viewer-impl.js

import {VisibilityState_Enum} from '#core/constants/visibility-state';
import {Observable} from '#core/data-structures/observable';
import {Deferred, tryResolve} from '#core/data-structures/promise';
import {isIframed} from '#core/dom';
import {duplicateErrorIfNecessary} from '#core/error';
import {stripUserError} from '#core/error/message-helpers';
import {isEnumValue} from '#core/types';
import {findIndex} from '#core/types/array';
import {map} from '#core/types/object';
import {endsWith} from '#core/types/string';
import {parseQueryString} from '#core/types/string/url';

import {Services} from '#service';

import {listen} from '#utils/event-helper';
import {dev, devAssert} from '#utils/log';

import {ViewerInterface} from './viewer-interface';

import {urls} from '../config';
import {reportError} from '../error-reporting';
import {registerServiceBuilderForDoc} from '../service-helpers';
import {
  getSourceOrigin,
  isProxyOrigin,
  parseUrlDeprecated,
  removeFragment,
  serializeQueryString,
} from '../url';

const TAG_ = 'Viewer';

/** @enum {string} */
export const Capability_Enum = {
  VIEWER_RENDER_TEMPLATE: 'viewerRenderTemplate',
};

/**
 * Max length for each array of the received message queue.
 * @const @private {number}
 */
const RECEIVED_MESSAGE_QUEUE_MAX_LENGTH = 50;

/**
 * Duration in milliseconds to wait for viewerOrigin to be set before an empty
 * string is returned.
 * @const
 * @private {number}
 */
const VIEWER_ORIGIN_TIMEOUT_ = 1000;

/**
 * Prefixes to remove when trimming a hostname for comparison.
 * @const
 * @private {!RegExp}
 */
const TRIM_ORIGIN_PATTERN_ =
  /^(https?:\/\/)((www[0-9]*|web|ftp|wap|home|mobile|amp|m)\.)+/i;

/**
 * An AMP representation of the Viewer. This class doesn't do any work itself
 * but instead delegates everything to the actual viewer. This class and the
 * actual Viewer are connected via "AMP.viewer" using three methods:
 * {@link getParam}, {@link receiveMessage} and {@link setMessageDeliverer}.
 * @implements {ViewerInterface}
 * @package Visible for type.
 */
export class ViewerImpl {
  /**
   * @param {!./ampdoc-impl.AmpDoc} ampdoc
   */
  constructor(ampdoc) {
    /** @const {!./ampdoc-impl.AmpDoc} */
    this.ampdoc = ampdoc;

    /** @const {!Window} */
    this.win = ampdoc.win;

    /** @private @const {boolean} */
    this.isIframed_ = isIframed(this.win);

    /** @private {boolean} */
    this.isRuntimeOn_ = true;

    /** @private {boolean} */
    this.overtakeHistory_ = false;

    /** @private {!Object<string, !Observable<!JsonObject>>} */
    this.messageObservables_ = map();

    /** @private {!Object<string, !./viewer-interface.RequestResponderDef>} */
    this.messageResponders_ = map();

    /** @private {!Observable<boolean>} */
    this.runtimeOnObservable_ = new Observable();

    /** @private {!Observable<!JsonObject>} */
    this.broadcastObservable_ = new Observable();

    /**
     * @private {?function(string, (?JsonObject|string|undefined), boolean):
     *     (Promise<*>|undefined)}
     */
    this.messageDeliverer_ = null;

    /** @private {?string} */
    this.messagingOrigin_ = null;

    /**
     * @private {!Array<!{
     *   eventType: string,
     *   data: (?JsonObject|string|undefined),
     *   awaitResponse: boolean,
     *   responsePromise: (Promise<*>|undefined),
     *   responseResolver: function(*)
     * }>}
     */
    this.messageQueue_ = [];

