maintain the att mtu only at the connection level

add support for notifying with a transient value

bumble/att.py

@@ -700,16 +700,26 @@ class Attribute(EventEmitter):
         else:
             self.value = value
 
+    def encode_value(self, value):
+        return value
+
+    def decode_value(self, value_bytes):
+        return value_bytes
+
     def read_value(self, connection):
         if read := getattr(self.value, 'read', None):
             try:
-                return read(connection)
+                value = read(connection)
             except ATT_Error as error:
                 raise ATT_Error(error_code=error.error_code, att_handle=self.handle)
         else:
-            return self.value
+            value = self.value
+
+        return self.encode_value(value)
+
+    def write_value(self, connection, value_bytes):
+        value = self.decode_value(value_bytes)
 
-    def write_value(self, connection, value):
         if write := getattr(self.value, 'write', None):
             try:
                 write(connection, value)
@@ -721,7 +731,11 @@ class Attribute(EventEmitter):
         self.emit('write', connection, value)
 
     def __repr__(self):
-        if len(self.value) > 0:
+        if type(self.value) is bytes:
+            value_str = self.value.hex()
+        else:
+            value_str = str(self.value)
+        if value_str:
             value_string = f', value={self.value.hex()}'
         else:
             value_string = ''

bumble/device.py

@@ -1210,17 +1210,17 @@ class Device(CompositeEventEmitter):
     def add_services(self, services):
         self.gatt_server.add_services(services)
 
-    async def notify_subscriber(self, connection, attribute, force=False):
-        await self.gatt_server.notify_subscriber(connection, attribute, force)
+    async def notify_subscriber(self, connection, attribute, value=None, force=False):
+        await self.gatt_server.notify_subscriber(connection, attribute, value, force)
 
-    async def notify_subscribers(self, attribute, force=False):
-        await self.gatt_server.notify_subscribers(attribute, force)
+    async def notify_subscribers(self, attribute, value=None, force=False):
+        await self.gatt_server.notify_subscribers(attribute, value, force)
 
-    async def indicate_subscriber(self, connection, attribute, force=False):
-        await self.gatt_server.indicate_subscriber(connection, attribute, force)
+    async def indicate_subscriber(self, connection, attribute, value=None, force=False):
+        await self.gatt_server.indicate_subscriber(connection, attribute, value, force)
 
-    async def indicate_subscribers(self, attribute):
-        await self.gatt_server.indicate_subscribers(attribute)
+    async def indicate_subscribers(self, attribute, value=None, force=False):
+        await self.gatt_server.indicate_subscribers(attribute, value, force)
 
     @host_event_handler
     def on_connection(self, connection_handle, transport, peer_address, peer_resolvable_address, role, connection_parameters):

bumble/gatt.py

@@ -303,6 +303,7 @@ class CharacteristicAdapter:
     '''
     def __init__(self, characteristic):
         self.wrapped_characteristic = characteristic
+        self.subscribers = {}  # Map from subscriber to proxy subscriber
 
         if (
             asyncio.iscoroutinefunction(characteristic.read_value) and
@@ -317,11 +318,21 @@ class CharacteristicAdapter:
         if hasattr(self.wrapped_characteristic, 'subscribe'):
             self.subscribe = self.wrapped_subscribe
 
+        if hasattr(self.wrapped_characteristic, 'unsubscribe'):
+            self.unsubscribe = self.wrapped_unsubscribe
+
     def __getattr__(self, name):
         return getattr(self.wrapped_characteristic, name)
 
     def __setattr__(self, name, value):
-        if name in {'wrapped_characteristic', 'read_value', 'write_value', 'subscribe'}:
+        if name in {
+            'wrapped_characteristic',
+            'subscribers',
+            'read_value',
+            'write_value',
+            'subscribe',
+            'unsubscribe'
+        }:
             super().__setattr__(name, value)
         else:
             setattr(self.wrapped_characteristic, name, value)
@@ -345,9 +356,26 @@ class CharacteristicAdapter:
         return value
 
     def wrapped_subscribe(self, subscriber=None):
-        return self.wrapped_characteristic.subscribe(
-            None if subscriber is None else lambda value: subscriber(self.decode_value(value))
-        )
+        if subscriber is not None:
+            if subscriber in self.subscribers:
+                # We already have a proxy subscriber
+                subscriber = self.subscribers[subscriber]
+            else:
+                # Create and register a proxy that will decode the value
+                original_subscriber = subscriber
+
+                def on_change(value):
+                    original_subscriber(self.decode_value(value))
+                self.subscribers[subscriber] = on_change
+                subscriber = on_change
+
+        return self.wrapped_characteristic.subscribe(subscriber)
+
+    def wrapped_unsubscribe(self, subscriber=None):
+        if subscriber in self.subscribers:
+            subscriber = self.subscribers.pop(subscriber)
+
+        return self.wrapped_characteristic.unsubscribe(subscriber)
 
     def __str__(self):
         wrapped = str(self.wrapped_characteristic)

bumble/gatt_client.py

@@ -58,10 +58,16 @@ class AttributeProxy(EventEmitter):
         self.type             = attribute_type
 
     async def read_value(self, no_long_read=False):
-        return await self.client.read_value(self.handle, no_long_read)
+        return self.decode_value(await self.client.read_value(self.handle, no_long_read))
 
     async def write_value(self, value, with_response=False):
-        return await self.client.write_value(self.handle, value, with_response)
+        return await self.client.write_value(self.handle, self.encode_value(value), with_response)
+
+    def encode_value(self, value):
+        return value
+
+    def decode_value(self, value_bytes):
+        return value_bytes
 
     def __str__(self):
         return f'Attribute(handle=0x{self.handle:04X}, type={self.uuid})'
@@ -98,6 +104,7 @@ class CharacteristicProxy(AttributeProxy):
         self.properties             = properties
         self.descriptors            = []
         self.descriptors_discovered = False
+        self.subscribers            = {}  # Map from subscriber to proxy subscriber
 
     def get_descriptor(self, descriptor_type):
         for descriptor in self.descriptors:
@@ -108,9 +115,25 @@ class CharacteristicProxy(AttributeProxy):
         return await self.client.discover_descriptors(self)
 
     async def subscribe(self, subscriber=None):
+        if subscriber is not None:
+            if subscriber in self.subscribers:
+                # We already have a proxy subscriber
+                subscriber = self.subscribers[subscriber]
+            else:
+                # Create and register a proxy that will decode the value
+                original_subscriber = subscriber
+
+                def on_change(value):
+                    original_subscriber(self.decode_value(value))
+                self.subscribers[subscriber] = on_change
+                subscriber = on_change
+
         return await self.client.subscribe(self, subscriber)
 
     async def unsubscribe(self, subscriber=None):
+        if subscriber in self.subscribers:
+            subscriber = self.subscribers.pop(subscriber)
+
         return await self.client.unsubscribe(self, subscriber)
 
     def __str__(self):
@@ -140,7 +163,6 @@ class ProfileServiceProxy:
 class Client:
     def __init__(self, connection):
         self.connection               = connection
-        self.mtu                      = ATT_DEFAULT_MTU
         self.mtu_exchange_done        = False
         self.request_semaphore        = asyncio.Semaphore(1)
         self.pending_request          = None
@@ -194,7 +216,7 @@ class Client:
 
