[BUG] Websocket connection initiated by front end even if not enabled in back end #3939

Activity

1. robertclaus

   assigned

   T4rk1n

   on Aug 3, 2026
2. robertclaus

   added

   bugsomething brokensomething broken

   P2considered for next cycleconsidered for next cycle

   size: 1

   on Aug 3, 2026
3. robertclaus commented on Aug 3, 2026

   

   robertclaus

   on Aug 3, 2026

   Contributor

   More actions

   @T4rk1n can you double check this? We should add tests for this if we didn't have them already.

   @andredfb do you have an example app you used to test this?
4. andredfb commented on Aug 3, 2026

   

   andredfb

   on Aug 3, 2026

   Author

   More actions

   Sorry, I should have specified earlier that I am using the fastapi backend. You can reproduce it with a minimum example:

   from dash import Dash
   from dash import html
   
   app = Dash(
       __name__,
       backend="fastapi",
       websocket_callbacks=False,
   )
   
   app.layout = html.H1("Websocket Test")
   
   if __name__ == "__main__":
       app.run()

   This results in the following in the browser console:
   

   And I am able to see the WS connection on the server side logs.
5. andredfb commented on Aug 3, 2026

   

   andredfb

   on Aug 3, 2026

   Author

   More actions

   As a side note, changing the debug config and the way the uvicorn server is called seems to change exactly how these things are logged in the console too. For example (I am not certain yet what the trigger is), but sometimes the Websocket connected log comes from websocketObserver.ts (webpack://dash_renderer/src/observers/websocketObserver.ts) and other times from the dash renderer.
6. robertclaus commented on Aug 4, 2026

   

   robertclaus

   on Aug 4, 2026

   Contributor

   More actions

   Thanks @andredfb ! Those details made it easy for @T4rk1n to track down!
7. T4rk1n

   closed this as completedin #3941on Aug 7, 2026