feat(service-worker): introduce the @angular/service-worker package (#19274)

This service worker is a conceptual derivative of the existing @angular/service-worker maintained at github.com/angular/mobile-toolkit, but has been rewritten to support use across a much wider variety of applications.

Entrypoints include:

@angular/service-worker: a library for use within Angular client apps to communicate with the service worker.
@angular/service-worker/gen: a library for generating ngsw.json files from glob-based SW config files.
@angular/service-worker/ngsw-worker.js: the bundled service worker script itself.
@angular/service-worker/ngsw-cli.js: a CLI tool for generating ngsw.json files from glob-based SW config files.

packages/service-worker/src/low_level.ts

@@ -0,0 +1,180 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {Injectable} from '@angular/core';
+import {BehaviorSubject} from 'rxjs/BehaviorSubject';
+import {Observable} from 'rxjs/Observable';
+import {ConnectableObservable} from 'rxjs/observable/ConnectableObservable';
+import {concat as obs_concat} from 'rxjs/observable/concat';
+import {defer as obs_defer} from 'rxjs/observable/defer';
+import {fromEvent as obs_fromEvent} from 'rxjs/observable/fromEvent';
+import {of as obs_of} from 'rxjs/observable/of';
+import {_throw as obs_throw} from 'rxjs/observable/throw';
+import {_do as op_do} from 'rxjs/operator/do';
+import {filter as op_filter} from 'rxjs/operator/filter';
+import {map as op_map} from 'rxjs/operator/map';
+import {publish as op_publish} from 'rxjs/operator/publish';
+import {startWith as op_startWith} from 'rxjs/operator/startWith';
+import {switchMap as op_switchMap} from 'rxjs/operator/switchMap';
+import {take as op_take} from 'rxjs/operator/take';
+import {toPromise as op_toPromise} from 'rxjs/operator/toPromise';
+
+const ERR_SW_NOT_SUPPORTED = 'Service workers are not supported by this browser';
+
+export interface Version {
+  hash: string;
+  appData?: Object;
+}
+
+/**
+ * @experimental
+ */
+export interface UpdateAvailableEvent {
+  type: 'UPDATE_AVAILABLE';
+  current: Version;
+  available: Version;
+}
+
+/**
+ * @experimental
+ */
+export interface UpdateActivatedEvent {
+  type: 'UPDATE_ACTIVATED';
+  previous?: Version;
+  current: Version;
+}
+
+export type IncomingEvent = UpdateAvailableEvent | UpdateActivatedEvent;
+
+interface TypedEvent {
+  type: string;
+}
+
+interface StatusEvent {
+  type: 'STATUS';
+  nonce: number;
+  status: boolean;
+  error?: string;
+}
+
+
+function errorObservable(message: string): Observable<any> {
+  return obs_defer(() => obs_throw(new Error(message)));
+}
+
+/**
+ * @experimental
+*/
+export class NgswCommChannel {
+  /**
+   * @internal
+   */
+  readonly worker: Observable<ServiceWorker>;
+
+  /**
+   * @internal
+   */
+  readonly registration: Observable<ServiceWorkerRegistration>;
+
+  /**
+   * @internal
+   */
+  readonly events: Observable<IncomingEvent>;
+
+  constructor(serviceWorker: ServiceWorkerContainer|undefined) {
+    if (!serviceWorker) {
+      this.worker = this.events = errorObservable(ERR_SW_NOT_SUPPORTED);
+    } else {
+      const controllerChangeEvents =
+          <Observable<any>>(obs_fromEvent(serviceWorker, 'controllerchange'));
+      const controllerChanges = <Observable<ServiceWorker|null>>(
+          op_map.call(controllerChangeEvents, () => serviceWorker.controller));
+
+      const currentController =
+          <Observable<ServiceWorker|null>>(obs_defer(() => obs_of(serviceWorker.controller)));
+
+      const controllerWithChanges =
+          <Observable<ServiceWorker|null>>(obs_concat(currentController, controllerChanges));
+      this.worker = <Observable<ServiceWorker>>(
+          op_filter.call(controllerWithChanges, (c: ServiceWorker) => !!c));
+
+      this.registration = <Observable<ServiceWorkerRegistration>>(
+          op_switchMap.call(this.worker, () => serviceWorker.getRegistration()));
+
+      const rawEvents = <Observable<MessageEvent>>(op_switchMap.call(
+          this.registration, (reg: ServiceWorkerRegistration) => obs_fromEvent(reg, 'message')));
+
+      const rawEventPayload =
+          <Observable<Object>>(op_map.call(rawEvents, (event: MessageEvent) => event.data));
+      const eventsUnconnected = <Observable<IncomingEvent>>(
+          op_filter.call(rawEventPayload, (event: Object) => !!event && !!(event as any)['type']));
+      const events = <ConnectableObservable<IncomingEvent>>(op_publish.call(eventsUnconnected));
+      this.events = events;
+      events.connect();
+    }
+  }
+
+  /**
+   * @internal
+   */
+  postMessage(action: string, payload: Object): Promise<void> {
+    const worker = op_take.call(this.worker, 1);
+    const sideEffect = op_do.call(worker, (sw: ServiceWorker) => {
+      sw.postMessage({
+          action, ...payload,
+      });
+    });
+    return <Promise<void>>(op_toPromise.call(sideEffect).then(() => undefined));
+  }
+
+  /**
+   * @internal
+   */
+  postMessageWithStatus(type: string, payload: Object, nonce: number): Promise<void> {
+    const waitForStatus = this.waitForStatus(nonce);
+    const postMessage = this.postMessage(type, payload);
+    return Promise.all([waitForStatus, postMessage]).then(() => undefined);
+  }
+
+  /**
+   * @internal
+   */
+  generateNonce(): number { return Math.round(Math.random() * 10000000); }
+
+  /**
+   * @internal
+   */
+  eventsOfType<T>(type: string): Observable<T> {
+    return <Observable<T>>(
+        op_filter.call(this.events, (event: T & TypedEvent) => { return event.type === type; }));
+  }
+
+  /**
+   * @internal
+   */
+  nextEventOfType<T>(type: string): Observable<T> {
+    return <Observable<T>>(op_take.call(this.eventsOfType(type), 1));
+  }
+
+  /**
+   * @internal
+   */
+  waitForStatus(nonce: number): Promise<void> {
+    const statusEventsWithNonce = <Observable<StatusEvent>>(
+        op_filter.call(this.eventsOfType('STATUS'), (event: StatusEvent) => event.nonce === nonce));
+    const singleStatusEvent = <Observable<StatusEvent>>(op_take.call(statusEventsWithNonce, 1));
+    const mapErrorAndValue =
+        <Observable<void>>(op_map.call(singleStatusEvent, (event: StatusEvent) => {
+          if (event.status) {
+            return undefined;
+          }
+          throw new Error(event.error !);
+        }));
+    return op_toPromise.call(mapErrorAndValue);
+  }
+}