Some characteristics are missing

[pierre-24]

• bleak version: 0.5.0
• Python version: 3.6.8
• Operating System: Ubuntu 18.04 (latest LTS update, so .3 or .4)

Description

While running the service_explorer.py on my device, I found that a few characteristics are missing. When I explicitely request this characteristic to be read, I get a bleak.exc.BleakError: Characteristic with UUID xxxx could not be found

What I Did

I ran the service_explorer.py script. The output is

Connected: True
[Service] f1196f50-71a4-11e6-bdf4-0800200c9a66: Unknown
    [Characteristic] f1196f57-71a4-11e6-bdf4-0800200c9a66: (write) | Name: , Value: None 
    [Characteristic] f1196f56-71a4-11e6-bdf4-0800200c9a66: (read,write) | Name: , Value: b'' 
    [Characteristic] f1196f55-71a4-11e6-bdf4-0800200c9a66: (notify) | Name: , Value: None 
        [Descriptor] 00002902-0000-1000-8000-00805f9b34fb: (Handle: 33) | Value: b'\x00\x00' 
    [Characteristic] f1196f54-71a4-11e6-bdf4-0800200c9a66: (read,write) | Name: , Value: b'' 
    [Characteristic] f1196f53-71a4-11e6-bdf4-0800200c9a66: (read) | Name: , Value: b'' 
    [Characteristic] f1196f52-71a4-11e6-bdf4-0800200c9a66: (read,notify) | Name: , Value: b'' 
        [Descriptor] 00002902-0000-1000-8000-00805f9b34fb: (Handle: 26) | Value: b'\x00\x00' 
    [Characteristic] f1196f51-71a4-11e6-bdf4-0800200c9a66: (read) | Name: , Value: b'' 
[Service] 0000180a-0000-1000-8000-00805f9b34fb: Device Information
    [Characteristic] 00002a26-0000-1000-8000-00805f9b34fb: (read) | Name: , Value: b'TFv3.1' 
[Service] 00001801-0000-1000-8000-00805f9b34fb: Generic Attribute Profile
    [Characteristic] 00002a05-0000-1000-8000-00805f9b34fb: (indicate) | Name: , Value: None 
        [Descriptor] 00002902-0000-1000-8000-00805f9b34fb: (Handle: 11) | Value: b'\x02\x00' 

On the other hand, if I use gatttool, I get the following

~$ gatttool -b 98:07:2D:EE:21:0E -I
[98:07:2D:EE:21:0E][LE]> connect
Attempting to connect to 98:07:2D:EE:21:0E
Connection successful
[98:07:2D:EE:21:0E][LE]> primary
attr handle: 0x0001, end grp handle: 0x0007 uuid: 00001800-0000-1000-8000-00805f9b34fb
attr handle: 0x0008, end grp handle: 0x000b uuid: 00001801-0000-1000-8000-00805f9b34fb
attr handle: 0x000c, end grp handle: 0x000e uuid: 0000180a-0000-1000-8000-00805f9b34fb
attr handle: 0x000f, end grp handle: 0x0014 uuid: 0000180f-0000-1000-8000-00805f9b34fb
attr handle: 0x0015, end grp handle: 0xffff uuid: f1196f50-71a4-11e6-bdf4-0800200c9a66
[98:07:2D:EE:21:0E][LE]> characteristics
handle: 0x0002, char properties: 0x0e, char value handle: 0x0003, uuid: 00002a00-0000-1000-8000-00805f9b34fb [* → Device Name]
handle: 0x0004, char properties: 0x02, char value handle: 0x0005, uuid: 00002a01-0000-1000-8000-00805f9b34fb [* → Appearance]
handle: 0x0006, char properties: 0x02, char value handle: 0x0007, uuid: 00002a04-0000-1000-8000-00805f9b34fb [* → Peripherical Prefered Connection Parameter]
handle: 0x0009, char properties: 0x20, char value handle: 0x000a, uuid: 00002a05-0000-1000-8000-00805f9b34fb
handle: 0x000d, char properties: 0x02, char value handle: 0x000e, uuid: 00002a26-0000-1000-8000-00805f9b34fb
handle: 0x0010, char properties: 0x12, char value handle: 0x0011, uuid: 00002a19-0000-1000-8000-00805f9b34fb
handle: 0x0016, char properties: 0x02, char value handle: 0x0017, uuid: f1196f51-71a4-11e6-bdf4-0800200c9a66
handle: 0x0018, char properties: 0x12, char value handle: 0x0019, uuid: f1196f52-71a4-11e6-bdf4-0800200c9a66
handle: 0x001b, char properties: 0x02, char value handle: 0x001c, uuid: f1196f53-71a4-11e6-bdf4-0800200c9a66
handle: 0x001d, char properties: 0x0a, char value handle: 0x001e, uuid: f1196f54-71a4-11e6-bdf4-0800200c9a66
handle: 0x001f, char properties: 0x10, char value handle: 0x0020, uuid: f1196f55-71a4-11e6-bdf4-0800200c9a66
handle: 0x0022, char properties: 0x0a, char value handle: 0x0023, uuid: f1196f56-71a4-11e6-bdf4-0800200c9a66
handle: 0x0024, char properties: 0x08, char value handle: 0x0025, uuid: f1196f57-71a4-11e6-bdf4-0800200c9a66
[98:07:2D:EE:21:0E][LE]> char-read-uuid 00002a00-0000-1000-8000-00805f9b34fb
handle: 0x0003   value: 50 69 65 72 72 65 20 2d 20 54 4d 32 

