Merge pull request #278 from zxzxwu/gatt2

Typing GATT

5 files changed, 245 insertions, 138 deletions

diff --git a/bumble/att.py b/bumble/att.py
index 55ae8a5..db8d2ba 100644
--- a/bumble/att.py
+++ b/bumble/att.py
@@ -23,13 +23,14 @@
 # Imports
 # -----------------------------------------------------------------------------
 from __future__ import annotations
+import enum
 import functools
 import struct
 from pyee import EventEmitter
-from typing import Dict, Type, TYPE_CHECKING
+from typing import Dict, Type, List, Protocol, Union, Optional, Any, TYPE_CHECKING
 
-from bumble.core import UUID, name_or_number, get_dict_key_by_value, ProtocolError
-from bumble.hci import HCI_Object, key_with_value, HCI_Constant
+from bumble.core import UUID, name_or_number, ProtocolError
+from bumble.hci import HCI_Object, key_with_value
 from bumble.colors import color
 
 if TYPE_CHECKING:
@@ -182,6 +183,7 @@ UUID_2_FIELD_SPEC    = lambda x, y: UUID.parse_uuid_2(x, y)  # noqa: E731
 # pylint: enable=line-too-long
 # pylint: disable=invalid-name
 
+
 # -----------------------------------------------------------------------------
 # Exceptions
 # -----------------------------------------------------------------------------
@@ -209,7 +211,7 @@ class ATT_PDU:
 
     pdu_classes: Dict[int, Type[ATT_PDU]] = {}
     op_code = 0
-    name = None
+    name: str
 
     @staticmethod
     def from_bytes(pdu):
@@ -720,47 +722,67 @@ class ATT_Handle_Value_Confirmation(ATT_PDU):
 
 
 # -----------------------------------------------------------------------------
-class Attribute(EventEmitter):
-    # Permission flags
-    READABLE = 0x01
-    WRITEABLE = 0x02
-    READ_REQUIRES_ENCRYPTION = 0x04
-    WRITE_REQUIRES_ENCRYPTION = 0x08
-    READ_REQUIRES_AUTHENTICATION = 0x10
-    WRITE_REQUIRES_AUTHENTICATION = 0x20
-    READ_REQUIRES_AUTHORIZATION = 0x40
-    WRITE_REQUIRES_AUTHORIZATION = 0x80
-
-    PERMISSION_NAMES = {
-        READABLE: 'READABLE',
-        WRITEABLE: 'WRITEABLE',
-        READ_REQUIRES_ENCRYPTION: 'READ_REQUIRES_ENCRYPTION',
-        WRITE_REQUIRES_ENCRYPTION: 'WRITE_REQUIRES_ENCRYPTION',
-        READ_REQUIRES_AUTHENTICATION: 'READ_REQUIRES_AUTHENTICATION',
-        WRITE_REQUIRES_AUTHENTICATION: 'WRITE_REQUIRES_AUTHENTICATION',
-        READ_REQUIRES_AUTHORIZATION: 'READ_REQUIRES_AUTHORIZATION',
-        WRITE_REQUIRES_AUTHORIZATION: 'WRITE_REQUIRES_AUTHORIZATION',
-    }
+class ConnectionValue(Protocol):
+    def read(self, connection) -> bytes:
+        ...
 
-    @staticmethod
-    def string_to_permissions(permissions_str: str):
-        try:
-            return functools.reduce(
-                lambda x, y: x | get_dict_key_by_value(Attribute.PERMISSION_NAMES, y),
-                permissions_str.split(","),
-                0,
-            )
-        except TypeError as exc:
-            raise TypeError(
-                f"Attribute::permissions error:\nExpected a string containing any of the keys, separated by commas: {','.join(Attribute.PERMISSION_NAMES.values())}\nGot: {permissions_str}"
-            ) from exc
+    def write(self, connection, value: bytes) -> None:
+        ...
 
