punktfunk/clients/android/README.md

punktfunk Android client

Native Android client for punktfunk/1, targeting phone + TV (Compose, D-pad + touch).

Architecture — Rust-heavy (like the Linux client, not thin-native like Apple)

Kotlin cannot import the cbindgen C header the way Swift can, so a native bridge is unavoidable. We write it in Rust and link punktfunk-core directly — so the Android client reuses the Linux client's orchestration (audio jitter ring, VK keymap inverse, latency/skew math, capture state machine, trust logic) instead of re-porting it into Kotlin.

Side	Owns
Rust (clients/android/native → libpunktfunk_android.so)	the JNI seam, NativeClient (QUIC control + UDP data plane), AnnexB→AMediaCodec decode, Opus+Oboe audio, VK keymap, latency math, trust/pairing
Kotlin (clients/android)	Compose UI (host grid / settings / stream), SurfaceView lifecycle, input capture, NsdManager discovery, Keystore identity, permissions

The single seam is io.unom.punktfunk.kit.NativeBridge ⇄ Java_io_unom_punktfunk_kit_NativeBridge_*.

Layout

clients/android/native/          Rust cdylib (workspace member)
  src/lib.rs                       JNI_OnLoad + abiVersion/coreVersion (native-link proof)
  src/session.rs                   session handle lifecycle (connect/close); plane pumps = TODO

clients/android/                   Gradle project (this dir)
  settings.gradle.kts · build.gradle.kts · gradle.properties · gradlew
  app/                             :app — Compose application (MainActivity)
  kit/                             :kit — Android library: NativeBridge + the cargo-ndk build
    build.gradle.kts               cargoNdk{Debug,Release} → src/main/jniLibs/<abi>/*.so

Prerequisites (already set up on the dev Mac)

• Android SDK + NDK r30 (30.0.14904198), platforms;android-37.0, build-tools;37.0.0
• JDK 21 for Gradle/AGP (the machine default JDK 25 is too new for AGP 9.2)
• Rust + rustup target add aarch64-linux-android x86_64-linux-android + cargo install cargo-ndk

Toolchain pinned: AGP 9.2.0 · Gradle 9.4.1 · Kotlin 2.3.21 · Compose BOM 2026.05.01 · compileSdk 37 · targetSdk 36 · minSdk 31 · ABIs arm64-v8a + x86_64.

Build & run

Android Studio: open clients/android — it uses its bundled JBR 21 automatically. The cargoNdk* task builds the .so as part of the normal build.

CLI (the machine default is JDK 25, so point Gradle at JDK 21):

export JAVA_HOME="$(brew --prefix openjdk@21)/libexec/openjdk.jdk/Contents/Home"
cd clients/android
./gradlew :app:assembleDebug      # cargo-ndk cross-compiles libpunktfunk_android.so first
./gradlew :app:installDebug       # onto a running emulator/device

# Emulators (created during env setup):  emulator -avd pf_phone   |   emulator -avd pf_tv

The debug APK lands in app/build/outputs/apk/debug/. The scaffold screen calls NativeBridge.abiVersion() across JNI — a live ABI version proves the whole native stack is wired.

Status

• Scaffold (done): Gradle modules, cargo-ndk wiring, JNI native-link proof, phone+TV-installable manifest. crates/punktfunk-core rcgen switched to the ring backend so the client .so is aws-lc-free.
• Next (Android stage 1): video decode (AMediaCodec async → SurfaceView), audio (Opus + Oboe + jitter ring), input capture → send_input, pairing/identity (Keystore-wrapped), mDNS discovery, the phone/TV Compose UI. The Rust-side homes are stubbed in clients/android/native/src/session.rs with port pointers to clients/linux.