Events
======

Events allow you to capture metrics on your application’s HTTP calls. Use events to monitor:

 * The size and frequency of the HTTP calls your application makes. If you’re making too many calls, or your calls are too large, you should know about it!
 * The performance of these calls on the underlying network. If the network’s performance isn’t sufficient, you need to either improve the network or use less of it.

### EventListener

### Threads

#### Application's calling thread

The application-layer must block on writing I/O. We can't return from a write until we've pushed its bytes onto the socket. Otherwise, if the write fails we are unable to deliver its IOException to the application. We would have told the application layer that the write succeeded, but it didn't!

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package okhttp3

import okio.IOException

/**
 * Listener for connection events. Extend this class to monitor the new connections and closes.
 *
 * All event methods must execute fast, without external locking, cannot throw exceptions,
 * attempt to mutate the event parameters, or be reentrant back into the client.

Interceptors
============

Interceptors are a powerful mechanism that can monitor, rewrite, and retry calls. Here's a simple interceptor that logs the outgoing request and the incoming response.

```java
class LoggingInterceptor implements Interceptor {
  @Override public Response intercept(Interceptor.Chain chain) throws IOException {
    Request request = chain.request();

    long t1 = System.nanoTime();

 *
 * Typically instances of this class are created, connected and exercised automatically by the HTTP
 * client. Applications may use this class to monitor HTTP connections as members of a
 * [connection pool][ConnectionPool].
 *
 * Do not confuse this class with the misnamed `HttpURLConnection`, which isn't so much a connection
 * as a single request/response exchange.
 *