P2P-Chat

Multi-platform P2P chat app using libp2p and Rust.

Modules

What Works

• Desktop <-> Android chat over TCP (direct dial, fixed port 53493).
  Messages are exchanged on topic chat. mDNS is enabled but unreliable on some networks, so Android dials the desktop's hardcoded IP.

• Desktop node listens on both TCP (port 53493) and WebRTC (port 9090/udp).
  Android uses TCP only.

• Android app loads native .so libraries built from Rust-Core; JNI symbols exported correctly with #[unsafe(no_mangle)] and --export-dynamic.
  The app works reliably between two Android devices (via mDNS) or between Android and desktop (via direct dial).

• Web-React UI is functional, Tailwind CSS works, Vite serves WASM module correctly.
  The browser dials the desktop's WebRTC address and initiates a connection.

• Web-WASM compiles to WASM and runs in the browser. It creates a libp2p swarm with WebRTC transport, subscribes to chat, and polls events.

Not Yet Working

• Browser <-> desktop chat via WebRTC – the connection fails during the DTLS handshake.
  Logs show:ICE connection state changed: connected Failed to start manager dtls: invalid named curve

This is caused by a known bug in the webrtc-rs crate (webrtc-rs/webrtc#417).
The browser sends a list of supported elliptic curves; the current Rust implementation only checks the first one and rejects the handshake if it's not recognised - even though the list also contains P-256 / P-384 / X25519, which are supported.

Planned Fix (Next Steps)

1. Upgrade libp2p-webrtc to a version that includes the fix from webrtc-rs v0.13.0 (once it is published on crates.io).

Alternatively patch the dependency locally using a fork or a path override.

2. Fallback to WebSocket transport – if WebRTC remains unstable, add a WebSocket listener on the desktop and use libp2p-websocket-websys in the browser. WebSockets are more stable for browser-to-server connections and still allow P2P via the same gossipsub overlay.

3. Remove hardcoded IP addresses – add a simple UI to input the desktop's address (or use mDNS in the browser via WebRTC signalling).

How to Run

Desktop Node

cd Rust-Core
cargo run

The node prints its TCP and WebRTC listen addresses. Use the WebRTC address (including the certhash) for the browser client.

Android App

cd Android-Kotlin
./gradlew assembleDebug
adb install -r app/build/outputs/apk/debug/app-debug.apk

• Ensure the desktop IP (192.168.1.6) is correct in Rust-Core/src/ffi/mod.rs.
• Rebuild the native library if the IP changes: bash build-android.sh.

Web App

cd Web-WASM
wasm-pack build --target web --out-dir ../Web-React/src/wasm

cd ../Web-React
npm install
npm run dev

• Update DESKTOP_WEBRTC_ADDR in src/App.tsx to the desktop’s WebRTC address (including the certhash).

Notes

• The .gitignore excludes node_modules/, dist/, and generated .so / .wasm files.
• The Android-Kotlin/app/src/main/jniLibs/ directory is ignored; native libraries must be rebuilt with build-android.sh.
• The desktop IP is currently hardcoded – change it in Rust-Core/src/ffi/mod.rs (for Android) and Web-React/src/App.tsx (for Web) when the laptop’s IP changes.