xml.html revision c1eed320bd131561460c68272079936dac11c48f
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 5.1"> 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 developed 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 brackets. HTML is the most well-known 24markup language. Though the library is written in C <a href="python.html">a 25variety of language bindings</a> make it available in other environments.</p> 26 27<p>Libxml2 implements a number of existing standards related to markup 28languages:</p> 29<ul> 30 <li>the XML standard: <a 31 href="http://www.w3.org/TR/REC-xml">http://www.w3.org/TR/REC-xml</a></li> 32 <li>Namespaces in XML: <a 33 href="http://www.w3.org/TR/REC-xml-names/">http://www.w3.org/TR/REC-xml-names/</a></li> 34 <li>XML Base: <a 35 href="http://www.w3.org/TR/xmlbase/">http://www.w3.org/TR/xmlbase/</a></li> 36 <li><a href="http://www.cis.ohio-state.edu/rfc/rfc2396.txt">RFC 2396</a> : 37 Uniform Resource Identifiers <a 38 href="http://www.ietf.org/rfc/rfc2396.txt">http://www.ietf.org/rfc/rfc2396.txt</a></li> 39 <li>XML Path Language (XPath) 1.0: <a 40 href="http://www.w3.org/TR/xpath">http://www.w3.org/TR/xpath</a></li> 41 <li>HTML4 parser: <a 42 href="http://www.w3.org/TR/html401/">http://www.w3.org/TR/html401/</a></li> 43 <li>most of XML Pointer Language (XPointer) Version 1.0: <a 44 href="http://www.w3.org/TR/xptr">http://www.w3.org/TR/xptr</a></li> 45 <li>XML Inclusions (XInclude) Version 1.0: <a 46 href="http://www.w3.org/TR/xinclude/">http://www.w3.org/TR/xinclude/</a></li> 47 <li>[ISO-8859-1], <a 48 href="http://www.cis.ohio-state.edu/rfc/rfc2044.txt">rfc2044</a> [UTF-8] 49 and <a href="http://www.cis.ohio-state.edu/rfc/rfc2781.txt">rfc2781</a> 50 [UTF-16] core encodings</li> 51 <li>part of SGML Open Technical Resolution TR9401:1997</li> 52 <li>XML Catalogs Working Draft 06 August 2001: <a 53 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> 54 <li>Canonical XML Version 1.0: <a 55 href="http://www.w3.org/TR/xml-c14n">http://www.w3.org/TR/xml-c14n</a> 56 and the Exclusive XML Canonicalization CR draft <a 57 href="http://www.w3.org/TR/xml-exc-c14n">http://www.w3.org/TR/xml-exc-c14n</a></li> 58</ul> 59 60<p>In most cases libxml tries to implement the specifications in a relatively 61strictly compliant way. As of release 2.4.16, libxml2 passes all 1800+ tests 62from the <a 63href="http://www.oasis-open.org/committees/xml-conformance/">OASIS XML Tests 64Suite</a>.</p> 65 66<p>To some extent libxml2 provides support for the following additional 67specifications but doesn't claim to implement them completely:</p> 68<ul> 69 <li>Document Object Model (DOM) <a 70 href="http://www.w3.org/TR/DOM-Level-2-Core/">http://www.w3.org/TR/DOM-Level-2-Core/</a> 71 it doesn't implement the API itself, gdome2 does this on top of 72 libxml2</li> 73 <li><a href="http://www.cis.ohio-state.edu/rfc/rfc959.txt">RFC 959</a> : 74 libxml implements a basic FTP client code</li> 75 <li><a href="http://www.cis.ohio-state.edu/rfc/rfc1945.txt">RFC 1945</a> : 76 HTTP/1.0, again a basic HTTP client code</li> 77 <li>SAX: a minimal SAX implementation compatible with early expat 78 versions</li> 79 <li>DocBook SGML v4: libxml2 includes a hackish parser to transition to 80 XML</li> 81</ul> 82 83<p>XML Schemas is being worked on but it would be far too early to make any 84conformance statement about it at the moment.</p> 85 86<p>Libxml2 is known to be very portable, the library should build and work 87without serious troubles on a variety of systems (Linux, Unix, Windows, 88CygWin, MacOS, MacOS X, RISC Os, OS/2, VMS, QNX, MVS, ...)</p> 89 90<p>Separate documents:</p> 91<ul> 92 <li><a href="http://xmlsoft.org/XSLT/">the libxslt page</a> providing an 93 implementation of XSLT 1.0 and common extensions like EXSLT for 94 libxml2</li> 95 <li><a href="http://www.cs.unibo.it/~casarini/gdome2/">the gdome2 page</a> 96 : a standard DOM2 implementation for libxml2</li> 97 <li><a href="http://www.aleksey.com/xmlsec/">the XMLSec page</a>: an 98 implementation of <a href="http://www.w3.org/TR/xmldsig-core/">W3C XML 99 Digital Signature</a> for libxml2</li> 100 <li>also check the related links section below for more related and active 101 projects.