I'm trying to connect to a BLE device via bleak - it works fine when I use client.start_notify on Windows 11 and andriod , but script fails , My logcat error: bleak.exc.BleakError: Descriptor None was not found!

[NewAge12]

@dlech @hbldh

def scan1(self):
    
    loop = asyncio.get_event_loop()
    loop.run_until_complete(self.begin_scan1())

async def begin_scan1(self):

    def callback2(sender, data):
        print(sender, data, 'llllll')
        self.val1 = data
        
    a = []
    scanned_devices = await bleak.BleakScanner.discover(1)

    if len(scanned_devices) == 0:
        print("NO DEVICES")
    scanned_devices.sort(key=lambda device: -device.rssi)
    for device in scanned_devices:
        device1 = f"{device.name}"
        print(device1)
        if device1 == "Bluno":
            # try:

            async with bleak.BleakClient(device) as client:
                print('rr')
                paired = client.pair(protection_level=2)
                print(f"Paired: {paired}")
                COLOR_CHARACTERISTIC = "0000dfb1-0000-1000-8000-00805f9b34fb"
                 

                uu = '1'
                write_value = bytearray([int(uu)])
                await client.write_gatt_char(COLOR_CHARACTERISTIC, write_value)
                await asyncio.sleep(4.0)
                print('www')
                await client.start_notify(COLOR_CHARACTERISTIC, callback2)
                print('wwee')



                await asyncio.sleep(10.0)
                print('rrrq')
                await client.stop_notify(COLOR_CHARACTERISTIC)

[NewAge12]

bleak.exc.BleakError: Descriptor None was not found!

[dlech]

Can out share the output of https://github.com/hbldh/bleak/blob/develop/examples/service_explorer.py when connected to this device?

[NewAge12]

@dlech @hbldh

INFO:bleak.backends.winrt.client:Services resolved for BleakClientWinRT (C4:BE:84:20:1B:59)
INFO:main:Connected: True
INFO:main:[Service] 00001800-0000-1000-8000-00805f9b34fb (Handle: 1): Generic Access Profile
INFO:main: [Characteristic] 00002a00-0000-1000-8000-00805f9b34fb (Handle: 2): (read), Value: b'Bluno'
INFO:main: [Characteristic] 00002a01-0000-1000-8000-00805f9b34fb (Handle: 4): (read), Value: b'\x00\x00'
INFO:main: [Characteristic] 00002a02-0000-1000-8000-00805f9b34fb (Handle: 6): (read), Value: b'\x00'
INFO:main: [Characteristic] 00002a03-0000-1000-8000-00805f9b34fb (Handle: 8): (write), Value: None
INFO:main: [Characteristic] 00002a04-0000-1000-8000-00805f9b34fb (Handle: 10): (read), Value: b'P\x00\xa0\x00\x00\x00\xe8\x03'
INFO:main:[Service] 00001801-0000-1000-8000-00805f9b34fb (Handle: 12): Generic Attribute Profile
INFO:main: [Characteristic] 00002a05-0000-1000-8000-00805f9b34fb (Handle: 13): (indicate), Value: None
INFO:main: [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 15): Client Characteristic Configuration) | Value: b'\x02\x00'
INFO:main:[Service] 0000180a-0000-1000-8000-00805f9b34fb (Handle: 16): Device Information
INFO:main: [Characteristic] 00002a23-0000-1000-8000-00805f9b34fb (Handle: 17): (read), Value: b'Y\x1b \x00\x00\x84\xbe\xc4'
INFO:main: [Characteristic] 00002a24-0000-1000-8000-00805f9b34fb (Handle: 19): (read), Value: b'DF Bluno'
INFO:main: [Characteristic] 00002a25-0000-1000-8000-00805f9b34fb (Handle: 21): (read), Value: b'0123456789'
INFO:main: [Characteristic] 00002a26-0000-1000-8000-00805f9b34fb (Handle: 23): (read), Value: b'FW V1.97'
INFO:main: [Characteristic] 00002a27-0000-1000-8000-00805f9b34fb (Handle: 25): (read), Value: b'HW V1.7'
INFO:main: [Characteristic] 00002a28-0000-1000-8000-00805f9b34fb (Handle: 27): (read), Value: b'SW V1.97'
INFO:main: [Characteristic] 00002a29-0000-1000-8000-00805f9b34fb (Handle: 29): (read), Value: b'DFRobot'
INFO:main: [Characteristic] 00002a2a-0000-1000-8000-00805f9b34fb (Handle: 31): (read), Value: b'\xfe\x00experimental'
INFO:main: [Characteristic] 00002a50-0000-1000-8000-00805f9b34fb (Handle: 33): (read), Value: b'\x01\r\x00\x00\x00\x10\x01'
INFO:main:[Service] 0000dfb0-0000-1000-8000-00805f9b34fb (Handle: 35): Vendor specific
INFO:main: [Characteristic] 0000dfb1-0000-1000-8000-00805f9b34fb (Handle: 36): Serial (read,write-without-response,write,notify), Value: b'\x01'
INFO:main: [Descriptor] 00002901-0000-1000-8000-00805f9b34fb (Handle: 38): Characteristic User Description) | Value: b'Serial'
INFO:main: [Characteristic] 0000dfb2-0000-1000-8000-00805f9b34fb (Handle: 39): AT Ctrl (read,write-without-response,write,notify), Value: b'\x02'
INFO:main: [Descriptor] 00002901-0000-1000-8000-00805f9b34fb (Handle: 41): Characteristic User Description) | Value: b'AT Ctrl'
Process finished with exit code 0

