App data

Every session starts from a fresh install. With app data turned on, Holtdroid can save the app’s private data from a session, by hand or when it ends, and you can start the next session of the same app from that save instead of signing in and clicking through onboarding again.

What is saved

The app’s internal storage: /data/data/<package> and /data/user_de/0/<package>. That covers databases, shared preferences, files, and the WebView’s cookies, local storage and IndexedDB. The cache (cache/ and code_cache/) is saved only when the server allows it and it is small enough. External storage (/sdcard/Android/data/<package>) is not saved.

A save is taken when:

• you press Stop, or the session is stopped for being idle or reaching its maximum lifetime, and Save app data when the session ends was on when it was launched. It is off by default. The launch dialog remembers the switch in your browser and applies it to every launch from then on, quick launch and launch links included;
• you press Save app data now next to the app’s name in the session header. The app is stopped while it is copied and started again.

A session that dies on its own (its node goes away) leaves no save.

Starting from a save

The launch dialog has an App data choice: Fresh install (the default) or one of your saves of that app, newest first. Tick Also restore the cache to bring the cache back too, when the save has one.

The quick launch button (⚡) shows a menu when you hover it:

• Fresh install: no app data;
• With app data: your newest save of the app;
• With app data and cache: the same, with its cache.

A plain click launches the way you picked last time, remembered in your browser. Until you pick, it uses your newest save, or a fresh install when there is none.

Managing saves

The App data page (the database icon in the header) lists your saves per app with their size, build and when they were last used. You can download a save as a .tar.zst archive, unless the server turned that off (tar --zstd -xf <file> unpacks it), and delete it. Saves are private: nobody else sees them, admins included.

Limitations

• Apps that encrypt their data with Android Keystore keys can’t read it on another device, because those keys stay on the device the save came from. Such apps may sign you out or reset parts of their state.
• Data from a newer build may break an older one, for example when its database can’t be downgraded. The launch dialog warns about that.

Configuration

appData:
  enabled: true
  cache: true # allow saving the cache
  maxCacheSize: 256MiB # a bigger cache is left out of the save
  maxSize: 1GiB # the cache is left out when it would push a save over this; bigger data isn't saved
  keep: 6 # saves kept per user and app, the most recently used ones; 0 = no limit
  maxAge: 168h # deleted this long after their last use; 0 = never
  export: true # let users download their saves
  timeout: 5m # how long a save may take before the session is stopped without it
  storage: # optional: where saves go; default is the shared storage under app-data/
    type: s3
    s3:
      endpoint: https://s3.example.com
      bucket: holtdroid
      prefix: app-data
      accessKey: env:S3_ACCESS_KEY
      secretKey: env:S3_SECRET_KEY

Key	Default	Meaning
appData.enabled	false	Save app data when sessions stop and offer it at launch
appData.cache	false	Also save cache/ and code_cache/
appData.maxCacheSize	256MiB	A cache bigger than this is not saved; the rest of the data still is
appData.maxSize	1GiB	The cache is dropped when it would push a save over this; data alone over it is not saved at all; 0 = no limit
appData.keep	6	Saves kept per user and app, the most recently used first; 0 = no limit
appData.maxAge	168h	A save unused this long is deleted; 0 = never
appData.export	true	Users may download their saves
appData.timeout	5m	Longest a save may take
appData.storage.*	shared	Same keys as storage; empty type = the shared storage

The shared storage is often an emptyDir cache (the chart’s default), which loses saves on every restart of the api. Point appData.storage at S3 or a persistent volume to keep them.

Sizes are measured on the device, before compression. Stopping a session waits for its save, so a big save makes Stop slower.