Decorating the cancellation token from a behaviour

[dazinator]

As per #592
It seems like a discussion was suggested, so I'd like to create on here.

[zachpainter77]

So.. what are you trying to achieve? It seems like people are wanting to set timeouts on mediator calls from a behavior. Is that correct? I could take a whack at it.

Edit: I have just completed a PR adding this support.

#1058

[dazinator]

Amazing thank you. I will watch the PR in anticipation! To elaborate on my use case:-

1. I have implemented a pipeline behavior to address distributed locking as a cross-cutting concern. The behavior acquires a distributed lock before forwarding the request.
2. The behavior works nicely, but we have a few requests that are long running async operations and we saw an instance where the lock was being lost.. the behavior is able to be notified when the lock is lost, but it has no way to signal the cancellation token of the active handler which continued to process the request.

The workaround is to add a seperate cancellation token to the request, which the behaviour can set, and signal independently - but then this means there are now two cancellation tokens for the handler to check so it isn't a clean as i'd like. One cancellation token should be enough to signal the cancellation of the async operation as per mediatr's handler method signature - it's just currently, mediatr doesn't give me a way to intercept that cancellation token, so I can't for example swap it for a linked cancellation token that incorporates cancellation token sources brought in by a behaviour.