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<br clear="all"><div class="SECT1">
<h1 class="SECT1"><a name="XMLSEC-NOTES-NEW-CRYPTO-KLASSES">Klasses and objects.</a></h1>
<p>The XML Security Library is written in C but it uses some OOP techniques:
the objects in the library have "klasses" and there is "klasses" inheritance.
(see <a href="xmlsec-signature-klasses.html">signature</a> and
<a href="xmlsec-encryption-klasses.html">encryption</a> klasses
diagrams). The "klass" is different from C++ "class" (btw, this is
one of the reasons why it is spelled differently). The idea of "klasses"
used in XML Security Library are close to one in the GLIB/GTK/GNOME
and many other C projects. If you ever seen an OOP code written in C
you should find everything familiar.
</p>
<p>XML Security Library "klass" includes three main parts:
</p>
<p></p>
<ul>
<li>
<p>"Klass" declaration structure that defines "klass" interfaces
and global constant data (for example, the human-readable name of
the "klass").
</p>
<div class="EXAMPLE">
<a name="AEN562"></a><p><b>Example 6. Base transform "klass" and its child XPath transform "klass" structure.</b></p>
<pre class="PROGRAMLISTING">struct _xmlSecTransformKlass {
/* data */
size_t klassSize;
size_t objSize;
const xmlChar* name;
const xmlChar* href;
xmlSecTransformUsage usage;
/* methods */
xmlSecTransformInitializeMethod initialize;
xmlSecTransformFinalizeMethod finalize;
xmlSecTransformNodeReadMethod readNode;
xmlSecTransformNodeWriteMethod writeNode;
...
};
...
static xmlSecTransformKlass xmlSecTransformXPathKlass = {
/* klass/object sizes */
sizeof(xmlSecTransformKlass), /* size_t klassSize */
xmlSecXPathTransformSize, /* size_t objSize */
xmlSecNameXPath, /* const xmlChar* name; */
xmlSecXPathNs, /* const xmlChar* href; */
xmlSecTransformUsageDSigTransform, /* xmlSecTransformUsage usage; */
xmlSecTransformXPathInitialize, /* xmlSecTransformInitializeMethod initialize; */
xmlSecTransformXPathFinalize, /* xmlSecTransformFinalizeMethod finalize; */
xmlSecTransformXPathNodeRead, /* xmlSecTransformNodeReadMethod readNode; */
NULL, /* xmlSecTransformNodeWriteMethod writeNode; */
...
};
</pre>
</div>
</li>
<li>
<p>"Klass" id which is simply a pointer to the "klass"
declaration strucutre. "Klass" id is used to bind "klass" objects
to the "klass" declaration and to pass "klass" strucutre to functions.
</p>
<div class="EXAMPLE">
<a name="AEN567"></a><p><b>Example 7. Base transform "klass" id declaration and its child XPath transform "klass" id implementation.</b></p>
<pre class="PROGRAMLISTING">typedef const struct _xmlSecTransformKlass xmlSecTransformKlass, *xmlSecTransformId;
...
#define xmlSecTransformXPathId xmlSecTransformXPathGetKlass()
...
xmlSecTransformId
xmlSecTransformXPathGetKlass(void) {
return(&xmlSecTransformXPathKlass);
}
</pre>
</div>
</li>
<li>
<p>"Klass" object structure that contains object specific
data. The child object specific data are placed after the parent "klass"
object data.
</p>
<div class="EXAMPLE">
<a name="AEN572"></a><p><b>Example 8. Base transform object strucutre and its child XPath transform object.</b></p>
<pre class="PROGRAMLISTING">struct _xmlSecTransform {
xmlSecTransformId id;
xmlSecTransformOperation operation;
xmlSecTransformStatus status;
xmlNodePtr hereNode;
/* transforms chain */
xmlSecTransformPtr next;
xmlSecTransformPtr prev;
...
};
...
/******************************************************************************
*
* XPath/XPointer transforms
*
* xmlSecPtrList with XPath expressions is located after xmlSecTransform structure
*
*****************************************************************************/
#define xmlSecXPathTransformSize \
(sizeof(xmlSecTransform) + sizeof(xmlSecPtrList))
#define xmlSecXPathTransformGetDataList(transform) \
((xmlSecTransformCheckSize((transform), xmlSecXPathTransformSize)) ? \
(xmlSecPtrListPtr)(((unsigned char*)(transform)) + sizeof(xmlSecTransform)) : \
(xmlSecPtrListPtr)NULL)
</pre>
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