better/safer Linux recommendations

use arg-less main() functions in all scripts

apps/show.py

@@ -90,7 +90,7 @@ class SnoopPacketReader:
 @click.command()
 @click.option('--format', type=click.Choice(['h4', 'snoop']), default='h4', help='Format of the input file')
 @click.argument('filename')
-def show(format, filename):
+def main(format, filename):
     input = open(filename, 'rb')
     if format == 'h4':
         packet_reader = PacketReader(input)
@@ -117,4 +117,4 @@ def show(format, filename):
 
 # -----------------------------------------------------------------------------
 if __name__ == '__main__':
-    show()
+    main()

apps/usb_probe.py

@@ -28,6 +28,8 @@
 # -----------------------------------------------------------------------------
 import os
 import logging
+import sys
+import click
 import usb1
 from colors import color
 
@@ -35,6 +37,7 @@ from colors import color
 # -----------------------------------------------------------------------------
 # Constants
 # -----------------------------------------------------------------------------
+USB_DEVICE_CLASS_DEVICE                          = 0x00
 USB_DEVICE_CLASS_WIRELESS_CONTROLLER             = 0xE0
 USB_DEVICE_SUBCLASS_RF_CONTROLLER                = 0x01
 USB_DEVICE_PROTOCOL_BLUETOOTH_PRIMARY_CONTROLLER = 0x01
@@ -75,9 +78,81 @@ USB_DEVICE_CLASSES = {
     0xFF: 'Vendor Specific'
 }
 
+USB_ENDPOINT_IN    = 0x80
+USB_ENDPOINT_TYPES = ['CONTROL', 'ISOCHRONOUS', 'BULK', 'INTERRUPT']
+
+USB_BT_HCI_CLASS_TUPLE = (
+    USB_DEVICE_CLASS_WIRELESS_CONTROLLER,
+    USB_DEVICE_SUBCLASS_RF_CONTROLLER,
+    USB_DEVICE_PROTOCOL_BLUETOOTH_PRIMARY_CONTROLLER
+)
+
 
 # -----------------------------------------------------------------------------
-def main():
+def show_device_details(device):
+    for configuration in device:
+        print(f'  Configuration {configuration.getConfigurationValue()}')
+        for interface in configuration:
+            for setting in interface:
+                alternateSetting = setting.getAlternateSetting()
+                suffix = f'/{alternateSetting}' if interface.getNumSettings() > 1 else ''
+                (class_string, subclass_string) = get_class_info(
+                    setting.getClass(),
+                    setting.getSubClass(),
+                    setting.getProtocol()
+                )
+                details = f'({class_string}, {subclass_string})'
+                print(f'      Interface: {setting.getNumber()}{suffix} {details}')
+                for endpoint in setting:
+                    endpoint_type = USB_ENDPOINT_TYPES[endpoint.getAttributes() & 3]
+                    endpoint_direction = 'OUT' if (endpoint.getAddress() & USB_ENDPOINT_IN == 0) else 'IN'
+                    print(f'        Endpoint 0x{endpoint.getAddress():02X}: {endpoint_type} {endpoint_direction}')
+
+
+# -----------------------------------------------------------------------------
+def get_class_info(cls, subclass, protocol):
+    class_info = USB_DEVICE_CLASSES.get(cls)
+    protocol_string = ''
+    if class_info is None:
+        class_string = f'0x{cls:02X}'
+    else:
+        if type(class_info) is tuple:
+            class_string = class_info[0]
+            subclass_info = class_info[1].get(subclass)
+            if subclass_info:
+                protocol_string = subclass_info.get(protocol)
+                if protocol_string is not None:
+                    protocol_string = f' [{protocol_string}]'
+
+        else:
+            class_string = class_info
+
+    subclass_string = f'{subclass}/{protocol}{protocol_string}'
+
+    return (class_string, subclass_string)
+
+
+# -----------------------------------------------------------------------------
+def is_bluetooth_hci(device):
+    # Check if the device class indicates a match
+    if (device.getDeviceClass(), device.getDeviceSubClass(), device.getDeviceProtocol()) == USB_BT_HCI_CLASS_TUPLE:
+        return True
+
+    # If the device class is 'Device', look for a matching interface
+    if device.getDeviceClass() == USB_DEVICE_CLASS_DEVICE:
+        for configuration in device:
+            for interface in configuration:
+                for setting in interface:
+                    if (setting.getClass(), setting.getSubClass(), setting.getProtocol()) == USB_BT_HCI_CLASS_TUPLE:
+                        return True
+
+    return False
+
+
+# -----------------------------------------------------------------------------
+@click.command()
+@click.option('--verbose', is_flag=True, default=False, help='Print more details')
+def main(verbose):
     logging.basicConfig(level = os.environ.get('BUMBLE_LOGLEVEL', 'WARNING').upper())
 
