xml.html revision ef90ba7e3b530a8eb9ed27f57f0ced139b839780
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>libxml does not compile with HP-UX's optional ANSI-C compiler</em> 243 <p>this is due to macro limitations. Try to add " -Wp,-H16800 -Ae" to the 244 CFLAGS</p> 245 <p>you can also install and use gcc instead or use a precompiled version 246 of libxml, both available from the <a 247 href="http://hpux.cae.wisc.edu/hppd/auto/summary_all.html">HP-UX Porting 248 and Archive Centre</a></p> 249 </li> 250 <li><em>make check fails on some platforms</em> 251 <p>Sometime the regression tests results don't completely match the value 252 produced by the parser, and the makefile uses diff to print the delta. On 253 some platforms the diff return breaks the compilation process, if the 254 diff is small this is probably not a serious problem</p> 255 </li> 256 <li><em>I use the CVS version and there is no configure script</em> 257 <p>The configure (and other Makefiles) are generated. Use the autogen.sh 258 script to regenerate the configure and Makefiles, like:</p> 259 <p><code>/autogen.sh --prefix=/usr --disable-shared</code></p> 260 </li> 261 <li><em>I have troubles when running make tests with gcc-3.0</em> 262 <p>It seems the initial release of gcc-3.0 has a problem with the 263 optimizer which miscompiles the URI module. Please use another 264 compiler</p> 265 </li> 266</ol> 267 268<h3><a name="Developer">Developer</a> corner</h3> 269<ol> 270 <li><em>xmlDocDump() generates output on one line</em> 271 <p>libxml will not <strong>invent</strong> spaces in the content of a 272 document since <strong>all spaces in the content of a document are 273 significant</strong>. If you build a tree from the API and want 274 indentation:</p> 275 <ol> 276 <li>the correct way is to generate those yourself too</li> 277 <li>the dangerous way is to ask libxml to add those blanks to your 278 content <strong>modifying the content of your document in the 279 process</strong>. The result may not be what you expect. There is 280 <strong>NO</strong> way to guarantee that such a modification won't 281 impact other part of the content of your document. See <a 282 href="http://xmlsoft.org/html/libxml-parser.html#XMLKEEPBLANKSDEFAULT">xmlKeepBlanksDefault 283 ()</a> and <a 284 href="http://xmlsoft.org/html/libxml-tree.html#XMLSAVEFORMATFILE">xmlSaveFormatFile 285 ()</a></li> 286 </ol> 287 </li> 288 <li>Extra nodes in the document: 289 <p><em>For a XML file as below:</em></p> 290 <pre><?xml version="1.0"?> 291<PLAN xmlns="http://www.argus.ca/autotest/1.0/"> 292<NODE CommFlag="0"/> 293<NODE CommFlag="1"/> 294</PLAN></pre> 295 <p><em>after parsing it with the function 296 pxmlDoc=xmlParseFile(...);</em></p> 297 <p><em>I want to the get the content of the first node (node with the 298 CommFlag="0")</em></p> 299 <p><em>so I did it as following;</em></p> 300 <pre>xmlNodePtr pode; 301pnode=pxmlDoc->children->children;</pre> 302 <p><em>but it does not work. If I change it to</em></p> 303 <pre>pnode=pxmlDoc->children->children->next;</pre> 304 <p><em>then it works. Can someone explain it to me.</em></p> 305 <p></p> 306 <p>In XML all characters in the content of the document are significant 307 <strong>including blanks and formatting line breaks</strong>.</p> 308 <p>The extra nodes you are wondering about are just that, text nodes with 309 the formatting spaces wich are part of the document but that people tend 310 to forget. There is a function <a 311 href="http://xmlsoft.org/html/libxml-parser.html">xmlKeepBlanksDefault 312 ()</a> to remove those at parse time, but that's an heuristic, and its 313 use should be limited to case where you are sure there is no 314 mixed-content in the document.</p> 315 </li> 316 <li><em>I get compilation errors of existing code like when accessing 317 <strong>root</strong> or <strong>childs fields</strong> of nodes</em> 318 <p>You are compiling code developed for libxml version 1 and using a 319 libxml2 development environment. Either switch back to libxml v1 devel or 320 even better fix the code to compile with libxml2 (or both) by <a 321 href="upgrade.html">following the instructions</a>.</p> 322 </li> 323 <li><em>I get compilation errors about non existing 324 <strong>xmlRootNode</strong> or <strong>xmlChildrenNode</strong> 325 fields</em> 326 <p>The source code you are using has been <a 327 href="upgrade.html">upgraded</a> to be able to compile with both libxml 328 and libxml2, but you need to install a more recent version: 329 libxml(-devel) >= 1.8.8 or libxml2(-devel) >= 2.1.0</p> 330 </li> 331 <li><em>XPath implementation looks seriously broken</em> 332 <p>XPath implementation prior to 2.3.0 was really incomplete, upgrade to 333 a recent version, the implementation and debug of libxslt generated fixes 334 for most obvious problems.</p> 335 </li> 336 <li><em>The example provided in the web page does not compile</em> 337 <p>It's hard to maintain the documentation in sync with the code 338 <grin/> ...</p> 339 <p>Check the previous points 1/ and 2/ raised before, and send 340 patches.</p> 341 </li> 342 <li><em>Where can I get more examples and informations than in the web 343 page</em> 344 <p>Ideally a libxml book would be nice. I have no such plan ... But you 345 can:</p> 346 <ul> 347 <li>check more deeply the <a href="html/libxml-lib.html">existing 348 generated doc</a></li> 349 <li>looks for examples of use for libxml function using the Gnome code 350 for example the following will query the full Gnome CVs base for the 351 use of the <strong>xmlAddChild()</strong> function: 352 <p><a 353 href="http://cvs.gnome.org/lxr/search?string=xmlAddChild">http://cvs.gnome.org/lxr/search?string=xmlAddChild</a></p> 354 <p>This may be slow, a large hardware donation to the gnome project 355 could cure this :-)</p> 356 </li> 357 <li><a 358 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gnome-xml">Browse 359 the libxml source</a> 360 , I try to write code as clean and documented as possible, so 361 looking at it may be helpful</li> 362 </ul> 363 </li> 364 <li>What about C++ ? 365 <p>libxml is written in pure C in order to allow easy reuse on a number 366 of platforms, including embedded systems. I don't intend to convert to 367 C++.</p> 368 <p>There is however a C++ wrapper provided by Ari Johnson 369 <ari@btigate.com> which may fullfill your needs:</p> 370 <p>Website: <a 371 href="http://lusis.org/~ari/xml++/">http://lusis.org/~ari/xml++/</a></p> 372 <p>Download: <a 373 href="http://lusis.org/~ari/xml++/libxml++.tar.gz">http://lusis.org/~ari/xml++/libxml++.tar.gz</a></p> 374 </li> 375 <li>How to validate a document a posteriori ? 376 <p>It is possible to validate documents which had not been validated at 377 initial parsing time or documents who have been built from scratch using 378 the API. Use the <a 379 href="http://xmlsoft.org/html/libxml-valid.html#XMLVALIDATEDTD">xmlValidateDtd()</a> 380 function. It is also possible to simply add a Dtd to an existing 381 document:</p> 382 <pre>xmlDocPtr doc; /* your existing document */ 383 xmlDtdPtr dtd = xmlParseDTD(NULL, filename_of_dtd); /* parse the DTD */ 384 dtd->name = xmlStrDup((xmlChar*)"root_name"); /* use the given root */ 385 386 doc->intSubset = dtd; 387 if (doc->children == NULL) xmlAddChild((xmlNodePtr)doc, (xmlNodePtr)dtd); 388 else xmlAddPrevSibling(doc->children, (xmlNodePtr)dtd); 389 </pre> 390 </li> 391 <li>etc ...</li> 392</ol> 393 394<p></p> 395 396<h2><a name="Documentat">Documentation</a></h2> 397 398<p>There are some on-line resources about using libxml:</p> 399<ol> 400 <li>Check the <a href="FAQ.html">FAQ</a></li> 401 <li>Check the <a href="http://xmlsoft.org/html/libxml-lib.html">extensive 402 documentation</a> automatically extracted from code comments (using <a 403 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gtk-doc">gtk 404 doc</a>).</li> 405 <li>Look at the documentation about <a href="encoding.html">libxml 406 internationalization support</a></li> 407 <li>This page provides a global overview and <a href="#real">some 408 examples</a> on how to use libxml.</li> 409 <li><a href="mailto:james@daa.com.au">James Henstridge</a> 410 wrote <a 411 href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">some nice 412 documentation</a> explaining how to use the libxml SAX interface.</li> 413 <li>George Lebl wrote <a 414 href="http://www-4.ibm.com/software/developer/library/gnome3/">an article 415 for IBM developerWorks</a> about using libxml.</li> 416 <li>Check <a href="http://cvs.gnome.org/lxr/source/gnome-xml/TODO">the TODO 417 file</a></li> 418 <li>Read the <a href="upgrade.html">1.x to 2.x upgrade path</a>. If you are 419 starting a new project using libxml you should really use the 2.x 420 version.</li> 421 <li>And don't forget to look at the <a href="/messages/">mailing-list 422 archive</a>.</li> 423</ol> 424 425<h2><a name="Reporting">Reporting bugs and getting help</a></h2> 426 427<p>Well, bugs or missing features are always possible, and I will make a 428point of fixing them in a timely fashion. The best way to report a bug is to 429use the <a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Gnome 430bug tracking database</a> (make sure to use the "libxml" module name). I look 431at reports there regularly and it's good to have a reminder when a bug is 432still open. Be sure to specify that the bug is for the package libxml.</p> 433 434<p>There is also a mailing-list <a 435href="mailto:xml@gnome.org">xml@gnome.org</a> for libxml, with an <a 436href="http://mail.gnome.org/archives/xml/">on-line archive</a> (<a 437href="http://xmlsoft.org/messages">old</a>). To subscribe to this list, 438please visit the <a 439href="http://mail.gnome.org/mailman/listinfo/xml">associated Web</a> page and 440follow the instructions. <strong>Do not send code, I won't debug it</strong> 441(but patches are really appreciated!).</p> 442 443<p>Check the following <strong><span style="color: #FF0000">before 444posting</span></strong>:</p> 445<ul> 446 <li>read the <a href="FAQ.html">FAQ</a></li> 447 <li>make sure you are <a href="ftp://xmlsoft.org/">using a recent 448 version</a>, and that the problem still shows up in those</li> 449 <li>check the <a href="http://mail.gnome.org/archives/xml/">list 450 archives</a> to see if the problem was reported already, in this case 451 there is probably a fix available, similary check the <a 452 href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">registered 453 open bugs</a></li> 454 <li>make sure you can reproduce the bug with xmllint or one of the test 455 programs found in source in the distribution</li> 456 <li>Please send the command showing the error as well as the input (as an 457 attachement)</li> 458</ul> 459 460<p>Then send the bug with associated informations to reproduce it to the <a 461href="mailto:xml@gnome.org">xml@gnome.org</a> list; if it's really libxml 462related I will approve it.. Please do not send me mail directly, it makes 463things really harder to track and in some cases I'm not the best person to 464answer a given question, ask the list instead.</p> 465 466<p>Of course, bugs reported with a suggested patch for fixing them will 467probably be processed faster.</p> 468 469<p>If you're looking for help, a quick look at <a 470href="http://mail.gnome.org/archives/xml/">the list archive</a> may actually 471provide the answer, I usually send source samples when answering libxml usage 472questions. The <a href="http://xmlsoft.org/html/book1.html">auto-generated 473documentantion</a> is not as polished as I would like (i need to learn more 474about Docbook), but it's a good starting point.</p> 475 476<h2><a name="help">How to help</a></h2> 477 478<p>You can help the project in various ways, the best thing to do first is to 479subscribe to the mailing-list as explained before, check the <a 480href="http://mail.gnome.org/archives/xml/">archives </a>and the <a 481href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Gnome bug 482database:</a>:</p> 483<ol> 484 <li>provide patches when you find problems</li> 485 <li>provide the diffs when you port libxml to a new platform. They may not 486 be integrated in all cases but help pinpointing portability problems 487 and</li> 488 <li>provide documentation fixes (either as patches to the code comments or 489 as HTML diffs).</li> 490 <li>provide new documentations pieces (translations, examples, etc ...)</li> 491 <li>Check the TODO file and try to close one of the items</li> 492 <li>take one of the points raised in the archive or the bug database and 493 provide a fix. <a href="mailto:daniel@veillard.com">Get in touch with me 494 </a>before to avoid synchronization problems and check that the suggested 495 fix will fit in nicely :-)</li> 496</ol> 497 498<h2><a name="Downloads">Downloads</a></h2> 499 500<p>The latest versions of libxml can be found on <a 501href="ftp://xmlsoft.org/">xmlsoft.org</a> (<a 502href="ftp://speakeasy.rpmfind.net/pub/libxml/">Seattle</a>, <a 503href="ftp://fr.rpmfind.net/pub/libxml/">France</a>) or on the <a 504href="ftp://ftp.gnome.org/pub/GNOME/MIRRORS.html">Gnome FTP server</a> either 505as a <a href="ftp://ftp.gnome.org/pub/GNOME/stable/sources/libxml/">source 506archive</a> or <a 507href="ftp://ftp.gnome.org/pub/GNOME/stable/redhat/i386/libxml/">RPM 508packages</a>. (NOTE that you need both the <a 509href="http://rpmfind.net/linux/RPM/libxml2.html">libxml(2)</a> and <a 510href="http://rpmfind.net/linux/RPM/libxml2-devel.html">libxml(2)-devel</a> 511packages installed to compile applications using libxml.) <a 512href="mailto:izlatkovic@daenet.de">Igor Zlatkovic</a> is now the maintainer 513of the Windows port, <a 514href="http://www.fh-frankfurt.de/~igor/projects/libxml/index.html">he 515provides binaries</a>. <a href="mailto:Gary.Pennington@sun.com">Gary 516Pennington</a> provides <a href="http://garypennington.net/libxml2/">Solaris 517binaries</a>.</p> 518 519<p><a name="Snapshot">Snapshot:</a></p> 520<ul> 521 <li>Code from the W3C cvs base libxml <a 522 href="ftp://xmlsoft.org/cvs-snapshot.tar.gz">cvs-snapshot.tar.gz</a></li> 523 <li>Docs, content of the web site, the list archive included <a 524 href="ftp://xmlsoft.org/libxml-docs.tar.gz">libxml-docs.tar.gz</a></li> 525</ul> 526 527<p><a name="Contribs">Contributions:</a></p> 528 529<p>I do accept external contributions, especially if compiling on another 530platform, get in touch with me to upload the package, wrappers for various 531languages have been provided, and can be found in the <a 532href="contribs.html">contrib section</a></p> 533 534<p>Libxml is also available from CVS:</p> 535<ul> 536 <li><p>The <a 537 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gnome-xml">Gnome 538 CVS base</a>. Check the <a 539 href="http://developer.gnome.org/tools/cvs.html">Gnome CVS Tools</a> 540 page; the CVS module is <b>gnome-xml</b>.</p> 541 </li> 542 <li>The <strong>libxslt</strong> module is also present there</li> 543</ul> 544 545<h2><a name="News">News</a></h2> 546 547<h3>CVS only : check the <a 548href="http://cvs.gnome.org/lxr/source/gnome-xml/ChangeLog">Changelog</a> file 549for a really accurate description</h3> 550 551<p>Items floating around but not actively worked on, get in touch with me if 552you want to test those</p> 553<ul> 554 <li>Implementing <a href="http://xmlsoft.org/XSLT">XSLT</a>, this is done 555 as a separate C library on top of libxml called libxslt</li> 556 <li>Finishing up <a href="http://www.w3.org/TR/xptr">XPointer</a> and <a 557 href="http://www.w3.org/TR/xinclude">XInclude</a></li> 558 <li>(seeems working but delayed from release) parsing/import of Docbook 559 SGML docs</li> 560</ul> 561 562<h3>2.4.12: Dec 7 2001</h3> 563<ul> 564 <li>a few bug fixes: thread (Gary Pennington), xmllint (Geert Kloosterman), 565 XML parser (Robin Berjon), XPointer (Danny Jamshy), I/O cleanups 566 (robert)</li> 567 <li>Eric Lavigne contributed project files for MacOS</li> 568 <li>some makefiles cleanups</li> 569</ul> 570 571<h3>2.4.11: Nov 26 2001</h3> 572<ul> 573 <li>fixed a couple of errors in the includes, fixed a few bugs, some code 574 cleanups</li> 575 <li>xmllint man pages improvement by Heiko Rupp</li> 576 <li>updated VMS build instructions from John A Fotheringham</li> 577 <li>Windows Makefiles updates from Igor</li> 578</ul> 579 580<h3>2.4.10: Nov 10 2001</h3> 581<ul> 582 <li>URI escaping fix (Joel Young)</li> 583 <li>added xmlGetNodePath() (for paths or XPointers generation)</li> 584 <li>Fixes namespace handling problems when using DTD and validation</li> 585 <li>improvements on xmllint: Morus Walter patches for --format and 586 --encode, Stefan Kost and Heiko Rupp improvements on the --shell</li> 587 <li>fixes for xmlcatalog linking pointed by Weiqi Gao</li> 588 <li>fixes to the HTML parser</li> 589</ul> 590 591<h3>2.4.9: Nov 6 2001</h3> 592<ul> 593 <li>fixes more catalog bugs</li> 594 <li>avoid a compilation problem, improve xmlGetLineNo()</li> 595</ul> 596 597<h3>2.4.8: Nov 4 2001</h3> 598<ul> 599 <li>fixed SGML catalogs broken in previous release, updated xmlcatalog 600 tool</li> 601 <li>fixed a compile errors and some includes troubles.