caspian-native

Optional Tauri packaging for applications built with the Caspian framework and PulsePoint. Version 0.0.1 packages the existing application in a system WebView; it does not translate HTML into operating-system widgets.

Support in 0.0.1

Android embedded Python is deliberately refused. A Caspian application may depend on native Python wheels such as asyncpg, cryptography, or Pillow; shipping an APK without proving every wheel for every ABI would produce a package that builds unreliably or fails on launch.

Install for development

python -m pip install -e ".[test,build]"

Tauri's CLI is installed separately so it can match the version selected by the generated application's native/Cargo.toml:

cargo install tauri-cli --version "^2" --locked

Add native packaging to a Caspian project

From a directory containing caspian.config.json:

caspian-native init --identifier com.example.myapp --windows
caspian-native doctor --target windows
caspian-native backend build
caspian-native dev --target windows
caspian-native build --target windows

For an Android thin client backed by a deployed Caspian server:

caspian-native init \
  --identifier com.example.myapp \
  --windows --android \
  --remote-url https://app.example.com
caspian-native doctor --target android
caspian-native build --target android

When Android is enabled, init also runs Tauri's non-interactive Android project initializer. dev and build repeat this check and automatically initialize native/gen/android for projects created by an earlier version. The generated tauri.android.conf.json removes the desktop-only Python sidecar from Android builds; Android always loads the configured remote server.

dev --target android starts the current project's standard npm run dev stack and exposes its BrowserSync port only to the connected device through adb reverse. The Android WebView loads BrowserSync's reload client, so Caspian source/public changes use the same coordinated Python restart and refresh flow as desktop browser development. Use --android-backend remote to test the configured deployment instead. Generated Android Rust targets include the linker flags needed for 16 KB page sizes when building with Android NDK r27 or older.

The generated files live under native/. Re-running init never overwrites a changed generated file unless --force is supplied.

Configuration

caspian.native.json is the source of truth:

{
  "$schema": "./caspian.native.schema.json",
  "schema": 1,
  "productName": "My App",
  "identifier": "com.example.myapp",
  "version": "0.0.1",
  "targets": ["windows"],
  "window": {
    "title": "My App",
    "width": 1200,
    "height": 800,
    "resizable": true
  },
  "backend": {
    "desktopMode": "embedded",
    "remoteUrl": null
  },
  "security": {
    "loopbackToken": true
  }
}

Runtime model

Embedded desktop mode builds main.py, the Caspian runtime, project modules, route index, and public/ into a one-file sidecar. The sidecar:

1. restores a per-installation AUTH_SECRET from application data;
2. imports the project's main.app in production mode;
3. binds 127.0.0.1 on an operating-system-assigned port;
4. prints the protected launch URL to the Tauri host;
5. serves the normal Caspian ASGI application with Uvicorn.

The WebView receives a per-launch token once. The native middleware exchanges it for an HttpOnly; SameSite=Strict cookie and refuses documents, assets, RPCs, uploads, streams, and WebSocket handshakes without that cookie.

Caspian's production session cookie normally has the Secure flag. A packaged loopback server intentionally uses http://127.0.0.1, so the adapter changes only that middleware option before Starlette constructs the stack. The app otherwise remains in production mode.

Native bridge

Pages may capability-check window.caspianNative:

const native = window.caspianNative;
if (native?.has("open-external")) {
  await native.invoke("open_external", { url: "https://example.com" });
}

The bridge allowlist is intentionally short: platform, application version, application data directory, external HTTP/HTTPS/mail links, and a user-driven file picker. An XSS can reach every bridge command, so commands must remain safe even when the calling page is compromised.

Current limitations

• The first embedded-backend implementation uses PyInstaller and has only been designed for Windows packaging.
• Dynamic route discovery requires project Python sources and settings/files-list.json to be bundled.
• Secrets from .env are never embedded. Remote database credentials and third-party credentials must be provisioned outside the package.
• Android remote mode requires connectivity and a deployed Caspian server.
• Installer signing and Android store signing are not automated in 0.0.1.