         # We can only send one request per connection
         if self.mtu_exchange_done:
-            return
+            return self.connection.att_mtu
 
         # Send the request
         self.mtu_exchange_done = True
@@ -207,8 +229,10 @@ class Client:
                 response
             )
 
-        self.mtu = max(ATT_DEFAULT_MTU, response.server_rx_mtu)
-        return self.mtu
+        # Compute the final MTU
+        self.connection.att_mtu = min(mtu, response.server_rx_mtu)
+
+        return self.connection.att_mtu
 
     def get_services_by_uuid(self, uuid):
         return [service for service in self.services if service.uuid == uuid]
@@ -570,12 +594,18 @@ class Client:
                 subscribers = subscriber_set.get(characteristic.handle, [])
                 if subscriber in subscribers:
                     subscribers.remove(subscriber)
+
+                    # Cleanup if we removed the last one
+                    if not subscribers:
+                        subscriber_set.remove(characteristic.handle)
         else:
             # Remove all subscribers for this attribute from the sets!
             self.notification_subscribers.pop(characteristic.handle, None)
             self.indication_subscribers.pop(characteristic.handle, None)
 
-        await self.write_value(cccd, b'\x00\x00', with_response=True)
+        if not self.notification_subscribers and not self.indication_subscribers:
+            # 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):
         '''
@@ -600,7 +630,7 @@ class Client:
         # If the value is the max size for the MTU, try to read more unless the caller
         # specifically asked not to do that
         attribute_value = response.attribute_value
-        if not no_long_read and len(attribute_value) == self.mtu - 1:
+        if not no_long_read and len(attribute_value) == self.connection.att_mtu - 1:
             logger.debug('using READ BLOB to get the rest of the value')
             offset = len(attribute_value)
             while True:
@@ -622,7 +652,7 @@ class Client:
                 part = response.part_attribute_value
                 attribute_value += part
 
-                if len(part) < self.mtu - 1:
+                if len(part) < self.connection.att_mtu - 1:
                     break
 
                 offset += len(part)

bumble/gatt_server.py

@@ -40,6 +40,12 @@ from .gatt import *
 logger = logging.getLogger(__name__)
 
 
+# -----------------------------------------------------------------------------
+# Constants
+# -----------------------------------------------------------------------------
+GATT_SERVER_DEFAULT_MAX_MTU = 517
+
+
 # -----------------------------------------------------------------------------
 # GATT Server
 # -----------------------------------------------------------------------------
@@ -49,9 +55,8 @@ class Server(EventEmitter):
         self.device                = device
         self.attributes            = []  # Attributes, ordered by increasing handle values
         self.attributes_by_handle  = {}  # Map for fast attribute access by handle
-        self.max_mtu               = 23  # FIXME: 517  # The max MTU we're willing to negotiate
+        self.max_mtu               = GATT_SERVER_DEFAULT_MAX_MTU  # The max MTU we're willing to negotiate
         self.subscribers           = {}  # Map of subscriber states by connection handle and attribute handle
-        self.mtus                  = {}  # Map of ATT MTU values by connection handle
         self.indication_semaphores = defaultdict(lambda: asyncio.Semaphore(1))
         self.pending_confirmations = defaultdict(lambda: None)
 
@@ -169,7 +174,7 @@ class Server(EventEmitter):
         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, force=False):
+    async def notify_subscriber(self, connection, attribute, value=None, force=False):
         # Check if there's a subscriber
         if not force:
             subscribers = self.subscribers.get(connection.handle)
@@ -184,13 +189,12 @@ class Server(EventEmitter):
                 logger.debug(f'not notifying, cccd={cccd.hex()}')
                 return
 
-        # Get the value
-        value = attribute.read_value(connection)
+        # Get or encode the value
+        value = attribute.read_value(connection) if value is None else attribute.encode_value(value)
 
         # Truncate if needed
-        mtu = self.get_mtu(connection)
-        if len(value) > mtu - 3:
-            value = value[:mtu - 3]
+        if len(value) > connection.att_mtu - 3:
+            value = value[:connection.att_mtu - 3]
 
         # Notify
         notification = ATT_Handle_Value_Notification(
@@ -198,27 +202,9 @@ class Server(EventEmitter):
             attribute_value  = value
         )
         logger.debug(f'GATT Notify from server: [0x{connection.handle:04X}] {notification}')
-        self.send_gatt_pdu(connection.handle, notification.to_bytes())
+        self.send_gatt_pdu(connection.handle, bytes(notification))
 
-    async def notify_subscribers(self, attribute, force=False):
-        # Get all the connections for which there's at least one subscription
-        connections = [
-            connection for connection in [
-                self.device.lookup_connection(connection_handle)
-                for (connection_handle, subscribers) in self.subscribers.items()
-                if force or subscribers.get(attribute.handle)
-            ]
-            if connection is not None
-        ]
-
-        # Notify for each connection
-        if connections:
-            await asyncio.wait([
-                self.notify_subscriber(connection, attribute, force)
-                for connection in connections
-            ])
-
-    async def indicate_subscriber(self, connection, attribute, force=False):
+    async def indicate_subscriber(self, connection, attribute, value=None, force=False):
         # Check if there's a subscriber
         if not force:
             subscribers = self.subscribers.get(connection.handle)
@@ -233,13 +219,12 @@ class Server(EventEmitter):
                 logger.debug(f'not indicating, cccd={cccd.hex()}')
                 return
 
-        # Get the value
-        value = attribute.read_value(connection)
+        # Get or encode the value
+        value = attribute.read_value(connection) if value is None else attribute.encode_value(value)
 
         # Truncate if needed
-        mtu = self.get_mtu(connection)
-        if len(value) > mtu - 3:
-            value = value[:mtu - 3]
+        if len(value) > connection.att_mtu - 3:
+            value = value[:connection.att_mtu - 3]
 
