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<a href="CedarBackup2-module.html">Package CedarBackup2</a> ::
<a href="CedarBackup2.util-module.html">Module util</a> ::
Class PathResolverSingleton
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<tr><td align="right"><font size="-2">[show private | <a href="../public/CedarBackup2.util.PathResolverSingleton-class.html">hide private</a>]</font></td></tr>
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<!-- =========== START OF CLASS DESCRIPTION =========== -->
<h2 class="class">Class PathResolverSingleton</h2>
<hr/>
<p>Singleton used for resolving executable paths.</p>
<p>Various functions throughout Cedar Backup (including extensions) need
a way to resolve the path of executables that they use. For instance, the
image functionality needs to find the <code>mkisofs</code> executable,
and the Subversion extension needs to find the <code>svnlook</code>
executable. Cedar Backup's original behavior was to assume that the
simple name (<code>"svnlook"</code> or whatever) was available
on the caller's <code>$PATH</code>, and to fail otherwise. However, this
turns out to be less than ideal, since for instance the root user might
not always have executables like <code>svnlook</code> in its path.</p>
<p>One solution is to specify a path (either via an absolute path or some
sort of path insertion or path appending mechanism) that would apply to
the <code>executeCommand()</code> function. This is not difficult to
implement, but it seem like kind of a "big hammer" solution.
Besides that, it might also represent a security flaw (for instance, I
prefer not to mess with root's <code>$PATH</code> on the application
level if I don't have to).</p>
<p>The alternative is to set up some sort of configuration for the path
to certain executables, i.e. "find <code>svnlook</code> in
<code>/usr/local/bin/svnlook</code>" or whatever. This
PathResolverSingleton aims to provide a good solution to the mapping
problem. Callers of all sorts (extensions or not) can get an instance of
the singleton. Then, they call the <code>lookup</code> method to try and
resolve the executable they are looking for. Through the
<code>lookup</code> method, the caller can also specify a default to use
if a mapping is not found. This way, with no real effort on the part of
the caller, behavior can neatly degrade to something equivalent to the
current behavior if there is no special mapping or if the singleton was
never initialized in the first place.</p>
<p>Even better, extensions automagically get access to the same resolver
functionality, and they don't even need to understand how the mapping
happens. All extension authors need to do is document what executables
their code requires, and the standard resolver configuration section will
meet their needs.</p>
The class should be initialized once through the constructor somewhere
in the main routine. Then, the main routine should call the <a
href="CedarBackup2.util.PathResolverSingleton-class.html#fill"
class="link"><code>fill</code></a> method to fill in the resolver's
internal structures. Everyone else who needs to resolve a path will get
an instance of the class using <a
href="CedarBackup2.util.PathResolverSingleton-class.html#getInstance"
class="link"><code>getInstance</code></a> and will then just call the <a
href="CedarBackup2.util.PathResolverSingleton-class.html#lookup"
class="link"><code>lookup</code></a> method.
<hr/>
<!-- =========== START OF METHOD SUMMARY =========== -->
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<th colspan="2">Method Summary</th></tr>
<tr><td align="right" valign="top" width="15%"><font size="-1"> </font></td>
<td><code><span class="summary-sig"><a href="CedarBackup2.util.PathResolverSingleton-class.html#__init__" class="summary-sig-name"><code>__init__</code></a>(<span class=summary-sig-arg>self</span>)</span></code>
<br />
Singleton constructor, which just creates the singleton instance.</td></tr>
<tr><td align="right" valign="top" width="15%"><font size="-1"> </font></td>
<td><code><span class="summary-sig"><a href="CedarBackup2.util.PathResolverSingleton-class.html#fill" class="summary-sig-name"><code>fill</code></a>(<span class=summary-sig-arg>self</span>,
<span class=summary-sig-arg>mapping</span>)</span></code>
<br />
Fills in the singleton's internal mapping from name to resource.</td></tr>
<tr><td align="right" valign="top" width="15%"><font size="-1"> </font></td>
<td><code><span class="summary-sig"><a href="CedarBackup2.util.PathResolverSingleton-class.html#lookup" class="summary-sig-name"><code>lookup</code></a>(<span class=summary-sig-arg>self</span>,
<span class=summary-sig-arg>name</span>,
<span class=summary-sig-arg>default</span>)</span></code>
<br />
Looks up name and returns the resolved path associated with the
name.</td></tr>
</table><br />
<!-- =========== START OF INSTANCE VARIABLE SUMMARY =========== -->
<table class="summary" border="1" cellpadding="3" cellspacing="0" width="100%" bgcolor="white">
