Fixes #77: Pass task_id into background handler of WS endpoint for ea…

…sy redefinition of on_receive

docs/receipts/websockets.md

@@ -58,9 +58,10 @@ data manager.
 task group and cancels all tasks within that scope. Simply return inside background
 handler, if you want to cancel a single task.
 
-**AVOID** stuff like this https://stackoverflow.com/a/60675826
-and, in general, passing event-handling primitives between tasks, 
-other than class-level anyio.Lock()
+**NOT RECOMMENDED** to use stuff like this https://stackoverflow.com/a/60675826. 
+However, should you need to do so, you may redefine method 
+`starlette_web.common.ws.base_endpoint.BaseWSEndpoint.on_receive` to use
+`anyio.TaskGroup.start` and return `CancelScope` from within background handler.
 
 ## Manually calling websocket.receive
 

starlette_web/common/ws/base_endpoint.py

@@ -67,7 +67,8 @@ async def on_connect(self, websocket: WebSocket) -> None:
 
     async def on_receive(self, websocket: WebSocket, data: Any) -> None:
         cleaned_data = self._validate(data)
-        self.task_group.start_soon(self._background_handler_wrap, websocket, cleaned_data)
+        task_id = get_random_string(50)
+        self.task_group.start_soon(self._background_handler_wrap, task_id, websocket, cleaned_data)
 
     async def on_disconnect(self, websocket: WebSocket, close_code: int) -> None:
         if self.task_group:
@@ -79,8 +80,7 @@ async def on_disconnect(self, websocket: WebSocket, close_code: int) -> None:
 
         logger.debug("WS connection has been closed.")
 
-    async def _background_handler_wrap(self, websocket: WebSocket, data: Dict):
-        task_id = get_random_string(50)
+    async def _background_handler_wrap(self, task_id: str, websocket: WebSocket, data: Dict):
         task_result = None
 
         try: