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

From: Geoffrey M Clemm <geoffrey.clemm@us.ibm.com>
Date: Fri, 13 Aug 2010 21:58:00 -0400
To: Julian Reschke <julian.reschke@gmx.de>
Cc: WebDAV <w3c-dist-auth@w3.org>, w3c-dist-auth-request@w3.org
Message-ID: <OFA38A80AA.050D584C-ON8525777F.000A0017-8525777F.000ACD46@us.ibm.com>

One of the things I'd like to see with this work is to settle the various
syntax debates, by just defining mappings to a variety of syntaxes.

One key part of this is already identified below, i.e. define a GET URI
scheme for any method that involves reading data.
In addition, define a POST body syntax for any method that is not in
HTTP/1.1.
Finally, define an AtomPub and JSON variant, in addition to the XML that
WebDAV would normally use.

This would then allow us to focus on the semantics, and avoid all the
syntax debates.
And if a particular syntax has trouble expressing some of the semantics,
that would highlight why one syntax might be preferable to another..

Cheers,
Geoff

Julian Reschke  wrote on 08/12/2010 04:36:59 AM:
> 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.
>
> WebDAV and AtomPub have been very successful so far. WebDAV gets used
> both as a plain remote filesystem protocol (as observed by clients being
> shipped with all operating systems, and both Apache httpd and IIS
> supporting it), and for specific applications, such as Versioning
> (subversion), Calendaring (CalDAV), etc. The same is true for AtomPub,
> which actually may not be used a lot in practice for the original use
> case (feed authoring), but for many other things instead.
>
> 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>
>
>
Received on Saturday, 14 August 2010 01:58:37 GMT

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