PWA Deep-Dive: Offline-Anwendungen im Griff

Progressive Web Apps bieten sich als plattformübergreifendes Anwendungsmodell als idealer Partner für in .NET geschriebene Backends an. Zentrale Eigenschaft einer jeden Progressive Web App (PWA) ist die Verbindungsunabhängigkeit. Dank dem Service Worker funktioniert die App auch dann, wenn der Anwender gerade offline ist: Im Tunnel, im Park oder im Dschungel. Zur Generierung eines Service Workers hilft das Toolkit Workbox. Anwenderdaten werden hingegen in der Browserdatenbank IndexedDB hinterlegt. Wo Daten offline gehalten werden, müssen aber auch deren Synchronisierung und Konfliktauflösung in der Architektur bedacht werden. Christian Liebel von Thinktecture zeigt Ihnen die Mechanik hinter der dem Service-Worker-Cache und der Browserdatenbank IndexedDB, sodass es auch Ihre PWA mit ihren nativen Gegenstücken problemlos aufnehmen kann.

Transcript

1. PWA Deep Dive Offlineanwendungen im Griff Christian Liebel @christianliebel Consultant
2. Hello, it’s me. PWA Deep Dive Offlineanwendungen im Griff Christian Liebel Follow me: @christianliebel Blog: christianliebel.com Email: christian.liebel @thinktecture.com Cross-Platform & Cloud & Enterprise Blockchain
3. PWA Deep Dive Offlineanwendungen im Griff - Das PWA-Anwendungsmodell - Web App Manifest - Service Worker und Cache API - Workbox: Toolkit für PWAs - Angular-Unterstützung für PWAs - Natives Look & Feel - Migrieren & veröffentlichen - Payment Request API & Apple Pay www.rheinwerk-verlag.de/4707
4. PWA Deep Dive Offlineanwendungen im Griff Responsive Linkable Discoverable Installable App-like Connectivity Independent Fresh Safe Re-engageable Progressive
5. PWA Deep Dive Offlineanwendungen im Griff
6. Service Worker & Cache API Source Files & Assets App & IndexedDB Structured Data PWA Deep Dive Offlineanwendungen im Griff Connectivity Independent
7. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Background Sync API PWA Deep Dive Offlineanwendungen im Griff Talking Points
8. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Background Sync API PWA Deep Dive Offlineanwendungen im Griff Talking Points
9. Offline Capability Challenge: Connection strength varies a lot (especially en route) Lie-Fi: Connection strength of a public WiFi is weak or even completely offline Goal: App works offline or with a weak connection at least within the possibilities (e.g. OneNote) PWA Deep Dive Offlineanwendungen im Griff Offline First
10. Principle PWA Deep Dive Offlineanwendungen im Griff Offline First - Draft and implement offline support first - Think about synchronization & conflicts - Don’t treat offline as an error - Make offline the default - Everything must be offline capable
11. PWA Deep Dive Offlineanwendungen im Griff Offline First System Website HTML/JS Local storage Central adapter Remote storage Server Internet
12. Locking Pessimistic - System locks access to resource if it is used by another user - No conflicts - Users don’t like this (offline = no locking possible!) Optimistic - Users can access arbitrary resources anytime - Requires data synchronization & conflict resolution (strategies depend on domain) PWA Deep Dive Offlineanwendungen im Griff Offline First
13. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Background Sync API PWA Deep Dive Offlineanwendungen im Griff Talking Points
14. Key Technology Service Worker Service Worker Internet Website HTML/JS Cache fetch Offlineanwendungen im Griff PWA Deep Dive
15. Worker snippet is executed in an own thread Worker can’t manipulate the parent document’s DOM Communication via thin API (postMessage) + Acts as a controller/proxy/interceptor + Performs background tasks Has to be installed before usage Relation: Scope (origin + path) Lifetime: Unrelated to tab/window PWA Deep Dive Offlineanwendungen im Griff Service Worker
16. Lifecycle PWA Deep Dive Offlineanwendungen im Griff Service Worker Installing Parsed Error Activated Idle Terminated fetch/ message
17. Platform Support Service Worker Offlineanwendungen im Griff PWA Deep Dive 17 11.1 44 40 4.1 Chrome 40 11.3
18. Basic Implementation navigator.serviceWorker.register('sw.js') .then(subscription => console.log(subscription)) .catch(err => console.error('Fehler', err)); self.addEventListener('install', event => {}); self.addEventListener('activate', () => {}); self.addEventListener('fetch', event => {}); PWA Deep Dive Offlineanwendungen im Griff Service Worker LIVE DEMO
19. Debugging PWA Deep Dive Offlineanwendungen im Griff Service Worker
20. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Background Sync API PWA Deep Dive Offlineanwendungen im Griff Talking Points
21. Introduction Cache: Key-value storage Key: HTTP(S) request, value: HTTP(S) response Survives browser restarts (Safari: unused caches are cleared “after a few weeks”) Can be accessed from both service worker and website Isolated per origin (protocol + hostname + port) Multiple named caches per origin Cache operations are asynchronous (Promises) PWA Deep Dive Offlineanwendungen im Griff Cache API
22. Usage 1. Open a cache 2. Store/read responses from the cache PWA Deep Dive Offlineanwendungen im Griff Cache API await caches.open('images') await cache.put(req, res) await cache.add(req) await cache.match(req)
23. and Service Worker PWA Deep Dive Offlineanwendungen im Griff Cache API Installing Parsed Error Activated Idle Terminated fetch/ message Install cache content Remove old caches Deliver from cache
24. Adding Requests to The Cache self.addEventListener('install', event => { event.waitUntil( caches.open('pwa-demo-v1') .then(cache => cache.addAll(['/', '/index.html'])) .then(() => self.skipWaiting()) ); }); PWA Deep Dive Offlineanwendungen im Griff Cache API LIVE DEMO
