xml.html revision 9ae4b7afa98d1904d786f5e10db49ada8a2945ad
1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 2 "http://www.w3.org/TR/html4/loose.dtd"> 3<html> 4<head> 5 <title>The XML C library for Gnome</title> 6 <meta name="GENERATOR" content="amaya V5.0"> 7 <meta http-equiv="Content-Type" content="text/html"> 8</head> 9 10<body bgcolor="#ffffff"> 11<h1 align="center">The XML C library for Gnome</h1> 12 13<h1>Note: this is the flat content of the <a href="index.html">web 14site</a></h1> 15 16<h1 style="text-align: center">libxml, a.k.a. gnome-xml</h1> 17 18<p></p> 19 20<p>Libxml is the XML C library developped for the Gnome project. XML itself 21is a metalanguage to design markup languages, i.e. text language where 22semantic and structure are added to the content using extra "markup" 23information enclosed between angle bracket. HTML is the most well-known 24markup language.</p> 25 26<p>Libxml2 implements a number of existing standards related to markup 27languages:</p> 28<ul> 29 <li>the XML standard: <a 30 href="http://www.w3.org/TR/REC-xml">http://www.w3.org/TR/REC-xml</a></li> 31 <li>Namespaces in XML: <a 32 href="http://www.w3.org/TR/REC-xml-names/">http://www.w3.org/TR/REC-xml-names/</a></li> 33 <li>XML Base: <a 34 href="http://www.w3.org/TR/xmlbase/">http://www.w3.org/TR/xmlbase/</a></li> 35 <li><a href="http://www.cis.ohio-state.edu/rfc/rfc2396.txt">RFC 2396</a> 36 : Uniform Resource Identifiers <a 37 href="http://www.ietf.org/rfc/rfc2396.txt">http://www.ietf.org/rfc/rfc2396.txt</a></li> 38 <li>XML Path Language (XPath) 1.0: <a 39 href="http://www.w3.org/TR/xpath">http://www.w3.org/TR/xpath</a></li> 40 <li>HTML4 parser: <a 41 href="http://www.w3.org/TR/html401/">http://www.w3.org/TR/html401/</a></li> 42 <li>most of XML Pointer Language (XPointer) Version 1.0: <a 43 href="http://www.w3.org/TR/xptr">http://www.w3.org/TR/xptr</a></li> 44 <li>XML Inclusions (XInclude) Version 1.0: <a 45 href="http://www.w3.org/TR/xinclude/">http://www.w3.org/TR/xinclude/</a></li> 46 <li>[ISO-8859-1], <a 47 href="http://www.cis.ohio-state.edu/rfc/rfc2044.txt">rfc2044</a> [UTF-8] 48 and <a href="http://www.cis.ohio-state.edu/rfc/rfc2781.txt">rfc2781</a> 49 [UTF-16] core encodings</li> 50 <li>part of SGML Open Technical Resolution TR9401:1997</li> 51 <li>XML Catalogs Working Draft 06 August 2001: <a 52 href="http://www.oasis-open.org/committees/entity/spec-2001-08-06.html">http://www.oasis-open.org/committees/entity/spec-2001-08-06.html</a></li> 53</ul> 54 55<p>In most cases libxml tries to implement the specifications in a relatively 56strict way. To some extent libxml2 provide some support for the following 57other specification but don't claim to implement them:</p> 58<ul> 59 <li>Document Object Model (DOM) <a 60 href="http://www.w3.org/TR/DOM-Level-2-Core/">http://www.w3.org/TR/DOM-Level-2-Core/</a> 61 it doesn't implement the API itself, gdome2 does this in top of 62 libxml2</li> 63 <li><a href="http://www.cis.ohio-state.edu/rfc/rfc959.txt">RFC 959</a> 64 : libxml implements a basic FTP client code</li> 65 <li><a href="http://www.cis.ohio-state.edu/rfc/rfc1945.txt">RFC 1945</a> 66 : HTTP/1.0, again a basic HTTP client code</li> 67 <li>SAX: a minimal SAX implementation compatible with early expat 68 versions</li> 69 <li>DocBook SGML v4: libxml2 includes a hackish parser to transition to 70 XML</li> 71</ul> 72 73<p></p> 74 75<p>Separate documents:</p> 76<ul> 77 <li><a href="http://xmlsoft.org/XSLT/">the libxslt page</a> 78 providing an implementation of XSLT 1.0 and extensions on top of 79 libxml2</li> 80 <li><a href="http://www.cs.unibo.it/~casarini/gdome2/">the gdome2 page</a> 81 : a standard DOM2 implementation based on libxml2</li> 82</ul> 83 84<h2><a name="Introducti">Introduction</a></h2> 85 86<p>This document describes libxml, the <a 87href="http://www.w3.org/XML/">XML</a> C library developped for the <a 88href="http://www.gnome.org/">Gnome</a> project. <a 89href="http://www.w3.org/XML/">XML is a standard</a> for building tag-based 90structured documents/data.</p> 91 92<p>Here are some key points about libxml:</p> 93<ul> 94 <li>Libxml exports Push and Pull type parser interfaces for both XML and 95 HTML.</li> 96 <li>Libxml can do DTD validation at parse time, using a parsed document 97 instance, or with an arbitrary DTD.</li> 98 <li>Libxml now includes nearly complete <a 99 href="http://www.w3.org/TR/xpath">XPath</a>, <a 100 href="http://www.w3.org/TR/xptr">XPointer</a> and <a 101 href="http://www.w3.org/TR/xinclude">XInclude</a> implementations.</li> 102 <li>It is written in plain C, making as few assumptions as possible, and 103 sticking closely to ANSI C/POSIX for easy embedding. Works on 104 Linux/Unix/Windows, ported to a number of other platforms.</li> 105 <li>Basic support for HTTP and FTP client allowing aplications to fetch 106 remote resources</li> 107 <li>The design is modular, most of the extensions can be compiled out.</li> 108 <li>The internal document repesentation is as close as possible to the <a 109 href="http://www.w3.org/DOM/">DOM</a> interfaces.</li> 110 <li>Libxml also has a <a href="http://www.megginson.com/SAX/index.html">SAX 111 like interface</a>; the interface is designed to be compatible with <a 112 href="http://www.jclark.com/xml/expat.html">Expat</a>.</li> 113 <li>This library is released both under the <a 114 href="http://www.w3.org/Consortium/Legal/copyright-software-19980720.html">W3C 115 IPR</a> and the <a href="http://www.gnu.org/copyleft/lesser.html">GNU 116 LGPL</a>. Use either at your convenience, basically this should make 117 everybody happy, if not, drop me a mail.</li> 118</ul> 119 120<p>Warning: unless you are forced to because your application links with a 121Gnome library requiring it, <strong><span 122style="background-color: #FF0000">Do Not Use libxml1</span></strong>, use 123libxml2</p> 124 125<h2><a name="FAQ">FAQ</a></h2> 126 127<p>Table of Content:</p> 128<ul> 129 <li><a href="FAQ.html#Licence">Licence(s)</a></li> 130 <li><a href="FAQ.html#Installati">Installation</a></li> 131 <li><a href="FAQ.html#Compilatio">Compilation</a></li> 132 <li><a href="FAQ.html#Developer">Developer corner</a></li> 133</ul> 134 135<h3><a name="Licence">Licence</a>(s)</h3> 136<ol> 137 <li><em>Licensing Terms for libxml</em> 138 <p>libxml is released under 2 (compatible) licences:</p> 139 <ul> 140 <li>the <a href="http://www.gnu.org/copyleft/lgpl.html">LGPL</a>: GNU 141 Library General Public License</li> 142 <li>the <a 143 href="http://www.w3.org/Consortium/Legal/copyright-software-19980720.html">W3C 144 IPR</a>: very similar to the XWindow licence</li> 145 </ul> 146 </li> 147 <li><em>Can I embed libxml in a proprietary application ?</em> 148 <p>Yes. The W3C IPR allows you to also keep proprietary the changes you 149 made to libxml, but it would be graceful to provide back bugfixes and 150 improvements as patches for possible incorporation in the main 151 development tree</p> 152 </li> 153</ol> 154 155<h3><a name="Installati">Installation</a></h3> 156<ol> 157 <li>Unless you are forced to because your application links with a Gnome 158 library requiring it, <strong><span style="background-color: #FF0000">Do 159 Not Use libxml1</span></strong>, use libxml2</li> 160 <li><em>Where can I get libxml</em> 161 ? 162 <p>The original distribution comes from <a 163 href="ftp://rpmfind.net/pub/libxml/">rpmfind.net</a> or <a 164 href="ftp://ftp.gnome.org/pub/GNOME/stable/sources/libxml/">gnome.org</a></p> 165 <p>Most linux and Bsd distribution includes libxml, this is probably the 166 safer way for end-users</p> 167 <p>David Doolin provides precompiled Windows versions at <a 168 href="http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/ ">http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/</a></p> 169 </li> 170 <li><em>I see libxml and libxml2 releases, which one should I install ?</em> 171 <ul> 172 <li>If you are not concerned by any existing backward compatibility 173 with existing application, install libxml2 only</li> 174 <li>If you are not doing development, you can safely install both. 175 usually the packages <a 176 href="http://rpmfind.net/linux/RPM/libxml.html">libxml</a> and <a 177 href="http://rpmfind.net/linux/RPM/libxml2.html">libxml2</a> are 178 compatible (this is not the case for development packages)</li> 179 <li>If you are a developer and your system provides separate packaging 180 for shared libraries and the development components, it is possible 181 to install libxml and libxml2, and also <a 182 href="http://rpmfind.net/linux/RPM/libxml-devel.html">libxml-devel</a> 183 and <a 184 href="http://rpmfind.net/linux/RPM/libxml2-devel.html">libxml2-devel</a> 185 too for libxml2 >= 2.3.0</li> 186 <li>If you are developing a new application, please develop against 187 libxml2(-devel)</li> 188 </ul> 189 </li> 190 <li><em>I can't install the libxml package it conflicts with libxml0</em> 191 <p>You probably have an old libxml0 package used to provide the shared 192 library for libxml.so.0, you can probably safely remove it. Anyway the 193 libxml packages provided on <a 194 href="ftp://rpmfind.net/pub/libxml/">rpmfind.net</a> provides 195 libxml.so.0</p> 196 </li> 197 <li><em>I can't install the libxml(2) RPM package due to failed 198 dependancies</em> 199 <p>The most generic solution is to refetch the latest src.rpm , and 200 rebuild it locally with</p> 201 <p><code>rpm --rebuild libxml(2)-xxx.src.rpm</code></p> 202 <p>if everything goes well it will generate two binary rpm (one providing 203 the shared libs and xmllint, and the other one, the -devel package 204 providing includes, static libraries and scripts needed to build 205 applications with libxml(2)) that you can install locally.</p> 206 </li> 207</ol> 208 209<h3><a name="Compilatio">Compilation</a></h3> 210<ol> 211 <li><em>What is the process to compile libxml ?</em> 212 <p>As most UNIX libraries libxml follows the "standard":</p> 213 <p><code>gunzip -c xxx.tar.gz | tar xvf -</code></p> 214 <p><code>cd libxml-xxxx</code></p> 215 <p><code>/configure --help</code></p> 216 <p>to see the options, then the compilation/installation proper</p> 217 <p><code>/configure [possible options]</code></p> 218 <p><code>make</code></p> 219 <p><code>make install</code></p> 220 <p>At that point you may have to rerun ldconfig or similar utility to 221 update your list of installed shared libs.</p> 222 </li> 223 <li><em>What other libraries are needed to compile/install libxml ?</em> 224 <p>Libxml does not requires any other library, the normal C ANSI API 225 should be sufficient (please report any violation to this rule you may 226 find).</p> 227 <p>However if found at configuration time libxml will detect and use the 228 following libs:</p> 229 <ul> 230 <li><a href="http://www.info-zip.org/pub/infozip/zlib/">libz</a> 231 : a highly portable and available widely compression library</li> 232 <li>iconv: a powerful character encoding conversion library. It's 233 included by default on recent glibc libraries, so it doesn't need to 234 be installed specifically on linux. It seems it's now <a 235 href="http://www.opennc.org/onlinepubs/7908799/xsh/iconv.html">part 236 of the official UNIX</a> specification. Here is one <a 237 href="http://clisp.cons.org/~haible/packages-libiconv.html">implementation 238 of the library</a> which source can be found <a 239 href="ftp://ftp.ilog.fr/pub/Users/haible/gnu/">here</a>.</li> 240 </ul> 241 </li> 242 <li><em>make check fails on some platforms</em> 243 <p>Sometime the regression tests results don't completely match the value 244 produced by the parser, and the makefile uses diff to print the delta. On 245 some platforms the diff return breaks the compilation process, if the 246 diff is small this is probably not a serious problem</p> 247 </li> 248 <li><em>I use the CVS version and there is no configure script</em> 249 <p>The configure (and other Makefiles) are generated. Use the autogen.sh 250 script to regenerate the configure and Makefiles, like:</p> 251 <p><code>/autogen.sh --prefix=/usr --disable-shared</code></p> 252 </li> 253 <li><em>I have troubles when running make tests with gcc-3.0</em> 254 <p>It seems the initial release of gcc-3.0 has a problem with the 255 optimizer which miscompiles the URI module. Please use another 256 compiler</p> 257 </li> 258</ol> 259 260<h3><a name="Developer">Developer</a> corner</h3> 261<ol> 262 <li><em>xmlDocDump() generates output on one line</em> 263 <p>libxml will not <strong>invent</strong> spaces in the content of a 264 document since <strong>all spaces in the content of a document are 265 significant</strong>. If you build a tree from the API and want 266 indentation:</p> 267 <ol> 268 <li>the correct way is to generate those yourself too</li> 269 <li>the dangerous way is to ask libxml to add those blanks to your 270 content <strong>modifying the content of your document in the 271 process</strong>. The result may not be what you expect. There is 272 <strong>NO</strong> way to guarantee that such a modification won't 273 impact other part of the content of your document. See <a 274 href="http://xmlsoft.org/html/libxml-parser.html#XMLKEEPBLANKSDEFAULT">xmlKeepBlanksDefault 275 ()</a> and <a 276 href="http://xmlsoft.org/html/libxml-tree.html#XMLSAVEFORMATFILE">xmlSaveFormatFile 277 ()</a></li> 278 </ol> 279 </li> 280 <li>Extra nodes in the document: 281 <p><em>For a XML file as below:</em></p> 282 <pre><?xml version="1.0"?> 283<PLAN xmlns="http://www.argus.ca/autotest/1.0/"> 284<NODE CommFlag="0"/> 285<NODE CommFlag="1"/> 286</PLAN></pre> 287 <p><em>after parsing it with the function 288 pxmlDoc=xmlParseFile(...);</em></p> 289 <p><em>I want to the get the content of the first node (node with the 290 CommFlag="0")</em></p> 291 <p><em>so I did it as following;</em></p> 292 <pre>xmlNodePtr pode; 293pnode=pxmlDoc->children->children;</pre> 294 <p><em>but it does not work. If I change it to</em></p> 295 <pre>pnode=pxmlDoc->children->children->next;</pre> 296 <p><em>then it works. Can someone explain it to me.</em></p> 297 <p></p> 298 <p>In XML all characters in the content of the document are significant 299 <strong>including blanks and formatting line breaks</strong>.</p> 300 <p>The extra nodes you are wondering about are just that, text nodes with 301 the formatting spaces wich are part of the document but that people tend 302 to forget. There is a function <a 303 href="http://xmlsoft.org/html/libxml-parser.html">xmlKeepBlanksDefault 304 ()</a> to remove those at parse time, but that's an heuristic, and its 305 use should be limited to case where you are sure there is no 306 mixed-content in the document.</p> 307 </li> 308 <li><em>I get compilation errors of existing code like when accessing 309 <strong>root</strong> or <strong>childs fields</strong> of nodes</em> 310 <p>You are compiling code developed for libxml version 1 and using a 311 libxml2 development environment. Either switch back to libxml v1 devel or 312 even better fix the code to compile with libxml2 (or both) by <a 313 href="upgrade.html">following the instructions</a>.</p> 314 </li> 315 <li><em>I get compilation errors about non existing 316 <strong>xmlRootNode</strong> or <strong>xmlChildrenNode</strong> 317 fields</em> 318 <p>The source code you are using has been <a 319 href="upgrade.html">upgraded</a> to be able to compile with both libxml 320 and libxml2, but you need to install a more recent version: 321 libxml(-devel) >= 1.8.8 or libxml2(-devel) >= 2.1.0</p> 322 </li> 323 <li><em>XPath implementation looks seriously broken</em> 324 <p>XPath implementation prior to 2.3.0 was really incomplete, upgrade to 325 a recent version, the implementation and debug of libxslt generated fixes 326 for most obvious problems.</p> 327 </li> 328 <li><em>The example provided in the web page does not compile</em> 329 <p>It's hard to maintain the documentation in sync with the code 330 <grin/> ...</p> 331 <p>Check the previous points 1/ and 2/ raised before, and send 332 patches.</p> 333 </li> 334 <li><em>Where can I get more examples and informations than in the web 335 page</em> 336 <p>Ideally a libxml book would be nice. I have no such plan ... But you 337 can:</p> 338 <ul> 339 <li>check more deeply the <a href="html/libxml-lib.html">existing 340 generated doc</a></li> 341 <li>looks for examples of use for libxml function using the Gnome code 342 for example the following will query the full Gnome CVs base for the 343 use of the <strong>xmlAddChild()</strong> function: 344 <p><a 345 href="http://cvs.gnome.org/lxr/search?string=xmlAddChild">http://cvs.gnome.org/lxr/search?string=xmlAddChild</a></p> 346 <p>This may be slow, a large hardware donation to the gnome project 347 could cure this :-)</p> 348 </li> 349 <li><a 350 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gnome-xml">Browse 351 the libxml source</a> 352 , I try to write code as clean and documented as possible, so 353 looking at it may be helpful</li> 354 </ul> 355 </li> 356 <li>What about C++ ? 357 <p>libxml is written in pure C in order to allow easy reuse on a number 358 of platforms, including embedded systems. I don't intend to convert to 359 C++.</p> 360 <p>There is however a C++ wrapper provided by Ari Johnson 361 <ari@btigate.com> which may fullfill your needs:</p> 362 <p>Website: <a 363 href="http://lusis.org/~ari/xml++/">http://lusis.org/~ari/xml++/</a></p> 364 <p>Download: <a 365 href="http://lusis.org/~ari/xml++/libxml++.tar.gz">http://lusis.org/~ari/xml++/libxml++.tar.gz</a></p> 366 </li> 367 <li>How to validate a document a posteriori ? 368 <p>It is possible to validate documents which had not been validated at 369 initial parsing time or documents who have been built from scratch using 370 the API. Use the <a 371 href="http://xmlsoft.org/html/libxml-valid.html#XMLVALIDATEDTD">xmlValidateDtd()</a> 372 function. It is also possible to simply add a Dtd to an existing 373 document:</p> 374 <pre>xmlDocPtr doc; /* your existing document */ 375 xmlDtdPtr dtd = xmlParseDTD(NULL, filename_of_dtd); /* parse the DTD */ 376 dtd->name = xmlStrDup((xmlChar*)"root_name"); /* use the given root */ 377 378 doc->intSubset = dtd; 379 if (doc->children == NULL) xmlAddChild((xmlNodePtr)doc, (xmlNodePtr)dtd); 380 else xmlAddPrevSibling(doc->children, (xmlNodePtr)dtd); 381 </pre> 382 </li> 383 <li>etc ...</li> 384</ol> 385 386<p></p> 387 388<h2><a name="Documentat">Documentation</a></h2> 389 390<p>There are some on-line resources about using libxml:</p> 391<ol> 392 <li>Check the <a href="FAQ.html">FAQ</a></li> 393 <li>Check the <a href="http://xmlsoft.org/html/libxml-lib.html">extensive 394 documentation</a> automatically extracted from code comments (using <a 395 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gtk-doc">gtk 396 doc</a>).