How to detect user disconnection from SSE stream?

[ababo]

Summary

I know similar questions have been asked here many times, but none of them seem to address the issue I'm facing at the moment.

I have a stream producing logic that performs a lot of work occasionally emitting events via async stream. To cancel it I use a one_shot receiver. It's not good enough for me to cancel it during a next 'yield' moment since it might take a while until a next SSE event is emitted. This async task needs to get a signal at time of disconnection to stop it, not when it decides to emit a next event (might take minutes to get there).

Currently I don't see any way to send this cancellation signal exactly at time when the client has just been disconnected.

axum version

0.8.1

[mladedav]

I don't think I completely understand, does the stream producing logic run inside the handler or does it run someone else and the handler just passes the messages to the client?

Anyway, do I understand it correctly that you have an async task that runs synchronously for several minutes without yielding? You might want to just add periodic yield_now calls in that case, not just for your cancellation logic but it might generally help tokio do its work better.

[ababo]

@mladedav Thanks for so fast response!

The mentioned logic runs inside its dedicated tokio task. The periodic yield_now() calls might help me, thanks for the suggestion. Luckily I control the logic implementation so I can simplify it dropping the one_shot cancellation receiver and to rely solely on yield_now().

I wonder if I could detect the disconnection using Sender::is_closed() if my function was returning a channel receiver instead of a stream (and then converted into a stream before being passed to Sse).

Anyway your suggestion seems to solve my issue (though I didn't yet try it), thank you.