-    def __init__(self, attribute_type, permissions, value=b''):
+
+# -----------------------------------------------------------------------------
+class Attribute(EventEmitter):
+    class Permissions(enum.IntFlag):
+        READABLE = 0x01
+        WRITEABLE = 0x02
+        READ_REQUIRES_ENCRYPTION = 0x04
+        WRITE_REQUIRES_ENCRYPTION = 0x08
+        READ_REQUIRES_AUTHENTICATION = 0x10
+        WRITE_REQUIRES_AUTHENTICATION = 0x20
+        READ_REQUIRES_AUTHORIZATION = 0x40
+        WRITE_REQUIRES_AUTHORIZATION = 0x80
+
+        @classmethod
+        def from_string(cls, permissions_str: str) -> Attribute.Permissions:
+            try:
+                return functools.reduce(
+                    lambda x, y: x | Attribute.Permissions[y],
+                    permissions_str.replace('|', ',').split(","),
+                    Attribute.Permissions(0),
+                )
+            except TypeError as exc:
+                # The check for `p.name is not None` here is needed because for InFlag
+                # enums, the .name property can be None, when the enum value is 0,
+                # so the type hint for .name is Optional[str].
+                enum_list: List[str] = [p.name for p in cls if p.name is not None]
+                enum_list_str = ",".join(enum_list)
+                raise TypeError(
+                    f"Attribute::permissions error:\nExpected a string containing any of the keys, separated by commas: {enum_list_str  }\nGot: {permissions_str}"
+                ) from exc
+
+    # Permission flags(legacy-use only)
+    READABLE = Permissions.READABLE
+    WRITEABLE = Permissions.WRITEABLE
+    READ_REQUIRES_ENCRYPTION = Permissions.READ_REQUIRES_ENCRYPTION
+    WRITE_REQUIRES_ENCRYPTION = Permissions.WRITE_REQUIRES_ENCRYPTION
+    READ_REQUIRES_AUTHENTICATION = Permissions.READ_REQUIRES_AUTHENTICATION
+    WRITE_REQUIRES_AUTHENTICATION = Permissions.WRITE_REQUIRES_AUTHENTICATION
+    READ_REQUIRES_AUTHORIZATION = Permissions.READ_REQUIRES_AUTHORIZATION
+    WRITE_REQUIRES_AUTHORIZATION = Permissions.WRITE_REQUIRES_AUTHORIZATION
+
+    value: Union[str, bytes, ConnectionValue]
+
+    def __init__(
+        self,
+        attribute_type: Union[str, bytes, UUID],
+        permissions: Union[str, Attribute.Permissions],
+        value: Union[str, bytes, ConnectionValue] = b'',
+    ) -> None:
         EventEmitter.__init__(self)
         self.handle = 0
         self.end_group_handle = 0
         if isinstance(permissions, str):
-            self.permissions = self.string_to_permissions(permissions)
+            self.permissions = Attribute.Permissions.from_string(permissions)
         else:
             self.permissions = permissions
 
@@ -778,22 +800,26 @@ class Attribute(EventEmitter):
         else:
             self.value = value
 
-    def encode_value(self, value):
+    def encode_value(self, value: Any) -> bytes:
         return value
 
-    def decode_value(self, value_bytes):
+    def decode_value(self, value_bytes: bytes) -> Any:
         return value_bytes
 
-    def read_value(self, connection: Connection):
+    def read_value(self, connection: Optional[Connection]) -> bytes:
         if (
-            self.permissions & self.READ_REQUIRES_ENCRYPTION
-        ) and not connection.encryption:
+            (self.permissions & self.READ_REQUIRES_ENCRYPTION)
+            and connection is not None
+            and not connection.encryption
+        ):
             raise ATT_Error(
                 error_code=ATT_INSUFFICIENT_ENCRYPTION_ERROR, att_handle=self.handle
             )
         if (
-            self.permissions & self.READ_REQUIRES_AUTHENTICATION
-        ) and not connection.authenticated:
+            (self.permissions & self.READ_REQUIRES_AUTHENTICATION)
+            and connection is not None
+            and not connection.authenticated
+        ):
             raise ATT_Error(
                 error_code=ATT_INSUFFICIENT_AUTHENTICATION_ERROR, att_handle=self.handle
             )
@@ -803,9 +829,9 @@ class Attribute(EventEmitter):
                 error_code=ATT_INSUFFICIENT_AUTHORIZATION_ERROR, att_handle=self.handle
             )
 
-        if read := getattr(self.value, 'read', None):
+        if hasattr(self.value, 'read'):
             try:
-                value = read(connection)  # pylint: disable=not-callable
+                value = self.value.read(connection)
             except ATT_Error as error:
                 raise ATT_Error(
                     error_code=error.error_code, att_handle=self.handle
@@ -815,7 +841,7 @@ class Attribute(EventEmitter):
 
         return self.encode_value(value)
 
-    def write_value(self, connection: Connection, value_bytes):
+    def write_value(self, connection: Connection, value_bytes: bytes) -> None:
         if (
             self.permissions & self.WRITE_REQUIRES_ENCRYPTION
         ) and not connection.encryption:
@@ -836,9 +862,9 @@ class Attribute(EventEmitter):
 
         value = self.decode_value(value_bytes)
 
