Scene edition Collaboration

[sdumetz]

Allowing collaboration on a scene would require some new features.

In short the process would be :

1. Compare the PUT request with the document it was referenced against to compute a list of changes
2. Apply this list of changes onto the document's latest revision if possible
3. fine-tune 2. conflicts resolution using field testing

The main building block missing here is the ability to compare a change against its reference. It could be done client-side by saving the Etag header to send it back as If-Match on save. It's a slightly unorthodox use of the If-Match header.

Another option is to send a Set-Cookie header on GET that references the current version, then get the cookie's value on PUT. That's slightly invasive, in particular if we do it on every scene requests. It might be acceptable because it's session cookies so it at least won't cause too much privacy concerns.

A third option would be to embed a unique ID into the document. It would be sent as-is to the client and then be parsed back on PUT, hinting at the reference's version. There would be practically no additional overhead because we have to parse the document on save anyways if we want to compute a diff so it's no big deal inserting a nonce into it before serialization.

the second and third options would require little to no client code change.

[sdumetz]

Cookie storage is looking bad : can't store a tab-specific cookie, so we have bad edge cases when a user opens multiple tabs.