I just can't reconcile the fact that if I hit an endpoint, and I get back certain data with a 2XX response code because I previously accessed a "login" resource, but I would have gotten a 4XX response code if I had not gone to that prior "login" resource that I haven't violated REST: my request for the second endpoint takes advantage of stored context on the server. Even worse, if I restart the server, change out its database, or make some other stateful change on it, the response changes. And I don't mean to imply that this is a universal sin of computing architecture, but it sure as hell looks like a violation of REST, and it begs the question of what our standard is. Headers, path-based nomenclature, network layering, authentication - I'm on board with all of that. I just worry that a lot of people might be falling victim to commonplace misconceptions of just what REST is, which in turn may be causing us (the web dev community) to make misplaced value judgments.
Rest doesn't mean no state in the world exists. It's not a violation at all that an endpoint changes its output. Rest only reasons about idempotency, not reproducibility.
> Rest only reasons about idempotency, not reproducibility.
Absolutely. If you GET a collection resource, then POST a new item into the collection, then GET the collection again, the response will have changed. Having these kind of temporal dependencies on the answer you receive is not something REST argues against.
None of that violates REST; REST is not statelessness. In fact, REST (REpresentational State Transfer) is all about state and how it is changed and how those changes are manifested.