-        if write := getattr(self.value, 'write', None):
+        if hasattr(self.value, 'write'):
             try:
-                write(connection, value)  # pylint: disable=not-callable
+                self.value.write(connection, value)  # pylint: disable=not-callable
             except ATT_Error as error:
                 raise ATT_Error(
                     error_code=error.error_code, att_handle=self.handle
diff --git a/bumble/gatt.py b/bumble/gatt.py
index 067f31d..fe3e85c 100644
--- a/bumble/gatt.py
+++ b/bumble/gatt.py
@@ -28,7 +28,7 @@ import enum
 import functools
 import logging
 import struct
-from typing import Optional, Sequence, List
+from typing import Optional, Sequence, Iterable, List, Union
 
 from .colors import color
 from .core import UUID, get_dict_key_by_value
@@ -187,7 +187,7 @@ GATT_CENTRAL_ADDRESS_RESOLUTION__CHARACTERISTIC                = UUID.from_16_bi
 # -----------------------------------------------------------------------------
 
 
-def show_services(services):
+def show_services(services: Iterable[Service]) -> None:
     for service in services:
         print(color(str(service), 'cyan'))
 
@@ -210,11 +210,11 @@ class Service(Attribute):
 
     def __init__(
         self,
-        uuid,
+        uuid: Union[str, UUID],
         characteristics: List[Characteristic],
         primary=True,
         included_services: List[Service] = [],
-    ):
+    ) -> None:
         # Convert the uuid to a UUID object if it isn't already
         if isinstance(uuid, str):
             uuid = UUID(uuid)
@@ -239,7 +239,7 @@ class Service(Attribute):
         """
         return None
 
-    def __str__(self):
+    def __str__(self) -> str:
         return (
             f'Service(handle=0x{self.handle:04X}, '
             f'end=0x{self.end_group_handle:04X}, '
@@ -255,9 +255,11 @@ class TemplateService(Service):
     to expose their UUID as a class property
     '''
 
-    UUID: Optional[UUID] = None
+    UUID: UUID
 
-    def __init__(self, characteristics, primary=True):
+    def __init__(
+        self, characteristics: List[Characteristic], primary: bool = True
+    ) -> None:
         super().__init__(self.UUID, characteristics, primary)
 
 
@@ -269,7 +271,7 @@ class IncludedServiceDeclaration(Attribute):
 
     service: Service
 
-    def __init__(self, service):
+    def __init__(self, service: Service) -> None:
         declaration_bytes = struct.pack(
             '<HH2s', service.handle, service.end_group_handle, service.uuid.to_bytes()
         )
@@ -278,7 +280,7 @@ class IncludedServiceDeclaration(Attribute):
         )
         self.service = service
 
-    def __str__(self):
+    def __str__(self) -> str:
         return (
             f'IncludedServiceDefinition(handle=0x{self.handle:04X}, '
             f'group_starting_handle=0x{self.service.handle:04X}, '
@@ -326,7 +328,7 @@ class Characteristic(Attribute):
                     f"Characteristic.Properties::from_string() error:\nExpected a string containing any of the keys, separated by , or |: {enum_list_str}\nGot: {properties_str}"
                 )
 
-        def __str__(self):
+        def __str__(self) -> str:
             # NOTE: we override this method to offer a consistent result between python
             # versions: the value returned by IntFlag.__str__() changed in version 11.
             return '|'.join(
@@ -348,10 +350,10 @@ class Characteristic(Attribute):
 
     def __init__(
         self,
-        uuid,
+        uuid: Union[str, bytes, UUID],
         properties: Characteristic.Properties,
-        permissions,
-        value=b'',
+        permissions: Union[str, Attribute.Permissions],
+        value: Union[str, bytes, CharacteristicValue] = b'',
         descriptors: Sequence[Descriptor] = (),
     ):
         super().__init__(uuid, permissions, value)
@@ -369,7 +371,7 @@ class Characteristic(Attribute):
     def has_properties(self, properties: Characteristic.Properties) -> bool:
         return self.properties & properties == properties
 
-    def __str__(self):
+    def __str__(self) -> str:
         return (
             f'Characteristic(handle=0x{self.handle:04X}, '
             f'end=0x{self.end_group_handle:04X}, '
@@ -386,7 +388,7 @@ class CharacteristicDeclaration(Attribute):
 
     characteristic: Characteristic
 
-    def __init__(self, characteristic, value_handle):
+    def __init__(self, characteristic: Characteristic, value_handle: int) -> None:
         declaration_bytes = (
             struct.pack('<BH', characteristic.properties, value_handle)
             + characteristic.uuid.to_pdu_bytes()
@@ -397,7 +399,7 @@ class CharacteristicDeclaration(Attribute):
         self.value_handle = value_handle
         self.characteristic = characteristic
 
-    def __str__(self):
+    def __str__(self) -> str:
         return (
             f'CharacteristicDeclaration(handle=0x{self.handle:04X}, '
             f'value_handle=0x{self.value_handle:04X}, '
@@ -520,7 +522,7 @@ class CharacteristicAdapter:
 
         return self.wrapped_characteristic.unsubscribe(subscriber)
 
-    def __str__(self):
+    def __str__(self) -> str:
         wrapped = str(self.wrapped_characteristic)
         return f'{self.__class__.__name__}({wrapped})'
 
@@ -600,10 +602,10 @@ class UTF8CharacteristicAdapter(CharacteristicAdapter):
     Adapter that converts strings to/from bytes using UTF-8 encoding
     '''
 
-    def encode_value(self, value):
+    def encode_value(self, value: str) -> bytes:
         return value.encode('utf-8')
 
-    def decode_value(self, value):
+    def decode_value(self, value: bytes) -> str:
         return value.decode('utf-8')
 
 
@@ -613,7 +615,7 @@ class Descriptor(Attribute):
     See Vol 3, Part G - 3.3.3 Characteristic Descriptor Declarations
     '''
 
-    def __str__(self):
+    def __str__(self) -> str:
         return (
             f'Descriptor(handle=0x{self.handle:04X}, '
             f'type={self.type}, '
diff --git a/bumble/gatt_client.py b/bumble/gatt_client.py
index a33039e..e3b8bb2 100644
--- a/bumble/gatt_client.py
+++ b/bumble/gatt_client.py
@@ -28,7 +28,18 @@ import asyncio
 import logging
 import struct
 from datetime import datetime
-from typing import List, Optional, Dict, Tuple, Callable, Union, Any
+from typing import (
+    List,
+    Optional,
+    Dict,
+    Tuple,
+    Callable,
+    Union,
+    Any,
+    Iterable,
+    Type,
+    TYPE_CHECKING,
+)
 
 from pyee import EventEmitter
 
@@ -66,8 +77,12 @@ from .gatt import (
     GATT_INCLUDE_ATTRIBUTE_TYPE,
     Characteristic,
     ClientCharacteristicConfigurationBits,
+    TemplateService,
 )
 
+if TYPE_CHECKING:
+    from bumble.device import Connection
+
 # -----------------------------------------------------------------------------
 # Logging
 # -----------------------------------------------------------------------------
@@ -78,16 +93,16 @@ logger = logging.getLogger(__name__)
 # Proxies
 # -----------------------------------------------------------------------------
 class AttributeProxy(EventEmitter):
-    client: Client
-
-    def __init__(self, client, handle, end_group_handle, attribute_type):
+    def __init__(
+        self, client: Client, handle: int, end_group_handle: int, attribute_type: UUID
+    ) -> None:
         EventEmitter.__init__(self)
         self.client = client
         self.handle = handle
         self.end_group_handle = end_group_handle
         self.type = attribute_type
 
-    async def read_value(self, no_long_read=False):
+    async def read_value(self, no_long_read: bool = False) -> bytes:
         return self.decode_value(
             await self.client.read_value(self.handle, no_long_read)
         )
@@ -97,13 +112,13 @@ class AttributeProxy(EventEmitter):
             self.handle, self.encode_value(value), with_response
         )
 
-    def encode_value(self, value):
+    def encode_value(self, value: Any) -> bytes:
         return value
 
-    def decode_value(self, value_bytes):
+    def decode_value(self, value_bytes: bytes) -> Any:
         return value_bytes
 
-    def __str__(self):
+    def __str__(self) -> str:
         return f'Attribute(handle=0x{self.handle:04X}, type={self.type})'
 
 
@@ -136,14 +151,14 @@ class ServiceProxy(AttributeProxy):
     def get_characteristics_by_uuid(self, uuid):
         return self.client.get_characteristics_by_uuid(uuid, self)
 
-    def __str__(self):
+    def __str__(self) -> str:
         return f'Service(handle=0x{self.handle:04X}, uuid={self.uuid})'
 
 
 class CharacteristicProxy(AttributeProxy):
     properties: Characteristic.Properties
     descriptors: List[DescriptorProxy]
-    subscribers: Dict[Any, Callable]
+    subscribers: Dict[Any, Callable[[bytes], Any]]
 
     def __init__(
         self,
@@ -171,7 +186,9 @@ class CharacteristicProxy(AttributeProxy):
         return await self.client.discover_descriptors(self)
 
     async def subscribe(
-        self, subscriber: Optional[Callable] = None, prefer_notify=True
+        self,
+        subscriber: Optional[Callable[[bytes], Any]] = None,
+        prefer_notify: bool = True,
     ):
         if subscriber is not None:
             if subscriber in self.subscribers:
@@ -195,7 +212,7 @@ class CharacteristicProxy(AttributeProxy):
 
         return await self.client.unsubscribe(self, subscriber)
 