</li> 397 <li>Look at the documentation about <a href="encoding.html">libxml 398 internationalization support</a></li> 399 <li>This page provides a global overview and <a href="#real">some 400 examples</a> on how to use libxml.</li> 401 <li><a href="mailto:james@daa.com.au">James Henstridge</a> 402 wrote <a 403 href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">some nice 404 documentation</a> explaining how to use the libxml SAX interface.</li> 405 <li>George Lebl wrote <a 406 href="http://www-4.ibm.com/software/developer/library/gnome3/">an article 407 for IBM developerWorks</a> about using libxml.</li> 408 <li>Check <a href="http://cvs.gnome.org/lxr/source/gnome-xml/TODO">the TODO 409 file</a></li> 410 <li>Read the <a href="upgrade.html">1.x to 2.x upgrade path</a>. If you are 411 starting a new project using libxml you should really use the 2.x 412 version.</li> 413 <li>And don't forget to look at the <a href="/messages/">mailing-list 414 archive</a>.</li> 415</ol> 416 417<h2><a name="Reporting">Reporting bugs and getting help</a></h2> 418 419<p>Well, bugs or missing features are always possible, and I will make a 420point of fixing them in a timely fashion. The best way to report a bug is to 421use the <a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Gnome 422bug tracking database</a> (make sure to use the "libxml" module name). I look 423at reports there regularly and it's good to have a reminder when a bug is 424still open. Be sure to specify that the bug is for the package libxml.</p> 425 426<p>There is also a mailing-list <a 427href="mailto:xml@gnome.org">xml@gnome.org</a> for libxml, with an <a 428href="http://mail.gnome.org/archives/xml/">on-line archive</a> (<a 429href="http://xmlsoft.org/messages">old</a>). To subscribe to this list, 430please visit the <a 431href="http://mail.gnome.org/mailman/listinfo/xml">associated Web</a> page and 432follow the instructions. <strong>Do not send code, I won't debug it</strong> 433(but patches are really appreciated!).</p> 434 435<p>Check the following <strong><span style="color: #FF0000">before 436posting</span></strong>:</p> 437<ul> 438 <li>read the <a href="FAQ.html">FAQ</a></li> 439 <li>make sure you are <a href="ftp://xmlsoft.org/">using a recent 440 version</a>, and that the problem still shows up in those</li> 441 <li>check the <a href="http://mail.gnome.org/archives/xml/">list 442 archives</a> to see if the problem was reported already, in this case 443 there is probably a fix available, similary check the <a 444 href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">registered 445 open bugs</a></li> 446 <li>make sure you can reproduce the bug with xmllint or one of the test 447 programs found in source in the distribution</li> 448 <li>Please send the command showing the error as well as the input (as an 449 attachement)</li> 450</ul> 451 452<p>Then send the bug with associated informations to reproduce it to the <a 453href="mailto:xml@gnome.org">xml@gnome.org</a> list; if it's really libxml 454related I will approve it.. Please do not send me mail directly, it makes 455things really harder to track and in some cases I'm not the best person to 456answer a given question, ask the list instead.</p> 457 458<p>Of course, bugs reported with a suggested patch for fixing them will 459probably be processed faster.</p> 460 461<p>If you're looking for help, a quick look at <a 462href="http://mail.gnome.org/archives/xml/">the list archive</a> may actually 463provide the answer, I usually send source samples when answering libxml usage 464questions. The <a href="http://xmlsoft.org/html/book1.html">auto-generated 465documentantion</a> is not as polished as I would like (i need to learn more 466about Docbook), but it's a good starting point.</p> 467 468<h2><a name="help">How to help</a></h2> 469 470<p>You can help the project in various ways, the best thing to do first is to 471subscribe to the mailing-list as explained before, check the <a 472href="http://mail.gnome.org/archives/xml/">archives </a>and the <a 473href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Gnome bug 474database:</a>:</p> 475<ol> 476 <li>provide patches when you find problems</li> 477 <li>provide the diffs when you port libxml to a new platform. They may not 478 be integrated in all cases but help pinpointing portability problems 479 and</li> 480 <li>provide documentation fixes (either as patches to the code comments or 481 as HTML diffs).</li> 482 <li>provide new documentations pieces (translations, examples, etc ...)</li> 483 <li>Check the TODO file and try to close one of the items</li> 484 <li>take one of the points raised in the archive or the bug database and 485 provide a fix. <a href="mailto:daniel@veillard.com">Get in touch with me 486 </a>before to avoid synchronization problems and check that the suggested 487 fix will fit in nicely :-)</li> 488</ol> 489 490<h2><a name="Downloads">Downloads</a></h2> 491 492<p>The latest versions of libxml can be found on <a 493href="ftp://xmlsoft.org/">xmlsoft.org</a> (<a 494href="ftp://speakeasy.rpmfind.net/pub/libxml/">Seattle</a>, <a 495href="ftp://fr.rpmfind.net/pub/libxml/">France</a>) or on the <a 496href="ftp://ftp.gnome.org/pub/GNOME/MIRRORS.html">Gnome FTP server</a> either 497as a <a href="ftp://ftp.gnome.org/pub/GNOME/stable/sources/libxml/">source 498archive</a> or <a 499href="ftp://ftp.gnome.org/pub/GNOME/stable/redhat/i386/libxml/">RPM 500packages</a>. (NOTE that you need both the <a 501href="http://rpmfind.net/linux/RPM/libxml2.html">libxml(2)</a> and <a 502href="http://rpmfind.net/linux/RPM/libxml2-devel.html">libxml(2)-devel</a> 503packages installed to compile applications using libxml.) <a 504href="mailto:izlatkovic@daenet.de">Igor Zlatkovic</a> is now the maintainer 505of the Windows port, <a 506href="http://www.fh-frankfurt.de/~igor/projects/libxml/index.html">he 507provides binaries</a>. <a href="mailto:Gary.Pennington@sun.com">Gary 508Pennington</a> provides <a href="http://garypennington.net/libxml2/">Solaris 509binaries</a>.</p> 510 511<p><a name="Snapshot">Snapshot:</a></p> 512<ul> 513 <li>Code from the W3C cvs base libxml <a 514 href="ftp://xmlsoft.org/cvs-snapshot.tar.gz">cvs-snapshot.tar.gz</a></li> 515 <li>Docs, content of the web site, the list archive included <a 516 href="ftp://xmlsoft.org/libxml-docs.tar.gz">libxml-docs.tar.gz</a></li> 517</ul> 518 519<p><a name="Contribs">Contributions:</a></p> 520 521<p>I do accept external contributions, especially if compiling on another 522platform, get in touch with me to upload the package, wrappers for various 523languages have been provided, and can be found in the <a 524href="contribs.html">contrib section</a></p> 525 526<p>Libxml is also available from CVS:</p> 527<ul> 528 <li><p>The <a 529 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gnome-xml">Gnome 530 CVS base</a>. Check the <a 531 href="http://developer.gnome.org/tools/cvs.html">Gnome CVS Tools</a> 532 page; the CVS module is <b>gnome-xml</b>.</p> 533 </li> 534 <li>The <strong>libxslt</strong> module is also present there</li> 535</ul> 536 537<h2><a name="News">News</a></h2> 538 539<h3>CVS only : check the <a 540href="http://cvs.gnome.org/lxr/source/gnome-xml/ChangeLog">Changelog</a> file 541for a really accurate description</h3> 542 543<p>Items floating around but not actively worked on, get in touch with me if 544you want to test those</p> 545<ul> 546 <li>Implementing <a href="http://xmlsoft.org/XSLT">XSLT</a>, this is done 547 as a separate C library on top of libxml called libxslt</li> 548 <li>Finishing up <a href="http://www.w3.org/TR/xptr">XPointer</a> and <a 549 href="http://www.w3.org/TR/xinclude">XInclude</a></li> 550 <li>(seeems working but delayed from release) parsing/import of Docbook 551 SGML docs</li> 552</ul> 553 554<h3>2.4.12: Dec 7 2001</h3> 555<ul> 556 <li>a few bug fixes: thread (Gary Pennington), xmllint (Geert Kloosterman), 557 XML parser (Robin Berjon), XPointer (Danny Jamshy), I/O cleanups 558 (robert)</li> 559 <li>Eric Lavigne contributed project files for MacOS</li> 560 <li>some makefiles cleanups</li> 561</ul> 562 563<h3>2.4.11: Nov 26 2001</h3> 564<ul> 565 <li>fixed a couple of errors in the includes, fixed a few bugs, some code 566 cleanups</li> 567 <li>xmllint man pages improvement by Heiko Rupp</li> 568 <li>updated VMS build instructions from John A Fotheringham</li> 569 <li>Windows Makefiles updates from Igor</li> 570</ul> 571 572<h3>2.4.10: Nov 10 2001</h3> 573<ul> 574 <li>URI escaping fix (Joel Young)</li> 575 <li>added xmlGetNodePath() (for paths or XPointers generation)</li> 576 <li>Fixes namespace handling problems when using DTD and validation</li> 577 <li>improvements on xmllint: Morus Walter patches for --format and 578 --encode, Stefan Kost and Heiko Rupp improvements on the --shell</li> 579 <li>fixes for xmlcatalog linking pointed by Weiqi Gao</li> 580 <li>fixes to the HTML parser</li> 581</ul> 582 583<h3>2.4.9: Nov 6 2001</h3> 584<ul> 585 <li>fixes more catalog bugs</li> 586 <li>avoid a compilation problem, improve xmlGetLineNo()</li> 587</ul> 588 589<h3>2.4.8: Nov 4 2001</h3> 590<ul> 591 <li>fixed SGML catalogs broken in previous release, updated xmlcatalog 592 tool</li> 593 <li>fixed a compile errors and some includes troubles.</li> 594</ul> 595 596<h3>2.4.7: Oct 30 2001</h3> 597<ul> 598 <li>exported some debugging interfaces</li> 599 <li>serious rewrite of the catalog code</li> 600 <li>integrated Gary Pennington thread safety patch, added configure option 601 and regression tests</li> 602 <li>removed an HTML parser bug</li> 603 <li>fixed a couple of potentially serious validation bugs</li> 604 <li>integrated the SGML DocBook support in xmllint</li> 605 <li>changed the nanoftp anonymous login passwd</li> 606 <li>some I/O cleanup and a couple of interfaces for Perl wrapper</li> 607 <li>general bug fixes</li> 608 <li>updated xmllint man page by John Fleck</li> 609 <li>some VMS and Windows updates</li> 610</ul> 611 612<h3>2.4.6: Oct 10 2001</h3> 613<ul> 614 <li>added an updated man pages by John Fleck</li> 615 <li>portability and configure fixes</li> 616 <li>an infinite loop on the HTML parser was removed (William)</li> 617 <li>Windows makefile patches from Igor</li> 618 <li>fixed half a dozen bugs reported fof libxml or libxslt</li> 619 <li>updated xmlcatalog to be able to modify SGML super catalogs</li> 620</ul> 621 622<h3>2.4.5: Sep 14 2001</h3> 623<ul> 624 <li>Remove a few annoying bugs in 2.4.4</li> 625 <li>forces the HTML serializer to output decimal charrefs since some 626 version of Netscape can't handle hexadecimal ones</li> 627</ul> 628 629<h3>1.8.16: Sep 14 2001</h3> 630<ul> 631 <li>maintenance release of the old libxml1 branch, couple of bug and 632 portability fixes</li> 633</ul> 634 635<h3>2.4.4: Sep 12 2001</h3> 636<ul> 637 <li>added --convert to xmlcatalog, bug fixes and cleanups of XML 638 Catalog</li> 639 <li>a few bug fixes and some portability changes</li> 640 <li>some documentation cleanups</li> 641</ul> 642 643<h3>2.4.3: Aug 23 2001</h3> 644<ul> 645 <li>XML Catalog support see the doc</li> 646 <li>New NaN/Infinity floating point code</li> 647 <li>A few bug fixes</li> 648</ul> 649 650<h3>2.4.2: Aug 15 2001</h3> 651<ul> 652 <li>adds xmlLineNumbersDefault() to control line number generation</li> 653 <li>lot of bug fixes</li> 654 <li>the Microsoft MSC projects files shuld now be up to date</li> 655 <li>inheritance of namespaces from DTD defaulted attributes</li> 656 <li>fixes a serious potential security bug</li> 657 <li>added a --format option to xmllint</li> 658</ul> 659 660<h3>2.4.1: July 24 2001</h3> 661<ul> 662 <li>possibility to keep line numbers in the tree</li> 663 <li>some computation NaN fixes</li> 664 <li>extension of the XPath API</li> 665 <li>cleanup for alpha and ia64 targets</li> 666 <li>patch to allow saving through HTTP PUT or POST</li> 667</ul> 668 669<h3>2.4.0: July 10 2001</h3> 670<ul> 671 <li>Fixed a few bugs in XPath, validation, and tree handling.</li> 672 <li>Fixed XML Base implementation, added a coupel of examples to the 673 regression tests</li> 674 <li>A bit of cleanup</li> 675</ul> 676 677<h3>2.3.14: July 5 2001</h3> 678<ul> 679 <li>fixed some entities problems and reduce mem requirement when 680 substituing them</li> 681 <li>lots of improvements in the XPath queries interpreter can be 682 substancially faster</li> 683 <li>Makefiles and configure cleanups</li> 684 <li>Fixes to XPath variable eval, and compare on empty node set</li> 685 <li>HTML tag closing bug fixed</li> 686 <li>Fixed an URI reference computating problem when validating</li> 687</ul> 688 689<h3>2.3.13: June 28 2001</h3> 690<ul> 691 <li>2.3.12 configure.in was broken as well as the push mode XML parser</li> 692 <li>a few more fixes for compilation on Windows MSC by Yon Derek</li> 693</ul> 694 695<h3>1.8.14: June 28 2001</h3> 696<ul> 697 <li>Zbigniew Chyla gave a patch to use the old XML parser in push mode</li> 698 <li>Small Makefile fix</li> 699</ul> 700 701<h3>2.3.12: June 26 2001</h3> 702<ul> 703 <li>lots of cleanup</li> 704 <li>a couple of validation fix</li> 705 <li>fixed line number counting</li> 706 <li>fixed serious problems in the XInclude processing</li> 707 <li>added support for UTF8 BOM at beginning of entities</li> 708 <li>fixed a strange gcc optimizer bugs in xpath handling of float, gcc-3.0 709 miscompile uri.c (William), Thomas Leitner provided a fix for the 710 optimizer on Tru64</li> 711 <li>incorporated Yon Derek and Igor Zlatkovic fixes and improvements for 712 compilation on Windows MSC</li> 713 <li>update of libxml-doc.el (Felix Natter)</li> 714 <li>fixed 2 bugs in URI normalization code</li> 715</ul> 716 717<h3>2.3.11: June 17 2001</h3> 718<ul> 719 <li>updates to trio, Makefiles and configure should fix some portability 720 problems (alpha)</li> 721 <li>fixed some HTML serialization problems (pre, script, and block/inline 722 handling), added encoding aware APIs, cleanup of this code</li> 723 <li>added xmlHasNsProp()</li> 724 <li>implemented a specific PI for encoding support in the DocBook SGML 725 parser</li> 726 <li>some XPath fixes (-Infinity, / as a function parameter and namespaces 727 node selection)</li> 728 <li>fixed a performance problem and an error in the validation code</li> 729 <li>fixed XInclude routine to implement the recursive behaviour</li> 730 <li>fixed xmlFreeNode problem when libxml is included statically twice</li> 731 <li>added --version to xmllint for bug reports</li> 732</ul> 733 734<h3>2.3.10: June 1 2001</h3> 735<ul> 736 <li>fixed the SGML catalog support</li> 737 <li>a number of reported bugs got fixed, in XPath, iconv detection, 738 XInclude processing</li> 739 <li>XPath string function should now handle unicode correctly</li> 740</ul> 741 742<h3>2.3.9: May 19 2001</h3> 743 744<p>Lots of bugfixes, and added a basic SGML catalog support:</p> 745<ul> 746 <li>HTML push bugfix #54891 and another patch from Jonas Borgstr�m</li> 747 <li>some serious speed optimisation again</li> 748 <li>some documentation cleanups</li> 749 <li>trying to get better linking on solaris (-R)</li> 750 <li>XPath API cleanup from Thomas Broyer</li> 751 <li>Validation bug fixed #54631, added a patch from Gary Pennington, fixed 752 xmlValidGetValidElements()</li> 753 <li>Added an INSTALL file</li> 754 <li>Attribute removal added to API: #54433</li> 755 <li>added a basic support for SGML catalogs</li> 756 <li>fixed xmlKeepBlanksDefault(0) API</li> 757 <li>bugfix in xmlNodeGetLang()</li> 758 <li>fixed a small configure portability problem</li> 759 <li>fixed an inversion of SYSTEM and PUBLIC identifier in HTML document</li> 760</ul> 761 762<h3>1.8.13: May 14 2001</h3> 763<ul> 764 <li>bugfixes release of the old libxml1 branch used by Gnome</li> 765</ul> 766 767<h3>2.3.8: May 3 2001</h3> 768<ul> 769 <li>Integrated an SGML DocBook parser for the Gnome project</li> 770 <li>Fixed a few things in the HTML parser</li> 771 <li>Fixed some XPath bugs raised by XSLT use, tried to fix the floating 772 point portability issue</li> 773 <li>Speed improvement (8M/s for SAX, 3M/s for DOM, 1.5M/s for 774 DOM+validation using the XML REC as input and a 700MHz celeron).</li> 775 <li>incorporated more Windows cleanup</li> 776 <li>added xmlSaveFormatFile()</li> 777 <li>fixed problems in copying nodes with entities references (gdome)</li> 778 <li>removed some troubles surrounding the new validation module</li> 779</ul> 780 781<h3>2.3.7: April 22 2001</h3> 782<ul> 783 <li>lots of small bug fixes, corrected XPointer</li> 784 <li>Non determinist content model validation support</li> 785 <li>added xmlDocCopyNode for gdome2</li> 786 <li>revamped the way the HTML parser handles end of tags</li> 787 <li>XPath: corrctions of namespacessupport and number formatting</li> 788 <li>Windows: Igor Zlatkovic patches for MSC compilation</li> 789 <li>HTML ouput fixes from P C Chow and William M. Brack</li> 790 <li>Improved validation speed sensible for DocBook</li> 791 <li>fixed a big bug with ID declared in external parsed entities</li> 792 <li>portability fixes, update of Trio from Bjorn Reese</li> 793</ul> 794 795<h3>2.3.6: April 8 2001</h3> 796<ul> 797 <li>Code cleanup using extreme gcc compiler warning options, found and 798 cleared half a dozen potential problem</li> 799 <li>the Eazel team found an XML parser bug</li> 800 <li>cleaned up the user of some of the string formatting function. used the 801 trio library code to provide the one needed when the platform is missing 802 them</li> 803 <li>xpath: removed a memory leak and fixed the predicate evaluation 804 problem, extended the testsuite and cleaned up the result. XPointer seems 805 broken ...</li> 806</ul> 807 808<h3>2.3.5: Mar 23 2001</h3> 809<ul> 810 <li>Biggest change is separate parsing and evaluation of XPath expressions, 811 there is some new APIs for this too</li> 812 <li>included a number of bug fixes(XML push parser, 51876, notations, 813 52299)</li> 814 <li>Fixed some portability issues</li> 815</ul> 816 817<h3>2.3.4: Mar 10 2001</h3> 818<ul> 819 <li>Fixed bugs #51860 and #51861</li> 820 <li>Added a global variable xmlDefaultBufferSize to allow default buffer 821 size to be application tunable.