margin-calendar/docs/mobile.md

Android and iOS

The same Rust core and the same React app, with a different shape of chrome and a different way of getting a token back from Google. Nothing is forked: the layout switches on a data-phone attribute and the OAuth flow switches on cfg(mobile).

Google will not let you reuse the desktop client

This is the part that cannot be automated away, so do it first or nothing will sign in.

Google issues OAuth clients per platform and refuses one in another's place. The desktop client redirects to a loopback port; Google rejects loopback redirects for Android and iOS client types outright, and iOS will not dependably keep a listener alive to catch one anyway. So a phone build redirects to a custom URI scheme instead, and needs its own client to do it.

Both mobile clients are public: no client secret exists, and PKCE is the only thing between an intercepted authorization code and a token. That is why the verifier is not optional anywhere in auth.rs.

In the Google Cloud console, on the same project that already has the Calendar API enabled:

1. Create an OAuth client of type Android. It wants the package name, which is studio.margin.calendar, and the SHA-1 fingerprint of the certificate that signs the build. For a debug build that is the shared debug keystore:

   keytool -list -v -keystore ~/.android/debug.keystore \
     -alias androiddebugkey -storepass android -keypass android
   

   A release build is signed with a different key and needs its fingerprint added too. An APK signed by a key Google has not been told about fails at consent, not at build.

2. Create an OAuth client of type iOS. It wants the bundle identifier, which is also studio.margin.calendar.

3. Put both client ids in google-credentials.json alongside the desktop one, matching google-credentials.example.json:

   {
     "installed": { "client_id": "...", "client_secret": "...", "...": "..." },
     "android": { "client_id": "YOUR_ANDROID_CLIENT_ID.apps.googleusercontent.com" },
     "ios": { "client_id": "YOUR_IOS_CLIENT_ID.apps.googleusercontent.com" }
   }
   

   The file is gitignored and embedded at build time. A build with no android or ios block compiles and then says so at runtime rather than failing to compile, which is the same bargain the desktop client already had.

The redirect schemes

Android redirects to studio.margin.calendar:/oauth2redirect. That is the package name, which is Google's documented form for an Android client, and being known at build time means it can sit in AndroidManifest.xml permanently rather than being pasted in per install.

iOS gets no such choice. Google requires the reversed client id, so the scheme is only knowable once your client id is: take the client id, drop the .apps.googleusercontent.com suffix, and prefix com.googleusercontent.apps..

Register it in src-tauri/tauri.conf.json, as a second entry in the deep link plugin's scheme list:

"deep-link": {
  "desktop": { "schemes": ["studio.margin.calendar"] },
  "mobile": [{ "scheme": ["studio.margin.calendar", "com.googleusercontent.apps.YOUR_ID"] }]
}

Not in Info.plist. Editing that by hand looks like it works and then silently stops working: the plugin's build script rewrites CFBundleURLTypes wholesale from this config on every build, and when the mobile array is empty it deletes the key outright. That one empty array is why the callback was dead on both platforms at first, so if a deep link ever stops arriving, look here before anywhere else.

If the console shows you something different from either default, put it in the client's block in google-credentials.json as redirect_uri and it wins over both. Whatever you put there still has to have its scheme registered above, or the OS has no reason to hand the link to this app.

Toolchain

iOS needs Xcode and the iOS Rust targets:

rustup target add aarch64-apple-ios aarch64-apple-ios-sim x86_64-apple-ios

Android needs the SDK, an NDK of r25 or newer, a JDK that the generated Gradle build accepts (21 works, 25 does not), and the four Android Rust targets:

rustup target add aarch64-linux-android armv7-linux-androideabi i686-linux-android x86_64-linux-android
export ANDROID_HOME=/opt/homebrew/share/android-commandlinetools
export NDK_HOME=$ANDROID_HOME/ndk/27.2.12479018
export JAVA_HOME=/opt/homebrew/opt/openjdk@21

Building

pnpm tauri ios init          # once, generates the Xcode project
pnpm tauri ios dev           # simulator, with the Vite dev server
pnpm tauri ios build

pnpm tauri android init      # once, generates the Gradle project
pnpm tauri android dev       # emulator or attached device
pnpm tauri android build

The generated projects are committed. Re-running init overwrites them, so check afterwards that MainActivity.kt still publishes the window insets, since nothing else on Android does.

Both dev commands start Vite themselves and fail outright if port 1430 is already taken, which it will be if a browser dev server is still up. Kill it, or pass a different port through --config.

Three failures that look like bugs and are not. Xcode refusing to build with "Entitlements file was modified during the build" is a stale mtime in DerivedData, fixed once by deleting ~/Library/Developer/Xcode/DerivedData/margin-calendar-*. An Android run panicking with "failed to build WebSocket client, Connection refused" is a stale $TMPDIR/studio.margin.calendar-server-addr pointing at a dead port; delete it. And an emulator that will not boot by name usually means avdmanager and emulator disagree about where AVDs live, which ANDROID_AVD_HOME settles.

Finally, an empty calendar on a device is correct. The browser fixture is gated on not being inside Tauri, so on a phone the real backend answers and there is nothing to show until an account is connected. Events without signing in only ever happen in a browser.

What is different on a phone

The desktop header carries three groups of controls across one row, which does not fit in 390 points. Under data-phone it becomes a top bar with the date and the day arrows and a bottom tab bar with the views, and everything the trailing icon row used to hold moves into an overflow sheet. Overlays become bottom sheets. Both bars pad themselves out of the way of the notch and the home indicator with env(safe-area-inset-*).

Under data-touch, which a tablet gets and a narrow desktop window does not, interaction changes rather than layout. Anything that only appeared on hover is always visible instead, because a finger cannot hover. Dragging out a new event waits for a long press, because on a touchscreen the alternative is that every tap on an empty afternoon starts creating something.

Navigation still moves one day at a time. A swipe is one day, not one week.

Both attributes are also set by the boot script in index.html before first paint, so a phone does not render the desktop layout for a frame and then jump.

Keeping out from under the system bars

--safe-top and --safe-bottom are env(safe-area-inset-*) by default, which is correct on iOS and wrong on Android in a way that is easy to miss. Android's WebView derives those values from the display cutout alone and never from the system bars, so it reports 0 at the bottom while the navigation bar really occupies 24dp of gesture pill or 48dp of buttons, and the tab bar renders underneath it. targetSdk is 36, so edge-to-edge is mandatory and there is nothing to opt out of. The top only looked right on a test device by luck, because that device had a cutout; a phone without one would have tucked the top bar under the status bar for the same reason.

So Android measures the bars natively. MainActivity.kt reads systemBars() or displayCutout() from WindowInsetsCompat, exposes them over a JavaScript bridge, and re-fires on every inset change, which covers rotation, the keyboard, and switching between gesture and button navigation live. src/safeArea.ts converts device pixels to CSS pixels and writes the two variables onto the root, where they beat the env() defaults. Off Android the bridge is simply absent and the defaults stand, so iOS and desktop are untouched.

Two consequences worth knowing. tauri android init regenerates MainActivity.kt, and nothing else on Android supplies these values, so check the bridge is still there after re-running it. And installing the inset listener makes env(safe-area-inset-*) read 0 inside that WebView, which does not matter only because those two token lines are the sole consumers and the bridge overrides both with better numbers. Anything new that reaches for env() directly on Android will get zero.

iOS needed one line of native code for the same class of problem, in the opposite direction.

UIKit hands a scroll view the safe areas as content insets unless told otherwise, and wry never tells it otherwise: it touches the scroll view only to switch bounces off. WebKit then lays the page out in what is left. On an iPhone 17 Pro that meant a layout viewport 778pt tall against an 874pt screen, still anchored at y 0, so the bottom 96pt of the display was outside the page altogether and showed as a dead band of shell colour under the tab bar. body is position: fixed, so nothing could paint down there whatever the stylesheet said.

stop_uikit_shrinking_the_viewport in lib.rs sets contentInsetAdjustmentBehavior to never through with_webview, which gives the page the whole screen back. The insets are not lost, they arrive as env(safe-area-inset-*) instead, which is where both bars already read them from.

Worth knowing before anyone tries to solve that in CSS, because it looks like a CSS problem and the obvious fix is worse than the bug. While the viewport was short, 100dvh was the only unit reporting the real box; vh, svh and lvh all reported the full screen. Sizing the root 100svh therefore did not reclaim the bottom of the screen, it laid the tab bar out past the clip where it was invisible and, less obviously, untappable. The root is height: 100%, which inherits whatever the box is and cannot drift if the native line ever regresses.

Limits worth knowing

There is no auto-updater and no process restart on mobile: the store is the update channel, and both plugins are compiled out rather than merely hidden.

The initial sync pulls the whole calendar history, because Google forbids timeMin alongside a syncToken. That is already the desktop behaviour and it is slower on a phone radio.