Method initialize

packages/service-worker/worker/src/driver.ts:648–780

* Attempt to quickly reach a state where it's safe to serve responses.

()

   * Attempt to quickly reach a state where it's safe to serve responses.
   */
  private async initialize(): Promise<void> {
    // On initialization, all of the serialized state is read out of the 'control'
    // table. This includes:
    // - map of hashes to manifests of currently loaded application versions
    // - map of client IDs to their pinned versions
    // - record of the most recently fetched manifest hash
    //
    // If these values don't exist in the DB, then this is the either the first time
    // the SW has run or the DB state has been wiped or is inconsistent. In that case,
    // load a fresh copy of the manifest and reset the state from scratch.

    const table = await this.controlTable;

    // Attempt to load the needed state from the DB. If this fails, the catch {} block
    // will populate these variables with freshly constructed values.
    let manifests: ManifestMap, assignments: ClientAssignments, latest: LatestEntry;
    try {
      // Read them from the DB simultaneously.
      [manifests, assignments, latest] = await Promise.all([
        table.read<ManifestMap>('manifests'),
        table.read<ClientAssignments>('assignments'),
        table.read<LatestEntry>('latest'),
      ]);

      // Make sure latest manifest is correctly installed. If not (e.g. corrupted data),
      // it could stay locked in EXISTING_CLIENTS_ONLY or SAFE_MODE state.
      if (!this.versions.has(latest.latest) && !manifests.hasOwnProperty(latest.latest)) {
        this.debugger.log(
          `Missing manifest for latest version hash ${latest.latest}`,
          'initialize: read from DB',
        );
        throw new Error(`Missing manifest for latest hash ${latest.latest}`);
      }

      // Successfully loaded from saved state. This implies a manifest exists, so
      // the update check needs to happen in the background.
      this.idle.schedule('init post-load (update)', async () => {
        await this.checkForUpdate();
      });
    } catch (_) {
      // Something went wrong. Try to start over by fetching a new manifest from the
      // server and building up an empty initial state.
      const manifest = await this.fetchLatestManifest();
      const hash = hashManifest(manifest);
      manifests = {[hash]: manifest};
      assignments = {};
      latest = {latest: hash};

      // Save the initial state to the DB.
      await Promise.all([
        table.write('manifests', manifests),
        table.write('assignments', assignments),
        table.write('latest', latest),
      ]);
    }

    // At this point, either the state has been loaded successfully, or fresh state
    // with a new copy of the manifest has been produced. At this point, the `Driver`