    /**
     * @private {!Object<string, !Array<!{
     *   data: !JsonObject,
     *   deferred: !Deferred
     * }>>}
     */
    this.receivedMessageQueue_ = map();

    /**
     * Subset of this.params_ that only contains parameters in the URL hash,
     * e.g. "#foo=bar".
     * @const @private {!Object<string, string>}
     */
    this.hashParams_ = map();

    if (ampdoc.isSingleDoc()) {
      Object.assign(this.hashParams_, parseQueryString(this.win.location.hash));
    }

    this.isRuntimeOn_ = !parseInt(ampdoc.getParam('off'), 10);
    dev().fine(TAG_, '- runtimeOn:', this.isRuntimeOn_);

    this.overtakeHistory_ = !!(
      parseInt(ampdoc.getParam('history'), 10) || this.overtakeHistory_
    );
    dev().fine(TAG_, '- history:', this.overtakeHistory_);

    dev().fine(TAG_, '- visibilityState:', this.ampdoc.getVisibilityState());

    /**
     * Whether the AMP document is embedded in a Chrome Custom Tab.
     * @private {?boolean}
     */
    this.isCctEmbedded_ = null;

    /**
     * Whether the AMP document was served by a proxy.
     * @private @const {boolean}
     */
    this.isProxyOrigin_ = isProxyOrigin(
      parseUrlDeprecated(this.ampdoc.win.location.href)
    );

    const messagingDeferred = new Deferred();
    /** @const @private {!Function} */
    this.messagingReadyResolver_ = messagingDeferred.resolve;
    /** @const @private {?Promise} */
    this.messagingReadyPromise_ = this.initMessagingChannel_(
      messagingDeferred.promise
    );

    /** @private {?Promise<boolean>} */
    this.isTrustedViewer_ = null;

    /** @private {?Promise<string>} */
    this.viewerOrigin_ = null;

    const referrerParam = ampdoc.getParam('referrer');
    /** @private {string} */
    this.unconfirmedReferrerUrl_ =
      this.isEmbedded() &&
      referrerParam != null &&
      this.isTrustedAncestorOrigins_() !== false
        ? referrerParam
        : this.win.document.referrer;

    /** @const @private {!Promise<string>} */
    this.referrerUrl_ = new Promise((resolve) => {
      if (this.isEmbedded() && ampdoc.getParam('referrer') != null) {
        // Viewer override, but only for allowlisted viewers. Only allowed for
        // iframed documents.
        this.isTrustedViewer().then((isTrusted) => {
          if (isTrusted) {
            resolve(ampdoc.getParam('referrer'));
          } else {
            resolve(this.win.document.referrer);
            if (this.unconfirmedReferrerUrl_ != this.win.document.referrer) {
              dev().expectedError(
                TAG_,
                'Untrusted viewer referrer override: ' +
                  this.unconfirmedReferrerUrl_ +
                  ' at ' +
                  this.messagingOrigin_
              );
              this.unconfirmedReferrerUrl_ = this.win.document.referrer;
            }
          }
        });
      } else {
        resolve(this.win.document.referrer);
      }
    });

    /** @private {string} */
    this.resolvedViewerUrl_ = removeFragment(this.win.location.href || '');

    /** @const @private {!Promise<string>} */
    this.viewerUrl_ = new Promise((resolve) => {
      /** @const {?string} */
      const viewerUrlOverride = ampdoc.getParam('viewerUrl');
      if (this.isEmbedded() && viewerUrlOverride) {
        // Viewer override, but only for allowlisted viewers. Only allowed for
        // iframed documents.
        this.isTrustedViewer().then((isTrusted) => {
          if (isTrusted) {
            this.resolvedViewerUrl_ = devAssert(viewerUrlOverride);
          } else {
            dev().expectedError(
              TAG_,
              'Untrusted viewer url override: ' +
                viewerUrlOverride +
                ' at ' +
                this.messagingOrigin_
            );
          }
          resolve(this.resolvedViewerUrl_);
        });
      } else {
        resolve(this.resolvedViewerUrl_);
      }
    });