     with usb1.USBContext() as context:
@@ -91,23 +166,28 @@ def main():
 
             device_id = (device.getVendorID(), device.getProductID())
 
-            device_is_bluetooth_hci = (
+            (device_class_string, device_subclass_string) = get_class_info(
-                device_class    == USB_DEVICE_CLASS_WIRELESS_CONTROLLER and
+                device_class,
-                device_subclass == USB_DEVICE_SUBCLASS_RF_CONTROLLER and
+                device_subclass,
-                device_protocol == USB_DEVICE_PROTOCOL_BLUETOOTH_PRIMARY_CONTROLLER
+                device_protocol
             )
 
-            device_class_details = ''
+            try:
-            device_class_info    = USB_DEVICE_CLASSES.get(device_class)
+                device_serial_number = device.getSerialNumber()
-            if device_class_info is not None:
+            except usb1.USBError:
-                if type(device_class_info) is tuple:
+                device_serial_number = None
-                    device_class = device_class_info[0]
-                    device_subclass_info = device_class_info[1].get(device_subclass)
-                    if device_subclass_info:
-                        device_class_details = f' [{device_subclass_info.get(device_protocol)}]'
-                else:
-                    device_class = device_class_info
 
+            try:
+                device_manufacturer = device.getManufacturer()
+            except usb1.USBError:
+                device_manufacturer = None
+
+            try:
+                device_product = device.getProduct()
+            except usb1.USBError:
+                device_product = None
+
+            device_is_bluetooth_hci = is_bluetooth_hci(device)
             if device_is_bluetooth_hci:
                 bluetooth_device_count += 1
                 fg_color = 'black'
@@ -123,33 +203,35 @@ def main():
             if device_is_bluetooth_hci:
                 bumble_transport_names.append(f'usb:{bluetooth_device_count - 1}')
 
-            serial_number_collision = False
-            if device_id in devices:
-                for device_serial in devices[device_id]:
-                    if device_serial == device.getSerialNumber():
-                        serial_number_collision = True
-
             if device_id not in devices:
                 bumble_transport_names.append(basic_transport_name)
             else:
                 bumble_transport_names.append(f'{basic_transport_name}#{len(devices[device_id])}')
 
-            if device.getSerialNumber() and not serial_number_collision:
+            if device_serial_number is not None:
-                bumble_transport_names.append(f'{basic_transport_name}/{device.getSerialNumber()}')
+                if device_id not in devices or device_serial_number not in devices[device_id]:
+                    bumble_transport_names.append(f'{basic_transport_name}/{device_serial_number}')
 
+            # Print the results
             print(color(f'ID {device.getVendorID():04X}:{device.getProductID():04X}', fg=fg_color, bg=bg_color))
             if bumble_transport_names:
                 print(color('  Bumble Transport Names:', 'blue'), ' or '.join(color(x, 'cyan' if device_is_bluetooth_hci else 'red') for x in bumble_transport_names))
             print(color('  Bus/Device:            ', 'green'), f'{device.getBusNumber():03}/{device.getDeviceAddress():03}')
-            if device.getSerialNumber():
+            print(color('  Class:                 ', 'green'), device_class_string)
-                print(color('  Serial:                ', 'green'), device.getSerialNumber())
+            print(color('  Subclass/Protocol:     ', 'green'), device_subclass_string)
-            print(color('  Class:                 ', 'green'), device_class)
+            if device_serial_number is not None:
-            print(color('  Subclass/Protocol:     ', 'green'), f'{device_subclass}/{device_protocol}{device_class_details}')
+                print(color('  Serial:                ', 'green'), device_serial_number)
-            print(color('  Manufacturer:          ', 'green'), device.getManufacturer())
+            if device_manufacturer is not None:
-            print(color('  Product:               ', 'green'), device.getProduct())
+                print(color('  Manufacturer:          ', 'green'), device_manufacturer)
+            if device_product is not None:
+                print(color('  Product:               ', 'green'), device_product)
+
+            if verbose:
+                show_device_details(device)
+
             print()
 