</li> 102</ul> 103 104<p>Logo designed by <a href="mailto:liyanage@access.ch">Marc Liyanage</a>.</p> 105 106<h2><a name="Introducti">Introduction</a></h2> 107 108<p>This document describes libxml, the <a 109href="http://www.w3.org/XML/">XML</a> C library developed for the <a 110href="http://www.gnome.org/">Gnome</a> project. <a 111href="http://www.w3.org/XML/">XML is a standard</a> for building tag-based 112structured documents/data.</p> 113 114<p>Here are some key points about libxml:</p> 115<ul> 116 <li>Libxml exports Push (progressive) and Pull (blocking) type parser 117 interfaces for both XML and HTML.</li> 118 <li>Libxml can do DTD validation at parse time, using a parsed document 119 instance, or with an arbitrary DTD.</li> 120 <li>Libxml includes complete <a 121 href="http://www.w3.org/TR/xpath">XPath</a>, <a 122 href="http://www.w3.org/TR/xptr">XPointer</a> and <a 123 href="http://www.w3.org/TR/xinclude">XInclude</a> implementations.</li> 124 <li>It is written in plain C, making as few assumptions as possible, and 125 sticking closely to ANSI C/POSIX for easy embedding. Works on 126 Linux/Unix/Windows, ported to a number of other platforms.</li> 127 <li>Basic support for HTTP and FTP client allowing applications to fetch 128 remote resources.</li> 129 <li>The design is modular, most of the extensions can be compiled out.</li> 130 <li>The internal document representation is as close as possible to the <a 131 href="http://www.w3.org/DOM/">DOM</a> interfaces.</li> 132 <li>Libxml also has a <a href="http://www.megginson.com/SAX/index.html">SAX 133 like interface</a>; the interface is designed to be compatible with <a 134 href="http://www.jclark.com/xml/expat.html">Expat</a>.</li> 135 <li>This library is released under the <a 136 href="http://www.opensource.org/licenses/mit-license.html">MIT 137 License</a>. See the Copyright file in the distribution for the precise 138 wording.</li> 139</ul> 140 141<p>Warning: unless you are forced to because your application links with a 142Gnome-1.X library requiring it, <strong><span 143style="background-color: #FF0000">Do Not Use libxml1</span></strong>, use 144libxml2</p> 145 146<h2><a name="FAQ">FAQ</a></h2> 147 148<p>Table of Contents:</p> 149<ul> 150 <li><a href="FAQ.html#License">License(s)</a></li> 151 <li><a href="FAQ.html#Installati">Installation</a></li> 152 <li><a href="FAQ.html#Compilatio">Compilation</a></li> 153 <li><a href="FAQ.html#Developer">Developer corner</a></li> 154</ul> 155 156<h3><a name="License">License</a>(s)</h3> 157<ol> 158 <li><em>Licensing Terms for libxml</em> 159 <p>libxml is released under the <a 160 href="http://www.opensource.org/licenses/mit-license.html">MIT 161 License</a>; see the file Copyright in the distribution for the precise 162 wording</p> 163 </li> 164 <li><em>Can I embed libxml in a proprietary application ?</em> 165 <p>Yes. The MIT License allows you to keep proprietary the changes you 166 made to libxml, but it would be graceful to send-back bug fixes and 167 improvements as patches for possible incorporation in the main 168 development tree.</p> 169 </li> 170</ol> 171 172<h3><a name="Installati">Installation</a></h3> 173<ol> 174 <li>Unless you are forced to because your application links with a Gnome 175 library requiring it, <strong><span style="background-color: #FF0000">Do 176 Not Use libxml1</span></strong>, use libxml2</li> 177 <li><em>Where can I get libxml</em> ? 178 <p>The original distribution comes from <a 179 href="ftp://rpmfind.net/pub/libxml/">rpmfind.net</a> or <a 180 href="ftp://ftp.gnome.org/pub/GNOME/sources/libxml2/2.4/">gnome.org</a></p> 181 <p>Most Linux and BSD distributions include libxml, this is probably the 182 safer way for end-users to use libxml.</p> 183 <p>David Doolin provides precompiled Windows versions at <a 184 href="http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/ ">http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/</a></p> 185 </li> 186 <li><em>I see libxml and libxml2 releases, which one should I install ?