    // Remove hash when we have an incoming click tracking string
    // (see impression.js).
    if (this.hashParams_['click']) {
      const newUrl = removeFragment(this.win.location.href);
      if (newUrl != this.win.location.href && this.win.history.replaceState) {
        // Persist the hash that we removed has location.originalHash.
        // This is currently used by mode.js to infer development mode.
        if (!this.win.location['originalHash']) {
          this.win.location['originalHash'] = this.win.location.hash;
        }
        this.win.history.replaceState({}, '', newUrl);
        delete this.hashParams_['click'];
        dev().fine(TAG_, 'replace fragment:' + this.win.location.href);
      }
    }

    // This fragment may get cleared by impression tracking. If so, it will be
    // restored afterward.
    this.ampdoc.whenFirstVisible().then(() => {
      this.maybeUpdateFragmentForCct();
    });

    if (this.ampdoc.isSingleDoc()) {
      this.visibleOnUserAction_();
    }
  }

  /**
   * 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 available when the document is embedded.
   *
   * @param {!Promise} messagingPromise
   * @return {?Promise}
   * @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() {
    return this.ampdoc;
  }

  /** @override */
  getParam(name) {
    return this.ampdoc.getParam(name);
  }

  /** @override */
  hasCapability(name) {
    const capabilities = this.ampdoc.getParam('cap');
    if (!capabilities) {
      return false;
    }
    // TODO(@cramforce): Consider caching the split.
    return capabilities.split(',').indexOf(name) != -1;
  }

  /** @override */
  isEmbedded() {
    return !!this.messagingReadyPromise_;
  }

  /** @override */
  isWebviewEmbedded() {
    return !this.isIframed_ && this.ampdoc.getParam('webview') == '1';
  }

  /** @override */
  isCctEmbedded() {
    if (this.isCctEmbedded_ != null) {
      return this.isCctEmbedded_;
    }
    this.isCctEmbedded_ = false;
    if (!this.isIframed_) {
      const queryParams = parseQueryString(this.win.location.search);
      this.isCctEmbedded_ =
        queryParams['amp_gsa'] === '1' &&
        (queryParams['amp_js_v'] || '').startsWith('a');
    }
    return this.isCctEmbedded_;
  }

  /** @override */
  isProxyOrigin() {
    return this.isProxyOrigin_;
  }

  /** @override */
  maybeUpdateFragmentForCct() {
    if (!this.isCctEmbedded()) {
      return;
    }
    // CCT only works with versions of Chrome that support the history API.
    if (!this.win.history.replaceState) {
      return;
    }
    const sourceOrigin = getSourceOrigin(this.win.location.href);
    const {canonicalUrl} = Services.documentInfoForDoc(this.ampdoc);
    const canonicalSourceOrigin = getSourceOrigin(canonicalUrl);
    if (this.hasRoughlySameOrigin_(sourceOrigin, canonicalSourceOrigin)) {
      this.hashParams_['ampshare'] = canonicalUrl;
      this.win.history.replaceState(
        {},
        '',
        '#' +
          serializeQueryString(/** @type {!JsonObject} */ (this.hashParams_))
      );
    }
  }

  /**
   * Compares URLs to determine if they match once common subdomains are
   * removed. Everything else must match.
   * @param {string} first Origin to compare.
   * @param {string} second Origin to compare.
   * @return {boolean} Whether the origins match without subdomains.
   * @private
   */
  hasRoughlySameOrigin_(first, second) {
    const trimOrigin = (origin) => {
      if (origin.split('.').length > 2) {
        return origin.replace(TRIM_ORIGIN_PATTERN_, '$1');
      }
      return origin;
    };
    return trimOrigin(first) == trimOrigin(second);
  }

