BLESession.setNotifications: Lookup CCCD to start or stop notifications

Per Bluetooth Core Specification Vol.3, Part G, Section 3.3.1.1, if
Notify property is set for a Characteristic, the Client Characteristic
Configuration Descriptor, or CCCD, shall exist. As noted in section
3.3.3.3 of the specification, notification of the Characteristic is
enabled or disabled by setting bit 0 of the CCCD.

This CCCD exists within the characteristic definition following the
Characteristic Value declaration, and section 3.3.3 of the specification
warns that the order of characteristic declaration shall not be assumed.
However, current pyscrlink code assumes that the CCCD comes just after
the Characteristic Value and CCCD handle is obtained just adding 1 to
the handle of the Characteristic Value. This works many of the BLE
devices but does not work all of them.

To get correct CCCD handle, look up descriptors of the Characteristic to
find out the CCCD.

Signed-off-by: Shin'ichiro Kawasaki <kawasaki@juno.dti.ne.jp>

pyscrlink/scratch_link.py

@@ -47,6 +47,8 @@ logger.propagate = False
 HOSTNAME="device-manager.scratch.mit.edu"
 scan_seconds=10.0
 
+CCCD_UUID = 0x2902
+
 class Session():
     """Base class for BTSession and BLESession"""
     def __init__(self, websocket, loop):
@@ -170,6 +172,9 @@ class BTSession(Session):
                 logger.debug(f"Found device {name} addr={address} class={device_class} rssi={rssi}")
                 major_class = (device_class & 0x1F00) >> 8
                 minor_class = (device_class & 0xFF) >> 2
+                if "LEGO Hub" in name:
+                    minor_class = 1
+                    logger.info(f"Pretend to be LEGO EV3 with LEGO Hub: class={major_class/minor_class}")
                 if major_class == self.major_class and minor_class == self.minor_class:
                     self.found_devices[address] = (name, device_class, rssi)
 
@@ -185,7 +190,13 @@ class BTSession(Session):
             self.ping_time = None
 
         def discover(self):
-            discoverer = self.BTDiscoverer(self.major_device_class, self.minor_device_class)
+            major = self.major_device_class
+            minor = self.minor_device_class
+            if major == 8 and minor == 1:
+                logger.info(f"Search LEGO Hub instead of LEGO EV3")
+                minor = 4
+            logger.debug(f"BT discover: class={major}/{minor}")
+            discoverer = self.BTDiscoverer(major, minor)
             discoverer.find_devices(lookup_names=True)
             while self.session.status == self.session.DISCOVERY and not discoverer.done and not self.cancel_discovery:
                 readable = select.select([discoverer], [], [], 0.5)[0]
@@ -203,7 +214,7 @@ class BTSession(Session):
         def run(self):
             while self.session.status != self.session.DONE:
 
-                logger.debug("loop in BT thread")
+                logger.debug(f"loop in BT thread: session status={self.session.status}")
                 current_time = int(round(time.time()))
 
                 if self.session.status == self.session.DISCOVERY and not self.cancel_discovery:
@@ -353,6 +364,14 @@ class BLESession(Session):
     scan_lock = threading.RLock()
     scan_started = False
 
+    @staticmethod
+    def _getDevName(dev):
+        """
+        Get AdType 0x09 (Completed local name). If it is not available,
+        get AdType 0x08 (Shortened local name).
+        """
+        return dev.getValueText(0x9) or dev.getValueText(0x8)
+
     class BLEThread(threading.Thread):
         """
         Separated thread to control notifications to Scratch.
@@ -372,7 +391,7 @@ class BLESession(Session):
                     for d in devices:
                         params = { 'rssi': d.rssi }
                         params['peripheralId'] = devices.index(d)
-                        params['name'] = d.getValueText(0x9) or d.getValueText(0x8)
+                        params['name'] = BLESession._getDevName(d)
                         self.session.notify('didDiscoverPeripheral', params)
                     time.sleep(1)
                 elif self.session.status == self.session.CONNECTED:
@@ -389,7 +408,8 @@ class BLESession(Session):
                                 logger.debug("after waitForNotification")
                             logger.debug("released lock for waitForNotification")
                         except Exception as e:
-                            logger.error(e)
+                            logger.error(f"Exception in waitForNotifications: "
+                                         f"{type(e).__name__}: {e}")
                             self.session.close()
                             break
                     else:
@@ -413,7 +433,8 @@ class BLESession(Session):
             self.restart_notification_event.set()
 
