add decorator to cancel disconnected requests

https://github.com/RedRoserade/fastapi-disconnect-example/blob/main/app.py

src/backend/base/langflow/api/utils.py

@@ -1,9 +1,11 @@
 import uuid
+import asyncio
+from functools import wraps
 import warnings
 from pathlib import Path
-from typing import TYPE_CHECKING, Optional
+from typing import TYPE_CHECKING, Optional, Any, Awaitable, Callable
 
-from fastapi import HTTPException
+from fastapi import HTTPException, Request
 from platformdirs import user_cache_dir
 from sqlmodel import Session
 
@@ -327,3 +329,62 @@ def parse_exception(exc):
         return exc.body["message"]
     return str(exc)
     return str(exc)
+
+
+async def disconnect_poller(request: Request, result: Any):
+    """
+    Poll for a disconnect.
+    If the request disconnects, stop polling and return.
+    """
+    try:
+        while not await request.is_disconnected():
+            await asyncio.sleep(0.01)
+
+        print("Request disconnected")
+
+        return result
+    except asyncio.CancelledError:
+        print("Stopping polling loop")
+
+
+def cancel_on_disconnect(handler: Callable[[Request], Awaitable[Any]]):
+    """
+    Decorator that will check if the client disconnects,
+    and cancel the task if required.
+    """
+
+    @wraps(handler)
+    async def cancel_on_disconnect_decorator(request: Request, *args, **kwargs):
+        sentinel = object()
+
+        # Create two tasks, one to poll the request and check if the
+        # client disconnected, and another which is the request handler
+        poller_task = asyncio.ensure_future(disconnect_poller(request, sentinel))
+        handler_task = asyncio.ensure_future(handler(request, *args, **kwargs))
+
+        done, pending = await asyncio.wait([poller_task, handler_task], return_when=asyncio.FIRST_COMPLETED)
+
+        # Cancel any outstanding tasks
+        for t in pending:
+            t.cancel()
+
+            try:
+                await t
+            except asyncio.CancelledError:
+                print(f"{t} was cancelled")
+            except Exception as exc:
+                print(f"{t} raised {exc} when being cancelled")
+
+        # Return the result if the handler finished first
+        if handler_task in done:
+            return await handler_task
+
+        # Otherwise, raise an exception
+        # This is not exactly needed, but it will prevent
+        # validation errors if your request handler is supposed
+        # to return something.
+        print("Raising an HTTP error because I was disconnected!!")
+
+        raise HTTPException(503)
+
+    return cancel_on_disconnect_decorator