BLESession: Introduce notification queue

During bluepy-scratch-link handles requests from Scratch, it throws away
notifications from BLE devices. This loses those notifications.

Not to lose the notifications, introduce a queue to keep notifications
from BLE devices. Once request handling completes, flush the
notifications kept in the queue.

scratch_link.py

@@ -22,6 +22,7 @@ from bluepy.btle import BTLEDisconnectError, BTLEManagementError
 
 import threading
 import time
+import queue
 
 logLevel = logging.INFO
 
@@ -52,7 +53,7 @@ class Session():
         self.websocket = websocket
         self.loop = loop
         self.lock = threading.RLock()
-        self.notification = None
+        self.notification_queue = queue.Queue()
 
     async def recv_request(self):
         """
@@ -89,12 +90,17 @@ class Session():
         logger.debug("default end_request")
         return False
 
-    def notify(self, method, params):
+    def notify(self):
         """
         Notify BT/BLE device events to scratch.
         """
         logger.debug("start to notify")
+        # flush notification queue
+        while not self.notification_queue.empty():
+            method, params = self.notification_queue.get()
+            self._send_notification(method, params)
 
+    def _send_notification(self, method, params):
         jsonn = { 'jsonrpc': "2.0", 'method': method }
         jsonn['params'] = params
         notification = json.dumps(jsonn)
@@ -337,7 +343,8 @@ class BLESession(Session):
                         params = { 'rssi': d.rssi }
                         params['peripheralId'] = devices.index(d)
                         params['name'] = d.getValueText(0x9)
-                        self.session.notify('didDiscoverPeripheral', params)
+                        self.session.notification_queue.put(('didDiscoverPeripheral', params))
+                        self.session.notify()
                     time.sleep(1)
                 elif self.session.status == self.session.CONNECTED:
                     logger.debug("in connected status:")
@@ -381,11 +388,12 @@ class BLESession(Session):
 
         def handleNotification(self, handle, data):
             logger.debug(f"BLE notification: {handle} {data}")
+            params = self.handles[handle].copy()
+            params['message'] = base64.standard_b64encode(data).decode('ascii')
+            self.session.notification_queue.put(('characteristicDidChange', params))
             if not self.restart_notification_event.is_set():
                 return
-            params = self.handles[handle]
+            self.session.notify()
-            params['message'] = base64.standard_b64encode(data).decode('ascii')
-            self.session.notify('characteristicDidChange', params)
 
     def __init__(self, websocket, loop):
         super().__init__(websocket, loop)