Scanning BLE devices returns empty uuids in metadata (?)

[rdagher]

• bleak version: 0.10.0
• Python version: Python 3.8.5
• Operating System: MacOS Catalina 10.15.7
• BlueZ version (bluetoothctl -v) in case of Linux: N/A

Description

Hi,

I wanted to test scanning devices and print the details of the scanned device (name, metadata, etc.).

The devices are detected (name, address), nevertheless the metadata field metadata = {'uuids': [], ...} does not contain the service uuids which is expected to be a list of one element, in my case 'uuids': ['680c21d9-c946-4c1f-9c11-baa1c21329e7'].

The reason is I want to filter the scan output, application-side, on the device's service uuid to only report devices of interest.

For the test, I have two BLE devices running (namely DWDBB5 and DWD48C) - scan using a mobile app on Android (nrfConnect):

What I Did

Attached the test script containing two simple scanning functions.
ble_scan.py.txt
ble_scan_log.txt

Here's a snippet of what I get as output:

import asyncio
from bleak import BleakScanner
from bleak.backends.device import BLEDevice

from ppretty import ppretty



def dev_dump(dev:BLEDevice):
    #print(ppretty(dev, show_protected=True, show_static=True, show_properties=True))
    print(f'device {dev}:')
    print(f'\taddr = {dev.address}')
    print(f'\tname = {dev.name}')
    print(f'\trssi = {dev.rssi}')
    print(f'\tdetails = {dev.details}')
    print(f'\tmetadata = {dev.metadata}')

    print(f'>> Services (Mac) = {dev.details.services}')
    print(ppretty(dev.details.services, show_protected=True, show_static=True, show_properties=True))

async def basic_scan():
    devices = await BleakScanner.discover()
    for d in devices:
        dev_dump(d)


async def adv_scan(scan_duration:int, service_uuid:str):
    # scan for devices
    scanner = BleakScanner(filters={"UUIDs":[service_uuid], "DuplicateData":False})
    def detection_callback(device, advertisement_data):
        print("detected:", device, " – RSSI:", device.rssi, " – adv data: ", advertisement_data)

    scanner.register_detection_callback(detection_callback)
    await scanner.start()
    await asyncio.sleep(scan_duration)
    await scanner.stop()
    scanned_devices = await scanner.get_discovered_devices()
    print(f'Device discovery filtered output:')
    for d in scanned_devices:
        dev_dump(d)




loop = asyncio.get_event_loop()

print('Basic Scan:')
loop.run_until_complete(basic_scan())
loop.run_until_complete(basic_scan())


DWM_SERVICE_UUID = '680c21d9-c946-4c1f-9c11-baa1c21329e7'
print(f'Filtering scan on service: {DWM_SERVICE_UUID}')
loop.run_until_complete(adv_scan(scan_duration=6, service_uuid=DWM_SERVICE_UUID))