         # Indicate
         indication = ATT_Handle_Value_Indication(
@@ -264,27 +249,32 @@ class Server(EventEmitter):
             finally:
                 self.pending_confirmations[connection.handle] = None
 
-    async def indicate_subscribers(self, attribute):
+    async def notify_or_indicate_subscribers(self, indicate, attribute, value=None, force=False):
         # Get all the connections for which there's at least one subscription
         connections = [
             connection for connection in [
                 self.device.lookup_connection(connection_handle)
                 for (connection_handle, subscribers) in self.subscribers.items()
-                if subscribers.get(attribute.handle)
+                if force or subscribers.get(attribute.handle)
             ]
             if connection is not None
         ]
 
-        # Indicate for each connection
+        # Indicate or notify for each connection
         if connections:
+            coroutine = self.indicate_subscriber if indicate else self.notify_subscriber
             await asyncio.wait([
-                self.indicate_subscriber(connection, attribute)
+                asyncio.create_task(coroutine(connection, attribute, value, force))
                 for connection in connections
             ])
 
+    async def notify_subscribers(self, attribute, value=None, force=False):
+        return await self.notify_or_indicate_subscribers(False, attribute, value, force)
+
+    async def indicate_subscribers(self, attribute, value=None, force=False):
+        return await self.notify_or_indicate_subscribers(True, attribute, value, force)
+
     def on_disconnection(self, connection):
-        if connection.handle in self.mtus:
-            del self.mtus[connection.handle]
         if connection.handle in self.subscribers:
             del self.subscribers[connection.handle]
         if connection.handle in self.indication_semaphores:
@@ -325,9 +315,6 @@ class Server(EventEmitter):
                 # Just ignore
                 logger.warning(f'{color("--- Ignoring GATT Request from [0x{connection.handle:04X}]:", "red")}  {att_pdu}')
 
-    def get_mtu(self, connection):
-        return self.mtus.get(connection.handle, ATT_DEFAULT_MTU)
-
     #######################################################
     # ATT handlers
     #######################################################
@@ -347,12 +334,16 @@ class Server(EventEmitter):
         '''
         See Bluetooth spec Vol 3, Part F - 3.4.2.1 Exchange MTU Request
         '''
-        mtu = max(ATT_DEFAULT_MTU, min(self.max_mtu, request.client_rx_mtu))
-        self.mtus[connection.handle] = mtu
-        self.send_response(connection, ATT_Exchange_MTU_Response(server_rx_mtu = mtu))
+        self.send_response(connection, ATT_Exchange_MTU_Response(server_rx_mtu = self.max_mtu))
 
-        # Notify the device
-        self.device.on_connection_att_mtu_update(connection.handle, mtu)
+        # Compute the final MTU
+        if request.client_rx_mtu >= ATT_DEFAULT_MTU:
+            mtu = min(self.max_mtu, request.client_rx_mtu)
+
+            # Notify the device
+            self.device.on_connection_att_mtu_update(connection.handle, mtu)
+        else:
+            logger.warning('invalid client_rx_mtu received, MTU not changed')
 
     def on_att_find_information_request(self, connection, request):
         '''
@@ -369,7 +360,7 @@ class Server(EventEmitter):
             return
 
         # Build list of returned attributes
-        pdu_space_available = self.get_mtu(connection) - 2
+        pdu_space_available = connection.att_mtu - 2
         attributes = []
         uuid_size = 0
         for attribute in (
@@ -420,7 +411,7 @@ class Server(EventEmitter):
         '''
 
         # Build list of returned attributes
-        pdu_space_available = self.get_mtu(connection) - 2
+        pdu_space_available = connection.att_mtu - 2
         attributes = []
         for attribute in (
             attribute for attribute in self.attributes if
@@ -468,8 +459,7 @@ class Server(EventEmitter):
         See Bluetooth spec Vol 3, Part F - 3.4.4.1 Read By Type Request
         '''
 
-        mtu = self.get_mtu(connection)
-        pdu_space_available = mtu - 2
+        pdu_space_available = connection.att_mtu - 2
         attributes = []
         for attribute in (
             attribute for attribute in self.attributes if
@@ -482,7 +472,7 @@ class Server(EventEmitter):
 
             # Check the attribute value size
             attribute_value = attribute.read_value(connection)
-            max_attribute_size = min(mtu - 4, 253)
+            max_attribute_size = min(connection.att_mtu - 4, 253)
             if len(attribute_value) > max_attribute_size:
                 # We need to truncate
                 attribute_value = attribute_value[:max_attribute_size]
@@ -522,7 +512,7 @@ class Server(EventEmitter):
         if attribute := self.get_attribute(request.attribute_handle):
             # TODO: check permissions
             value = attribute.read_value(connection)
-            value_size = min(self.get_mtu(connection) - 1, len(value))
+            value_size = min(connection.att_mtu - 1, len(value))
             response = ATT_Read_Response(
                 attribute_value = value[:value_size]
             )
@@ -541,7 +531,6 @@ class Server(EventEmitter):
 
         if attribute := self.get_attribute(request.attribute_handle):
             # TODO: check permissions
-            mtu = self.get_mtu(connection)
             value = attribute.read_value(connection)
             if request.value_offset > len(value):
                 response = ATT_Error_Response(
@@ -549,14 +538,14 @@ class Server(EventEmitter):
                     attribute_handle_in_error = request.attribute_handle,
                     error_code                = ATT_INVALID_OFFSET_ERROR
                 )
-            elif len(value) <= mtu - 1:
+            elif len(value) <= connection.att_mtu - 1:
                 response = ATT_Error_Response(
                     request_opcode_in_error   = request.op_code,
                     attribute_handle_in_error = request.attribute_handle,
                     error_code                = ATT_ATTRIBUTE_NOT_LONG_ERROR
                 )
             else:
-                part_size = min(mtu - 1, len(value) - request.value_offset)
+                part_size = min(connection.att_mtu - 1, len(value) - request.value_offset)
                 response = ATT_Read_Blob_Response(
                     part_attribute_value = value[request.value_offset:request.value_offset + part_size]
                 )
@@ -585,8 +574,7 @@ class Server(EventEmitter):
             self.send_response(connection, response)
             return
 
