CoLink Android

Android client for CoLink — clipboard sync, file transfer, text messaging, and CastBoard display.

Tech stack: Kotlin 2 · Jetpack Compose (Material 3) · Hilt · OkHttp/Retrofit · Ktor CIO · Room · Bouncy Castle · Android NSD

Requirements

• Android Studio Hedgehog or later
• JDK 21
• Android SDK: compileSdk 36, minSdk 26

Setup

Create local.properties in the project root:

SERVER_BASE_URL=https://sync.colink.evative7.host
# Optional: point to a local CastBoard dev server
# CASTBOARD_DEV_URL=http://10.0.2.2:5173

Build

# Debug build (app ID: com.colink.android.debug)
./gradlew assembleDebug
./gradlew installDebug

# Release build (app ID: com.colink.android)
./gradlew assembleRelease

Release builds require signing config in local.properties:

KEYSTORE_FILE=release.jks
KEYSTORE_PASSWORD=...
KEY_ALIAS=...
KEY_PASSWORD=...

Architecture

The app runs a persistent foreground service (CoLinkService) that maintains both LAN (mDNS + WebSocket) and cloud (WebSocket relay) connections simultaneously.

• LAN discovery: Android NSD (mDNS)
• LAN crypto: Ed25519 identity, X25519 ECDH + HKDF-SHA256 session key, AES-256-GCM / ChaCha20-Poly1305
• CastBoard: embedded WebView loading bundled assets from app/src/main/assets/castboard/