</em> 187 <ul> 188 <li>If you are not constrained by backward compatibility issues with 189 existing applications, install libxml2 only</li> 190 <li>If you are not doing development, you can safely install both. 191 Usually the packages <a 192 href="http://rpmfind.net/linux/RPM/libxml.html">libxml</a> and <a 193 href="http://rpmfind.net/linux/RPM/libxml2.html">libxml2</a> are 194 compatible (this is not the case for development packages).</li> 195 <li>If you are a developer and your system provides separate packaging 196 for shared libraries and the development components, it is possible 197 to install libxml and libxml2, and also <a 198 href="http://rpmfind.net/linux/RPM/libxml-devel.html">libxml-devel</a> 199 and <a 200 href="http://rpmfind.net/linux/RPM/libxml2-devel.html">libxml2-devel</a> 201 too for libxml2 >= 2.3.0</li> 202 <li>If you are developing a new application, please develop against 203 libxml2(-devel)</li> 204 </ul> 205 </li> 206 <li><em>I can't install the libxml package, it conflicts with libxml0</em> 207 <p>You probably have an old libxml0 package used to provide the shared 208 library for libxml.so.0, you can probably safely remove it. The libxml 209 packages provided on <a 210 href="ftp://rpmfind.net/pub/libxml/">rpmfind.net</a> provide 211 libxml.so.0</p> 212 </li> 213 <li><em>I can't install the libxml(2) RPM package due to failed 214 dependencies</em> 215 <p>The most generic solution is to re-fetch the latest src.rpm , and 216 rebuild it locally with</p> 217 <p><code>rpm --rebuild libxml(2)-xxx.src.rpm</code>.</p> 218 <p>If everything goes well it will generate two binary rpm packages (one 219 providing the shared libs and xmllint, and the other one, the -devel 220 package, providing includes, static libraries and scripts needed to build 221 applications with libxml(2)) that you can install locally.</p> 222 </li> 223</ol> 224 225<h3><a name="Compilatio">Compilation</a></h3> 226<ol> 227 <li><em>What is the process to compile libxml ?</em> 228 <p>As most UNIX libraries libxml follows the "standard":</p> 229 <p><code>gunzip -c xxx.tar.gz | tar xvf -</code></p> 230 <p><code>cd libxml-xxxx</code></p> 231 <p><code>/configure --help</code></p> 232 <p>to see the options, then the compilation/installation proper</p> 233 <p><code>/configure [possible options]</code></p> 234 <p><code>make</code></p> 235 <p><code>make install</code></p> 236 <p>At that point you may have to rerun ldconfig or a similar utility to 237 update your list of installed shared libs.</p> 238 </li> 239 <li><em>What other libraries are needed to compile/install libxml ?</em> 240 <p>Libxml does not require any other library, the normal C ANSI API 241 should be sufficient (please report any violation to this rule you may 242 find).</p> 243 <p>However if found at configuration time libxml will detect and use the 244 following libs:</p> 245 <ul> 246 <li><a href="http://www.info-zip.org/pub/infozip/zlib/">libz</a> : a 247 highly portable and available widely compression library.</li> 248 <li>iconv: a powerful character encoding conversion library. It is 249 included by default in recent glibc libraries, so it doesn't need to 250 be installed specifically on Linux. It now seems a <a 251 href="http://www.opennc.org/onlinepubs/7908799/xsh/iconv.html">part 252 of the official UNIX</a> specification. Here is one <a 253 href="http://www.gnu.org/software/libiconv/">implementation of the 254 library</a> which source can be found <a 255 href="ftp://ftp.ilog.fr/pub/Users/haible/gnu/">here</a>.</li> 256 </ul> 257 </li> 258 <li><em>Make check fails on some platforms</em> 259 <p>Sometimes the regression tests' results don't completely match the 260 value produced by the parser, and the makefile uses diff to print the 261 delta. On some platforms the diff return breaks the compilation process; 262 if the diff is small this is probably not a serious problem.</p> 263 <p>Sometimes (especially on Solaris) make checks fail due to limitations 264 in make. Try using GNU-make instead.</p> 265 </li> 266 <li><em>I use the CVS version and there is no configure script</em> 267 <p>The configure script (and other Makefiles) are generated. Use the 268 autogen.sh script to regenerate the configure script and Makefiles, 269 like:</p> 270 <p><code>/autogen.sh --prefix=/usr --disable-shared</code></p> 271 </li> 272 <li><em>I have troubles when running make tests with gcc-3.0</em> 273 <p>It seems the initial release of gcc-3.0 has a problem with the 274 optimizer which miscompiles the URI module. Please use another 275 compiler.