fix(bluetooth-low-energy): add timeout for app discovery

If peripherals are slow to respond when querying services and
characteristics we should drop the connection at some point, otherwise
we end up blocking the scanning for too long.

src/integrations/bluetooth-low-energy/bluetooth-low-energy.service.ts

@@ -26,6 +26,7 @@ import { Sensor } from '../../entities/sensor';
 import { RoomPresenceProxyHandler } from '../room-presence/room-presence.proxy';
 import { BluetoothLowEnergyPresenceSensor } from './bluetooth-low-energy-presence.sensor';
 import { BluetoothService } from '../bluetooth/bluetooth.service';
+import { promiseWithTimeout } from '../../util/promises';
 
 export const NEW_DISTANCE_CHANNEL = 'bluetooth-low-energy.new-distance';
 export const APP_DISCOVERY_CHANNEL = 'bluetooth-low-energy.app-discovery';
@@ -151,22 +152,10 @@ export class BluetoothLowEnergyService
     );
 
     try {
-      const services = await peripheral.discoverServicesAsync([
-        '5403c8a75c9647e99ab859e373d875a7',
-      ]);
-
-      if (services.length > 0) {
-        const characteristics = await services[0].discoverCharacteristicsAsync([
-          '21c46f33e813440786012ad281030052',
-        ]);
-
-        if (characteristics.length > 0) {
-          const data = await characteristics[0].readAsync();
-          return data.toString('utf-8');
-        }
-      }
-
-      return null;
+      return await promiseWithTimeout<string>(
+        BluetoothLowEnergyService.readCompanionAppId(peripheral),
+        15 * 1000
+      );
     } catch (e) {
       this.logger.error(
         `Failed to search for companion app at tag ${tag.id}: ${e.message}`,
@@ -528,4 +517,30 @@ export class BluetoothLowEnergyService
       this.companionAppBlacklist.delete(event.tagId);
     }
   }
+
+  /**
+   * Read companion app ID from a peripheral by looking at the relevant characteristic.
+   *
+   * @param peripheral - peripheral to read from
+   */
+  private static async readCompanionAppId(
+    peripheral: Peripheral
+  ): Promise<string> {
+    const services = await peripheral.discoverServicesAsync([
+      '5403c8a75c9647e99ab859e373d875a7',
+    ]);
+
+    if (services.length > 0) {
+      const characteristics = await services[0].discoverCharacteristicsAsync([
+        '21c46f33e813440786012ad281030052',
+      ]);
+
+      if (characteristics.length > 0) {
+        const data = await characteristics[0].readAsync();
+        return data.toString('utf-8');
+      }
+    }
+
+    return null;
+  }
 }