv4IsDown() {

        .build().also {
          listener.satisfactionFailure(call, it)
        }
    }

    // If we don't need the network, we're done.
    if (networkRequest == null) {
      return cacheResponse!!.newBuilder()
        .cacheResponse(cacheResponse.stripBody())
        .build().also {
          listener.cacheHit(call, it)
        }
    }

    if (cacheResponse != null) {