-        mtu = self.get_mtu(connection)
-        pdu_space_available = mtu - 2
+        pdu_space_available = connection.att_mtu - 2
         attributes = []
         for attribute in (
             attribute for attribute in self.attributes if
@@ -597,7 +585,7 @@ class Server(EventEmitter):
         ):
             # Check the attribute value size
             attribute_value = attribute.read_value(connection)
-            max_attribute_size = min(mtu - 6, 251)
+            max_attribute_size = min(connection.att_mtu - 6, 251)
             if len(attribute_value) > max_attribute_size:
                 # We need to truncate
                 attribute_value = attribute_value[:max_attribute_size]

bumble/helpers.py

@@ -18,6 +18,8 @@
 import logging
 from colors import color
 
+from bumble.smp import SMP_CID, SMP_Command
+
 from .core import name_or_number
 from .gatt import ATT_PDU, ATT_CID
 from .l2cap import (
@@ -73,6 +75,9 @@ class PacketTracer:
             if l2cap_pdu.cid == ATT_CID:
                 att_pdu = ATT_PDU.from_bytes(l2cap_pdu.payload)
                 self.analyzer.emit(att_pdu)
+            elif l2cap_pdu.cid == SMP_CID:
+                smp_command = SMP_Command.from_bytes(l2cap_pdu.payload)
+                self.analyzer.emit(smp_command)
             elif l2cap_pdu.cid == L2CAP_SIGNALING_CID or l2cap_pdu.cid == L2CAP_LE_SIGNALING_CID:
                 control_frame = L2CAP_Control_Frame.from_bytes(l2cap_pdu.payload)
                 self.analyzer.emit(control_frame)

bumble/smp.py

@@ -155,6 +155,7 @@ SMP_CT2_AUTHREQ      = 0b00100000
 SMP_CTKD_H7_LEBR_SALT = bytes.fromhex('00000000000000000000000000000000746D7031')
 SMP_CTKD_H7_BRLE_SALT = bytes.fromhex('00000000000000000000000000000000746D7032')
 
+
 # -----------------------------------------------------------------------------
 # Utils
 # -----------------------------------------------------------------------------
@@ -879,7 +880,7 @@ class Session:
                 )
             )
         )
-    
+
     async def derive_ltk(self):
         link_key = await self.manager.device.get_link_key(self.connection.peer_address)
         assert link_key is not None
@@ -914,7 +915,7 @@ class Session:
             csrk = bytes(16)  # FIXME: testing
             if self.initiator_key_distribution & SMP_SIGN_KEY_DISTRIBUTION_FLAG:
                 self.send_command(SMP_Signing_Information_Command(signature_key=csrk))
-            
+
             # CTKD, calculate BR/EDR link key
             if self.initiator_key_distribution & SMP_LINK_KEY_DISTRIBUTION_FLAG:
                 ilk = crypto.h7(
@@ -946,7 +947,7 @@ class Session:
             csrk = bytes(16)  # FIXME: testing
             if self.responder_key_distribution & SMP_SIGN_KEY_DISTRIBUTION_FLAG:
                 self.send_command(SMP_Signing_Information_Command(signature_key=csrk))
-            
+
             # CTKD, calculate BR/EDR link key
             if self.responder_key_distribution & SMP_LINK_KEY_DISTRIBUTION_FLAG:
                 ilk = crypto.h7(
@@ -980,12 +981,7 @@ class Session:
             self.peer_expected_distributions.remove(command_class)
             logger.debug(f'remaining distributions: {[c.__name__ for c in self.peer_expected_distributions]}')
             if not self.peer_expected_distributions:
-                # The initiator can now send its keys
-                if self.is_initiator:
-                    self.distribute_keys()
-
-                # Nothing left to expect, we're done
-                asyncio.create_task(self.on_pairing())
+                self.on_peer_key_distribution_complete()
         else:
             logger.warn(color(f'!!! unexpected key distribution command: {command_class.__name__}', 'red'))
             self.send_pairing_failed(SMP_UNSPECIFIED_REASON_ERROR)
@@ -1006,12 +1002,23 @@ class Session:
         self.connection.remove_listener('connection_encryption_key_refresh', self.on_connection_encryption_key_refresh)
         self.manager.on_session_end(self)
 
+    def on_peer_key_distribution_complete(self):
+        # The initiator can now send its keys
+        if self.is_initiator:
+            self.distribute_keys()
+
+        asyncio.create_task(self.on_pairing())
+
     def on_connection_encryption_change(self):
         if self.connection.is_encrypted:
             if self.is_responder:
                 # The responder distributes its keys first, the initiator later
                 self.distribute_keys()
 
+            # If we're not expecting key distributions from the peer, we're done
+            if not self.peer_expected_distributions:
+                self.on_peer_key_distribution_complete()
+
     def on_connection_encryption_key_refresh(self):
         # Do as if the connection had just been encrypted
         self.on_connection_encryption_change()

bumble/transport/usb.py

@@ -56,18 +56,19 @@ async def open_usb_transport(spec):
 
     USB_RECIPIENT_DEVICE                             = 0x00
     USB_REQUEST_TYPE_CLASS                           = 0x01 << 5
-    USB_ENDPOINT_EVENTS_IN                           = 0x81
-    USB_ENDPOINT_ACL_IN                              = 0x82
-    USB_ENDPOINT_ACL_OUT                             = 0x02
     USB_DEVICE_CLASS_WIRELESS_CONTROLLER             = 0xE0
     USB_DEVICE_SUBCLASS_RF_CONTROLLER                = 0x01
     USB_DEVICE_PROTOCOL_BLUETOOTH_PRIMARY_CONTROLLER = 0x01
+    USB_ENDPOINT_TRANSFER_TYPE_BULK                  = 0x02
+    USB_ENDPOINT_TRANSFER_TYPE_INTERRUPT             = 0x03
+    USB_ENDPOINT_IN                                  = 0x80
 
     READ_SIZE = 1024
 
     class UsbPacketSink:
-        def __init__(self, device):
+        def __init__(self, device, acl_out):
             self.device      = device
+            self.acl_out     = acl_out
             self.transfer    = device.getTransfer()
             self.packets     = collections.deque()  # Queue of packets waiting to be sent
             self.loop        = asyncio.get_running_loop()
@@ -116,7 +117,7 @@ async def open_usb_transport(spec):
             packet_type = packet[0]
             if packet_type == hci.HCI_ACL_DATA_PACKET:
                 self.transfer.setBulk(
-                    USB_ENDPOINT_ACL_OUT,
+                    self.acl_out,
                     packet[1:],
                     callback=self.on_packet_sent
                 )
@@ -152,10 +153,12 @@ async def open_usb_transport(spec):
                     logger.debug('OUT transfer likely already completed')
 