</li> 602</ul> 603 604<h3>2.4.7: Oct 30 2001</h3> 605<ul> 606 <li>exported some debugging interfaces</li> 607 <li>serious rewrite of the catalog code</li> 608 <li>integrated Gary Pennington thread safety patch, added configure option 609 and regression tests</li> 610 <li>removed an HTML parser bug</li> 611 <li>fixed a couple of potentially serious validation bugs</li> 612 <li>integrated the SGML DocBook support in xmllint</li> 613 <li>changed the nanoftp anonymous login passwd</li> 614 <li>some I/O cleanup and a couple of interfaces for Perl wrapper</li> 615 <li>general bug fixes</li> 616 <li>updated xmllint man page by John Fleck</li> 617 <li>some VMS and Windows updates</li> 618</ul> 619 620<h3>2.4.6: Oct 10 2001</h3> 621<ul> 622 <li>added an updated man pages by John Fleck</li> 623 <li>portability and configure fixes</li> 624 <li>an infinite loop on the HTML parser was removed (William)</li> 625 <li>Windows makefile patches from Igor</li> 626 <li>fixed half a dozen bugs reported fof libxml or libxslt</li> 627 <li>updated xmlcatalog to be able to modify SGML super catalogs</li> 628</ul> 629 630<h3>2.4.5: Sep 14 2001</h3> 631<ul> 632 <li>Remove a few annoying bugs in 2.4.4</li> 633 <li>forces the HTML serializer to output decimal charrefs since some 634 version of Netscape can't handle hexadecimal ones</li> 635</ul> 636 637<h3>1.8.16: Sep 14 2001</h3> 638<ul> 639 <li>maintenance release of the old libxml1 branch, couple of bug and 640 portability fixes</li> 641</ul> 642 643<h3>2.4.4: Sep 12 2001</h3> 644<ul> 645 <li>added --convert to xmlcatalog, bug fixes and cleanups of XML 646 Catalog</li> 647 <li>a few bug fixes and some portability changes</li> 648 <li>some documentation cleanups</li> 649</ul> 650 651<h3>2.4.3: Aug 23 2001</h3> 652<ul> 653 <li>XML Catalog support see the doc</li> 654 <li>New NaN/Infinity floating point code</li> 655 <li>A few bug fixes</li> 656</ul> 657 658<h3>2.4.2: Aug 15 2001</h3> 659<ul> 660 <li>adds xmlLineNumbersDefault() to control line number generation</li> 661 <li>lot of bug fixes</li> 662 <li>the Microsoft MSC projects files shuld now be up to date</li> 663 <li>inheritance of namespaces from DTD defaulted attributes</li> 664 <li>fixes a serious potential security bug</li> 665 <li>added a --format option to xmllint</li> 666</ul> 667 668<h3>2.4.1: July 24 2001</h3> 669<ul> 670 <li>possibility to keep line numbers in the tree</li> 671 <li>some computation NaN fixes</li> 672 <li>extension of the XPath API</li> 673 <li>cleanup for alpha and ia64 targets</li> 674 <li>patch to allow saving through HTTP PUT or POST</li> 675</ul> 676 677<h3>2.4.0: July 10 2001</h3> 678<ul> 679 <li>Fixed a few bugs in XPath, validation, and tree handling.</li> 680 <li>Fixed XML Base implementation, added a coupel of examples to the 681 regression tests</li> 682 <li>A bit of cleanup</li> 683</ul> 684 685<h3>2.3.14: July 5 2001</h3> 686<ul> 687 <li>fixed some entities problems and reduce mem requirement when 688 substituing them</li> 689 <li>lots of improvements in the XPath queries interpreter can be 690 substancially faster</li> 691 <li>Makefiles and configure cleanups</li> 692 <li>Fixes to XPath variable eval, and compare on empty node set</li> 693 <li>HTML tag closing bug fixed</li> 694 <li>Fixed an URI reference computating problem when validating</li> 695</ul> 696 697<h3>2.3.13: June 28 2001</h3> 698<ul> 699 <li>2.3.12 configure.in was broken as well as the push mode XML parser</li> 700 <li>a few more fixes for compilation on Windows MSC by Yon Derek</li> 701</ul> 702 703<h3>1.8.14: June 28 2001</h3> 704<ul> 705 <li>Zbigniew Chyla gave a patch to use the old XML parser in push mode</li> 706 <li>Small Makefile fix</li> 707</ul> 708 709<h3>2.3.12: June 26 2001</h3> 710<ul> 711 <li>lots of cleanup</li> 712 <li>a couple of validation fix</li> 713 <li>fixed line number counting</li> 714 <li>fixed serious problems in the XInclude processing</li> 715 <li>added support for UTF8 BOM at beginning of entities</li> 716 <li>fixed a strange gcc optimizer bugs in xpath handling of float, gcc-3.0 717 miscompile uri.c (William), Thomas Leitner provided a fix for the 718 optimizer on Tru64</li> 719 <li>incorporated Yon Derek and Igor Zlatkovic fixes and improvements for 720 compilation on Windows MSC</li> 721 <li>update of libxml-doc.el (Felix Natter)</li> 722 <li>fixed 2 bugs in URI normalization code</li> 723</ul> 724 725<h3>2.3.11: June 17 2001</h3> 726<ul> 727 <li>updates to trio, Makefiles and configure should fix some portability 728 problems (alpha)</li> 729 <li>fixed some HTML serialization problems (pre, script, and block/inline 730 handling), added encoding aware APIs, cleanup of this code</li> 731 <li>added xmlHasNsProp()</li> 732 <li>implemented a specific PI for encoding support in the DocBook SGML 733 parser</li> 734 <li>some XPath fixes (-Infinity, / as a function parameter and namespaces 735 node selection)</li> 736 <li>fixed a performance problem and an error in the validation code</li> 737 <li>fixed XInclude routine to implement the recursive behaviour</li> 738 <li>fixed xmlFreeNode problem when libxml is included statically twice</li> 739 <li>added --version to xmllint for bug reports</li> 740</ul> 741 742<h3>2.3.10: June 1 2001</h3> 743<ul> 744 <li>fixed the SGML catalog support</li> 745 <li>a number of reported bugs got fixed, in XPath, iconv detection, 746 XInclude processing</li> 747 <li>XPath string function should now handle unicode correctly</li> 748</ul> 749 750<h3>2.3.9: May 19 2001</h3> 751 752<p>Lots of bugfixes, and added a basic SGML catalog support:</p> 753<ul> 754 <li>HTML push bugfix #54891 and another patch from Jonas Borgstr�m</li> 755 <li>some serious speed optimisation again</li> 756 <li>some documentation cleanups</li> 757 <li>trying to get better linking on solaris (-R)</li> 758 <li>XPath API cleanup from Thomas Broyer</li> 759 <li>Validation bug fixed #54631, added a patch from Gary Pennington, fixed 760 xmlValidGetValidElements()</li> 761 <li>Added an INSTALL file</li> 762 <li>Attribute removal added to API: #54433</li> 763 <li>added a basic support for SGML catalogs</li> 764 <li>fixed xmlKeepBlanksDefault(0) API</li> 765 <li>bugfix in xmlNodeGetLang()</li> 766 <li>fixed a small configure portability problem</li> 767 <li>fixed an inversion of SYSTEM and PUBLIC identifier in HTML document</li> 768</ul> 769 770<h3>1.8.13: May 14 2001</h3> 771<ul> 772 <li>bugfixes release of the old libxml1 branch used by Gnome</li> 773</ul> 774 775<h3>2.3.8: May 3 2001</h3> 776<ul> 777 <li>Integrated an SGML DocBook parser for the Gnome project</li> 778 <li>Fixed a few things in the HTML parser</li> 779 <li>Fixed some XPath bugs raised by XSLT use, tried to fix the floating 780 point portability issue</li> 781 <li>Speed improvement (8M/s for SAX, 3M/s for DOM, 1.5M/s for 782 DOM+validation using the XML REC as input and a 700MHz celeron).</li> 783 <li>incorporated more Windows cleanup</li> 784 <li>added xmlSaveFormatFile()</li> 785 <li>fixed problems in copying nodes with entities references (gdome)</li> 786 <li>removed some troubles surrounding the new validation module</li> 787</ul> 788 789<h3>2.3.7: April 22 2001</h3> 790<ul> 791 <li>lots of small bug fixes, corrected XPointer</li> 792 <li>Non determinist content model validation support</li> 793 <li>added xmlDocCopyNode for gdome2</li> 794 <li>revamped the way the HTML parser handles end of tags</li> 795 <li>XPath: corrctions of namespacessupport and number formatting</li> 796 <li>Windows: Igor Zlatkovic patches for MSC compilation</li> 797 <li>HTML ouput fixes from P C Chow and William M. Brack</li> 798 <li>Improved validation speed sensible for DocBook</li> 799 <li>fixed a big bug with ID declared in external parsed entities</li> 800 <li>portability fixes, update of Trio from Bjorn Reese</li> 801</ul> 802 803<h3>2.3.6: April 8 2001</h3> 804<ul> 805 <li>Code cleanup using extreme gcc compiler warning options, found and 806 cleared half a dozen potential problem</li> 807 <li>the Eazel team found an XML parser bug</li> 808 <li>cleaned up the user of some of the string formatting function. used the 809 trio library code to provide the one needed when the platform is missing 810 them</li> 811 <li>xpath: removed a memory leak and fixed the predicate evaluation 812 problem, extended the testsuite and cleaned up the result. XPointer seems 813 broken ...</li> 814</ul> 815 816<h3>2.3.5: Mar 23 2001</h3> 817<ul> 818 <li>Biggest change is separate parsing and evaluation of XPath expressions, 819 there is some new APIs for this too</li> 820 <li>included a number of bug fixes(XML push parser, 51876, notations, 821 52299)</li> 822 <li>Fixed some portability issues</li> 823</ul> 824 825<h3>2.3.4: Mar 10 2001</h3> 826<ul> 827 <li>Fixed bugs #51860 and #51861</li> 828 <li>Added a global variable xmlDefaultBufferSize to allow default buffer 829 size to be application tunable.</li> 830 <li>Some cleanup in the validation code, still a bug left and this part 831 should probably be rewritten to support ambiguous content model :-\</li> 832 <li>Fix a couple of serious bugs introduced or raised by changes in 2.3.3 833 parser</li> 834 <li>Fixed another bug in xmlNodeGetContent()</li> 835 <li>Bjorn fixed XPath node collection and Number formatting</li> 836 <li>Fixed a loop reported in the HTML parsing</li> 837 <li>blank space are reported even if the Dtd content model proves that they 838 are formatting spaces, this is for XmL conformance</li> 839</ul> 840 841<h3>2.3.3: Mar 1 2001</h3> 842<ul> 843 <li>small change in XPath for XSLT</li> 844 <li>documentation cleanups</li> 845 <li>fix in validation by Gary Pennington</li> 846 <li>serious parsing performances improvements</li> 847</ul> 848 849<h3>2.3.2: Feb 24 2001</h3> 850<ul> 851 <li>chasing XPath bugs, found a bunch, completed some TODO</li> 852 <li>fixed a Dtd parsing bug</li> 853 <li>fixed a bug in xmlNodeGetContent</li> 854 <li>ID/IDREF support partly rewritten by Gary Pennington</li> 855</ul> 856 857<h3>2.3.1: Feb 15 2001</h3> 858<ul> 859 <li>some XPath and HTML bug fixes for XSLT</li> 860 <li>small extension of the hash table interfaces for DOM gdome2 861 implementation</li> 862 <li>A few bug fixes</li> 863</ul> 864 865<h3>2.3.0: Feb 8 2001 (2.2.12 was on 25 Jan but I didn't kept track)</h3> 866<ul> 867 <li>Lots of XPath bug fixes</li> 868 <li>Add a mode with Dtd lookup but without validation error reporting for 869 XSLT</li> 870 <li>Add support for text node without escaping (XSLT)</li> 871 <li>bug fixes for xmlCheckFilename</li> 872 <li>validation code bug fixes from Gary Pennington</li> 873 <li>Patch from Paul D. Smith correcting URI path normalization</li> 874 <li>Patch to allow simultaneous install of libxml-devel and 875 libxml2-devel</li> 876 <li>the example Makefile is now fixed</li> 877 <li>added HTML to the RPM packages</li> 878 <li>tree copying bugfixes</li> 879 <li>updates to Windows makefiles</li> 880 <li>optimisation patch from Bjorn Reese</li> 881</ul> 882 883<h3>2.2.11: Jan 4 2001</h3> 884<ul> 885 <li>bunch of bug fixes (memory I/O, xpath, ftp/http, ...)</li> 886 <li>added htmlHandleOmittedElem()</li> 887 <li>Applied Bjorn Reese's IPV6 first patch</li> 888 <li>Applied Paul D. Smith patches for validation of XInclude results</li> 889 <li>added XPointer xmlns() new scheme support</li> 890</ul> 891 892<h3>2.2.10: Nov 25 2000</h3> 893<ul> 894 <li>Fix the Windows problems of 2.2.8</li> 895 <li>integrate OpenVMS patches</li> 896 <li>better handling of some nasty HTML input</li> 897 <li>Improved the XPointer implementation</li> 898 <li>integrate a number of provided patches</li> 899</ul> 900 901<h3>2.2.9: Nov 25 2000</h3> 902<ul> 903 <li>erroneous release :-(</li> 904</ul> 905 906<h3>2.2.8: Nov 13 2000</h3> 907<ul> 908 <li>First version of <a href="http://www.w3.org/TR/xinclude">XInclude</a> 909 support</li> 910 <li>Patch in conditional section handling</li> 911 <li>updated MS compiler project</li> 912 <li>fixed some XPath problems</li> 913 <li>added an URI escaping function</li> 914 <li>some other bug fixes</li> 915</ul> 916 917<h3>2.2.7: Oct 31 2000</h3> 918<ul> 919 <li>added message redirection</li> 920 <li>XPath improvements (thanks TOM !)</li> 921 <li>xmlIOParseDTD() added</li> 922 <li>various small fixes in the HTML, URI, HTTP and XPointer support</li> 923 <li>some cleanup of the Makefile, autoconf and the distribution content</li> 924</ul> 925 926<h3>2.2.6: Oct 25 2000:</h3> 927<ul> 928 <li>Added an hash table module, migrated a number of internal structure to 929 those</li> 930 <li>Fixed a posteriori validation problems</li> 931 <li>HTTP module cleanups</li> 932 <li>HTML parser improvements (tag errors, script/style handling, attribute 933 normalization)</li> 934 <li>coalescing of adjacent text nodes</li> 935 <li>couple of XPath bug fixes, exported the internal API</li> 936</ul> 937 938<h3>2.2.5: Oct 15 2000:</h3> 939<ul> 940 <li>XPointer implementation and testsuite</li> 941 <li>Lot of XPath fixes, added variable and functions registration, more 942 tests</li> 943 <li>Portability fixes, lots of enhancements toward an easy Windows build 944 and release</li> 945 <li>Late validation fixes</li> 946 <li>Integrated a lot of contributed patches</li> 947 <li>added memory management docs</li> 948 <li>a performance problem when using large buffer seems fixed</li> 949</ul> 950 951<h3>2.2.4: Oct 1 2000:</h3> 952<ul> 953 <li>main XPath problem fixed</li> 954 <li>Integrated portability patches for Windows</li> 955 <li>Serious bug fixes on the URI and HTML code</li> 956</ul> 957 958<h3>2.2.3: Sep 17 2000</h3> 959<ul> 960 <li>bug fixes</li> 961 <li>cleanup of entity handling code</li> 962 <li>overall review of all loops in the parsers, all sprintf usage has been 963 checked too</li> 964 <li>Far better handling of larges Dtd. Validating against Docbook XML Dtd 965 works smoothly now.</li> 966</ul> 967 968<h3>1.8.10: Sep 6 2000</h3> 969<ul> 970 <li>bug fix release for some Gnome projects</li> 971</ul> 972 973<h3>2.2.2: August 12 2000</h3> 974<ul> 975 <li>mostly bug fixes</li> 976 <li>started adding routines to access xml parser context options</li> 977</ul> 978 979<h3>2.2.1: July 21 2000</h3> 980<ul> 981 <li>a purely bug fixes release</li> 982 <li>fixed an encoding support problem when parsing from a memory block</li> 983 <li>fixed a DOCTYPE parsing problem</li> 984 <li>removed a bug in the function allowing to override the memory 985 allocation routines</li> 986</ul> 987 988<h3>2.2.0: July 14 2000</h3> 989<ul> 990 <li>applied a lot of portability fixes</li> 991 <li>better encoding support/cleanup and saving (content is now always 992 encoded in UTF-8)</li> 993 <li>the HTML parser now correctly handles encodings</li> 994 <li>added xmlHasProp()</li> 995 <li>fixed a serious problem with &#38;</li> 996 <li>propagated the fix to FTP client</li> 997 <li>cleanup, bugfixes, etc ...</li> 998 <li>Added a page about <a href="encoding.html">libxml Internationalization 999 support</a></li> 1000</ul> 1001 1002<h3>1.8.9: July 9 2000</h3> 1003<ul> 1004 <li>fixed the spec the RPMs should be better</li> 1005 <li>fixed a serious bug in the FTP implementation, released 1.8.9 to solve 1006 rpmfind users problem</li> 1007</ul> 1008 1009<h3>2.1.1: July 1 2000</h3> 1010<ul> 1011 <li>fixes a couple of bugs in the 2.1.0 packaging</li> 1012 <li>improvements on the HTML parser</li> 1013</ul> 1014 1015<h3>2.1.0 and 1.8.8: June 29 2000</h3> 1016<ul> 1017 <li>1.8.8 is mostly a comodity package for upgrading to libxml2 accoding to 1018 <a href="upgrade.html">new instructions</a>. It fixes a nasty problem 1019 about &#38; charref parsing</li> 1020 <li>2.1.0 also ease the upgrade from libxml v1 to the recent version. it 1021 also contains numerous fixes and enhancements: 1022 <ul> 1023 <li>added xmlStopParser() to stop parsing</li> 1024 <li>improved a lot parsing speed when there is large CDATA blocs</li> 1025 <li>includes XPath patches provided by Picdar Technology</li> 1026 <li>tried to fix as much as possible DtD validation and namespace 1027 related problems</li> 1028 <li>output to a given encoding has been added/tested</li> 1029 <li>lot of various fixes</li> 1030 </ul> 1031 </li> 1032</ul> 1033 1034<h3>2.0.0: Apr 12 2000</h3> 1035<ul> 1036 <li>First public release of libxml2. If you are using libxml, it's a good 1037 idea to check the 1.x to 2.x upgrade instructions. NOTE: while initally 1038 scheduled for Apr 3 the relase occured only on Apr 12 due to massive 1039 workload.</li> 1040 <li>The include are now located under $prefix/include/libxml (instead of 1041 $prefix/include/gnome-xml), they also are referenced by 1042 <pre>#include <libxml/xxx.h></pre> 1043 <p>instead of</p> 1044 <pre>#include "xxx.h"</pre> 1045 </li> 1046 <li>a new URI module for parsing URIs and following strictly RFC 2396</li> 1047 <li>the memory allocation routines used by libxml can now be overloaded 1048 dynamically by using xmlMemSetup()</li> 1049 <li>The previously CVS only tool tester has been renamed 1050 <strong>xmllint</strong> and is now installed as part of the libxml2 1051 package</li> 1052 <li>The I/O interface has been revamped. There is now ways to plug in 1053 specific I/O modules, either at the URI scheme detection level using 1054 xmlRegisterInputCallbacks() or by passing I/O functions when creating a 1055 parser context using xmlCreateIOParserCtxt()</li> 1056 <li>there is a C preprocessor macro LIBXML_VERSION providing the version 1057 number of the libxml module in use</li> 1058 <li>a number of optional features of libxml can now be excluded at 1059 configure time (FTP/HTTP/HTML/XPath/Debug)</li> 1060</ul> 1061 1062<h3>2.0.0beta: Mar 14 2000</h3> 1063<ul> 1064 <li>This is a first Beta release of libxml version 2</li> 1065 <li>It's available only from<a href="ftp://xmlsoft.org/">xmlsoft.org 1066 FTP</a>, it's packaged as libxml2-2.0.0beta and available as tar and 1067 RPMs</li> 1068 <li>This version is now the head in the Gnome CVS base, the old one is 1069 available under the tag LIB_XML_1_X</li> 1070 <li>This includes a very large set of changes. Froma programmatic point of 1071 view applications should not have to be modified too much, check the <a 1072 href="upgrade.html">upgrade page</a></li> 1073 <li>Some interfaces may changes (especially a bit about encoding).