[dlech]

INFO:main: [Characteristic] 0000dfb1-0000-1000-8000-00805f9b34fb (Handle: 36): Serial (read,write-without-response,write,notify), Value: b'\x01'
INFO:main: [Descriptor] 00002901-0000-1000-8000-00805f9b34fb (Handle: 38): Characteristic User Description) | Value: b'Serial'

This is the "COLOR" characteristic. It does not have a "Client Characteristic Configuration" descriptor, so that explains the error seen on Android. I'm not sure how it works on Windows. You could capture Bluetooth packets on Windows to get a better idea of what is going on under the hood on Windows.

Perhaps we just need to surround

bleak/bleak/backends/p4android/client.py

Lines 497 to 500 in 46c828b

	await self.write_gatt_descriptor(
	characteristic.notification_descriptor,
	defs.BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE,
	)

with if characteristic.notification_descriptor:.

[NewAge12]

@dlech @hbldh
The "COLOR" characteristic is just a variable for the UUID . As seen from the get_services list only the '0000dfb1-0000-1000-8000-00805f9b34fb' UUID has the capabilities to read and write data from device to hardware. We did try surrounding
if characteristic.notification_descriptor:
await self.write_gatt_descriptor(
characteristic.notification_descriptor,
defs.BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE,
)
still no solution

INFO:main: [Characteristic] 0000dfb1-0000-1000-8000-00805f9b34fb (Handle: 36): Serial (read,write-without-response,write,notify), Value: b'\x01'
INFO:main: [Descriptor] 00002901-0000-1000-8000-00805f9b34fb (Handle: 38): Characteristic User Description) | Value: b'Serial'

This is the "COLOR" characteristic. It does not have a "Client Characteristic Configuration" descriptor, so that explains the error seen on Android. I'm not sure how it works on Windows. You could capture Bluetooth packets on Windows to get a better idea of what is going on under the hood on Windows.

Perhaps we just need to surround

bleak/bleak/backends/p4android/client.py

Lines 497 to 500 in 46c828b

	await self.write_gatt_descriptor(
	characteristic.notification_descriptor,
	defs.BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE,
	)

with if characteristic.notification_descriptor:.

@dlech @hbldh
The "COLOR" characteristic is just a variable for the UUID . As seen from the get_services list only the '0000dfb1-0000-1000-8000-00805f9b34fb' UUID has the capabilities to read and write data from device to hardware. We did try surrounding
if characteristic.notification_descriptor:
await self.write_gatt_descriptor(
characteristic.notification_descriptor,
defs.BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE,
)
able to write data with this UUID but for reading there is no function neither read_gatt_char works for start_notify!!!