-    def __str__(self):
+    def __str__(self) -> str:
         return (
             f'Characteristic(handle=0x{self.handle:04X}, '
             f'uuid={self.uuid}, '
@@ -207,7 +224,7 @@ class DescriptorProxy(AttributeProxy):
     def __init__(self, client, handle, descriptor_type):
         super().__init__(client, handle, 0, descriptor_type)
 
-    def __str__(self):
+    def __str__(self) -> str:
         return f'Descriptor(handle=0x{self.handle:04X}, type={self.type})'
 
 
@@ -216,8 +233,10 @@ class ProfileServiceProxy:
     Base class for profile-specific service proxies
     '''
 
+    SERVICE_CLASS: Type[TemplateService]
+
     @classmethod
-    def from_client(cls, client):
+    def from_client(cls, client: Client) -> ProfileServiceProxy:
         return ServiceProxy.from_client(cls, client, cls.SERVICE_CLASS.UUID)
 
 
@@ -227,8 +246,12 @@ class ProfileServiceProxy:
 class Client:
     services: List[ServiceProxy]
     cached_values: Dict[int, Tuple[datetime, bytes]]
+    notification_subscribers: Dict[int, Callable[[bytes], Any]]
+    indication_subscribers: Dict[int, Callable[[bytes], Any]]
+    pending_response: Optional[asyncio.futures.Future[ATT_PDU]]
+    pending_request: Optional[ATT_PDU]
 
-    def __init__(self, connection):
+    def __init__(self, connection: Connection) -> None:
         self.connection = connection
         self.mtu_exchange_done = False
         self.request_semaphore = asyncio.Semaphore(1)
@@ -241,16 +264,16 @@ class Client:
         self.services = []
         self.cached_values = {}
 
-    def send_gatt_pdu(self, pdu):
+    def send_gatt_pdu(self, pdu: bytes) -> None:
         self.connection.send_l2cap_pdu(ATT_CID, pdu)
 
-    async def send_command(self, command):
+    async def send_command(self, command: ATT_PDU) -> None:
         logger.debug(
             f'GATT Command from client: [0x{self.connection.handle:04X}] {command}'
         )
         self.send_gatt_pdu(command.to_bytes())
 
-    async def send_request(self, request):
+    async def send_request(self, request: ATT_PDU):
         logger.debug(
             f'GATT Request from client: [0x{self.connection.handle:04X}] {request}'
         )
@@ -279,14 +302,14 @@ class Client:
 
         return response
 
-    def send_confirmation(self, confirmation):
+    def send_confirmation(self, confirmation: ATT_Handle_Value_Confirmation) -> None:
         logger.debug(
             f'GATT Confirmation from client: [0x{self.connection.handle:04X}] '
             f'{confirmation}'
         )
         self.send_gatt_pdu(confirmation.to_bytes())
 
-    async def request_mtu(self, mtu):
+    async def request_mtu(self, mtu: int) -> int:
         # Check the range
         if mtu < ATT_DEFAULT_MTU:
             raise ValueError(f'MTU must be >= {ATT_DEFAULT_MTU}')
@@ -313,10 +336,12 @@ class Client:
 
         return self.connection.att_mtu
 
-    def get_services_by_uuid(self, uuid):
+    def get_services_by_uuid(self, uuid: UUID) -> List[ServiceProxy]:
         return [service for service in self.services if service.uuid == uuid]
 
-    def get_characteristics_by_uuid(self, uuid, service=None):
+    def get_characteristics_by_uuid(
+        self, uuid: UUID, service: Optional[ServiceProxy] = None
+    ) -> List[CharacteristicProxy]:
         services = [service] if service else self.services
         return [
             c
@@ -363,7 +388,7 @@ class Client:
         if not already_known:
             self.services.append(service)
 
-    async def discover_services(self, uuids=None) -> List[ServiceProxy]:
+    async def discover_services(self, uuids: Iterable[UUID] = []) -> List[ServiceProxy]:
         '''
         See Vol 3, Part G - 4.4.1 Discover All Primary Services
         '''
@@ -435,7 +460,7 @@ class Client:
 
         return services
 
-    async def discover_service(self, uuid):
+    async def discover_service(self, uuid: Union[str, UUID]) -> List[ServiceProxy]:
         '''
         See Vol 3, Part G - 4.4.2 Discover Primary Service by Service UUID
         '''
@@ -468,7 +493,7 @@ class Client:
                         f'{HCI_Constant.error_name(response.error_code)}'
                     )
                     # TODO raise appropriate exception
-                    return
+                    return []
                 break
 
             for attribute_handle, end_group_handle in response.handles_information:
@@ -480,7 +505,7 @@ class Client:
                     logger.warning(
                         f'bogus handle values: {attribute_handle} {end_group_handle}'
                     )
-                    return
+                    return []
 
