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From Julian Reschke <julian.resc...@gmx.de>
Subject Fwd: Proposal for work on an efficient, browser-friendly, HTTP-based communication protocol for fine-grained information exchange
Date Thu, 12 Aug 2010 09:53:39 GMT
FYI - a proposal for collaboration on an authoring protocol that would 
be more browser-friendly than WebDAV or AtomPub -- for now we started 
discussion on the IETF WebDAV mailing list (hosted by the W3C -- see 
<http://lists.w3.org/Archives/Public/w3c-dist-auth/>).

Feedback appreciated.

-------- Original Message --------
Subject: Proposal for work on an efficient, browser-friendly, HTTP-based 
communication protocol for fine-grained information exchange
Date: Thu, 12 Aug 2010 10:36:59 +0200
From: Julian Reschke <julian.reschke@gmx.de>
To: WebDAV <w3c-dist-auth@w3.org>

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 NĂ¼scheler



PS: people not familiar with the IETF may want to have a look at
<http://www.ietf.org/tao.html>


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