</li> 1074 <li>the updates includes: 1075 <ul> 1076 <li>fix I18N support. ISO-Latin-x/UTF-8/UTF-16 (nearly) seems correctly 1077 handled now</li> 1078 <li>Better handling of entities, especially well formedness checking 1079 and proper PEref extensions in external subsets</li> 1080 <li>DTD conditional sections</li> 1081 <li>Validation now correcly handle entities content</li> 1082 <li><a href="http://rpmfind.net/tools/gdome/messages/0039.html">change 1083 structures to accomodate DOM</a></li> 1084 </ul> 1085 </li> 1086 <li>Serious progress were made toward compliance, <a 1087 href="conf/result.html">here are the result of the test</a> against the 1088 OASIS testsuite (except the japanese tests since I don't support that 1089 encoding yet). This URL is rebuilt every couple of hours using the CVS 1090 head version.</li> 1091</ul> 1092 1093<h3>1.8.7: Mar 6 2000</h3> 1094<ul> 1095 <li>This is a bug fix release:</li> 1096 <li>It is possible to disable the ignorable blanks heuristic used by 1097 libxml-1.x, a new function xmlKeepBlanksDefault(0) will allow this. Note 1098 that for adherence to XML spec, this behaviour will be disabled by 1099 default in 2.x . The same function will allow to keep compatibility for 1100 old code.</li> 1101 <li>Blanks in <a> </a> constructs are not ignored anymore, 1102 avoiding heuristic is really the Right Way :-\</li> 1103 <li>The unchecked use of snprintf which was breaking libxml-1.8.6 1104 compilation on some platforms has been fixed</li> 1105 <li>nanoftp.c nanohttp.c: Fixed '#' and '?' stripping when processing 1106 URIs</li> 1107</ul> 1108 1109<h3>1.8.6: Jan 31 2000</h3> 1110<ul> 1111 <li>added a nanoFTP transport module, debugged until the new version of <a 1112 href="http://rpmfind.net/linux/rpm2html/rpmfind.html">rpmfind</a> can use 1113 it without troubles</li> 1114</ul> 1115 1116<h3>1.8.5: Jan 21 2000</h3> 1117<ul> 1118 <li>adding APIs to parse a well balanced chunk of XML (production <a 1119 href="http://www.w3.org/TR/REC-xml#NT-content">[43] content</a> of the 1120 XML spec)</li> 1121 <li>fixed a hideous bug in xmlGetProp pointed by Rune.Djurhuus@fast.no</li> 1122 <li>Jody Goldberg <jgoldberg@home.com> provided another patch trying 1123 to solve the zlib checks problems</li> 1124 <li>The current state in gnome CVS base is expected to ship as 1.8.5 with 1125 gnumeric soon</li> 1126</ul> 1127 1128<h3>1.8.4: Jan 13 2000</h3> 1129<ul> 1130 <li>bug fixes, reintroduced xmlNewGlobalNs(), fixed xmlNewNs()</li> 1131 <li>all exit() call should have been removed from libxml</li> 1132 <li>fixed a problem with INCLUDE_WINSOCK on WIN32 platform</li> 1133 <li>added newDocFragment()</li> 1134</ul> 1135 1136<h3>1.8.3: Jan 5 2000</h3> 1137<ul> 1138 <li>a Push interface for the XML and HTML parsers</li> 1139 <li>a shell-like interface to the document tree (try tester --shell :-)</li> 1140 <li>lots of bug fixes and improvement added over XMas hollidays</li> 1141 <li>fixed the DTD parsing code to work with the xhtml DTD</li> 1142 <li>added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()</li> 1143 <li>Fixed bugs in xmlNewNs()</li> 1144 <li>External entity loading code has been revamped, now it uses 1145 xmlLoadExternalEntity(), some fix on entities processing were added</li> 1146 <li>cleaned up WIN32 includes of socket stuff</li> 1147</ul> 1148 1149<h3>1.8.2: Dec 21 1999</h3> 1150<ul> 1151 <li>I got another problem with includes and C++, I hope this issue is fixed 1152 for good this time</li> 1153 <li>Added a few tree modification functions: xmlReplaceNode, 1154 xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and 1155 xmlDocSetRootElement</li> 1156 <li>Tried to improve the HTML output with help from <a 1157 href="mailto:clahey@umich.edu">Chris Lahey</a></li> 1158</ul> 1159 1160<h3>1.8.1: Dec 18 1999</h3> 1161<ul> 1162 <li>various patches to avoid troubles when using libxml with C++ compilers 1163 the "namespace" keyword and C escaping in include files</li> 1164 <li>a problem in one of the core macros IS_CHAR was corrected</li> 1165 <li>fixed a bug introduced in 1.8.0 breaking default namespace processing, 1166 and more specifically the Dia application</li> 1167 <li>fixed a posteriori validation (validation after parsing, or by using a 1168 Dtd not specified in the original document)</li> 1169 <li>fixed a bug in</li> 1170</ul> 1171 1172<h3>1.8.0: Dec 12 1999</h3> 1173<ul> 1174 <li>cleanup, especially memory wise</li> 1175 <li>the parser should be more reliable, especially the HTML one, it should 1176 not crash, whatever the input !</li> 1177 <li>Integrated various patches, especially a speedup improvement for large 1178 dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>, 1179 configure with --with-buffers to enable them.</li> 1180 <li>attribute normalization, oops should have been added long ago !</li> 1181 <li>attributes defaulted from Dtds should be available, xmlSetProp() now 1182 does entities escapting by default.</li> 1183</ul> 1184 1185<h3>1.7.4: Oct 25 1999</h3> 1186<ul> 1187 <li>Lots of HTML improvement</li> 1188 <li>Fixed some errors when saving both XML and HTML</li> 1189 <li>More examples, the regression tests should now look clean</li> 1190 <li>Fixed a bug with contiguous charref</li> 1191</ul> 1192 1193<h3>1.7.3: Sep 29 1999</h3> 1194<ul> 1195 <li>portability problems fixed</li> 1196 <li>snprintf was used unconditionnally, leading to link problems on system 1197 were it's not available, fixed</li> 1198</ul> 1199 1200<h3>1.7.1: Sep 24 1999</h3> 1201<ul> 1202 <li>The basic type for strings manipulated by libxml has been renamed in 1203 1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason 1204 is that CHAR was conflicting with a predefined type on Windows. However 1205 on non WIN32 environment, compatibility is provided by the way of a 1206 <strong>#define </strong>.</li> 1207 <li>Changed another error : the use of a structure field called errno, and 1208 leading to troubles on platforms where it's a macro</li> 1209</ul> 1210 1211<h3>1.7.0: sep 23 1999</h3> 1212<ul> 1213 <li>Added the ability to fetch remote DTD or parsed entities, see the <a 1214 href="html/libxml-nanohttp.html">nanohttp</a> module.</li> 1215 <li>Added an errno to report errors by another mean than a simple printf 1216 like callback</li> 1217 <li>Finished ID/IDREF support and checking when validation</li> 1218 <li>Serious memory leaks fixed (there is now a <a 1219 href="html/libxml-xmlmemory.html">memory wrapper</a> module)</li> 1220 <li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a> 1221 implementation</li> 1222 <li>Added an HTML parser front-end</li> 1223</ul> 1224 1225<h2><a name="XML">XML</a></h2> 1226 1227<p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for 1228markup-based structured documents. Here is <a name="example">an example XML 1229document</a>:</p> 1230<pre><?xml version="1.0"?> 1231<EXAMPLE prop1="gnome is great" prop2="&amp; linux too"> 1232 <head> 1233 <title>Welcome to Gnome</title> 1234 </head> 1235 <chapter> 1236 <title>The Linux adventure</title> 1237 <p>bla bla bla ...</p> 1238 <image href="linus.gif"/> 1239 <p>...</p> 1240 </chapter> 1241</EXAMPLE></pre> 1242 1243<p>The first line specifies that it's an XML document and gives useful 1244information about its encoding. Then the document is a text format whose 1245structure is specified by tags between brackets. <strong>Each tag opened has 1246to be closed</strong>. XML is pedantic about this. However, if a tag is empty 1247(no content), a single tag can serve as both the opening and closing tag if 1248it ends with <code>/></code> rather than with <code>></code>. Note 1249that, for example, the image tag has no content (just an attribute) and is 1250closed by ending the tag with <code>/></code>.</p> 1251 1252<p>XML can be applied sucessfully to a wide range of uses, from long term 1253structured document maintenance (where it follows the steps of SGML) to 1254simple data encoding mechanisms like configuration file formatting (glade), 1255spreadsheets (gnumeric), or even shorter lived documents such as WebDAV where 1256it is used to encode remote calls between a client and a server.</p> 1257 1258<h2><a name="XSLT">XSLT</a></h2> 1259 1260<p>Check <a href="http://xmlsoft.org/XSLT">the separate libxslt page</a></p> 1261 1262<p><a href="http://www.w3.org/TR/xslt">XSL Transformations</a>, is a 1263language for transforming XML documents into other XML documents (or 1264HTML/textual output).</p> 1265 1266<p>A separate library called libxslt is being built on top of libxml2. This 1267module "libxslt" can be found in the Gnome CVS base too.</p> 1268 1269<p>You can check the <a 1270href="http://cvs.gnome.org/lxr/source/libxslt/FEATURES">features</a> 1271supported and the progresses on the <a 1272href="http://cvs.gnome.org/lxr/source/libxslt/ChangeLog">Changelog</a></p> 1273 1274<h2><a name="architecture">libxml architecture</a></h2> 1275 1276<p>Libxml is made of multiple components; some of them are optional, and most 1277of the block interfaces are public. The main components are:</p> 1278<ul> 1279 <li>an Input/Output layer</li> 1280 <li>FTP and HTTP client layers (optional)</li> 1281 <li>an Internationalization layer managing the encodings support</li> 1282 <li>a URI module</li> 1283 <li>the XML parser and its basic SAX interface</li> 1284 <li>an HTML parser using the same SAX interface (optional)</li> 1285 <li>a SAX tree module to build an in-memory DOM representation</li> 1286 <li>a tree module to manipulate the DOM representation</li> 1287 <li>a validation module using the DOM representation (optional)</li> 1288 <li>an XPath module for global lookup in a DOM representation 1289 (optional)</li> 1290 <li>a debug module (optional)</li> 1291</ul> 1292 1293<p>Graphically this gives the following:</p> 1294 1295<p><img src="libxml.gif" alt="a graphical view of the various"></p> 1296 1297<p></p> 1298 1299<h2><a name="tree">The tree output</a></h2> 1300 1301<p>The parser returns a tree built during the document analysis. The value 1302returned is an <strong>xmlDocPtr</strong> (i.e., a pointer to an 1303<strong>xmlDoc</strong> structure). This structure contains information such 1304as the file name, the document type, and a <strong>children</strong> pointer 1305which is the root of the document (or more exactly the first child under the 1306root which is the document). The tree is made of <strong>xmlNode</strong>s, 1307chained in double-linked lists of siblings and with a children<->parent 1308relationship. An xmlNode can also carry properties (a chain of xmlAttr 1309structures). An attribute may have a value which is a list of TEXT or 1310ENTITY_REF nodes.</p> 1311 1312<p>Here is an example (erroneous with respect to the XML spec since there 1313should be only one ELEMENT under the root):</p> 1314 1315<p><img src="structure.gif" alt=" structure.gif "></p> 1316 1317<p>In the source package there is a small program (not installed by default) 1318called <strong>xmllint</strong> which parses XML files given as argument and 1319prints them back as parsed. This is useful for detecting errors both in XML 1320code and in the XML parser itself. It has an option <strong>--debug</strong> 1321which prints the actual in-memory structure of the document; here is the 1322result with the <a href="#example">example</a> given before:</p> 1323<pre>DOCUMENT 1324version=1.0 1325standalone=true 1326 ELEMENT EXAMPLE 1327 ATTRIBUTE prop1 1328 TEXT 1329 content=gnome is great 1330 ATTRIBUTE prop2 1331 ENTITY_REF 1332 TEXT 1333 content= linux too 1334 ELEMENT head 1335 ELEMENT title 1336 TEXT 1337 content=Welcome to Gnome 1338 ELEMENT chapter 1339 ELEMENT title 1340 TEXT 1341 content=The Linux adventure 1342 ELEMENT p 1343 TEXT 1344 content=bla bla bla ... 1345 ELEMENT image 1346 ATTRIBUTE href 1347 TEXT 1348 content=linus.gif 1349 ELEMENT p 1350 TEXT 1351 content=...</pre> 1352 1353<p>This should be useful for learning the internal representation model.</p> 1354 1355<h2><a name="interface">The SAX interface</a></h2> 1356 1357<p>Sometimes the DOM tree output is just too large to fit reasonably into 1358memory. In that case (and if you don't expect to save back the XML document 1359loaded using libxml), it's better to use the SAX interface of libxml. SAX is 1360a <strong>callback-based interface</strong> to the parser. Before parsing, 1361the application layer registers a customized set of callbacks which are 1362called by the library as it progresses through the XML input.</p> 1363 1364<p>To get more detailed step-by-step guidance on using the SAX interface of 1365libxml, see the <a 1366href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">nice 1367documentation</a>.written by <a href="mailto:james@daa.com.au">James 1368Henstridge</a>.</p> 1369 1370<p>You can debug the SAX behaviour by using the <strong>testSAX</strong> 1371program located in the gnome-xml module (it's usually not shipped in the 1372binary packages of libxml, but you can find it in the tar source 1373distribution). Here is the sequence of callbacks that would be reported by 1374testSAX when parsing the example XML document shown earlier:</p> 1375<pre>SAX.setDocumentLocator() 1376SAX.startDocument() 1377SAX.getEntity(amp) 1378SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp; linux too') 1379SAX.characters( , 3) 1380SAX.startElement(head) 1381SAX.characters( , 4) 1382SAX.startElement(title) 1383SAX.characters(Welcome to Gnome, 16) 1384SAX.endElement(title) 1385SAX.characters( , 3) 1386SAX.endElement(head) 1387SAX.characters( , 3) 1388SAX.startElement(chapter) 1389SAX.characters( , 4) 1390SAX.startElement(title) 1391SAX.characters(The Linux adventure, 19) 1392SAX.endElement(title) 1393SAX.characters( , 4) 1394SAX.startElement(p) 1395SAX.characters(bla bla bla ..., 15) 1396SAX.endElement(p) 1397SAX.characters( , 4) 1398SAX.startElement(image, href='linus.gif') 1399SAX.endElement(image) 1400SAX.characters( , 4) 1401SAX.startElement(p) 1402SAX.characters(..., 3) 1403SAX.endElement(p) 1404SAX.characters( , 3) 1405SAX.endElement(chapter) 1406SAX.characters( , 1) 1407SAX.endElement(EXAMPLE) 1408SAX.endDocument()</pre> 1409 1410<p>Most of the other interfaces of libxml are based on the DOM tree-building 1411facility, so nearly everything up to the end of this document presupposes the 1412use of the standard DOM tree build. Note that the DOM tree itself is built by 1413a set of registered default callbacks, without internal specific 1414interface.</p> 1415 1416<h2><a name="Validation">Validation & DTDs</a></h2> 1417 1418<p>Table of Content:</p> 1419<ol> 1420 <li><a href="#General5">General overview</a></li> 1421 <li><a href="#definition">The definition</a></li> 1422 <li><a href="#Simple">Simple rules</a> 1423 <ol> 1424 <li><a href="#reference">How to reference a DTD from a document</a></li> 1425 <li><a href="#Declaring">Declaring elements</a></li> 1426 <li><a href="#Declaring1">Declaring attributes</a></li> 1427 </ol> 1428 </li> 1429 <li><a href="#Some">Some examples</a></li> 1430 <li><a href="#validate">How to validate</a></li> 1431 <li><a href="#Other">Other resources</a></li> 1432</ol> 1433 1434<h3><a name="General5">General overview</a></h3> 1435 1436<p>Well what is validation and what is a DTD ?</p> 1437 1438<p>DTD is the acronym for Document Type Definition. This is a description of 1439the content for a familly of XML files. This is part of the XML 1.0 1440specification, and alows to describe and check that a given document instance 1441conforms to a set of rules detailing its structure and content.</p> 1442 1443<p>Validation is the process of checking a document against a DTD (more 1444generally against a set of construction rules).</p> 1445 1446<p>The validation process and building DTDs are the two most difficult parts 1447of the XML life cycle. Briefly a DTD defines all the possibles element to be 1448found within your document, what is the formal shape of your document tree 1449(by defining the allowed content of an element, either text, a regular 1450expression for the allowed list of children, or mixed content i.e. both text 1451and children). The DTD also defines the allowed attributes for all elements 1452and the types of the attributes.</p> 1453 1454<h3><a name="definition1">The definition</a></h3> 1455 1456<p>The <a href="http://www.w3.org/TR/REC-xml">W3C XML Recommendation</a> (<a 1457href="http://www.xml.com/axml/axml.html">Tim Bray's annotated version of 1458Rev1</a>):</p> 1459<ul> 1460 <li><a href="http://www.w3.org/TR/REC-xml#elemdecls">Declaring 1461 elements</a></li> 1462 <li><a href="http://www.w3.org/TR/REC-xml#attdecls">Declaring 1463 attributes</a></li> 1464</ul> 1465 1466<p>(unfortunately) all this is inherited from the SGML world, the syntax is 1467ancient...