How to do something after a service responded to a request?

[johannescpk]

If I have a service_fn that returns a response and I'd like to do something after the response was fully sent, how would I approach that?

[johannescpk]

After looking around a bit, it seems the only viable solution is writing a tower service for the request handler and wrapping that into a layer.

Nope, doesn't work either as that only transforms the request/response.

[olix0r]

I'd use tokio::spawn to create a background task that runs independently of the request's task.

[johannescpk]

Good idea, thanks. I suppose you don't have a guarantee that the spawned task actually runs after the request fully completed tho, right?

[olix0r]

Generally, that's a very hard problem to solve. If you really need to guarantee that some action happens, you'd have to write to some sort of durable work queue before responding so that if process crashes after the response is sent the work can still continue. Even if you're not trying to defend against that sort of catastrophe, you can't really guarantee that an arbitrary background task will ever complete.

Or if you're trying to ensure that the task doesn't start running until the response is completed: I would probably create a custom Body type that holds an Arc<tokio::sync::Notify> with a Drop impl that calls Notify::notify_waiters. The tokio::spawn task can await on Notify::notified to be notified when the response has been fully processed by the hyper server.