</li> 822 <li>Some cleanup in the validation code, still a bug left and this part 823 should probably be rewritten to support ambiguous content model :-\</li> 824 <li>Fix a couple of serious bugs introduced or raised by changes in 2.3.3 825 parser</li> 826 <li>Fixed another bug in xmlNodeGetContent()</li> 827 <li>Bjorn fixed XPath node collection and Number formatting</li> 828 <li>Fixed a loop reported in the HTML parsing</li> 829 <li>blank space are reported even if the Dtd content model proves that they 830 are formatting spaces, this is for XmL conformance</li> 831</ul> 832 833<h3>2.3.3: Mar 1 2001</h3> 834<ul> 835 <li>small change in XPath for XSLT</li> 836 <li>documentation cleanups</li> 837 <li>fix in validation by Gary Pennington</li> 838 <li>serious parsing performances improvements</li> 839</ul> 840 841<h3>2.3.2: Feb 24 2001</h3> 842<ul> 843 <li>chasing XPath bugs, found a bunch, completed some TODO</li> 844 <li>fixed a Dtd parsing bug</li> 845 <li>fixed a bug in xmlNodeGetContent</li> 846 <li>ID/IDREF support partly rewritten by Gary Pennington</li> 847</ul> 848 849<h3>2.3.1: Feb 15 2001</h3> 850<ul> 851 <li>some XPath and HTML bug fixes for XSLT</li> 852 <li>small extension of the hash table interfaces for DOM gdome2 853 implementation</li> 854 <li>A few bug fixes</li> 855</ul> 856 857<h3>2.3.0: Feb 8 2001 (2.2.12 was on 25 Jan but I didn't kept track)</h3> 858<ul> 859 <li>Lots of XPath bug fixes</li> 860 <li>Add a mode with Dtd lookup but without validation error reporting for 861 XSLT</li> 862 <li>Add support for text node without escaping (XSLT)</li> 863 <li>bug fixes for xmlCheckFilename</li> 864 <li>validation code bug fixes from Gary Pennington</li> 865 <li>Patch from Paul D. Smith correcting URI path normalization</li> 866 <li>Patch to allow simultaneous install of libxml-devel and 867 libxml2-devel</li> 868 <li>the example Makefile is now fixed</li> 869 <li>added HTML to the RPM packages</li> 870 <li>tree copying bugfixes</li> 871 <li>updates to Windows makefiles</li> 872 <li>optimisation patch from Bjorn Reese</li> 873</ul> 874 875<h3>2.2.11: Jan 4 2001</h3> 876<ul> 877 <li>bunch of bug fixes (memory I/O, xpath, ftp/http, ...)</li> 878 <li>added htmlHandleOmittedElem()</li> 879 <li>Applied Bjorn Reese's IPV6 first patch</li> 880 <li>Applied Paul D. Smith patches for validation of XInclude results</li> 881 <li>added XPointer xmlns() new scheme support</li> 882</ul> 883 884<h3>2.2.10: Nov 25 2000</h3> 885<ul> 886 <li>Fix the Windows problems of 2.2.8</li> 887 <li>integrate OpenVMS patches</li> 888 <li>better handling of some nasty HTML input</li> 889 <li>Improved the XPointer implementation</li> 890 <li>integrate a number of provided patches</li> 891</ul> 892 893<h3>2.2.9: Nov 25 2000</h3> 894<ul> 895 <li>erroneous release :-(</li> 896</ul> 897 898<h3>2.2.8: Nov 13 2000</h3> 899<ul> 900 <li>First version of <a href="http://www.w3.org/TR/xinclude">XInclude</a> 901 support</li> 902 <li>Patch in conditional section handling</li> 903 <li>updated MS compiler project</li> 904 <li>fixed some XPath problems</li> 905 <li>added an URI escaping function</li> 906 <li>some other bug fixes</li> 907</ul> 908 909<h3>2.2.7: Oct 31 2000</h3> 910<ul> 911 <li>added message redirection</li> 912 <li>XPath improvements (thanks TOM !)</li> 913 <li>xmlIOParseDTD() added</li> 914 <li>various small fixes in the HTML, URI, HTTP and XPointer support</li> 915 <li>some cleanup of the Makefile, autoconf and the distribution content</li> 916</ul> 917 918<h3>2.2.6: Oct 25 2000:</h3> 919<ul> 920 <li>Added an hash table module, migrated a number of internal structure to 921 those</li> 922 <li>Fixed a posteriori validation problems</li> 923 <li>HTTP module cleanups</li> 924 <li>HTML parser improvements (tag errors, script/style handling, attribute 925 normalization)</li> 926 <li>coalescing of adjacent text nodes</li> 927 <li>couple of XPath bug fixes, exported the internal API</li> 928</ul> 929 930<h3>2.2.5: Oct 15 2000:</h3> 931<ul> 932 <li>XPointer implementation and testsuite</li> 933 <li>Lot of XPath fixes, added variable and functions registration, more 934 tests</li> 935 <li>Portability fixes, lots of enhancements toward an easy Windows build 936 and release</li> 937 <li>Late validation fixes</li> 938 <li>Integrated a lot of contributed patches</li> 939 <li>added memory management docs</li> 940 <li>a performance problem when using large buffer seems fixed</li> 941</ul> 942 943<h3>2.2.4: Oct 1 2000:</h3> 944<ul> 945 <li>main XPath problem fixed</li> 946 <li>Integrated portability patches for Windows</li> 947 <li>Serious bug fixes on the URI and HTML code</li> 948</ul> 949 950<h3>2.2.3: Sep 17 2000</h3> 951<ul> 952 <li>bug fixes</li> 953 <li>cleanup of entity handling code</li> 954 <li>overall review of all loops in the parsers, all sprintf usage has been 955 checked too</li> 956 <li>Far better handling of larges Dtd. Validating against Docbook XML Dtd 957 works smoothly now.</li> 958</ul> 959 960<h3>1.8.10: Sep 6 2000</h3> 961<ul> 962 <li>bug fix release for some Gnome projects</li> 963</ul> 964 965<h3>2.2.2: August 12 2000</h3> 966<ul> 967 <li>mostly bug fixes</li> 968 <li>started adding routines to access xml parser context options</li> 969</ul> 970 971<h3>2.2.1: July 21 2000</h3> 972<ul> 973 <li>a purely bug fixes release</li> 974 <li>fixed an encoding support problem when parsing from a memory block</li> 975 <li>fixed a DOCTYPE parsing problem</li> 976 <li>removed a bug in the function allowing to override the memory 977 allocation routines</li> 978</ul> 979 980<h3>2.2.0: July 14 2000</h3> 981<ul> 982 <li>applied a lot of portability fixes</li> 983 <li>better encoding support/cleanup and saving (content is now always 984 encoded in UTF-8)</li> 985 <li>the HTML parser now correctly handles encodings</li> 986 <li>added xmlHasProp()</li> 987 <li>fixed a serious problem with &#38;</li> 988 <li>propagated the fix to FTP client</li> 989 <li>cleanup, bugfixes, etc ...</li> 990 <li>Added a page about <a href="encoding.html">libxml Internationalization 991 support</a></li> 992</ul> 993 994<h3>1.8.9: July 9 2000</h3> 995<ul> 996 <li>fixed the spec the RPMs should be better</li> 997 <li>fixed a serious bug in the FTP implementation, released 1.8.9 to solve 998 rpmfind users problem</li> 999</ul> 1000 1001<h3>2.1.1: July 1 2000</h3> 1002<ul> 1003 <li>fixes a couple of bugs in the 2.1.0 packaging</li> 1004 <li>improvements on the HTML parser</li> 1005</ul> 1006 1007<h3>2.1.0 and 1.8.8: June 29 2000</h3> 1008<ul> 1009 <li>1.8.8 is mostly a comodity package for upgrading to libxml2 accoding to 1010 <a href="upgrade.html">new instructions</a>. It fixes a nasty problem 1011 about &#38; charref parsing</li> 1012 <li>2.1.0 also ease the upgrade from libxml v1 to the recent version. it 1013 also contains numerous fixes and enhancements: 1014 <ul> 1015 <li>added xmlStopParser() to stop parsing</li> 1016 <li>improved a lot parsing speed when there is large CDATA blocs</li> 1017 <li>includes XPath patches provided by Picdar Technology</li> 1018 <li>tried to fix as much as possible DtD validation and namespace 1019 related problems</li> 1020 <li>output to a given encoding has been added/tested</li> 1021 <li>lot of various fixes</li> 1022 </ul> 1023 </li> 1024</ul> 1025 1026<h3>2.0.0: Apr 12 2000</h3> 1027<ul> 1028 <li>First public release of libxml2. If you are using libxml, it's a good 1029 idea to check the 1.x to 2.x upgrade instructions. NOTE: while initally 1030 scheduled for Apr 3 the relase occured only on Apr 12 due to massive 1031 workload.</li> 1032 <li>The include are now located under $prefix/include/libxml (instead of 1033 $prefix/include/gnome-xml), they also are referenced by 1034 <pre>#include <libxml/xxx.h></pre> 1035 <p>instead of</p> 1036 <pre>#include "xxx.h"</pre> 1037 </li> 1038 <li>a new URI module for parsing URIs and following strictly RFC 2396</li> 1039 <li>the memory allocation routines used by libxml can now be overloaded 1040 dynamically by using xmlMemSetup()</li> 1041 <li>The previously CVS only tool tester has been renamed 1042 <strong>xmllint</strong> and is now installed as part of the libxml2 1043 package</li> 1044 <li>The I/O interface has been revamped. There is now ways to plug in 1045 specific I/O modules, either at the URI scheme detection level using 1046 xmlRegisterInputCallbacks() or by passing I/O functions when creating a 1047 parser context using xmlCreateIOParserCtxt()</li> 1048 <li>there is a C preprocessor macro LIBXML_VERSION providing the version 1049 number of the libxml module in use</li> 1050 <li>a number of optional features of libxml can now be excluded at 1051 configure time (FTP/HTTP/HTML/XPath/Debug)</li> 1052</ul> 1053 1054<h3>2.0.0beta: Mar 14 2000</h3> 1055<ul> 1056 <li>This is a first Beta release of libxml version 2</li> 1057 <li>It's available only from<a href="ftp://xmlsoft.org/">xmlsoft.org 1058 FTP</a>, it's packaged as libxml2-2.0.0beta and available as tar and 1059 RPMs</li> 1060 <li>This version is now the head in the Gnome CVS base, the old one is 1061 available under the tag LIB_XML_1_X</li> 1062 <li>This includes a very large set of changes. Froma programmatic point of 1063 view applications should not have to be modified too much, check the <a 1064 href="upgrade.html">upgrade page</a></li> 1065 <li>Some interfaces may changes (especially a bit about encoding).</li> 1066 <li>the updates includes: 1067 <ul> 1068 <li>fix I18N support. ISO-Latin-x/UTF-8/UTF-16 (nearly) seems correctly 1069 handled now</li> 1070 <li>Better handling of entities, especially well formedness checking 1071 and proper PEref extensions in external subsets</li> 1072 <li>DTD conditional sections</li> 1073 <li>Validation now correcly handle entities content</li> 1074 <li><a href="http://rpmfind.net/tools/gdome/messages/0039.html">change 1075 structures to accomodate DOM</a></li> 1076 </ul> 1077 </li> 1078 <li>Serious progress were made toward compliance, <a 1079 href="conf/result.html">here are the result of the test</a> against the 1080 OASIS testsuite (except the japanese tests since I don't support that 1081 encoding yet). This URL is rebuilt every couple of hours using the CVS 1082 head version.</li> 1083</ul> 1084 1085<h3>1.8.7: Mar 6 2000</h3> 1086<ul> 1087 <li>This is a bug fix release:</li> 1088 <li>It is possible to disable the ignorable blanks heuristic used by 1089 libxml-1.x, a new function xmlKeepBlanksDefault(0) will allow this. Note 1090 that for adherence to XML spec, this behaviour will be disabled by 1091 default in 2.x . The same function will allow to keep compatibility for 1092 old code.</li> 1093 <li>Blanks in <a> </a> constructs are not ignored anymore, 1094 avoiding heuristic is really the Right Way :-\</li> 1095 <li>The unchecked use of snprintf which was breaking libxml-1.8.6 1096 compilation on some platforms has been fixed</li> 1097 <li>nanoftp.c nanohttp.c: Fixed '#' and '?' stripping when processing 1098 URIs</li> 1099</ul> 1100 1101<h3>1.8.6: Jan 31 2000</h3> 1102<ul> 1103 <li>added a nanoFTP transport module, debugged until the new version of <a 1104 href="http://rpmfind.net/linux/rpm2html/rpmfind.html">rpmfind</a> can use 1105 it without troubles</li> 1106</ul> 1107 1108<h3>1.8.5: Jan 21 2000</h3> 1109<ul> 1110 <li>adding APIs to parse a well balanced chunk of XML (production <a 1111 href="http://www.w3.org/TR/REC-xml#NT-content">[43] content</a> of the 1112 XML spec)</li> 1113 <li>fixed a hideous bug in xmlGetProp pointed by Rune.Djurhuus@fast.no</li> 1114 <li>Jody Goldberg <jgoldberg@home.com> provided another patch trying 1115 to solve the zlib checks problems</li> 1116 <li>The current state in gnome CVS base is expected to ship as 1.8.5 with 1117 gnumeric soon</li> 1118</ul> 1119 1120<h3>1.8.4: Jan 13 2000</h3> 1121<ul> 1122 <li>bug fixes, reintroduced xmlNewGlobalNs(), fixed xmlNewNs()</li> 1123 <li>all exit() call should have been removed from libxml</li> 1124 <li>fixed a problem with INCLUDE_WINSOCK on WIN32 platform</li> 1125 <li>added newDocFragment()</li> 1126</ul> 1127 1128<h3>1.8.3: Jan 5 2000</h3> 1129<ul> 1130 <li>a Push interface for the XML and HTML parsers</li> 1131 <li>a shell-like interface to the document tree (try tester --shell :-)</li> 1132 <li>lots of bug fixes and improvement added over XMas hollidays</li> 1133 <li>fixed the DTD parsing code to work with the xhtml DTD</li> 1134 <li>added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()</li> 1135 <li>Fixed bugs in xmlNewNs()</li> 1136 <li>External entity loading code has been revamped, now it uses 1137 xmlLoadExternalEntity(), some fix on entities processing were added</li> 1138 <li>cleaned up WIN32 includes of socket stuff</li> 1139</ul> 1140 1141<h3>1.8.2: Dec 21 1999</h3> 1142<ul> 1143 <li>I got another problem with includes and C++, I hope this issue is fixed 1144 for good this time</li> 1145 <li>Added a few tree modification functions: xmlReplaceNode, 1146 xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and 1147 xmlDocSetRootElement</li> 1148 <li>Tried to improve the HTML output with help from <a 1149 href="mailto:clahey@umich.edu">Chris Lahey</a></li> 1150</ul> 1151 1152<h3>1.8.1: Dec 18 1999</h3> 1153<ul> 1154 <li>various patches to avoid troubles when using libxml with C++ compilers 1155 the "namespace" keyword and C escaping in include files</li> 1156 <li>a problem in one of the core macros IS_CHAR was corrected</li> 1157 <li>fixed a bug introduced in 1.8.0 breaking default namespace processing, 1158 and more specifically the Dia application</li> 1159 <li>fixed a posteriori validation (validation after parsing, or by using a 1160 Dtd not specified in the original document)</li> 1161 <li>fixed a bug in</li> 1162</ul> 1163 1164<h3>1.8.0: Dec 12 1999</h3> 1165<ul> 1166 <li>cleanup, especially memory wise</li> 1167 <li>the parser should be more reliable, especially the HTML one, it should 1168 not crash, whatever the input !</li> 1169 <li>Integrated various patches, especially a speedup improvement for large 1170 dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>, 1171 configure with --with-buffers to enable them.</li> 1172 <li>attribute normalization, oops should have been added long ago !</li> 1173 <li>attributes defaulted from Dtds should be available, xmlSetProp() now 1174 does entities escapting by default.</li> 1175</ul> 1176 1177<h3>1.7.4: Oct 25 1999</h3> 1178<ul> 1179 <li>Lots of HTML improvement</li> 1180 <li>Fixed some errors when saving both XML and HTML</li> 1181 <li>More examples, the regression tests should now look clean</li> 1182 <li>Fixed a bug with contiguous charref</li> 1183</ul> 1184 1185<h3>1.7.3: Sep 29 1999</h3> 1186<ul> 1187 <li>portability problems fixed</li> 1188 <li>snprintf was used unconditionnally, leading to link problems on system 1189 were it's not available, fixed</li> 1190</ul> 1191 1192<h3>1.7.1: Sep 24 1999</h3> 1193<ul> 1194 <li>The basic type for strings manipulated by libxml has been renamed in 1195 1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason 1196 is that CHAR was conflicting with a predefined type on Windows. However 1197 on non WIN32 environment, compatibility is provided by the way of a 1198 <strong>#define </strong>.</li> 1199 <li>Changed another error : the use of a structure field called errno, and 1200 leading to troubles on platforms where it's a macro</li> 1201</ul> 1202 1203<h3>1.7.0: sep 23 1999</h3> 1204<ul> 1205 <li>Added the ability to fetch remote DTD or parsed entities, see the <a 1206 href="html/libxml-nanohttp.html">nanohttp</a> module.</li> 1207 <li>Added an errno to report errors by another mean than a simple printf 1208 like callback</li> 1209 <li>Finished ID/IDREF support and checking when validation</li> 1210 <li>Serious memory leaks fixed (there is now a <a 1211 href="html/libxml-xmlmemory.html">memory wrapper</a> module)</li> 1212 <li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a> 1213 implementation</li> 1214 <li>Added an HTML parser front-end</li> 1215</ul> 1216 1217<h2><a name="XML">XML</a></h2> 1218 1219<p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for 1220markup-based structured documents. Here is <a name="example">an example XML 1221document</a>:</p> 1222<pre><?xml version="1.0"?> 1223<EXAMPLE prop1="gnome is great" prop2="&amp; linux too"> 1224 <head> 1225 <title>Welcome to Gnome</title> 1226 </head> 1227 <chapter> 1228 <title>The Linux adventure</title> 1229 <p>bla bla bla ...</p> 1230 <image href="linus.gif"/> 1231 <p>...</p> 1232 </chapter> 1233</EXAMPLE></pre> 1234 1235<p>The first line specifies that it's an XML document and gives useful 1236information about its encoding. Then the document is a text format whose 1237structure is specified by tags between brackets. <strong>Each tag opened has 1238to be closed</strong>. XML is pedantic about this. However, if a tag is empty 1239(no content), a single tag can serve as both the opening and closing tag if 1240it ends with <code>/></code> rather than with <code>></code>. Note 1241that, for example, the image tag has no content (just an attribute) and is 1242closed by ending the tag with <code>/></code>.</p> 1243 1244<p>XML can be applied sucessfully to a wide range of uses, from long term 1245structured document maintenance (where it follows the steps of SGML) to 1246simple data encoding mechanisms like configuration file formatting (glade), 1247spreadsheets (gnumeric), or even shorter lived documents such as WebDAV where 1248it is used to encode remote calls between a client and a server.</p> 1249 1250<h2><a name="XSLT">XSLT</a></h2> 1251 1252<p>Check <a href="http://xmlsoft.org/XSLT">the separate libxslt page</a></p> 1253 1254<p><a href="http://www.w3.org/TR/xslt">XSL Transformations</a>, is a 1255language for transforming XML documents into other XML documents (or 1256HTML/textual output).</p> 1257 1258<p>A separate library called libxslt is being built on top of libxml2. This 1259module "libxslt" can be found in the Gnome CVS base too.</p> 1260 1261<p>You can check the <a 1262href="http://cvs.gnome.org/lxr/source/libxslt/FEATURES">features</a> 1263supported and the progresses on the <a 1264href="http://cvs.gnome.org/lxr/source/libxslt/ChangeLog">Changelog</a></p> 1265 1266<h2><a name="architecture">libxml architecture</a></h2> 1267 1268<p>Libxml is made of multiple components; some of them are optional, and most 1269of the block interfaces are public. The main components are:</p> 1270<ul> 1271 <li>an Input/Output layer</li> 1272 <li>FTP and HTTP client layers (optional)</li> 1273 <li>an Internationalization layer managing the encodings support</li> 1274 <li>a URI module</li> 1275 <li>the XML parser and its basic SAX interface</li> 1276 <li>an HTML parser using the same SAX interface (optional)</li> 1277 <li>a SAX tree module to build an in-memory DOM representation</li> 1278 <li>a tree module to manipulate the DOM representation</li> 1279 <li>a validation module using the DOM representation (optional)</li> 1280 <li>an XPath module for global lookup in a DOM representation 1281 (optional)</li> 1282 <li>a debug module (optional)</li> 1283</ul> 1284 1285<p>Graphically this gives the following:</p> 1286 1287<p><img src="libxml.gif" alt="a graphical view of the various"></p> 1288 1289<p></p> 1290 1291<h2><a name="tree">The tree output</a></h2> 1292 1293<p>The parser returns a tree built during the document analysis. The value 1294returned is an <strong>xmlDocPtr</strong> (i.e., a pointer to an 1295<strong>xmlDoc</strong> structure). This structure contains information such 1296as the file name, the document type, and a <strong>children</strong> pointer 1297which is the root of the document (or more exactly the first child under the 1298root which is the document). The tree is made of <strong>xmlNode</strong>s, 1299chained in double-linked lists of siblings and with a children<->parent 1300relationship. An xmlNode can also carry properties (a chain of xmlAttr 1301structures). An attribute may have a value which is a list of TEXT or 1302ENTITY_REF nodes.