</p> 1468 1469<h3><a name="Simple1">Simple rules</a></h3> 1470 1471<p>Writing DTD can be done in multiple ways, the rules to build them if you 1472need something fixed or something which can evolve over time can be radically 1473different. Really complex DTD like Docbook ones are flexible but quite harder 1474to design. I will just focuse on DTDs for a formats with a fixed simple 1475structure. It is just a set of basic rules, and definitely not exhaustive nor 1476useable for complex DTD design.</p> 1477 1478<h4><a name="reference1">How to reference a DTD from a document</a>:</h4> 1479 1480<p>Assuming the top element of the document is <code>spec</code> and the dtd 1481is placed in the file <code>mydtd</code> in the subdirectory 1482<code>dtds</code> of the directory from where the document were loaded:</p> 1483 1484<p><code><!DOCTYPE spec SYSTEM "dtds/mydtd"></code></p> 1485 1486<p>Notes:</p> 1487<ul> 1488 <li>the system string is actually an URI-Reference (as defined in <a 1489 href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>) so you can use a 1490 full URL string indicating the location of your DTD on the Web, this is a 1491 really good thing to do if you want others to validate your document</li> 1492 <li>it is also possible to associate a <code>PUBLIC</code> identifier (a 1493 magic string) so that the DTd is looked up in catalogs on the client side 1494 without having to locate it on the web</li> 1495 <li>a dtd contains a set of elements and attributes declarations, but they 1496 don't define what the root of the document should be. This is explicitely 1497 told to the parser/validator as the first element of the 1498 <code>DOCTYPE</code> declaration.</li> 1499</ul> 1500 1501<h4><a name="Declaring2">Declaring elements</a>:</h4> 1502 1503<p>The following declares an element <code>spec</code>:</p> 1504 1505<p><code><!ELEMENT spec (front, body, back?)></code></p> 1506 1507<p>it also expresses that the spec element contains one <code>front</code>, 1508one <code>body</code> and one optionnal <code>back</code> children elements 1509in this order. The declaration of one element of the structure and its 1510content are done in a single declaration. Similary the following declares 1511<code>div1</code> elements:</p> 1512 1513<p><code><!ELEMENT div1 (head, (p | list | note)*, div2*)></code></p> 1514 1515<p>means div1 contains one <code>head</code> then a series of optional 1516<code>p</code>, <code>list</code>s and <code>note</code>s and then an 1517optional <code>div2</code>. And last but not least an element can contain 1518text:</p> 1519 1520<p><code><!ELEMENT b (#PCDATA)></code></p> 1521 1522<p><code>b</code> contains text or being of mixed content (text and elements 1523in no particular order):</p> 1524 1525<p><code><!ELEMENT p (#PCDATA|a|ul|b|i|em)*></code></p> 1526 1527<p><code>p </code>can contain text or <code>a</code>, <code>ul</code>, 1528<code>b</code>, <code>i </code>or <code>em</code> elements in no particular 1529order.</p> 1530 1531<h4><a name="Declaring1">Declaring attributes</a>:</h4> 1532 1533<p>again the attributes declaration includes their content definition:</p> 1534 1535<p><code><!ATTLIST termdef name CDATA #IMPLIED></code></p> 1536 1537<p>means that the element <code>termdef</code> can have a <code>name</code> 1538attribute containing text (<code>CDATA</code>) and which is optionnal 1539(<code>#IMPLIED</code>). The attribute value can also be defined within a 1540set:</p> 1541 1542<p><code><!ATTLIST list type (bullets|ordered|glossary) 1543"ordered"></code></p> 1544 1545<p>means <code>list</code> element have a <code>type</code> attribute with 3 1546allowed values "bullets", "ordered" or "glossary" and which default to 1547"ordered" if the attribute is not explicitely specified.</p> 1548 1549<p>The content type of an attribute can be text (<code>CDATA</code>), 1550anchor/reference/references 1551(<code>ID</code>/<code>IDREF</code>/<code>IDREFS</code>), entity(ies) 1552(<code>ENTITY</code>/<code>ENTITIES</code>) or name(s) 1553(<code>NMTOKEN</code>/<code>NMTOKENS</code>). The following defines that a 1554<code>chapter</code> element can have an optional <code>id</code> attribute 1555of type <code>ID</code>, usable for reference from attribute of type 1556IDREF:</p> 1557 1558<p><code><!ATTLIST chapter id ID #IMPLIED></code></p> 1559 1560<p>The last value of an attribute definition can be <code>#REQUIRED 1561</code>meaning that the attribute has to be given, <code>#IMPLIED</code> 1562meaning that it is optional, or the default value (possibly prefixed by 1563<code>#FIXED</code> if it is the only allowed).</p> 1564 1565<p>Notes:</p> 1566<ul> 1567 <li>usually the attributes pertaining to a given element are declared in a 1568 single expression, but it is just a convention adopted by a lot of DTD 1569 writers: 1570 <pre><!ATTLIST termdef 1571 id ID #REQUIRED 1572 name CDATA #IMPLIED></pre> 1573 <p>The previous construct defines both <code>id</code> and 1574 <code>name</code> attributes for the element <code>termdef</code></p> 1575 </li> 1576</ul> 1577 1578<h3><a name="Some1">Some examples</a></h3> 1579 1580<p>The directory <code>test/valid/dtds/</code> in the libxml distribution 1581contains some complex DTD examples. The <code>test/valid/dia.xml</code> 1582example shows an XML file where the simple DTD is directly included within 1583the document.</p> 1584 1585<h3><a name="validate1">How to validate</a></h3> 1586 1587<p>The simplest is to use the xmllint program comming with libxml. The 1588<code>--valid</code> option turn on validation of the files given as input, 1589for example the following validates a copy of the first revision of the XML 15901.0 specification:</p> 1591 1592<p><code>xmllint --valid --noout test/valid/REC-xml-19980210.xml</code></p> 1593 1594<p>the -- noout is used to not output the resulting tree.</p> 1595 1596<p>The <code>--dtdvalid dtd</code> allows to validate the document(s) against 1597a given DTD.</p> 1598 1599<p>Libxml exports an API to handle DTDs and validation, check the <a 1600href="http://xmlsoft.org/html/libxml-valid.html">associated 1601description</a>.</p> 1602 1603<h3><a name="Other1">Other resources</a></h3> 1604 1605<p>DTDs are as old as SGML. So there may be a number of examples on-line, I 1606will just list one for now, others pointers welcome:</p> 1607<ul> 1608 <li><a href="http://www.xml101.com:8081/dtd/">XML-101 DTD</a></li> 1609</ul> 1610 1611<p>I suggest looking at the examples found under test/valid/dtd and any of 1612the large number of books available on XML. The dia example in test/valid 1613should be both simple and complete enough to allow you to build your own.</p> 1614 1615<p></p> 1616 1617<h2><a name="Memory">Memory Management</a></h2> 1618 1619<p>Table of Content:</p> 1620<ol> 1621 <li><a href="#General3">General overview</a></li> 1622 <li><a href="#setting">Setting libxml set of memory routines</a></li> 1623 <li><a href="#cleanup">Cleaning up after parsing</a></li> 1624 <li><a href="#Debugging">Debugging routines</a></li> 1625 <li><a href="#General4">General memory requirements</a></li> 1626</ol> 1627 1628<h3><a name="General3">General overview</a></h3> 1629 1630<p>The module <code><a 1631href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlmemory.h</a></code> 1632provides the interfaces to the libxml memory system:</p> 1633<ul> 1634 <li>libxml does not use the libc memory allocator directly but xmlFree(), 1635 xmlMalloc() and xmlRealloc()</li> 1636 <li>those routines can be reallocated to a specific set of routine, by 1637 default the libc ones i.e. free(), malloc() and realloc()</li> 1638 <li>the xmlmemory.c module includes a set of debugging routine</li> 1639</ul> 1640 1641<h3><a name="setting">Setting libxml set of memory routines</a></h3> 1642 1643<p>It is sometimes useful to not use the default memory allocator, either for 1644debugging, analysis or to implement a specific behaviour on memory management 1645(like on embedded systems). Two function calls are available to do so:</p> 1646<ul> 1647 <li><a href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemGet ()</a> 1648 which return the current set of functions in use by the parser</li> 1649 <li><a 1650 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemSetup()</a> 1651 which allow to set up a new set of memory allocation functions</li> 1652</ul> 1653 1654<p>Of course a call to xmlMemSetup() should probably be done before calling 1655any other libxml routines (unless you are sure your allocations routines are 1656compatibles).</p> 1657 1658<h3><a name="cleanup">Cleaning up after parsing</a></h3> 1659 1660<p>Libxml is not stateless, there is a few set of memory structures needing 1661allocation before the parser is fully functionnal (some encoding structures 1662for example). This also mean that once parsing is finished there is a tiny 1663amount of memory (a few hundred bytes) which can be recollected if you don't 1664reuse the parser immediately:</p> 1665<ul> 1666 <li><a href="http://xmlsoft.org/html/libxml-parser.html">xmlCleanupParser 1667 ()</a> 1668 is a centralized routine to free the parsing states. Note that it won't 1669 deallocate any produced tree if any (use the xmlFreeDoc() and related 1670 routines for this).</li> 1671 <li><a href="http://xmlsoft.org/html/libxml-parser.html">xmlInitParser 1672 ()</a> 1673 is the dual routine allowing to preallocate the parsing state which can 1674 be useful for example to avoid initialization reentrancy problems when 1675 using libxml in multithreaded applications</li> 1676</ul> 1677 1678<p>Generally xmlCleanupParser() is safe, if needed the state will be rebuild 1679at the next invocation of parser routines, but be careful of the consequences 1680in multithreaded applications.</p> 1681 1682<h3><a name="Debugging">Debugging routines</a></h3> 1683 1684<p>When configured using --with-mem-debug flag (off by default), libxml uses 1685a set of memory allocation debugging routineskeeping track of all allocated 1686blocks and the location in the code where the routine was called. A couple of 1687other debugging routines allow to dump the memory allocated infos to a file 1688or call a specific routine when a given block number is allocated:</p> 1689<ul> 1690 <li><a 1691 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMallocLoc()</a> 1692 <a 1693 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlReallocLoc()</a> 1694 and <a 1695 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemStrdupLoc()</a> 1696 are the memory debugging replacement allocation routines</li> 1697 <li><a href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemoryDump 1698 ()</a> 1699 dumps all the informations about the allocated memory block lefts in the 1700 <code>.memdump</code> file</li> 1701</ul> 1702 1703<p>When developping libxml memory debug is enabled, the tests programs call 1704xmlMemoryDump () and the "make test" regression tests will check for any 1705memory leak during the full regression test sequence, this helps a lot 1706ensuring that libxml does not leak memory and bullet proof memory 1707allocations use (some libc implementations are known to be far too permissive 1708resulting in major portability problems!).</p> 1709 1710<p>If the .memdump reports a leak, it displays the allocation function and 1711also tries to give some informations about the content and structure of the 1712allocated blocks left. This is sufficient in most cases to find the culprit, 1713but not always. Assuming the allocation problem is reproductible, it is 1714possible to find more easilly:</p> 1715<ol> 1716 <li>write down the block number xxxx not allocated</li> 1717 <li>export the environement variable XML_MEM_BREAKPOINT=xxxx</li> 1718 <li>run the program under a debugger and set a breakpoint on 1719 xmlMallocBreakpoint() a specific function called when this precise block 1720 is allocated</li> 1721 <li>when the breakpoint is reached you can then do a fine analysis of the 1722 allocation an step to see the condition resulting in the missing 1723 deallocation.</li> 1724</ol> 1725 1726<p>I used to use a commercial tool to debug libxml memory problems but after 1727noticing that it was not detecting memory leaks that simple mechanism was 1728used and proved extremely efficient until now.</p> 1729 1730<h3><a name="General4">General memory requirements</a></h3> 1731 1732<p>How much libxml memory require ? It's hard to tell in average it depends 1733of a number of things:</p> 1734<ul> 1735 <li>the parser itself should work in a fixed amout of memory, except for 1736 information maintained about the stacks of names and entities locations. 1737 The I/O and encoding handlers will probably account for a few KBytes. 1738 This is true for both the XML and HTML parser (though the HTML parser 1739 need more state).</li> 1740 <li>If you are generating the DOM tree then memory requirements will grow 1741 nearly lineary with the size of the data. In general for a balanced 1742 textual document the internal memory requirement is about 4 times the 1743 size of the UTF8 serialization of this document (exmple the XML-1.0 1744 recommendation is a bit more of 150KBytes and takes 650KBytes of main 1745 memory when parsed). Validation will add a amount of memory required for 1746 maintaining the external Dtd state which should be linear with the 1747 complexity of the content model defined by the Dtd</li> 1748 <li>If you don't care about the advanced features of libxml like 1749 validation, DOM, XPath or XPointer, but really need to work fixed memory 1750 requirements, then the SAX interface should be used.</li> 1751</ul> 1752 1753<p></p> 1754 1755<h2><a name="Encodings">Encodings support</a></h2> 1756 1757<p>Table of Content:</p> 1758<ol> 1759 <li><a href="encoding.html#What">What does internationalization support 1760 mean ?</a></li> 1761 <li><a href="encoding.html#internal">The internal encoding, how and 1762 why</a></li> 1763 <li><a href="encoding.html#implemente">How is it implemented ?</a></li> 1764 <li><a href="encoding.html#Default">Default supported encodings</a></li> 1765 <li><a href="encoding.html#extend">How to extend the existing 1766 support</a></li> 1767</ol> 1768 1769<h3><a name="What">What does internationalization support mean ?</a></h3> 1770 1771<p>XML was designed from the start to allow the support of any character set 1772by using Unicode. Any conformant XML parser has to support the UTF-8 and 1773UTF-16 default encodings which can both express the full unicode ranges. UTF8 1774is a variable length encoding whose greatest point are to resuse the same 1775emcoding for ASCII and to save space for Western encodings, but it is a bit 1776more complex to handle in practice. UTF-16 use 2 bytes per characters (and 1777sometimes combines two pairs), it makes implementation easier, but looks a 1778bit overkill for Western languages encoding. Moreover the XML specification 1779allows document to be encoded in other encodings at the condition that they 1780are clearly labelled as such. For example the following is a wellformed XML 1781document encoded in ISO-8859 1 and using accentuated letter that we French 1782likes for both markup and content:</p> 1783<pre><?xml version="1.0" encoding="ISO-8859-1"?> 1784<tr�s>l�</tr�s></pre> 1785 1786<p>Having internationalization support in libxml means the foolowing:</p> 1787<ul> 1788 <li>the document is properly parsed</li> 1789 <li>informations about it's encoding are saved</li> 1790 <li>it can be modified</li> 1791 <li>it can be saved in its original encoding</li> 1792 <li>it can also be saved in another encoding supported by libxml (for 1793 example straight UTF8 or even an ASCII form)</li> 1794</ul> 1795 1796<p>Another very important point is that the whole libxml API, with the 1797exception of a few routines to read with a specific encoding or save to a 1798specific encoding, is completely agnostic about the original encoding of the 1799document.</p> 1800 1801<p>It should be noted too that the HTML parser embedded in libxml now obbey 1802the same rules too, the following document will be (as of 2.2.2) handled in 1803an internationalized fashion by libxml too:</p> 1804<pre><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" 1805 "http://www.w3.org/TR/REC-html40/loose.dtd"> 1806<html lang="fr"> 1807<head> 1808 <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"> 1809</head> 1810<body> 1811<p>W3C cr�e des standards pour le Web.</body> 1812</html></pre> 1813 1814<h3><a name="internal">The internal encoding, how and why</a></h3> 1815 1816<p>One of the core decision was to force all documents to be converted to a 1817default internal encoding, and that encoding to be UTF-8, here are the 1818rationale for those choices:</p> 1819<ul> 1820 <li>keeping the native encoding in the internal form would force the libxml 1821 users (or the code associated) to be fully aware of the encoding of the 1822 original document, for examples when adding a text node to a document, 1823 the content would have to be provided in the document encoding, i.e. the 1824 client code would have to check it before hand, make sure it's conformant 1825 to the encoding, etc ... Very hard in practice, though in some specific 1826 cases this may make sense.