         def add_handle(self, serviceId, charId, handle):
-            logger.debug(f"add handle for notification: {handle}")
+            logger.debug(f"add handle for notification: "
+                         f"{serviceId} {charId} {handle}")
             params = { 'serviceId': UUID(serviceId).getCommonName(),
                        'characteristicId': charId,
                        'encoding': 'base64' }
@@ -421,6 +442,14 @@ class BLESession(Session):
 
         def handleNotification(self, handle, data):
             logger.debug(f"BLE notification: {handle} {data}")
+            if handle not in self.handles:
+                logger.error(f"Notification with unknown handle: {handle}")
+                keys = list(self.handles.keys())
+                if keys and len(keys) == 1:
+                    logger.debug(f"Debug: override {handle} with {keys[0]}")
+                    handle = keys[0]
+                else:
+                    return
             params = self.handles[handle].copy()
             params['message'] = base64.standard_b64encode(data).decode('ascii')
             self.session.notify('characteristicDidChange', params)
@@ -453,12 +482,14 @@ class BLESession(Session):
     def __del__(self):
         self.close()
 
-    def _get_dev_uuid(self, dev):
+    def _get_dev_uuids(self, dev):
         for adtype in self.SERVICE_CLASS_UUID_ADTYPES:
-            service_class_uuid = dev.getValueText(adtype)
-            if service_class_uuid:
-                logger.debug(self.SERVICE_CLASS_UUID_ADTYPES[adtype])
-                return UUID(service_class_uuid)
+            service_class_uuids = dev.getValue(adtype)
+            if service_class_uuids:
+                for u in service_class_uuids:
+                    a = self.SERVICE_CLASS_UUID_ADTYPES[adtype]
+                    logger.debug(f"service class uuid for {a}/{adtype}: {u}")
+                return service_class_uuids
         return None
 
     def matches(self, dev, filters):
@@ -471,18 +502,19 @@ class BLESession(Session):
                 for s in f['services']:
                     logger.debug(f"service to check: {s}")
                     given_uuid = s
-                    logger.debug(f"given: {given_uuid}")
-                    dev_uuid = self._get_dev_uuid(dev)
-                    if not dev_uuid:
+                    logger.debug(f"given UUID: {given_uuid} hash={UUID(given_uuid).__hash__()}")
+                    dev_uuids = self._get_dev_uuids(dev)
+                    if not dev_uuids:
                         continue
-                    logger.debug(f"dev: {dev_uuid}")
-                    logger.debug(given_uuid == dev_uuid)
-                    if given_uuid == dev_uuid:
+                    for u in dev_uuids:
+                        logger.debug(f"dev UUID: {u} hash={u.__hash__()}")
+                        logger.debug(given_uuid == u)
+                        if given_uuid == u:
                             logger.debug("match...")
                             return True
             if 'namePrefix' in f:
                 # 0x08: Shortened Local Name
-                deviceName = dev.getValueText(0x08)
+                deviceName = self._getDevName(dev)
                 if not deviceName:
                     continue
                 logger.debug(f"Name of \"{deviceName}\" begins with: \"{f['namePrefix']}\"?")
@@ -598,7 +630,7 @@ class BLESession(Session):
         elif self.status == self.DISCOVERY and method == 'connect':
             logger.debug("connecting to the BLE device")
             self.device = BLESession.found_devices[params['peripheralId']]
-            self.deviceName = self.device.getValueText(0x9) or self.device.getValueText(0x8)
+            self.deviceName = self._getDevName(self.device)
             try:
                 self.perip = Peripheral(self.device)
                 logger.info(f"connected to the BLE peripheral: {self.deviceName}")
@@ -675,11 +707,19 @@ class BLESession(Session):
         service = self._get_service(service_id)
         c = self._get_characteristic(chara_id)
         handle = c.getHandle()
+        # get CCCD or Client Characterstic Configuration Descriptor
+        cccd = None
+        for d in c.getDescriptors():
+            if d.uuid == UUID(CCCD_UUID):
+                cccd = d
+        if not cccd:
+            logger.error("Characteristic {char_id} does not have CCCD")
+            return
         # prepare notification handler
         self.delegate.add_handle(service_id, chara_id, handle)
         # request notification to the BLE device
         with self.lock:
-            self.perip.writeCharacteristic(handle + 1, value, True)
+            self.perip.writeCharacteristic(cccd.handle, value, True)
 
     def startNotifications(self, service_id, chara_id):
         logger.debug(f"start notification for {chara_id}")