  /** @override */
  isRuntimeOn() {
    return this.isRuntimeOn_;
  }

  /** @override */
  toggleRuntime() {
    this.isRuntimeOn_ = !this.isRuntimeOn_;
    dev().fine(TAG_, 'Runtime state:', this.isRuntimeOn_);
    this.runtimeOnObservable_.fire(this.isRuntimeOn_);
  }

  /** @override */
  onRuntimeState(handler) {
    return this.runtimeOnObservable_.add(handler);
  }

  /** @override */
  isOvertakeHistory() {
    return this.overtakeHistory_;
  }

  /**
   * Passthrough for ampdoc visibility state. Only to be used by viewer
   * integration.
   * @restricted
   * TODO(#22733): remove if no longer used by the viewer.
   */
  getVisibilityState() {
    return this.ampdoc.getVisibilityState();
  }

  /**
   * Passthrough for ampdoc visibility state. Only to be used by viewer
   * integration.
   * @restricted
   * TODO(#22733): remove if no longer used by the viewer.
   */
  isVisible() {
    return this.ampdoc.isVisible();
  }

  /**
   * Passthrough for ampdoc visibility state. Only to be used by viewer
   * integration.
   * @restricted
   * TODO(#22733): remove if no longer used by the viewer.
   */
  hasBeenVisible() {
    return this.ampdoc.hasBeenVisible();
  }

  /**
   * Passthrough for ampdoc visibility state. Only to be used by viewer
   * integration.
   * @restricted
   * TODO(#22733): remove if no longer used by the viewer.
   */
  whenFirstVisible() {
    return this.ampdoc.whenFirstVisible();
  }

  /**
   * Passthrough for ampdoc visibility state. Only to be used by viewer
   * integration.
   * @restricted
   * TODO(#22733): remove if no longer used by the viewer.
   */
  whenNextVisible() {
    return this.ampdoc.whenNextVisible();
  }

  /**
   * Passthrough for ampdoc visibility state. Only to be used by viewer
   * integration.
   * @restricted
   * TODO(#22733): remove if no longer used by the viewer.
   */
  getFirstVisibleTime() {
    return this.ampdoc.getFirstVisibleTime();
  }

  /**
   * Passthrough for ampdoc visibility state. Only to be used by viewer
   * integration.
   * @restricted
   * TODO(#22733): remove if no longer used by the viewer.
   */
  getLastVisibleTime() {
    return this.ampdoc.getLastVisibleTime();
  }

  /**
   * Passthrough for ampdoc visibility state. Only to be used by viewer
   * integration.
   * @restricted
   * TODO(#22733): remove if no longer used by the viewer.
   */
  onVisibilityChanged(handler) {
    return this.ampdoc.onVisibilityChanged(handler);
  }

  /**
   * Sets the viewer defined visibility state.
   * @param {?string|undefined} state
   * @private
   */
  setVisibilityState_(state) {
    if (!state) {
      return;
    }

    devAssert(isEnumValue(VisibilityState_Enum, state));

    // The viewer is informing us we are not currently active because we are
    // being pre-rendered, or the user swiped to another doc (or closed the
    // viewer). Unfortunately, the viewer sends HIDDEN instead of PRERENDER or
    // INACTIVE, though we know better.
    if (state === VisibilityState_Enum.HIDDEN) {
      state =
        this.ampdoc.getLastVisibleTime() != null
          ? VisibilityState_Enum.INACTIVE
          : VisibilityState_Enum.PRERENDER;
    }

    this.ampdoc.overrideVisibilityState(state);
    dev().fine(
      TAG_,
      'visibilitychange event:',
      this.ampdoc.getVisibilityState()
    );
  }

  /** @override */
  getResolvedViewerUrl() {
    return this.resolvedViewerUrl_;
  }

  /**
   * Returns the promise that will yield the viewer URL value. It's by default
   * the current page's URL. The trusted viewers are allowed to override this
   * value.
   * @return {!Promise<string>}
   * @visibleForTesting
   */
  getViewerUrl() {
    return this.viewerUrl_;
  }