</li> 1827 <li>the second decision was which encoding. From the XML spec only UTF8 and 1828 UTF16 really makes sense as being the two only encodings for which there 1829 is amndatory support. UCS-4 (32 bits fixed size encoding) could be 1830 considered an intelligent choice too since it's a direct Unicode mapping 1831 support. I selected UTF-8 on the basis of efficiency and compatibility 1832 with surrounding software: 1833 <ul> 1834 <li>UTF-8 while a bit more complex to convert from/to (i.e. slightly 1835 more costly to import and export CPU wise) is also far more compact 1836 than UTF-16 (and UCS-4) for a majority of the documents I see it used 1837 for right now (RPM RDF catalogs, advogato data, various configuration 1838 file formats, etc.) and the key point for today's computer 1839 architecture is efficient uses of caches. If one nearly double the 1840 memory requirement to store the same amount of data, this will trash 1841 caches (main memory/external caches/internal caches) and my take is 1842 that this harms the system far more than the CPU requirements needed 1843 for the conversion to UTF-8</li> 1844 <li>Most of libxml version 1 users were using it with straight ASCII 1845 most of the time, doing the conversion with an internal encoding 1846 requiring all their code to be rewritten was a serious show-stopper 1847 for using UTF-16 or UCS-4.</li> 1848 <li>UTF-8 is being used as the de-facto internal encoding standard for 1849 related code like the <a href="http://www.pango.org/">pango</a> 1850 upcoming Gnome text widget, and a lot of Unix code (yep another place 1851 where Unix programmer base takes a different approach from Microsoft 1852 - they are using UTF-16)</li> 1853 </ul> 1854 </li> 1855</ul> 1856 1857<p>What does this mean in practice for the libxml user:</p> 1858<ul> 1859 <li>xmlChar, the libxml data type is a byte, those bytes must be assembled 1860 as UTF-8 valid strings. The proper way to terminate an xmlChar * string 1861 is simply to append 0 byte, as usual.</li> 1862 <li>One just need to make sure that when using chars outside the ASCII set, 1863 the values has been properly converted to UTF-8</li> 1864</ul> 1865 1866<h3><a name="implemente">How is it implemented ?</a></h3> 1867 1868<p>Let's describe how all this works within libxml, basically the I18N 1869(internationalization) support get triggered only during I/O operation, i.e. 1870when reading a document or saving one. Let's look first at the reading 1871sequence:</p> 1872<ol> 1873 <li>when a document is processed, we usually don't know the encoding, a 1874 simple heuristic allows to detect UTF-18 and UCS-4 from whose where the 1875 ASCII range (0-0x7F) maps with ASCII</li> 1876 <li>the xml declaration if available is parsed, including the encoding 1877 declaration. At that point, if the autodetected encoding is different 1878 from the one declared a call to xmlSwitchEncoding() is issued.</li> 1879 <li>If there is no encoding declaration, then the input has to be in either 1880 UTF-8 or UTF-16, if it is not then at some point when processing the 1881 input, the converter/checker of UTF-8 form will raise an encoding error. 1882 You may end-up with a garbled document, or no document at all ! Example: 1883 <pre>~/XML -> /xmllint err.xml 1884err.xml:1: error: Input is not proper UTF-8, indicate encoding ! 1885<tr�s>l�</tr�s> 1886 ^ 1887err.xml:1: error: Bytes: 0xE8 0x73 0x3E 0x6C 1888<tr�s>l�</tr�s> 1889 ^</pre> 1890 </li> 1891 <li>xmlSwitchEncoding() does an encoding name lookup, canonalize it, and 1892 then search the default registered encoding converters for that encoding. 1893 If it's not within the default set and iconv() support has been compiled 1894 it, it will ask iconv for such an encoder. If this fails then the parser 1895 will report an error and stops processing: 1896 <pre>~/XML -> /xmllint err2.xml 1897err2.xml:1: error: Unsupported encoding UnsupportedEnc 1898<?xml version="1.0" encoding="UnsupportedEnc"?> 1899 ^</pre> 1900 </li> 1901 <li>From that point the encoder process progressingly the input (it is 1902 plugged as a front-end to the I/O module) for that entity. It captures 1903 and convert on-the-fly the document to be parsed to UTF-8. The parser 1904 itself just does UTF-8 checking of this input and process it 1905 transparently. The only difference is that the encoding information has 1906 been added to the parsing context (more precisely to the input 1907 corresponding to this entity).</li> 1908 <li>The result (when using DOM) is an internal form completely in UTF-8 1909 with just an encoding information on the document node.</li> 1910</ol> 1911 1912<p>Ok then what's happen when saving the document (assuming you 1913colllected/built an xmlDoc DOM like structure) ? It depends on the function 1914called, xmlSaveFile() will just try to save in the original encoding, while 1915xmlSaveFileTo() and xmlSaveFileEnc() can optionally save to a given 1916encoding:</p> 1917<ol> 1918 <li>if no encoding is given, libxml will look for an encoding value 1919 associated to the document and if it exists will try to save to that 1920 encoding, 1921 <p>otherwise everything is written in the internal form, i.e. UTF-8</p> 1922 </li> 1923 <li>so if an encoding was specified, either at the API level or on the 1924 document, libxml will again canonalize the encoding name, lookup for a 1925 converter in the registered set or through iconv. If not found the 1926 function will return an error code</li> 1927 <li>the converter is placed before the I/O buffer layer, as another kind of 1928 buffer, then libxml will simply push the UTF-8 serialization to through 1929 that buffer, which will then progressively be converted and pushed onto 1930 the I/O layer.</li> 1931 <li>It is possible that the converter code fails on some input, for example 1932 trying to push an UTF-8 encoded chinese character through the UTF-8 to 1933 ISO-8859-1 converter won't work. Since the encoders are progressive they 1934 will just report the error and the number of bytes converted, at that 1935 point libxml will decode the offending character, remove it from the 1936 buffer and replace it with the associated charRef encoding &#123; and 1937 resume the convertion. This guarante that any document will be saved 1938 without losses (except for markup names where this is not legal, this is 1939 a problem in the current version, in pactice avoid using non-ascci 1940 characters for tags or attributes names @@). A special "ascii" encoding 1941 name is used to save documents to a pure ascii form can be used when 1942 portability is really crucial</li> 1943</ol> 1944 1945<p>Here is a few examples based on the same test document:</p> 1946<pre>~/XML -> /xmllint isolat1 1947<?xml version="1.0" encoding="ISO-8859-1"?> 1948<tr�s>l�</tr�s> 1949~/XML -> /xmllint --encode UTF-8 isolat1 1950<?xml version="1.0" encoding="UTF-8"?> 1951<très>l� �</très> 1952~/XML -> </pre> 1953 1954<p>The same processing is applied (and reuse most of the code) for HTML I18N 1955processing. Looking up and modifying the content encoding is a bit more 1956difficult since it is located in a <meta> tag under the <head>, 1957so a couple of functions htmlGetMetaEncoding() and htmlSetMetaEncoding() have 1958been provided. The parser also attempts to switch encoding on the fly when 1959detecting such a tag on input. Except for that the processing is the same 1960(and again reuses the same code).</p> 1961 1962<h3><a name="Default">Default supported encodings</a></h3> 1963 1964<p>libxml has a set of default converters for the following encodings 1965(located in encoding.c):</p> 1966<ol> 1967 <li>UTF-8 is supported by default (null handlers)</li> 1968 <li>UTF-16, both little and big endian</li> 1969 <li>ISO-Latin-1 (ISO-8859-1) covering most western languages</li> 1970 <li>ASCII, useful mostly for saving</li> 1971 <li>HTML, a specific handler for the conversion of UTF-8 to ASCII with HTML 1972 predefined entities like &copy; for the Copyright sign.</li> 1973</ol> 1974 1975<p>More over when compiled on an Unix platfor with iconv support the full set 1976of encodings supported by iconv can be instantly be used by libxml. On a 1977linux machine with glibc-2.1 the list of supported encodings and aliases fill 19783 full pages, and include UCS-4, the full set of ISO-Latin encodings, and the 1979various Japanese ones.</p> 1980 1981<h4>Encoding aliases</h4> 1982 1983<p>From 2.2.3, libxml has support to register encoding names aliases. The 1984goal is to be able to parse document whose encoding is supported but where 1985the name differs (for example from the default set of names accepted by 1986iconv). The following functions allow to register and handle new aliases for 1987existing encodings. Once registered libxml will automatically lookup the 1988aliases when handling a document:</p> 1989<ul> 1990 <li>int xmlAddEncodingAlias(const char *name, const char *alias);</li> 1991 <li>int xmlDelEncodingAlias(const char *alias);</li> 1992 <li>const char * xmlGetEncodingAlias(const char *alias);</li> 1993 <li>void xmlCleanupEncodingAliases(void);</li> 1994</ul> 1995 1996<h3><a name="extend">How to extend the existing support</a></h3> 1997 1998<p>Well adding support for new encoding, or overriding one of the encoders 1999(assuming it is buggy) should not be hard, just write an input and output 2000conversion routines to/from UTF-8, and register them using 2001xmlNewCharEncodingHandler(name, xxxToUTF8, UTF8Toxxx), and they will be 2002called automatically if the parser(s) encounter such an encoding name 2003(register it uppercase, this will help). The description of the encoders, 2004their arguments and expected return values are described in the encoding.h 2005header.</p> 2006 2007<p>A quick note on the topic of subverting the parser to use a different 2008internal encoding than UTF-8, in some case people will absolutely want to 2009keep the internal encoding different, I think it's still possible (but the 2010encoding must be compliant with ASCII on the same subrange) though I didn't 2011tried it. The key is to override the default conversion routines (by 2012registering null encoders/decoders for your charsets), and bypass the UTF-8 2013checking of the parser by setting the parser context charset 2014(ctxt->charset) to something different than XML_CHAR_ENCODING_UTF8, but 2015there is no guarantee taht this will work. You may also have some troubles 2016saving back.</p> 2017 2018<p>Basically proper I18N support is important, this requires at least 2019libxml-2.0.0, but a lot of features and corrections are really available only 2020starting 2.2.</p> 2021 2022<h2><a name="IO">I/O Interfaces</a></h2> 2023 2024<p>Table of Content:</p> 2025<ol> 2026 <li><a href="#General1">General overview</a></li> 2027 <li><a href="#basic">The basic buffer type</a></li> 2028 <li><a href="#Input">Input I/O handlers</a></li> 2029 <li><a href="#Output">Output I/O handlers</a></li> 2030 <li><a href="#entities">The entities loader</a></li> 2031 <li><a href="#Example2">Example of customized I/O</a></li> 2032</ol> 2033 2034<h3><a name="General1">General overview</a></h3> 2035 2036<p>The module <code><a 2037href="http://xmlsoft.org/html/libxml-xmlio.html">xmlIO.h</a></code> provides 2038the interfaces to the libxml I/O system. This consists of 4 main parts:</p> 2039<ul> 2040 <li>Entities loader, this is a routine which tries to fetch the entities 2041 (files) based on their PUBLIC and SYSTEM identifiers. The default loader 2042 don't look at the public identifier since libxml do not maintain a 2043 catalog. You can redefine you own entity loader by using 2044 <code>xmlGetExternalEntityLoader()</code> and 2045 <code>xmlSetExternalEntityLoader()</code>. <a href="#entities">Check the 2046 example</a>.</li> 2047 <li>Input I/O buffers which are a commodity structure used by the parser(s) 2048 input layer to handle fetching the informations to feed the parser. This 2049 provides buffering and is also a placeholder where the encoding 2050 convertors to UTF8 are piggy-backed.</li> 2051 <li>Output I/O buffers are similar to the Input ones and fulfill similar 2052 task but when generating a serialization from a tree.</li> 2053 <li>A mechanism to register sets of I/O callbacks and associate them with 2054 specific naming schemes like the protocol part of the URIs. 2055 <p>This affect the default I/O operations and allows to use specific I/O 2056 handlers for certain names.</p> 2057 </li> 2058</ul> 2059 2060<p>The general mechanism used when loading http://rpmfind.net/xml.html for 2061example in the HTML parser is the following:</p> 2062<ol> 2063 <li>The default entity loader calls <code>xmlNewInputFromFile()</code> with 2064 the parsing context and the URI string.</li> 2065 <li>the URI string is checked against the existing registered handlers 2066 using their match() callback function, if the HTTP module was compiled 2067 in, it is registered and its match() function will succeeds</li> 2068 <li>the open() function of the handler is called and if successful will 2069 return an I/O Input buffer</li> 2070 <li>the parser will the start reading from this buffer and progressively 2071 fetch information from the resource, calling the read() function of the 2072 handler until the resource is exhausted</li> 2073 <li>if an encoding change is detected it will be installed on the input 2074 buffer, providing buffering and efficient use of the conversion 2075 routines</li> 2076 <li>once the parser has finished, the close() function of the handler is 2077 called once and the Input buffer and associed resources are 2078 deallocated.</li> 2079</ol> 2080 2081<p>The user defined callbacks are checked first to allow overriding of the 2082default libxml I/O routines.</p> 2083 2084<h3><a name="basic">The basic buffer type</a></h3> 2085 2086<p>All the buffer manipulation handling is done using the 2087<code>xmlBuffer</code> type define in <code><a 2088href="http://xmlsoft.org/html/libxml-tree.html">tree.h</a> </code>which is a 2089resizable memory buffer. The buffer allocation strategy can be selected to be 2090either best-fit or use an exponential doubling one (CPU vs. memory use 2091tradeoff). The values are <code>XML_BUFFER_ALLOC_EXACT</code> and 2092<code>XML_BUFFER_ALLOC_DOUBLEIT</code>, and can be set individually or on a 2093system wide basis using <code>xmlBufferSetAllocationScheme()</code>. A number 2094of functions allows to manipulate buffers with names starting with the 2095<code>xmlBuffer...</code> prefix.</p> 2096 2097<h3><a name="Input">Input I/O handlers</a></h3> 2098 2099<p>An Input I/O handler is a simple structure 2100<code>xmlParserInputBuffer</code> containing a context associated to the 2101resource (file descriptor, or pointer to a protocol handler), the read() and 2102close() callbacks to use and an xmlBuffer. And extra xmlBuffer and a charset 2103encoding handler are also present to support charset conversion when 2104needed.</p> 2105 2106<h3><a name="Output">Output I/O handlers</a></h3> 2107 2108<p>An Output handler <code>xmlOutputBuffer</code> is completely similar to an 2109Input one except the callbacks are write() and close().</p> 2110 2111<h3><a name="entities">The entities loader</a></h3> 2112 2113<p>The entity loader resolves requests for new entities and create inputs for 2114the parser. Creating an input from a filename or an URI string is done 2115through the xmlNewInputFromFile() routine. The default entity loader do not 2116handle the PUBLIC identifier associated with an entity (if any). So it just 2117calls xmlNewInputFromFile() with the SYSTEM identifier (which is mandatory in 2118XML).</p> 2119 2120<p>If you want to hook up a catalog mechanism then you simply need to 2121override the default entity loader, here is an example:</p> 2122<pre>#include <libxml/xmlIO.h> 2123 2124xmlExternalEntityLoader defaultLoader = NULL; 2125 2126xmlParserInputPtr 2127xmlMyExternalEntityLoader(const char *URL, const char *ID, 2128 xmlParserCtxtPtr ctxt) { 2129 xmlParserInputPtr ret; 2130 const char *fileID = NULL; 2131 /* lookup for the fileID depending on ID */ 2132 2133 ret = xmlNewInputFromFile(ctxt, fileID); 2134 if (ret != NULL) 2135 return(ret); 2136 if (defaultLoader != NULL) 2137 ret = defaultLoader(URL, ID, ctxt); 2138 return(ret); 2139} 2140 2141int main(..) { 2142 ... 2143 2144 /* 2145 * Install our own entity loader 2146 */ 2147 defaultLoader = xmlGetExternalEntityLoader(); 2148 xmlSetExternalEntityLoader(xmlMyExternalEntityLoader); 2149 2150 ... 2151}</pre> 2152 2153<h3><a name="Example2">Example of customized I/O</a></h3> 2154 2155<p>This example come from <a href="http://xmlsoft.org/messages/0708.html">a 2156real use case</a>, xmlDocDump() closes the FILE * passed by the application 2157and this was a problem. The <a 2158href="http://xmlsoft.org/messages/0711.html">solution</a> was to redefine a 2159new output handler with the closing call deactivated:</p> 2160<ol> 2161 <li>First define a new I/O ouput allocator where the output don't close the 2162 file: 2163 <pre>xmlOutputBufferPtr 2164xmlOutputBufferCreateOwn(FILE *file, xmlCharEncodingHandlerPtr encoder) { 2165����xmlOutputBufferPtr ret; 2166���� 2167����if (xmlOutputCallbackInitialized == 0) 2168��������xmlRegisterDefaultOutputCallbacks(); 2169 2170����if (file == NULL) return(NULL); 2171����ret = xmlAllocOutputBuffer(encoder); 2172����if (ret != NULL) { 2173��������ret->context = file; 2174��������ret->writecallback = xmlFileWrite; 2175��������ret->closecallback = NULL; /* No close callback */ 2176����} 2177����return(ret); <br> 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187 2188 2189 2190 2191} </pre> 2192 </li> 2193 <li>And then use it to save the document: 2194 <pre>FILE *f; 2195xmlOutputBufferPtr output; 2196xmlDocPtr doc; 2197int res; 2198 2199f = ... 2200doc = .... 