<tr bgcolor="#70b0f0" class="summary">
<th colspan="2">Instance Variable Summary</th></tr>
<tr><td align="right" valign="top" width="15%"><font size="-1"> </font></td>
<td><b><a href="../private/CedarBackup2.util.PathResolverSingleton-class.html#_mapping"><code>_mapping</code></a></b>: Internal mapping from resource name to path.</td></tr>
</table><br />
<!-- =========== START OF CLASS VARIABLE SUMMARY =========== -->
<table class="summary" border="1" cellpadding="3" cellspacing="0" width="100%" bgcolor="white">
<tr bgcolor="#70b0f0" class="summary">
<th colspan="2">Class Variable Summary</th></tr>
<tr><td align="right" valign="top" width="15%"><font size="-1"><code>_Helper</code></font></td>
<td><b><a href="CedarBackup2.util.PathResolverSingleton-class.html#getInstance"><code>getInstance</code></a></b> = <span title="<CedarBackup2.util._Helper instance at 0x4028e0ac>"><code><CedarBackup2.util._Helper instance at 0x4<span class="variable-ellipsis">...</span></code>
</span></td></tr>
<tr><td align="right" valign="top" width="15%"><font size="-1"><code>classobj</code></font></td>
<td><a name="_Helper"></a><b><code>_Helper</code></b> = <a href="../private/CedarBackup2.util._Helper-class.html"><code>CedarBackup2.util._Helper</code></a></td></tr>
<tr><td align="right" valign="top" width="15%"><font size="-1"><code>NoneType</code></font></td>
<td><b><a href="../private/CedarBackup2.util.PathResolverSingleton-class.html#_instance"><code>_instance</code></a></b>: Holds a reference to the singleton</td></tr>
</table><br />
<!-- =========== START OF METHOD DETAILS =========== -->
<table class="details" border="1" cellpadding="3" cellspacing="0" width="100%" bgcolor="white">
<tr bgcolor="#70b0f0" class="details">
<th colspan="2">Method Details</th></tr>
</table>
<a name="__init__"></a>
<table width="100%" class="func-details" bgcolor="#e0e0e0"><tr><td>
<h3><span class="sig"><span class="sig-name">__init__</span>(<span class=sig-arg>self</span>)</span>
<br /><i>(Constructor)</i>
</h3>
Singleton constructor, which just creates the singleton
instance.
<dl><dt></dt><dd>
</dd></dl>
</td></tr></table>
<a name="fill"></a>
<table width="100%" class="func-details" bgcolor="#e0e0e0"><tr><td>
<h3><span class="sig"><span class="sig-name">fill</span>(<span class=sig-arg>self</span>,
<span class=sig-arg>mapping</span>)</span>
</h3>
Fills in the singleton's internal mapping from name to resource.
<dl><dt></dt><dd>
<dl><dt><b>Parameters:</b></dt>
<dd><code><b>mapping</b></code> -
Mapping from resource name to path.
<br /><i>
(type=Dictionary mapping name to path, both as strings.)</i>
</dd>
</dl>
</dd></dl>
</td></tr></table>
<a name="lookup"></a>
<table width="100%" class="func-details" bgcolor="#e0e0e0"><tr><td>
<h3><span class="sig"><span class="sig-name">lookup</span>(<span class=sig-arg>self</span>,
<span class=sig-arg>name</span>,
<span class=sig-arg>default</span>=<span class=sig-default>None</span>)</span>
</h3>
Looks up name and returns the resolved path associated with the
name.
<dl><dt></dt><dd>
<dl><dt><b>Parameters:</b></dt>
<dd><code><b>name</b></code> -
Name of the path resource to resolve.
<dd><code><b>default</b></code> -
Default to return if resource cannot be resolved.
</dd>
</dl>
<dl><dt><b>Returns:</b></dt>
<dd>
Resolved path associated with name, or default if name can't
be resolved.
</dd>
</dl>
</dd></dl>
</td></tr></table>
<br />
<!-- =========== START OF INSTANCE VARIABLE DETAILS =========== -->
<table class="details" border="1" cellpadding="3" cellspacing="0" width="100%" bgcolor="white">
<tr bgcolor="#70b0f0" class="details">
<th colspan="2">Instance Variable Details</th></tr>
</table>
<table width="100%" class="var-details" bgcolor="#e0e0e0"><tr><td>
<a name="_mapping"></a>
<h3>_mapping</h3>
Internal mapping from resource name to path.
</td></tr></table>
<br />
<!-- =========== START OF CLASS VARIABLE DETAILS =========== -->
<table class="details" border="1" cellpadding="3" cellspacing="0" width="100%" bgcolor="white">
<tr bgcolor="#70b0f0" class="details">
<th colspan="2">Class Variable Details</th></tr>
</table>
<table width="100%" class="var-details" bgcolor="#e0e0e0"><tr><td>
<a name="getInstance"></a>
<h3>getInstance</h3>
<dl>
<dt></dt>
<dd>
<dl>
<dt><b>Type:</b></dt>
<dd>
<code>_Helper</code>
</dd>
<span title="<CedarBackup2.util._Helper instance at 0x4028e0ac>"> <dt><b>Value:</b></dt>
<dd><table><tr><td>
<pre class="variable">
<CedarBackup2.util._Helper instance at 0x4028e0ac> </pre>
</td></tr></table></dd>
</span> </dl>
</dd>
</dl></td></tr></table>
<table width="100%" class="var-details" bgcolor="#e0e0e0"><tr><td>
<a name="_instance"></a>
<h3>_instance</h3>
Holds a reference to the singleton
<dl>
<dt></dt>
<dd>
<dl>
<dt><b>Type:</b></dt>
<dd>
<code>NoneType</code>
</dd>
<span title="None"> <dt><b>Value:</b></dt>
<dd><table><tr><td>
<pre class="variable">
None </pre>
</td></tr></table></dd>
</span> </dl>
</dd>
</dl></td></tr></table>
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