mirror of
https://gitlab.gnome.org/GNOME/libxml2
synced 2025-03-28 21:33:13 +00:00
34ce8bece2
* configure.in: preparing 2.4.18 * doc/*: updated and rebuilt the web site * *.c libxml.h: implement the new IN_LIBXML scheme discussed with the Windows and Cygwin maintainers. * parser.c: humm, changed the way the SAX parser work when xmlSubstituteEntitiesDefault(1) is set, it will then do the entity registration and loading by itself in case the user provided SAX getEntity() returns NULL. * testSAX.c: added --noent to test the behaviour. Daniel
247 lines
12 KiB
HTML
247 lines
12 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">
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<html>
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<head>
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<meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type">
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<style type="text/css"><!--
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TD {font-family: Verdana,Arial,Helvetica}
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BODY {font-family: Verdana,Arial,Helvetica; margin-top: 2em; margin-left: 0em; margin-right: 0em}
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H1 {font-family: Verdana,Arial,Helvetica}
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H2 {font-family: Verdana,Arial,Helvetica}
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H3 {font-family: Verdana,Arial,Helvetica}
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A:link, A:visited, A:active { text-decoration: underline }
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--></style>
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<title>I/O Interfaces</title>
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</head>
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<body bgcolor="#8b7765" text="#000000" link="#000000" vlink="#000000">
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<table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr>
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<td width="180">
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<a href="http://www.gnome.org/"><img src="smallfootonly.gif" alt="Gnome Logo"></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo"></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo"></a>
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</td>
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<td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center">
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<h1>The XML C library for Gnome</h1>
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<h2>I/O Interfaces</h2>
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</td></tr></table></td></tr></table></td>
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</tr></table>
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<table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr>
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<td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td>
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<table width="100%" border="0" cellspacing="1" cellpadding="3">
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<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr>
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<tr><td bgcolor="#fffacd"><ul>
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<li><a href="index.html">Home</a></li>
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<li><a href="intro.html">Introduction</a></li>
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<li><a href="FAQ.html">FAQ</a></li>
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<li><a href="docs.html">Documentation</a></li>
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<li><a href="bugs.html">Reporting bugs and getting help</a></li>
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<li><a href="help.html">How to help</a></li>
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<li><a href="downloads.html">Downloads</a></li>
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<li><a href="news.html">News</a></li>
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<li><a href="XMLinfo.html">XML</a></li>
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<li><a href="XSLT.html">XSLT</a></li>
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<li><a href="python.html">Python and bindings</a></li>
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<li><a href="architecture.html">libxml architecture</a></li>
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<li><a href="tree.html">The tree output</a></li>
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<li><a href="interface.html">The SAX interface</a></li>
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<li><a href="xmldtd.html">Validation & DTDs</a></li>
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<li><a href="xmlmem.html">Memory Management</a></li>
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<li><a href="encoding.html">Encodings support</a></li>
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<li><a href="xmlio.html">I/O Interfaces</a></li>
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<li><a href="catalog.html">Catalog support</a></li>
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<li><a href="library.html">The parser interfaces</a></li>
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<li><a href="entities.html">Entities or no entities</a></li>
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<li><a href="namespaces.html">Namespaces</a></li>
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<li><a href="upgrade.html">Upgrading 1.x code</a></li>
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<li><a href="threads.html">Thread safety</a></li>
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<li><a href="DOM.html">DOM Principles</a></li>
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<li><a href="example.html">A real example</a></li>
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<li><a href="contribs.html">Contributions</a></li>
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<li>
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<a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a>
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</li>
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</ul></td></tr>
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</table>
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<table width="100%" border="0" cellspacing="1" cellpadding="3">
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<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>API Indexes</b></center></td></tr>
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<tr><td bgcolor="#fffacd"><ul>
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<li><a href="APIchunk0.html">Alphabetic</a></li>
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<li><a href="APIconstructors.html">Constructors</a></li>
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<li><a href="APIfunctions.html">Functions/Types</a></li>
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<li><a href="APIfiles.html">Modules</a></li>
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<li><a href="APIsymbols.html">Symbols</a></li>
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</ul></td></tr>
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</table>
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<table width="100%" border="0" cellspacing="1" cellpadding="3">
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<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr>
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<tr><td bgcolor="#fffacd"><ul>
