.build()
    ```

 *  New: Add `cacheHit`, `cacheMiss`, and `cacheConditionalHit()` events to `EventListener`. Use
    these in logs, metrics, and even test cases to confirm your cache headers are configured as
    expected.

 *  New: Constant string `okhttp3.VERSION`. This is a string like "4.5.0-RC1", "4.5.0", or

 * limitations under the License.
 */
package okhttp3

import java.io.IOException
import java.net.InetAddress
import java.net.InetSocketAddress
import java.net.Proxy

/**
 * Listener for metrics events. Extend this class to monitor the quantity, size, and duration of
 * your application's HTTP calls.
 *
 * All start/connect/acquire events will eventually receive a matching end/release event, either