* Send a notification back to the API user (the external developer), as a callback.
        * At this point is that the API will somehow send a POST request to the
            external API with the notification of the invoice event
            (e.g. "payment successful").
    """
    # Send the invoice, collect the money, send the notification (the callback)
    return {"msg": "Invoice received"}

import okhttp3.Call
import okhttp3.Callback
import okhttp3.OkHttpClient
import okhttp3.Request
import okhttp3.Response

class AsynchronousGet {
  private val client = OkHttpClient()

  fun run() {
    val request =
      Request.Builder()
        .url("http://publicobject.com/helloworld.txt")
        .build()

    client.newCall(request).enqueue(
      object : Callback {
        override fun onFailure(

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

import java.io.IOException;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.Headers;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.ResponseBody;

public final class AsynchronousGet {

  }

  /**
   * Streams lines from a URL, stopping when our callback returns false, or we have read all of the
   * lines.
   *
   * @param url the URL to read from
   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @param callback the LineProcessor to use to handle the lines
   * @return the output of processing the lines

   *
   * @param future The future attach the callback to.
   * @param callback The callback to invoke when {@code future} is completed.
   * @param executor The executor to run {@code callback} when the future completes.
   * @since 10.0
   */
  public static <V extends @Nullable Object> void addCallback(
      final ListenableFuture<V> future,
      final FutureCallback<? super V> callback,
      Executor executor) {

import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Proxy;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.Connection;
import okhttp3.EventListener;
import okhttp3.Handshake;
import okhttp3.HttpUrl;
import okhttp3.OkHttpClient;
import okhttp3.Protocol;
import okhttp3.Request;
import okhttp3.Response;

      return;
    }

    @SuppressWarnings("unchecked") // verified safe by isInstanceOfThrowableClass
    X castThrowable = (X) throwable;
    T fallbackResult;
    try {
      fallbackResult = doFallback(localFallback, castThrowable);
    } catch (Throwable t) {
      restoreInterruptIfIsInterruptedException(t);
      setException(t);
      return;
    } finally {
      exceptionType = null;

                if (builderEntityCall != null) {
                    builderEntityCall.callback(builder);
                }
                bulkBuilder.add((IndexRequestBuilder) builder);
            } else if (builder instanceof UpdateRequestBuilder) {
                if (builderEntityCall != null) {
                    builderEntityCall.callback(builder);
                }
                bulkBuilder.add((UpdateRequestBuilder) builder);

                if (builderEntityCall != null) {
                    builderEntityCall.callback(builder);
                }
                bulkBuilder.add((IndexRequestBuilder) builder);
            } else if (builder instanceof UpdateRequestBuilder) {
                if (builderEntityCall != null) {
                    builderEntityCall.callback(builder);
                }
                bulkBuilder.add((UpdateRequestBuilder) builder);

    }

  /**
   * A callback to be invoked each time the dispatcher becomes idle (when the number of running
   * calls returns to zero).
   *
   * Note: The time at which a [call][Call] is considered idle is different depending on whether it
   * was run [asynchronously][Call.enqueue] or [synchronously][Call.execute]. Asynchronous calls
   * become idle after the [onResponse][Callback.onResponse] or [onFailure][Callback.onFailure]