Concurrency Control

HTTP If-Match Turns Representation State Into a Write Precondition

An HTTP origin can refuse a PUT or DELETE before applying it when the request carries If-Match and the selected representation no longer has an accepted entity tag. The condition converts a representation validator into a write precondition: a client can say that a mutation is valid only against state matching a version it previously observed. This mechanism addresses a specific concurrency boundary. It can prevent one client from silently replacing resource state after another client has changed the selected representation. It does not turn HTTP into a transaction protocol, lock the resource between requests, or guarantee that an entity tag represents every piece of application state involved in a mutation.