                 # Create a service proxy for this service
                 service = ServiceProxy(
@@ -721,7 +746,7 @@ class Client:
 
         return descriptors
 
-    async def discover_attributes(self):
+    async def discover_attributes(self) -> List[AttributeProxy]:
         '''
         Discover all attributes, regardless of type
         '''
@@ -844,7 +869,9 @@ class Client:
             # No more subscribers left
             await self.write_value(cccd, b'\x00\x00', with_response=True)
 
-    async def read_value(self, attribute, no_long_read=False):
+    async def read_value(
+        self, attribute: Union[int, AttributeProxy], no_long_read: bool = False
+    ) -> Any:
         '''
         See Vol 3, Part G - 4.8.1 Read Characteristic Value
 
@@ -905,7 +932,9 @@ class Client:
         # Return the value as bytes
         return attribute_value
 
-    async def read_characteristics_by_uuid(self, uuid, service):
+    async def read_characteristics_by_uuid(
+        self, uuid: UUID, service: Optional[ServiceProxy]
+    ) -> List[bytes]:
         '''
         See Vol 3, Part G - 4.8.2 Read Using Characteristic UUID
         '''
@@ -960,7 +989,12 @@ class Client:
 
         return characteristics_values
 
-    async def write_value(self, attribute, value, with_response=False):
+    async def write_value(
+        self,
+        attribute: Union[int, AttributeProxy],
+        value: bytes,
+        with_response: bool = False,
+    ) -> None:
         '''
         See Vol 3, Part G - 4.9.1 Write Without Response & 4.9.3 Write Characteristic
         Value
@@ -990,7 +1024,7 @@ class Client:
                 )
             )
 
-    def on_gatt_pdu(self, att_pdu):
+    def on_gatt_pdu(self, att_pdu: ATT_PDU) -> None:
         logger.debug(
             f'GATT Response to client: [0x{self.connection.handle:04X}] {att_pdu}'
         )
@@ -1013,6 +1047,7 @@ class Client:
                     return
 
             # Return the response to the coroutine that is waiting for it
+            assert self.pending_response is not None
             self.pending_response.set_result(att_pdu)
         else:
             handler_name = f'on_{att_pdu.name.lower()}'
@@ -1060,7 +1095,7 @@ class Client:
         # Confirm that we received the indication
         self.send_confirmation(ATT_Handle_Value_Confirmation())
 
-    def cache_value(self, attribute_handle: int, value: bytes):
+    def cache_value(self, attribute_handle: int, value: bytes) -> None:
         self.cached_values[attribute_handle] = (
             datetime.now(),
             value,
diff --git a/bumble/gatt_server.py b/bumble/gatt_server.py
index 3624905..cdf1b5e 100644
--- a/bumble/gatt_server.py
+++ b/bumble/gatt_server.py
@@ -23,11 +23,12 @@
 # -----------------------------------------------------------------------------
 # Imports
 # -----------------------------------------------------------------------------
+from __future__ import annotations
 import asyncio
 import logging
 from collections import defaultdict
 import struct
-from typing import List, Tuple, Optional, TypeVar, Type
+from typing import List, Tuple, Optional, TypeVar, Type, Dict, Iterable, TYPE_CHECKING
 from pyee import EventEmitter
 
 from .colors import color
@@ -42,6 +43,7 @@ from .att import (
     ATT_INVALID_OFFSET_ERROR,
     ATT_REQUEST_NOT_SUPPORTED_ERROR,
     ATT_REQUESTS,
+    ATT_PDU,
     ATT_UNLIKELY_ERROR_ERROR,
     ATT_UNSUPPORTED_GROUP_TYPE_ERROR,
     ATT_Error,
@@ -73,6 +75,8 @@ from .gatt import (
     Service,
 )
 
+if TYPE_CHECKING:
+    from bumble.device import Device, Connection
 
 # -----------------------------------------------------------------------------
 # Logging
@@ -91,8 +95,13 @@ GATT_SERVER_DEFAULT_MAX_MTU = 517
 # -----------------------------------------------------------------------------
 class Server(EventEmitter):
     attributes: List[Attribute]
+    services: List[Service]
+    attributes_by_handle: Dict[int, Attribute]
+    subscribers: Dict[int, Dict[int, bytes]]
+    indication_semaphores: defaultdict[int, asyncio.Semaphore]
+    pending_confirmations: defaultdict[int, Optional[asyncio.futures.Future]]
 
-    def __init__(self, device):
+    def __init__(self, device: Device) -> None:
         super().__init__()
         self.device = device
         self.services = []
@@ -107,16 +116,16 @@ class Server(EventEmitter):
         self.indication_semaphores = defaultdict(lambda: asyncio.Semaphore(1))
         self.pending_confirmations = defaultdict(lambda: None)
 