-            devices.setdefault(device_id, []).append(device.getSerialNumber())
+            devices.setdefault(device_id, []).append(device_serial_number)
 
 
 # -----------------------------------------------------------------------------

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):
+    async def notify_subscriber(self, connection, attribute, value=None, force=False):
-        await self.gatt_server.notify_subscriber(connection, attribute, force)
+        await self.gatt_server.notify_subscriber(connection, attribute, value, force)
 
-    async def notify_subscribers(self, attribute, force=False):
+    async def notify_subscribers(self, attribute, value=None, force=False):
-        await self.gatt_server.notify_subscribers(attribute, force)
+        await self.gatt_server.notify_subscribers(attribute, value, force)
 
-    async def indicate_subscriber(self, connection, attribute, force=False):
+    async def indicate_subscriber(self, connection, attribute, value=None, force=False):
-        await self.gatt_server.indicate_subscriber(connection, attribute, force)
+        await self.gatt_server.indicate_subscriber(connection, attribute, value, force)
 
-    async def indicate_subscribers(self, attribute):
+    async def indicate_subscribers(self, attribute, value=None, force=False):
-        await self.gatt_server.indicate_subscribers(attribute)
+        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(
+        if subscriber is not None:
-            None if subscriber is None else lambda value: subscriber(self.decode_value(value))
+            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)
+        # Compute the final MTU
-        return self.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
+        # Get or encode the value
-        value = attribute.read_value(connection)
+        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) > connection.att_mtu - 3:
-        if len(value) > mtu - 3:
+            value = value[:connection.att_mtu - 3]
-            value = value[: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):
+    async def indicate_subscriber(self, connection, 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 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):
         # 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
+        # Get or encode the value
-        value = attribute.read_value(connection)
+        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) > connection.att_mtu - 3:
-        if len(value) > mtu - 3:
+            value = value[:connection.att_mtu - 3]
-            value = value[: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.send_response(connection, ATT_Exchange_MTU_Response(server_rx_mtu = self.max_mtu))
-        self.mtus[connection.handle] = mtu
-        self.send_response(connection, ATT_Exchange_MTU_Response(server_rx_mtu = mtu))
 
-        # Notify the device
+        # Compute the final MTU
-        self.device.on_connection_att_mtu_update(connection.handle, 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 = connection.att_mtu - 2
-        pdu_space_available = 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 = connection.att_mtu - 2
-        pdu_space_available = 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/transport/usb.py

@@ -36,7 +36,7 @@ logger = logging.getLogger(__name__)
 async def open_usb_transport(spec):
     '''
     Open a USB transport.
-    The parameter string has this syntax:
+    The moniker string has this syntax:
     either <index> or
     <vendor>:<product> or
     <vendor>:<product>/<serial-number>] or
@@ -47,15 +47,21 @@ async def open_usb_transport(spec):
     /<serial-number> suffix or #<index> suffix max be specified when more than one device with
     the same vendor and product identifiers are present.
 
+    In addition, if the moniker ends with the symbol "!", the device will be used in "forced" mode:
+    the first USB interface of the device will be used, regardless of the interface class/subclass.
+    This may be useful for some devices that use a custom class/subclass but may nonetheless work as-is.
+
     Examples:
     0 --> the first BT USB dongle
     04b4:f901 --> the BT USB dongle with vendor=04b4 and product=f901
     04b4:f901#2 --> the third USB device with vendor=04b4 and product=f901
     04b4:f901/00E04C239987 --> the BT USB dongle with vendor=04b4 and product=f901 and serial number 00E04C239987
+    usb:0B05:17CB! --> the BT USB dongle vendor=0B05 and product=17CB, in "forced" mode.
     '''
 
