![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 {
  private long callStartNanos;

  font-size: 25px;
  line-height: 40px;
  padding: 3px 10px;
  display: inline-block;
  border-radius: 6px;
  color: #f0f0f0;
  margin: 5px 0;
  width: auto;
}

.logo {
  text-align: center;
  margin-top: 150px;

  value: String,
) = apply {
  headersCheckName(name)
  headersCheckValue(value, name)
  removeAll(name)
  commonAddLenient(name, value)
}

/** Equivalent to `build().get(name)`, but potentially faster. */
internal fun Headers.Builder.commonGet(name: String): String? {
  for (i in namesAndValues.size - 2 downTo 0 step 2) {
    if (name.equals(namesAndValues[i], ignoreCase = true)) {
      return namesAndValues[i + 1]

URLs that share the same address may also share the same underlying TCP socket connection. Sharing a connection has substantial performance benefits: lower latency, higher throughput (due to [TCP slow start](https://www.igvita.com/2011/10/20/faster-web-vs-tcp-slow-start/)) and conserved battery. OkHttp uses a [ConnectionPool](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-connection-pool/) that automatically reuses HTTP/1.x connections and multiplexes HTTP/2 connections.

 [conscrypt]: https://github.com/google/conscrypt/
 [get_example]: https://raw.github.com/square/okhttp/master/samples/guide/src/main/java/okhttp3/guide/GetExample.java
 [kotlin]: https://kotlinlang.org/
 [okhttp3_pro]: https://raw.githubusercontent.com/square/okhttp/master/okhttp/src/main/resources/META-INF/proguard/okhttp3.pro
 [okhttp_312x]: https://github.com/square/okhttp/tree/okhttp_3.12.x

If you're in a tricky situation and prepared to deal with the consequences, rewriting response headers is a powerful way to work around problems. For example, you can fix a server's misconfigured `Cache-Control` response header to enable better response caching:

```java
/** Dangerous interceptor that rewrites the server's cache-control header. */
private static final Interceptor REWRITE_CACHE_CONTROL_INTERCEPTOR = new Interceptor() {

    }
  }

  public static void main(String[] args) throws IOException {
    GetExample example = new GetExample();
    String response = example.run("https://raw.github.com/square/okhttp/master/README.md");
    System.out.println(response);
  }

  AnnotationTarget.FIELD,
  AnnotationTarget.LOCAL_VARIABLE,
  AnnotationTarget.VALUE_PARAMETER,
  AnnotationTarget.CONSTRUCTOR,
  AnnotationTarget.FUNCTION,
  AnnotationTarget.PROPERTY_GETTER,
  AnnotationTarget.PROPERTY_SETTER,
  AnnotationTarget.TYPEALIAS,
)
@RequiresOptIn(level = RequiresOptIn.Level.ERROR)

    return parentFile.isDescendentOf(directory)
  }

  /**
   * See FinalizationTester for discussion on how to best trigger GC in tests.
   * https://android.googlesource.com/platform/libcore/+/master/support/src/test/java/libcore/
   * java/lang/ref/FinalizationTester.java
   */
  @Throws(Exception::class)
  @JvmStatic
  fun awaitGarbageCollection() {
    Runtime.getRuntime().gc()
    Thread.sleep(100)

<a name="http2_naughty"></a>
#### ² HTTP/2 Cipher Suite Denylist

Cipher suites that are [discouraged for use][http2_denylist] with HTTP/2. OkHttp includes them because better suites are not commonly available. For example, none of the better cipher suites listed above shipped with Android 4.4 or Java 7.

[OkHttp30]: https://square.github.io/okhttp/changelog_3x/#version-300