PWA Deep-Dive: Offline-Anwendungen im Griff

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.

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Christian Liebel

April 06, 2019
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  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