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PWA and TWA Setup

This application exposes basic Progressive Web App (PWA) features and can also be deployed as a Trusted Web Activity (TWA) on Android. The following configuration options are available.

Offline Support

  • The file app/static/offline.html is served at /offline.html when the service worker is registered.
  • The PWA manifest at app/static/manifest.json is available from /manifest.json.
  • The manifest enables the window-controls-overlay display mode for desktop browsers using display_override.
  • The service worker is registered from the root path: /sw.js.
  • When a new version is detected, the page reloads automatically so updated assets load immediately.
  • Background sync ensures actions performed while offline are sent when connectivity returns.
  • The manifest includes a share_target entry so the site can receive shared images and text via the Web Share Target API. Shared data is POSTed to the route /share-target.
  • The manifest sets handle_links to preferred so links open directly in the installed app when possible.
  • The manifest includes a launch_handler object specifying "client_mode": "focus-existing" so that repeated launches reuse the existing window.

Background & Periodic Sync

  • The service worker listens for sync and periodicsync events.
  • A tag of sync-notifications triggers a refresh of the unread notification count when connectivity returns.
  • A tag of periodic-notifications performs the same refresh at regular intervals when supported by the browser.

Push Notifications

  • If the user grants permission, push messages received by the service worker display a notification using the app icon.

TWA Asset Links

  • The route /.well-known/assetlinks.json dynamically returns the digital asset links used for TWA verification.
  • The SHA256 fingerprint of your Android signing certificate must be configured in the .env file.

Configuration Keys

  • Environment variable: TWA_SHA256_FINGERPRINT
  • TOML: 
    [twa]
SHA256_CERT_FINGERPRINT = "YOUR:SHA256:FINGERPRINT"

The fingerprint will be inserted into the generated assetlinks.json response at runtime.

File Handlers

The manifest supports the file_handlers property so the application can register itself as the default handler for specific file types. By default, the provided manifest declares support for common image formats. When a user chooses "Always open with QuestByCycle" for a supported image, the site will launch to / where the uploaded file can be processed.