[occi-wg] Your Questions...

[Andy Edmonds]

Thanks for the useful feedback Cyril! :-)
There has been quite some discussion both here on the mailing list, in F2Fs
and also on the IRC about the use of headers. In fact, I think what you
raise here is quite a good summary of those discussions that were had. Using
the OCCI text syntax within the header, from my POV, is now largely
historical and for the those related comments I can't disagree. What should
be noted is that the HTTP rendering spec details how a text-based syntax can
be relayed between client and service. It does note that the content can be
in the header but the default is in the body.

To other aspects - yes filtering in my view is simple and there has been
talk about making it a little more encompassing (e.g. addition of logical
operators). The origins of actions are from this detailed conversation [1]
over on Tim Bray's blog. We'd love to know more about any reservations about
the linking scheme. Also do you see anything that could be brought to the
spec to improve it?

Regards,

Andy
andy.edmonds.be

[1] http://www.tbray.org/ongoing/When/200x/2009/03/20/Rest-Casuistry


On Mon, Jul 11, 2011 at 10:32, Cyril Rohr <contact at crohr.me> wrote:

> Hi Andy, all,
>
> It's hard to be constructive in 140 characters, so thanks for letting me
> elaborate on this list.
>
> My concerns are related to the "RESTful HTTP Rendering" spec [1], which
> views
> HTTP headers as the primary mean of transferring resource representations
> between a user-agent and an OCCI server. I can see how you you may have
> ended
> there (no need to define a media type, "universality" of the HTTP protocol,
> new RFC drafts about `Category` [4] and `Link` [5] headers popping up,
> etc.),
> but that just looks wrong to me for the following reasons:
>
> * The most obvious, and a point that you raise in the spec [1], is that the
>   HTTP header max size is often limited by intermediaries (for instance,
>   default limit on Squid is 20KB [2]), while body max size is not. The spec
>   warns:
>
>   "Space in the HTTP header section of a HTTP request is a limited
> resource.
>   By this, it is noted that many HTTP servers limit the number of bytes
> that
>   can be placed in the HTTP Header area. Implementers MUST be aware of this
>   limitation in their own implementation and take appropriate measures so
> that
>   truncation of header data does NOT occur."
>
>   You can't assume that there won't be intermediaries between the
> user-agent
>   and the server (proxies, caches, etc.), therefore I don't see how an
>   implementer can do anything about the header size limit, which means it
> is
>   safe to assume that the HTTP Rendering via `text/occi` is broken (unless
> you
>   have already thought about a possible solution, in which case it should
> be
>   included in the spec). You can't even use the `Content-MD5` [3] header to
>   provide an end-to-end message integrity check. And the message header is
> not
>   compressible, contrary to the message body.
>
> * More generally, methods and headers are there to indicate the purpose of
> a
>   request, not the resource representation itself.
>
> * Finally, you define a `text/occi` content-type, which looks like an empty
>   shell. I mean, if I understand correctly, the only payload you'll ever
> have
>   is "OK" on successful operations. AFAIK, a media type definition [6] is
>   mainly about the structure and semantics of the message body. It's not
> about
>   defining custom HTTP headers to replace the message body.
>
> I also have some concerns about the filtering mechanism, linking mechanism
> and
> the way you define actions, but if I had to sum up my position it would be
> that I have the feeling that you went extreme with the REST concept, and
> tried
> to put in the spec as much novelty (in terms of recent HTTP-related
> specs/drafts) as you could. Nothing wrong with that, but the result is
> somewhat convoluted. Also, the decision to put everything in the header
> part
> of the message renders a lot of standard HTTP header fields useless.
>
> I appreciate the effort and time it takes to build a spec like this. From a
> standardization body though, I would have expected that you properly define
> a
> new media type for the rendering, not custom header extensions. I recall a
> (now dead?) XHTML based rendering doc, which had some flaws but was going
> more
> in that direction. I can see that you plan on specifying new content types
> in
> the future: I think it would be good to shift the attention back to the
> body.
>
> Thank you for your time.
> Best Regards,
>
> Cyril
> --
> http://crohr.me
>
> [1] <http://ogf.org/documents/GFD.185.pdf>
> [2] <
> http://www.squid-cache.org/Versions/v2/2.6/cfgman/request_header_max_size.html
> >
> [3] <http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html>
> [4] <http://tools.ietf.org/html/draft-johnston-http-category-header-01>
> [5] <http://tools.ietf.org/rfc/rfc5988.txt>
> [6] <http://www.ietf.org/rfc/rfc1521.txt>
>
> On 8 Jul 2011, at 18:03, Andy Edmonds wrote:
>
> Hey Cyril,
> I saw some of your comments [1] [2] on twitter about OCCI. It'd be great if
> you could elaborate on them on the list as everyone here really values
> useful and constructive comments and critique.
>
> BTW: you might have been viewing older OCCI specs. The latest published are
> here [3].
>
> Cheers,
>
> Andy
> andy.edmonds.be
>
> [1] https://twitter.com/#!/crohr/status/89318560417067008
> [2] https://twitter.com/#!/crohr/status/89320097755312128
> [3] http://ogf.org/gf/docs/
>
>
>
>
>
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