How do I reconnect to a bluetooth device on App Startup?

[Daxter98]

Hello!

I'm trying to reconnect to a previously connected device (the device is a Shelly Plus 1) on app startup. The idea is to have a way to configure the desired device to use with the app, store the device UUID (which contains the device MAC Address), and connect to this selected device every time the app restarts.

I read the documentation, and I know it says to never use device UUID and instead use service UUID. I'm trying to use known service UUIDs to find all the Shelly devices and then match the device UUID with the one I have previously selected, but the scan results are empty.

public static readonly Guid ShellyGattServiceUuid = new("5f6d4f53-5f52-5043-5f53-56435f49445f");
public static readonly Guid RpcCharDataUuid = new("5f6d4f53-5f52-5043-5f64-6174615f5f5f");

var scanResults = await bleManager
    .Scan(new ScanConfig(ShellyDeviceConstants.RpcCharRxCtlUuid.ToString())) <-- One of them
    .Timeout(TimeSpan.FromSeconds(5))
    .Catch<ScanResult, TimeoutException>(_ => Observable.Empty<ScanResult>())
    .FirstOrDefaultAsync();

Any help it's appreciated. Thanks in advance!

Edit: Missing Info - I'm targeting Android 11 using Shiny 3.3.4, .NET 9.0

[aritchie]

This is a great question and unfortunately, a loaded one since there isn't really a "right answer". The first thing you'll want to understand is truly WHY the peripheral UUID is not a safe id to use. The fact is, it is a temporary ID. Apple specifically changes this because they want to protect the privacy/tracking of a user. If you can read the ID of any device, you can start correlating where a user is with minimal effort. The thinking is that if you "own" the peripherals, you own the firmware, build your IDs into that.

With that being said and without knowing the Shelly device myself, you've got a few options you can look into beyond just find devices with a specific service UUID

• Does the manufacturer data of the peripheral emit anything specific?
• Does it have a device info characteristic that you could connect to and read any specifics from? This obviously is not a great option if there are lots of devices

[Daxter98]

Reading some documentation and experimenting, I found the manufacturer emits a manufacturer ID to identify Shelly devices only:
ALLTERCO_MFID = 0x0BA9 # Manufacturer ID for Shelly devices

For the second question, yes, all Shelly devices use the characteristic "RPC_CHAR_DATA_UUID: 5f6d4f53-5f52-414d-5f64-6174615f5f5f" for communicating with the device. This characteristic, documented in the Shelly KB, is where you write the encoded JSON-RPC requests and read the responses using BLE GATT.

The response I get from using the Shelly.GetDeviceInfo RPC method looks something like this:
{
"id": "shellypro4pm-f008d1d8b8b8",
"mac": "F008D1D8B8B8",
...
}

I'm expecting to have at least one or two devices next to each other. Maybe I can connect to each device, use the RPC method to read the device info, and use that to determine which device I should connect to?

Thanks for your time Mr. Ritchie!