* 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

  /**
   * A duplex request body is special in how it is **transmitted** on the network and
   * in the **API contract** between OkHttp and the application.
   *
   * This method returns false unless it is overridden by a subclass.
   *
   * ### Duplex Transmission
   *
   * With regular HTTP calls the request always completes sending before the response may begin