     USB_RECIPIENT_DEVICE                             = 0x00
     USB_REQUEST_TYPE_CLASS                           = 0x01 << 5
+    USB_DEVICE_CLASS_DEVICE                          = 0x00
     USB_DEVICE_CLASS_WIRELESS_CONTROLLER             = 0xE0
     USB_DEVICE_SUBCLASS_RF_CONTROLLER                = 0x01
     USB_DEVICE_PROTOCOL_BLUETOOTH_PRIMARY_CONTROLLER = 0x01
@@ -63,6 +69,12 @@ async def open_usb_transport(spec):
     USB_ENDPOINT_TRANSFER_TYPE_INTERRUPT             = 0x03
     USB_ENDPOINT_IN                                  = 0x80
 
+    USB_BT_HCI_CLASS_TUPLE = (
+        USB_DEVICE_CLASS_WIRELESS_CONTROLLER,
+        USB_DEVICE_SUBCLASS_RF_CONTROLLER,
+        USB_DEVICE_PROTOCOL_BLUETOOTH_PRIMARY_CONTROLLER
+    )
+
     READ_SIZE = 1024
 
     class UsbPacketSink:
@@ -280,6 +292,13 @@ async def open_usb_transport(spec):
     context.open()
     try:
         found = None
+
+        if spec.endswith('!'):
+            spec = spec[:-1]
+            forced_mode = True
+        else:
+            forced_mode = False
+
         if ':' in spec:
             vendor_id, product_id = spec.split(':')
             serial_number = None
@@ -291,10 +310,14 @@ async def open_usb_transport(spec):
                 device_index = int(device_index_str)
 
             for device in context.getDeviceIterator(skip_on_error=True):
+                try:
+                    device_serial_number = device.getSerialNumber()
+                except usb1.USBError:
+                    device_serial_number = None
                 if (
                     device.getVendorID() == int(vendor_id, 16) and
                     device.getProductID() == int(product_id, 16) and
-                    (serial_number is None or device.getSerialNumber() == serial_number)
+                    (serial_number is None or serial_number == device_serial_number)
                 ):
                     if device_index == 0:
                         found = device
@@ -302,13 +325,27 @@ async def open_usb_transport(spec):
                     device_index -= 1
                 device.close()
         else:
+            # Look for a compatible device by index
+            def device_is_bluetooth_hci(device):
+                # Check if the device class indicates a match
+                if (device.getDeviceClass(), device.getDeviceSubClass(), device.getDeviceProtocol()) == \
+                        USB_BT_HCI_CLASS_TUPLE:
+                    return True
+
+                # If the device class is 'Device', look for a matching interface
+                if device.getDeviceClass() == USB_DEVICE_CLASS_DEVICE:
+                    for configuration in device:
+                        for interface in configuration:
+                            for setting in interface:
+                                if (setting.getClass(), setting.getSubClass(), setting.getProtocol()) == \
+                                        USB_BT_HCI_CLASS_TUPLE:
+                                    return True
+
+                return False
+
             device_index = int(spec)
             for device in context.getDeviceIterator(skip_on_error=True):
-                if (
+                if device_is_bluetooth_hci(device):
-                    device.getDeviceClass()    == USB_DEVICE_CLASS_WIRELESS_CONTROLLER and
-                    device.getDeviceSubClass() == USB_DEVICE_SUBCLASS_RF_CONTROLLER and
-                    device.getDeviceProtocol() == USB_DEVICE_PROTOCOL_BLUETOOTH_PRIMARY_CONTROLLER
-                ):
                     if device_index == 0:
                         found = device
                         break
@@ -329,9 +366,8 @@ async def open_usb_transport(spec):
                     setting = None
                     for setting in interface:
                         if (
-                            setting.getClass() != USB_DEVICE_CLASS_WIRELESS_CONTROLLER or
+                            not forced_mode and
-                            setting.getSubClass() != USB_DEVICE_SUBCLASS_RF_CONTROLLER or
+                            (setting.getClass(), setting.getSubClass(), setting.getProtocol()) != USB_BT_HCI_CLASS_TUPLE
-                            setting.getProtocol() != USB_DEVICE_PROTOCOL_BLUETOOTH_PRIMARY_CONTROLLER
                         ):
                             continue
 

