Merge pull request #387 from google/gbg/async-gatt-server

support async read/write for characteristic values

apps/console.py

@@ -777,7 +777,7 @@ async def do_show_local_values(self):
                 if not service:
                     continue
                 values = [
-                    attribute.read_value(connection)
+                    await attribute.read_value(connection)
                     for connection in self.device.connections.values()
                 ]
                 if not values:
@@ -796,11 +796,11 @@ async def do_show_local_values(self):
                 if not characteristic:
                     continue
                 values = [
-                    attribute.read_value(connection)
+                    await attribute.read_value(connection)
                     for connection in self.device.connections.values()
                 ]
                 if not values:
-                    values = [attribute.read_value(None)]
+                    values = [await attribute.read_value(None)]
 
                 # TODO: future optimization: convert CCCD value to human readable string
 
@@ -944,7 +944,7 @@ async def do_local_write(self, params):
 
         # send data to any subscribers
         if isinstance(attribute, Characteristic):
-            attribute.write_value(None, value)
+            await attribute.write_value(None, value)
             if attribute.has_properties(Characteristic.NOTIFY):
                 await self.device.gatt_server.notify_subscribers(attribute)
             if attribute.has_properties(Characteristic.INDICATE):

bumble/att.py

@@ -25,9 +25,21 @@
 from __future__ import annotations
 import enum
 import functools
+import inspect
 import struct
+from typing import (
+    Any,
+    Awaitable,
+    Callable,
+    Dict,
+    List,
+    Optional,
+    Type,
+    Union,
+    TYPE_CHECKING,
+)
+
 from pyee import EventEmitter
-from typing import Dict, Type, List, Protocol, Union, Optional, Any, TYPE_CHECKING
 
 from bumble.core import UUID, name_or_number, ProtocolError
 from bumble.hci import HCI_Object, key_with_value
@@ -722,12 +734,38 @@ class ATT_Handle_Value_Confirmation(ATT_PDU):
 
 
 # -----------------------------------------------------------------------------
-class ConnectionValue(Protocol):
-    def read(self, connection) -> bytes:
-        ...
+class AttributeValue:
+    '''
+    Attribute value where reading and/or writing is delegated to functions
+    passed as arguments to the constructor.
+    '''
+
+    def __init__(
+        self,
+        read: Union[
+            Callable[[Optional[Connection]], bytes],
+            Callable[[Optional[Connection]], Awaitable[bytes]],
+            None,
+        ] = None,
+        write: Union[
+            Callable[[Optional[Connection], bytes], None],
+            Callable[[Optional[Connection], bytes], Awaitable[None]],
+            None,
+        ] = None,
+    ):
+        self._read = read
+        self._write = write
+
+    def read(self, connection: Optional[Connection]) -> Union[bytes, Awaitable[bytes]]:
+        return self._read(connection) if self._read else b''
+
+    def write(
+        self, connection: Optional[Connection], value: bytes
+    ) -> Union[Awaitable[None], None]:
+        if self._write:
+            return self._write(connection, value)
 
-    def write(self, connection, value: bytes) -> None:
-        ...
+        return None
 
 
 # -----------------------------------------------------------------------------
@@ -770,13 +808,13 @@ def from_string(cls, permissions_str: str) -> Attribute.Permissions:
     READ_REQUIRES_AUTHORIZATION = Permissions.READ_REQUIRES_AUTHORIZATION
     WRITE_REQUIRES_AUTHORIZATION = Permissions.WRITE_REQUIRES_AUTHORIZATION
 
-    value: Union[str, bytes, ConnectionValue]
+    value: Union[bytes, AttributeValue]
 
     def __init__(
         self,
         attribute_type: Union[str, bytes, UUID],
         permissions: Union[str, Attribute.Permissions],
-        value: Union[str, bytes, ConnectionValue] = b'',
+        value: Union[str, bytes, AttributeValue] = b'',
     ) -> None:
         EventEmitter.__init__(self)
         self.handle = 0
@@ -806,7 +844,7 @@ def encode_value(self, value: Any) -> bytes:
     def decode_value(self, value_bytes: bytes) -> Any:
         return value_bytes
 
-    def read_value(self, connection: Optional[Connection]) -> bytes:
+    async def read_value(self, connection: Optional[Connection]) -> bytes:
         if (
             (self.permissions & self.READ_REQUIRES_ENCRYPTION)
             and connection is not None
@@ -832,6 +870,8 @@ def read_value(self, connection: Optional[Connection]) -> bytes:
         if hasattr(self.value, 'read'):
             try:
                 value = self.value.read(connection)
+                if inspect.isawaitable(value):
+                    value = await value
             except ATT_Error as error:
                 raise ATT_Error(
                     error_code=error.error_code, att_handle=self.handle
@@ -841,7 +881,7 @@ def read_value(self, connection: Optional[Connection]) -> bytes:
 
         return self.encode_value(value)
 
