What REST PUT/POST/DELETE calls should return by a convention?

1. According to the "REST ideology" what should be in the response body for a PUT/POST/DELETE requests?

2. What about return codes? Is HTTP_OK enough?

3. What is the reason for such conventions, if any?

I've found a good post describing POST/PUT differences: POST vs PUT But it still doesn't answer my question.

Forgive the flippancy, but if you are doing REST over HTTP then RFC7231 describes exactly what behaviour is expected from GET, PUT, POST and DELETE.

Update (Jul 3 '14):
The HTTP spec intentionally does not define what is returned from POST or DELETE. The spec only defines what needs to be defined. The rest is left up to the implementer to choose.

Overall, the conventions are “think like you're just delivering web pages”.

For a PUT, I'd return the same view that you'd get if you did a GET immediately after; that would result in a 200 (well, assuming the rendering succeeds of course). For a POST, I'd do a redirect to the resource created (assuming you're doing a creation operation; if not, just return the results); the code for a successful create is a 201, which is really the only HTTP code for a redirect that isn't in the 300 range.

I've never been happy about what a DELETE should return (my code currently produces an HTTP 204 and an empty body in this case).

Creating a resource is generally mapped to POST, and that should return the location of the new resource; for example, in a Rails scaffold a CREATE will redirect to the SHOW for the newly created resource. The same approach might make sense for updating (PUT), but that's less of a convention; an update need only indicate success. A delete probably only needs to indicate success as well; if you wanted to redirect, returning the LIST of resources probably makes the most sense.

Success can be indicated by HTTP_OK, yes.

The only hard-and-fast rule in what I've said above is that a CREATE should return the location of the new resource. That seems like a no-brainer to me; it makes perfect sense that the client will need to be able to access the new item.