Delivery Format: support specifying the event format

[Cali0707]

Problem
Currently, when dispatching an event, we generally send it in the binary event format. However, to integrate with some systems (such as AWS EventBridge) we will need to be able to support sending events in structured format.

To support this, we are going to add a new field to the Delivery spec of resources, which will look like:

spec:
  delivery:
    format: ingress|structured|binary|null

If set to binary, then the component would deliver the event in binary format. If set to structured, then the component would deliver the event in structured format. If set to ingress, then the component would send the event in the format that the broker received it.

Persona:
Which persona is this feature for?
System integrators

Exit Criteria
An e2e test for each resource that supports the delivery spec that verifies that the event was received in structured format.

Time Estimate (optional):
How many developer-days do you think this may take to resolve?
10 days

Additional context (optional)

[Cali0707]

cc @pierDipi @matzew @creydr any thoughts about this?

If this design makes sense, I'll open an equivalent issue for subscriptions

[pierDipi]

Maybe even a delivery spec field

spec:
  delivery:
    format: input|structured|binary|null

[Cali0707]

@pierDipi I've updated this issue to be more generic (just sending structured events from the delivery spec), and I'll open individual sub issues to add support for this

[Cali0707]

@pierDipi should we have a feature flag for this?

[matzew]

Would we than start to track what we actually received? currently we accept binary/structure, but dispatch via binary due to reasons.

For ingress would we need extra logic to remember what came in? Not sure

[Cali0707]

Would we than start to track what we actually received? currently we accept binary/structure, but dispatch via binary due to reasons.

For ingress would we need extra logic to remember what came in? Not sure

@matzew the current idea is to add a new CE extensions to the events at ingress which indicated the format we received them in

See for example #8076

[matzew]

should we have a feature flag for this?

I think if we keep the current behavior (e.g. we emit as binary), nothing changes. so the new field seems to have no impact...

But, perhaps that can lead to side effects? 🤔

[matzew]

So, I'd go just structured or binary (default) for the egress to other systems. If we really want something like ingress, we can always add that as a future option.

But I guess just structured or binary, as default - and also not bother on the feature flag for this.