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# Copyright 2021-2025 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from __future__ import annotations
import struct
from typing import TYPE_CHECKING
from bumble import att, crypto, gatt, gatt_client
if TYPE_CHECKING:
from bumble import device
# -----------------------------------------------------------------------------
class GenericAttributeProfileService(gatt.TemplateService):
'''See Vol 3, Part G - 7 - DEFINED GENERIC ATTRIBUTE PROFILE SERVICE.'''
UUID = gatt.GATT_GENERIC_ATTRIBUTE_SERVICE
client_supported_features_characteristic: gatt.Characteristic[bytes] | None = None
server_supported_features_characteristic: gatt.Characteristic[bytes] | None = None
database_hash_characteristic: gatt.Characteristic[bytes] | None = None
service_changed_characteristic: gatt.Characteristic[bytes] | None = None
def __init__(
self,
server_supported_features: gatt.ServerSupportedFeatures | None = None,
database_hash_enabled: bool = True,
service_change_enabled: bool = True,
) -> None:
if server_supported_features is not None:
self.server_supported_features_characteristic = gatt.Characteristic(
uuid=gatt.GATT_SERVER_SUPPORTED_FEATURES_CHARACTERISTIC,
properties=gatt.Characteristic.Properties.READ,
permissions=gatt.Characteristic.Permissions.READABLE,
value=bytes([server_supported_features]),
)
if database_hash_enabled:
self.database_hash_characteristic = gatt.Characteristic(
uuid=gatt.GATT_DATABASE_HASH_CHARACTERISTIC,
properties=gatt.Characteristic.Properties.READ,
permissions=gatt.Characteristic.Permissions.READABLE,
value=gatt.CharacteristicValue(read=self.get_database_hash),
)
if service_change_enabled:
self.service_changed_characteristic = gatt.Characteristic(
uuid=gatt.GATT_SERVICE_CHANGED_CHARACTERISTIC,
properties=gatt.Characteristic.Properties.INDICATE,
permissions=gatt.Characteristic.Permissions(0),
value=b'',
)
if (database_hash_enabled and service_change_enabled) or (
server_supported_features
and (
server_supported_features & gatt.ServerSupportedFeatures.EATT_SUPPORTED
)
): # TODO: Support Multiple Handle Value Notifications
self.client_supported_features_characteristic = gatt.Characteristic(
uuid=gatt.GATT_CLIENT_SUPPORTED_FEATURES_CHARACTERISTIC,
properties=(
gatt.Characteristic.Properties.READ
| gatt.Characteristic.Properties.WRITE
),
permissions=(
gatt.Characteristic.Permissions.READABLE
| gatt.Characteristic.Permissions.WRITEABLE
),
value=bytes(1),
)
super().__init__(
characteristics=[
c
for c in (
self.service_changed_characteristic,
self.client_supported_features_characteristic,
self.database_hash_characteristic,
self.server_supported_features_characteristic,
)
if c is not None
],
primary=True,
)
@classmethod
def get_attribute_data(cls, attribute: att.Attribute) -> bytes:
if attribute.type in (
gatt.GATT_PRIMARY_SERVICE_ATTRIBUTE_TYPE,
gatt.GATT_SECONDARY_SERVICE_ATTRIBUTE_TYPE,
gatt.GATT_INCLUDE_ATTRIBUTE_TYPE,
gatt.GATT_CHARACTERISTIC_ATTRIBUTE_TYPE,
gatt.GATT_CHARACTERISTIC_EXTENDED_PROPERTIES_DESCRIPTOR,
):
assert isinstance(attribute.value, bytes)
return (
struct.pack("<H", attribute.handle)
+ attribute.type.to_bytes()
+ attribute.value
)
elif attribute.type in (
gatt.GATT_CHARACTERISTIC_USER_DESCRIPTION_DESCRIPTOR,
gatt.GATT_CLIENT_CHARACTERISTIC_CONFIGURATION_DESCRIPTOR,
gatt.GATT_SERVER_CHARACTERISTIC_CONFIGURATION_DESCRIPTOR,
gatt.GATT_CHARACTERISTIC_PRESENTATION_FORMAT_DESCRIPTOR,
gatt.GATT_CHARACTERISTIC_AGGREGATE_FORMAT_DESCRIPTOR,
):
return struct.pack("<H", attribute.handle) + attribute.type.to_bytes()
return b''
def get_database_hash(self, connection: device.Connection) -> bytes:
m = b''.join(
[
self.get_attribute_data(attribute)
for attribute in connection.device.gatt_server.attributes
]
)
return crypto.aes_cmac(m=m, k=bytes(16))
class GenericAttributeProfileServiceProxy(gatt_client.ProfileServiceProxy):
SERVICE_CLASS = GenericAttributeProfileService
client_supported_features_characteristic: (
gatt_client.CharacteristicProxy[bytes] | None
) = None
server_supported_features_characteristic: (
gatt_client.CharacteristicProxy[bytes] | None
) = None
database_hash_characteristic: gatt_client.CharacteristicProxy[bytes] | None = None
service_changed_characteristic: gatt_client.CharacteristicProxy[bytes] | None = None
_CHARACTERISTICS = {
gatt.GATT_CLIENT_SUPPORTED_FEATURES_CHARACTERISTIC: 'client_supported_features_characteristic',
gatt.GATT_SERVER_SUPPORTED_FEATURES_CHARACTERISTIC: 'server_supported_features_characteristic',
gatt.GATT_DATABASE_HASH_CHARACTERISTIC: 'database_hash_characteristic',
gatt.GATT_SERVICE_CHANGED_CHARACTERISTIC: 'service_changed_characteristic',
}
def __init__(self, service_proxy: gatt_client.ServiceProxy) -> None:
self.service_proxy = service_proxy
for uuid, attribute_name in self._CHARACTERISTICS.items():
if characteristics := self.service_proxy.get_characteristics_by_uuid(uuid):
setattr(self, attribute_name, characteristics[0])
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