docs/mkdocs/mkdocs.yml

@@ -45,6 +45,10 @@ nav:
     - HCI Bridge: apps_and_tools/hci_bridge.md
     - Golden Gate Bridge: apps_and_tools/gg_bridge.md
     - Show: apps_and_tools/show.md
+    - GATT Dump: apps_and_tools/gatt_dump.md
+    - Pair: apps_and_tools/pair.md
+    - Unbond: apps_and_tools/unbond.md
+    - USB Probe: apps_and_tools/usb_probe.md
   - Hardware:
     - Overview: hardware/index.md
   - Platforms:

docs/mkdocs/requirements.txt

@@ -1,6 +1,6 @@
 # This requirements file is for python3
-mkdocs == 1.2.3
+mkdocs == 1.4.0
-mkdocs-material == 7.1.7
+mkdocs-material == 8.5.6
-mkdocs-material-extensions == 1.0.1
+mkdocs-material-extensions == 1.0.3
-pymdown-extensions == 8.2
+pymdown-extensions == 9.6
-mkdocstrings == 0.15.1
+mkdocstrings-python == 0.7.1

docs/mkdocs/src/apps_and_tools/usb_probe.md

@@ -13,17 +13,29 @@ type of device (there's no way to tell).
 
 ## Usage
 
-This command line tool takes no arguments.
+This command line tool may be invoked with no arguments, or with `--verbose`
+for extra details.
 When installed from PyPI, run as
 ```
 $ bumble-usb-probe
 ```
 
+or, for extra details, with the `--verbose` argument
+```
+$ bumble-usb-probe --v
+```
+
 When running from the source distribution:
 ```
 $ python3 apps/usb-probe.py
 ```
 
+or 
+
+```
+$ python3 apps/usb-probe.py --verbose
+```
+
 !!! example
     ```
     $ python3 apps/usb_probe.py 

docs/mkdocs/src/platforms/linux.md

@@ -1,48 +1,86 @@
 :material-linux: LINUX PLATFORM
 ===============================
 
-In addition to all the standard functionality available from the project by running the python tools and/or writing your own apps by leveraging the API, it is also possible on Linux hosts to interface the Bumble stack with the native BlueZ stack, and with Bluetooth controllers.
+Using Bumble With Physical Bluetooth Controllers
+------------------------------------------------
 
-Using Bumble With BlueZ
+A Bumble application can interface with a local Bluetooth controller on a Linux host.
------------------------
+The 3 main types of physical Bluetooth controllers are:
 
-A Bumble virtual controller can be attached to the BlueZ stack.
+  * Bluetooth USB Dongle
-Attaching a controller to BlueZ can be done by either simulating a UART HCI interface, or by using the VHCI driver interface if available.
+  * HCI over  UART (via a serial port)
-In both cases, the controller can run locally on the Linux host, or remotely on a different host, with a bridge between the remote controller and the local BlueZ host, which may be useful when the BlueZ stack is running on an embedded system, or a host on which running the Bumble controller is not convenient.
+  * Kernel-managed Bluetooth HCI (HCI Sockets)
 
-### Using VHCI
+!!! tip "Conflicts with the kernel and BlueZ"
+    If your use a USB dongle that is recognized by your kernel as a supported Bluetooth device, it is
+    likely that the kernel driver will claim that USB device and attach it to the BlueZ stack. 
+    If you want to claim ownership of it to use with Bumble, you will need to set the state of the corresponding HCI interface as `DOWN`. 
+    HCI interfaces are numbered, starting from 0 (i.e `hci0`, `hci1`, ...).
 