     class UsbPacketSource(asyncio.Protocol, ParserSource):
-        def __init__(self, context, device):
+        def __init__(self, context, device, acl_in, events_in):
             super().__init__()
             self.context         = context
             self.device          = device
+            self.acl_in          = acl_in
+            self.events_in       = events_in
             self.loop            = asyncio.get_running_loop()
             self.queue           = asyncio.Queue()
             self.closed          = False
@@ -172,7 +175,7 @@ async def open_usb_transport(spec):
             # Set up transfer objects for input
             self.events_in_transfer = device.getTransfer()
             self.events_in_transfer.setInterrupt(
-                USB_ENDPOINT_EVENTS_IN,
+                self.events_in,
                 READ_SIZE,
                 callback=self.on_packet_received,
                 user_data=hci.HCI_EVENT_PACKET
@@ -181,7 +184,7 @@ async def open_usb_transport(spec):
 
             self.acl_in_transfer = device.getTransfer()
             self.acl_in_transfer.setBulk(
-                USB_ENDPOINT_ACL_IN,
+                self.acl_in,
                 READ_SIZE,
                 callback=self.on_packet_received,
                 user_data=hci.HCI_ACL_DATA_PACKET
@@ -248,7 +251,7 @@ async def open_usb_transport(spec):
             await self.event_loop_done
 
     class UsbTransport(Transport):
-        def __init__(self, context, device, interface, source, sink):
+        def __init__(self, context, device, interface, setting, source, sink):
             super().__init__(source, sink)
             self.context   = context
             self.device    = device
@@ -257,6 +260,10 @@ async def open_usb_transport(spec):
             # Get exclusive access
             device.claimInterface(interface)
 
+            # Set the alternate setting if not the default
+            if setting != 0:
+                device.setInterfaceAltSetting(interface, setting)
+
             # The source and sink can now start
             source.start()
             sink.start()
@@ -313,10 +320,63 @@ async def open_usb_transport(spec):
             raise ValueError('device not found')
 
         logger.debug(f'USB Device: {found}')
-        device = found.open()
 
-        # Use the first interface
-        interface = 0
+        # Look for the first interface with the right class and endpoints
+        def find_endpoints(device):
+            for (configuration_index, configuration) in enumerate(device):
+                interface = None
+                for interface in configuration:
+                    setting = None
+                    for setting in interface:
+                        if (
+                            setting.getClass() != USB_DEVICE_CLASS_WIRELESS_CONTROLLER or
+                            setting.getSubClass() != USB_DEVICE_SUBCLASS_RF_CONTROLLER or
+                            setting.getProtocol() != USB_DEVICE_PROTOCOL_BLUETOOTH_PRIMARY_CONTROLLER
+                        ):
+                            continue
+
+                        events_in = None
+                        acl_in    = None
+                        acl_out   = None
+                        for endpoint in setting:
+                            attributes = endpoint.getAttributes()
+                            address    = endpoint.getAddress()
+                            if attributes & 0x03 == USB_ENDPOINT_TRANSFER_TYPE_BULK:
+                                if address & USB_ENDPOINT_IN and acl_in is None:
+                                    acl_in = address
+                                elif acl_out is None:
+                                    acl_out = address
+                            elif attributes & 0x03 == USB_ENDPOINT_TRANSFER_TYPE_INTERRUPT:
+                                if address & USB_ENDPOINT_IN and events_in is None:
+                                    events_in = address
+
+                        # Return if we found all 3 endpoints
+                        if acl_in is not None and acl_out is not None and events_in is not None:
+                            return (
+                                configuration_index + 1,
+                                setting.getNumber(),
+                                setting.getAlternateSetting(),
+                                acl_in,
+                                acl_out,
+                                events_in
+                            )
+                        else:
+                            logger.debug(f'skipping configuration {configuration_index + 1} / interface {setting.getNumber()}')
+
+        endpoints = find_endpoints(found)
+        if endpoints is None:
+            raise ValueError('no compatible interface found for device')
+        (configuration, interface, setting, acl_in, acl_out, events_in) = endpoints
+        logger.debug(
+            f'selected endpoints: configuration={configuration}, '
+            f'interface={interface}, '
+            f'setting={setting}, '
+            f'acl_in=0x{acl_in:02X}, '
+            f'acl_out=0x{acl_out:02X}, '
+            f'events_in=0x{events_in:02X}, '
+        )
+
+        device = found.open()
 
         # Detach the kernel driver if supported and needed
         if usb1.hasCapability(usb1.CAP_SUPPORTS_DETACH_KERNEL_DRIVER):
@@ -329,21 +389,21 @@ async def open_usb_transport(spec):
 
         # Set the configuration if needed
         try:
-            configuration = device.getConfiguration()
-            logger.debug(f'current configuration = {configuration}')
+            current_configuration = device.getConfiguration()
+            logger.debug(f'current configuration = {current_configuration}')
         except usb1.USBError:
-            configuration = 0
+            current_configuration = 0
 
-        if configuration != 1:
+        if current_configuration != configuration:
             try:
-                logger.debug('setting configuration 1')
-                device.setConfiguration(1)
+                logger.debug(f'setting configuration {configuration}')
+                device.setConfiguration(configuration)
             except usb1.USBError:
-                logger.warning('failed to set configuration 1')
+                logger.warning('failed to set configuration')
 
-        source = UsbPacketSource(context, device)
-        sink   = UsbPacketSink(device)
-        return UsbTransport(context, device, interface, source, sink)
+        source = UsbPacketSource(context, device, acl_in, events_in)
+        sink   = UsbPacketSink(device, acl_out)
+        return UsbTransport(context, device, interface, setting, source, sink)
     except usb1.USBError as error:
         logger.warning(color(f'!!! failed to open USB device: {error}', 'red'))
         context.close()

tests/gatt_test.py

@@ -22,6 +22,7 @@ import struct
 import pytest
 
 from bumble.controller import Controller
+from bumble.gatt_client import CharacteristicProxy
 from bumble.link import LocalLink
 from bumble.device import Device, Peer
 from bumble.host import Host
@@ -53,29 +54,29 @@ def basic_check(x):
     parsed = ATT_PDU.from_bytes(pdu)
     x_str = str(x)
     parsed_str = str(parsed)
-    assert(x_str == parsed_str)
+    assert x_str == parsed_str
 
 
 # -----------------------------------------------------------------------------
 def test_UUID():
     u = UUID.from_16_bits(0x7788)
-    assert(str(u) == 'UUID-16:7788')
+    assert str(u) == 'UUID-16:7788'
     u = UUID.from_32_bits(0x11223344)
-    assert(str(u) == 'UUID-32:11223344')
+    assert str(u) == 'UUID-32:11223344'
     u = UUID('61A3512C-09BE-4DDC-A6A6-0B03667AAFC6')
-    assert(str(u) == '61A3512C-09BE-4DDC-A6A6-0B03667AAFC6')
+    assert str(u) == '61A3512C-09BE-4DDC-A6A6-0B03667AAFC6'
     v = UUID(str(u))
-    assert(str(v) == '61A3512C-09BE-4DDC-A6A6-0B03667AAFC6')
+    assert str(v) == '61A3512C-09BE-4DDC-A6A6-0B03667AAFC6'
     w = UUID.from_bytes(v.to_bytes())
-    assert(str(w) == '61A3512C-09BE-4DDC-A6A6-0B03667AAFC6')
+    assert str(w) == '61A3512C-09BE-4DDC-A6A6-0B03667AAFC6'
 
     u1 = UUID.from_16_bits(0x1234)
     b1 = u1.to_bytes(force_128 = True)
     u2 = UUID.from_bytes(b1)
-    assert(u1 == u2)
+    assert u1 == u2
 
     u3 = UUID.from_16_bits(0x180a)
-    assert(str(u3) == 'UUID-16:180A (Device Information)')
+    assert str(u3) == 'UUID-16:180A (Device Information)'
 
 
 # -----------------------------------------------------------------------------
@@ -98,6 +99,122 @@ def test_ATT_Read_By_Group_Type_Request():
     basic_check(pdu)
 
 
+# -----------------------------------------------------------------------------
+@pytest.mark.asyncio
+async def test_characteristic_encoding():
+    class Foo(Characteristic):
+        def encode_value(self, value):
+            return bytes([value])
+
+        def decode_value(self, value_bytes):
+            return value_bytes[0]
+
+    c = Foo(GATT_BATTERY_LEVEL_CHARACTERISTIC, Characteristic.READ, Characteristic.READABLE, 123)
+    x = c.read_value(None)
+    assert x == bytes([123])
+    c.write_value(None, bytes([122]))
+    assert c.value == 122
+
+    class FooProxy(CharacteristicProxy):
+        def __init__(self, characteristic):
+            super().__init__(
+                characteristic.client,
+                characteristic.handle,
+                characteristic.end_group_handle,
+                characteristic.uuid,
+                characteristic.properties
+            )
+
+        def encode_value(self, value):
+            return bytes([value])
+
+        def decode_value(self, value_bytes):
+            return value_bytes[0]
+
+    [client, server] = LinkedDevices().devices[:2]
+
+    characteristic = Characteristic(
+        'FDB159DB-036C-49E3-B3DB-6325AC750806',
+        Characteristic.READ | Characteristic.WRITE | Characteristic.NOTIFY,
+        Characteristic.READABLE | Characteristic.WRITEABLE,
+        bytes([123])
+    )
+
+    service = Service(
+        '3A657F47-D34F-46B3-B1EC-698E29B6B829',
+        [characteristic]
+    )
+    server.add_service(service)
+
+    await client.power_on()
+    await server.power_on()
+    connection = await client.connect(server.random_address)
+    peer = Peer(connection)
+
+    await peer.discover_services()
+    await peer.discover_characteristics()
+    c = peer.get_characteristics_by_uuid(characteristic.uuid)
+    assert len(c) == 1
+    c = c[0]
+    cp = FooProxy(c)
+
+    v = await cp.read_value()
+    assert v == 123
+    await cp.write_value(124)
+    await async_barrier()
+    assert characteristic.value == bytes([124])
+
+    last_change = None
+
+    def on_change(value):
+        nonlocal last_change
+        last_change = value
+
+    await c.subscribe(on_change)
+    await server.notify_subscribers(characteristic)
+    await async_barrier()
+    assert last_change == characteristic.value
+    last_change = None
+
+    await server.notify_subscribers(characteristic, value=bytes([125]))
+    await async_barrier()
+    assert last_change == bytes([125])
+    last_change = None
+
+    await c.unsubscribe(on_change)
+    await server.notify_subscribers(characteristic)
+    await async_barrier()
+    assert last_change is None
+
+    await cp.subscribe(on_change)
+    await server.notify_subscribers(characteristic)
+    await async_barrier()
+    assert last_change == characteristic.value[0]
+    last_change = None
+
+    await server.notify_subscribers(characteristic, value=bytes([126]))
+    await async_barrier()
+    assert last_change == 126
+    last_change = None
+
+    await cp.unsubscribe(on_change)
+    await server.notify_subscribers(characteristic)
+    await async_barrier()
+    assert last_change is None
+
+    cd = DelegatedCharacteristicAdapter(c, decode=lambda x: x[0])
+    await cd.subscribe(on_change)
+    await server.notify_subscribers(characteristic)
+    await async_barrier()
+    assert last_change == characteristic.value[0]
+    last_change = None
+
+    await cd.unsubscribe(on_change)
+    await server.notify_subscribers(characteristic)
+    await async_barrier()
+    assert last_change is None
+
+
 # -----------------------------------------------------------------------------
 def test_CharacteristicAdapter():
     # Check that the CharacteristicAdapter base class is transparent
@@ -106,21 +223,21 @@ def test_CharacteristicAdapter():
     a = CharacteristicAdapter(c)
 
     value = a.read_value(None)
-    assert(value == v)
+    assert value == v
 
     v = bytes([3, 4, 5])
     a.write_value(None, v)
-    assert(c.value == v)
+    assert c.value == v
 
     # Simple delegated adapter
     a = DelegatedCharacteristicAdapter(c, lambda x: bytes(reversed(x)), lambda x: bytes(reversed(x)))
 
     value = a.read_value(None)
-    assert(value == bytes(reversed(v)))
+    assert value == bytes(reversed(v))
 
     v = bytes([3, 4, 5])
     a.write_value(None, v)
-    assert(a.value == bytes(reversed(v)))
+    assert a.value == bytes(reversed(v))
 
     # Packed adapter with single element format
     v = 1234
@@ -129,10 +246,10 @@ def test_CharacteristicAdapter():
     a = PackedCharacteristicAdapter(c, '>H')
 
     value = a.read_value(None)
-    assert(value == pv)
+    assert value == pv
     c.value = None
     a.write_value(None, pv)
-    assert(a.value == v)
+    assert a.value == v
 
     # Packed adapter with multi-element format
     v1 = 1234
@@ -142,10 +259,10 @@ def test_CharacteristicAdapter():
     a = PackedCharacteristicAdapter(c, '>HH')
 
     value = a.read_value(None)
-    assert(value == pv)
+    assert value == pv
     c.value = None
     a.write_value(None, pv)
-    assert(a.value == (v1, v2))
+    assert a.value == (v1, v2)
 
