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<h2 class="title" style="clear: both"><a id="svn.webdav.autoversioning"></a>Autoversioning</h2>
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<p>While the Subversion client is not a full DeltaV client, and
the Subversion server is not a full DeltaV server, there's still a
glimmer of WebDAV interoperability to be happy about:
<em class="firstterm">autoversioning</em>.</p>
<p>Autoversioning is an optional feature defined in the DeltaV
standard. A typical DeltaV server will reject an ignorant
WebDAV client attempting to do a <code class="literal">PUT</code> to a
file that's under version control. To change a
version-controlled file, the server expects a series of proper
versioning requests: something like
<code class="literal">MKACTIVITY</code>, <code class="literal">CHECKOUT</code>,
<code class="literal">PUT</code>, <code class="literal">CHECKIN</code>. But if the
DeltaV server supports autoversioning, write requests from
basic WebDAV clients are accepted. The server behaves as though the
client <span class="emphasis"><em>had</em></span> issued the proper series of
versioning requests, performing a commit under the hood. In
other words, it allows a DeltaV server to interoperate with
ordinary WebDAV clients that don't understand versioning.</p>
<p>Because so many operating systems already have integrated
WebDAV clients, the use case for this feature can be incredibly
appealing to administrators working with non-technical users.
Imagine an office of ordinary users running Microsoft Windows or
Mac OS. Each user <span class="quote">“<span class="quote">mounts</span>”</span> the Subversion
repository, which appears to be an ordinary network folder.
They use the shared folder as they always do: open files, edit
them, and save them. Meanwhile, the server is automatically
versioning everything. Any administrator (or knowledgeable
user) can still use a Subversion client to search history and
retrieve older versions of data.</p>
<p>This scenario isn't fiction—it's real and it works.
To activate autoversioning in <span class="command"><strong>mod_dav_svn</strong></span>,
use the <code class="literal">SVNAutoversioning</code> directive within
the <code class="filename">httpd.conf</code> <code class="literal">Location</code>
block, like so:</p>
<div class="informalexample">
<pre class="programlisting">
<Location /repos>
DAV svn
SVNPath /var/svn/repository
SVNAutoversioning on
</Location>
</pre>
</div>
<p>When Subversion autoversioning is active, write requests
from WebDAV clients result in automatic commits. A generic log
message is automatically generated and attached to each
revision.</p>
<p>Before activating this feature, however, understand what
you're getting into. WebDAV clients tend to do
<span class="emphasis"><em>many</em></span> write requests, resulting in a huge
number of automatically committed revisions. For example, when
saving data, many clients will do a <code class="literal">PUT</code> of a
0-byte file (as a way of reserving a name) followed by another
<code class="literal">PUT</code> with the real file data. The single
file-write results in two separate commits. Also consider that
many applications auto-save every few minutes, resulting in even
more commits.</p>
<p>If you have a post-commit hook program that sends email, you
may want to disable email generation either altogether or on
certain sections of the repository; it depends on whether you
think the influx of emails will still prove to be valuable
notifications or not. Also, a smart post-commit hook program
can distinguish between a transaction created via autoversioning
and one created through a normal Subversion commit operation.
The trick is to look for a revision property
named <code class="literal">svn:autoversioned</code>. If present, the
commit was made by a generic WebDAV client.</p>
<p>Another feature that may be a useful complement for
Subversion's autoversioning comes from Apache's
<code class="literal">mod_mime</code> module. If a WebDAV client adds a
new file to the repository, there's no opportunity for the user
to set the the <code class="literal">svn:mime-type</code> property. This
might cause the file to appear as a generic icon when viewed
within a WebDAV shared folder, not having an association with
any application. One remedy is to have a sysadmin (or other
Subversion-knowledgeable person) check out a working copy and
manually set the <code class="literal">svn:mime-type</code> property on
necessary files. But there's potentially no end to such cleanup
tasks. Instead, you can use the
<code class="literal">ModMimeUsePathInfo</code> directive in your
Subversion <code class="literal"><Location></code> block:</p>
<div class="informalexample">
<pre class="programlisting">
<Location /repos>
DAV svn
SVNPath /var/svn/repository
SVNAutoversioning on
ModMimeUsePathInfo on
</Location>
</pre>
</div>
<p>This directive allows <code class="literal">mod_mime</code> to attempt
automatic deduction of the MIME type on new files that enter the
repository via autoversioning. The module looks at the file's
named extension and possibly the contents as well; if the file
matches some common patterns, the
file's <code class="literal">svn:mime-type</code> property will be set
automatically.</p>
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<p>You are reading <em>Version Control with Subversion</em> (for Subversion 1.7), by Ben Collins-Sussman, Brian W. Fitzpatrick, and C. Michael Pilato.<br />
This work is licensed under the <a href="http://creativecommons.org/licenses/by/2.0/">Creative Commons Attribution License v2.0</a>.<br />
To submit comments, corrections, or other contributions to the text, please visit <a href="http://www.svnbook.com/">http://www.svnbook.com/</a>.</p>
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