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gerrit-public.fairphone.software / platform / external / libxml2 / refs/heads/odm/dev/target/13/fp5 / . / doc / xmlio.html
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Daniel Veillardd2190fa2010-09-30 13:58:22 +0200[diff] [blame]1<?xml version="1.0" encoding="UTF-8"?>
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
Daniel Veillardd2190fa2010-09-30 13:58:22 +0200[diff] [blame]3<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><link rel="SHORTCUT ICON" href="/favicon.ico" /><style type="text/css">
Daniel Veillard373a4752002-02-21 14:46:29 +0000[diff] [blame]4TD {font-family: Verdana,Arial,Helvetica}
5BODY {font-family: Verdana,Arial,Helvetica; margin-top: 2em; margin-left: 0em; margin-right: 0em}
6H1 {font-family: Verdana,Arial,Helvetica}
7H2 {font-family: Verdana,Arial,Helvetica}
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Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]9A:link, A:visited, A:active { text-decoration: underline }
Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]10</style><title>I/O Interfaces</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"><table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr><td width="120"><a href="http://swpat.ffii.org/"><img src="epatents.png" alt="Action against software patents" /></a></td><td width="180"><a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 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><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo" /></a></div></td><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"><h1>The XML C parser and toolkit of Gnome</h1><h2>I/O Interfaces</h2></td></tr></table></td></tr></table></td></tr></table><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><td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Developer Menu</b></center></td></tr><tr><td bgcolor="#fffacd"><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="20" value="" /><input name="submit" type="submit" value="Search ..." /></form><ul><li><a href="index.html" style="font-weight:bold">Main Menu</a></li><li><a href="html/index.html" style="font-weight:bold">Reference Manual</a></li><li><a href="examples/index.html" style="font-weight:bold">Code Examples</a></li><li><a href="guidelines.html">XML Guidelines</a></li><li><a href="tutorial/index.html">Tutorial</a></li><li><a href="xmlreader.html">The Reader Interface</a></li><li><a href="ChangeLog.html">ChangeLog</a></li><li><a href="XSLT.html">XSLT</a></li><li><a href="python.html">Python and bindings</a></li><li><a href="architecture.html">libxml2 architecture</a></li><li><a href="tree.html">The tree output</a></li><li><a href="interface.html">The SAX interface</a></li><li><a href="xmlmem.html">Memory Management</a></li><li><a href="xmlio.html">I/O Interfaces</a></li><li><a href="library.html">The parser interfaces</a></li><li><a href="entities.html">Entities or no entities</a></li><li><a href="namespaces.html">Namespaces</a></li><li><a href="upgrade.html">Upgrading 1.x code</a></li><li><a href="threads.html">Thread safety</a></li><li><a href="DOM.html">DOM Principles</a></li><li><a href="example.html">A real example</a></li><li><a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a></li></ul></td></tr></table><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>API Indexes</b></center></td></tr><tr><td bgcolor="#fffacd"><ul><li><a href="APIchunk0.html">Alphabetic</a></li><li><a href="APIconstructors.html">Constructors</a></li><li><a href="APIfunctions.html">Functions/Types</a></li><li><a href="APIfiles.html">Modules</a></li><li><a href="APIsymbols.html">Symbols</a></li></ul></td></tr></table><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr><tr><td bgcolor="#fffacd"><ul><li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li><li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li><li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li><li><a href="http://www.aleksey.com/xmlsec/">XML-DSig xmlsec</a></li><li><a href="ftp://xmlsoft.org/">FTP</a></li><li><a href="http://www.zlatkovic.com/projects/libxml/">Windows binaries</a></li><li><a href="http://opencsw.org/packages/libxml2">Solaris binaries</a></li><li><a href="http://www.explain.com.au/oss/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://lxml.de/">lxml Python bindings</a></li><li><a href="http://cpan.uwinnipeg.ca/dist/XML-LibXML">Perl bindings</a></li><li><a href="http://libxmlplusplus.sourceforge.net/">C++ bindings</a></li><li><a href="http://www.zend.com/php5/articles/php5-xmlphp.php#Heading4">PHP bindings</a></li><li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal bindings</a></li><li><a href="http://libxml.rubyforge.org/">Ruby bindings</a></li><li><a href="http://tclxml.sourceforge.net/">Tcl bindings</a></li><li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml2">Bug Tracker</a></li></ul></td></tr></table></td></tr></table></td><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"><p>Table of Content:</p><ol>