-    def __str__(self):
+    def __str__(self) -> str:
         return "\n".join(map(str, self.attributes))
 
-    def send_gatt_pdu(self, connection_handle, pdu):
+    def send_gatt_pdu(self, connection_handle: int, pdu: bytes) -> None:
         self.device.send_l2cap_pdu(connection_handle, ATT_CID, pdu)
 
-    def next_handle(self):
+    def next_handle(self) -> int:
         return 1 + len(self.attributes)
 
-    def get_advertising_service_data(self):
+    def get_advertising_service_data(self) -> Dict[Attribute, bytes]:
         return {
             attribute: data
             for attribute in self.attributes
@@ -124,7 +133,7 @@ class Server(EventEmitter):
             and (data := attribute.get_advertising_data())
         }
 
-    def get_attribute(self, handle):
+    def get_attribute(self, handle: int) -> Optional[Attribute]:
         attribute = self.attributes_by_handle.get(handle)
         if attribute:
             return attribute
@@ -173,12 +182,17 @@ class Server(EventEmitter):
 
         return next(
             (
-                (attribute, self.get_attribute(attribute.characteristic.handle))
+                (
+                    attribute,
+                    self.get_attribute(attribute.characteristic.handle),
+                )  # type: ignore
                 for attribute in map(
                     self.get_attribute,
                     range(service_handle.handle, service_handle.end_group_handle + 1),
                 )
-                if attribute.type == GATT_CHARACTERISTIC_ATTRIBUTE_TYPE
+                if attribute is not None
+                and attribute.type == GATT_CHARACTERISTIC_ATTRIBUTE_TYPE
+                and isinstance(attribute, CharacteristicDeclaration)
                 and attribute.characteristic.uuid == characteristic_uuid
             ),
             None,
@@ -197,7 +211,7 @@ class Server(EventEmitter):
 
         return next(
             (
-                attribute
+                attribute  # type: ignore
                 for attribute in map(
                     self.get_attribute,
                     range(
@@ -205,12 +219,12 @@ class Server(EventEmitter):
                         characteristic_value.end_group_handle + 1,
                     ),
                 )
-                if attribute.type == descriptor_uuid
+                if attribute is not None and attribute.type == descriptor_uuid
             ),
             None,
         )
 
-    def add_attribute(self, attribute):
+    def add_attribute(self, attribute: Attribute) -> None:
         # Assign a handle to this attribute
         attribute.handle = self.next_handle()
         attribute.end_group_handle = (
@@ -220,7 +234,7 @@ class Server(EventEmitter):
         # Add this attribute to the list
         self.attributes.append(attribute)
 
-    def add_service(self, service: Service):
+    def add_service(self, service: Service) -> None:
         # Add the service attribute to the DB
         self.add_attribute(service)
 
@@ -285,11 +299,13 @@ class Server(EventEmitter):
         service.end_group_handle = self.attributes[-1].handle
         self.services.append(service)
 
-    def add_services(self, services):
+    def add_services(self, services: Iterable[Service]) -> None:
         for service in services:
             self.add_service(service)
 
-    def read_cccd(self, connection, characteristic):
+    def read_cccd(
+        self, connection: Optional[Connection], characteristic: Characteristic
+    ) -> bytes:
         if connection is None:
             return bytes([0, 0])
 
@@ -300,7 +316,12 @@ class Server(EventEmitter):
 
         return cccd or bytes([0, 0])
 
-    def write_cccd(self, connection, characteristic, value):
+    def write_cccd(
+        self,
+        connection: Connection,
+        characteristic: Characteristic,
+        value: bytes,
+    ) -> None:
         logger.debug(
             f'Subscription update for connection=0x{connection.handle:04X}, '
             f'handle=0x{characteristic.handle:04X}: {value.hex()}'
@@ -327,13 +348,19 @@ class Server(EventEmitter):
             indicate_enabled,
         )
 
-    def send_response(self, connection, response):
+    def send_response(self, connection: Connection, response: ATT_PDU) -> None:
         logger.debug(
             f'GATT Response from server: [0x{connection.handle:04X}] {response}'
         )
         self.send_gatt_pdu(connection.handle, response.to_bytes())
 
-    async def notify_subscriber(self, connection, attribute, value=None, force=False):
+    async def notify_subscriber(
+        self,
+        connection: Connection,
+        attribute: Attribute,
+        value: Optional[bytes] = None,
+        force: bool = False,
+    ) -> None:
         # Check if there's a subscriber
         if not force:
             subscribers = self.subscribers.get(connection.handle)
@@ -370,7 +397,13 @@ class Server(EventEmitter):
         )
         self.send_gatt_pdu(connection.handle, bytes(notification))
 
