If you’re one of that exceedingly rare breed who regularly check or subscribe to my blog, you probably want to give this post a miss. This one is more for people who find me through Google. A specific solution to a specific, geeky, problem.
First a little scene setting…
I have a REST API that uses ETags for, amongst other things, concurrency control. That is, the version of an entity is (opaquely) identified by an ETag. You need to specify that ETag when you try and make any changes to that entity. If someone else changes the entity before you do, your ETag won’t match, so your update will fail, and you won’t unintentionally roll-back their change.
The REST API returns no content (HTTP 204) in response to a successful PUT request to edit an entity, and includes the new ETag representing the version of the updated entity.
I have a Dojo web tool that uses xhr.put to submit edits to the REST API. In order to make further subsequent edits to an entity without reloading the page, it stores the ETag that it gets back in the response header after every PUT.
In short, Internet Explorer. 🙂