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Re: Subversion's "magic" URLs

From: Branko Čibej <brane_at_xbc.nu>
Date: 2002-02-21 22:09:45 CET

Greg Stein wrote:

>On Thu, Feb 21, 2002 at 08:16:10AM +0100, Branko Äibej wrote:
>>I just had a brainstorm (caused by lack of sleep, no doubt).
>>When accessing a repository over WebDAV, we store all sorts of private
>>URLs into the WC. These are supposed to be opaque, and their form (iirc,
>>the $svn component) can be configured on the server.
>[ note that the stuff we store is really just a cache; if it isn't present,
> then we go and fetch it; we cache to avoid those round trips ]
>>Now, I wondered, could we instead create those URLs in the form of a
>>/query/ against the repository? E.g., instead of writing
>> http://svn.collab.net/repos/svn/$svn/ver/13.22/trunk/HACKING
>>could we instead write
>> http://svn.collab.net/repos/svn/?ver=13.22&path=trunk/HACKING
>Nope, sorry.
>The problem is that the latter identifies a single resource on that server:
>/repos/svn/. The query parameters are handled by the (single) resource, but
>it is still just one resource.
>The resulting effect is that you do not have separate, cacheable resources.
>>The thing is, DAV allowes this,
Typo. I meant to say, "*if* DAV allows this" ...

>Well, I'm not sure it would allow it. I think you'd end up in a bog of
>modelling problems when you try to define "why" that one resource has
>different responses to GET, different properties based on the Request-URI,
>etc. I think it would get problematic enough that it would end up failing
>one or more state invariants of RFC 2616 (HTTP) or RFC 2518 (DAV).
>>I'm probably hallucinating, aren't I.
>Not at all. Quite lucid except for a subtle difference in intended
>semantics. Otherwise, it would have been a neat idea :-)
Yes, I was afraid it wouldn't be so simple. I shouldn've guessed that,
if it were possible, you woulld have thought of it long ago. :-)

>I think the general thing for people to consider, who are interested in this
>stuff, is to understand the "data model" of WebDAV/DeltaV, if you will. For
>example, the differences and relationships between plain resources,
>version-controlled resources, version resources, baselines, baseline
>collections, etc. There is a good start on all of that in the webdav-usage
>document (http://svn.collab.net/repos/svn/trunk/www/webdav-usage.html), but
>it also depends on a good working knowledge of the DeltaV specification
>(http://www.webdav.org/deltav/). And some of that is further based on HTTP
>modelling and WebDAV.
>[ here is where Greg Hudson sadly shakes his head at the semantic overheads
> necessary to fully understanding SVN's networking mechanism :-) ]

Brane Čibej   <brane_at_xbc.nu>   http://www.xbc.nu/brane/
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Received on Sat Oct 21 14:37:09 2006

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