</p> 1303 1304<p>Here is an example (erroneous with respect to the XML spec since there 1305should be only one ELEMENT under the root):</p> 1306 1307<p><img src="structure.gif" alt=" structure.gif "></p> 1308 1309<p>In the source package there is a small program (not installed by default) 1310called <strong>xmllint</strong> which parses XML files given as argument and 1311prints them back as parsed. This is useful for detecting errors both in XML 1312code and in the XML parser itself. It has an option <strong>--debug</strong> 1313which prints the actual in-memory structure of the document; here is the 1314result with the <a href="#example">example</a> given before:</p> 1315<pre>DOCUMENT 1316version=1.0 1317standalone=true 1318 ELEMENT EXAMPLE 1319 ATTRIBUTE prop1 1320 TEXT 1321 content=gnome is great 1322 ATTRIBUTE prop2 1323 ENTITY_REF 1324 TEXT 1325 content= linux too 1326 ELEMENT head 1327 ELEMENT title 1328 TEXT 1329 content=Welcome to Gnome 1330 ELEMENT chapter 1331 ELEMENT title 1332 TEXT 1333 content=The Linux adventure 1334 ELEMENT p 1335 TEXT 1336 content=bla bla bla ... 1337 ELEMENT image 1338 ATTRIBUTE href 1339 TEXT 1340 content=linus.gif 1341 ELEMENT p 1342 TEXT 1343 content=...</pre> 1344 1345<p>This should be useful for learning the internal representation model.</p> 1346 1347<h2><a name="interface">The SAX interface</a></h2> 1348 1349<p>Sometimes the DOM tree output is just too large to fit reasonably into 1350memory. In that case (and if you don't expect to save back the XML document 1351loaded using libxml), it's better to use the SAX interface of libxml. SAX is 1352a <strong>callback-based interface</strong> to the parser. Before parsing, 1353the application layer registers a customized set of callbacks which are 1354called by the library as it progresses through the XML input.</p> 1355 1356<p>To get more detailed step-by-step guidance on using the SAX interface of 1357libxml, see the <a 1358href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">nice 1359documentation</a>.written by <a href="mailto:james@daa.com.au">James 1360Henstridge</a>.</p> 1361 1362<p>You can debug the SAX behaviour by using the <strong>testSAX</strong> 1363program located in the gnome-xml module (it's usually not shipped in the 1364binary packages of libxml, but you can find it in the tar source 1365distribution). Here is the sequence of callbacks that would be reported by 1366testSAX when parsing the example XML document shown earlier:</p> 1367<pre>SAX.setDocumentLocator() 1368SAX.startDocument() 1369SAX.getEntity(amp) 1370SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp; linux too') 1371SAX.characters( , 3) 1372SAX.startElement(head) 1373SAX.characters( , 4) 1374SAX.startElement(title) 1375SAX.characters(Welcome to Gnome, 16) 1376SAX.endElement(title) 1377SAX.characters( , 3) 1378SAX.endElement(head) 1379SAX.characters( , 3) 1380SAX.startElement(chapter) 1381SAX.characters( , 4) 1382SAX.startElement(title) 1383SAX.characters(The Linux adventure, 19) 1384SAX.endElement(title) 1385SAX.characters( , 4) 1386SAX.startElement(p) 1387SAX.characters(bla bla bla ..., 15) 1388SAX.endElement(p) 1389SAX.characters( , 4) 1390SAX.startElement(image, href='linus.gif') 1391SAX.endElement(image) 1392SAX.characters( , 4) 1393SAX.startElement(p) 1394SAX.characters(..., 3) 1395SAX.endElement(p) 1396SAX.characters( , 3) 1397SAX.endElement(chapter) 1398SAX.characters( , 1) 1399SAX.endElement(EXAMPLE) 1400SAX.endDocument()</pre> 1401 1402<p>Most of the other interfaces of libxml are based on the DOM tree-building 1403facility, so nearly everything up to the end of this document presupposes the 1404use of the standard DOM tree build. Note that the DOM tree itself is built by 1405a set of registered default callbacks, without internal specific 1406interface.</p> 1407 1408<h2><a name="Validation">Validation & DTDs</a></h2> 1409 1410<p>Table of Content:</p> 1411<ol> 1412 <li><a href="#General5">General overview</a></li> 1413 <li><a href="#definition">The definition</a></li> 1414 <li><a href="#Simple">Simple rules</a> 1415 <ol> 1416 <li><a href="#reference">How to reference a DTD from a document</a></li> 1417 <li><a href="#Declaring">Declaring elements</a></li> 1418 <li><a href="#Declaring1">Declaring attributes</a></li> 1419 </ol> 1420 </li> 1421 <li><a href="#Some">Some examples</a></li> 1422 <li><a href="#validate">How to validate</a></li> 1423 <li><a href="#Other">Other resources</a></li> 1424</ol> 1425 1426<h3><a name="General5">General overview</a></h3> 1427 1428<p>Well what is validation and what is a DTD ?</p> 1429 1430<p>DTD is the acronym for Document Type Definition. This is a description of 1431the content for a familly of XML files. This is part of the XML 1.0 1432specification, and alows to describe and check that a given document instance 1433conforms to a set of rules detailing its structure and content.</p> 1434 1435<p>Validation is the process of checking a document against a DTD (more 1436generally against a set of construction rules).</p> 1437 1438<p>The validation process and building DTDs are the two most difficult parts 1439of the XML life cycle. Briefly a DTD defines all the possibles element to be 1440found within your document, what is the formal shape of your document tree 1441(by defining the allowed content of an element, either text, a regular 1442expression for the allowed list of children, or mixed content i.e. both text 1443and children). The DTD also defines the allowed attributes for all elements 1444and the types of the attributes.</p> 1445 1446<h3><a name="definition1">The definition</a></h3> 1447 1448<p>The <a href="http://www.w3.org/TR/REC-xml">W3C XML Recommendation</a> (<a 1449href="http://www.xml.com/axml/axml.html">Tim Bray's annotated version of 1450Rev1</a>):</p> 1451<ul> 1452 <li><a href="http://www.w3.org/TR/REC-xml#elemdecls">Declaring 1453 elements</a></li> 1454 <li><a href="http://www.w3.org/TR/REC-xml#attdecls">Declaring 1455 attributes</a></li> 1456</ul> 1457 1458<p>(unfortunately) all this is inherited from the SGML world, the syntax is 1459ancient...</p> 1460 1461<h3><a name="Simple1">Simple rules</a></h3> 1462 1463<p>Writing DTD can be done in multiple ways, the rules to build them if you 1464need something fixed or something which can evolve over time can be radically 1465different. Really complex DTD like Docbook ones are flexible but quite harder 1466to design. I will just focuse on DTDs for a formats with a fixed simple 1467structure. It is just a set of basic rules, and definitely not exhaustive nor 1468useable for complex DTD design.</p> 1469 1470<h4><a name="reference1">How to reference a DTD from a document</a>:</h4> 1471 1472<p>Assuming the top element of the document is <code>spec</code> and the dtd 1473is placed in the file <code>mydtd</code> in the subdirectory 1474<code>dtds</code> of the directory from where the document were loaded:</p> 1475 1476<p><code><!DOCTYPE spec SYSTEM "dtds/mydtd"></code></p> 1477 1478<p>Notes:</p> 1479<ul> 1480 <li>the system string is actually an URI-Reference (as defined in <a 1481 href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>) so you can use a 1482 full URL string indicating the location of your DTD on the Web, this is a 1483 really good thing to do if you want others to validate your document</li> 1484 <li>it is also possible to associate a <code>PUBLIC</code> identifier (a 1485 magic string) so that the DTd is looked up in catalogs on the client side 1486 without having to locate it on the web</li> 1487 <li>a dtd contains a set of elements and attributes declarations, but they 1488 don't define what the root of the document should be. This is explicitely 1489 told to the parser/validator as the first element of the 1490 <code>DOCTYPE</code> declaration.</li> 1491</ul> 1492 1493<h4><a name="Declaring2">Declaring elements</a>:</h4> 1494 1495<p>The following declares an element <code>spec</code>:</p> 1496 1497<p><code><!ELEMENT spec (front, body, back?)></code></p> 1498 1499<p>it also expresses that the spec element contains one <code>front</code>, 1500one <code>body</code> and one optionnal <code>back</code> children elements 1501in this order. The declaration of one element of the structure and its 1502content are done in a single declaration. Similary the following declares 1503<code>div1</code> elements:</p> 1504 1505<p><code><!ELEMENT div1 (head, (p | list | note)*, div2*)></code></p> 1506 1507<p>means div1 contains one <code>head</code> then a series of optional 1508<code>p</code>, <code>list</code>s and <code>note</code>s and then an 1509optional <code>div2</code>. And last but not least an element can contain 1510text:</p> 1511 1512<p><code><!ELEMENT b (#PCDATA)></code></p> 1513 1514<p><code>b</code> contains text or being of mixed content (text and elements 1515in no particular order):</p> 1516 1517<p><code><!ELEMENT p (#PCDATA|a|ul|b|i|em)*></code></p> 1518 1519<p><code>p </code>can contain text or <code>a</code>, <code>ul</code>, 1520<code>b</code>, <code>i </code>or <code>em</code> elements in no particular 1521order.</p> 1522 1523<h4><a name="Declaring1">Declaring attributes</a>:</h4> 1524 1525<p>again the attributes declaration includes their content definition:</p> 1526 1527<p><code><!ATTLIST termdef name CDATA #IMPLIED></code></p> 1528 1529<p>means that the element <code>termdef</code> can have a <code>name</code> 1530attribute containing text (<code>CDATA</code>) and which is optionnal 1531(<code>#IMPLIED</code>). The attribute value can also be defined within a 1532set:</p> 1533 1534<p><code><!ATTLIST list type (bullets|ordered|glossary) 1535"ordered"></code></p> 1536 1537<p>means <code>list</code> element have a <code>type</code> attribute with 3 1538allowed values "bullets", "ordered" or "glossary" and which default to 1539"ordered" if the attribute is not explicitely specified.</p> 1540 1541<p>The content type of an attribute can be text (<code>CDATA</code>), 1542anchor/reference/references 1543(<code>ID</code>/<code>IDREF</code>/<code>IDREFS</code>), entity(ies) 1544(<code>ENTITY</code>/<code>ENTITIES</code>) or name(s) 1545(<code>NMTOKEN</code>/<code>NMTOKENS</code>). The following defines that a 1546<code>chapter</code> element can have an optional <code>id</code> attribute 1547of type <code>ID</code>, usable for reference from attribute of type 1548IDREF:</p> 1549 1550<p><code><!ATTLIST chapter id ID #IMPLIED></code></p> 1551 1552<p>The last value of an attribute definition can be <code>#REQUIRED 1553</code>meaning that the attribute has to be given, <code>#IMPLIED</code> 1554meaning that it is optional, or the default value (possibly prefixed by 1555<code>#FIXED</code> if it is the only allowed).</p> 1556 1557<p>Notes:</p> 1558<ul> 1559 <li>usually the attributes pertaining to a given element are declared in a 1560 single expression, but it is just a convention adopted by a lot of DTD 1561 writers: 1562 <pre><!ATTLIST termdef 1563 id ID #REQUIRED 1564 name CDATA #IMPLIED></pre> 1565 <p>The previous construct defines both <code>id</code> and 1566 <code>name</code> attributes for the element <code>termdef</code></p> 1567 </li> 1568</ul> 1569 1570<h3><a name="Some1">Some examples</a></h3> 1571 1572<p>The directory <code>test/valid/dtds/</code> in the libxml distribution 1573contains some complex DTD examples. The <code>test/valid/dia.xml</code> 1574example shows an XML file where the simple DTD is directly included within 1575the document.</p> 1576 1577<h3><a name="validate1">How to validate</a></h3> 1578 1579<p>The simplest is to use the xmllint program comming with libxml. The 1580<code>--valid</code> option turn on validation of the files given as input, 1581for example the following validates a copy of the first revision of the XML 15821.0 specification:</p> 1583 1584<p><code>xmllint --valid --noout test/valid/REC-xml-19980210.xml</code></p> 1585 1586<p>the -- noout is used to not output the resulting tree.</p> 1587 1588<p>The <code>--dtdvalid dtd</code> allows to validate the document(s) against 1589a given DTD.</p> 1590 1591<p>Libxml exports an API to handle DTDs and validation, check the <a 1592href="http://xmlsoft.org/html/libxml-valid.html">associated 1593description</a>.</p> 1594 1595<h3><a name="Other1">Other resources</a></h3> 1596 1597<p>DTDs are as old as SGML. So there may be a number of examples on-line, I 1598will just list one for now, others pointers welcome:</p> 1599<ul> 1600 <li><a href="http://www.xml101.com:8081/dtd/">XML-101 DTD</a></li> 1601</ul> 1602 1603<p>I suggest looking at the examples found under test/valid/dtd and any of 1604the large number of books available on XML. The dia example in test/valid 1605should be both simple and complete enough to allow you to build your own.</p> 1606 1607<p></p> 1608 1609<h2><a name="Memory">Memory Management</a></h2> 1610 1611<p>Table of Content:</p> 1612<ol> 1613 <li><a href="#General3">General overview</a></li> 1614 <li><a href="#setting">Setting libxml set of memory routines</a></li> 1615 <li><a href="#cleanup">Cleaning up after parsing</a></li> 1616 <li><a href="#Debugging">Debugging routines</a></li> 1617 <li><a href="#General4">General memory requirements</a></li> 1618</ol> 1619 1620<h3><a name="General3">General overview</a></h3> 1621 1622<p>The module <code><a 1623href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlmemory.h</a></code> 1624provides the interfaces to the libxml memory system:</p> 1625<ul> 1626 <li>libxml does not use the libc memory allocator directly but xmlFree(), 1627 xmlMalloc() and xmlRealloc()</li> 1628 <li>those routines can be reallocated to a specific set of routine, by 1629 default the libc ones i.e. free(), malloc() and realloc()</li> 1630 <li>the xmlmemory.c module includes a set of debugging routine</li> 1631</ul> 1632 1633<h3><a name="setting">Setting libxml set of memory routines</a></h3> 1634 1635<p>It is sometimes useful to not use the default memory allocator, either for 1636debugging, analysis or to implement a specific behaviour on memory management 1637(like on embedded systems). Two function calls are available to do so:</p> 1638<ul> 1639 <li><a href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemGet ()</a> 1640 which return the current set of functions in use by the parser</li> 1641 <li><a 1642 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemSetup()</a> 1643 which allow to set up a new set of memory allocation functions</li> 1644</ul> 1645 1646<p>Of course a call to xmlMemSetup() should probably be done before calling 1647any other libxml routines (unless you are sure your allocations routines are 1648compatibles).</p> 1649 1650<h3><a name="cleanup">Cleaning up after parsing</a></h3> 1651 1652<p>Libxml is not stateless, there is a few set of memory structures needing 1653allocation before the parser is fully functionnal (some encoding structures 1654for example). This also mean that once parsing is finished there is a tiny 1655amount of memory (a few hundred bytes) which can be recollected if you don't 1656reuse the parser immediately:</p> 1657<ul> 1658 <li><a href="http://xmlsoft.org/html/libxml-parser.html">xmlCleanupParser 1659 ()</a> 1660 is a centralized routine to free the parsing states. Note that it won't 1661 deallocate any produced tree if any (use the xmlFreeDoc() and related 1662 routines for this).</li> 1663 <li><a href="http://xmlsoft.org/html/libxml-parser.html">xmlInitParser 1664 ()</a> 1665 is the dual routine allowing to preallocate the parsing state which can 1666 be useful for example to avoid initialization reentrancy problems when 1667 using libxml in multithreaded applications</li> 1668</ul> 1669 1670<p>Generally xmlCleanupParser() is safe, if needed the state will be rebuild 1671at the next invocation of parser routines, but be careful of the consequences 1672in multithreaded applications.</p> 1673 1674<h3><a name="Debugging">Debugging routines</a></h3> 1675 1676<p>When configured using --with-mem-debug flag (off by default), libxml uses 1677a set of memory allocation debugging routineskeeping track of all allocated 1678blocks and the location in the code where the routine was called. A couple of 1679other debugging routines allow to dump the memory allocated infos to a file 1680or call a specific routine when a given block number is allocated:</p> 1681<ul> 1682 <li><a 1683 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMallocLoc()</a> 1684 <a 1685 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlReallocLoc()</a> 1686 and <a 1687 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemStrdupLoc()</a> 1688 are the memory debugging replacement allocation routines</li> 1689 <li><a href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemoryDump 1690 ()</a> 1691 dumps all the informations about the allocated memory block lefts in the 1692 <code>.memdump</code> file</li> 1693</ul> 1694 1695<p>When developping libxml memory debug is enabled, the tests programs call 1696xmlMemoryDump () and the "make test" regression tests will check for any 1697memory leak during the full regression test sequence, this helps a lot 1698ensuring that libxml does not leak memory and bullet proof memory 1699allocations use (some libc implementations are known to be far too permissive 1700resulting in major portability problems!).</p> 1701 1702<p>If the .memdump reports a leak, it displays the allocation function and 1703also tries to give some informations about the content and structure of the 1704allocated blocks left. This is sufficient in most cases to find the culprit, 1705but not always. Assuming the allocation problem is reproductible, it is 1706possible to find more easilly:</p> 1707<ol> 1708 <li>write down the block number xxxx not allocated</li> 1709 <li>export the environement variable XML_MEM_BREAKPOINT=xxxx</li> 1710 <li>run the program under a debugger and set a breakpoint on 1711 xmlMallocBreakpoint() a specific function called when this precise block 1712 is allocated</li> 1713 <li>when the breakpoint is reached you can then do a fine analysis of the 1714 allocation an step to see the condition resulting in the missing 1715 deallocation.</li> 1716</ol> 1717 1718<p>I used to use a commercial tool to debug libxml memory problems but after 1719noticing that it was not detecting memory leaks that simple mechanism was 1720used and proved extremely efficient until now.