BLE events still triggered after SensorArray stop

[marcuspridham]

Describe the bug

After calling SensorArray stop, there is still ConcreteBLETransmitter and ConcreteBLEReceiver events. The underlying CBCentralManager and CBPeripheralManager are still calling the delegate methods hooked up to them.

Logs taken from device with SensorArray stopped:

2021-05-28 17:10:21.471899-0400 Herald-for-iOS[887:243757] [BLE.ConcreteBLETransmitter] didReceiveWrite (central=39FBFF6F-7306-586E-793E-87B2A6FDB272)

2021-05-28 17:10:55.173120-0400 Herald-for-iOS[887:244035] [BLE.ConcreteBLEReceiver] taskInitiateNextAction (goal=characteristics,device=BLEDevice[id=39FBFF6F-7306-586E-793E-87B2A6FDB272,os=ios,payload=YryXEA,address=nil])

A clear and concise description of what the bug is.

Smartphone and App information (REQUIRED):

• Device: iPhone 6, iPhone 7
• OS exact version: iOS 14.4.2, iOS 14.5
• Herald demonstration app version: latest develop branch
• Have you reproduced this issue on the latest 'develop' Herald branch?: Yes

To Reproduce

Steps to reproduce the behavior:

1. Open Herald demonstration app on 2 iPhones.
2. Click the Personal Phone link on both phones in the app.
3. Click on toggle in the top right on ONE of the phones (ideally one with XCode attached) to turn off the sensor array.
4. Notice that the XCode logs still show ConcreteBLETransmitter and ConcreteBLEReceiver events.
5. Kill and start the demonstration app on the other phone (should clear the BLEDatabase). Notice: That the detection and read information information across the phones is still updated even though the one has the Sensor Array off. The phones are still seeing each other.

Expected behavior

• BLE events to stop on the phone with Sensor Array stopped.

[wmthornton]

I'm wondering if this has something to do with the implementation of AirTags and the "Find My" feature in the latest iOS versions.... Since the AirTags rely on a consistent BLE connection to transmit data across the "Find My" network, is it possible that the BLE APIs were changed in a way that is causing the issues here?

[adamfowleruk]

Information from our investigation. Not a bug therefore.

For iOS devices, while Bluetooth is ON, the advertiser will continue to function to handle read/write/notify events with another recently connected iOS device, despite a call to peripheral.stopAdvertising() until either device changes BLE address, or switches Bluetooth OFF. This is an undocumented behaviour of the iOS BLE API covering at least iOS 9.3 - 14.2. Herald manages this by absorbing the internal events (wakeTransmitter, readPayload) and suppresses callbacks to SensorArray delegates, until these events cease due to BLE address change (circa 15 minutes). In short, on SensorArray.stop(), Herald should not generate any callbacks to the SensorArray delegates, but the log may show internal BLE activities for some time.

For investigation, additional logging was introduced to ConcreteBLETransmitter. The log shows SensorArray.stop() has correctly stopped the BLE central and peripheral. The test does also show calls to didReceiveWrite and didReceiveRead from the recently connected iOS device, however a scan using another device running nRF Connect app confirms the advert has stopped, and no delegate calls were generated by these activities.

2021-04-24 11:45:21.047592+0100 Herald-for-iOS[232:5717] [SensorArray] stop
2021-04-24 11:45:21.052020+0100 Herald-for-iOS[232:5717] [ConcreteMobilitySensor] stop
2021-04-24 11:45:21.056756+0100 Herald-for-iOS[232:5717] [ConcreteMobilitySensor] stopUpdatingLocation
2021-04-24 11:45:21.060800+0100 Herald-for-iOS[232:5717] [ConcreteMobilitySensor] stopRangingBeacons(ios<13.0,beaconUUID=428132AF-4746-42D3-801E-4572D65BFD9B)
2021-04-24 11:45:21.062575+0100 Herald-for-iOS[232:5717] [BLE.ConcreteBLESensor] stop
2021-04-24 11:45:21.067654+0100 Herald-for-iOS[232:5717] [BLE.ConcreteBLETransmitter] stop, transmitter disabled
2021-04-24 11:45:21.071578+0100 Herald-for-iOS[232:5717] [BLE.ConcreteBLETransmitter] stopAdvertising()
2021-04-24 11:45:21.072365+0100 Herald-for-iOS[232:5717] [BLE.ConcreteBLETransmitter] stopAdvertising, notify timer cancelled
2021-04-24 11:45:21.075662+0100 Herald-for-iOS[232:5717] [BLE.ConcreteBLEReceiver] stop, receiver disabled
2021-04-24 11:45:21.080992+0100 Herald-for-iOS[232:5939] [BLE.ConcreteBLETransmitter] stopAdvertising, peripheral stopped advertising
2021-04-24 11:45:21.082608+0100 Herald-for-iOS[232:5717] [BLE.ConcreteBLEReceiver] disconnect (source=stop,peripheral=6CE293F9-3C5B-F0EA-E70B-57D5126DDB5F)