</p> 276 </li> 277</ol> 278 279<h3><a name="Developer">Developer</a> corner</h3> 280<ol> 281 <li><em>xmlDocDump() generates output on one line.</em> 282 <p>Libxml will not <strong>invent</strong> spaces in the content of a 283 document since <strong>all spaces in the content of a document are 284 significant</strong>. If you build a tree from the API and want 285 indentation:</p> 286 <ol> 287 <li>the correct way is to generate those yourself too.</li> 288 <li>the dangerous way is to ask libxml to add those blanks to your 289 content <strong>modifying the content of your document in the 290 process</strong>. The result may not be what you expect. There is 291 <strong>NO</strong> way to guarantee that such a modification won't 292 affect other parts of the content of your document. See <a 293 href="http://xmlsoft.org/html/libxml-parser.html#XMLKEEPBLANKSDEFAULT">xmlKeepBlanksDefault 294 ()</a> and <a 295 href="http://xmlsoft.org/html/libxml-tree.html#XMLSAVEFORMATFILE">xmlSaveFormatFile 296 ()</a></li> 297 </ol> 298 </li> 299 <li>Extra nodes in the document: 300 <p><em>For a XML file as below:</em></p> 301 <pre><?xml version="1.0"?> 302<PLAN xmlns="http://www.argus.ca/autotest/1.0/"> 303<NODE CommFlag="0"/> 304<NODE CommFlag="1"/> 305</PLAN></pre> 306 <p><em>after parsing it with the function 307 pxmlDoc=xmlParseFile(...);</em></p> 308 <p><em>I want to the get the content of the first node (node with the 309 CommFlag="0")</em></p> 310 <p><em>so I did it as following;</em></p> 311 <pre>xmlNodePtr pnode; 312pnode=pxmlDoc->children->children;</pre> 313 <p><em>but it does not work. If I change it to</em></p> 314 <pre>pnode=pxmlDoc->children->children->next;</pre> 315 <p><em>then it works. Can someone explain it to me.</em></p> 316 <p></p> 317 <p>In XML all characters in the content of the document are significant 318 <strong>including blanks and formatting line breaks</strong>.</p> 319 <p>The extra nodes you are wondering about are just that, text nodes with 320 the formatting spaces which are part of the document but that people tend 321 to forget. There is a function <a 322 href="http://xmlsoft.org/html/libxml-parser.html">xmlKeepBlanksDefault 323 ()</a> to remove those at parse time, but that's an heuristic, and its 324 use should be limited to cases where you are certain there is no 325 mixed-content in the document.</p> 326 </li> 327 <li><em>I get compilation errors of existing code like when accessing 328 <strong>root</strong> or <strong>child fields</strong> of nodes.</em> 329 <p>You are compiling code developed for libxml version 1 and using a 330 libxml2 development environment. Either switch back to libxml v1 devel or 331 even better fix the code to compile with libxml2 (or both) by <a 332 href="upgrade.html">following the instructions</a>.</p> 333 </li> 334 <li><em>I get compilation errors about non existing 335 <strong>xmlRootNode</strong> or <strong>xmlChildrenNode</strong> 336 fields.</em> 337 <p>The source code you are using has been <a 338 href="upgrade.html">upgraded</a> to be able to compile with both libxml 339 and libxml2, but you need to install a more recent version: 340 libxml(-devel) >= 1.8.8 or libxml2(-devel) >= 2.1.0</p> 341 </li> 342 <li><em>XPath implementation looks seriously broken</em> 343 <p>XPath implementation prior to 2.3.0 was really incomplete. Upgrade to 344 a recent version, there are no known bugs in the current version.</p> 345 </li> 346 <li><em>The example provided in the web page does not compile.</em> 347 <p>It's hard to maintain the documentation in sync with the code 348 <grin/> ...</p> 349 <p>Check the previous points 1/ and 2/ raised before, and please send 350 patches.</p> 351 </li> 352 <li><em>Where can I get more examples and information than privoded on the 353 web page?</em> 354 <p>Ideally a libxml book would be nice. I have no such plan ... But you 355 can:</p> 356 <ul> 357 <li>check more deeply the <a href="html/libxml-lib.html">existing 358 generated doc</a></li> 359 <li>look for examples of use for libxml function using the Gnome code. 360 For example the following will query the full Gnome CVS base for the 361 use of the <strong>xmlAddChild()</strong> function: 362 <p><a 363 href="http://cvs.gnome.org/lxr/search?string=xmlAddChild">http://cvs.gnome.org/lxr/search?string=xmlAddChild</a></p> 364 <p>This may be slow, a large hardware donation to the gnome project 365 could cure this :-)</p> 366 </li> 367 <li><a 368 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gnome-xml">Browse 369 the libxml source</a> , I try to write code as clean and documented 370 as possible, so looking at it may be helpful. In particular the code 371 of xmllint.c and of the various testXXX.c test programs should 372 provide good examples of how to do things with the library.</li> 373 </ul> 374 </li> 375 <li>What about C++ ? 376 <p>libxml is written in pure C in order to allow easy reuse on a number 377 of platforms, including embedded systems. I don't intend to convert to 378 C++.</p> 379 <p>There are however a few C++ wrappers which may fulfill your needs:</p> 380 <ul> 381 <li>by Ari Johnson <ari@btigate.com>: 382 <p>Website: <a 383 href="http://lusis.org/~ari/xml++/">http://lusis.org/~ari/xml++/</a></p> 384 <p>Download: <a 385 href="http://lusis.org/~ari/xml++/libxml++.tar.gz">http://lusis.org/~ari/xml++/libxml++.tar.gz</a></p> 386 </li> 387 <li>by Peter Jones <pjones@pmade.org> 388 <p>Website: <a 389 href="http://pmade.org/pjones/software/xmlwrapp/">http://pmade.org/pjones/software/xmlwrapp/</a></p> 390 </li> 391 </ul> 392 </li> 393 <li>How to validate a document a posteriori ? 394 <p>It is possible to validate documents which had not been validated at 395 initial parsing time or documents which have been built from scratch 396 using the API. Use the <a 397 href="http://xmlsoft.org/html/libxml-valid.html#XMLVALIDATEDTD">xmlValidateDtd()</a> 398 function. It is also possible to simply add a DTD to an existing 399 document:</p> 400 <pre>xmlDocPtr doc; /* your existing document */ 401xmlDtdPtr dtd = xmlParseDTD(NULL, filename_of_dtd); /* parse the DTD */ 402 403 dtd->name = xmlStrDup((xmlChar*)"root_name"); /* use the given root */ 404 405 doc->intSubset = dtd; 406 if (doc->children == NULL) xmlAddChild((xmlNodePtr)doc, (xmlNodePtr)dtd); 407 else xmlAddPrevSibling(doc->children, (xmlNodePtr)dtd); 408 </pre> 409 </li> 410 <li>So what is this funky "xmlChar" used all the time? 411 <p>It is a null terminated sequence of utf-8 characters. And only utf-8! 412 You need to convert strings encoded in different ways to utf-8 before 413 passing them to the API. This can be accomplished with the iconv library 414 for instance.</p> 415 </li> 416 <li>etc ...</li> 417</ol> 418 419<p></p> 420 421<h2><a name="Documentat">Documentation</a></h2> 422 423<p>There are several on-line resources related to using libxml:</p> 424<ol> 425 <li>Use the <a href="search.php">search engine</a> to lookup 426 informations.</li> 427 <li>Check the <a href="FAQ.html">FAQ.</a></li> 428 <li>Check the <a href="http://xmlsoft.org/html/libxml-lib.html">extensive 429 documentation</a> automatically extracted from code comments (using <a 430 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gtk-doc">gtk 431 doc</a>).</li> 432 <li>Look at the documentation about <a href="encoding.html">libxml 433 internationalization support</a>.</li> 434 <li>This page provides a global overview and <a href="example.html">some 435 examples</a> on how to use libxml.</li> 436 <li>John Fleck's libxml tutorial: <a href="tutorial/index.html">html</a> or 437 <a href="tutorial/xmltutorial.pdf">pdf</a>.</li> 438 <li><a href="mailto:james@daa.com.au">James Henstridge</a> wrote <a 439 href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">some nice 440 documentation</a> explaining how to use the libxml SAX interface.</li> 441 <li>George Lebl wrote <a 442 href="http://www-4.ibm.com/software/developer/library/gnome3/">an article 443 for IBM developerWorks</a> about using libxml.</li> 444 <li>Check <a href="http://cvs.gnome.org/lxr/source/gnome-xml/TODO">the TODO 445 file</a>.</li> 446 <li>Read the <a href="upgrade.html">1.x to 2.x upgrade path</a> 447 description. If you are starting a new project using libxml you should 448 really use the 2.x version.