-With the [VHCI transport](../transports/vhci.md) you can attach a Bumble virtual controller to the BlueZ stack. Once attached, the controller will appear just like any other controller, and thus can be used with the standard BlueZ tools.
+    For example, to bring `hci0` down:
-
-!!! example "Attaching a virtual controller"
-    With the example app `run_controller.py`:
     ```
-    PYTHONPATH=. python3 examples/run_controller.py F6:F7:F8:F9:FA:FB examples/device1.json vhci
+    $ sudo hciconfig hci0 down
-    ```
-    
-    You should see a 'Virtual Bus' controller. For example:
-    ```
-    $ hciconfig
-    hci0:	Type: Primary  Bus: Virtual
-        BD Address: F6:F7:F8:F9:FA:FB  ACL MTU: 27:64  SCO MTU: 0:0
-        UP RUNNING 
-        RX bytes:0 acl:0 sco:0 events:43 errors:0
-        TX bytes:274 acl:0 sco:0 commands:43 errors:0
     ```
 
-    And scanning for devices should show the virtual 'Bumble' device that's running as part of the `run_controller.py` example app:
+    You can use the `hciconfig` command with no arguments to get a list of HCI interfaces seen by
+    the kernel.
+
+    Also, if `bluetoothd` is running on your system, it will likely re-claim the interface after you
+    close it, so you may need to bring the interface back `UP` before using it again, or to disable
+    `bluetoothd` altogether (see the section further below about BlueZ and `bluetoothd`).
+
+### Using a USB Dongle
+
+See the [USB Transport page](../transports/usb.md) for general information on how to use HCI USB controllers.
+
+!!! tip "USB Permissions"
+    By default, when running as a regular user, you won't have the permission to use
+    arbitrary USB devices.
+    You can change the permissions for a specific USB device based on its bus number and 
+    device number (you can use `lsusb` to find the Bus and Device numbers for your Bluetooth
+    dongle).
+
+    Example:
     ```
-    pi@raspberrypi:~ $ sudo hcitool -i hci2 lescan
+    $ sudo chmod o+w /dev/bus/usb/001/004
-    LE Scan ...
-    F0:F1:F2:F3:F4:F5 Bumble
     ```
+    This will change the permissions for Device 4 on Bus 1.
+
+    Note that the USB Bus number and Device number may change depending on where you plug the USB
+    dongle and what other USB devices and hubs are also plugged in.
+
+    If you need to make the permission changes permanent across reboots, you can create a `udev`
+    rule for your specific Bluetooth dongle. Visit [this Arch Linux Wiki page](https://wiki.archlinux.org/title/udev) for a
+    good overview of how you may do that.
+
+### Using HCI over UART
+
+See the [Serial Transport page](../transports/serial.md) for general information on how to use HCI over a UART (serial port).
 
 ### Using HCI Sockets
 
 HCI sockets provide a way to send/receive HCI packets to/from a Bluetooth controller managed by the kernel.
-The HCI device referenced by an `hci-socket` transport (`hciX`, where `X` is an integer, with `hci0` being the first controller device, and so on) must be in the `DOWN` state before it can be opened as a transport.
+See the [HCI Socket Transport page](../transports/hci_socket.md) for details on the `hci-socket` tansport syntax.
-You can bring a HCI controller `UP` or `DOWN` with `hciconfig`.
 