-    def write_value(self, connection: Connection, value_bytes: bytes) -> None:
+    async def write_value(self, connection: Connection, value_bytes: bytes) -> None:
         if (
             self.permissions & self.WRITE_REQUIRES_ENCRYPTION
         ) and not connection.encryption:
@@ -864,7 +904,9 @@ def write_value(self, connection: Connection, value_bytes: bytes) -> None:
 
         if hasattr(self.value, 'write'):
             try:
-                self.value.write(connection, value)  # pylint: disable=not-callable
+                result = self.value.write(connection, value)
+                if inspect.isawaitable(result):
+                    await result
             except ATT_Error as error:
                 raise ATT_Error(
                     error_code=error.error_code, att_handle=self.handle

bumble/gatt.py

@@ -23,16 +23,28 @@
 # Imports
 # -----------------------------------------------------------------------------
 from __future__ import annotations
-import asyncio
 import enum
 import functools
 import logging
 import struct
-from typing import Optional, Sequence, Iterable, List, Union
-
-from .colors import color
-from .core import UUID, get_dict_key_by_value
-from .att import Attribute
+from typing import (
+    Callable,
+    Dict,
+    Iterable,
+    List,
+    Optional,
+    Sequence,
+    Union,
+    TYPE_CHECKING,
+)
+
+from bumble.colors import color
+from bumble.core import UUID
+from bumble.att import Attribute, AttributeValue
+
+if TYPE_CHECKING:
+    from bumble.gatt_client import AttributeProxy
+    from bumble.device import Connection
 
 
 # -----------------------------------------------------------------------------
@@ -522,56 +534,43 @@ def __str__(self) -> str:
 
 
 # -----------------------------------------------------------------------------
-class CharacteristicValue:
-    '''
-    Characteristic value where reading and/or writing is delegated to functions
-    passed as arguments to the constructor.
-    '''
-
-    def __init__(self, read=None, write=None):
-        self._read = read
-        self._write = write
-
-    def read(self, connection):
-        return self._read(connection) if self._read else b''
-
-    def write(self, connection, value):
-        if self._write:
-            self._write(connection, value)
+class CharacteristicValue(AttributeValue):
+    """Same as AttributeValue, for backward compatibility"""
 
 
 # -----------------------------------------------------------------------------
 class CharacteristicAdapter:
     '''
-    An adapter that can adapt any object with `read_value` and `write_value`
-    methods (like Characteristic and CharacteristicProxy objects) by wrapping
-    those methods with ones that return/accept encoded/decoded values.
-    Objects with async methods are considered proxies, so the adaptation is one
-    where the return value of `read_value` is decoded and the value passed to
-    `write_value` is encoded. Other objects are considered local characteristics
-    so the adaptation is one where the return value of `read_value` is encoded
-    and the value passed to `write_value` is decoded.
-    If the characteristic has a `subscribe` method, it is wrapped with one where
-    the values are decoded before being passed to the subscriber.
+    An adapter that can adapt Characteristic and AttributeProxy objects
+    by wrapping their `read_value()` and `write_value()` methods with ones that
+    return/accept encoded/decoded values.
+
+    For proxies (i.e used by a GATT client), the adaptation is one where the return
+    value of `read_value()` is decoded and the value passed to `write_value()` is
+    encoded. The `subscribe()` method, is wrapped with one where the values are decoded
+    before being passed to the subscriber.
+
+    For local values (i.e hosted by a GATT server) the adaptation is one where the
+    return value of `read_value()` is encoded and the value passed to `write_value()`
+    is decoded.
     '''
 
-    def __init__(self, characteristic):
+    read_value: Callable
+    write_value: Callable
+
+    def __init__(self, characteristic: Union[Characteristic, AttributeProxy]):
         self.wrapped_characteristic = characteristic
-        self.subscribers = {}  # Map from subscriber to proxy subscriber
+        self.subscribers: Dict[
+            Callable, Callable
+        ] = {}  # Map from subscriber to proxy subscriber
 
-        if asyncio.iscoroutinefunction(
-            characteristic.read_value
-        ) and asyncio.iscoroutinefunction(characteristic.write_value):
-            self.read_value = self.read_decoded_value
-            self.write_value = self.write_decoded_value
-        else:
+        if isinstance(characteristic, Characteristic):
             self.read_value = self.read_encoded_value
             self.write_value = self.write_encoded_value
-
-        if hasattr(self.wrapped_characteristic, 'subscribe'):
+        else:
+            self.read_value = self.read_decoded_value
+            self.write_value = self.write_decoded_value
             self.subscribe = self.wrapped_subscribe
-
-        if hasattr(self.wrapped_characteristic, 'unsubscribe'):
             self.unsubscribe = self.wrapped_unsubscribe
 
     def __getattr__(self, name):
@@ -590,11 +589,13 @@ def __setattr__(self, name, value):
         else:
             setattr(self.wrapped_characteristic, name, value)
 
-    def read_encoded_value(self, connection):
-        return self.encode_value(self.wrapped_characteristic.read_value(connection))
+    async def read_encoded_value(self, connection):
+        return self.encode_value(
+            await self.wrapped_characteristic.read_value(connection)
+        )
 
-    def write_encoded_value(self, connection, value):
-        return self.wrapped_characteristic.write_value(
+    async def write_encoded_value(self, connection, value):
+        return await self.wrapped_characteristic.write_value(
             connection, self.decode_value(value)
         )
 
@@ -729,13 +730,24 @@ class Descriptor(Attribute):
     '''
 
     def __str__(self) -> str:
+        if isinstance(self.value, bytes):
+            value_str = self.value.hex()
+        elif isinstance(self.value, CharacteristicValue):
+            value = self.value.read(None)
+            if isinstance(value, bytes):
+                value_str = value.hex()
+            else:
+                value_str = '<async>'
+        else:
+            value_str = '<...>'
         return (
             f'Descriptor(handle=0x{self.handle:04X}, '
             f'type={self.type}, '
-            f'value={self.read_value(None).hex()})'
+            f'value={value_str})'
         )
 
 
+# -----------------------------------------------------------------------------
 class ClientCharacteristicConfigurationBits(enum.IntFlag):
     '''
     See Vol 3, Part G - 3.3.3.3 - Table 3.11 Client Characteristic Configuration bit