-    async def indicate_subscriber(self, connection, attribute, value=None, force=False):
+    async def indicate_subscriber(
+        self,
+        connection: Connection,
+        attribute: Attribute,
+        value: Optional[bytes] = None,
+        force: bool = False,
+    ) -> None:
         # Check if there's a subscriber
         if not force:
             subscribers = self.subscribers.get(connection.handle)
@@ -411,15 +444,13 @@ class Server(EventEmitter):
             assert self.pending_confirmations[connection.handle] is None
 
             # Create a future value to hold the eventual response
-            self.pending_confirmations[
+            pending_confirmation = self.pending_confirmations[
                 connection.handle
             ] = asyncio.get_running_loop().create_future()
 
             try:
                 self.send_gatt_pdu(connection.handle, indication.to_bytes())
-                await asyncio.wait_for(
-                    self.pending_confirmations[connection.handle], GATT_REQUEST_TIMEOUT
-                )
+                await asyncio.wait_for(pending_confirmation, GATT_REQUEST_TIMEOUT)
             except asyncio.TimeoutError as error:
                 logger.warning(color('!!! GATT Indicate timeout', 'red'))
                 raise TimeoutError(f'GATT timeout for {indication.name}') from error
@@ -427,8 +458,12 @@ class Server(EventEmitter):
                 self.pending_confirmations[connection.handle] = None
 
     async def notify_or_indicate_subscribers(
-        self, indicate, attribute, value=None, force=False
-    ):
+        self,
+        indicate: bool,
+        attribute: Attribute,
+        value: Optional[bytes] = None,
+        force: bool = False,
+    ) -> None:
         # Get all the connections for which there's at least one subscription
         connections = [
             connection
@@ -450,13 +485,23 @@ class Server(EventEmitter):
                 ]
             )
 
-    async def notify_subscribers(self, attribute, value=None, force=False):
+    async def notify_subscribers(
+        self,
+        attribute: Attribute,
+        value: Optional[bytes] = None,
+        force: bool = False,
+    ):
         return await self.notify_or_indicate_subscribers(False, attribute, value, force)
 
-    async def indicate_subscribers(self, attribute, value=None, force=False):
+    async def indicate_subscribers(
+        self,
+        attribute: Attribute,
+        value: Optional[bytes] = None,
+        force: bool = False,
+    ):
         return await self.notify_or_indicate_subscribers(True, attribute, value, force)
 
-    def on_disconnection(self, connection):
+    def on_disconnection(self, connection: Connection) -> None:
         if connection.handle in self.subscribers:
             del self.subscribers[connection.handle]
         if connection.handle in self.indication_semaphores:
@@ -464,7 +509,7 @@ class Server(EventEmitter):
         if connection.handle in self.pending_confirmations:
             del self.pending_confirmations[connection.handle]
 
-    def on_gatt_pdu(self, connection, att_pdu):
+    def on_gatt_pdu(self, connection: Connection, att_pdu: ATT_PDU) -> None:
         logger.debug(f'GATT Request to server: [0x{connection.handle:04X}] {att_pdu}')
         handler_name = f'on_{att_pdu.name.lower()}'
         handler = getattr(self, handler_name, None)
@@ -506,7 +551,7 @@ class Server(EventEmitter):
     #######################################################
     # ATT handlers
     #######################################################
-    def on_att_request(self, connection, pdu):
+    def on_att_request(self, connection: Connection, pdu: ATT_PDU) -> None:
         '''
         Handler for requests without a more specific handler
         '''
@@ -679,7 +724,6 @@ class Server(EventEmitter):
             and attribute.handle <= request.ending_handle
             and pdu_space_available
         ):
-
             try:
                 attribute_value = attribute.read_value(connection)
             except ATT_Error as error:
diff --git a/tests/gatt_test.py b/tests/gatt_test.py
index dd0277e..d9f6d60 100644
--- a/tests/gatt_test.py
+++ b/tests/gatt_test.py
@@ -891,10 +891,10 @@ async def async_main():
 
 
 # -----------------------------------------------------------------------------
-def test_attribute_string_to_permissions():
-    assert Attribute.string_to_permissions('READABLE') == 1
-    assert Attribute.string_to_permissions('WRITEABLE') == 2
-    assert Attribute.string_to_permissions('READABLE,WRITEABLE') == 3
+def test_permissions_from_string():
+    assert Attribute.Permissions.from_string('READABLE') == 1
+    assert Attribute.Permissions.from_string('WRITEABLE') == 2
+    assert Attribute.Permissions.from_string('READABLE,WRITEABLE') == 3
 
 
 # -----------------------------------------------------------------------------