1<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Parsing XML</title><link rel="stylesheet" type="text/css" href="../manual.css"><meta name="generator" content="DocBook XSL Stylesheets V1.76.1"><link rel="home" href="index.html" title="neon HTTP/WebDAV client library"><link rel="up" href="api.html" title="Chapter��2.��The neon C language interface"><link rel="prev" href="api.html" title="Chapter��2.��The neon C language interface"><link rel="next" href="ref.html" title="neon API reference"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Parsing XML</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="api.html">Prev</a>��</td><th width="60%" align="center">Chapter��2.��The neon C language interface</th><td width="20%" align="right">��<a accesskey="n" href="ref.html">Next</a></td></tr></table><hr></div><div class="sect1" title="Parsing XML"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="xml"></a>Parsing XML</h2></div></div></div><p>The neon XML interface is exposed by the 2 <code class="filename">ne_xml.h</code> header file. This interface gives a 3 wrapper around the standard <a class="ulink" href="http://www.saxproject.org/" target="_top">SAX</a> API used by XML 4 parsers, with an additional abstraction, <em class="firstterm">stacked SAX 5 handlers</em>, and also giving consistent <a class="ulink" href="http://www.w3.org/TR/REC-xml-names" target="_top">XML Namespace</a> support.</p><div class="sect2" title="Introduction to SAX"><div class="titlepage"><div><div><h3 class="title"><a name="xml-sax"></a>Introduction to SAX</h3></div></div></div><p>A SAX-based parser works by emitting a sequence of 6 <em class="firstterm">events</em> to reflect the tokens being parsed 7 from the XML document. For example, parsing the following document 8 fragment: 9 10</p><pre class="programlisting"> 11<hello>world</hello> 12</pre><p> 13 14 results in the following events: 15 16 </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="emphasis"><em>start-element</em></span> "hello"</li><li class="listitem"><span class="emphasis"><em>character-data</em></span> "world"</li><li class="listitem"><span class="emphasis"><em>end-element</em></span> "hello"</li></ol></div><p> 17 18 This example demonstrates the three event types used used in the 19 subset of SAX exposed by the neon XML interface: <span class="emphasis"><em>start-element</em></span>, 20 <span class="emphasis"><em>character-data</em></span> and <span class="emphasis"><em>end-element</em></span>. In a C API, an <span class="quote">���<span class="quote">event</span>���</span> is 21 implemented as a function callback; three callback types are used in 22 neon, one for each type of event.</p></div><div class="sect2" title="Stacked SAX handlers"><div class="titlepage"><div><div><h3 class="title"><a name="xml-stacked"></a>Stacked SAX handlers</h3></div></div></div><p>WebDAV property values are represented as fragments of XML, 23 transmitted as parts of larger XML documents over HTTP (notably in 24 the body of the response to a <code class="literal">PROPFIND</code> request). 25 When neon parses such documents, the SAX events generated for 26 these property value fragments may need to be handled by the 27 application, since neon has no knowledge of the structure of 28 properties used by the application.</p><p>To solve this problem<sup>[<a name="foot.xml.sax" href="#ftn.foot.xml.sax" class="footnote">1</a>]</sup> the neon XML interface introduces 29 the concept of a <em class="firstterm">SAX handler</em>. A SAX handler 30 comprises a <span class="emphasis"><em>start-element</em></span>, <span class="emphasis"><em>character-data</em></span> and <span class="emphasis"><em>end-element</em></span> callback; the 31 <span class="emphasis"><em>start-element</em></span> callback being defined such that each handler may 32 <span class="emphasis"><em>accept</em></span> or <span class="emphasis"><em>decline</em></span> the 33 <span class="emphasis"><em>start-element</em></span> event. Handlers are composed into a <em class="firstterm">handler 34 stack</em> before parsing a document. When a new <span class="emphasis"><em>start-element</em></span> 35 event is generated by the XML parser, neon invokes each <span class="emphasis"><em>start-element</em></span> 36 callback in the handler stack in turn until one accepts the event. 37 The handler which accepts the event will then be subsequently be 38 passed <span class="emphasis"><em>character-data</em></span> events if the element contains character data, 39 followed by an <span class="emphasis"><em>end-element</em></span> event when the element is closed. If no 40 handler in the stack accepts a <span class="emphasis"><em>start-element</em></span> event, the branch of the 41 tree is ignored.</p><p>To illustrate, given a handler A, which accepts the 42 <code class="literal">cat</code> and <code class="literal">age</code> elements, and a 43 handler B, which accepts the <code class="literal">name</code> element, the 44 following document: 45 46</p><div class="example"><a name="xml-example"></a><p class="title"><b>Example��2.1.