     # Mapped adapter
     v1 = 1234
@@ -156,10 +273,10 @@ def test_CharacteristicAdapter():
     a = MappedCharacteristicAdapter(c, '>HH', ('v1', 'v2'))
 
     value = a.read_value(None)
-    assert(value == pv)
+    assert value == pv
     c.value = None
     a.write_value(None, pv)
-    assert(a.value == mapped)
+    assert a.value == mapped
 
     # UTF-8 adapter
     v = 'Hello π'
@@ -168,10 +285,10 @@ def test_CharacteristicAdapter():
     a = UTF8CharacteristicAdapter(c)
 
     value = a.read_value(None)
-    assert(value == ev)
+    assert value == ev
     c.value = None
     a.write_value(None, ev)
-    assert(a.value == v)
+    assert a.value == v
 
 
 # -----------------------------------------------------------------------------
@@ -179,24 +296,25 @@ def test_CharacteristicValue():
     b = bytes([1, 2, 3])
     c = CharacteristicValue(read=lambda _: b)
     x = c.read(None)
-    assert(x == b)
+    assert x == b
 
     result = []
     c = CharacteristicValue(write=lambda connection, value: result.append((connection, value)))
     z = object()
     c.write(z, b)
-    assert(result == [(z, b)])
+    assert result == [(z, b)]
 
 
 # -----------------------------------------------------------------------------
-class TwoDevices:
+class LinkedDevices:
     def __init__(self):
-        self.connections = [None, None]
+        self.connections = [None, None, None]
 
         self.link = LocalLink()
         self.controllers = [
             Controller('C1', link = self.link),
-            Controller('C2', link = self.link)
+            Controller('C2', link = self.link),
+            Controller('C3', link = self.link)
         ]
         self.devices = [
             Device(
@@ -204,12 +322,16 @@ class TwoDevices:
                 host    = Host(self.controllers[0], AsyncPipeSink(self.controllers[0]))
             ),
             Device(
-                address = 'F5:F4:F3:F2:F1:F0',
+                address = 'F1:F2:F3:F4:F5:F6',
                 host    = Host(self.controllers[1], AsyncPipeSink(self.controllers[1]))
+            ),
+            Device(
+                address = 'F2:F3:F4:F5:F6:F7',
+                host    = Host(self.controllers[2], AsyncPipeSink(self.controllers[2]))
             )
         ]
 
-        self.paired = [None, None]
+        self.paired = [None, None, None]
 
 
 # -----------------------------------------------------------------------------
@@ -222,7 +344,7 @@ async def async_barrier():
 # -----------------------------------------------------------------------------
 @pytest.mark.asyncio
 async def test_read_write():
-    [client, server] = TwoDevices().devices
+    [client, server] = LinkedDevices().devices[:2]
 
     characteristic1 = Characteristic(
         'FDB159DB-036C-49E3-B3DB-6325AC750806',
@@ -265,41 +387,41 @@ async def test_read_write():
     await peer.discover_services()
     await peer.discover_characteristics()
     c = peer.get_characteristics_by_uuid(characteristic1.uuid)
-    assert(len(c) == 1)
+    assert len(c) == 1
     c1 = c[0]
     c = peer.get_characteristics_by_uuid(characteristic2.uuid)
-    assert(len(c) == 1)
+    assert len(c) == 1
     c2 = c[0]
 
     v1 = await peer.read_value(c1)
-    assert(v1 == b'')
+    assert v1 == b''
     b = bytes([1, 2, 3])
     await peer.write_value(c1, b)
     await async_barrier()
-    assert(characteristic1.value == b)
+    assert characteristic1.value == b
     v1 = await peer.read_value(c1)
-    assert(v1 == b)
-    assert(type(characteristic1._last_value) is tuple)
-    assert(len(characteristic1._last_value) == 2)
-    assert(str(characteristic1._last_value[0].peer_address) == str(client.random_address))
-    assert(characteristic1._last_value[1] == b)
+    assert v1 == b
+    assert type(characteristic1._last_value is tuple)
+    assert len(characteristic1._last_value) == 2
+    assert str(characteristic1._last_value[0].peer_address) == str(client.random_address)
+    assert characteristic1._last_value[1] == b
     bb = bytes([3, 4, 5, 6])
     characteristic1.value = bb
     v1 = await peer.read_value(c1)
-    assert(v1 == bb)
+    assert v1 == bb
 
     await peer.write_value(c2, b)
     await async_barrier()
-    assert(type(characteristic2._last_value) is tuple)
-    assert(len(characteristic2._last_value) == 2)
-    assert(str(characteristic2._last_value[0].peer_address) == str(client.random_address))
-    assert(characteristic2._last_value[1] == b)
+    assert type(characteristic2._last_value is tuple)
+    assert len(characteristic2._last_value) == 2
+    assert str(characteristic2._last_value[0].peer_address) == str(client.random_address)
+    assert characteristic2._last_value[1] == b
 
 
 # -----------------------------------------------------------------------------
 @pytest.mark.asyncio
 async def test_read_write2():
-    [client, server] = TwoDevices().devices
+    [client, server] = LinkedDevices().devices[:2]
 
     v = bytes([0x11, 0x22, 0x33, 0x44])
     characteristic1 = Characteristic(
@@ -324,32 +446,32 @@ async def test_read_write2():
 
     await peer.discover_services()
     c = peer.get_services_by_uuid(service1.uuid)
-    assert(len(c) == 1)
+    assert len(c) == 1
     s = c[0]
     await s.discover_characteristics()
     c = s.get_characteristics_by_uuid(characteristic1.uuid)
-    assert(len(c) == 1)
+    assert len(c) == 1
     c1 = c[0]
 
     v1 = await c1.read_value()
-    assert(v1 == v)
+    assert v1 == v
 
     a1 = PackedCharacteristicAdapter(c1, '>I')
     v1 = await a1.read_value()
-    assert(v1 == struct.unpack('>I', v)[0])
+    assert v1 == struct.unpack('>I', v)[0]
 
     b = bytes([0x55, 0x66, 0x77, 0x88])
     await a1.write_value(struct.unpack('>I', b)[0])
     await async_barrier()
-    assert(characteristic1.value == b)
+    assert characteristic1.value == b
     v1 = await a1.read_value()
-    assert(v1 == struct.unpack('>I', b)[0])
+    assert v1 == struct.unpack('>I', b)[0]
 