11 <li><a href="#General1">General overview</a></li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]12 <li><a href="#basic">The basic buffer type</a></li>
13 <li><a href="#Input">Input I/O handlers</a></li>
14 <li><a href="#Output">Output I/O handlers</a></li>
15 <li><a href="#entities">The entities loader</a></li>
16 <li><a href="#Example2">Example of customized I/O</a></li>
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]17</ol><h3><a name="General1" id="General1">General overview</a></h3><p>The module <code><a href="http://xmlsoft.org/html/libxml-xmlio.html">xmlIO.h</a></code> provides
Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]18the interfaces to the libxml2 I/O system. This consists of 4 main parts:</p><ul>
19 <li>Entities loader, this is a routine which tries to fetch the entities
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]20 (files) based on their PUBLIC and SYSTEM identifiers. The default loader
21 don't look at the public identifier since libxml2 do not maintain a
22 catalog. You can redefine you own entity loader by using
23 <code>xmlGetExternalEntityLoader()</code> and
24 <code>xmlSetExternalEntityLoader()</code>. <a href="#entities">Check the
25 example</a>.</li>
26 <li>Input I/O buffers which are a commodity structure used by the parser(s)
William M. Brack43a87292007-02-15 20:41:02 +0000[diff] [blame]27 input layer to handle fetching the information to feed the parser. This
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]28 provides buffering and is also a placeholder where the encoding
29 converters to UTF8 are piggy-backed.</li>
30 <li>Output I/O buffers are similar to the Input ones and fulfill similar
31 task but when generating a serialization from a tree.</li>
32 <li>A mechanism to register sets of I/O callbacks and associate them with
33 specific naming schemes like the protocol part of the URIs.
34 <p>This affect the default I/O operations and allows to use specific I/O
35 handlers for certain names.</p>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]36 </li>
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]37</ul><p>The general mechanism used when loading http://rpmfind.net/xml.html for
Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]38example in the HTML parser is the following:</p><ol>
39 <li>The default entity loader calls <code>xmlNewInputFromFile()</code> with
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]40 the parsing context and the URI string.</li>
41 <li>the URI string is checked against the existing registered handlers
42 using their match() callback function, if the HTTP module was compiled
43 in, it is registered and its match() function will succeeds</li>
44 <li>the open() function of the handler is called and if successful will
45 return an I/O Input buffer</li>
46 <li>the parser will the start reading from this buffer and progressively
47 fetch information from the resource, calling the read() function of the
48 handler until the resource is exhausted</li>
49 <li>if an encoding change is detected it will be installed on the input
50 buffer, providing buffering and efficient use of the conversion
51 routines</li>
52 <li>once the parser has finished, the close() function of the handler is
53 called once and the Input buffer and associated resources are
54 deallocated.</li>
55</ol><p>The user defined callbacks are checked first to allow overriding of the
56default libxml2 I/O routines.</p><h3><a name="basic" id="basic">The basic buffer type</a></h3><p>All the buffer manipulation handling is done using the
57<code>xmlBuffer</code> type define in <code><a href="http://xmlsoft.org/html/libxml-tree.html">tree.h</a> </code>which is a
58resizable memory buffer. The buffer allocation strategy can be selected to be
59either best-fit or use an exponential doubling one (CPU vs. memory use
60trade-off). The values are <code>XML_BUFFER_ALLOC_EXACT</code> and
61<code>XML_BUFFER_ALLOC_DOUBLEIT</code>, and can be set individually or on a
62system wide basis using <code>xmlBufferSetAllocationScheme()</code>. A number