</p> 1721 1722<h3><a name="General4">General memory requirements</a></h3> 1723 1724<p>How much libxml memory require ? It's hard to tell in average it depends 1725of a number of things:</p> 1726<ul> 1727 <li>the parser itself should work in a fixed amout of memory, except for 1728 information maintained about the stacks of names and entities locations. 1729 The I/O and encoding handlers will probably account for a few KBytes. 1730 This is true for both the XML and HTML parser (though the HTML parser 1731 need more state).</li> 1732 <li>If you are generating the DOM tree then memory requirements will grow 1733 nearly lineary with the size of the data. In general for a balanced 1734 textual document the internal memory requirement is about 4 times the 1735 size of the UTF8 serialization of this document (exmple the XML-1.0 1736 recommendation is a bit more of 150KBytes and takes 650KBytes of main 1737 memory when parsed). Validation will add a amount of memory required for 1738 maintaining the external Dtd state which should be linear with the 1739 complexity of the content model defined by the Dtd</li> 1740 <li>If you don't care about the advanced features of libxml like 1741 validation, DOM, XPath or XPointer, but really need to work fixed memory 1742 requirements, then the SAX interface should be used.</li> 1743</ul> 1744 1745<p></p> 1746 1747<h2><a name="Encodings">Encodings support</a></h2> 1748 1749<p>Table of Content:</p> 1750<ol> 1751 <li><a href="encoding.html#What">What does internationalization support 1752 mean ?</a></li> 1753 <li><a href="encoding.html#internal">The internal encoding, how and 1754 why</a></li> 1755 <li><a href="encoding.html#implemente">How is it implemented ?</a></li> 1756 <li><a href="encoding.html#Default">Default supported encodings</a></li> 1757 <li><a href="encoding.html#extend">How to extend the existing 1758 support</a></li> 1759</ol> 1760 1761<h3><a name="What">What does internationalization support mean ?</a></h3> 1762 1763<p>XML was designed from the start to allow the support of any character set 1764by using Unicode. Any conformant XML parser has to support the UTF-8 and 1765UTF-16 default encodings which can both express the full unicode ranges. UTF8 1766is a variable length encoding whose greatest point are to resuse the same 1767emcoding for ASCII and to save space for Western encodings, but it is a bit 1768more complex to handle in practice. UTF-16 use 2 bytes per characters (and 1769sometimes combines two pairs), it makes implementation easier, but looks a 1770bit overkill for Western languages encoding. Moreover the XML specification 1771allows document to be encoded in other encodings at the condition that they 1772are clearly labelled as such. For example the following is a wellformed XML 1773document encoded in ISO-8859 1 and using accentuated letter that we French 1774likes for both markup and content:</p> 1775<pre><?xml version="1.0" encoding="ISO-8859-1"?> 1776<tr�s>l�</tr�s></pre> 1777 1778<p>Having internationalization support in libxml means the foolowing:</p> 1779<ul> 1780 <li>the document is properly parsed</li> 1781 <li>informations about it's encoding are saved</li> 1782 <li>it can be modified</li> 1783 <li>it can be saved in its original encoding</li> 1784 <li>it can also be saved in another encoding supported by libxml (for 1785 example straight UTF8 or even an ASCII form)</li> 1786</ul> 1787 1788<p>Another very important point is that the whole libxml API, with the 1789exception of a few routines to read with a specific encoding or save to a 1790specific encoding, is completely agnostic about the original encoding of the 1791document.</p> 1792 1793<p>It should be noted too that the HTML parser embedded in libxml now obbey 1794the same rules too, the following document will be (as of 2.2.2) handled in 1795an internationalized fashion by libxml too:</p> 1796<pre><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" 1797 "http://www.w3.org/TR/REC-html40/loose.dtd"> 1798<html lang="fr"> 1799<head> 1800 <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"> 1801</head> 1802<body> 1803<p>W3C cr�e des standards pour le Web.</body> 1804</html></pre> 1805 1806<h3><a name="internal">The internal encoding, how and why</a></h3> 1807 1808<p>One of the core decision was to force all documents to be converted to a 1809default internal encoding, and that encoding to be UTF-8, here are the 1810rationale for those choices:</p> 1811<ul> 1812 <li>keeping the native encoding in the internal form would force the libxml 1813 users (or the code associated) to be fully aware of the encoding of the 1814 original document, for examples when adding a text node to a document, 1815 the content would have to be provided in the document encoding, i.e. the 1816 client code would have to check it before hand, make sure it's conformant 1817 to the encoding, etc ... Very hard in practice, though in some specific 1818 cases this may make sense.</li> 1819 <li>the second decision was which encoding. From the XML spec only UTF8 and 1820 UTF16 really makes sense as being the two only encodings for which there 1821 is amndatory support. UCS-4 (32 bits fixed size encoding) could be 1822 considered an intelligent choice too since it's a direct Unicode mapping 1823 support. I selected UTF-8 on the basis of efficiency and compatibility 1824 with surrounding software: 1825 <ul> 1826 <li>UTF-8 while a bit more complex to convert from/to (i.e. slightly 1827 more costly to import and export CPU wise) is also far more compact 1828 than UTF-16 (and UCS-4) for a majority of the documents I see it used 1829 for right now (RPM RDF catalogs, advogato data, various configuration 1830 file formats, etc.) and the key point for today's computer 1831 architecture is efficient uses of caches. If one nearly double the 1832 memory requirement to store the same amount of data, this will trash 1833 caches (main memory/external caches/internal caches) and my take is 1834 that this harms the system far more than the CPU requirements needed 1835 for the conversion to UTF-8</li> 1836 <li>Most of libxml version 1 users were using it with straight ASCII 1837 most of the time, doing the conversion with an internal encoding 1838 requiring all their code to be rewritten was a serious show-stopper 1839 for using UTF-16 or UCS-4.</li> 1840 <li>UTF-8 is being used as the de-facto internal encoding standard for 1841 related code like the <a href="http://www.pango.org/">pango</a> 1842 upcoming Gnome text widget, and a lot of Unix code (yep another place 1843 where Unix programmer base takes a different approach from Microsoft 1844 - they are using UTF-16)</li> 1845 </ul> 1846 </li> 1847</ul> 1848 1849<p>What does this mean in practice for the libxml user:</p> 1850<ul> 1851 <li>xmlChar, the libxml data type is a byte, those bytes must be assembled 1852 as UTF-8 valid strings. The proper way to terminate an xmlChar * string 1853 is simply to append 0 byte, as usual.</li> 1854 <li>One just need to make sure that when using chars outside the ASCII set, 1855 the values has been properly converted to UTF-8</li> 1856</ul> 1857 1858<h3><a name="implemente">How is it implemented ?</a></h3> 1859 1860<p>Let's describe how all this works within libxml, basically the I18N 1861(internationalization) support get triggered only during I/O operation, i.e. 1862when reading a document or saving one. Let's look first at the reading 1863sequence:</p> 1864<ol> 1865 <li>when a document is processed, we usually don't know the encoding, a 1866 simple heuristic allows to detect UTF-18 and UCS-4 from whose where the 1867 ASCII range (0-0x7F) maps with ASCII</li> 1868 <li>the xml declaration if available is parsed, including the encoding 1869 declaration. At that point, if the autodetected encoding is different 1870 from the one declared a call to xmlSwitchEncoding() is issued.</li> 1871 <li>If there is no encoding declaration, then the input has to be in either 1872 UTF-8 or UTF-16, if it is not then at some point when processing the 1873 input, the converter/checker of UTF-8 form will raise an encoding error. 1874 You may end-up with a garbled document, or no document at all ! Example: 1875 <pre>~/XML -> /xmllint err.xml 1876err.xml:1: error: Input is not proper UTF-8, indicate encoding ! 1877<tr�s>l�</tr�s> 1878 ^ 1879err.xml:1: error: Bytes: 0xE8 0x73 0x3E 0x6C 1880<tr�s>l�</tr�s> 1881 ^</pre> 1882 </li> 1883 <li>xmlSwitchEncoding() does an encoding name lookup, canonalize it, and 1884 then search the default registered encoding converters for that encoding. 1885 If it's not within the default set and iconv() support has been compiled 1886 it, it will ask iconv for such an encoder. If this fails then the parser 1887 will report an error and stops processing: 1888 <pre>~/XML -> /xmllint err2.xml 1889err2.xml:1: error: Unsupported encoding UnsupportedEnc 1890<?xml version="1.0" encoding="UnsupportedEnc"?> 1891 ^</pre> 1892 </li> 1893 <li>From that point the encoder process progressingly the input (it is 1894 plugged as a front-end to the I/O module) for that entity. It captures 1895 and convert on-the-fly the document to be parsed to UTF-8. The parser 1896 itself just does UTF-8 checking of this input and process it 1897 transparently. The only difference is that the encoding information has 1898 been added to the parsing context (more precisely to the input 1899 corresponding to this entity).</li> 1900 <li>The result (when using DOM) is an internal form completely in UTF-8 1901 with just an encoding information on the document node.</li> 1902</ol> 1903 1904<p>Ok then what's happen when saving the document (assuming you 1905colllected/built an xmlDoc DOM like structure) ? It depends on the function 1906called, xmlSaveFile() will just try to save in the original encoding, while 1907xmlSaveFileTo() and xmlSaveFileEnc() can optionally save to a given 1908encoding:</p> 1909<ol> 1910 <li>if no encoding is given, libxml will look for an encoding value 1911 associated to the document and if it exists will try to save to that 1912 encoding, 1913 <p>otherwise everything is written in the internal form, i.e. UTF-8</p> 1914 </li> 1915 <li>so if an encoding was specified, either at the API level or on the 1916 document, libxml will again canonalize the encoding name, lookup for a 1917 converter in the registered set or through iconv. If not found the 1918 function will return an error code</li> 1919 <li>the converter is placed before the I/O buffer layer, as another kind of 1920 buffer, then libxml will simply push the UTF-8 serialization to through 1921 that buffer, which will then progressively be converted and pushed onto 1922 the I/O layer.</li> 1923 <li>It is possible that the converter code fails on some input, for example 1924 trying to push an UTF-8 encoded chinese character through the UTF-8 to 1925 ISO-8859-1 converter won't work. Since the encoders are progressive they 1926 will just report the error and the number of bytes converted, at that 1927 point libxml will decode the offending character, remove it from the 1928 buffer and replace it with the associated charRef encoding &#123; and 1929 resume the convertion. This guarante that any document will be saved 1930 without losses (except for markup names where this is not legal, this is 1931 a problem in the current version, in pactice avoid using non-ascci 1932 characters for tags or attributes names @@). A special "ascii" encoding 1933 name is used to save documents to a pure ascii form can be used when 1934 portability is really crucial</li> 1935</ol> 1936 1937<p>Here is a few examples based on the same test document:</p> 1938<pre>~/XML -> /xmllint isolat1 1939<?xml version="1.0" encoding="ISO-8859-1"?> 1940<tr�s>l�</tr�s> 1941~/XML -> /xmllint --encode UTF-8 isolat1 1942<?xml version="1.0" encoding="UTF-8"?> 1943<très>l� �</très> 1944~/XML -> </pre> 1945 1946<p>The same processing is applied (and reuse most of the code) for HTML I18N 1947processing. Looking up and modifying the content encoding is a bit more 1948difficult since it is located in a <meta> tag under the <head>, 1949so a couple of functions htmlGetMetaEncoding() and htmlSetMetaEncoding() have 1950been provided. The parser also attempts to switch encoding on the fly when 1951detecting such a tag on input. Except for that the processing is the same 1952(and again reuses the same code).</p> 1953 1954<h3><a name="Default">Default supported encodings</a></h3> 1955 1956<p>libxml has a set of default converters for the following encodings 1957(located in encoding.c):</p> 1958<ol> 1959 <li>UTF-8 is supported by default (null handlers)</li> 1960 <li>UTF-16, both little and big endian</li> 1961 <li>ISO-Latin-1 (ISO-8859-1) covering most western languages</li> 1962 <li>ASCII, useful mostly for saving</li> 1963 <li>HTML, a specific handler for the conversion of UTF-8 to ASCII with HTML 1964 predefined entities like &copy; for the Copyright sign.</li> 1965</ol> 1966 1967<p>More over when compiled on an Unix platfor with iconv support the full set 1968of encodings supported by iconv can be instantly be used by libxml. On a 1969linux machine with glibc-2.1 the list of supported encodings and aliases fill 19703 full pages, and include UCS-4, the full set of ISO-Latin encodings, and the 1971various Japanese ones.</p> 1972 1973<h4>Encoding aliases</h4> 1974 1975<p>From 2.2.3, libxml has support to register encoding names aliases. The 1976goal is to be able to parse document whose encoding is supported but where 1977the name differs (for example from the default set of names accepted by 1978iconv). The following functions allow to register and handle new aliases for 1979existing encodings. Once registered libxml will automatically lookup the 1980aliases when handling a document:</p> 1981<ul> 1982 <li>int xmlAddEncodingAlias(const char *name, const char *alias);</li> 1983 <li>int xmlDelEncodingAlias(const char *alias);</li> 1984 <li>const char * xmlGetEncodingAlias(const char *alias);</li> 1985 <li>void xmlCleanupEncodingAliases(void);</li> 1986</ul> 1987 1988<h3><a name="extend">How to extend the existing support</a></h3> 1989 1990<p>Well adding support for new encoding, or overriding one of the encoders 1991(assuming it is buggy) should not be hard, just write an input and output 1992conversion routines to/from UTF-8, and register them using 1993xmlNewCharEncodingHandler(name, xxxToUTF8, UTF8Toxxx), and they will be 1994called automatically if the parser(s) encounter such an encoding name 1995(register it uppercase, this will help). The description of the encoders, 1996their arguments and expected return values are described in the encoding.h 1997header.</p> 1998 1999<p>A quick note on the topic of subverting the parser to use a different 2000internal encoding than UTF-8, in some case people will absolutely want to 2001keep the internal encoding different, I think it's still possible (but the 2002encoding must be compliant with ASCII on the same subrange) though I didn't 2003tried it. The key is to override the default conversion routines (by 2004registering null encoders/decoders for your charsets), and bypass the UTF-8 2005checking of the parser by setting the parser context charset 2006(ctxt->charset) to something different than XML_CHAR_ENCODING_UTF8, but 2007there is no guarantee taht this will work. You may also have some troubles 2008saving back.</p> 2009 2010<p>Basically proper I18N support is important, this requires at least 2011libxml-2.0.0, but a lot of features and corrections are really available only 2012starting 2.2.</p> 2013 2014<h2><a name="IO">I/O Interfaces</a></h2> 2015 2016<p>Table of Content:</p> 2017<ol> 2018 <li><a href="#General1">General overview</a></li> 2019 <li><a href="#basic">The basic buffer type</a></li> 2020 <li><a href="#Input">Input I/O handlers</a></li> 2021 <li><a href="#Output">Output I/O handlers</a></li> 2022 <li><a href="#entities">The entities loader</a></li> 2023 <li><a href="#Example2">Example of customized I/O</a></li> 2024</ol> 2025 2026<h3><a name="General1">General overview</a></h3> 2027 2028<p>The module <code><a 2029href="http://xmlsoft.org/html/libxml-xmlio.html">xmlIO.h</a></code> provides 2030the interfaces to the libxml I/O system. This consists of 4 main parts:</p> 2031<ul> 2032 <li>Entities loader, this is a routine which tries to fetch the entities 2033 (files) based on their PUBLIC and SYSTEM identifiers. The default loader 2034 don't look at the public identifier since libxml do not maintain a 2035 catalog. You can redefine you own entity loader by using 2036 <code>xmlGetExternalEntityLoader()</code> and 2037 <code>xmlSetExternalEntityLoader()</code>. <a href="#entities">Check the 2038 example</a>.</li> 2039 <li>Input I/O buffers which are a commodity structure used by the parser(s) 2040 input layer to handle fetching the informations to feed the parser. This 2041 provides buffering and is also a placeholder where the encoding 2042 convertors to UTF8 are piggy-backed.</li> 2043 <li>Output I/O buffers are similar to the Input ones and fulfill similar 2044 task but when generating a serialization from a tree.</li> 2045 <li>A mechanism to register sets of I/O callbacks and associate them with 2046 specific naming schemes like the protocol part of the URIs. 2047 <p>This affect the default I/O operations and allows to use specific I/O 2048 handlers for certain names.</p> 2049 </li> 2050</ul> 2051 2052<p>The general mechanism used when loading http://rpmfind.net/xml.html for 2053example in the HTML parser is the following:</p> 2054<ol> 2055 <li>The default entity loader calls <code>xmlNewInputFromFile()</code> with 2056 the parsing context and the URI string.</li> 2057 <li>the URI string is checked against the existing registered handlers 2058 using their match() callback function, if the HTTP module was compiled 2059 in, it is registered and its match() function will succeeds</li> 2060 <li>the open() function of the handler is called and if successful will 2061 return an I/O Input buffer</li> 2062 <li>the parser will the start reading from this buffer and progressively 2063 fetch information from the resource, calling the read() function of the 2064 handler until the resource is exhausted</li> 2065 <li>if an encoding change is detected it will be installed on the input 2066 buffer, providing buffering and efficient use of the conversion 2067 routines</li> 2068 <li>once the parser has finished, the close() function of the handler is 2069 called once and the Input buffer and associed resources are 2070 deallocated.</li> 2071</ol> 2072 2073<p>The user defined callbacks are checked first to allow overriding of the 2074default libxml I/O routines.