Syncwagon is an Android application that brings “browse-first, download-later” functionality to mobile devices, similar to Synctrain (Sushitrain). It allows users to browse files located on remote Syncthing peers without synchronizing entire directories, enabling on-demand downloading and selective synchronization.

• Browse-First Paradigm: View remote files without downloading them
• On-Demand Downloads: Download files only when you need them
• Selective Sync: Pin specific files/folders for permanent synchronization
• Hybrid Architecture: Go core (Syncthing protocol) + Android UI (Jetpack Compose)
• Native Performance: Leverages official Syncthing Go implementation via gomobile

• Frontend (Android/Kotlin): Jetpack Compose UI, OS interactions, file I/O, service lifecycle
• Backend (Go/Gomobile): Syncthing protocol implementation, compiled to AAR library
• Communication: JNI/Gomobile bindings between Android and Go layers

/
├── .github/           # GitHub workflows and CI configuration
├── app/               # Android application (Kotlin + Jetpack Compose)
│   └── src/
│       ├── main/      # Main application code
│       ├── test/      # Unit tests
│       └── androidTest/ # Instrumentation tests
├── core/              # Go module (Syncthing wrapper)
│   ├── syncwagon.go   # Core Go implementation
│   ├── go.mod         # Go module definition
│   └── go.sum         # Go dependency checksums
├── docs/              # Documentation
│   └── spec.org       # Technical specification
├── flake.nix          # Nix development environment
├── flake.lock         # Nix dependency lock file
└── todo.org           # Development roadmap and checklist

• Nix (with flakes enabled) - For reproducible development environment
• direnv (optional but recommended) - Automatic environment activation

• Linux or macOS (x86_64 or aarch64)
• ~10GB disk space for dependencies
• Internet connection for initial setup

1. Clone the repository:

   git clone https://github.com/vdemeester/syncwagon.git
   cd syncwagon
       

2. Enter the Nix development environment:

   nix develop
       

   Or, if using direnv:

   direnv allow
       

3. The development environment provides:
   • Go 1.25.4
   • gomobile (installed automatically on first use)
   • JDK 17
   • Android SDK (API 33-34, NDK 26)
   • Gradle 8.14.3
   • Code formatters (gofmt, ktlint)
   • Pre-commit hooks (via git-hooks.nix)

The Nix flake (flake.nix) provides a fully reproducible development environment including:

• Android SDK: Managed via tadfisher/android-nixpkgs
• Pre-commit Hooks: Automatic code formatting via git-hooks.nix
  • Go: gofmt, govet
  • Kotlin: ktlint (when enabled)
  • Standard checks: trailing whitespace, end-of-file fixers

./gradlew assembleDebug

Output: app/build/outputs/apk/debug/app-debug.apk

./gradlew assembleRelease

Output: app/build/outputs/apk/release/app-release-unsigned.apk

cd core
go build -v ./...

./gradlew clean

cd core
go test -v ./...

./gradlew testDebugUnitTest

./gradlew connectedDebugAndroidTest

Note: Requires a connected Android device or emulator.

Pre-commit hooks are automatically installed when you enter the Nix development environment. They run:

• gofmt on Go code
• govet on Go code

To manually run all pre-commit hooks:

git commit --dry-run

cd core
gofmt -l .      # List files that need formatting
go vet ./...    # Run static analysis

ktlint 'app/src/**/*.kt'

./gradlew lint

Reports: app/build/reports/lint-results.html

✅ Completed:

• Nix development environment with Android SDK
• Project structure (Android + Go)
• Basic Android app with Jetpack Compose
• Gradle build configuration
• GitHub Actions CI workflow
• Pre-commit hooks

🚧 In Progress:

• Go-Android bridge integration (gomobile)
• Core Syncthing protocol implementation

📋 Planned:

• File browser UI
• On-demand download functionality
• Selective sync (pinning)
• Background service

See todo.org for detailed development roadmap.

• Technical Specification - Detailed architecture and requirements
• Development TODO - Phase-by-phase implementation checklist
• Syncthing Documentation - Official Syncthing protocol docs

This project follows a structured development approach:

1. Read the spec: docs/spec.org contains the full technical specification
2. Check the TODO: todo.org tracks current and planned work
3. Development workflow:
   • Use nix develop for a consistent environment
   • Pre-commit hooks ensure code quality
   • CI runs on all pull requests
   • Sign your commits (git commit --signoff)

[License information to be added]

• Syncthing - The underlying synchronization protocol
• Sushitrain - Inspiration for the browse-first paradigm
• android-nixpkgs - Nix-based Android SDK management