What should event.payload["timestamp"] represent?

[glasserc]

Refs #945 and #1731. The documentation describes the timestamp field as representing "the time of the event". However, as far as I can tell, the timestamp field in an event represents a collection timestamp calculated relatively early in the request, before the action that triggered event happened. It doesn't represent the time that the event happens, nor the current last_modified / collection_timestamp of anything reflected in the event.

I think I'd like to change the timestamp key in the payload to correspond to the updated collection timestamp of the (parent_id, collection_id) for which the event was fired.

[leplatrem]

I would agree with changing that indeed: use the current timestamp before serving the response instead of the one when the request kicks in.

We should still be able to have individual or intermediate timestamps in the impact_records attribute I believe.

More generally, we should tackle #945, the semantics of the «global» fields of an event are wrong.

Note: if someone reads this, the terms collection and records in this issue represents the internal notion of kinto.core, and applies to buckets, groups, collections, records, accounts... in kinto. See #710

[glasserc]

Thinking about this further, I think that although #1770 is a valid short-term fix, it feels a little odd for me to bless one specific attribute about the resource as "part of the payload". Maybe the right fix is for the payload to include the model or resource or something so that the recipient of the event can decide what attributes it wants.