2201 2202output = xmlOutputBufferCreateOwn(f, NULL); 2203res = xmlSaveFileTo(output, doc, NULL); 2204 </pre> 2205 </li> 2206</ol> 2207 2208<h2><a name="Catalog">Catalog support</a></h2> 2209 2210<p>Table of Content:</p> 2211<ol> 2212 <li><a href="General2">General overview</a></li> 2213 <li><a href="#definition">The definition</a></li> 2214 <li><a href="#Simple">Using catalogs</a></li> 2215 <li><a href="#Some">Some examples</a></li> 2216 <li><a href="#reference">How to tune catalog usage</a></li> 2217 <li><a href="#validate">How to debug catalog processing</a></li> 2218 <li><a href="#Declaring">How to create and maintain catalogs</a></li> 2219 <li><a href="#implemento">The implementor corner quick review of the 2220 API</a></li> 2221 <li><a href="#Other">Other resources</a></li> 2222</ol> 2223 2224<h3><a name="General2">General overview</a></h3> 2225 2226<p>What is a catalog? Basically it's a lookup mechanism used when an entity 2227(a file or a remote resource) references another entity. The catalog lookup 2228is inserted between the moment the reference is recognized by the software 2229(XML parser, stylesheet processing, or even images referenced for inclusion 2230in a rendering) and the time where loading that resource is actually 2231started.</p> 2232 2233<p>It is basically used for 3 things:</p> 2234<ul> 2235 <li>mapping from "logical" names, the public identifiers and a more 2236 concrete name usable for download (and URI). For example it can associate 2237 the logical name 2238 <p>"-//OASIS//DTD DocBook XML V4.1.2//EN"</p> 2239 <p>of the DocBook 4.1.2 XML DTD with the actual URL where it can be 2240 downloaded</p> 2241 <p>http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd</p> 2242 </li> 2243 <li>remapping from a given URL to another one, like an HTTP indirection 2244 saying that 2245 <p>"http://www.oasis-open.org/committes/tr.xsl"</p> 2246 <p>should really be looked at</p> 2247 <p>"http://www.oasis-open.org/committes/entity/stylesheets/base/tr.xsl"</p> 2248 </li> 2249 <li>providing a local cache mechanism allowing to load the entities 2250 associated to public identifiers or remote resources, this is a really 2251 important feature for any significant deployment of XML or SGML since it 2252 allows to avoid the aleas and delays associated to fetching remote 2253 resources.</li> 2254</ul> 2255 2256<h3><a name="definition">The definitions</a></h3> 2257 2258<p>Libxml, as of 2.4.3 implements 2 kind of catalogs:</p> 2259<ul> 2260 <li>the older SGML catalogs, the official spec is SGML Open Technical 2261 Resolution TR9401:1997, but is better understood by reading <a 2262 href="http://www.jclark.com/sp/catalog.htm">the SP Catalog page</a> from 2263 James Clark. This is relatively old and not the preferred mode of 2264 operation of libxml.</li> 2265 <li><a href="http://www.oasis-open.org/committees/entity/spec.html">XML 2266 Catalogs</a> 2267 is far more flexible, more recent, uses an XML syntax and should scale 2268 quite better. This is the default option of libxml.</li> 2269</ul> 2270 2271<p></p> 2272 2273<h3><a name="Simple">Using catalog</a></h3> 2274 2275<p>In a normal environment libxml will by default check the presence of a 2276catalog in /etc/xml/catalog, and assuming it has been correctly populated, 2277the processing is completely transparent to the document user. To take a 2278concrete example, suppose you are authoring a DocBook document, this one 2279starts with the following DOCTYPE definition:</p> 2280<pre><?xml version='1.0'?> 2281<!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN" 2282 "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd"></pre> 2283 2284<p>When validating the document with libxml, the catalog will be 2285automatically consulted to lookup the public identifier "-//Norman Walsh//DTD 2286DocBk XML V3.1.4//EN" and the system identifier 2287"http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd", and if these entities have 2288been installed on your system and the catalogs actually point to them, libxml 2289will fetch them from the local disk.</p> 2290 2291<p style="font-size: 10pt"><strong>Note</strong>: Really don't use this 2292DOCTYPE example it's a really old version, but is fine as an example.</p> 2293 2294<p>Libxml will check the catalog each time that it is requested to load an 2295entity, this includes DTD, external parsed entities, stylesheets, etc ... If 2296your system is correctly configured all the authoring phase and processing 2297should use only local files, even if your document stays portable because it 2298uses the canonical public and system ID, referencing the remote document.</p> 2299 2300<h3><a name="Some">Some examples:</a></h3> 2301 2302<p>Here is a couple of fragments from XML Catalogs used in libxml early 2303regression tests in <code>test/catalogs</code> :</p> 2304<pre><?xml version="1.0"?> 2305<!DOCTYPE catalog PUBLIC 2306 "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" 2307 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 2308<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"> 2309 <public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN" 2310 uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/> 2311...</pre> 2312 2313<p>This is the beginning of a catalog for DocBook 4.1.2, XML Catalogs are 2314written in XML, there is a specific namespace for catalog elements 2315"urn:oasis:names:tc:entity:xmlns:xml:catalog". The first entry in this 2316catalog is a <code>public</code> mapping it allows to associate a Public 2317Identifier with an URI.</p> 2318<pre>... 2319 <rewriteSystem systemIdStartString="http://www.oasis-open.org/docbook/" 2320 rewritePrefix="file:///usr/share/xml/docbook/"/> 2321...</pre> 2322 2323<p>A <code>rewriteSystem</code> is a very powerful instruction, it says that 2324any URI starting with a given prefix should be looked at another URI 2325constructed by replacing the prefix with an new one. In effect this acts like 2326a cache system for a full area of the Web. In practice it is extremely useful 2327with a file prefix if you have installed a copy of those resources on your 2328local system.</p> 2329<pre>... 2330<delegatePublic publicIdStartString="-//OASIS//DTD XML Catalog //" 2331 catalog="file:///usr/share/xml/docbook.xml"/> 2332<delegatePublic publicIdStartString="-//OASIS//ENTITIES DocBook XML" 2333 catalog="file:///usr/share/xml/docbook.xml"/> 2334<delegatePublic publicIdStartString="-//OASIS//DTD DocBook XML" 2335 catalog="file:///usr/share/xml/docbook.xml"/> 2336<delegateSystem systemIdStartString="http://www.oasis-open.org/docbook/" 2337 catalog="file:///usr/share/xml/docbook.xml"/> 2338<delegateURI uriStartString="http://www.oasis-open.org/docbook/" 2339 catalog="file:///usr/share/xml/docbook.xml"/> 2340...</pre> 2341 2342<p>Delegation is the core features which allows to build a tree of catalogs, 2343easier to maintain than a single catalog, based on Public Identifier, System 2344Identifier or URI prefixes it instructs the catalog software to look up 2345entries in another resource. This feature allow to build hierarchies of 2346catalogs, the set of entries presented should be sufficient to redirect the 2347resolution of all DocBook references to the specific catalog in 2348<code>/usr/share/xml/docbook.xml</code> this one in turn could delegate all 2349references for DocBook 4.2.1 to a specific catalog installed at the same time 2350as the DocBook resources on the local machine.</p> 2351 2352<h3><a name="reference">How to tune catalog usage:</a></h3> 2353 2354<p>The user can change the default catalog behaviour by redirecting queries 2355to its own set of catalogs, this can be done by setting the 2356<code>XML_CATALOG_FILES</code> environment variable to a list of catalogs, an 2357empty one should deactivate loading the default <code>/etc/xml/catalog</code> 2358default catalog</p> 2359 2360<h3><a name="validate">How to debug catalog processing:</a></h3> 2361 2362<p>Setting up the <code>XML_DEBUG_CATALOG</code> environment variable will 2363make libxml output debugging informations for each catalog operations, for 2364example:</p> 2365<pre>orchis:~/XML -> xmllint --memory --noout test/ent2 2366warning: failed to load external entity "title.xml" 2367orchis:~/XML -> export XML_DEBUG_CATALOG= 2368orchis:~/XML -> xmllint --memory --noout test/ent2 2369Failed to parse catalog /etc/xml/catalog 2370Failed to parse catalog /etc/xml/catalog 2371warning: failed to load external entity "title.xml" 2372Catalogs cleanup 2373orchis:~/XML -> </pre> 2374 2375<p>The test/ent2 references an entity, running the parser from memory makes 2376the base URI unavailable and the the "title.xml" entity cannot be loaded. 2377Setting up the debug environment variable allows to detect that an attempt is 2378made to load the <code>/etc/xml/catalog</code> but since it's not present the 2379resolution fails.</p> 2380 2381<p>But the most advanced way to debug XML catalog processing is to use the 2382<strong>xmlcatalog</strong> command shipped with libxml2, it allows to load 2383catalogs and make resolution queries to see what is going on. This is also 2384used for the regression tests:</p> 2385<pre>orchis:~/XML -> /xmlcatalog test/catalogs/docbook.xml \ 2386 "-//OASIS//DTD DocBook XML V4.1.2//EN" 2387http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd 2388orchis:~/XML -> </pre> 2389 2390<p>For debugging what is going on, adding one -v flags increase the verbosity 2391level to indicate the processing done (adding a second flag also indicate 2392what elements are recognized at parsing):</p> 2393<pre>orchis:~/XML -> /xmlcatalog -v test/catalogs/docbook.xml \ 2394 "-//OASIS//DTD DocBook XML V4.1.2//EN" 2395Parsing catalog test/catalogs/docbook.xml's content 2396Found public match -//OASIS//DTD DocBook XML V4.1.2//EN 2397http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd 2398Catalogs cleanup 2399orchis:~/XML -> </pre> 2400 2401<p>A shell interface is also available to debug and process multiple queries 2402(and for regression tests):</p> 2403<pre>orchis:~/XML -> /xmlcatalog -shell test/catalogs/docbook.xml \ 2404 "-//OASIS//DTD DocBook XML V4.1.2//EN" 2405> help 2406Commands available: 2407public PublicID: make a PUBLIC identifier lookup 2408system SystemID: make a SYSTEM identifier lookup 2409resolve PublicID SystemID: do a full resolver lookup 2410add 'type' 'orig' 'replace' : add an entry 2411del 'values' : remove values 2412dump: print the current catalog state 2413debug: increase the verbosity level 2414quiet: decrease the verbosity level 2415exit: quit the shell 2416> public "-//OASIS//DTD DocBook XML V4.1.2//EN" 2417http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd 2418> quit 2419orchis:~/XML -> </pre> 2420 2421<p>This should be sufficient for most debugging purpose, this was actually 2422used heavily to debug the XML Catalog implementation itself.</p> 2423 2424<h3><a name="Declaring">How to create and maintain</a> catalogs:</h3> 2425 2426<p>Basically XML Catalogs are XML files, you can either use XML tools to 2427manage them or use <strong>xmlcatalog</strong> for this. The basic step is 2428to create a catalog the -create option provide this facility:</p> 2429<pre>orchis:~/XML -> /xmlcatalog --create tst.xml 2430<?xml version="1.0"?> 2431<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" 2432 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 2433<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/> 2434orchis:~/XML -> </pre> 2435 2436<p>By default xmlcatalog does not overwrite the original catalog and save the 2437result on the standard output, this can be overridden using the -noout 2438option. The <code>-add</code> command allows to add entries in the 2439catalog:</p> 2440<pre>orchis:~/XML -> /xmlcatalog --noout --create --add "public" \ 2441 "-//OASIS//DTD DocBook XML V4.1.2//EN" \ 2442 http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd tst.xml 2443orchis:~/XML -> cat tst.xml 2444<?xml version="1.0"?> 2445<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" \ 2446 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 2447<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"> 2448<public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN" 2449 uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/> 2450</catalog> 2451orchis:~/XML -> </pre> 2452 2453<p>The <code>-add</code> option will always take 3 parameters even if some of 2454the XML Catalog constructs (like nextCatalog) will have only a single 2455argument, just pass a third empty string, it will be ignored.</p> 2456 2457<p>Similarly the <code>-del</code> option remove matching entries from the 2458catalog:</p> 2459<pre>orchis:~/XML -> /xmlcatalog --del \ 2460 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" tst.xml 2461<?xml version="1.0"?> 2462<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" 2463 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 2464<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/> 2465orchis:~/XML -> </pre> 2466 2467<p>The catalog is now empty. Note that the matching of <code>-del</code> is 2468exact and would have worked in a similar fashion with the Public ID 2469string.</p> 2470 2471<p>This is rudimentary but should be sufficient to manage a not too complex 2472catalog tree of resources.</p> 2473 2474<h3><a name="implemento">The implementor corner quick review of the 2475API:</a></h3> 2476 2477<p>First, and like for every other module of libxml, there is an 2478automatically generated <a href="html/libxml-catalog.html">API page for 2479catalog support</a>.</p> 2480 2481<p>The header for the catalog interfaces should be included as:</p> 2482<pre>#include <libxml/catalog.h></pre> 2483 2484<p>The API is voluntarily kept very simple. First it is not obvious that 2485applications really need access to it since it is the default behaviour of 2486libxml (Note: it is possible to completely override libxml default catalog by 2487using <a href="html/libxml-parser.html">xmlSetExternalEntityLoader</a> to 2488plug an application specific resolver).</p> 2489 2490<p>Basically libxml support 2 catalog lists:</p> 2491<ul> 2492 <li>the default one, global shared by all the application</li> 2493 <li>a per-document catalog, this one is built if the document uses the 2494 <code>oasis-xml-catalog</code> PIs to specify its own catalog list, it is 2495 associated to the parser context and destroyed when the parsing context 2496 is destroyed.</li> 2497</ul> 2498 2499<p>the document one will be used first if it exists.</p> 2500 2501<h4>Initialization routines:</h4> 2502 2503<p>xmlInitializeCatalog(), xmlLoadCatalog() and xmlLoadCatalogs() should be 2504used at startup to initialize the catalog, if the catalog should be 2505initialized with specific values xmlLoadCatalog() or xmlLoadCatalogs() 2506should be called before xmlInitializeCatalog() which would otherwise do a 2507default initialization first.</p> 2508 2509<p>The xmlCatalogAddLocal() call is used by the parser to grow the document 2510own catalog list if needed.</p> 2511 2512<h4>Preferences setup:</h4> 2513 2514<p>The XML Catalog spec requires the possibility to select default 2515preferences between public and system delegation, 2516xmlCatalogSetDefaultPrefer() allows this, xmlCatalogSetDefaults() and 2517xmlCatalogGetDefaults() allow to control if XML Catalogs resolution should 2518be forbidden, allowed for global catalog, for document catalog or both, the 2519default is to allow both.</p> 2520 2521<p>And of course xmlCatalogSetDebug() allows to generate debug messages 2522(through the xmlGenericError() mechanism).</p> 2523 2524<h4>Querying routines:</h4> 2525 2526<p>xmlCatalogResolve(), xmlCatalogResolveSystem(), xmlCatalogResolvePublic() 2527and xmlCatalogResolveURI() are relatively explicit if you read the XML 2528Catalog specification they correspond to section 7 algorithms, they should 2529also work if you have loaded an SGML catalog with a simplified semantic.</p> 2530 2531<p>xmlCatalogLocalResolve() and xmlCatalogLocalResolveURI() are the same but 2532operate on the document catalog list</p> 2533 2534<h4>Cleanup and Miscellaneous:</h4> 2535 2536<p>xmlCatalogCleanup() free-up the global catalog, xmlCatalogFreeLocal() is 2537the per-document equivalent.</p> 2538 2539<p>xmlCatalogAdd() and xmlCatalogRemove() are used to dynamically modify the 2540first catalog in the global list, and xmlCatalogDump() allows to dump a 2541catalog state, those routines are primarily designed for xmlcatalog, I'm not 2542sure that exposing more complex interfaces (like navigation ones) would be 2543really useful.</p> 2544 2545<p>The xmlParseCatalogFile() is a function used to load XML Catalog files, 2546it's similar as xmlParseFile() except it bypass all catalog lookups, it's 2547provided because this functionality may be useful for client tools.</p> 2548 2549<h4>threaded environments:</h4> 2550 2551<p>Since the catalog tree is built progressively, some care has been taken to 2552try to avoid troubles in multithreaded environments. The code is now thread 2553safe assuming that the libxml library has been compiled with threads 2554support.</p> 2555 2556<p></p> 2557 2558<h3><a name="Other">Other resources</a></h3> 2559 2560<p>The XML Catalog specification is relatively recent so there isn't much 2561literature to point at:</p> 2562<ul> 2563 <li>You can find an good rant from Norm Walsh about <a 2564 href="http://www.arbortext.com/Think_Tank/XML_Resources/Issue_Three/issue_three.html">the 2565 need for catalogs</a>, it provides a lot of context informations even if 2566 I don't agree with everything presented.