ShareThing

ShareThing is a privacy-first peer-to-peer file sharing client split into a Flutter UI and platform-specific libp2p nodes.

Architecture

• ui/
  • Flutter UI, persistent state, and process orchestration
  • stores config and local friend data as JSON files
  • does not perform peer discovery, transport negotiation, or file byte streaming
• engine/
  • legacy Kotlin JVM desktop node source
  • communicates with Flutter over newline-delimited JSON on stdin/stdout
• p2pbridge/
  • Go libp2p implementation used by Android and desktop
  • exposes the shared node runtime plus a native desktop executable

JSON Contract

Flutter sends newline-delimited JSON commands to the node layer. The primary command types are:

• START_NODE
• STOP_NODE
• SEND_FILE
• ACCEPT_FILE
• REJECT_FILE

The node emits JSON events back to Flutter. The primary event types are:

• NODE_STARTED
• PEER_DISCOVERED
• PEER_NICKNAME_CHANGED
• INCOMING_FILE_REQUEST
• TRANSFER_UPDATE

Storage

Client data is stored in platform-appropriate application directories:

• Linux
  • config: ~/.config/sharething/
  • data: ~/.local/share/sharething/
• Windows
  • config: %APPDATA%\\ShareThing\\
  • data: %LOCALAPPDATA%\\ShareThing\\
• macOS
  • ~/Library/Application Support/ShareThing/
• Android
  • app-specific support/data directories

Current State

• Desktop node startup and identity persistence are wired.
• Flutter friend/config storage is file-backed JSON.
• Dart-side LAN networking and Dart-side file streaming were removed to restore the intended architecture boundary.
• SEND_FILE, ACCEPT_FILE, and REJECT_FILE are part of the shared contract, but full node-side transfer handling is not implemented yet.

Build

Desktop Engine

cd p2pbridge
./build.sh

Flutter UI

Use fvm:

cd ui
fvm flutter analyze
fvm flutter test
fvm flutter build linux

Building the Android Engine (go-libp2p)

Android does not support JVM-based libp2p, so a separate Go bridge is used instead. This must be built once and copied into the Flutter project before running on Android.

1. Install Go

Download and install Go from https://go.dev/dl/ (1.21 or newer). go get github.com/libp2p/go-libp2p@v0.38.1

2. Install gomobile

go install golang.org/x/mobile/cmd/gomobile@latest
gomobile init

3. Build the .aar

cd p2pbridge
gomobile bind -target android/arm64 -androidapi 21 -o p2p.aar .

This produces two files: p2p.aar and p2p-sources.jar.

4. Copy into the Flutter project

cp p2p.aar ../ui/android/app/libs/
cp p2p-sources.jar ../ui/android/app/libs/

Desktop Packaging

The desktop app now launches a native Go executable from ui/assets/engine/. Development builds look for p2pbridge/build/p2p_engine[.exe] first, then fall back to the bundled Flutter asset.

The desktop engine should always be built with CGO_ENABLED=0 so the resulting binary is statically linked and can replace the previous jar-based package cleanly.