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

From: Julian Reschke <julian.reschke@gmx.de>
Date: Thu, 12 Aug 2010 10:36:59 +0200
Message-ID: <4C63B2AB.6090701@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 Nüscheler



PS: people not familiar with the IETF may want to have a look at 
<http://www.ietf.org/tao.html>
Received on Thursday, 12 August 2010 08:37:42 GMT

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