63of functions allows to manipulate buffers with names starting with the
64<code>xmlBuffer...</code> prefix.</p><h3><a name="Input" id="Input">Input I/O handlers</a></h3><p>An Input I/O handler is a simple structure
65<code>xmlParserInputBuffer</code> containing a context associated to the
66resource (file descriptor, or pointer to a protocol handler), the read() and
67close() callbacks to use and an xmlBuffer. And extra xmlBuffer and a charset
68encoding handler are also present to support charset conversion when
69needed.</p><h3><a name="Output" id="Output">Output I/O handlers</a></h3><p>An Output handler <code>xmlOutputBuffer</code> is completely similar to an
70Input one except the callbacks are write() and close().</p><h3><a name="entities" id="entities">The entities loader</a></h3><p>The entity loader resolves requests for new entities and create inputs for
71the parser. Creating an input from a filename or an URI string is done
72through the xmlNewInputFromFile() routine. The default entity loader do not
73handle the PUBLIC identifier associated with an entity (if any). So it just
74calls xmlNewInputFromFile() with the SYSTEM identifier (which is mandatory in
75XML).</p><p>If you want to hook up a catalog mechanism then you simply need to
76override the default entity loader, here is an example:</p><pre>#include &lt;libxml/xmlIO.h&gt;
Daniel Veillard2bb89092000-08-31 14:57:50 +0000[diff] [blame]77
78xmlExternalEntityLoader defaultLoader = NULL;
79
80xmlParserInputPtr
81xmlMyExternalEntityLoader(const char *URL, const char *ID,
82 xmlParserCtxtPtr ctxt) {
83 xmlParserInputPtr ret;
84 const char *fileID = NULL;
85 /* lookup for the fileID depending on ID */
86
87 ret = xmlNewInputFromFile(ctxt, fileID);
88 if (ret != NULL)
89 return(ret);
90 if (defaultLoader != NULL)
91 ret = defaultLoader(URL, ID, ctxt);
92 return(ret);
93}
94
95int main(..) {
96 ...
97
98 /*
99 * Install our own entity loader
100 */
101 defaultLoader = xmlGetExternalEntityLoader();
102 xmlSetExternalEntityLoader(xmlMyExternalEntityLoader);
103
104 ...
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]105}</pre><h3><a name="Example2" id="Example2">Example of customized I/O</a></h3><p>This example come from <a href="http://xmlsoft.org/messages/0708.html">a
106real use case</a>, xmlDocDump() closes the FILE * passed by the application
107and this was a problem. The <a href="http://xmlsoft.org/messages/0711.html">solution</a> was to redefine a
Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]108new output handler with the closing call deactivated:</p><ol>
109 <li>First define a new I/O output allocator where the output don't close
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]110 the file:
Daniel Veillarda7ad4522000-08-31 14:19:54 +0000[diff] [blame]111 <pre>xmlOutputBufferPtr
112xmlOutputBufferCreateOwn(FILE *file, xmlCharEncodingHandlerPtr encoder) {
Daniel Veillardd2190fa2010-09-30 13:58:22 +0200[diff] [blame]113    xmlOutputBufferPtr ret;
114    
115    if (xmlOutputCallbackInitialized == 0)
116        xmlRegisterDefaultOutputCallbacks();
Daniel Veillarda7ad4522000-08-31 14:19:54 +0000[diff] [blame]117
Daniel Veillardd2190fa2010-09-30 13:58:22 +0200[diff] [blame]118    if (file == NULL) return(NULL);
119    ret = xmlAllocOutputBuffer(encoder);
120    if (ret != NULL) {
121        ret-&gt;context = file;
122        ret-&gt;writecallback = xmlFileWrite;
123        ret-&gt;closecallback = NULL; /* No close callback */
124    }
125    return(ret);
Daniel Veillard96984452000-08-31 13:50:12 +0000[diff] [blame]126} </pre>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]127 </li>
128 <li>And then use it to save the document:
Daniel Veillard96984452000-08-31 13:50:12 +0000[diff] [blame]129 <pre>FILE *f;
Daniel Veillarda7ad4522000-08-31 14:19:54 +0000[diff] [blame]130xmlOutputBufferPtr output;
131xmlDocPtr doc;
Daniel Veillard96984452000-08-31 13:50:12 +0000[diff] [blame]132int res;
Daniel Veillarda7ad4522000-08-31 14:19:54 +0000[diff] [blame]133
Daniel Veillard96984452000-08-31 13:50:12 +0000[diff] [blame]134f = ...
135doc = ....
Daniel Veillard96984452000-08-31 13:50:12 +0000[diff] [blame]136
Daniel Veillarda7ad4522000-08-31 14:19:54 +0000[diff] [blame]137output = xmlOutputBufferCreateOwn(f, NULL);
138res = xmlSaveFileTo(output, doc, NULL);
Daniel Veillard96984452000-08-31 13:50:12 +0000[diff] [blame]139 </pre>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]140 </li>
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]141</ol><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html>