Vato

Minimal Android chat client for a local LLM. A tiny Java WebView app ships a chat UI that talks to a Rust proxy exposing an OpenAI-compatible API; the proxy shells out to the local omp CLI to run the model. No cloud, no SDK/Gradle — just aapt2/javac/d8 + cargo.

Architecture

┌────────────────────────┐   HTTP    ┌──────────────────────┐  spawns  ┌──────────────┐
│ Android WebView (Java) │ ────────► │ vato-proxy (Rust)    │ ───────► │ omp CLI      │
│  assets/index.html     │  /v1/...  │  :8080               │          │ (model:      │
│  chat UI               │ ◄──────── │  OpenAI-compat API   │ ◄─────── │  unqwen)     │
└────────────────────────┘           └──────────────────────┘          └──────────────┘

1. Android app (src/com/vato/qwenchat/MainActivity.java) — single Activity wrapping a WebView that loads the bundled chat UI (assets/index.html). Handles file upload (onShowFileChooser), downloads, and back-navigation.
2. WebView UI posts to /v1/chat/completions; server URL is selectable via chips (Tailscale / LAN / localhost) in the UI.
3. vato-proxy (server/) — stdlib-only Rust (no async runtime). Exposes:
   • GET /v1/models — model listing
   • POST /v1/chat/completions — builds a prompt (system + recent history + user msg) and runs omp -p --model unqwen -e extensions/sqz.ts, returning a clean reply.

Layout

Path	What
AndroidManifest.xml	package com.vato.qwenchat, minSdk 24, targetSdk 34
src/com/vato/qwenchat/MainActivity.java	WebView host + file chooser / download handling
assets/index.html	bundled chat UI (the page the WebView loads)
server/src/main.rs	vato-proxy — OpenAI-compat HTTP → omp bridge
build.sh	aapt2 → javac → d8 → zipalign → apksigner pipeline

Prerequisites & Setup (Fresh System)

1. Backend Proxy (vato-proxy)

• Rust & Cargo: 1.70+ (curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh)
• C compiler / headers: gcc / clang / build-essential (for libc bindings)
• OMP CLI: omp installed and available in $PATH (or specified via OMP_BIN)
• Model: A working model configured in omp (defaults to unqwen, override with VATO_MODEL=<name>)

2. Android APK Build

No Android Studio or Gradle needed — builds entirely via standard CLI tools:

• JDK 17+ or 21: javac and keytool in $PATH or $JAVA_HOME/bin
• Android SDK: Set ANDROID_HOME (defaults to ~/.android/sdk):
  • Platform: platforms/android-34/android.jar
  • Build Tools: build-tools/34.0.0 (must contain aapt2, d8, zipalign, apksigner)
• Utilities: bash, zip, du

Install Android SDK CLI components via sdkmanager:

sdkmanager "platforms;android-34" "build-tools;34.0.0"

3. Android Client Device

• Android 7.0+ (API 24+) phone or emulator
• Connected to the same local Wi-Fi or Tailscale network as your host

---

Build & Run

1. Start the proxy:

cd server && cargo run --release   # listens on port 8080

2. Build the APK:

./build.sh   # builds vato.apk; generates debug keystore automatically on first run

3. Install on phone:

adb install -r vato.apk
# Or navigate to http://<host-ip>:8080/download on your phone's browser

Config knobs

• Model / omp path: OMP_BIN, VATO_MODEL environment variables (defaults: omp, unqwen).
• Default server the app dials: DEFAULT_SERVER in assets/index.html (configurable via in-app Settings).

Security & Network Exposure

vato-proxy binds across all local IPv4 interfaces on port 8080 with Access-Control-Allow-Origin: * and no authentication. Incoming prompts are forwarded directly to omp.

• Local LAN / Tailscale only: Designed strictly for a trusted local home Wi-Fi or private Tailscale VPN.
• Do not expose to public internet: Never port-forward port 8080 or run vato-proxy on a public IP (e.g., VPS / cloud host) without an authenticating reverse proxy.
• Shared Wi-Fi warning: On untrusted or public Wi-Fi networks (cafes, dorms, coworking spaces), other devices on the same subnet can reach the proxy and trigger queries.