Passive scanning with bluez or_pattern to filter on device address

[LeCyberDucky]

Hey there!

I'm trying to monitor measurements from a bluetooth scale via passive scanning using a Raspberry 3b+. But I'm unable to get even a minimal example to work.

I'm running Raspbian 12, bookworm (Linux 6.1.41-v7+ armv7l).
I built bluez from source a couple of days ago (including experimental features), landing me at version 5.76.

Here's the code I have at the moment:

import asyncio
import bleak

filter_settings = {
    "or_patterns": [[0x1B, 0x00, b'\xD8\xE7\x2F\xA6\x11\x21']]
}

async def main():
    async with bleak.BleakScanner(scanning_mode = "passive", bluez = filter_settings) as scanner:
        print("Scanning!")

        n = 0
        async for bd, ad in scanner.advertisement_data():
            print(f"{n}: {bd!r} with {ad!r}\n")
            n += 1

asyncio.run(main())

The 0x1B part of the pattern is the LE Bluetooth Device Address, as stated here: https://www.bluetooth.com/wp-content/uploads/Files/Specification/HTML/Assigned_Numbers/out/en/Assigned_Numbers.pdf?v=1720033659741
and here https://www.bluetooth.com/specifications/css-11/

The b'\xD8\xE7\x2F\xA6\x11\x21' part is the MAC address of my device.

I get no results whatsoever using the above code. Does anybody have an idea about what might be going wrong?

---

Edit: From looking through the issues for this repo, I just stumbled upon the btmon tool. Running this in another window, while executing the above script, yields an error:
= bluetoothd: Invalid argument of property Patterns of the Adv Monitor at path /org/bleak/3072/197..

This begs the question what is wrong with my pattern.

---

Edit 2:
I found an issue with some example code showing just how wrong my attempt at creating a pattern was.
Now I have this:

import asyncio
import bleak
from bleak.backends.bluezdbus.advertisement_monitor import OrPattern
from bleak.backends.bluezdbus.scanner import BlueZScannerArgs

filter_settings = BlueZScannerArgs(
    or_patterns = [OrPattern(0, 0x1B, b'\xD8\xE7\x2F\xA6\x11\x21')]
)

async def main():
    async with bleak.BleakScanner(scanning_mode = "passive", bluez = filter_settings) as scanner:
        print("Scanning!")

        n = 0
        async for bd, ad in scanner.advertisement_data():
            print(f"{n}: {bd!r} with {ad!r}\n")
            n += 1

asyncio.run(main())

With that, my program still doesn't provide any results. But btmon gives me a bunch of much more interesting output. In fact, the data I'm looking for appears in the output of btmon:

= bluetoothd: Path /org/bleak/3435/1972420368 reserved for Adv Monitor app :1.79                     [hci0] 1124.949840
@ MGMT Command: Add Advertisement Patterns Monitor (0x0052) plen 35                         {0x0001} [hci0] 1124.954358
        Number of patterns: 1
          Pattern 1:
            AD type: 27
            Offset: 0
            Length: 6
            Value [6]: d8e72fa61121
@ MGMT Event: Command Complete (0x0001) plen 5                                              {0x0001} [hci0] 1124.954404
      Add Advertisement Patterns Monitor (0x0052) plen 2
        Status: Success (0x00)
        Handle: 1
< HCI Command: LE Set Scan Parameters (0x08|0x000b) plen 7                                        #1 [hci0] 1124.954589
        Type: Passive (0x00)
        Interval: 60.000 msec (0x0060)
        Window: 30.000 msec (0x0030)
        Own address type: Public (0x00)
        Filter policy: Accept all advertisement (0x00)
> HCI Event: Command Complete (0x0e) plen 4                                                       #2 [hci0] 1124.954918
      LE Set Scan Parameters (0x08|0x000b) ncmd 1
        Status: Success (0x00)
< HCI Command: LE Set Scan Enable (0x08|0x000c) plen 2                                            #3 [hci0] 1124.954985
        Scanning: Enabled (0x01)
        Filter duplicates: Enabled (0x01)
> HCI Event: Command Complete (0x0e) plen 4                                                       #4 [hci0] 1124.955331
      LE Set Scan Enable (0x08|0x000c) ncmd 1
        Status: Success (0x00)

> HCI Event: LE Meta Event (0x3e) plen 36                                                        #34 [hci0] 1134.929495
      LE Advertising Report (0x02)
        Num reports: 1
        Event type: Connectable undirected - ADV_IND (0x00)
        Address type: Public (0x00)
        Address: D8:E7:2F:A6:11:21 (Chipsea Technologies (Shenzhen) Corp.)
        Data length: 24
        Flags: 0x06
          LE General Discoverable Mode
          BR/EDR Not Supported
        16-bit Service UUIDs (partial): 1 entry
          Body Composition (0x181b)
        Service Data: Body Composition (0x181b)
          Data[13]: 0204b207011209080a0000083e
        RSSI: -50 dBm (0xce)
@ MGMT Event: ADV Monitor Device Found (0x002f) plen 40                                     {0x0001} [hci0] 1134.929549
        Handle: 0
        Address: D8:E7:2F:A6:11:21 (Chipsea Technologies (Shenzhen) Corp.)
        Addr Type: 1
        RSSI: -50
        Flags: 0x00000000
        AD Data Len: 24
        AD Data[24]: 02010603021b1810161b180204b207011209080a0000083e

[dlech]

and here https://www.bluetooth.com/specifications/css-11/

This has an "X" in the "AD" and "SRD" columns for "LE Bluetooth Device Address", so I don't think this would work.

I think the best you can do is filter on the service UUID in the Service Data.

[dlech]

Maybe a change/regression in BlueZ? I'm using BlueZ 5.72 on Ubuntu.

Or it could be that the adapter has hardware pattern matching that isn't working correctly and a different adapter might work better.

[LeCyberDucky]

I tried downgrading to BlueZ 5.72, but that did not help.

I've now raised an issue with BlueZ bluez/bluez#901. I might also end up dusting off my laptop, just to experiment with different hardware.

I'll update you if anything interesting happens.

[MurrayGroves]

@LeCyberDucky did you ever get this working? No matter what OrPattern I add I can't get anything to show up on passive scanning, only active.

[MurrayGroves]

I managed to get it working by adding --experimental to Bluetoothd. I assumed since it hadn't errored at me that it wasn't necessary anymore.

[LeCyberDucky]

@MurrayGroves sorry, I haven't had the time to get back into this. Cool that you found a workaround, though. Thanks for the update!