Getting started

Install

flutter pub add dart_libp2p_ble

The package needs Flutter 3.24 or later and dart_libp2p 4.10.0 or later. It runs on Android, iOS and macOS. It is a Flutter package, because the Bluetooth plugin is: a plain Dart program can use only the in-memory radios.

Before the first run, add the Bluetooth permissions and usage descriptions for each platform. Platforms lists them.

A host on Bluetooth LE

Give the host a BleTransport and listen on its address. The transport needs your peer ID, because it publishes it to nearby devices.

final keyPair = await generateEd25519KeyPair();
final peerId = PeerId.fromPublicKey(keyPair.publicKey);
final ble = BleTransport(radio: BluetoothLowEnergyRadio(), localPeer: peerId);
final host = await Libp2p.new_([
  Libp2p.identity(keyPair),
  Libp2p.transport(ble),
  Libp2p.listenAddrs([ble.listenAddr]), // /ble/<token>
  // No IP network: turn off the NAT and relay services.
  Libp2p.autoNAT(false),
  Libp2p.relay(false),
  Libp2p.autoRelay(false),
  Libp2p.holePunching(false),
]);
await host.start();
print('listening on ${ble.listenAddr}');

Three things matter here:

• The listen address is /ble/<token>. The token is 6 random characters, new each time the transport is made. Listening starts the GATT service and advertises the token.
• The NAT and relay services are off. They need an IP network. With only BLE, they have nothing to do.
• BLE can be one of several transports. Add TCP or UDX too, and the host uses BLE for /ble addresses and the others for IP addresses.

Connect to nearby devices

BleDiscovery scans for other nodes and connects to them. peerFound tells you about each new peer it connects to:

final discovery = BleDiscovery(host: host, transport: ble);
discovery.peerFound.listen((peer) async {
  final result = await PingService(host).ping(peer).first;
  print('ping ${peer.toBase58()}: ${result.rtt?.inMilliseconds} ms');
});
await discovery.start();

Run the app on two devices, near each other:

listening on /ble/k3vq7m
ping 12D3KooW…: <round trip> ms

peerFound only reports the peers that this node dialed. When the other node dials first, watch the host’s network instead (host.network.peers, or the EvtPeerConnectednessChanged event).

Without discovery

If you already know a nearby node’s token and peer ID (from a QR code, say), dial it as any other address:

await host.connect(AddrInfo(peerId, [MultiAddr('/ble/k3vq7m')]));

The device must be in range and advertising. The radio scans for the token and connects.

Next

• Platforms: permissions, and what to expect on each platform.
• Discovery: build a mesh, and tune when nodes dial.