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Re: Proposal for work on an efficient, browser-friendly, HTTP-based communication protocol for fine-grained information exchange

From: Yves Lafon <ylafon@w3.org>
Date: Thu, 19 Aug 2010 08:51:33 -0400 (EDT)
To: Julian Reschke <julian.reschke@gmx.de>
cc: WebDAV <w3c-dist-auth@w3.org>
Message-ID: <alpine.DEB.1.10.1008190847580.18764@wnl.j3.bet>
On Thu, 12 Aug 2010, Julian Reschke wrote:

> Proposal for work on an efficient, browser-friendly, HTTP-based communication 
> protocol for fine-grained information exchange
>
> HTTP/1.1 (RFC 2616) already contains a set of tools for modifying resources , 
> namely the methods PUT, POST, and DELETE.
>
> Many systems have been built on top of this, most of them in an ad-hoc manner 
> (which is ok when client and server are controlled by the same developers).
>
> We would like to cover some of the following use cases extending the resource 
> oriented model.
>
> (1) An simple javascript based browser application should be able to read 
> fine-grained information (comparable to WebDAV properties) in a simple manner 
> using a defined JSON format to be consumed in an intuitive fashion.
>
> (2) A simple HTML Form should be able to write information in a patch 
> oriented manner containing both binary (file) data and fine-grained, typed 
> information using a multipart POST.
>
> (3) A simple javascript application should be able to write information in a 
> patch oriented fashion using a defined JSON-diff PATCH content-type to update 
> fine-grained information.
>
> There are also several extensions/applications of HTTP in this space, such 
> as:
>
> - WebDAV (RFC 4918), which defines (a) a collection model and methods to 
> manipulate collections/namespaces, (b) a metadata (=property) model, and (c) 
> locking. Other RFCs add extensions on top of this, such as Versioning (RFC 
> 3253) and ACLs (RFC 3744).
>
> - The Atom feed format (RFC 4287) and AtomPub (RFC 5023) use a simpler, not 
> necessarily hierarchic collection model (which, depending on the use case, 
> may be a plus), but does not provide many features WebDAV + friends define. 
> Notably, namespace operations are absent.

It seems that there are two main uses cases here, the first one is to
replace WebDAV's way of handling metadata on a resource, and the second
one goes into the service/data discovery space. Would it be better to
divide clearly the tasks along those lines ?

Also, at that point, the format (JSON) is irrelevant, the data format
should come after defining the goals, and the protocol bits. XFORMS has 
been mentionned, but once again it is premature, and this discussion 
should take place after figuring out the right interactions needed.

For service discovery, well-known URIs is a possibility, especially for
services "on the server", but it might also be useful to to this via Link:
(like a Printer Resource claiming that it can be contacted via IPP, 
without having to contact a wkURI first), so extending the scope would 
be good.

>
> Both of those protocol specifications are not easily consumed by websites and 
> applications running current browsers and require a lot of client-sided 
> scripting to cover simple read and write use cases.
>
> There's a proposal for a protocol called "JSOP", which addresses these use 
> cases, which we may want to consider as input for this work: 
> <http://www.slideshare.net/uncled/jsop>
>
> So what's wrong with WebDAV?
>
> Since the time WebDAV was designed, we have learned a lot how to use the Web 
> and HTTP. Such as:
>
> - if you want to expose data for read operations, make it available to GET, 
> and assign URIs,
>
> - consider cacheability, atomicity, and performance of sync operations (for 
> instance, syncing large collections),
>
> - be careful with new HTTP methods -- avoid them for things that are not of 
> generic use (good: MKCOL, bad: MKCALENDAR) and keep in mind that certain 
> platforms (HTML forms, Flash...) can't use them,
>
> - when defining formats, also define internet media types.
>
> Also, in the last few months, new (and not so new) techniques have finally 
> been published as RFCs, such as:
>
> - HTTP PATCH method (RFC 5789)
>
> - HTTP Link Header and Link Relations Registry 
> (http://tools.ietf.org/html/draft-nottingham-http-link-header-10, in the RFC 
> Editor queue)
>
> - Service Discovery through well-known URIs (RFC 5785)
>
> Another potential building block are URI templates (work in progress: 
> http://tools.ietf.org/html/draft-gregorio-uritemplate-04)
>
> Considering all of these pieces, it's quite obvious that there's a number of 
> specs that would be useful on their own, but could also, combined together, 
> form the basis of an interesting authoring protocol:
>
>
> # Data Model
>
> 1) Define a collection model (hierarchy, naming), and a representation 
> format.
>
> Can we re-use the WebDAV collection model here? Web application authors 
> probably would prefer a JSON representation, so can we simply define this as 
> an alternate representation of a DAV:multistatus description of a collection?
>
> 2) Define namespace operations in terms of manipulating collection 
> representations (also consider a mapping to COPY/MOVE).
>
> 3) Define a media type to use with PATCH for modifying these representations.
>
> 4) Define a property model (something like the intersection between WebDAV 
> properties and Java Content Repository (JSR-283) properties?)
>
>
> # Authoring through HTML forms and POST
>
> Define how POST with multipart/form-data (RFC 2388) can be used for authoring 
> both content and properties.
>
>
> # URIs for collection browsing
>
> Assign either hardwired or discoverable URIs for inspecting collections (URI 
> templates?). Or maybe link relations for collection navigation (similar work 
> for versioning: RFC 5829).
>
>
> # Improvements to WebDAV
>
> 1) Clarify how MOVE and COPY can operate on non-WebDAV resources (this 
> question comes up quite frequently).
>
> 2) Define how to use POST on WebDAV collections to add members (done: see 
> http://greenbytes.de/tech/webdav/#draft-reschke-webdav-post, in RFC Editor 
> queue).
>
> 3) Define media types (multiple?) for DAV:multistatus.
>
> 4) Define a discovery mechanism for GETtable representations of 
> PROPFIND/REPORT results (old proposal: 
> http://greenbytes.de/tech/webdav/draft-reschke-http-get-location-latest.html).
>
> 5) Define a mapping between link-typed WebDAV properties and generic Link 
> relations (see proposal: 
> http://lists.w3.org/Archives/Public/w3c-dist-auth/2008OctDec/0026.html).
>
> Although some of this will only be partially related to WebDAV, we think that 
> this mailing list might be a good venue for discussion.
>
>
> Expected deliverables from this activity would be:
>
> 1) Definition of a very simply data model and a representation format for it 
> (required JSON, optionally XML).
>
> 2) A format suitable for manipulating the data format above using PATCH 
> (potentially tunneled through POST).
>
> 3) A binding from multipart/form-data/POST to this model.
>
> 4) A separate (?) document explaining how these ingredients would be combined 
> in practice.
>
> Extensions to WebDAV and mappings from/to WebDAV could be useful, but would 
> not be a core part of this activity. (That is, we can do without if no 
> volunteers speak up).
>
> Note  that not all of these specs necessarily need to be on the standards 
> track; for instance, there might be candidates for Informational RFCs as 
> well (see <http://tools.ietf.org/html/rfc2026#section-4> for details).
>
>
> Feedback appreciated.
>
> Julian Reschke
> David Nüscheler
>
>
>
> PS: people not familiar with the IETF may want to have a look at 
> <http://www.ietf.org/tao.html>
>
>
>

-- 
Baroula que barouleras, au tiéu toujou t'entourneras.

         ~~Yves
Received on Thursday, 19 August 2010 12:51:35 GMT

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