on windows sometimes WebSocket messages never received

[jonathon-love]

hi,

we use tornado in our desktop application, and we do have super-obscure issues on windows machines from time to time (this was an earlier one for example: https://github.com/tornadoweb/tornado/issues/2347)

the latest one is that on a couple of machines on_message() of WebSocket is never called. at a js console i go:

let ws = new WebSocket('ws://127.0.0.1:XX/coms')

and open() in WebSocket is called (and returns)

but ws.send('fred') does not result in on_message() being called (the message fred does appear in the frames of the connection in the js dev tools however)

if at the js console i go:

ws.close()

on_close() is called, but not for a while ... so it looks like it times out.

i appreciate this is almost definitely a "yeah, windows is sometimes weird" issue, but i did wonder if you had any suggestions for debugging this. these issues are ultra-rare, i'd guess they affect < 1 in 1000 of our windows users.

with thanks

[mivade]

I remember once seeing an issue like this on a Windows machine. The problem ended up being that some antivirus program that was installed and configured in such a way that blocked a lot of websocket connections (or at least caused a ~10 minute delay before things started going through).

[jonathon-love]

ah! it had no affect on outbound web traffic? only affected access to localhost?

(i checked, and websockets online work fine)

with thanks

[mivade]

I'm not sure how widespread the issue was. In that instance, the affected computer had a websocket connecting to a local IP address rather than localhost.