+The HCI device referenced by an `hci-socket` transport (`hci<X>`, where `<X>` is an integer, with `hci0` being the first controller device, and so on) must be in the `DOWN` state before it can be opened as a transport.
+You can bring a HCI controller `UP` or `DOWN` with `hciconfig hci<X> up` and `hciconfig hci<X> up`.
+
+!!! tip "HCI Socket Permissions"
+    By default, when running as a regular user, you won't have the permission to use
+    an HCI socket to a Bluetooth controller (you may see an exception like `PermissionError: [Errno 1] Operation not permitted`).
+
+    If you want to run without using `sudo`, you need to manage the capabilities by adding the appropriate entries in `/etc/security/capability.conf` to grant a user or group the `cap_net_admin` capability.  
+    See [this manpage](https://manpages.ubuntu.com/manpages/bionic/man5/capability.conf.5.html) for details.
+    
+    Alternatively, if you are just experimenting temporarily, the `capsh` command may be useful in order
+    to execute a single command with enhanced permissions, as in this example:
+
+
+    ```
+    $ sudo capsh --caps="cap_net_admin+eip cap_setpcap,cap_setuid,cap_setgid+ep" --keep=1 --user=$USER --addamb=cap_net_admin  -- -c "<path/to/executable> <executable-args>"
+    ```
+    Where `<path/to/executable>` is the path to your `python3` executable or to one of the Bumble bundled command-line applications.
+    
 !!! tip "List all available controllers"
     The command
     ```
@@ -72,29 +110,16 @@ You can bring a HCI controller `UP` or `DOWN` with `hciconfig`.
     ```
     $ hciconfig hci0 down
     ``` 
-    (or `hciX` with `X` being the index of the controller device you want to use), but a simpler solution is to just stop the `bluetoothd` daemon, with a command like:
+    (or `hci<X>` with `<X>` being the index of the controller device you want to use), but a simpler solution is to just stop the `bluetoothd` daemon, with a command like:
     ```
     $ sudo systemctl stop bluetooth.service
     ```
     You can always re-start the daemon with
     ```
     $ sudo systemctl start bluetooth.service
-    ```
 
-### Using a Simulated UART HCI
+Bumble on the Raspberry Pi
-
+--------------------------
-### Bridge to a Remote Controller
-
-
-Using Bumble With Bluetooth Controllers
----------------------------------------
-
-A Bumble application can interface with a local Bluetooth controller.
-If your Bluetooth controller is a standard HCI USB controller, see the [USB Transport page](../transports/usb.md) for details on how to use HCI USB controllers.
-If your Bluetooth controller is a standard HCI UART controller, see the [Serial Transport page](../transports/serial.md).
-Alternatively, a Bumble Host object can communicate with one of the platform's controllers via an HCI Socket.
-
-`<details to be filled in>`
 
 ### Raspberry Pi 4 :fontawesome-brands-raspberry-pi:
 
@@ -102,9 +127,10 @@ You can use the Bluetooth controller either via the kernel, or directly to the d
 
 #### Via The Kernel
 
-Use an HCI Socket transport
+Use an HCI Socket transport (see section above)
 
 #### Directly
+
 In order to use the Bluetooth controller directly on a Raspberry Pi 4 board, you need to ensure that it isn't being used by the BlueZ stack (which it probably is by default).
 
 ```
@@ -136,3 +162,47 @@ should detach the controller from the stack, after which you can use the HCI UAR
     python3 run_scanner.py serial:/dev/serial1,3000000
     ```
 