��An example XML document</b></p><div class="example-contents"><pre class="programlisting"> 47<cat> 48 <age>3</age> 49 <name>Bob</name> 50</cat> 51</pre></div></div><p><br class="example-break"> 52 53 would be parsed as follows: 54 55 </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">A <span class="emphasis"><em>start-element</em></span> "cat" ��� <span class="emphasis"><em>accept</em></span></li><li class="listitem">A <span class="emphasis"><em>start-element</em></span> "age" ��� <span class="emphasis"><em>accept</em></span></li><li class="listitem">A <span class="emphasis"><em>character-data</em></span> "3"</li><li class="listitem">A <span class="emphasis"><em>end-element</em></span> "age"</li><li class="listitem">A <span class="emphasis"><em>start-element</em></span> "name" ��� <span class="emphasis"><em>decline</em></span></li><li class="listitem">B <span class="emphasis"><em>start-element</em></span> "name" ��� <span class="emphasis"><em>accept</em></span></li><li class="listitem">B <span class="emphasis"><em>character-data</em></span> "Bob"</li><li class="listitem">B <span class="emphasis"><em>end-element</em></span> "name"</li><li class="listitem">A <span class="emphasis"><em>end-element</em></span> "cat"</li></ol></div><p>The search for a handler which will accept a <span class="emphasis"><em>start-element</em></span> event 56 begins at the handler of the parent element and continues toward the 57 top of the stack. For the root element, it begins at the base of 58 the stack. In the above example, handler A is at the base, and 59 handler B at the top; if the <code class="literal">name</code> element had any 60 children, only B's <span class="emphasis"><em>start-element</em></span> would be invoked to accept 61 them.</p></div><div class="sect2" title="Maintaining state"><div class="titlepage"><div><div><h3 class="title"><a name="xml-state"></a>Maintaining state</h3></div></div></div><p>To facilitate communication between independent handlers, a 62 <em class="firstterm">state integer</em> is associated with each element 63 being parsed. This integer is returned by <span class="emphasis"><em>start-element</em></span> callback and 64 is passed to the subsequent <span class="emphasis"><em>character-data</em></span> and <span class="emphasis"><em>end-element</em></span> callbacks 65 associated with the element. The state integer of the parent 66 element is also passed to each <span class="emphasis"><em>start-element</em></span> callback, the value zero 67 used for the root element (which by definition has no 68 parent).</p><p>To further extend <a class="xref" href="xml.html#xml-example" title="Example��2.1.��An example XML document">Example��2.1, ���An example XML document���</a>: if handler A 69 defines that the state of the root element <code class="sgmltag-element">cat</code> 70 will be <code class="literal">42</code>, the event trace would be as 71 follows: 72 73 </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">A <span class="emphasis"><em>start-element</em></span> (parent = 0, "cat") ��� 74 <span class="emphasis"><em>accept</em></span>, state = 42 75 </li><li class="listitem">A <span class="emphasis"><em>start-element</em></span> (parent = 42, "age") ��� 76 <span class="emphasis"><em>accept</em></span>, state = 50 77 </li><li class="listitem">A <span class="emphasis"><em>character-data</em></span> (state = 50, "3")</li><li class="listitem">A <span class="emphasis"><em>end-element</em></span> (state = 50, "age")</li><li class="listitem">A <span class="emphasis"><em>start-element</em></span> (parent = 42, "name") ��� 78 <span class="emphasis"><em>decline</em></span></li><li class="listitem">B <span class="emphasis"><em>start-element</em></span> (parent = 42, "name") ��� 79 <span class="emphasis"><em>accept</em></span>, state = 99</li><li class="listitem">B <span class="emphasis"><em>character-data</em></span> (state = 99, "Bob")</li><li class="listitem">B <span class="emphasis"><em>end-element</em></span> (state = 99, "name")</li><li class="listitem">A <span class="emphasis"><em>end-element</em></span> (state = 42, "cat")</li></ol></div><p>To avoid collisions between state integers used by different 80 handlers, the interface definition of any handler includes the range 81 of integers it will use.</p></div><div class="sect2" title="XML namespaces"><div class="titlepage"><div><div><h3 class="title"><a name="xml-ns"></a>XML namespaces</h3></div></div></div><p>To support XML namespaces, every element name is represented 82 as a <span class="emphasis"><em>(namespace, name)</em></span> pair. The <span class="emphasis"><em>start-element</em></span> 83 and <span class="emphasis"><em>end-element</em></span> callbacks are passed namespace and name strings 84 accordingly. If an element in the XML document has no declared 85 namespace, the namespace given will be the empty string, 86 <code class="literal">""</code>.</p></div><div class="footnotes"><br><hr width="100" align="left"><div class="footnote"><p><sup>[<a id="ftn.foot.xml.sax" href="#foot.xml.sax" class="para">1</a>] </sup>This 87 <span class="quote">���<span class="quote">problem</span>���</span> only needs solving because the SAX interface 88 is so inflexible when implemented as C function callbacks; a better 89 approach would be to use an XML parser interface which is not based 90 on callbacks.</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="api.html">Prev</a>��</td><td width="20%" align="center"><a accesskey="u" href="api.html">Up</a></td><td width="40%" align="right">��<a accesskey="n" href="ref.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter��2.��The neon C language interface��</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">��neon API reference</td></tr></table></div></body></html> 91