</li> 2567 <li>An <a href="http://home.ccil.org/~cowan/XML/XCatalog.html">old XML 2568 catalog proposal</a> from John Cowan</li> 2569 <li>The <a href="http://www.rddl.org/">Resource Directory Description 2570 Language</a> (RDDL) another catalog system but more oriented toward 2571 providing metadata for XML namespaces.</li> 2572 <li>the page from the OASIS Technical <a 2573 href="http://www.oasis-open.org/committees/entity/">Committee on Entity 2574 Resolution</a> who maintains XML Catalog, you will find pointers to the 2575 specification update, some background and pointers to others tools 2576 providing XML Catalog support</li> 2577 <li>I have uploaded <a href="ftp://xmlsoft.org/test/dbk412catalog.tar.gz">a 2578 mall tarball</a> containing XML Catalogs for DocBook 4.1.2 which seems to 2579 work fine for me</li> 2580 <li>The <a href="http://www.xmlsoft.org/xmlcatalog_man.html">xmlcatalog 2581 manual page</a></li> 2582</ul> 2583 2584<p>If you have suggestions for corrections or additions, simply contact 2585me:</p> 2586 2587<h2><a name="library">The parser interfaces</a></h2> 2588 2589<p>This section is directly intended to help programmers getting bootstrapped 2590using the XML library from the C language. It is not intended to be 2591extensive. I hope the automatically generated documents will provide the 2592completeness required, but as a separate set of documents. The interfaces of 2593the XML library are by principle low level, there is nearly zero abstraction. 2594Those interested in a higher level API should <a href="#DOM">look at 2595DOM</a>.</p> 2596 2597<p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are 2598separated from the <a href="html/libxml-htmlparser.html">HTML parser 2599interfaces</a>. Let's have a look at how the XML parser can be called:</p> 2600 2601<h3><a name="Invoking">Invoking the parser : the pull method</a></h3> 2602 2603<p>Usually, the first thing to do is to read an XML input. The parser accepts 2604documents either from in-memory strings or from files. The functions are 2605defined in "parser.h":</p> 2606<dl> 2607 <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt> 2608 <dd><p>Parse a null-terminated string containing the document.</p> 2609 </dd> 2610</dl> 2611<dl> 2612 <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt> 2613 <dd><p>Parse an XML document contained in a (possibly compressed) 2614 file.</p> 2615 </dd> 2616</dl> 2617 2618<p>The parser returns a pointer to the document structure (or NULL in case of 2619failure).</p> 2620 2621<h3 id="Invoking1">Invoking the parser: the push method</h3> 2622 2623<p>In order for the application to keep the control when the document is 2624being fetched (which is common for GUI based programs) libxml provides a push 2625interface, too, as of version 1.8.3. Here are the interface functions:</p> 2626<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax, 2627 void *user_data, 2628 const char *chunk, 2629 int size, 2630 const char *filename); 2631int xmlParseChunk (xmlParserCtxtPtr ctxt, 2632 const char *chunk, 2633 int size, 2634 int terminate);</pre> 2635 2636<p>and here is a simple example showing how to use the interface:</p> 2637<pre> FILE *f; 2638 2639 f = fopen(filename, "r"); 2640 if (f != NULL) { 2641 int res, size = 1024; 2642 char chars[1024]; 2643 xmlParserCtxtPtr ctxt; 2644 2645 res = fread(chars, 1, 4, f); 2646 if (res > 0) { 2647 ctxt = xmlCreatePushParserCtxt(NULL, NULL, 2648 chars, res, filename); 2649 while ((res = fread(chars, 1, size, f)) > 0) { 2650 xmlParseChunk(ctxt, chars, res, 0); 2651 } 2652 xmlParseChunk(ctxt, chars, 0, 1); 2653 doc = ctxt->myDoc; 2654 xmlFreeParserCtxt(ctxt); 2655 } 2656 }</pre> 2657 2658<p>The HTML parser embedded into libxml also has a push interface; the 2659functions are just prefixed by "html" rather than "xml".</p> 2660 2661<h3 id="Invoking2">Invoking the parser: the SAX interface</h3> 2662 2663<p>The tree-building interface makes the parser memory-hungry, first loading 2664the document in memory and then building the tree itself. Reading a document 2665without building the tree is possible using the SAX interfaces (see SAX.h and 2666<a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James 2667Henstridge's documentation</a>). Note also that the push interface can be 2668limited to SAX: just use the two first arguments of 2669<code>xmlCreatePushParserCtxt()</code>.</p> 2670 2671<h3><a name="Building">Building a tree from scratch</a></h3> 2672 2673<p>The other way to get an XML tree in memory is by building it. Basically 2674there is a set of functions dedicated to building new elements. (These are 2675also described in <libxml/tree.h>.) For example, here is a piece of 2676code that produces the XML document used in the previous examples:</p> 2677<pre> #include <libxml/tree.h> 2678 xmlDocPtr doc; 2679 xmlNodePtr tree, subtree; 2680 2681 doc = xmlNewDoc("1.0"); 2682 doc->children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL); 2683 xmlSetProp(doc->children, "prop1", "gnome is great"); 2684 xmlSetProp(doc->children, "prop2", "& linux too"); 2685 tree = xmlNewChild(doc->children, NULL, "head", NULL); 2686 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome"); 2687 tree = xmlNewChild(doc->children, NULL, "chapter", NULL); 2688 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure"); 2689 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ..."); 2690 subtree = xmlNewChild(tree, NULL, "image", NULL); 2691 xmlSetProp(subtree, "href", "linus.gif");</pre> 2692 2693<p>Not really rocket science ...</p> 2694 2695<h3><a name="Traversing">Traversing the tree</a></h3> 2696 2697<p>Basically by <a href="html/libxml-tree.html">including "tree.h"</a> your 2698code has access to the internal structure of all the elements of the tree. 2699The names should be somewhat simple like <strong>parent</strong>, 2700<strong>children</strong>, <strong>next</strong>, <strong>prev</strong>, 2701<strong>properties</strong>, etc... For example, still with the previous 2702example:</p> 2703<pre><code>doc->children->children->children</code></pre> 2704 2705<p>points to the title element,</p> 2706<pre>doc->children->children->next->children->children</pre> 2707 2708<p>points to the text node containing the chapter title "The Linux 2709adventure".</p> 2710 2711<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be 2712present before the document root, so <code>doc->children</code> may point 2713to an element which is not the document Root Element; a function 2714<code>xmlDocGetRootElement()</code> was added for this purpose.</p> 2715 2716<h3><a name="Modifying">Modifying the tree</a></h3> 2717 2718<p>Functions are provided for reading and writing the document content. Here 2719is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p> 2720<dl> 2721 <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const 2722 xmlChar *value);</code></dt> 2723 <dd><p>This sets (or changes) an attribute carried by an ELEMENT node. 2724 The value can be NULL.</p> 2725 </dd> 2726</dl> 2727<dl> 2728 <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar 2729 *name);</code></dt> 2730 <dd><p>This function returns a pointer to new copy of the property 2731 content. Note that the user must deallocate the result.</p> 2732 </dd> 2733</dl> 2734 2735<p>Two functions are provided for reading and writing the text associated 2736with elements:</p> 2737<dl> 2738 <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar 2739 *value);</code></dt> 2740 <dd><p>This function takes an "external" string and converts it to one 2741 text node or possibly to a list of entity and text nodes. All 2742 non-predefined entity references like &Gnome; will be stored 2743 internally as entity nodes, hence the result of the function may not be 2744 a single node.</p> 2745 </dd> 2746</dl> 2747<dl> 2748 <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int 2749 inLine);</code></dt> 2750 <dd><p>This function is the inverse of 2751 <code>xmlStringGetNodeList()</code>. It generates a new string 2752 containing the content of the text and entity nodes. Note the extra 2753 argument inLine. If this argument is set to 1, the function will expand 2754 entity references. For example, instead of returning the &Gnome; 2755 XML encoding in the string, it will substitute it with its value (say, 2756 "GNU Network Object Model Environment").</p> 2757 </dd> 2758</dl> 2759 2760<h3><a name="Saving">Saving a tree</a></h3> 2761 2762<p>Basically 3 options are possible:</p> 2763<dl> 2764 <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int 2765 *size);</code></dt> 2766 <dd><p>Returns a buffer into which the document has been saved.</p> 2767 </dd> 2768</dl> 2769<dl> 2770 <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt> 2771 <dd><p>Dumps a document to an open file descriptor.</p> 2772 </dd> 2773</dl> 2774<dl> 2775 <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt> 2776 <dd><p>Saves the document to a file. In this case, the compression 2777 interface is triggered if it has been turned on.</p> 2778 </dd> 2779</dl> 2780 2781<h3><a name="Compressio">Compression</a></h3> 2782 2783<p>The library transparently handles compression when doing file-based 2784accesses. The level of compression on saves can be turned on either globally 2785or individually for one file:</p> 2786<dl> 2787 <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt> 2788 <dd><p>Gets the document compression ratio (0-9).</p> 2789 </dd> 2790</dl> 2791<dl> 2792 <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt> 2793 <dd><p>Sets the document compression ratio.</p> 2794 </dd> 2795</dl> 2796<dl> 2797 <dt><code>int xmlGetCompressMode(void);</code></dt> 2798 <dd><p>Gets the default compression ratio.</p> 2799 </dd> 2800</dl> 2801<dl> 2802 <dt><code>void xmlSetCompressMode(int mode);</code></dt> 2803 <dd><p>Sets the default compression ratio.</p> 2804 </dd> 2805</dl> 2806 2807<h2><a name="Entities">Entities or no entities</a></h2> 2808 2809<p>Entities in principle are similar to simple C macros. An entity defines an 2810abbreviation for a given string that you can reuse many times throughout the 2811content of your document. Entities are especially useful when a given string 2812may occur frequently within a document, or to confine the change needed to a 2813document to a restricted area in the internal subset of the document (at the 2814beginning). Example:</p> 2815<pre>1 <?xml version="1.0"?> 28162 <!DOCTYPE EXAMPLE SYSTEM "example.dtd" [ 28173 <!ENTITY xml "Extensible Markup Language"> 28184 ]> 28195 <EXAMPLE> 28206 &xml; 28217 </EXAMPLE></pre> 2822 2823<p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing 2824its name with '&' and following it by ';' without any spaces added. There 2825are 5 predefined entities in libxml allowing you to escape charaters with 2826predefined meaning in some parts of the xml document content: 2827<strong>&lt;</strong> for the character '<', <strong>&gt;</strong> 2828for the character '>', <strong>&apos;</strong> for the character ''', 2829<strong>&quot;</strong> for the character '"', and 2830<strong>&amp;</strong> for the character '&'.</p> 2831 2832<p>One of the problems related to entities is that you may want the parser to 2833substitute an entity's content so that you can see the replacement text in 2834your application. Or you may prefer to keep entity references as such in the 2835content to be able to save the document back without losing this usually 2836precious information (if the user went through the pain of explicitly 2837defining entities, he may have a a rather negative attitude if you blindly 2838susbtitute them as saving time). The <a 2839href="html/libxml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a> 2840function allows you to check and change the behaviour, which is to not 2841substitute entities by default.</p> 2842 2843<p>Here is the DOM tree built by libxml for the previous document in the 2844default case:</p> 2845<pre>/gnome/src/gnome-xml -> /xmllint --debug test/ent1 2846DOCUMENT 2847version=1.0 2848 ELEMENT EXAMPLE 2849 TEXT 2850 content= 2851 ENTITY_REF 2852 INTERNAL_GENERAL_ENTITY xml 2853 content=Extensible Markup Language 2854 TEXT 2855 content=</pre> 2856 2857<p>And here is the result when substituting entities:</p> 2858<pre>/gnome/src/gnome-xml -> /tester --debug --noent test/ent1 2859DOCUMENT 2860version=1.0 2861 ELEMENT EXAMPLE 2862 TEXT 2863 content= Extensible Markup Language</pre> 2864 2865<p>So, entities or no entities? Basically, it depends on your use case. I 2866suggest that you keep the non-substituting default behaviour and avoid using 2867entities in your XML document or data if you are not willing to handle the 2868entity references elements in the DOM tree.</p> 2869 2870<p>Note that at save time libxml enforces the conversion of the predefined 2871entities where necessary to prevent well-formedness problems, and will also 2872transparently replace those with chars (i.e. it will not generate entity 2873reference elements in the DOM tree or call the reference() SAX callback when 2874finding them in the input).</p> 2875 2876<p><span style="background-color: #FF0000">WARNING</span>: handling entities 2877on top of the libxml SAX interface is difficult!!! If you plan to use 2878non-predefined entities in your documents, then the learning cuvre to handle 2879then using the SAX API may be long. If you plan to use complex documents, I 2880strongly suggest you consider using the DOM interface instead and let libxml 2881deal with the complexity rather than trying to do it yourself.</p> 2882 2883<h2><a name="Namespaces">Namespaces</a></h2> 2884 2885<p>The libxml library implements <a 2886href="http://www.w3.org/TR/REC-xml-names/">XML namespaces</a> support by 2887recognizing namespace contructs in the input, and does namespace lookup 2888automatically when building the DOM tree. A namespace declaration is 2889associated with an in-memory structure and all elements or attributes within 2890that namespace point to it. Hence testing the namespace is a simple and fast 2891equality operation at the user level.</p> 2892 2893<p>I suggest that people using libxml use a namespace, and declare it in the 2894root element of their document as the default namespace. Then they don't need 2895to use the prefix in the content but we will have a basis for future semantic 2896refinement and merging of data from different sources. This doesn't increase 2897the size of the XML output significantly, but significantly increases its 2898value in the long-term. Example:</p> 2899<pre><mydoc xmlns="http://mydoc.example.org/schemas/"> 2900 <elem1>...</elem1> 2901 <elem2>...</elem2> 2902</mydoc></pre> 2903 2904<p>The namespace value has to be an absolute URL, but the URL doesn't have to 2905point to any existing resource on the Web. It will bind all the element and 2906atributes with that URL. I suggest to use an URL within a domain you control, 2907and that the URL should contain some kind of version information if possible. 2908For example, <code>"http://www.gnome.org/gnumeric/1.0/"</code> is a good 2909namespace scheme.</p> 2910 2911<p>Then when you load a file, make sure that a namespace carrying the 2912version-independent prefix is installed on the root element of your document, 2913and if the version information don't match something you know, warn the user 2914and be liberal in what you accept as the input. Also do *not* try to base 2915namespace checking on the prefix value. <foo:text> may be exactly the 2916same as <bar:text> in another document. What really matters is the URI 2917associated with the element or the attribute, not the prefix string (which is 2918just a shortcut for the full URI). In libxml, element and attributes have an 2919<code>ns</code> field pointing to an xmlNs structure detailing the namespace 2920prefix and its URI.</p> 2921 2922<p>@@Interfaces@@</p> 2923 2924<p>@@Examples@@</p> 2925 2926<p>Usually people object to using namespaces together with validity checking. 2927I will try to make sure that using namespaces won't break validity checking, 2928so even if you plan to use or currently are using validation I strongly 2929suggest adding namespaces to your document. A default namespace scheme 2930<code>xmlns="http://...."</code> should not break validity even on less 2931flexible parsers. Using namespaces to mix and differentiate content coming 2932from multiple DTDs will certainly break current validation schemes. I will 2933try to provide ways to do this, but this may not be portable or 2934standardized.</p> 2935 2936<h2><a name="Upgrading">Upgrading 1.x code</a></h2> 2937 2938<p>Incompatible changes:</p> 2939 2940<p>Version 2 of libxml is the first version introducing serious backward 2941incompatible changes. The main goals were:</p> 2942<ul> 2943 <li>a general cleanup. A number of mistakes inherited from the very early 2944 versions couldn't be changed due to compatibility constraints. Example 2945 the "childs" element in the nodes.</li> 2946 <li>Uniformization of the various nodes, at least for their header and link 2947 parts (doc, parent, children, prev, next), the goal is a simpler 2948 programming model and simplifying the task of the DOM implementors.