![Events Diagram](../assets/images/events@2x.png)

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

    buffer.writeUtf8CodePoint(0x1a)
    buffer.writeUtf8CodePoint(0x0a)
    server.enqueue(
      MockResponse.Builder()
        .body(buffer)
        .setHeader("Content-Type", "image/png; charset=utf-8")
        .build(),
    )
    val response = client.newCall(request().build()).execute()
    response.body.close()
    applicationLogs
      .assertLogEqual("--> GET $url")

     * 3
     * Content-Type: image/png
     * Content-Length: 100
     * Cache-Control: max-age=600
     * ```
     *
     * A typical HTTPS file looks like this:
     *
     * ```
     * https://google.com/foo
     * GET
     * 2
     * Accept-Language: fr-CA
     * Accept-Charset: UTF-8
     * HTTP/1.1 200 OK
     * 3
     * Content-Type: image/png
     * Content-Length: 100

![Interceptors Diagram](../assets/images/interceptors@2x.png)

### Application Interceptors

Interceptors are registered as either _application_ or _network_ interceptors. We'll use the `LoggingInterceptor` defined above to show the difference.

      MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart("title", "Square Logo")
        .addFormDataPart(
          "image",
          "logo-square.png",
          File("docs/images/logo-square.png").asRequestBody(MEDIA_TYPE_PNG),
        )
        .build()

    val request =
      Request.Builder()
        .header("Authorization", "Client-ID $IMGUR_CLIENT_ID")

            .setType(MultipartBody.FORM)
            .addFormDataPart("title", "Square Logo")
            .addFormDataPart("image", "logo-square.png",
                File("docs/images/logo-square.png").asRequestBody(MEDIA_TYPE_PNG))
            .build()

        val request = Request.Builder()
            .header("Authorization", "Client-ID $IMGUR_CLIENT_ID")

      file.name.endsWith(".jpeg") -> "image/jpeg"
      file.name.endsWith(".jpg") -> "image/jpeg"
      file.name.endsWith(".js") -> "application/javascript"
      file.name.endsWith(".png") -> "image/png"
      else -> "text/plain"
    }
  }

  companion object {
    val logger: Logger = Logger.getLogger(Http2Server::class.java.name)

    @JvmStatic
    fun main(args: Array<String>) {

  /**
   * Returns the high-level media type, such as "text", "image", "audio", "video", or "application".
   */
  @get:JvmName("type") val type: String,
  /**
   * Returns a specific media subtype, such as "plain" or "png", "mpeg", "mp4" or "xml".
   */
  @get:JvmName("subtype") val subtype: String,
  /** Alternating parameter names with their values, like `["charset", "utf-8"]`. */
  internal val parameterNamesAndValues: Array<String>,
) {

Unfortunately it crashes on OkHttp 4.x’s bytecode. Until [Google’s bug][advanced_profiling_bug] is
fixed you must disable advanced profiling in Android Studio.

![Disable Advanced Profiling](../assets/images/disable_advanced_profiling@2x.png)


R8 / ProGuard
-------------

R8 and ProGuard are both code optimizers for `.class` files.

R8 is the [default optimizer][r8] in Android Studio 3.4 and newer. It works well with all