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Gradle's Exec resolves command[0] via the JVM/daemon's inherited PATH, not
the environment("PATH", …) set on the task (that only reaches the spawned
child). A GUI Android Studio launch — and any daemon it starts — has no
~/.cargo/bin on its PATH, so a bare "cargo" fails with "A problem occurred
starting process 'command 'cargo''". Use the already-computed cargoBin
absolute path; the env PATH still lets cargo/cargo-ndk find their subtools.
Also refresh the README prereqs: add the missing cmake;3.22.1 SDK package
(the cmake crate builds libopus with it) and drop the broken
`brew --prefix openjdk@21` JAVA_HOME hint in favour of `java_home -v 21`.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
72 lines
3.7 KiB
Markdown
72 lines
3.7 KiB
Markdown
# punktfunk Android client
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Native Android client for **punktfunk/1**, targeting **phone + TV** (Compose, D-pad + touch).
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## Architecture — Rust-heavy (like the Linux client, not thin-native like Apple)
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Kotlin cannot `import` the cbindgen C header the way Swift can, so a native bridge is unavoidable.
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We write it in **Rust** and link `punktfunk-core` directly — so the Android client reuses the Linux
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client's orchestration (audio jitter ring, VK keymap inverse, latency/skew math, capture state
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machine, trust logic) instead of re-porting it into Kotlin.
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| Side | Owns |
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|------|------|
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| **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 |
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| **Kotlin** (`clients/android`) | Compose UI (host grid / settings / stream), `SurfaceView` lifecycle, input capture, `NsdManager` discovery, Keystore identity, permissions |
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The single seam is `io.unom.punktfunk.kit.NativeBridge` ⇄ `Java_io_unom_punktfunk_kit_NativeBridge_*`.
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## Layout
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```
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clients/android/native/ Rust cdylib (workspace member)
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src/lib.rs JNI_OnLoad + abiVersion/coreVersion (native-link proof)
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src/session.rs session handle lifecycle (connect/close); plane pumps = TODO
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clients/android/ Gradle project (this dir)
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settings.gradle.kts · build.gradle.kts · gradle.properties · gradlew
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app/ :app — Compose application (MainActivity)
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kit/ :kit — Android library: NativeBridge + the cargo-ndk build
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build.gradle.kts cargoNdk{Debug,Release} → src/main/jniLibs/<abi>/*.so
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```
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## Prerequisites
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- Android SDK + **NDK r30** (`30.0.14904198`), `platforms;android-37.0`, `build-tools;37.0.0`,
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**`cmake;3.22.1`** (`sdkmanager "cmake;3.22.1"` — the `cmake` crate builds libopus with it)
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- **JDK 21** for Gradle/AGP (AGP 9.2 runs on JDK 17–21, *not* a newer default JDK like 25)
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- Rust + `rustup target add aarch64-linux-android x86_64-linux-android` + `cargo install cargo-ndk`
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Toolchain pinned: AGP 9.2.0 · Gradle 9.4.1 · Kotlin 2.3.21 · Compose BOM 2026.05.01 ·
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compileSdk 37 · targetSdk 36 · minSdk 31 · ABIs arm64-v8a + x86_64.
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## Build & run
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**Android Studio:** open `clients/android` — it uses its bundled JBR 21 automatically. The
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`cargoNdk*` task builds the `.so` as part of the normal build.
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**CLI** (point Gradle at a JDK 21 if your machine default is newer, e.g. JDK 25):
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```sh
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# Adoptium/Temurin 21 (installed by the Android Studio setup, or `brew install temurin@21`):
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export JAVA_HOME="$(/usr/libexec/java_home -v 21)"
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cd clients/android
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./gradlew :app:assembleDebug # cargo-ndk cross-compiles libpunktfunk_android.so first
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./gradlew :app:installDebug # onto a running emulator/device
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# Emulators (created during env setup): emulator -avd pf_phone | emulator -avd pf_tv
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```
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The debug APK lands in `app/build/outputs/apk/debug/`. The scaffold screen calls
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`NativeBridge.abiVersion()` across JNI — a live ABI version proves the whole native stack is wired.
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## Status
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- **Scaffold (done):** Gradle modules, cargo-ndk wiring, JNI native-link proof, phone+TV-installable
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manifest. `crates/punktfunk-core` `rcgen` switched to the `ring` backend so the client `.so` is
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aws-lc-free.
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- **Next (Android stage 1):** video decode (`AMediaCodec` async → `SurfaceView`), audio
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(Opus + Oboe + jitter ring), input capture → `send_input`, pairing/identity (Keystore-wrapped),
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mDNS discovery, the phone/TV Compose UI. The Rust-side homes are stubbed in
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`clients/android/native/src/session.rs` with port pointers to `clients/linux`.
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