+
+Using Bumble With BlueZ
+-----------------------
+
+In addition to all the standard functionality available from the project by running the python tools and/or writing your own apps by leveraging the API, it is also possible on Linux hosts to interface the Bumble stack with the native BlueZ stack, and with Bluetooth controllers.
+
+A Bumble virtual controller can be attached to the BlueZ stack.
+Attaching a controller to BlueZ can be done by either simulating a UART HCI interface, or by using the VHCI driver interface if available.
+In both cases, the controller can run locally on the Linux host, or remotely on a different host, with a bridge between the remote controller and the local BlueZ host, which may be useful when the BlueZ stack is running on an embedded system, or a host on which running the Bumble controller is not convenient.
+
+### Using VHCI
+
+With the [VHCI transport](../transports/vhci.md) you can attach a Bumble virtual controller to the BlueZ stack. Once attached, the controller will appear just like any other controller, and thus can be used with the standard BlueZ tools.
+
+!!! example "Attaching a virtual controller"
+    With the example app `run_controller.py`:
+    ```
+    python3 examples/run_controller.py F6:F7:F8:F9:FA:FB examples/device1.json vhci
+    ```
+    
+    You should see a 'Virtual Bus' controller. For example:
+    ```
+    $ hciconfig
+    hci0:	Type: Primary  Bus: Virtual
+        BD Address: F6:F7:F8:F9:FA:FB  ACL MTU: 27:64  SCO MTU: 0:0
+        UP RUNNING 
+        RX bytes:0 acl:0 sco:0 events:43 errors:0
+        TX bytes:274 acl:0 sco:0 commands:43 errors:0
+    ```
+
+    And scanning for devices should show the virtual 'Bumble' device that's running as part of the `run_controller.py` example app:
+    ```
+    pi@raspberrypi:~ $ sudo hcitool -i hci2 lescan
+    LE Scan ...
+    F0:F1:F2:F3:F4:F5 Bumble
+    ```
+
+    ```
+
+### Using a Simulated UART HCI
+
+### Bridge to a Remote Controller
+
+

docs/mkdocs/src/transports/usb.md

@@ -5,6 +5,7 @@ The USB transport interfaces with a local Bluetooth USB dongle.
 
 ## Moniker
 The moniker for a USB transport is either:
+
   * `usb:<index>`
   * `usb:<vendor>:<product>`
   * `usb:<vendor>:<product>/<serial-number>`
@@ -16,6 +17,10 @@ In the `usb:<vendor>:<product>#<index>` form, matching devices are the ones with
 
 `<vendor>` and `<product>` are a vendor ID and product ID in hexadecimal.
 
+In addition, if the moniker ends with the symbol "!", the device will be used in "forced" mode:
+the first USB interface of the device will be used, regardless of the interface class/subclass.
+This may be useful for some devices that use a custom class/subclass but may nonetheless work as-is.
+
 !!! examples
     `usb:04b4:f901`  
     The USB dongle with `<vendor>` equal to `04b4` and `<product>` equal to `f901`
@@ -29,6 +34,10 @@ In the `usb:<vendor>:<product>#<index>` form, matching devices are the ones with
     `usb:04b4:f901/#1`
     The second USB dongle with `<vendor>` equal to `04b4` and `<product>` equal to `f901`
 
+    `usb:0B05:17CB!`
+    The BT USB dongle vendor=0B05 and product=17CB, in "forced" mode.
+
+
 ## Alternative
 The library includes two different implementations of the USB transport, implemented using different python bindings for `libusb`.
 Using the transport prefix `pyusb:` instead of `usb:` selects the implementation based on  [PyUSB](https://pypi.org/project/pyusb/), using the synchronous API of `libusb`, whereas the default implementation is based on [libusb1](https://pypi.org/project/libusb1/), using the asynchronous API of `libusb`. In order to use the alternative PyUSB-based implementation, you need to ensure that you have installed that python module, as it isn't installed by default as a dependency of Bumble.

setup.cfg

@@ -67,6 +67,6 @@ development =
     invoke >= 1.4
     nox >= 2022
 documentation =
-    mkdocs >= 1.2.3
+    mkdocs >= 1.4.0
-    mkdocs-material >= 8.1.9
+    mkdocs-material >= 8.5.6
     mkdocstrings[python] >= 0.19.0

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 v1 == b
-    assert(type(characteristic1._last_value) is tuple)
+    assert type(characteristic1._last_value is tuple)
-    assert(len(characteristic1._last_value) == 2)
+    assert len(characteristic1._last_value) == 2
-    assert(str(characteristic1._last_value[0].peer_address) == str(client.random_address))
+    assert str(characteristic1._last_value[0].peer_address) == str(client.random_address)
-    assert(characteristic1._last_value[1] == b)
+    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 type(characteristic2._last_value is tuple)
-    assert(len(characteristic2._last_value) == 2)
+    assert len(characteristic2._last_value) == 2
-    assert(str(characteristic2._last_value[0].peer_address) == str(client.random_address))
+    assert str(characteristic2._last_value[0].peer_address) == str(client.random_address)
-    assert(characteristic2._last_value[1] == b)
+    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[1] == characteristic1
-    assert(server._last_subscription[2])
+    assert server._last_subscription[2]
-    assert(not server._last_subscription[3])
+    assert not server._last_subscription[3]
-    assert(characteristic1._last_subscription[1])
+    assert characteristic1._last_subscription[1]
-    assert(not characteristic1._last_subscription[2])
+    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._called
-    assert(c1._last_update == characteristic1.value)
+    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._called
-    assert(c2._last_update == characteristic2.value)
+    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._called
-    assert(c3._last_update == characteristic3.value)
+    assert c3._last_update == characteristic3.value
-    assert(c3._called_2)
+    assert c3._called_2
-    assert(c3._last_update_2 == characteristic3.value)
+    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._called
-    assert(c3._last_update == characteristic3.value)
+    assert c3._last_update == characteristic3.value
-    assert(c3._called_2)
+    assert c3._called_2
-    assert(c3._last_update_2 == characteristic3.value)
+    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
-    assert(not c3._called_2)
+    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__':