</p> 2075 2076<h3><a name="basic">The basic buffer type</a></h3> 2077 2078<p>All the buffer manipulation handling is done using the 2079<code>xmlBuffer</code> type define in <code><a 2080href="http://xmlsoft.org/html/libxml-tree.html">tree.h</a> </code>which is a 2081resizable memory buffer. The buffer allocation strategy can be selected to be 2082either best-fit or use an exponential doubling one (CPU vs. memory use 2083tradeoff). The values are <code>XML_BUFFER_ALLOC_EXACT</code> and 2084<code>XML_BUFFER_ALLOC_DOUBLEIT</code>, and can be set individually or on a 2085system wide basis using <code>xmlBufferSetAllocationScheme()</code>. A number 2086of functions allows to manipulate buffers with names starting with the 2087<code>xmlBuffer...</code> prefix.</p> 2088 2089<h3><a name="Input">Input I/O handlers</a></h3> 2090 2091<p>An Input I/O handler is a simple structure 2092<code>xmlParserInputBuffer</code> containing a context associated to the 2093resource (file descriptor, or pointer to a protocol handler), the read() and 2094close() callbacks to use and an xmlBuffer. And extra xmlBuffer and a charset 2095encoding handler are also present to support charset conversion when 2096needed.</p> 2097 2098<h3><a name="Output">Output I/O handlers</a></h3> 2099 2100<p>An Output handler <code>xmlOutputBuffer</code> is completely similar to an 2101Input one except the callbacks are write() and close().</p> 2102 2103<h3><a name="entities">The entities loader</a></h3> 2104 2105<p>The entity loader resolves requests for new entities and create inputs for 2106the parser. Creating an input from a filename or an URI string is done 2107through the xmlNewInputFromFile() routine. The default entity loader do not 2108handle the PUBLIC identifier associated with an entity (if any). So it just 2109calls xmlNewInputFromFile() with the SYSTEM identifier (which is mandatory in 2110XML).</p> 2111 2112<p>If you want to hook up a catalog mechanism then you simply need to 2113override the default entity loader, here is an example:</p> 2114<pre>#include <libxml/xmlIO.h> 2115 2116xmlExternalEntityLoader defaultLoader = NULL; 2117 2118xmlParserInputPtr 2119xmlMyExternalEntityLoader(const char *URL, const char *ID, 2120 xmlParserCtxtPtr ctxt) { 2121 xmlParserInputPtr ret; 2122 const char *fileID = NULL; 2123 /* lookup for the fileID depending on ID */ 2124 2125 ret = xmlNewInputFromFile(ctxt, fileID); 2126 if (ret != NULL) 2127 return(ret); 2128 if (defaultLoader != NULL) 2129 ret = defaultLoader(URL, ID, ctxt); 2130 return(ret); 2131} 2132 2133int main(..) { 2134 ... 2135 2136 /* 2137 * Install our own entity loader 2138 */ 2139 defaultLoader = xmlGetExternalEntityLoader(); 2140 xmlSetExternalEntityLoader(xmlMyExternalEntityLoader); 2141 2142 ... 2143}</pre> 2144 2145<h3><a name="Example2">Example of customized I/O</a></h3> 2146 2147<p>This example come from <a href="http://xmlsoft.org/messages/0708.html">a 2148real use case</a>, xmlDocDump() closes the FILE * passed by the application 2149and this was a problem. The <a 2150href="http://xmlsoft.org/messages/0711.html">solution</a> was to redefine a 2151new output handler with the closing call deactivated:</p> 2152<ol> 2153 <li>First define a new I/O ouput allocator where the output don't close the 2154 file: 2155 <pre>xmlOutputBufferPtr 2156xmlOutputBufferCreateOwn(FILE *file, xmlCharEncodingHandlerPtr encoder) { 2157����xmlOutputBufferPtr ret; 2158���� 2159����if (xmlOutputCallbackInitialized == 0) 2160��������xmlRegisterDefaultOutputCallbacks(); 2161 2162����if (file == NULL) return(NULL); 2163����ret = xmlAllocOutputBuffer(encoder); 2164����if (ret != NULL) { 2165��������ret->context = file; 2166��������ret->writecallback = xmlFileWrite; 2167��������ret->closecallback = NULL; /* No close callback */ 2168����} 2169����return(ret); <br> 2170 2171 2172 2173 2174 2175 2176 2177 2178 2179 2180 2181 2182 2183 2184} </pre> 2185 </li> 2186 <li>And then use it to save the document: 2187 <pre>FILE *f; 2188xmlOutputBufferPtr output; 2189xmlDocPtr doc; 2190int res; 2191 2192f = ... 2193doc = .... 2194 2195output = xmlOutputBufferCreateOwn(f, NULL); 2196res = xmlSaveFileTo(output, doc, NULL); 2197 </pre> 2198 </li> 2199</ol> 2200 2201<h2><a name="Catalog">Catalog support</a></h2> 2202 2203<p>Table of Content:</p> 2204<ol> 2205 <li><a href="General2">General overview</a></li> 2206 <li><a href="#definition">The definition</a></li> 2207 <li><a href="#Simple">Using catalogs</a></li> 2208 <li><a href="#Some">Some examples</a></li> 2209 <li><a href="#reference">How to tune catalog usage</a></li> 2210 <li><a href="#validate">How to debug catalog processing</a></li> 2211 <li><a href="#Declaring">How to create and maintain catalogs</a></li> 2212 <li><a href="#implemento">The implementor corner quick review of the 2213 API</a></li> 2214 <li><a href="#Other">Other resources</a></li> 2215</ol> 2216 2217<h3><a name="General2">General overview</a></h3> 2218 2219<p>What is a catalog? Basically it's a lookup mechanism used when an entity 2220(a file or a remote resource) references another entity. The catalog lookup 2221is inserted between the moment the reference is recognized by the software 2222(XML parser, stylesheet processing, or even images referenced for inclusion 2223in a rendering) and the time where loading that resource is actually 2224started.</p> 2225 2226<p>It is basically used for 3 things:</p> 2227<ul> 2228 <li>mapping from "logical" names, the public identifiers and a more 2229 concrete name usable for download (and URI). For example it can associate 2230 the logical name 2231 <p>"-//OASIS//DTD DocBook XML V4.1.2//EN"</p> 2232 <p>of the DocBook 4.1.2 XML DTD with the actual URL where it can be 2233 downloaded</p> 2234 <p>http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd</p> 2235 </li> 2236 <li>remapping from a given URL to another one, like an HTTP indirection 2237 saying that 2238 <p>"http://www.oasis-open.org/committes/tr.xsl"</p> 2239 <p>should really be looked at</p> 2240 <p>"http://www.oasis-open.org/committes/entity/stylesheets/base/tr.xsl"</p> 2241 </li> 2242 <li>providing a local cache mechanism allowing to load the entities 2243 associated to public identifiers or remote resources, this is a really 2244 important feature for any significant deployment of XML or SGML since it 2245 allows to avoid the aleas and delays associated to fetching remote 2246 resources.</li> 2247</ul> 2248 2249<h3><a name="definition">The definitions</a></h3> 2250 2251<p>Libxml, as of 2.4.3 implements 2 kind of catalogs:</p> 2252<ul> 2253 <li>the older SGML catalogs, the official spec is SGML Open Technical 2254 Resolution TR9401:1997, but is better understood by reading <a 2255 href="http://www.jclark.com/sp/catalog.htm">the SP Catalog page</a> from 2256 James Clark. This is relatively old and not the preferred mode of 2257 operation of libxml.</li> 2258 <li><a href="http://www.oasis-open.org/committees/entity/spec.html">XML 2259 Catalogs</a> 2260 is far more flexible, more recent, uses an XML syntax and should scale 2261 quite better. This is the default option of libxml.</li> 2262</ul> 2263 2264<p></p> 2265 2266<h3><a name="Simple">Using catalog</a></h3> 2267 2268<p>In a normal environment libxml will by default check the presence of a 2269catalog in /etc/xml/catalog, and assuming it has been correctly populated, 2270the processing is completely transparent to the document user. To take a 2271concrete example, suppose you are authoring a DocBook document, this one 2272starts with the following DOCTYPE definition:</p> 2273<pre><?xml version='1.0'?> 2274<!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN" 2275 "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd"></pre> 2276 2277<p>When validating the document with libxml, the catalog will be 2278automatically consulted to lookup the public identifier "-//Norman Walsh//DTD 2279DocBk XML V3.1.4//EN" and the system identifier 2280"http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd", and if these entities have 2281been installed on your system and the catalogs actually point to them, libxml 2282will fetch them from the local disk.</p> 2283 2284<p style="font-size: 10pt"><strong>Note</strong>: Really don't use this 2285DOCTYPE example it's a really old version, but is fine as an example.</p> 2286 2287<p>Libxml will check the catalog each time that it is requested to load an 2288entity, this includes DTD, external parsed entities, stylesheets, etc ... If 2289your system is correctly configured all the authoring phase and processing 2290should use only local files, even if your document stays portable because it 2291uses the canonical public and system ID, referencing the remote document.</p> 2292 2293<h3><a name="Some">Some examples:</a></h3> 2294 2295<p>Here is a couple of fragments from XML Catalogs used in libxml early 2296regression tests in <code>test/catalogs</code> :</p> 2297<pre><?xml version="1.0"?> 2298<!DOCTYPE catalog PUBLIC 2299 "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" 2300 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 2301<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"> 2302 <public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN" 2303 uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/> 2304...</pre> 2305 2306<p>This is the beginning of a catalog for DocBook 4.1.2, XML Catalogs are 2307written in XML, there is a specific namespace for catalog elements 2308"urn:oasis:names:tc:entity:xmlns:xml:catalog". The first entry in this 2309catalog is a <code>public</code> mapping it allows to associate a Public 2310Identifier with an URI.</p> 2311<pre>... 2312 <rewriteSystem systemIdStartString="http://www.oasis-open.org/docbook/" 2313 rewritePrefix="file:///usr/share/xml/docbook/"/> 2314...</pre> 2315 2316<p>A <code>rewriteSystem</code> is a very powerful instruction, it says that 2317any URI starting with a given prefix should be looked at another URI 2318constructed by replacing the prefix with an new one. In effect this acts like 2319a cache system for a full area of the Web. In practice it is extremely useful 2320with a file prefix if you have installed a copy of those resources on your 2321local system.</p> 2322<pre>... 2323<delegatePublic publicIdStartString="-//OASIS//DTD XML Catalog //" 2324 catalog="file:///usr/share/xml/docbook.xml"/> 2325<delegatePublic publicIdStartString="-//OASIS//ENTITIES DocBook XML" 2326 catalog="file:///usr/share/xml/docbook.xml"/> 2327<delegatePublic publicIdStartString="-//OASIS//DTD DocBook XML" 2328 catalog="file:///usr/share/xml/docbook.xml"/> 2329<delegateSystem systemIdStartString="http://www.oasis-open.org/docbook/" 2330 catalog="file:///usr/share/xml/docbook.xml"/> 2331<delegateURI uriStartString="http://www.oasis-open.org/docbook/" 2332 catalog="file:///usr/share/xml/docbook.xml"/> 2333...</pre> 2334 2335<p>Delegation is the core features which allows to build a tree of catalogs, 2336easier to maintain than a single catalog, based on Public Identifier, System 2337Identifier or URI prefixes it instructs the catalog software to look up 2338entries in another resource. This feature allow to build hierarchies of 2339catalogs, the set of entries presented should be sufficient to redirect the 2340resolution of all DocBook references to the specific catalog in 2341<code>/usr/share/xml/docbook.xml</code> this one in turn could delegate all 2342references for DocBook 4.2.1 to a specific catalog installed at the same time 2343as the DocBook resources on the local machine.</p> 2344 2345<h3><a name="reference">How to tune catalog usage:</a></h3> 2346 2347<p>The user can change the default catalog behaviour by redirecting queries 2348to its own set of catalogs, this can be done by setting the 2349<code>XML_CATALOG_FILES</code> environment variable to a list of catalogs, an 2350empty one should deactivate loading the default <code>/etc/xml/catalog</code> 2351default catalog</p> 2352 2353<h3><a name="validate">How to debug catalog processing:</a></h3> 2354 2355<p>Setting up the <code>XML_DEBUG_CATALOG</code> environment variable will 2356make libxml output debugging informations for each catalog operations, for 2357example:</p> 2358<pre>orchis:~/XML -> xmllint --memory --noout test/ent2 2359warning: failed to load external entity "title.xml" 2360orchis:~/XML -> export XML_DEBUG_CATALOG= 2361orchis:~/XML -> xmllint --memory --noout test/ent2 2362Failed to parse catalog /etc/xml/catalog 2363Failed to parse catalog /etc/xml/catalog 2364warning: failed to load external entity "title.xml" 2365Catalogs cleanup 2366orchis:~/XML -> </pre> 2367 2368<p>The test/ent2 references an entity, running the parser from memory makes 2369the base URI unavailable and the the "title.xml" entity cannot be loaded. 2370Setting up the debug environment variable allows to detect that an attempt is 2371made to load the <code>/etc/xml/catalog</code> but since it's not present the 2372resolution fails.</p> 2373 2374<p>But the most advanced way to debug XML catalog processing is to use the 2375<strong>xmlcatalog</strong> command shipped with libxml2, it allows to load 2376catalogs and make resolution queries to see what is going on. This is also 2377used for the regression tests:</p> 2378<pre>orchis:~/XML -> /xmlcatalog test/catalogs/docbook.xml \ 2379 "-//OASIS//DTD DocBook XML V4.1.2//EN" 2380http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd 2381orchis:~/XML -> </pre> 2382 2383<p>For debugging what is going on, adding one -v flags increase the verbosity 2384level to indicate the processing done (adding a second flag also indicate 2385what elements are recognized at parsing):</p> 2386<pre>orchis:~/XML -> /xmlcatalog -v test/catalogs/docbook.xml \ 2387 "-//OASIS//DTD DocBook XML V4.1.2//EN" 2388Parsing catalog test/catalogs/docbook.xml's content 2389Found public match -//OASIS//DTD DocBook XML V4.1.2//EN 2390http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd 2391Catalogs cleanup 2392orchis:~/XML -> </pre> 2393 2394<p>A shell interface is also available to debug and process multiple queries 2395(and for regression tests):</p> 2396<pre>orchis:~/XML -> /xmlcatalog -shell test/catalogs/docbook.xml \ 2397 "-//OASIS//DTD DocBook XML V4.1.2//EN" 2398> help 2399Commands available: 2400public PublicID: make a PUBLIC identifier lookup 2401system SystemID: make a SYSTEM identifier lookup 2402resolve PublicID SystemID: do a full resolver lookup 2403add 'type' 'orig' 'replace' : add an entry 2404del 'values' : remove values 2405dump: print the current catalog state 2406debug: increase the verbosity level 2407quiet: decrease the verbosity level 2408exit: quit the shell 2409> public "-//OASIS//DTD DocBook XML V4.1.2//EN" 2410http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd 2411> quit 2412orchis:~/XML -> </pre> 2413 2414<p>This should be sufficient for most debugging purpose, this was actually 2415used heavily to debug the XML Catalog implementation itself.</p> 2416 2417<h3><a name="Declaring">How to create and maintain</a> catalogs:</h3> 2418 2419<p>Basically XML Catalogs are XML files, you can either use XML tools to 2420manage them or use <strong>xmlcatalog</strong> for this. The basic step is 2421to create a catalog the -create option provide this facility:</p> 2422<pre>orchis:~/XML -> /xmlcatalog --create tst.xml 2423<?xml version="1.0"?> 2424<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" 2425 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 2426<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/> 2427orchis:~/XML -> </pre> 2428 2429<p>By default xmlcatalog does not overwrite the original catalog and save the 2430result on the standard output, this can be overridden using the -noout 2431option. The <code>-add</code> command allows to add entries in the 2432catalog:</p> 2433<pre>orchis:~/XML -> /xmlcatalog --noout --create --add "public" \ 2434 "-//OASIS//DTD DocBook XML V4.1.2//EN" \ 2435 http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd tst.xml 2436orchis:~/XML -> cat tst.xml 2437<?xml version="1.0"?> 2438<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" \ 2439 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 2440<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"> 2441<public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN" 2442 uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/> 2443</catalog> 2444orchis:~/XML -> </pre> 2445 2446<p>The <code>-add</code> option will always take 3 parameters even if some of 2447the XML Catalog constructs (like nextCatalog) will have only a single 2448argument, just pass a third empty string, it will be ignored.</p> 2449 2450<p>Similarly the <code>-del</code> option remove matching entries from the 2451catalog:</p> 2452<pre>orchis:~/XML -> /xmlcatalog --del \ 2453 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" tst.xml 2454<?xml version="1.0"?> 2455<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" 2456 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 2457<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/> 2458orchis:~/XML -> </pre> 2459 2460<p>The catalog is now empty. Note that the matching of <code>-del</code> is 2461exact and would have worked in a similar fashion with the Public ID 2462string.</p> 2463 2464<p>This is rudimentary but should be sufficient to manage a not too complex 2465catalog tree of resources.</p> 2466 2467<h3><a name="implemento">The implementor corner quick review of the 2468API:</a></h3> 2469 2470<p>First, and like for every other module of libxml, there is an 2471automatically generated <a href="html/libxml-catalog.html">API page for 2472catalog support</a>.</p> 2473 2474<p>The header for the catalog interfaces should be included as:</p> 2475<pre>#include <libxml/catalog.h></pre> 2476 2477<p>The API is voluntarily kept very simple. First it is not obvious that 2478applications really need access to it since it is the default behaviour of 2479libxml (Note: it is possible to completely override libxml default catalog by 2480using <a href="html/libxml-parser.html">xmlSetExternalEntityLoader</a> to 2481plug an application specific resolver).</p> 2482 2483<p>Basically libxml support 2 catalog lists:</p> 2484<ul> 2485 <li>the default one, global shared by all the application</li> 2486 <li>a per-document catalog, this one is built if the document uses the 2487 <code>oasis-xml-catalog</code> PIs to specify its own catalog list, it is 2488 associated to the parser context and destroyed when the parsing context 2489 is destroyed.</li> 2490</ul> 2491 2492<p>the document one will be used first if it exists.</p> 2493 2494<h4>Initialization routines:</h4> 2495 2496<p>xmlInitializeCatalog(), xmlLoadCatalog() and xmlLoadCatalogs() should be 2497used at startup to initialize the catalog, if the catalog should be 2498initialized with specific values xmlLoadCatalog() or xmlLoadCatalogs() 2499should be called before xmlInitializeCatalog() which would otherwise do a 2500default initialization first.