Zotero Connector Background Process and Service Worker

this.init = async function() {
  if (_initializedPromise) return _initializedPromise;
  _cache = {"import":[], "export":[], "web":[], "search":[]};
  _translators = {};
  _initializedPromise = new Promise(async (resolve, reject) => {
    try {
      let translators = Zotero.Prefs.get("translatorMetadata");
      // No stored translators — fetch everything from the repo
      if (typeof translators !== "object" || !translators.length) {
        Zotero.debug(`Translators: First time launch, getting all translators.`);
        await this.updateFromRemote(true);
      }
      else {
        this._load(translators);
      }
      this.keepTranslatorsUpdated();
      resolve();
    }
    catch (e) { /* … */ }
  });
}

var backgroundInclude = [
  'zotero_config.js',
  'zotero.js',
  'i18n.js',
  'translate/promise.js',
  // … utilities …
  'prefs.js',
  'api.js',
  'http.js',
  'oauthsimple.js',
  'proxy.js',
  'connector.js',
  'updaterFix.js',
  'repo.js',
  'translate/debug.js',
  'translate/tlds.js',
  'translate/translator.js',
  'itemSaver_background.js',
  'translators.js',
  'cachedTypes.js',
  'errors_webkit.js',
  'zotero-google-docs-integration/api.js',
  'messages.js',
  'messaging.js',
];

var backgroundIncludeBrowserExt = ['browser-polyfill.js'].concat(backgroundInclude, [
  'webRequestIntercept.js',
  'contentTypeHandler.js',
  'saveWithoutProgressWindow.js',
  'messagingGeneric.js',
  'browserAttachmentMonitor/browserAttachmentMonitor.js',
  'offscreen/offscreenFunctionOverrides.js',
  'background/offscreenManager.js',
]);

Zotero.OffscreenManager = {
  offscreenPageInitialized: false,
  messagingDeferred: Zotero.Promise.defer(),
  offscreenUrl: 'offscreen/offscreen.html',

  async init() {
    const offscreenPage = await this.getOffscreenPage();
    if (!offscreenPage) {
      // Make sure we're waiting for a new deferred
      this.messagingDeferred = Zotero.Promise.defer();
      // Create offscreen document
      await browser.offscreen.createDocument({
        url: this.offscreenUrl,
        reasons: ['DOM_PARSER'],
        justification: 'Scraping the document with Zotero Translators',
      });
    }
    else {
      // Service worker restarted; notify offscreen page to reinit messaging
      offscreenPage.postMessage('service-worker-restarted');
    }
    await this.messagingDeferred.promise;
    // …
  },
  // …
};

const LET_DIE_AFTER = 10*60e3; // 1 hour (comment in source; actual value is 10 minutes)

const startedOn = Date.now();
let interval;

function keepAlive() {
  if (startedOn + LET_DIE_AFTER < Date.now()
      && !Zotero.Connector_Browser.shouldKeepServiceWorkerAlive()) {
    clearInterval(interval);
  }
  chrome.runtime.getPlatformInfo();
}
interval = setInterval(keepAlive, 20e3);

this._keepServiceWorkerAlive = 0;

this.shouldKeepServiceWorkerAlive = () => this._keepServiceWorkerAlive;
// Parallel async functions may call this, so we use a counter to make sure
// one keep-alive function finishing does not kill the service worker for other
// still-running functions
this.setKeepServiceWorkerAlive = (val) => this._keepServiceWorkerAlive += val ? 1 : -1;

this.init = function() {
  if (Zotero.isBrowserExt) {
    browser.runtime.onMessage.addListener(function(request, sender) {
      // All Zotero messages are arrays — ignore SingleFile objects, etc.
      if (!Array.isArray(request)) {
        return;
      }

      return Zotero.Messaging.receiveMessage(
        request[0],   // message name  e.g. "Translators.getWebTranslatorsForLocation"
        request[1],   // args array
        sender.tab,
        sender.frameId
      )
      .catch(function(err) {
        err = JSON.stringify(Object.assign({
          name: err.name,
          message: err.message,
          stack: err.stack
        }, err));
        return ['error', err];
      });
    });
  }
  Zotero.Messaging.initialized = true;
};