Motivation

As reported by #12390, when evaluate large payload for PutEvents, LocalStack would fail. I could reproduce the issue and saw LocalStack consumes as much as 20GB of memory while trying to evaluate the payload given by the user.
This payload was very complex, with lots of nested dictionaries and list. List are "exploding" the complexity, creating "or" conditions and new "branches" to evaluate.

This is because we're using recursion to evaluate EventPattern against payload, and we would try to get the event payload in a flat shape to be able to be evaluated against the Pattern (due to how AWS treats the . notation).

I've added some conditions checks to only evaluate the payload when relevant to the Event Pattern, and to not evaluate "branches" of the payload. This fixes the issue and the memory usage, as payloads now stay "simple" and without the bounds.

I've also added some small unit tests because the doc strings were getting a bit too big to explain all the behavior.

\cc @cloutierMat as we worked on this together for SNS

fixes #12390

See https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-create-pattern.html

Reading again, this should have been considered from the start with the following (my bad!):

EventBridge ignores the fields in the event that aren't included in the event pattern.

Changes

• add a check to not evaluate the payload "branch" if not relevant to the pattern

We will need to port this fix to the SNS Filter policy engine as well, I'll tackle that in a follow up.