Add event handling

With this MR, VAPython receives event-handling capabilities. These allow VAPython to receive and subscribe to events from the VAServer. Furthermore, the VAServer recognises VAPython as a connected client due to the persistent network stream.

scripts/templates/wrapper.py.j2

 import asyncio
 import warnings
-from typing import List, Optional, Tuple, Union
+from threading import Thread
+from typing import Callable, List, Optional, Tuple, Union
 
 from grpclib.client import Channel
 
@@ -21,6 +22,9 @@ class VAInterface:
         """Initializes the VAInterface object"""
         self._service: Optional[vanet.VaStub] = None
         self._channel: Optional[Channel] = None
+        self._event_callbacks: List[Callable[[vanet.Event], None]] = []
+        self._event_thread: Optional[Thread] = None
+        self.__loop: Optional[asyncio.AbstractEventLoop] = None
 
     def __del__(self):
         """Destructor for the VAInterface object
@@ -31,7 +35,7 @@ class VAInterface:
         if self._channel:
             self._channel.close()
 
-    def connect(self, host: str = "localhost", port: int = 12340, channel: Union[Channel, None] = None) -> None:
+    def connect(self, host: str = "localhost", port: int = 12340, channel: Union[Channel, None] = None, *, add_event_handling: bool = True) -> None:
         """Connects to the VA server
 
         Args:
@@ -39,19 +43,37 @@ class VAInterface:
             port: The port number of the VA server.
             channel: The channel to use for the connection.
                 If not provided, a new channel will be created, this is the default and should be used in most cases.
+            add_event_handling: If True, VAPython will receive events from the VAServer.
+                If False, no events will be received and the server will not be able to determine that a client is connected.
+                However, not sending events can reduce network traffic.
         """
 
         with warnings.catch_warnings():
             warnings.filterwarnings("ignore", category=DeprecationWarning)
             if channel:
                 self._channel = channel
-                self.loop = asyncio.get_running_loop()
+                self.__loop = asyncio.get_running_loop()
             else:
-                self.loop = asyncio.get_event_loop()
-                self._channel = Channel(host=host, port=port, loop=self.loop)
+                self.__loop = asyncio.get_event_loop()
+                self._channel = Channel(host=host, port=port, loop=self._loop)
 
             self._service = vanet.VaStub(self._channel)
-            #todo setup event handling
+
+            if add_event_handling:
+                # Event loop in separate thread, based on: https://gist.github.com/dmfigol/3e7d5b84a16d076df02baa9f53271058
+                async def handle_events():
+                    async for event in self.service.attach_event_handler(vanet.betterproto_lib_google_protobuf.Empty()):
+                        for event_callback in self._event_callbacks:
+                            event_callback(event)
+
+                def background_event_tread(loop: asyncio.AbstractEventLoop) -> None:
+                    asyncio.set_event_loop(loop)
+                    loop.run_forever()
+
+                self._event_thread = Thread(target=background_event_tread, args=(self._loop,) , daemon=True)
+                self._event_thread.start()
+
+                asyncio.run_coroutine_threadsafe(handle_events(), self._loop)
 
     def disconnect(self):
         """Disconnects from the VA server"""
@@ -91,7 +113,7 @@ class VAInterface:
         """
 
         {% endif %}
-        return_value = self.loop.run_until_complete(
+        return_value = self._loop.run_until_complete(
             self.service.{{ method.org_name }}(
                 vanet.{{ method.message_type }}(
                     {% for arg in method.args %}
@@ -138,4 +160,33 @@ class VAInterface:
             msg = "Not connected to a server"
             raise ValueError(msg)
 
-        return self._service
\ No newline at end of file
+        return self._service
+
+    @property
+    def _loop(self) -> asyncio.AbstractEventLoop:
+        """The event loop
+
+        Returns:
+            The event loop.
+        """
+        if not self.__loop:
+            msg = "Not connected to a server"
+            raise ValueError(msg)
+
+        return self.__loop
+
+    def attach_event_handler(self, callback: Callable[[vanet.Event], None]) -> None:
+        """Attaches a callback function to the event handler
+
+        Args:
+            callback: The callback function to attach.
+        """
+        self._event_callbacks.append(callback)
+
+    def detach_event_handler(self, callback: Callable[[vanet.Event], None]) -> None:
+        """Detaches a callback function from the event handler
+
+        Args:
+            callback: The callback function to detach.
+        """
+        self._event_callbacks.remove(callback)
\ No newline at end of file