  /** @override */
  maybeGetMessagingOrigin() {
    return this.messagingOrigin_;
  }

  /** @override */
  getUnconfirmedReferrerUrl() {
    return this.unconfirmedReferrerUrl_;
  }

  /** @override */
  getReferrerUrl() {
    return this.referrerUrl_;
  }

  /** @override */
  isTrustedViewer() {
    if (!this.isTrustedViewer_) {
      const isTrustedAncestorOrigins = this.isTrustedAncestorOrigins_();
      this.isTrustedViewer_ =
        isTrustedAncestorOrigins !== undefined
          ? Promise.resolve(isTrustedAncestorOrigins)
          : this.messagingReadyPromise_.then((origin) => {
              return origin ? this.isTrustedViewerOrigin_(origin) : false;
            });
    }
    return /** @type {!Promise<boolean>} */ (this.isTrustedViewer_);
  }

  /**
   * Whether the viewer is has been allowlisted for more sensitive operations
   * by looking at the ancestorOrigins.
   * @return {boolean|undefined}
   */
  isTrustedAncestorOrigins_() {
    if (!this.isEmbedded()) {
      // Not embedded in IFrame - can't trust the viewer.
      return false;
    } else if (
      this.win.location.ancestorOrigins &&
      !this.isWebviewEmbedded() &&
      !this.isCctEmbedded()
    ) {
      // Ancestors when available take precedence. This is the main API used
      // for this determination. Fallback is only done when this API is not
      // supported by the browser.
      return (
        this.win.location.ancestorOrigins.length > 0 &&
        this.isTrustedViewerOrigin_(this.win.location.ancestorOrigins[0])
      );
    }
  }

  /** @override */
  getViewerOrigin() {
    if (!this.viewerOrigin_) {
      let origin;
      if (!this.isEmbedded()) {
        // Viewer is only determined for iframed documents at this time.
        origin = '';
      } else if (
        this.win.location.ancestorOrigins &&
        this.win.location.ancestorOrigins.length > 0
      ) {
        origin = this.win.location.ancestorOrigins[0];
      }
      this.viewerOrigin_ =
        origin !== undefined
          ? Promise.resolve(origin)
          : Services.timerFor(this.win)
              .timeoutPromise(
                VIEWER_ORIGIN_TIMEOUT_,
                this.messagingReadyPromise_
              )
              .catch(() => '');
    }
    return /** @type {!Promise<string>} */ (this.viewerOrigin_);
  }

  /**
   * @param {string} urlString
   * @return {boolean}
   * @private
   */
  isTrustedViewerOrigin_(urlString) {
    /** @const {!Location} */
    const url = parseUrlDeprecated(urlString);
    const {protocol} = url;
    // Mobile WebView x-thread is allowed.
    if (protocol == 'x-thread:') {
      return true;
    }
    if (protocol != 'https:') {
      // Non-https origins are never trusted.
      return false;
    }
    return urls.trustedViewerHosts.some((th) => th.test(url.hostname));
  }

  /** @override */
  onMessage(eventType, handler) {
    let observable = this.messageObservables_[eventType];
    if (!observable) {
      observable = new Observable();
      this.messageObservables_[eventType] = observable;
    }
    const unlistenFn = observable.add(handler);
    if (this.receivedMessageQueue_[eventType]) {
      this.receivedMessageQueue_[eventType].forEach((message) => {
        observable.fire(message.data);
        message.deferred.resolve();
      });
      this.receivedMessageQueue_[eventType] = [];
    }
    return unlistenFn;
  }