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<li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li>
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<li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li>
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<li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li>
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<li><a href="http://www.aleksey.com/xmlsec/">XML-DSig xmlsec</a></li>
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<li><a href="ftp://xmlsoft.org/">FTP</a></li>
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<li><a href="http://www.fh-frankfurt.de/~igor/projects/libxml/">Windows binaries</a></li>
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<li><a href="http://garypennington.net/libxml2/">Solaris binaries</a></li>
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<li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml&product=libxml2">Bug Tracker</a></li>
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</ul></td></tr>
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</table>
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</td></tr></table></td>
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<td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd">
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<p>Table of Content:</p>
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<ol>
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<li><a href="#General1">General overview</a></li>
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<li><a href="#basic">The basic buffer type</a></li>
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<li><a href="#Input">Input I/O handlers</a></li>
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<li><a href="#Output">Output I/O handlers</a></li>
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<li><a href="#entities">The entities loader</a></li>
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<li><a href="#Example2">Example of customized I/O</a></li>
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</ol>
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<h3><a name="General1">General overview</a></h3>
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<p>The module <code><a href="http://xmlsoft.org/html/libxml-xmlio.html">xmlIO.h</a></code> provides
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the interfaces to the libxml I/O system. This consists of 4 main parts:</p>
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<ul>
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<li>Entities loader, this is a routine which tries to fetch the entities
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(files) based on their PUBLIC and SYSTEM identifiers. The default loader
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don't look at the public identifier since libxml do not maintain a
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catalog. You can redefine you own entity loader by using
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<code>xmlGetExternalEntityLoader()</code> and
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<code>xmlSetExternalEntityLoader()</code>. <a href="#entities">Check the
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example</a>.</li>
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<li>Input I/O buffers which are a commodity structure used by the parser(s)
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input layer to handle fetching the informations to feed the parser. This
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provides buffering and is also a placeholder where the encoding
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convertors to UTF8 are piggy-backed.</li>
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<li>Output I/O buffers are similar to the Input ones and fulfill similar
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task but when generating a serialization from a tree.</li>
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<li>A mechanism to register sets of I/O callbacks and associate them with
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specific naming schemes like the protocol part of the URIs.
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<p>This affect the default I/O operations and allows to use specific I/O
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handlers for certain names.</p>
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</li>
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</ul>
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<p>The general mechanism used when loading http://rpmfind.net/xml.html for
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example in the HTML parser is the following:</p>
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<ol>
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<li>The default entity loader calls <code>xmlNewInputFromFile()</code> with
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the parsing context and the URI string.</li>
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<li>the URI string is checked against the existing registered handlers
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using their match() callback function, if the HTTP module was compiled
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in, it is registered and its match() function will succeeds</li>
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<li>the open() function of the handler is called and if successful will
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return an I/O Input buffer</li>
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<li>the parser will the start reading from this buffer and progressively
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fetch information from the resource, calling the read() function of the
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handler until the resource is exhausted</li>
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<li>if an encoding change is detected it will be installed on the input
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buffer, providing buffering and efficient use of the conversion
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routines</li>
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<li>once the parser has finished, the close() function of the handler is
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called once and the Input buffer and associed resources are
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deallocated.</li>
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</ol>
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<p>The user defined callbacks are checked first to allow overriding of the
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default libxml I/O routines.</p>
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<h3><a name="basic">The basic buffer type</a></h3>
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<p>All the buffer manipulation handling is done using the
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<code>xmlBuffer</code> type define in <code><a href="http://xmlsoft.org/html/libxml-tree.html">tree.h</a></code>which is a
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resizable memory buffer. The buffer allocation strategy can be selected to be
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either best-fit or use an exponential doubling one (CPU vs. memory use
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tradeoff). The values are <code>XML_BUFFER_ALLOC_EXACT</code> and
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<code>XML_BUFFER_ALLOC_DOUBLEIT</code>, and can be set individually or on a
