FileSync

Mobile Screen	Desktop Screen

A cross-platform Flutter app for sharing and syncing folders between nearby devices over a local network — no internet connection or cloud account required.

How it works

FileSync uses mDNS (via Bonsoir) to automatically discover other devices running the app on the same network. Each device runs a lightweight HTTP server on port 4000 that exposes its shared folders. When you sync, only files you don't already have are downloaded — existing files are sent as an exclusion list so the remote device can zip and serve only what's missing.

Device A Device B
──────── ────────
Share folder ──── mDNS discovery ──▶ See Device A
Browse folders
◀─── HTTP sync ───────── Download new files

Features

• Automatic device discovery — finds other FileSync devices on your LAN via mDNS, no manual IP entry needed
• Folder sharing — choose any local folder to expose to nearby devices
• Incremental sync — only missing files are downloaded; existing files are skipped
• Background downloads — syncs run in the background with progress notifications
• Cross-platform — Android, iOS, Windows, Linux, and macOS
• No cloud dependency — everything stays on your local network

Getting started

Prerequisites

• Flutter SDK ≥ 3.41.0 (Dart SDK ^3.11.1)
• Devices must be on the same Wi-Fi or local network

Install dependencies

flutter pub get

Run code generation (required for Drift database)

dart run build_runner build

Run the app

flutter run

Building for release

The repository includes a GitHub Actions workflow (.github/workflows/build_release.yml) that builds and publishes releases for Android, iOS, Windows, and Linux.

Trigger a release by pushing a version tag:

git tag v1.0.0
git push origin v1.0.0

Or trigger a manual build from the Actions tab, selecting your target platforms.

Required secrets (set in repo Settings → Secrets)

Secret	Description
ANDROID_KEYSTORE_BASE64	Base64-encoded JKS/PKCS12 keystore
ANDROID_KEY_ALIAS	Key alias inside the keystore
ANDROID_KEY_PASSWORD	Key password
ANDROID_STORE_PASSWORD	Store password
IOS_CERTIFICATE_BASE64	Base64-encoded .p12 distribution certificate
IOS_CERTIFICATE_PASSWORD	.p12 password
IOS_PROVISION_PROFILE_BASE64	Base64-encoded .mobileprovision
IOS_TEAM_ID	Apple developer team ID (10 characters)
IOS_BUNDLE_ID	e.g. com.yourcompany.filesync

Project structure

lib/
├── main.dart # App entry point; starts mDNS broadcast and HTTP server
├── constants.dart # App-wide constants (port, service type, DB name)
├── models/
│ ├── database.dart # Drift database schema (shared folders table)
│ ├── discovery.dart # mDNS discovery state machine
│ └── remote_folder.dart # Remote folder model
├── services/
│ ├── app_broadcast_service.dart # Registers and broadcasts this device via mDNS
│ ├── http_server.dart # Shelf HTTP server (runs in a background isolate)
│ └── sync_service.dart # Sync logic: fetch folder list, diff, download, extract
├── providers/ # Riverpod providers
├── pages/
│ ├── nearby_devices.dart # Discover and list nearby FileSync devices
│ ├── nearby_device.dart # Browse a specific device's shared folders
│ └── shared_folders.dart # Manage your own shared folders
├── widgets/ # Reusable UI components
├── router/ # go_router navigation
├── theme/ # Light and dark themes
└── utils/ # Path normalisation, sorting, folder opening

Key dependencies

Package	Purpose
bonsoir	mDNS device discovery and broadcast
shelf + shelf_router	Embedded HTTP server
drift	Local SQLite database for shared folder registry
flutter_riverpod	State management
background_downloader	Background file downloads with progress notifications
archive	Zip creation (server side) and extraction (client side)
go_router	Declarative navigation

HTTP API

The embedded server exposes two endpoints on port 4000:

Method	Path	Description
GET	/shared-folders	Returns { id: name } map of all shared folders
POST	/shared-folders/<id>/sync	Streams a zip of the folder, excluding paths provided in the request body

The sync endpoint accepts an optional JSON array (or object with path keys) of relative file paths that the client already has. These are excluded from the zip, so only new or missing files are transferred.

Permissions

Android requires the following permissions (declared in AndroidManifest.xml):

• INTERNET — network communication
• MANAGE_EXTERNAL_STORAGE — reading and writing files outside app-private storage
• POST_NOTIFICATIONS — download progress notifications

On first sync the app will request storage and notification permissions at runtime.

License

MIT