* Test to confirm that events are reported at the time they occur and no earlier and no later.
   * This inserts a bunch of synthetic 250 ms delays into both client and server and confirms that
   * the same delays make it back into the events.
   *
   * We've had bugs where we report an event when we request data rather than when the data actually
   * arrives. https://github.com/square/okhttp/issues/5578
   */

These loosely follow the model set in [Google Cloud Policies](https://cloud.google.com/load-balancing/docs/ssl-policies-concepts). We [track changes](../security/tls_configuration_history.md) to this policy.

By default, OkHttp will attempt a `MODERN_TLS` connection.  However by configuring the client connectionSpecs you can allow a fall back to `COMPATIBLE_TLS` connection if the modern configuration fails.

```java
OkHttpClient client = new OkHttpClient.Builder()

      var low = 0
      var high = size
      var match: String? = null
      while (low < high) {
        var mid = (low + high) / 2
        // Search for a '\n' that marks the start of a value. Don't go back past the start of the
        // array.
        while (mid > -1 && this[mid] != '\n'.code.toByte()) {
          mid--
        }
        mid++

        // Now look for the ending '\n'.
        var end = 1

 * Events and sequences of events may be repeated for retries and follow-ups.
 *
 * All event methods must execute fast, without external locking, cannot throw exceptions, attempt
 * to mutate the event parameters, or be re-entrant back into the client. Any IO - writing to files
 * or network should be done asynchronously.
 */
abstract class EventListener {
  /**
   * Invoked as soon as a call is enqueued or executed by a client. In case of thread or stream

          source.skip(remainingByteCount)
          closeLater(ErrorCode.FLOW_CONTROL_ERROR)
          return
        }

        // Discard data received after the stream is finished. It's probably a benign race.
        if (finished) {
          source.skip(remainingByteCount)
          return
        }

        // Fill the receive buffer without holding any locks.

    assertThat(response.body.string()).isEqualTo("")
    server.takeRequest() // seed
    return server.takeRequest()
  }

  /**
   * For Last-Modified and Date headers, we should echo the date back in the exact format we were
   * served.
   */
  @Test
  fun retainServedDateFormat() {
    // Serve a response with a non-standard date format that OkHttp supports.

    assertThat(ping.payload2).isEqualTo(0)
    assertThat(ping.ack).isTrue()
  }

  @Test fun clientPingsServer() {
    // Write the mocking script.
    peer.sendFrame().settings(Settings())
    peer.acceptFrame() // ACK
    peer.acceptFrame() // PING
    peer.sendFrame().ping(true, Http2Connection.AWAIT_PING, 5)
    peer.play()

    // Play it back.
    val connection = connect(peer)

      }
  },
  "customizations": {
      "vscode": {
          "settings": {
              "java.server.launchMode": "Standard"
          },
          "extensions": [
              "vscjava.vscode-java-pack",
              "vscjava.vscode-gradle"
          ]
      }
  }

      "plan 1 TLS connected",
    )

    taskFaker.assertNoMoreTasks()
  }

  /**
   * This test performs two races:
   *
   *  * The first race is between plan0 and plan1, with a 250 ms head start for plan0.
   *  * The second race is between plan2 and plan3, with a 250 ms head start for plan2.
   *
   * We get plan0 and plan1 from the route planner.

   * - Both request discover no existing connection. They both make a connection.
   * - The first request "wins the race".
   * - The second request discovers it "lost the race" and closes the connection it just opened.
   * - The second request uses the coalesced connection from request1.
   * - The coalesced connection is violently closed after servicing the first request.