Proof-of-Concept: extract GAN smart cube MAC address using Web Bluetooth

gan-connect-poc.ts

/**
 * 
 * Proof-of-Concept: extract GAN smart cube MAC address using Web Bluetooth.
 * MAC address resides at last 6 bytes in Manufacturer Specific Data field 
 * of the bluetooth advertising packet.
 * 
 * In order for this to work it is necessary to enable following flag in Chrome:
 * 
 * chrome://flags/#enable-web-bluetooth-new-permissions-backend
 * 
 */

const BT_GAN_MANUFACTURER_ID: number = 0x0001;
const BT_GAN_SERVICES = ['6e400001-b5a3-f393-e0a9-e50e24dc4179'];

export interface GanConnection {
    device?: BluetoothDevice;
    server?: BluetoothRemoteGATTServer;
    deviceName?: string;
    deviceMAC?: string;
}

// Extract MAC from last 6 bytes of Manufacturer Specific Data
function extractMAC(manufacturerData: BluetoothManufacturerData): string {
    var mac: Array<string> = [];
    var dataView = manufacturerData.get(BT_GAN_MANUFACTURER_ID);
    if (dataView && dataView.byteLength > 6) {
        for (let i = 1; i <= 6; i++) {
            mac.push(dataView.getUint8(dataView.byteLength - i).toString(16).padStart(2, '0'));
        }
    }
    return mac.join(':');
}

// Wait for single advertising packet from device
async function waitForAdvertismentFromDevice(bluetoothDevice: BluetoothDevice): Promise<BluetoothAdvertisingEvent> {
    return new Promise<BluetoothAdvertisingEvent>((resolve) => {
        var abortController = new AbortController();
        bluetoothDevice.addEventListener("advertisementreceived", (advertisingEvent) => {
            abortController.abort();
            resolve(advertisingEvent);
        });
        bluetoothDevice.watchAdvertisements({ signal: abortController.signal });
    });
}

export async function connectToGANCube(): Promise<GanConnection> {

    var conn: GanConnection = {};

    // Request user for the bluetooth device (popup selection dialog)
    conn.device = await navigator.bluetooth.requestDevice(
        {
            filters: [{ namePrefix: "GAN" }],
            optionalServices: BT_GAN_SERVICES,
            optionalManufacturerData: [BT_GAN_MANUFACTURER_ID]
        }
    );

    // Wait for advertising packet from requested device
    var advEvt = await waitForAdvertismentFromDevice(conn.device);
    conn.deviceName = advEvt.name;
    conn.deviceMAC = extractMAC(advEvt.manufacturerData);

    // Connect to GATT server
    conn.server = await conn.device.gatt?.connect();
    return conn;

}