</p> 2501 2502<p>The xmlCatalogAddLocal() call is used by the parser to grow the document 2503own catalog list if needed.</p> 2504 2505<h4>Preferences setup:</h4> 2506 2507<p>The XML Catalog spec requires the possibility to select default 2508preferences between public and system delegation, 2509xmlCatalogSetDefaultPrefer() allows this, xmlCatalogSetDefaults() and 2510xmlCatalogGetDefaults() allow to control if XML Catalogs resolution should 2511be forbidden, allowed for global catalog, for document catalog or both, the 2512default is to allow both.</p> 2513 2514<p>And of course xmlCatalogSetDebug() allows to generate debug messages 2515(through the xmlGenericError() mechanism).</p> 2516 2517<h4>Querying routines:</h4> 2518 2519<p>xmlCatalogResolve(), xmlCatalogResolveSystem(), xmlCatalogResolvePublic() 2520and xmlCatalogResolveURI() are relatively explicit if you read the XML 2521Catalog specification they correspond to section 7 algorithms, they should 2522also work if you have loaded an SGML catalog with a simplified semantic.</p> 2523 2524<p>xmlCatalogLocalResolve() and xmlCatalogLocalResolveURI() are the same but 2525operate on the document catalog list</p> 2526 2527<h4>Cleanup and Miscellaneous:</h4> 2528 2529<p>xmlCatalogCleanup() free-up the global catalog, xmlCatalogFreeLocal() is 2530the per-document equivalent.</p> 2531 2532<p>xmlCatalogAdd() and xmlCatalogRemove() are used to dynamically modify the 2533first catalog in the global list, and xmlCatalogDump() allows to dump a 2534catalog state, those routines are primarily designed for xmlcatalog, I'm not 2535sure that exposing more complex interfaces (like navigation ones) would be 2536really useful.</p> 2537 2538<p>The xmlParseCatalogFile() is a function used to load XML Catalog files, 2539it's similar as xmlParseFile() except it bypass all catalog lookups, it's 2540provided because this functionality may be useful for client tools.</p> 2541 2542<h4>threaded environments:</h4> 2543 2544<p>Since the catalog tree is built progressively, some care has been taken to 2545try to avoid troubles in multithreaded environments. The code is now thread 2546safe assuming that the libxml library has been compiled with threads 2547support.</p> 2548 2549<p></p> 2550 2551<h3><a name="Other">Other resources</a></h3> 2552 2553<p>The XML Catalog specification is relatively recent so there isn't much 2554literature to point at:</p> 2555<ul> 2556 <li>You can find an good rant from Norm Walsh about <a 2557 href="http://www.arbortext.com/Think_Tank/XML_Resources/Issue_Three/issue_three.html">the 2558 need for catalogs</a>, it provides a lot of context informations even if 2559 I don't agree with everything presented.</li> 2560 <li>An <a href="http://home.ccil.org/~cowan/XML/XCatalog.html">old XML 2561 catalog proposal</a> from John Cowan</li> 2562 <li>The <a href="http://www.rddl.org/">Resource Directory Description 2563 Language</a> (RDDL) another catalog system but more oriented toward 2564 providing metadata for XML namespaces.</li> 2565 <li>the page from the OASIS Technical <a 2566 href="http://www.oasis-open.org/committees/entity/">Committee on Entity 2567 Resolution</a> who maintains XML Catalog, you will find pointers to the 2568 specification update, some background and pointers to others tools 2569 providing XML Catalog support</li> 2570 <li>I have uploaded <a href="ftp://xmlsoft.org/test/dbk412catalog.tar.gz">a 2571 mall tarball</a> containing XML Catalogs for DocBook 4.1.2 which seems to 2572 work fine for me</li> 2573 <li>The <a href="http://www.xmlsoft.org/xmlcatalog_man.html">xmlcatalog 2574 manual page</a></li> 2575</ul> 2576 2577<p>If you have suggestions for corrections or additions, simply contact 2578me:</p> 2579 2580<h2><a name="library">The parser interfaces</a></h2> 2581 2582<p>This section is directly intended to help programmers getting bootstrapped 2583using the XML library from the C language. It is not intended to be 2584extensive. I hope the automatically generated documents will provide the 2585completeness required, but as a separate set of documents. The interfaces of 2586the XML library are by principle low level, there is nearly zero abstraction. 2587Those interested in a higher level API should <a href="#DOM">look at 2588DOM</a>.</p> 2589 2590<p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are 2591separated from the <a href="html/libxml-htmlparser.html">HTML parser 2592interfaces</a>. Let's have a look at how the XML parser can be called:</p> 2593 2594<h3><a name="Invoking">Invoking the parser : the pull method</a></h3> 2595 2596<p>Usually, the first thing to do is to read an XML input. The parser accepts 2597documents either from in-memory strings or from files. The functions are 2598defined in "parser.h":</p> 2599<dl> 2600 <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt> 2601 <dd><p>Parse a null-terminated string containing the document.</p> 2602 </dd> 2603</dl> 2604<dl> 2605 <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt> 2606 <dd><p>Parse an XML document contained in a (possibly compressed) 2607 file.</p> 2608 </dd> 2609</dl> 2610 2611<p>The parser returns a pointer to the document structure (or NULL in case of 2612failure).</p> 2613 2614<h3 id="Invoking1">Invoking the parser: the push method</h3> 2615 2616<p>In order for the application to keep the control when the document is 2617being fetched (which is common for GUI based programs) libxml provides a push 2618interface, too, as of version 1.8.3. Here are the interface functions:</p> 2619<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax, 2620 void *user_data, 2621 const char *chunk, 2622 int size, 2623 const char *filename); 2624int xmlParseChunk (xmlParserCtxtPtr ctxt, 2625 const char *chunk, 2626 int size, 2627 int terminate);</pre> 2628 2629<p>and here is a simple example showing how to use the interface:</p> 2630<pre> FILE *f; 2631 2632 f = fopen(filename, "r"); 2633 if (f != NULL) { 2634 int res, size = 1024; 2635 char chars[1024]; 2636 xmlParserCtxtPtr ctxt; 2637 2638 res = fread(chars, 1, 4, f); 2639 if (res > 0) { 2640 ctxt = xmlCreatePushParserCtxt(NULL, NULL, 2641 chars, res, filename); 2642 while ((res = fread(chars, 1, size, f)) > 0) { 2643 xmlParseChunk(ctxt, chars, res, 0); 2644 } 2645 xmlParseChunk(ctxt, chars, 0, 1); 2646 doc = ctxt->myDoc; 2647 xmlFreeParserCtxt(ctxt); 2648 } 2649 }</pre> 2650 2651<p>The HTML parser embedded into libxml also has a push interface; the 2652functions are just prefixed by "html" rather than "xml".</p> 2653 2654<h3 id="Invoking2">Invoking the parser: the SAX interface</h3> 2655 2656<p>The tree-building interface makes the parser memory-hungry, first loading 2657the document in memory and then building the tree itself. Reading a document 2658without building the tree is possible using the SAX interfaces (see SAX.h and 2659<a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James 2660Henstridge's documentation</a>). Note also that the push interface can be 2661limited to SAX: just use the two first arguments of 2662<code>xmlCreatePushParserCtxt()</code>.</p> 2663 2664<h3><a name="Building">Building a tree from scratch</a></h3> 2665 2666<p>The other way to get an XML tree in memory is by building it. Basically 2667there is a set of functions dedicated to building new elements. (These are 2668also described in <libxml/tree.h>.) For example, here is a piece of 2669code that produces the XML document used in the previous examples:</p> 2670<pre> #include <libxml/tree.h> 2671 xmlDocPtr doc; 2672 xmlNodePtr tree, subtree; 2673 2674 doc = xmlNewDoc("1.0"); 2675 doc->children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL); 2676 xmlSetProp(doc->children, "prop1", "gnome is great"); 2677 xmlSetProp(doc->children, "prop2", "& linux too"); 2678 tree = xmlNewChild(doc->children, NULL, "head", NULL); 2679 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome"); 2680 tree = xmlNewChild(doc->children, NULL, "chapter", NULL); 2681 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure"); 2682 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ..."); 2683 subtree = xmlNewChild(tree, NULL, "image", NULL); 2684 xmlSetProp(subtree, "href", "linus.gif");</pre> 2685 2686<p>Not really rocket science ...</p> 2687 2688<h3><a name="Traversing">Traversing the tree</a></h3> 2689 2690<p>Basically by <a href="html/libxml-tree.html">including "tree.h"</a> your 2691code has access to the internal structure of all the elements of the tree. 2692The names should be somewhat simple like <strong>parent</strong>, 2693<strong>children</strong>, <strong>next</strong>, <strong>prev</strong>, 2694<strong>properties</strong>, etc... For example, still with the previous 2695example:</p> 2696<pre><code>doc->children->children->children</code></pre> 2697 2698<p>points to the title element,</p> 2699<pre>doc->children->children->next->children->children</pre> 2700 2701<p>points to the text node containing the chapter title "The Linux 2702adventure".</p> 2703 2704<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be 2705present before the document root, so <code>doc->children</code> may point 2706to an element which is not the document Root Element; a function 2707<code>xmlDocGetRootElement()</code> was added for this purpose.</p> 2708 2709<h3><a name="Modifying">Modifying the tree</a></h3> 2710 2711<p>Functions are provided for reading and writing the document content. Here 2712is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p> 2713<dl> 2714 <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const 2715 xmlChar *value);</code></dt> 2716 <dd><p>This sets (or changes) an attribute carried by an ELEMENT node. 2717 The value can be NULL.</p> 2718 </dd> 2719</dl> 2720<dl> 2721 <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar 2722 *name);</code></dt> 2723 <dd><p>This function returns a pointer to new copy of the property 2724 content. Note that the user must deallocate the result.</p> 2725 </dd> 2726</dl> 2727 2728<p>Two functions are provided for reading and writing the text associated 2729with elements:</p> 2730<dl> 2731 <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar 2732 *value);</code></dt> 2733 <dd><p>This function takes an "external" string and converts it to one 2734 text node or possibly to a list of entity and text nodes. All 2735 non-predefined entity references like &Gnome; will be stored 2736 internally as entity nodes, hence the result of the function may not be 2737 a single node.</p> 2738 </dd> 2739</dl> 2740<dl> 2741 <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int 2742 inLine);</code></dt> 2743 <dd><p>This function is the inverse of 2744 <code>xmlStringGetNodeList()</code>. It generates a new string 2745 containing the content of the text and entity nodes. Note the extra 2746 argument inLine. If this argument is set to 1, the function will expand 2747 entity references. For example, instead of returning the &Gnome; 2748 XML encoding in the string, it will substitute it with its value (say, 2749 "GNU Network Object Model Environment").</p> 2750 </dd> 2751</dl> 2752 2753<h3><a name="Saving">Saving a tree</a></h3> 2754 2755<p>Basically 3 options are possible:</p> 2756<dl> 2757 <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int 2758 *size);</code></dt> 2759 <dd><p>Returns a buffer into which the document has been saved.</p> 2760 </dd> 2761</dl> 2762<dl> 2763 <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt> 2764 <dd><p>Dumps a document to an open file descriptor.</p> 2765 </dd> 2766</dl> 2767<dl> 2768 <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt> 2769 <dd><p>Saves the document to a file. In this case, the compression 2770 interface is triggered if it has been turned on.</p> 2771 </dd> 2772</dl> 2773 2774<h3><a name="Compressio">Compression</a></h3> 2775 2776<p>The library transparently handles compression when doing file-based 2777accesses. The level of compression on saves can be turned on either globally 2778or individually for one file:</p> 2779<dl> 2780 <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt> 2781 <dd><p>Gets the document compression ratio (0-9).</p> 2782 </dd> 2783</dl> 2784<dl> 2785 <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt> 2786 <dd><p>Sets the document compression ratio.</p> 2787 </dd> 2788</dl> 2789<dl> 2790 <dt><code>int xmlGetCompressMode(void);</code></dt> 2791 <dd><p>Gets the default compression ratio.</p> 2792 </dd> 2793</dl> 2794<dl> 2795 <dt><code>void xmlSetCompressMode(int mode);</code></dt> 2796 <dd><p>Sets the default compression ratio.</p> 2797 </dd> 2798</dl> 2799 2800<h2><a name="Entities">Entities or no entities</a></h2> 2801 2802<p>Entities in principle are similar to simple C macros. An entity defines an 2803abbreviation for a given string that you can reuse many times throughout the 2804content of your document. Entities are especially useful when a given string 2805may occur frequently within a document, or to confine the change needed to a 2806document to a restricted area in the internal subset of the document (at the 2807beginning). Example:</p> 2808<pre>1 <?xml version="1.0"?> 28092 <!DOCTYPE EXAMPLE SYSTEM "example.dtd" [ 28103 <!ENTITY xml "Extensible Markup Language"> 28114 ]> 28125 <EXAMPLE> 28136 &xml; 28147 </EXAMPLE></pre> 2815 2816<p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing 2817its name with '&' and following it by ';' without any spaces added. There 2818are 5 predefined entities in libxml allowing you to escape charaters with 2819predefined meaning in some parts of the xml document content: 2820<strong>&lt;</strong> for the character '<', <strong>&gt;</strong> 2821for the character '>', <strong>&apos;</strong> for the character ''', 2822<strong>&quot;</strong> for the character '"', and 2823<strong>&amp;</strong> for the character '&'.</p> 2824 2825<p>One of the problems related to entities is that you may want the parser to 2826substitute an entity's content so that you can see the replacement text in 2827your application. Or you may prefer to keep entity references as such in the 2828content to be able to save the document back without losing this usually 2829precious information (if the user went through the pain of explicitly 2830defining entities, he may have a a rather negative attitude if you blindly 2831susbtitute them as saving time). The <a 2832href="html/libxml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a> 2833function allows you to check and change the behaviour, which is to not 2834substitute entities by default.</p> 2835 2836<p>Here is the DOM tree built by libxml for the previous document in the 2837default case:</p> 2838<pre>/gnome/src/gnome-xml -> /xmllint --debug test/ent1 2839DOCUMENT 2840version=1.0 2841 ELEMENT EXAMPLE 2842 TEXT 2843 content= 2844 ENTITY_REF 2845 INTERNAL_GENERAL_ENTITY xml 2846 content=Extensible Markup Language 2847 TEXT 2848 content=</pre> 2849 2850<p>And here is the result when substituting entities:</p> 2851<pre>/gnome/src/gnome-xml -> /tester --debug --noent test/ent1 2852DOCUMENT 2853version=1.0 2854 ELEMENT EXAMPLE 2855 TEXT 2856 content= Extensible Markup Language</pre> 2857 2858<p>So, entities or no entities? Basically, it depends on your use case. I 2859suggest that you keep the non-substituting default behaviour and avoid using 2860entities in your XML document or data if you are not willing to handle the 2861entity references elements in the DOM tree.</p> 2862 2863<p>Note that at save time libxml enforces the conversion of the predefined 2864entities where necessary to prevent well-formedness problems, and will also 2865transparently replace those with chars (i.e. it will not generate entity 2866reference elements in the DOM tree or call the reference() SAX callback when 2867finding them in the input).</p> 2868 2869<p><span style="background-color: #FF0000">WARNING</span>: handling entities 2870on top of the libxml SAX interface is difficult!!! If you plan to use 2871non-predefined entities in your documents, then the learning cuvre to handle 2872then using the SAX API may be long. If you plan to use complex documents, I 2873strongly suggest you consider using the DOM interface instead and let libxml 2874deal with the complexity rather than trying to do it yourself.</p> 2875 2876<h2><a name="Namespaces">Namespaces</a></h2> 2877 2878<p>The libxml library implements <a 2879href="http://www.w3.org/TR/REC-xml-names/">XML namespaces</a> support by 2880recognizing namespace contructs in the input, and does namespace lookup 2881automatically when building the DOM tree. A namespace declaration is 2882associated with an in-memory structure and all elements or attributes within 2883that namespace point to it. Hence testing the namespace is a simple and fast 2884equality operation at the user level.</p> 2885 2886<p>I suggest that people using libxml use a namespace, and declare it in the 2887root element of their document as the default namespace. Then they don't need 2888to use the prefix in the content but we will have a basis for future semantic 2889refinement and merging of data from different sources. This doesn't increase 2890the size of the XML output significantly, but significantly increases its 2891value in the long-term. Example:</p> 2892<pre><mydoc xmlns="http://mydoc.example.org/schemas/"> 2893 <elem1>...</elem1> 2894 <elem2>...</elem2> 2895</mydoc></pre> 2896 2897<p>The namespace value has to be an absolute URL, but the URL doesn't have to 2898point to any existing resource on the Web. It will bind all the element and 2899atributes with that URL. I suggest to use an URL within a domain you control, 2900and that the URL should contain some kind of version information if possible. 2901For example, <code>"http://www.gnome.org/gnumeric/1.0/"</code> is a good 2902namespace scheme.</p> 2903 2904<p>Then when you load a file, make sure that a namespace carrying the 2905version-independent prefix is installed on the root element of your document, 2906and if the version information don't match something you know, warn the user 2907and be liberal in what you accept as the input. Also do *not* try to base 2908namespace checking on the prefix value. <foo:text> may be exactly the 2909same as <bar:text> in another document. What really matters is the URI 2910associated with the element or the attribute, not the prefix string (which is 2911just a shortcut for the full URI). In libxml, element and attributes have an 2912<code>ns</code> field pointing to an xmlNs structure detailing the namespace 2913prefix and its URI.</p> 2914 2915<p>@@Interfaces@@</p> 2916 2917<p>@@Examples@@</p> 2918 2919<p>Usually people object to using namespaces together with validity checking. 