Feature/format chars

[Carglglz]

Preview of hbldh#237

[Carglglz]

This adds the feature discussed in hbldh#237:
It is included in bleak.utils:

• get_char_xml (function): to parse characteristic metadata
• get_char_value (function): to unpack the raw bytes of read_gatt_char into the proper values
• (optional) pformat_char_value, map_char_value, dict_char_value, pformat_char_flags: post-processing of the characteristic value

Example: service_explorer.py:

$ python3.8 service_explorer.py
Connected: True
[Service] 180A: Device Information
        [Characteristic] 00002a01-0000-1000-8000-00805f9b34fb: (Handle: 12) (read) | Name: , Value: b'\x00\x03'
        [Characteristic] 00002a29-0000-1000-8000-00805f9b34fb: (Handle: 14) (read) | Name: , Value: b'Espressif Incorporated'
        [Characteristic] 00002a24-0000-1000-8000-00805f9b34fb: (Handle: 16) (read) | Name: , Value: b'esp32'
        [Characteristic] 00002a26-0000-1000-8000-00805f9b34fb: (Handle: 18) (read) | Name: , Value: b'micropython-1.12.0'
[Service] 180F: Battery Service
        [Characteristic] 00002a19-0000-1000-8000-00805f9b34fb: (Handle: 21) (read) | Name: , Value: b'^'
        [Characteristic] 00002a1a-0000-1000-8000-00805f9b34fb: (Handle: 23) (read,notify) | Name: , Value: b'\xbf'
                [Descriptor] 2902: (Handle: 25) | Value: b'\x00\x00'
[Service] 181A: Environmental Sensing
        [Characteristic] 00002a6e-0000-1000-8000-00805f9b34fb: (Handle: 27) (read,notify) | Name: , Value: b'Z\x16'
                [Descriptor] 2902: (Handle: 29) | Value: b'\x00\x00'"""

Example: service_explorer.py with get_char_value and pformat_char_value

    for char in service.characteristics:
                if "read" in char.properties:
                    try:
                        value = bytes(await client.read_gatt_char(char.uuid))
                        value = get_char_value(value, char)
                        pretty_format = pformat_char_value(value,
                                                           one_line=True,
                                                           prnt=False, rtn=True)
                    except Exception as e:
                        print(e)
                        value = str(e).encode()
                        pretty_format = value
                else:
                    value = None
                    pretty_format = value
                log.info(
                    "\t[Characteristic] {0}: (Handle: {1}) ({2}) | Name: {3}, Value: {4} ".format(
                        char.uuid,
                        char.handle,
                        ",".join(char.properties),
                        uuidstr_to_str(char.uuid),
                        pretty_format,
                    )
                )

$ python3.8 service_explorer.py
Connected: True
[Service] 180A: Device Information

        [Characteristic] 00002a01-0000-1000-8000-00805f9b34fb: (Handle: 12) (read) | Name: Appearance, Value: Category: Generic Thermometer
        [Characteristic] 00002a29-0000-1000-8000-00805f9b34fb: (Handle: 14) (read) | Name: Manufacturer Name String, Value: Manufacturer Name: Espressif Incorporated
        [Characteristic] 00002a24-0000-1000-8000-00805f9b34fb: (Handle: 16) (read) | Name: Model Number String, Value: Model Number: esp32
        [Characteristic] 00002a26-0000-1000-8000-00805f9b34fb: (Handle: 18) (read) | Name: Firmware Revision String, Value: Firmware Revision: micropython-1.12.0
[Service] 180F: Battery Service
        [Characteristic] 00002a19-0000-1000-8000-00805f9b34fb: (Handle: 21) (read) | Name: Battery Level, Value: Level: 94 %
        [Characteristic] 00002a1a-0000-1000-8000-00805f9b34fb: (Handle: 23) (read,notify) | Name: Battery Power State, Value: State: {'BitGroup 0': 'Present', 'BitGroup 2': 'Discharging', 'BitGroup 4':
'Charging (Chargeable)', 'BitGroup 6': 'Good Level'}
                [Descriptor] 2902: (Handle: 25) | Value: b'\x00\x00'
[Service] 181A: Environmental Sensing
        [Characteristic] 00002a6e-0000-1000-8000-00805f9b34fb: (Handle: 27) (read,notify) | Name: Temperature, Value: Temperature: 57.22 °C
                [Descriptor] 2902: (Handle: 29) | Value: b'\x00\x00'