(please scroll right for the additional information)

As you can see, the three first characteristics (marked by a star in the output, added by me) are not reported by the script. Of course, reading their values through gatttool works correctly (see last line), but as I mention, the following does not:

# not the smartest piece of code, but I'm just playing around ;)
import asyncio

from bleak import BleakClient

UUID_GENERIC = '0000{}-0000-1000-8000-00805f9b34fb'

CHARACTERISTIC_DEVICE_NAME = UUID_GENERIC.format('2a00')
CHARACTERISTIC_BATTERY_LEVEL = UUID_GENERIC.format('2a19')
CHARACTERISTIC_FIRMWARE_REV = UUID_GENERIC.format('2a26')

CURRENT_CHAR = CHARACTERISTIC_DEVICE_NAME

async def run(address, loop):
    async with BleakClient(address, loop=loop) as client:
        char_value = await client.read_gatt_char(CURRENT_CHAR)
        print("{} = {} ({})".format(CURRENT_CHAR, char_value.hex(), char_value.decode()))

if __name__ == '__main__':
    address = '98:07:2D:EE:21:0E'
    loop = asyncio.get_event_loop()
    loop.run_until_complete(run(address, loop))

Since it results in bleak.exc.BleakError: Characteristic with UUID 00002a00-0000-1000-8000-00805f9b34fb could not be found!. Reading CHARACTERISTIC_BATTERY_LEVEL does, on the other hand, work.

In itself, I'm not interested in those characteristics, but I think it worth reporting :)

[hbldh]

Hello and thank you for reporting this. It is confusing, I can give you that, but it is a BlueZ backend specific thing and not entirely a bug.

The Battery level has been moved from being reported as a regular characteristic to a separate interface in the BlueZ DBus API in version 5.48. It will not show up as a characteristic in bleak due to that, but it should be handled by the current code.

The Device name was new though. I cannot find the documentation to support it, but I think the BlueZ DBus API renders that information on the device interface and I have drafted a fix for it, accessing the name where I believe it is located in the BlueZ DBus representation of the device. That change will be released with version 0.5.1.

The Peripherical Prefered Connection Parameter I have no fix for as of now. I have not device with that charactersitic, so I cannot test it. Can you give me an example value of the content of it?

Is firmware rev also problematic? I have no problems accessing it on my device by uuid?

[pierre-24]

Hello. Thanks for investigating the issue :)

Firmware rev is ok, but it was appearing in service_explorer.py, so it should not cause any issue.

Concerning Peripherical Prefered Connection Parameter, the value on my device is 50 00 a0 00 00 00 e8 03 (obtained using gatttool), but I have no idea on how to interpret this, since the documentation of this device does not mention anything on that, and I actually just reported it because it showed up in the list :-°