$ python ble_scan.py 
Basic Scan:
device 7C8844F3-6F25-40FF-BAB6-532F089721ED: Apple, Inc. (b'\t\x06\x03\n\xc0\xa8\x01\n'):
	addr = 7C8844F3-6F25-40FF-BAB6-532F089721ED
	name = Unknown
	rssi = 0
	details = <CBPeripheral: 0x7f988c0a2e10, identifier = 7C8844F3-6F25-40FF-BAB6-532F089721ED, name = (null), state = disconnected>
	metadata = {'uuids': [], 'manufacturer_data': {76: b'\t\x06\x03\n\xc0\xa8\x01\n'}, 'delegate': <CentralManagerDelegate: 0x7f988af235d0>}
>> Services (Mac) = <native-selector services of <CBPeripheral: 0x7f988c0a2e10, identifier = 7C8844F3-6F25-40FF-BAB6-532F089721ED, name = (null), state = disconnected>>
native_selector(
    definingClass = <class 'objc.CBPeripheral'>, 
    isClassMethod = False, 
    ..., 
    self = objc.NSKVONotifying_CBPeripheral(), 
    signature = bytes()
)
Filtering scan on service: 680c21d9-c946-4c1f-9c11-baa1c21329e7
detected: 52AE0205-7F1E-4597-869C-CBB46747834B: DWD48C  – RSSI: -58  – adv data:  AdvertisementData(local_name='DWD48C')
detected: 6CC6A737-C441-4BB3-BF09-2F48E19FA89F: Unknown  – RSSI: -91  – adv data:  AdvertisementData(manufacturer_data={2305: b'q\x108\xef`\n?x\xf2p\xd9tR'}, service_uuids=['0000febe-0000-1000-8000-00805f9b34fb', '0000fe26-0000-1000-8000-00805f9b34fb'])
detected: 6CFADC06-2C11-4884-9F4F-FA3CBAA4D672: DWDBB5  – RSSI: -66  – adv data:  AdvertisementData(local_name='DWDBB5')
Device discovery filtered output:
device 52AE0205-7F1E-4597-869C-CBB46747834B: DWD48C:
	addr = 52AE0205-7F1E-4597-869C-CBB46747834B
	name = DWD48C
	rssi = 0
	details = <CBPeripheral: 0x7f988c071570, identifier = 52AE0205-7F1E-4597-869C-CBB46747834B, name = DWD48C, state = disconnected>
	metadata = {'uuids': [], 'manufacturer_data': {}, 'delegate': <CentralManagerDelegate: 0x7f988ac4e250>}
>> Services (Mac) = <native-selector services of <CBPeripheral: 0x7f988c071570, identifier = 52AE0205-7F1E-4597-869C-CBB46747834B, name = DWD48C, state = disconnected>>
native_selector(
    definingClass = <class 'objc.CBPeripheral'>, 
    isClassMethod = False, 
    ..., 
    self = objc.NSKVONotifying_CBPeripheral(), 
    signature = bytes()
)
device 6CC6A737-C441-4BB3-BF09-2F48E19FA89F: This value has special meaning depending on the context in which it used. Link Manager Protocol (LMP): This value may be used in the internal and interoperability tests before a Company ID has been assigned. This value shall not be used in shipping end products. Device ID Profile: This value is reserved as the default vendor ID when no Device ID service record is present in a remote device. (b'q\x108\xef`\n?x\xf2p\xd9tR'):
	addr = 6CC6A737-C441-4BB3-BF09-2F48E19FA89F
	name = Unknown
	rssi = 0
	details = <CBPeripheral: 0x7f988ac24310, identifier = 6CC6A737-C441-4BB3-BF09-2F48E19FA89F, name = (null), state = disconnected>
	metadata = {'uuids': ['0000febe-0000-1000-8000-00805f9b34fb', '0000fe26-0000-1000-8000-00805f9b34fb'], 'manufacturer_data': {2305: b'q\x108\xef`\n?x\xf2p\xd9tR'}, 'delegate': <CentralManagerDelegate: 0x7f988ac4e250>}
>> Services (Mac) = <native-selector services of <CBPeripheral: 0x7f988ac24310, identifier = 6CC6A737-C441-4BB3-BF09-2F48E19FA89F, name = (null), state = disconnected>>
native_selector(
    definingClass = <class 'objc.CBPeripheral'>, 
    isClassMethod = False, 
    ..., 
    self = objc.NSKVONotifying_CBPeripheral(), 
    signature = bytes()
)
device 6CFADC06-2C11-4884-9F4F-FA3CBAA4D672: DWDBB5:
	addr = 6CFADC06-2C11-4884-9F4F-FA3CBAA4D672
	name = DWDBB5
	rssi = 0
	details = <CBPeripheral: 0x7f988de0edb0, identifier = 6CFADC06-2C11-4884-9F4F-FA3CBAA4D672, name = DWDBB5, state = disconnected>
	metadata = {'uuids': [], 'manufacturer_data': {}, 'delegate': <CentralManagerDelegate: 0x7f988ac4e250>}
>> Services (Mac) = <native-selector services of <CBPeripheral: 0x7f988de0edb0, identifier = 6CFADC06-2C11-4884-9F4F-FA3CBAA4D672, name = DWDBB5, state = disconnected>>
native_selector(
    definingClass = <class 'objc.CBPeripheral'>, 
    isClassMethod = False, 
    ..., 
    self = objc.NSKVONotifying_CBPeripheral(), 
    signature = bytes()
)

Thanks in advance for your help, and I hope I did not misinterpret the semantics of the uuids field. I was counting on this field from the scan results for a simple filtering.

P.S I am aware of the fact that filtering is not yet provided on Mac and of issue #230.

P.S Suspecting relation to issue #329.

P.S For now, I have currently a terribly slow and ugly workaround that uses service discovery on the scanned device, which becomes terribly slow when many BLE devices are around and especially some of them refusing/stalling (for a reason) to respond to service discovery.

Regards,
Roudy

[dlech]

Yes, there is some work to be done to bring metadata up to date with the new register_detection_callback() and make it work in a more consistent way cross-platform (very briefly discussed in #334).

For now you can probably work around it by collecting the needed information yourself in the callback instead of using the metadata attribute.

[huseyinege]

I have checked the bleak/backends/corebluetooth/scanner.py and it is the updated version. However i have the same problem. This is my piece of code:
async def run():
scanner = BleakScanner()
scanner.register_detection_callback(detection_callback)
await scanner.start()
await asyncio.sleep(20.0)
await scanner.stop()
scanned_devices= await scanner.get_discovered_devices()
for d in scanned_devices:
if d.address in Dict:
print(d)
print(d.metadata.values())

And this is the output i get:
E3:EB:F8:F2:9E:9D: Nordic_UART
dict_values([[], {89: b''}])
CA:56:C9:07:54:CF: Nordic_UART
dict_values([[], {89: b''}])