2920I will try to make sure that using namespaces won't break validity checking, 2921so even if you plan to use or currently are using validation I strongly 2922suggest adding namespaces to your document. A default namespace scheme 2923<code>xmlns="http://...."</code> should not break validity even on less 2924flexible parsers. Using namespaces to mix and differentiate content coming 2925from multiple DTDs will certainly break current validation schemes. I will 2926try to provide ways to do this, but this may not be portable or 2927standardized.</p> 2928 2929<h2><a name="Upgrading">Upgrading 1.x code</a></h2> 2930 2931<p>Incompatible changes:</p> 2932 2933<p>Version 2 of libxml is the first version introducing serious backward 2934incompatible changes. The main goals were:</p> 2935<ul> 2936 <li>a general cleanup. A number of mistakes inherited from the very early 2937 versions couldn't be changed due to compatibility constraints. Example 2938 the "childs" element in the nodes.</li> 2939 <li>Uniformization of the various nodes, at least for their header and link 2940 parts (doc, parent, children, prev, next), the goal is a simpler 2941 programming model and simplifying the task of the DOM implementors.</li> 2942 <li>better conformances to the XML specification, for example version 1.x 2943 had an heuristic to try to detect ignorable white spaces. As a result the 2944 SAX event generated were ignorableWhitespace() while the spec requires 2945 character() in that case. This also mean that a number of DOM node 2946 containing blank text may populate the DOM tree which were not present 2947 before.</li> 2948</ul> 2949 2950<h3>How to fix libxml-1.x code:</h3> 2951 2952<p>So client code of libxml designed to run with version 1.x may have to be 2953changed to compile against version 2.x of libxml. Here is a list of changes 2954that I have collected, they may not be sufficient, so in case you find other 2955change which are required, <a href="mailto:Daniel.�eillardw3.org">drop me a 2956mail</a>:</p> 2957<ol> 2958 <li>The package name have changed from libxml to libxml2, the library name 2959 is now -lxml2 . There is a new xml2-config script which should be used to 2960 select the right parameters libxml2</li> 2961 <li>Node <strong>childs</strong> field has been renamed 2962 <strong>children</strong> so s/childs/children/g should be applied 2963 (probablility of having "childs" anywere else is close to 0+</li> 2964 <li>The document don't have anymore a <strong>root</strong> element it has 2965 been replaced by <strong>children</strong> and usually you will get a 2966 list of element here. For example a Dtd element for the internal subset 2967 and it's declaration may be found in that list, as well as processing 2968 instructions or comments found before or after the document root element. 2969 Use <strong>xmlDocGetRootElement(doc)</strong> to get the root element of 2970 a document. Alternatively if you are sure to not reference Dtds nor have 2971 PIs or comments before or after the root element 2972 s/->root/->children/g will probably do it.</li> 2973 <li>The white space issue, this one is more complex, unless special case of 2974 validating parsing, the line breaks and spaces usually used for indenting 2975 and formatting the document content becomes significant. So they are 2976 reported by SAX and if your using the DOM tree, corresponding nodes are 2977 generated. Too approach can be taken: 2978 <ol> 2979 <li>lazy one, use the compatibility call 2980 <strong>xmlKeepBlanksDefault(0)</strong> but be aware that you are 2981 relying on a special (and possibly broken) set of heuristics of 2982 libxml to detect ignorable blanks. Don't complain if it breaks or 2983 make your application not 100% clean w.r.t. to it's input.</li> 2984 <li>the Right Way: change you code to accept possibly unsignificant 2985 blanks characters, or have your tree populated with weird blank text 2986 nodes. You can spot them using the comodity function 2987 <strong>xmlIsBlankNode(node)</strong> returning 1 for such blank 2988 nodes.</li> 2989 </ol> 2990 <p>Note also that with the new default the output functions don't add any 2991 extra indentation when saving a tree in order to be able to round trip 2992 (read and save) without inflating the document with extra formatting 2993 chars.</p> 2994 </li> 2995 <li>The include path has changed to $prefix/libxml/ and the includes 2996 themselves uses this new prefix in includes instructions... If you are 2997 using (as expected) the 2998 <pre>xml2-config --cflags</pre> 2999 <p>output to generate you compile commands this will probably work out of 3000 the box</p> 3001 </li> 3002 <li>xmlDetectCharEncoding takes an extra argument indicating the lenght in 3003 byte of the head of the document available for character detection.</li> 3004</ol> 3005 3006<h3>Ensuring both libxml-1.x and libxml-2.x compatibility</h3> 3007 3008<p>Two new version of libxml (1.8.11) and libxml2 (2.3.4) have been released 3009to allow smoth upgrade of existing libxml v1code while retaining 3010compatibility. They offers the following:</p> 3011<ol> 3012 <li>similar include naming, one should use 3013 <strong>#include<libxml/...></strong> in both cases.</li> 3014 <li>similar identifiers defined via macros for the child and root fields: 3015 respectively <strong>xmlChildrenNode</strong> and 3016 <strong>xmlRootNode</strong></li> 3017 <li>a new macro <strong>LIBXML_TEST_VERSION</strong> which should be 3018 inserted once in the client code</li> 3019</ol> 3020 3021<p>So the roadmap to upgrade your existing libxml applications is the 3022following:</p> 3023<ol> 3024 <li>install the libxml-1.8.8 (and libxml-devel-1.8.8) packages</li> 3025 <li>find all occurences where the xmlDoc <strong>root</strong> field is 3026 used and change it to <strong>xmlRootNode</strong></li> 3027 <li>similary find all occurences where the xmlNode <strong>childs</strong> 3028 field is used and change it to <strong>xmlChildrenNode</strong></li> 3029 <li>add a <strong>LIBXML_TEST_VERSION</strong> macro somewhere in your 3030 <strong>main()</strong> or in the library init entry point</li> 3031 <li>Recompile, check compatibility, it should still work</li> 3032 <li>Change your configure script to look first for xml2-config and fallback 3033 using xml-config . Use the --cflags and --libs ouptut of the command as 3034 the Include and Linking parameters needed to use libxml.</li> 3035 <li>install libxml2-2.3.x and libxml2-devel-2.3.x (libxml-1.8.y and 3036 libxml-devel-1.8.y can be kept simultaneously)</li> 3037 <li>remove your config.cache, relaunch your configuration mechanism, and 3038 recompile, if steps 2 and 3 were done right it should compile as-is</li> 3039 <li>Test that your application is still running correctly, if not this may 3040 be due to extra empty nodes due to formating spaces being kept in libxml2 3041 contrary to libxml1, in that case insert xmlKeepBlanksDefault(1) in your 3042 code before calling the parser (next to 3043 <strong>LIBXML_TEST_VERSION</strong> is a fine place).</li> 3044</ol> 3045 3046<p>Following those steps should work. It worked for some of my own code.</p> 3047 3048<p>Let me put some emphasis on the fact that there is far more changes from 3049libxml 1.x to 2.x than the ones you may have to patch for. The overall code 3050has been considerably cleaned up and the conformance to the XML specification 3051has been drastically improved too. Don't take those changes as an excuse to 3052not upgrade, it may cost a lot on the long term ...</p> 3053 3054<h2><a name="Thread">Thread safety</a></h2> 3055 3056<p>Starting with 2.4.7, libxml makes provisions to ensure that concurent 3057threads can safely work in parallel parsing different documents. There is 3058however a couple of things to do to ensure it:</p> 3059<ul> 3060 <li>configure the library accordingly using the --with-threads options</li> 3061 <li>call xmlInitParser() in the "main" thread before using any of the 3062 libxml API (except possibly selecting a different memory allocator)</li> 3063</ul> 3064 3065<p>Note that the thread safety cannot be ensured for multiple threads sharing 3066the same document, the locking must be done at the application level, libxml 3067exports a basic mutex and reentrant mutexes API in <libxml/threads.h>. 3068The parts of the library checked for thread safety are:</p> 3069<ul> 3070 <li>concurrent loading</li> 3071 <li>file access resolution</li> 3072 <li>catalog access</li> 3073 <li>catalog building</li> 3074 <li>entities lookup/accesses</li> 3075 <li>validation</li> 3076 <li>global variables per-thread override</li> 3077 <li>memory handling</li> 3078</ul> 3079 3080<p>XPath is supposed to be thread safe now, but this wasn't tested 3081seriously.</p> 3082 3083<h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2> 3084 3085<p><a href="http://www.w3.org/DOM/">DOM</a> stands for the <em>Document 3086Object Model</em>; this is an API for accessing XML or HTML structured 3087documents. Native support for DOM in Gnome is on the way (module gnome-dom), 3088and will be based on gnome-xml. This will be a far cleaner interface to 3089manipulate XML files within Gnome since it won't expose the internal 3090structure.</p> 3091 3092<p>The current DOM implementation on top of libxml is the <a 3093href="http://cvs.gnome.org/lxr/source/gdome2/">gdome2 Gnome module</a>, this 3094is a full DOM interface, thanks to Paolo Casarini, check the <a 3095href="http://www.cs.unibo.it/~casarini/gdome2/">Gdome2 homepage</a> for more 3096informations.</p> 3097 3098<h2><a name="Example"></a><a name="real">A real example</a></h2> 3099 3100<p>Here is a real size example, where the actual content of the application 3101data is not kept in the DOM tree but uses internal structures. It is based on 3102a proposal to keep a database of jobs related to Gnome, with an XML based 3103storage structure. Here is an <a href="gjobs.xml">XML encoded jobs 3104base</a>:</p> 3105<pre><?xml version="1.0"?> 3106<gjob:Helping xmlns:gjob="http://www.gnome.org/some-location"> 3107 <gjob:Jobs> 3108 3109 <gjob:Job> 3110 <gjob:Project ID="3"/> 3111 <gjob:Application>GBackup</gjob:Application> 3112 <gjob:Category>Development</gjob:Category> 3113 3114 <gjob:Update> 3115 <gjob:Status>Open</gjob:Status> 3116 <gjob:Modified>Mon, 07 Jun 1999 20:27:45 -0400 MET DST</gjob:Modified> 3117 <gjob:Salary>USD 0.00</gjob:Salary> 3118 </gjob:Update> 3119 3120 <gjob:Developers> 3121 <gjob:Developer> 3122 </gjob:Developer> 3123 </gjob:Developers> 3124 3125 <gjob:Contact> 3126 <gjob:Person>Nathan Clemons</gjob:Person> 3127 <gjob:Email>nathan@windsofstorm.net</gjob:Email> 3128 <gjob:Company> 3129 </gjob:Company> 3130 <gjob:Organisation> 3131 </gjob:Organisation> 3132 <gjob:Webpage> 3133 </gjob:Webpage> 3134 <gjob:Snailmail> 3135 </gjob:Snailmail> 3136 <gjob:Phone> 3137 </gjob:Phone> 3138 </gjob:Contact> 3139 3140 <gjob:Requirements> 3141 The program should be released as free software, under the GPL. 3142 </gjob:Requirements> 3143 3144 <gjob:Skills> 3145 </gjob:Skills> 3146 3147 <gjob:Details> 3148 A GNOME based system that will allow a superuser to configure 3149 compressed and uncompressed files and/or file systems to be backed 3150 up with a supported media in the system. This should be able to 3151 perform via find commands generating a list of files that are passed 3152 to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine 3153 or via operations performed on the filesystem itself. Email 3154 notification and GUI status display very important. 3155 </gjob:Details> 3156 3157 </gjob:Job> 3158 3159 </gjob:Jobs> 3160</gjob:Helping></pre> 3161 3162<p>While loading the XML file into an internal DOM tree is a matter of 3163calling only a couple of functions, browsing the tree to gather the ata and 3164generate the internal structures is harder, and more error prone.</p> 3165 3166<p>The suggested principle is to be tolerant with respect to the input 3167structure. For example, the ordering of the attributes is not significant, 3168the XML specification is clear about it. It's also usually a good idea not to 3169depend on the order of the children of a given node, unless it really makes 3170things harder. Here is some code to parse the information for a person:</p> 3171<pre>/* 3172 * A person record 3173 */ 3174typedef struct person { 3175 char *name; 3176 char *email; 3177 char *company; 3178 char *organisation; 3179 char *smail; 3180 char *webPage; 3181 char *phone; 3182} person, *personPtr; 3183 3184/* 3185 * And the code needed to parse it 3186 */ 3187personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) { 3188 personPtr ret = NULL; 3189 3190DEBUG("parsePerson\n"); 3191 /* 3192 * allocate the struct 3193 */ 3194 ret = (personPtr) malloc(sizeof(person)); 3195 if (ret == NULL) { 3196 fprintf(stderr,"out of memory\n"); 3197 return(NULL); 3198 } 3199 memset(ret, 0, sizeof(person)); 3200 3201 /* We don't care what the top level element name is */ 3202 cur = cur->xmlChildrenNode; 3203 while (cur != NULL) { 3204 if ((!strcmp(cur->name, "Person")) && (cur->ns == ns)) 3205 ret->name = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3206 if ((!strcmp(cur->name, "Email")) && (cur->ns == ns)) 3207 ret->email = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3208 cur = cur->next; 3209 } 3210 3211 return(ret); 3212}</pre> 3213 3214<p>Here are a couple of things to notice:</p> 3215<ul> 3216 <li>Usually a recursive parsing style is the more convenient one: XML data 3217 is by nature subject to repetitive constructs and usually exibits highly 3218 stuctured patterns.</li> 3219 <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, 3220 i.e. the pointer to the global XML document and the namespace reserved to 3221 the application. Document wide information are needed for example to 3222 decode entities and it's a good coding practice to define a namespace for 3223 your application set of data and test that the element and attributes 3224 you're analyzing actually pertains to your application space. This is 3225 done by a simple equality test (cur->ns == ns).</li> 3226 <li>To retrieve text and attributes value, you can use the function 3227 <em>xmlNodeListGetString</em> to gather all the text and entity reference 3228 nodes generated by the DOM output and produce an single text string.</li> 3229</ul> 3230 3231<p>Here is another piece of code used to parse another level of the 3232structure:</p> 3233<pre>#include <libxml/tree.h> 3234/* 3235 * a Description for a Job 3236 */ 3237typedef struct job { 3238 char *projectID; 3239 char *application; 3240 char *category; 3241 personPtr contact; 3242 int nbDevelopers; 3243 personPtr developers[100]; /* using dynamic alloc is left as an exercise */ 3244} job, *jobPtr; 3245 3246/* 3247 * And the code needed to parse it 3248 */ 3249jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) { 3250 jobPtr ret = NULL; 3251 3252DEBUG("parseJob\n"); 3253 /* 3254 * allocate the struct 3255 */ 3256 ret = (jobPtr) malloc(sizeof(job)); 3257 if (ret == NULL) { 3258 fprintf(stderr,"out of memory\n"); 3259 return(NULL); 3260 } 3261 memset(ret, 0, sizeof(job)); 3262 3263 /* We don't care what the top level element name is */ 3264 cur = cur->xmlChildrenNode; 3265 while (cur != NULL) { 3266 3267 if ((!strcmp(cur->name, "Project")) && (cur->ns == ns)) { 3268 ret->projectID = xmlGetProp(cur, "ID"); 3269 if (ret->projectID == NULL) { 3270 fprintf(stderr, "Project has no ID\n"); 3271 } 3272 } 3273 if ((!strcmp(cur->name, "Application")) && (cur->ns == ns)) 3274 ret->application = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3275 if ((!strcmp(cur->name, "Category")) && (cur->ns == ns)) 3276 ret->category = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3277 if ((!strcmp(cur->name, "Contact")) && (cur->ns == ns)) 3278 ret->contact = parsePerson(doc, ns, cur); 3279 cur = cur->next; 3280 } 3281 3282 return(ret); 3283}</pre> 3284 3285<p>Once you are used to it, writing this kind of code is quite simple, but 3286boring. Ultimately, it could be possble to write stubbers taking either C 3287data structure definitions, a set of XML examples or an XML DTD and produce 3288the code needed to import and export the content between C data and XML 3289storage. This is left as an exercise to the reader :-)</p> 3290 3291<p>Feel free to use <a href="example/gjobread.c">the code for the full C 3292parsing example</a> as a template, it is also available with Makefile in the 3293Gnome CVS base under gnome-xml/example</p> 3294 3295<h2><a name="Contributi">Contributions</a></h2> 3296<ul> 3297 <li>Bjorn Reese, William Brack and Thomas Broyer have provided a number of 3298 patches, Gary Pennington worked on the validation API, threading support 3299 and Solaris port.</li> 3300 <li>John Fleck helps maintaining the documentation and man pages.</li> 3301 <li><a href="mailto:ari@lusis.org">Ari Johnson</a> 3302 provides a C++ wrapper for libxml:<br> 3303 Website: <a 3304 href="http://lusis.org/~ari/xml++/">http://lusis.org/~ari/xml++/</a><br> 3305 Download: <a 3306 href="http://lusis.org/~ari/xml++/libxml++.tar.gz">http://lusis.org/~ari/xml++/libxml++.tar.gz</a></li> 3307 <li><a href="mailto:izlatkovic@daenet.de">Igor Zlatkovic</a> 3308 is now the maintainer of the Windows port, <a 3309 href="http://www.fh-frankfurt.de/~igor/projects/libxml/index.html">he 3310 provides binaries</a></li> 3311 <li><a href="mailto:Gary.Pennington@sun.com">Gary Pennington</a> 3312 provides <a href="http://garypennington.net/libxml2/">Solaris 3313 binaries</a></li> 3314 <li><a 3315 href="http://mail.gnome.org/archives/xml/2001-March/msg00014.html">Matt 3316 Sergeant</a> 3317 developped <a href="http://axkit.org/download/">XML::LibXSLT</a>, a perl 3318 wrapper for libxml2/libxslt as part of the <a 3319 href="http://axkit.com/">AxKit XML application server</a></li> 3320 <li><a href="mailto:fnatter@gmx.net">Felix Natter</a> 3321 and <a href="mailto:geertk@ai.rug.nl">Geert Kloosterman</a> provide <a 3322 href="libxml-doc.el">an emacs module</a> to lookup libxml(2) functions 3323 documentation</li> 3324 <li><a href="mailto:sherwin@nlm.nih.gov">Ziying Sherwin</a> 3325 provided <a href="http://xmlsoft.org/messages/0488.html">man 3326 pages</a></li> 3327 <li>there is a module for <a 3328 href="http://acs-misc.sourceforge.net/nsxml.html">libxml/libxslt support 3329 in OpenNSD/AOLServer</a></li> 3330 <li><a href="mailto:dkuhlman@cutter.rexx.com">Dave Kuhlman</a> 3331 provides libxml/libxslt <a href="http://www.rexx.com/~dkuhlman">wrappers 3332 for Python</a></li> 3333 <li>Petr Kozelka provides <a 3334 href="http://sourceforge.net/projects/libxml2-pas">Pascal units to glue 3335 libxml2</a> with Kylix and Delphi and other Pascal compilers</li> 3336</ul> 3337 3338<p></p> 3339</body> 3340</html> 3341