  /** @override */
  onMessageRespond(eventType, responder) {
    this.messageResponders_[eventType] = responder;
    if (this.receivedMessageQueue_[eventType]) {
      this.receivedMessageQueue_[eventType].forEach((message) => {
        message.deferred.resolve(responder(message.data));
      });
      this.receivedMessageQueue_[eventType] = [];
    }
    return () => {
      if (this.messageResponders_[eventType] === responder) {
        delete this.messageResponders_[eventType];
      }
    };
  }

  /** @override */
  receiveMessage(eventType, data, unusedAwaitResponse) {
    if (eventType == 'visibilitychange') {
      this.setVisibilityState_(data['state']);
      return Promise.resolve();
    }
    if (eventType == 'broadcast') {
      this.broadcastObservable_.fire(
        /** @type {!JsonObject|undefined} */ (data)
      );
      return Promise.resolve();
    }
    const observable = this.messageObservables_[eventType];
    const responder = this.messageResponders_[eventType];

    // Queue the message if there are no handlers. Returns a pending promise to
    // be resolved once a handler/responder is registered.
    if (!observable && !responder) {
      this.receivedMessageQueue_[eventType] =
        this.receivedMessageQueue_[eventType] || [];
      if (
        this.receivedMessageQueue_[eventType].length >=
        RECEIVED_MESSAGE_QUEUE_MAX_LENGTH
      ) {
        return undefined;
      }
      const deferred = new Deferred();
      this.receivedMessageQueue_[eventType].push({data, deferred});
      return deferred.promise;
    }
    if (observable) {
      observable.fire(data);
    }
    if (responder) {
      return responder(data);
    } else if (observable) {
      return Promise.resolve();
    }
  }

  /** @override */
  setMessageDeliverer(deliverer, origin) {
    if (this.messageDeliverer_) {
      throw new Error('message channel can only be initialized once');
    }
    if (origin == null) {
      throw new Error('message channel must have an origin');
    }
    dev().fine(TAG_, 'message channel established with origin: ', origin);
    this.messageDeliverer_ = deliverer;
    this.messagingOrigin_ = origin;
    this.messagingReadyResolver_(origin);

    if (this.messageQueue_.length > 0) {
      const queue = this.messageQueue_.slice(0);
      this.messageQueue_ = [];
      queue.forEach((message) => {
        const responsePromise = this.messageDeliverer_(
          message.eventType,
          message.data,
          message.awaitResponse
        );

        if (message.awaitResponse) {
          message.responseResolver(responsePromise);
        }
      });
    }
  }

  /** @override */
  maybeGetMessageDeliverer() {
    return this.messageDeliverer_;
  }

  /** @override */
  sendMessage(eventType, data, cancelUnsent = false) {
    this.sendMessageInternal_(eventType, data, cancelUnsent, false);
  }

  /** @override */
  sendMessageAwaitResponse(eventType, data, cancelUnsent = false) {
    return this.sendMessageInternal_(eventType, data, cancelUnsent, true);
  }

  /**
   * Sends the message to the viewer.
   *
   * @param {string} eventType
   * @param {?JsonObject|string|undefined} data
   * @param {boolean} cancelUnsent
   * @param {boolean} awaitResponse
   * @return {!Promise<(?JsonObject|string|undefined)>} the response promise
   */
  sendMessageInternal_(eventType, data, cancelUnsent, awaitResponse) {
    if (this.messageDeliverer_) {
      // Certain message deliverers return fake "Promise" instances called
      // "Thenables". Convert from these values into trusted Promise instances,
      // assimilating with the resolved (or rejected) internal value.
      return /** @type {!Promise<?JsonObject|string|undefined>} */ (
        tryResolve(() =>
          this.messageDeliverer_(
            eventType,
            /** @type {?JsonObject|string|undefined} */ (data),
            awaitResponse
          )
        )
      );
    }

    if (!this.messagingReadyPromise_) {
      if (awaitResponse) {
        return Promise.reject(getChannelError());
      } else {
        return Promise.resolve();
      }
    }