[NewAge12]

@dlech @hbldh
Any update on the issue?

[apacodes]

I ran into the same thing, my fix was to pin bleak to 0.20.2 which resolves the "error" and makes the call to start_notify() work as expected.

I haven't checked if the pinning causes other packets to be downgraded (since the problem is currently time sensitive) but i do as of now assume that this was caused by a change in bleak.

[dlech]

@apacodes it sounds like there is a regression between 0.20.2 and 0.21.0? If so, can you please start a new issue with more detail about the problem?

[apacodes]

Yes.

I will investigate an do so in the coming days.

[ccwang65]

This issue may because of files in: bleak/backends/p4android
defs.py last line #89:

CLIENT_CHARACTERISTIC_CONFIGURATION_UUID = "2902"

characteristic.py #90

    if descriptor.uuid == defs.CLIENT_CHARACTERISTIC_CONFIGURATION_UUID:
        self.__notification_descriptor = descriptor

Maybe we need to use back the full string:

CLIENT_CHARACTERISTIC_CONFIGURATION_UUID = "00002902-0000-1000-8000-00805f9b34fb"

[skywodd]

Hello,

I'm currently having the same error (Descriptor None was not found).

I've solved the issue by monkey patching the CLIENT_CHARACTERISTIC_CONFIGURATION_UUID constant at startup in my app using :

from bleak.backends.p4android import defs
defs.CLIENT_CHARACTERISTIC_CONFIGURATION_UUID = "00002902-0000-1000-8000-00805f9b34fb"

I think bleak/backends/p4android/characteristic.py should check for both the full and short uuid constant to avoid regression.

(Bleak version 0.21.1 with Python-for-Android, Kivy and Buildozer, running on Android 13.1)

[dlech]

Thanks for confirming. I would take a pull request for this. I think the short version is wrong and we don't need to have both.

[narodnik]

Confirming this as well. I tried downgrading to 0.20.2 but it did not work either.

04-06 14:56:18.361 13037 13062 I python  :  Traceback (most recent call last):
04-06 14:56:18.361 13037 13062 I python  :    File "/home/narodnik/src/pump/ecgapp/.buildozer/android/app/main.py", line 101, in <module>
04-06 14:56:18.362 13037 13062 I python  :    File "/home/narodnik/src/pump/ecgapp/.buildozer/android/platform/build-arm64-v8a_armeabi-v7a/build/other_builds/python3/arm64-v8a__ndk_target_21/python3/Lib/asyncio/base_events.py", line 653, in run_until_complete
04-06 14:56:18.363 13037 13062 I python  :    File "/home/narodnik/src/pump/ecgapp/.buildozer/android/app/main.py", line 67, in monitor_hr
04-06 14:56:18.364 13037 13062 I python  :    File "/home/narodnik/src/pump/ecgapp/.buildozer/android/app/main.py", line 76, in run_sensor
04-06 14:56:18.364 13037 13062 I python  :    File "/home/narodnik/src/pump/ecgapp/.buildozer/android/app/polarh10.py", line 295, in start_hr_stream
04-06 14:56:18.365 13037 13062 I python  :    File "/home/narodnik/src/pump/ecgapp/.buildozer/android/platform/build-arm64-v8a_armeabi-v7a/build/python-installs/ecgapp/arm64-v8a/bleak/__init__.py", line 834, in start_notify
04-06 14:56:18.366 13037 13062 I python  :    File "/home/narodnik/src/pump/ecgapp/.buildozer/android/platform/build-arm64-v8a_armeabi-v7a/build/python-installs/ecgapp/arm64-v8a/bleak/backends/p4android/client.py", line 450, in start_notify
04-06 14:56:18.366 13037 13062 I python  :    File "/home/narodnik/src/pump/ecgapp/.buildozer/android/platform/build-arm64-v8a_armeabi-v7a/build/python-installs/ecgapp/arm64-v8a/bleak/backends/p4android/client.py", line 418, in write_gatt_descriptor
04-06 14:56:18.367 13037 13062 I python  :  bleak.exc.BleakError: Descriptor None was not found!

The monkey patch above worked though.

I also had to copy the .java files as documented in another issue.