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system wide basis using <code>xmlBufferSetAllocationScheme()</code>. A number
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of functions allows to manipulate buffers with names starting with the
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<code>xmlBuffer...</code> prefix.</p>
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<h3><a name="Input">Input I/O handlers</a></h3>
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<p>An Input I/O handler is a simple structure
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<code>xmlParserInputBuffer</code> containing a context associated to the
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resource (file descriptor, or pointer to a protocol handler), the read() and
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close() callbacks to use and an xmlBuffer. And extra xmlBuffer and a charset
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encoding handler are also present to support charset conversion when
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needed.</p>
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<h3><a name="Output">Output I/O handlers</a></h3>
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<p>An Output handler <code>xmlOutputBuffer</code> is completely similar to an
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Input one except the callbacks are write() and close().</p>
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<h3><a name="entities">The entities loader</a></h3>
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<p>The entity loader resolves requests for new entities and create inputs for
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the parser. Creating an input from a filename or an URI string is done
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through the xmlNewInputFromFile() routine. The default entity loader do not
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handle the PUBLIC identifier associated with an entity (if any). So it just
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calls xmlNewInputFromFile() with the SYSTEM identifier (which is mandatory in
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XML).</p>
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<p>If you want to hook up a catalog mechanism then you simply need to
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override the default entity loader, here is an example:</p>
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<pre>#include <libxml/xmlIO.h>
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xmlExternalEntityLoader defaultLoader = NULL;
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xmlParserInputPtr
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xmlMyExternalEntityLoader(const char *URL, const char *ID,
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xmlParserCtxtPtr ctxt) {
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xmlParserInputPtr ret;
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const char *fileID = NULL;
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/* lookup for the fileID depending on ID */
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ret = xmlNewInputFromFile(ctxt, fileID);
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if (ret != NULL)
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return(ret);
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if (defaultLoader != NULL)
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ret = defaultLoader(URL, ID, ctxt);
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return(ret);
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}
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int main(..) {
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...
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/*
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* Install our own entity loader
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*/
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defaultLoader = xmlGetExternalEntityLoader();
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xmlSetExternalEntityLoader(xmlMyExternalEntityLoader);
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...
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}</pre>
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<h3><a name="Example2">Example of customized I/O</a></h3>
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<p>This example come from <a href="http://xmlsoft.org/messages/0708.html">a
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real use case</a>, xmlDocDump() closes the FILE * passed by the application
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and this was a problem. The <a href="http://xmlsoft.org/messages/0711.html">solution</a> was to redefine a
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new output handler with the closing call deactivated:</p>
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<ol>
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<li>First define a new I/O ouput allocator where the output don't close the
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file:
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<pre>xmlOutputBufferPtr
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xmlOutputBufferCreateOwn(FILE *file, xmlCharEncodingHandlerPtr encoder) {
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD>xmlOutputBufferPtr ret;
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD>
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD>if (xmlOutputCallbackInitialized == 0)
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>xmlRegisterDefaultOutputCallbacks();
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD>if (file == NULL) return(NULL);
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ret = xmlAllocOutputBuffer(encoder);
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD>if (ret != NULL) {
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ret->context = file;
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ret->writecallback = xmlFileWrite;
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ret->closecallback = NULL; /* No close callback */
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD>}
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD>return(ret); <br>
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} </pre>
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</li>
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<li>And then use it to save the document:
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<pre>FILE *f;
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xmlOutputBufferPtr output;
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xmlDocPtr doc;
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int res;
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f = ...
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doc = ....
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output = xmlOutputBufferCreateOwn(f, NULL);
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res = xmlSaveFileTo(output, doc, NULL);
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</pre>
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</li>
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</ol>
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<p><a href="bugs.html">Daniel Veillard</a></p>
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</td></tr></table></td></tr></table></td></tr></table></td>
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</tr></table></td></tr></table>
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</body>
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</html>
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