Re: If-Match and Weak ETags

Is there a process available to this group in which we can assemble errata for consideration by the original LDP working group? Or can we publish a note on this topic on our own account? Speaking under my implementor's hat (Fedora Commons) this is a very practical issue. We have users asking today how we expect to deal with concurrency in light of this bind.

---
A. Soroka
The University of Virginia Library

> On Aug 16, 2016, at 10:49 AM, Benjamin Armintor <armintor@gmail.com> wrote:
> 
> For what it's worth, I don't see another way to reconcile RFC 7232 and LDP 1.0 besides using If-Unmodified-Since. The spec is out of joint with HTTP 1.1.
> 
> Regards,
> 
> Ben
> 
> On Mon, Aug 15, 2016 at 3:44 PM, Tom Johnson <tom@dp.la> wrote:
> A couple of us have run into an issue with the ETag expectations of LDP, and are hoping that some discussion can resolve the issue.
> 
> The LDP specification (4.2.4.5)[0] has a few SHOULDs relating to client and server use of `If-Match` headers; namely, that clients SHOULD use them on modification, and that servers SHOULD require their use.
> 
> RFC 7232 (sec. 3.1)[1] states that "An origin server MUST use the strong comparison function when comparing entity-tags for If-Match" (RFC 2616 contains the same restriction).
> 
> These two clauses seem to recommend that a server SHOULD generate strong ETags for its resources---I don't believe a server can respect the recommendation of 4.2.4.5 any other way. 
> 
> As far as I know, no one has implemented strong ETags for content negotiable RDF resources. Short of caching all responses between updates, I'm not sure it's possible for an LDP server backed by a triplestore to make the relevant guarantees about the representations it returns.
> 
> For clients, given that LDP servers are normally returning weak ETags, using `If-Match` is not a serious option (a weak etag will never match in strong comparison).
> 
> Should LDP servers ignore 4.2.4.5? Can we recommend an alternate pattern for verification (`If-Unmodified-Since`)?
> 
> As further background, a key point of discussion in the LDP WG's handling of this a thread from Feb. 2013.[2]  The message linked refers to ignoring RFC 2616, based on a then current draft of 7232. This suggests to me that LDP is genuinely giving bad (out of date) advice, here.
> 
> Best,
> 
> Tom
> 
> [0] https://www.w3.org/TR/ldp/#ldpr-put-precond
> [1] https://tools.ietf.org/html/rfc7232#section-3.1
> [2] https://lists.w3.org/Archives/Public/public-ldp-wg/2013Feb/0035.html
> 
> 
>

Received on Sunday, 21 August 2016 01:16:02 UTC