 
 # -----------------------------------------------------------------------------
 @pytest.mark.asyncio
 async def test_subscribe_notify():
-    [client, server] = TwoDevices().devices
+    [client, server] = LinkedDevices().devices[:2]
 
     characteristic1 = Characteristic(
         'FDB159DB-036C-49E3-B3DB-6325AC750806',
@@ -410,13 +532,13 @@ async def test_subscribe_notify():
     await peer.discover_services()
     await peer.discover_characteristics()
     c = peer.get_characteristics_by_uuid(characteristic1.uuid)
-    assert(len(c) == 1)
+    assert len(c) == 1
     c1 = c[0]
     c = peer.get_characteristics_by_uuid(characteristic2.uuid)
-    assert(len(c) == 1)
+    assert len(c) == 1
     c2 = c[0]
     c = peer.get_characteristics_by_uuid(characteristic3.uuid)
-    assert(len(c) == 1)
+    assert len(c) == 1
     c3 = c[0]
 
     c1._called = False
@@ -429,23 +551,32 @@ async def test_subscribe_notify():
     c1.on('update', on_c1_update)
     await peer.subscribe(c1)
     await async_barrier()
-    assert(server._last_subscription[1] == characteristic1)
-    assert(server._last_subscription[2])
-    assert(not server._last_subscription[3])
-    assert(characteristic1._last_subscription[1])
-    assert(not characteristic1._last_subscription[2])
+    assert server._last_subscription[1] == characteristic1
+    assert server._last_subscription[2]
+    assert not server._last_subscription[3]
+    assert characteristic1._last_subscription[1]
+    assert not characteristic1._last_subscription[2]
     await server.indicate_subscribers(characteristic1)
     await async_barrier()
-    assert(not c1._called)
+    assert not c1._called
     await server.notify_subscribers(characteristic1)
     await async_barrier()
-    assert(c1._called)
-    assert(c1._last_update == characteristic1.value)
+    assert c1._called
+    assert c1._last_update == characteristic1.value
+
+    c1._called = False
+    c1._last_update = None
+    c1_value = characteristic1.value
+    await server.notify_subscribers(characteristic1, bytes([0, 1, 2]))
+    await async_barrier()
+    assert c1._called
+    assert c1._last_update == bytes([0, 1, 2])
+    assert characteristic1.value == c1_value
 
     c1._called = False
     await peer.unsubscribe(c1)
     await server.notify_subscribers(characteristic1)
-    assert(not c1._called)
+    assert not c1._called
 
     c2._called = False
     c2._last_update = None
@@ -458,17 +589,17 @@ async def test_subscribe_notify():
     await async_barrier()
     await server.notify_subscriber(characteristic2._last_subscription[0], characteristic2)
     await async_barrier()
-    assert(not c2._called)
+    assert not c2._called
     await server.indicate_subscriber(characteristic2._last_subscription[0], characteristic2)
     await async_barrier()
-    assert(c2._called)
-    assert(c2._last_update == characteristic2.value)
+    assert c2._called
+    assert c2._last_update == characteristic2.value
 
     c2._called = False
     await peer.unsubscribe(c2, on_c2_update)
     await server.indicate_subscriber(characteristic2._last_subscription[0], characteristic2)
     await async_barrier()
-    assert(not c2._called)
+    assert not c2._called
 
     def on_c3_update(value):
         c3._called = True
@@ -483,17 +614,17 @@ async def test_subscribe_notify():
     await async_barrier()
     await server.notify_subscriber(characteristic3._last_subscription[0], characteristic3)
     await async_barrier()
-    assert(c3._called)
-    assert(c3._last_update == characteristic3.value)
-    assert(c3._called_2)
-    assert(c3._last_update_2 == characteristic3.value)
+    assert c3._called
+    assert c3._last_update == characteristic3.value
+    assert c3._called_2
+    assert c3._last_update_2 == characteristic3.value
     characteristic3.value = bytes([1, 2, 3])
     await server.indicate_subscriber(characteristic3._last_subscription[0], characteristic3)
     await async_barrier()
-    assert(c3._called)
-    assert(c3._last_update == characteristic3.value)
-    assert(c3._called_2)
-    assert(c3._last_update_2 == characteristic3.value)
+    assert c3._called
+    assert c3._last_update == characteristic3.value
+    assert c3._called_2
+    assert c3._last_update_2 == characteristic3.value
 
     c3._called = False
     c3._called_2 = False
@@ -501,8 +632,44 @@ async def test_subscribe_notify():
     await server.notify_subscriber(characteristic3._last_subscription[0], characteristic3)
     await server.indicate_subscriber(characteristic3._last_subscription[0], characteristic3)
     await async_barrier()
-    assert(not c3._called)
-    assert(not c3._called_2)
+    assert not c3._called
+    assert not c3._called_2
+
+
+# -----------------------------------------------------------------------------
+@pytest.mark.asyncio
+async def test_mtu_exchange():
+    [d1, d2, d3] = LinkedDevices().devices[:3]
+
+    d3.gatt_server.max_mtu = 100
+
+    d3_connections = []
+    @d3.on('connection')
+    def on_d3_connection(connection):
+        d3_connections.append(connection)
+
+    await d1.power_on()
+    await d2.power_on()
+    await d3.power_on()
+
+    d1_connection = await d1.connect(d3.random_address)
+    assert len(d3_connections) == 1
+    assert d3_connections[0] is not None
+
+    d2_connection = await d2.connect(d3.random_address)
+    assert len(d3_connections) == 2
+    assert d3_connections[1] is not None
+
+    d1_peer = Peer(d1_connection)
+    d2_peer = Peer(d2_connection)
+
+    d1_client_mtu = await d1_peer.request_mtu(220)
+    assert d1_client_mtu == 100
+    assert d1_connection.att_mtu == 100
+
+    d2_client_mtu = await d2_peer.request_mtu(50)
+    assert d2_client_mtu == 50
+    assert d2_connection.att_mtu == 50
 
 
 # -----------------------------------------------------------------------------
@@ -510,6 +677,9 @@ async def async_main():
     await test_read_write()
     await test_read_write2()
     await test_subscribe_notify()
+    await test_characteristic_encoding()
+    await test_mtu_exchange()
+
 
 # -----------------------------------------------------------------------------
 if __name__ == '__main__':

tests/self_test.py

@@ -246,8 +246,7 @@ IO_CAP = [
 SC = [False, True]
 MITM = [False, True]
 # Key distribution is a 4-bit bitmask
-# IdKey is necessary for current SMP structure
-KEY_DIST = [i for i in range(16) if (i & SMP_ID_KEY_DISTRIBUTION_FLAG)]
+KEY_DIST = range(16)
 
 @pytest.mark.asyncio
 @pytest.mark.parametrize('io_cap, sc, mitm, key_dist',