    if (!cancelUnsent) {
      return this.messagingReadyPromise_.then(() => {
        return this.messageDeliverer_(eventType, data, awaitResponse);
      });
    }

    const found = findIndex(
      this.messageQueue_,
      (m) => m.eventType == eventType
    );

    let message;
    if (found != -1) {
      message = this.messageQueue_.splice(found, 1)[0];
      message.data = data;
      message.awaitResponse = message.awaitResponse || awaitResponse;
    } else {
      const deferred = new Deferred();
      const {promise: responsePromise, resolve: responseResolver} = deferred;

      message = {
        eventType,
        data,
        awaitResponse,
        responsePromise,
        responseResolver,
      };
    }
    this.messageQueue_.push(message);
    return message.responsePromise;
  }

  /** @override */
  broadcast(message) {
    if (!this.messagingReadyPromise_) {
      // Messaging is not expected.
      return Promise.resolve(false);
    }

    return this.sendMessageInternal_('broadcast', message, false, false).then(
      () => true,
      () => false
    );
  }

  /** @override */
  onBroadcast(handler) {
    return this.broadcastObservable_.add(handler);
  }

  /** @override */
  whenMessagingReady() {
    return this.messagingReadyPromise_;
  }

  /** @override */
  replaceUrl(newUrl) {
    if (
      !newUrl ||
      !this.ampdoc.isSingleDoc() ||
      !this.win.history.replaceState
    ) {
      return;
    }

    try {
      // The origin and source origin must match.
      const url = parseUrlDeprecated(this.win.location.href);
      const replaceUrl = parseUrlDeprecated(
        removeFragment(newUrl) + this.win.location.hash
      );
      if (
        url.origin == replaceUrl.origin &&
        getSourceOrigin(url) == getSourceOrigin(replaceUrl)
      ) {
        this.win.history.replaceState({}, '', replaceUrl.href);
        this.win.location['originalHref'] = url.href;
        dev().fine(TAG_, 'replace url:' + replaceUrl.href);
      }
    } catch (e) {
      dev().error(TAG_, 'replaceUrl failed', e);
    }
  }

  /**
   * Defense in-depth against viewer communication issues: Will make the
   * document visible if it receives a user action without having been
   * made visible by the viewer.
   */
  visibleOnUserAction_() {
    if (this.ampdoc.getVisibilityState() == VisibilityState_Enum.VISIBLE) {
      return;
    }
    const unlisten = [];
    const doUnlisten = () => unlisten.forEach((fn) => fn());
    const makeVisible = () => {
      this.setVisibilityState_(VisibilityState_Enum.VISIBLE);
      doUnlisten();
      dev().expectedError(TAG_, 'Received user action in non-visible doc');
    };
    const options = {
      capture: true,
      passive: true,
    };
    unlisten.push(
      listen(this.win, 'keydown', makeVisible, options),
      listen(this.win, 'touchstart', makeVisible, options),
      listen(this.win, 'mousedown', makeVisible, options)
    );
    this.whenFirstVisible().then(doUnlisten);
  }
}

/**
 * Creates a dev error for the case where a channel cannot be established.
 * @param {*=} opt_reason
 * @return {!Error}
 */
function getChannelError(opt_reason) {
  let channelError;
  if (opt_reason instanceof Error) {
    opt_reason = duplicateErrorIfNecessary(opt_reason);
    opt_reason.message = 'No messaging channel: ' + opt_reason.message;
    channelError = opt_reason;
  } else {
    channelError = new Error('No messaging channel: ' + opt_reason);
  }
  // Force convert user error to dev error
  channelError.message = stripUserError(channelError.message);
  return channelError;
}

/**
 * @param {!./ampdoc-impl.AmpDoc} ampdoc
 */
export function installViewerServiceForDoc(ampdoc) {
  registerServiceBuilderForDoc(
    ampdoc,
    'viewer',
    ViewerImpl,
    /* opt_instantiate */ true
  );
}