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Re: I-D for WebDAV methods - APPEND and PATCH

From: Lisa Dusseault <lisa@osafoundation.org>
Date: Mon, 14 Aug 2006 17:35:59 -0700
Message-Id: <93905300-7859-4959-975B-90118022BDCA@osafoundation.org>
Cc: "Julian Reschke" <julian.reschke@gmx.de>, w3c-dist-auth@w3.org
To: Suma Potluri <suma@soe.ucsc.edu>

On Aug 4, 2006, at 12:05 AM, Suma Potluri wrote:

> Hi Julian,
> Thanks for your response. I wasn't aware of the earlier draft on  
> PATCH by
> Lisa Dusseault when I submitted this latest draft. I admit that I  
> should
> have done a little more research into it before submitting the new  
> I-D. In
> any case, I noticed that there hasn't been much activity in this area
> since the past two years. I would be happy to collaboratively work  
> with
> Lisa Dusseault or anyone else that would be interested in these  
> methods,
> so that we could get something useful out of this.

That would be great.  I've been letting the  PATCH document languish  
waiting for some broader consensus for a resolution to the question  
of what Content-Type means. That's the essential difference between  
patch draft -05 and draft -06.  The changes made to 06 were inspired  
by Jeff Mogul; I find his entity/instance model elegant in its  
resolution of a few modeling problems, even if it wasn't how HTTP was  
initially intended to be modeled.  However, Roy Fielding has objected  
to draft -06 and to Mogul's model and I didn't see a clear consensus  
which way to go.


> As for the earlier discussion on the PATCH method, I have a few
> questions/comments.
> 1) There seemed to be an extensive debate about using a new header  
> field
> for the patch format. The way I thought it was that there could
> potentially be many patch-types with each patch-type working on a  
> set of
> content-types (one indicated by the 'getcontenttype' property). So  
> each
> patch-type is mapped to a set of content-types that it would work on.
> Using the content-type header to indicate the patch-type that would  
> map
> against a set of content-types seemed confusing. But as I was  
> reading the
> earlier discussion, there were some convincing objections against  
> using a
> new header field. If the Content-Type header is the preferred way to
> define the patch format, we could proceed with that.
> 2) I also noticed that one of the earlier suggestions was to use the
> normal diff or diff -e as the required patch format for text files  
> which
> was what I proposed in the I-D. It is a simple and widely used diff  
> format
> that could be easily generated by the clients. For binary files we  
> could
> explore the option of using gdiff as the required diff format.
> 3) APPEND is a simple and efficient method, since there is no need  
> to be
> concerned about the patch formats and content-types. For clients  
> that do
> mostly appends, this could be very useful. I'd be interested to hear
> comments from the client's perspective with regards to using this  
> method
> as opposed to the PATCH method.
> Also I have been working on the mod_dav server and was able to get a
> working implementation for the two methods - APPEND and PATCH  
> according to
> the I-D specification. I am planning to do some performance testing  
> to see
> how these methods compare to the PUT method. If we could reach an
> agreement on the specification, I could change the prototype  
> accordingly
> before testing these methods.
> Again thanks for your comments,
> -Suma
>> Hi Suma,
>> there's quite a lot of previous discussion on the HTTP WG mailing  
>> list
> that you should review, for instance around the thread
>> <http://lists.w3.org/Archives/Public/ietf-http-wg/2004OctDec/ 
>> thread.html#msg4>).
>> So I would approach the topic this way:
>> - discuss on the HTTP WG mailing list, not here. This is not  
>> specific to
> WebDAV,
>> - realize that APPEND is a special case of PATCH,
>> - also realize that PATCH itself doesn't need a lot of work. By
>> submitting a PATCH request a client asks the server to modify the
> existing resource based on the instructions in the message body.  
> Full stop.
>> How the message body is to be interpreted depends on it's Content- 
>> Type
> (so you don't need "Patch-Type" at all). All the spec really needs to
> specify is at least one very simply diff format, and a MIME type  
> for it.
>> Speaking of which I see use cases for at least two patch formats (one
> for textual diffs such as in the Unix diff command output), and one  
> for
> modifying parts on binaries (seek/write/etc).
>> <http://greenbytes.de/tech/webdav/draft-dusseault-http- 
>> patch-04.html> of
> the PATCH draft actually used that model, and IMHO it was a mistake to
> move away from it. Quite logically, draft 05 it good serious  
> pushback from
> Roy Fielding
>> (<http://lists.w3.org/Archives/Public/ietf-http-wg/2004OctDec/ 
>> 0011.html>).
>> Best regards, Julian
Received on Tuesday, 15 August 2006 00:36:25 UTC

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