Compare-and-swap for HTTP PUT?

Question

Is there a way to make a compare-and-swap-style mechanism the only way to modify certain resources, whilst following the HTTP standard?

There's an If-Match header which implements the correct behaviour however this header is optional: as far as I can tell, if If-Match is not provided, the server should honour the PUT. (That is, it's up to the client to decide whether it wants to compare-and-swap, or just swap.) Would it be acceptable to respond with 412 Precondition Failed if the client tries to PUT or POST without providing an If-Match header?

Answer 1

No, but you can use status code 428 Precondition Required (see http://greenbytes.de/tech/webdav/rfc6585.html#status-428).