Method initMessagingChannel_

src/service/viewer-impl.js:280–317

* Initialize messaging channel with Viewer host. * This promise will resolve when communications channel has been * established or timeout in 20 seconds. The timeout is needed to avoid * this promise becoming a memory leak with accumulating undelivered * messages. The promise is only ava

(messagingPromise)

   * @private
   */
  initMessagingChannel_(messagingPromise) {
    const isEmbedded = !!(
      (this.isIframed_ &&
        !this.win.__AMP_TEST_IFRAME &&
        // Checking param "origin", as we expect all viewers to provide it.
        // See https://github.com/ampproject/amphtml/issues/4183
        // There appears to be a bug under investigation where the
        // origin is sometimes failed to be detected. Since failure mode
        // if we fail to initialize communication is very bad, we also check
        // for visibilityState.
        // After https://github.com/ampproject/amphtml/issues/6070
        // is fixed we should probably only keep the amp_js_v check here.
        (this.ampdoc.getParam('origin') ||
          this.ampdoc.getParam('visibilityState') ||
          // Parent asked for viewer JS. We must be embedded.
          this.win.location.search.indexOf('amp_js_v') != -1)) ||
      this.isWebviewEmbedded() ||
      this.isCctEmbedded() ||
      !this.ampdoc.isSingleDoc()
    );

    if (!isEmbedded) {
      return null;
    }
    const timeoutMessage = 'initMessagingChannel timeout';
    return Services.timerFor(this.win)
      .timeoutPromise(20000, messagingPromise, timeoutMessage)
      .catch((reason) => {
        let error = getChannelError(
          /** @type {!Error|string|undefined} */ (reason)
        );
        if (error && endsWith(error.message, timeoutMessage)) {
          error = dev().createExpectedError(error);
        }
        reportError(error);
        throw error;
      });
  }

  /** @override */
  getAmpDoc() {