</li> 2949 <li>better conformances to the XML specification, for example version 1.x 2950 had an heuristic to try to detect ignorable white spaces. As a result the 2951 SAX event generated were ignorableWhitespace() while the spec requires 2952 character() in that case. This also mean that a number of DOM node 2953 containing blank text may populate the DOM tree which were not present 2954 before.</li> 2955</ul> 2956 2957<h3>How to fix libxml-1.x code:</h3> 2958 2959<p>So client code of libxml designed to run with version 1.x may have to be 2960changed to compile against version 2.x of libxml. Here is a list of changes 2961that I have collected, they may not be sufficient, so in case you find other 2962change which are required, <a href="mailto:Daniel.�eillardw3.org">drop me a 2963mail</a>:</p> 2964<ol> 2965 <li>The package name have changed from libxml to libxml2, the library name 2966 is now -lxml2 . There is a new xml2-config script which should be used to 2967 select the right parameters libxml2</li> 2968 <li>Node <strong>childs</strong> field has been renamed 2969 <strong>children</strong> so s/childs/children/g should be applied 2970 (probablility of having "childs" anywere else is close to 0+</li> 2971 <li>The document don't have anymore a <strong>root</strong> element it has 2972 been replaced by <strong>children</strong> and usually you will get a 2973 list of element here. For example a Dtd element for the internal subset 2974 and it's declaration may be found in that list, as well as processing 2975 instructions or comments found before or after the document root element. 2976 Use <strong>xmlDocGetRootElement(doc)</strong> to get the root element of 2977 a document. Alternatively if you are sure to not reference Dtds nor have 2978 PIs or comments before or after the root element 2979 s/->root/->children/g will probably do it.</li> 2980 <li>The white space issue, this one is more complex, unless special case of 2981 validating parsing, the line breaks and spaces usually used for indenting 2982 and formatting the document content becomes significant. So they are 2983 reported by SAX and if your using the DOM tree, corresponding nodes are 2984 generated. Too approach can be taken: 2985 <ol> 2986 <li>lazy one, use the compatibility call 2987 <strong>xmlKeepBlanksDefault(0)</strong> but be aware that you are 2988 relying on a special (and possibly broken) set of heuristics of 2989 libxml to detect ignorable blanks. Don't complain if it breaks or 2990 make your application not 100% clean w.r.t. to it's input.</li> 2991 <li>the Right Way: change you code to accept possibly unsignificant 2992 blanks characters, or have your tree populated with weird blank text 2993 nodes. You can spot them using the comodity function 2994 <strong>xmlIsBlankNode(node)</strong> returning 1 for such blank 2995 nodes.</li> 2996 </ol> 2997 <p>Note also that with the new default the output functions don't add any 2998 extra indentation when saving a tree in order to be able to round trip 2999 (read and save) without inflating the document with extra formatting 3000 chars.</p> 3001 </li> 3002 <li>The include path has changed to $prefix/libxml/ and the includes 3003 themselves uses this new prefix in includes instructions... If you are 3004 using (as expected) the 3005 <pre>xml2-config --cflags</pre> 3006 <p>output to generate you compile commands this will probably work out of 3007 the box</p> 3008 </li> 3009 <li>xmlDetectCharEncoding takes an extra argument indicating the lenght in 3010 byte of the head of the document available for character detection.</li> 3011</ol> 3012 3013<h3>Ensuring both libxml-1.x and libxml-2.x compatibility</h3> 3014 3015<p>Two new version of libxml (1.8.11) and libxml2 (2.3.4) have been released 3016to allow smoth upgrade of existing libxml v1code while retaining 3017compatibility. They offers the following:</p> 3018<ol> 3019 <li>similar include naming, one should use 3020 <strong>#include<libxml/...></strong> in both cases.</li> 3021 <li>similar identifiers defined via macros for the child and root fields: 3022 respectively <strong>xmlChildrenNode</strong> and 3023 <strong>xmlRootNode</strong></li> 3024 <li>a new macro <strong>LIBXML_TEST_VERSION</strong> which should be 3025 inserted once in the client code</li> 3026</ol> 3027 3028<p>So the roadmap to upgrade your existing libxml applications is the 3029following:</p> 3030<ol> 3031 <li>install the libxml-1.8.8 (and libxml-devel-1.8.8) packages</li> 3032 <li>find all occurences where the xmlDoc <strong>root</strong> field is 3033 used and change it to <strong>xmlRootNode</strong></li> 3034 <li>similary find all occurences where the xmlNode <strong>childs</strong> 3035 field is used and change it to <strong>xmlChildrenNode</strong></li> 3036 <li>add a <strong>LIBXML_TEST_VERSION</strong> macro somewhere in your 3037 <strong>main()</strong> or in the library init entry point</li> 3038 <li>Recompile, check compatibility, it should still work</li> 3039 <li>Change your configure script to look first for xml2-config and fallback 3040 using xml-config . Use the --cflags and --libs ouptut of the command as 3041 the Include and Linking parameters needed to use libxml.</li> 3042 <li>install libxml2-2.3.x and libxml2-devel-2.3.x (libxml-1.8.y and 3043 libxml-devel-1.8.y can be kept simultaneously)</li> 3044 <li>remove your config.cache, relaunch your configuration mechanism, and 3045 recompile, if steps 2 and 3 were done right it should compile as-is</li> 3046 <li>Test that your application is still running correctly, if not this may 3047 be due to extra empty nodes due to formating spaces being kept in libxml2 3048 contrary to libxml1, in that case insert xmlKeepBlanksDefault(1) in your 3049 code before calling the parser (next to 3050 <strong>LIBXML_TEST_VERSION</strong> is a fine place).</li> 3051</ol> 3052 3053<p>Following those steps should work. It worked for some of my own code.</p> 3054 3055<p>Let me put some emphasis on the fact that there is far more changes from 3056libxml 1.x to 2.x than the ones you may have to patch for. The overall code 3057has been considerably cleaned up and the conformance to the XML specification 3058has been drastically improved too. Don't take those changes as an excuse to 3059not upgrade, it may cost a lot on the long term ...</p> 3060 3061<h2><a name="Thread">Thread safety</a></h2> 3062 3063<p>Starting with 2.4.7, libxml makes provisions to ensure that concurent 3064threads can safely work in parallel parsing different documents. There is 3065however a couple of things to do to ensure it:</p> 3066<ul> 3067 <li>configure the library accordingly using the --with-threads options</li> 3068 <li>call xmlInitParser() in the "main" thread before using any of the 3069 libxml API (except possibly selecting a different memory allocator)</li> 3070</ul> 3071 3072<p>Note that the thread safety cannot be ensured for multiple threads sharing 3073the same document, the locking must be done at the application level, libxml 3074exports a basic mutex and reentrant mutexes API in <libxml/threads.h>. 3075The parts of the library checked for thread safety are:</p> 3076<ul> 3077 <li>concurrent loading</li> 3078 <li>file access resolution</li> 3079 <li>catalog access</li> 3080 <li>catalog building</li> 3081 <li>entities lookup/accesses</li> 3082 <li>validation</li> 3083 <li>global variables per-thread override</li> 3084 <li>memory handling</li> 3085</ul> 3086 3087<p>XPath is supposed to be thread safe now, but this wasn't tested 3088seriously.</p> 3089 3090<h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2> 3091 3092<p><a href="http://www.w3.org/DOM/">DOM</a> stands for the <em>Document 3093Object Model</em>; this is an API for accessing XML or HTML structured 3094documents. Native support for DOM in Gnome is on the way (module gnome-dom), 3095and will be based on gnome-xml. This will be a far cleaner interface to 3096manipulate XML files within Gnome since it won't expose the internal 3097structure.</p> 3098 3099<p>The current DOM implementation on top of libxml is the <a 3100href="http://cvs.gnome.org/lxr/source/gdome2/">gdome2 Gnome module</a>, this 3101is a full DOM interface, thanks to Paolo Casarini, check the <a 3102href="http://www.cs.unibo.it/~casarini/gdome2/">Gdome2 homepage</a> for more 3103informations.</p> 3104 3105<h2><a name="Example"></a><a name="real">A real example</a></h2> 3106 3107<p>Here is a real size example, where the actual content of the application 3108data is not kept in the DOM tree but uses internal structures. It is based on 3109a proposal to keep a database of jobs related to Gnome, with an XML based 3110storage structure. Here is an <a href="gjobs.xml">XML encoded jobs 3111base</a>:</p> 3112<pre><?xml version="1.0"?> 3113<gjob:Helping xmlns:gjob="http://www.gnome.org/some-location"> 3114 <gjob:Jobs> 3115 3116 <gjob:Job> 3117 <gjob:Project ID="3"/> 3118 <gjob:Application>GBackup</gjob:Application> 3119 <gjob:Category>Development</gjob:Category> 3120 3121 <gjob:Update> 3122 <gjob:Status>Open</gjob:Status> 3123 <gjob:Modified>Mon, 07 Jun 1999 20:27:45 -0400 MET DST</gjob:Modified> 3124 <gjob:Salary>USD 0.00</gjob:Salary> 3125 </gjob:Update> 3126 3127 <gjob:Developers> 3128 <gjob:Developer> 3129 </gjob:Developer> 3130 </gjob:Developers> 3131 3132 <gjob:Contact> 3133 <gjob:Person>Nathan Clemons</gjob:Person> 3134 <gjob:Email>nathan@windsofstorm.net</gjob:Email> 3135 <gjob:Company> 3136 </gjob:Company> 3137 <gjob:Organisation> 3138 </gjob:Organisation> 3139 <gjob:Webpage> 3140 </gjob:Webpage> 3141 <gjob:Snailmail> 3142 </gjob:Snailmail> 3143 <gjob:Phone> 3144 </gjob:Phone> 3145 </gjob:Contact> 3146 3147 <gjob:Requirements> 3148 The program should be released as free software, under the GPL. 3149 </gjob:Requirements> 3150 3151 <gjob:Skills> 3152 </gjob:Skills> 3153 3154 <gjob:Details> 3155 A GNOME based system that will allow a superuser to configure 3156 compressed and uncompressed files and/or file systems to be backed 3157 up with a supported media in the system. This should be able to 3158 perform via find commands generating a list of files that are passed 3159 to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine 3160 or via operations performed on the filesystem itself. Email 3161 notification and GUI status display very important. 3162 </gjob:Details> 3163 3164 </gjob:Job> 3165 3166 </gjob:Jobs> 3167</gjob:Helping></pre> 3168 3169<p>While loading the XML file into an internal DOM tree is a matter of 3170calling only a couple of functions, browsing the tree to gather the ata and 3171generate the internal structures is harder, and more error prone.</p> 3172 3173<p>The suggested principle is to be tolerant with respect to the input 3174structure. For example, the ordering of the attributes is not significant, 3175the XML specification is clear about it. It's also usually a good idea not to 3176depend on the order of the children of a given node, unless it really makes 3177things harder. Here is some code to parse the information for a person:</p> 3178<pre>/* 3179 * A person record 3180 */ 3181typedef struct person { 3182 char *name; 3183 char *email; 3184 char *company; 3185 char *organisation; 3186 char *smail; 3187 char *webPage; 3188 char *phone; 3189} person, *personPtr; 3190 3191/* 3192 * And the code needed to parse it 3193 */ 3194personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) { 3195 personPtr ret = NULL; 3196 3197DEBUG("parsePerson\n"); 3198 /* 3199 * allocate the struct 3200 */ 3201 ret = (personPtr) malloc(sizeof(person)); 3202 if (ret == NULL) { 3203 fprintf(stderr,"out of memory\n"); 3204 return(NULL); 3205 } 3206 memset(ret, 0, sizeof(person)); 3207 3208 /* We don't care what the top level element name is */ 3209 cur = cur->xmlChildrenNode; 3210 while (cur != NULL) { 3211 if ((!strcmp(cur->name, "Person")) && (cur->ns == ns)) 3212 ret->name = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3213 if ((!strcmp(cur->name, "Email")) && (cur->ns == ns)) 3214 ret->email = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3215 cur = cur->next; 3216 } 3217 3218 return(ret); 3219}</pre> 3220 3221<p>Here are a couple of things to notice:</p> 3222<ul> 3223 <li>Usually a recursive parsing style is the more convenient one: XML data 3224 is by nature subject to repetitive constructs and usually exibits highly 3225 stuctured patterns.</li> 3226 <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, 3227 i.e. the pointer to the global XML document and the namespace reserved to 3228 the application. Document wide information are needed for example to 3229 decode entities and it's a good coding practice to define a namespace for 3230 your application set of data and test that the element and attributes 3231 you're analyzing actually pertains to your application space. This is 3232 done by a simple equality test (cur->ns == ns).</li> 3233 <li>To retrieve text and attributes value, you can use the function 3234 <em>xmlNodeListGetString</em> to gather all the text and entity reference 3235 nodes generated by the DOM output and produce an single text string.</li> 3236</ul> 3237 3238<p>Here is another piece of code used to parse another level of the 3239structure:</p> 3240<pre>#include <libxml/tree.h> 3241/* 3242 * a Description for a Job 3243 */ 3244typedef struct job { 3245 char *projectID; 3246 char *application; 3247 char *category; 3248 personPtr contact; 3249 int nbDevelopers; 3250 personPtr developers[100]; /* using dynamic alloc is left as an exercise */ 3251} job, *jobPtr; 3252 3253/* 3254 * And the code needed to parse it 3255 */ 3256jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) { 3257 jobPtr ret = NULL; 3258 3259DEBUG("parseJob\n"); 3260 /* 3261 * allocate the struct 3262 */ 3263 ret = (jobPtr) malloc(sizeof(job)); 3264 if (ret == NULL) { 3265 fprintf(stderr,"out of memory\n"); 3266 return(NULL); 3267 } 3268 memset(ret, 0, sizeof(job)); 3269 3270 /* We don't care what the top level element name is */ 3271 cur = cur->xmlChildrenNode; 3272 while (cur != NULL) { 3273 3274 if ((!strcmp(cur->name, "Project")) && (cur->ns == ns)) { 3275 ret->projectID = xmlGetProp(cur, "ID"); 3276 if (ret->projectID == NULL) { 3277 fprintf(stderr, "Project has no ID\n"); 3278 } 3279 } 3280 if ((!strcmp(cur->name, "Application")) && (cur->ns == ns)) 3281 ret->application = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3282 if ((!strcmp(cur->name, "Category")) && (cur->ns == ns)) 3283 ret->category = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3284 if ((!strcmp(cur->name, "Contact")) && (cur->ns == ns)) 3285 ret->contact = parsePerson(doc, ns, cur); 3286 cur = cur->next; 3287 } 3288 3289 return(ret); 3290}</pre> 3291 3292<p>Once you are used to it, writing this kind of code is quite simple, but 3293boring. Ultimately, it could be possble to write stubbers taking either C 3294data structure definitions, a set of XML examples or an XML DTD and produce 3295the code needed to import and export the content between C data and XML 3296storage. This is left as an exercise to the reader :-)</p> 3297 3298<p>Feel free to use <a href="example/gjobread.c">the code for the full C 3299parsing example</a> as a template, it is also available with Makefile in the 3300Gnome CVS base under gnome-xml/example</p> 3301 3302<h2><a name="Contributi">Contributions</a></h2> 3303<ul> 3304 <li>Bjorn Reese, William Brack and Thomas Broyer have provided a number of 3305 patches, Gary Pennington worked on the validation API, threading support 3306 and Solaris port.</li> 3307 <li>John Fleck helps maintaining the documentation and man pages.</li> 3308 <li><a href="mailto:ari@lusis.org">Ari Johnson</a> 3309 provides a C++ wrapper for libxml:<br> 3310 Website: <a 3311 href="http://lusis.org/~ari/xml++/">http://lusis.org/~ari/xml++/</a><br> 3312 Download: <a 3313 href="http://lusis.org/~ari/xml++/libxml++.tar.gz">http://lusis.org/~ari/xml++/libxml++.tar.gz</a></li> 3314 <li><a href="mailto:izlatkovic@daenet.de">Igor Zlatkovic</a> 3315 is now the maintainer of the Windows port, <a 3316 href="http://www.fh-frankfurt.de/~igor/projects/libxml/index.html">he 3317 provides binaries</a></li> 3318 <li><a href="mailto:Gary.Pennington@sun.com">Gary Pennington</a> 3319 provides <a href="http://garypennington.net/libxml2/">Solaris 3320 binaries</a></li> 3321 <li><a 3322 href="http://mail.gnome.org/archives/xml/2001-March/msg00014.html">Matt 3323 Sergeant</a> 3324 developped <a href="http://axkit.org/download/">XML::LibXSLT</a>, a perl 3325 wrapper for libxml2/libxslt as part of the <a 3326 href="http://axkit.com/">AxKit XML application server</a></li> 3327 <li><a href="mailto:fnatter@gmx.net">Felix Natter</a> 3328 and <a href="mailto:geertk@ai.rug.nl">Geert Kloosterman</a> provide <a 3329 href="libxml-doc.el">an emacs module</a> to lookup libxml(2) functions 3330 documentation</li> 3331 <li><a href="mailto:sherwin@nlm.nih.gov">Ziying Sherwin</a> 3332 provided <a href="http://xmlsoft.org/messages/0488.html">man 3333 pages</a></li> 3334 <li>there is a module for <a 3335 href="http://acs-misc.sourceforge.net/nsxml.html">libxml/libxslt support 3336 in OpenNSD/AOLServer</a></li> 3337 <li><a href="mailto:dkuhlman@cutter.rexx.com">Dave Kuhlman</a> 3338 provides libxml/libxslt <a href="http://www.rexx.com/~dkuhlman">wrappers 3339 for Python</a></li> 3340 <li>Petr Kozelka provides <a 3341 href="http://sourceforge.net/projects/libxml2-pas">Pascal units to glue 3342 libxml2</a> with Kylix and Delphi and other Pascal compilers</li> 3343</ul> 3344 3345<p></p> 3346</body> 3347</html> 3348