25. Delivering from The Cache self.addEventListener('fetch', event => { event.respondWith( caches.match(event.request) .then(response => response || fetch(event.request)) ); }); PWA Deep Dive Offlineanwendungen im Griff Cache API LIVE DEMO
26. Debugging PWA Deep Dive Offlineanwendungen im Griff Cache API
27. Caching Strategies 1. Cache only 2. Network only 3. Cache falling back to network 4. Cache & network race 5. Network falling back to cache 6. Cache then network 7. Generic Fallback 8. Service-Worker-side templating PWA Deep Dive Offlineanwendungen im Griff Cache API https://jakearchibald.com/2014/offline-cookbook/
28. PWA Deep Dive Offlineanwendungen im Griff Cache Then Network System Website HTML/JS Cache Storage Remote storage Server Internet 2. fetch HTTP Service Worker 1. lookup
29. Use Cases Service Worker - everything that’s part of a website/app version - application source files - assets Application - dynamic content known during runtime - “read later”, profile images, … - lookup without fetch PWA Deep Dive Offlineanwendungen im Griff Cache API
30. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Background Sync API PWA Deep Dive Offlineanwendungen im Griff Talking Points
31. Overview Toolchain by Google: Service Worker generator and runtime library Automatically creates a Service Worker implementation for you Can extend an existing Service Worker implementation with caching Command line tool: workbox npm i -g workbox-cli PWA Deep Dive Offlineanwendungen im Griff Workbox
32. Commands workbox wizard workbox generateSW workbox injectManifest PWA Deep Dive Offlineanwendungen im Griff Workbox LIVE DEMO
33. Routing & Strategies workbox.routing.registerRoute( new RegExp('/social-timeline/'), workbox.strategies.networkFirst() ); PWA Deep Dive Offlineanwendungen im Griff Workbox
34. Client Library import { Workbox } from 'workbox-window'; if ('serviceWorker' in navigator) { const wb = new Workbox('service-worker.js'); wb.addEventListener('installed', event => { if (event.isUpdate) { if (confirm('New content is available! Click OK to refresh')) { window.location.reload(); } } }); wb.register(); } PWA Deep Dive Offlineanwendungen im Griff Workbox https://medium.com/@webmaxru/workbox-4-implementing-refresh-to-update-version-flow-using-the-workbox-window-module-41284967e79c
35. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Background Sync API PWA Deep Dive Offlineanwendungen im Griff Talking Points
36. Angular supports service worker and cache manifest generation (for productive builds only) npm i -g @angular/cli ng new myApp cd myApp ng add @angular/pwa ng build --prod PWA Deep Dive Offlineanwendungen im Griff Angular Demo App LIVE DEMO
37. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Background Sync API PWA Deep Dive Offlineanwendungen im Griff Talking Points
38. Motivation The web platform has different techniques to store arbitrary data (e.g. application state) offline: • Web Storage API (Local Storage/Session Storage—synchronous!) • Cookies (inconvenient) • WebSQL (deprecated) • IndexedDB PWA Deep Dive Offlineanwendungen im Griff IndexedDB
39. Overview Indexed Database (IndexedDB) is a database in the browser capable of storing structured data in tables with keys and value Data is stored permanently (survives browser restarts) Service Worker and website share access to the same IndexedDB database (e.g. for synchronization purposes) PWA Deep Dive Offlineanwendungen im Griff IndexedDB
40. Browser Support PWA Deep Dive Offlineanwendungen im Griff IndexedDB 10 7.1 4 11
41. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Background Sync API PWA Deep Dive Offlineanwendungen im Griff Talking Points
42. Overview Dexie is a minimalistic wrapper for IndexedDB Operations are based on promises instead of callbacks Near native performance (also for bulk inserts) Open-source PWA Deep Dive Offlineanwendungen im Griff Dexie.js
43. Table API const table = db.table('todos'); table.toArray() // get all items as an array table.add() // insert an object table.put() // update or insert an object table.filter(i => i.id !== 3) // apply JS filter on value table.where({ name: 'Peter' }) // query items by key PWA Deep Dive Offlineanwendungen im Griff Dexie.js
44. const dexie = new Dexie('Meine-DB'); dexie.version(1).stores({ todos: 'id++,done' }); PWA Deep Dive Offlineanwendungen im Griff Dexie.js LIVE DEMO
45. IndexedDB Debugging PWA Deep Dive Offlineanwendungen im Griff Dexie.js
46. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Background Sync API PWA Deep Dive Offlineanwendungen im Griff Talking Points
47. Syncs data when the client is next online (if the client is already online, syncs immediately) This also works when the client application closed Currently only supports one-off synchronization PWA Deep Dive Offlineanwendungen im Griff Background Sync API
48. self.addEventListener('sync', event => { if (event.tag === 'upload-photos') { event.waitUntil(/* … */); } }); registration.sync.register('upload-photos'); PWA Deep Dive Offlineanwendungen im Griff Background Sync API LIVE DEMO
49. Browser Support PWA Deep Dive Offlineanwendungen im Griff Background Sync API WIP — WIP 49
50. https://pwapraxis.liebel.io PWA Deep Dive Offlineanwendungen im Griff Demo LIVE DEMO
51. Make use of the Offline First pattern Use Cache API for HTTPS requests Use IndexedDB for structured data Use Service Workers for initial caching and delivering cached content Think about data synchronization & conflict handling for structured data Background Sync API can sync data even when the app is closed Make your users happy! PWA Deep Dive Offlineanwendungen im Griff Summary
52. Thank you for your kind attention! Christian Liebel @christianliebel christian.liebel@thinktecture.com