</li> 449 <li>And don't forget to look at the <a 450 href="http://mail.gnome.org/archives/xml/">mailing-list archive</a>.</li> 451</ol> 452 453<h2><a name="Reporting">Reporting bugs and getting help</a></h2> 454 455<p>Well, bugs or missing features are always possible, and I will make a 456point of fixing them in a timely fashion. The best way to report a bug is to 457use the <a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Gnome 458bug tracking database</a> (make sure to use the "libxml2" module name). I 459look at reports there regularly and it's good to have a reminder when a bug 460is still open. Be sure to specify that the bug is for the package libxml2.</p> 461 462<p>There is also a mailing-list <a 463href="mailto:xml@gnome.org">xml@gnome.org</a> for libxml, with an <a 464href="http://mail.gnome.org/archives/xml/">on-line archive</a> (<a 465href="http://xmlsoft.org/messages">old</a>). To subscribe to this list, 466please visit the <a 467href="http://mail.gnome.org/mailman/listinfo/xml">associated Web</a> page and 468follow the instructions. <strong>Do not send code, I won't debug it</strong> 469(but patches are really appreciated!).</p> 470 471<p>Check the following <strong><span style="color: #FF0000">before 472posting</span></strong>:</p> 473<ul> 474 <li>Read the <a href="FAQ.html">FAQ</a> and <a href="search.php">use the 475 search engine</a> to get informations related to your problem.</li> 476 <li>Make sure you are <a href="ftp://xmlsoft.org/">using a recent 477 version</a>, and that the problem still shows up in a recent version.</li> 478 <li>Check the <a href="http://mail.gnome.org/archives/xml/">list 479 archives</a> to see if the problem was reported already. In this case 480 there is probably a fix available, similarly check the <a 481 href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">registered 482 open bugs</a>.</li> 483 <li>Make sure you can reproduce the bug with xmllint or one of the test 484 programs found in source in the distribution.</li> 485 <li>Please send the command showing the error as well as the input (as an 486 attachment)</li> 487</ul> 488 489<p>Then send the bug with associated informations to reproduce it to the <a 490href="mailto:xml@gnome.org">xml@gnome.org</a> list; if it's really libxml 491related I will approve it.. Please do not send mail to me directly, it makes 492things really hard to track and in some cases I am not the best person to 493answer a given question. Ask the list instead.</p> 494 495<p>Of course, bugs reported with a suggested patch for fixing them will 496probably be processed faster than those without.</p> 497 498<p>If you're looking for help, a quick look at <a 499href="http://mail.gnome.org/archives/xml/">the list archive</a> may actually 500provide the answer. I usually send source samples when answering libxml usage 501questions. The <a href="http://xmlsoft.org/html/book1.html">auto-generated 502documentation</a> is not as polished as I would like (i need to learn more 503about DocBook), but it's a good starting point.</p> 504 505<h2><a name="help">How to help</a></h2> 506 507<p>You can help the project in various ways, the best thing to do first is to 508subscribe to the mailing-list as explained before, check the <a 509href="http://mail.gnome.org/archives/xml/">archives </a>and the <a 510href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Gnome bug 511database</a>:</p> 512<ol> 513 <li>Provide patches when you find problems.</li> 514 <li>Provide the diffs when you port libxml to a new platform. They may not 515 be integrated in all cases but help pinpointing portability problems 516 and</li> 517 <li>Provide documentation fixes (either as patches to the code comments or 518 as HTML diffs).</li> 519 <li>Provide new documentations pieces (translations, examples, etc 520 ...).</li> 521 <li>Check the TODO file and try to close one of the items.</li> 522 <li>Take one of the points raised in the archive or the bug database and 523 provide a fix. <a href="mailto:daniel@veillard.com">Get in touch with me 524 </a>before to avoid synchronization problems and check that the suggested 525 fix will fit in nicely :-)</li> 526</ol> 527 528<h2><a name="Downloads">Downloads</a></h2> 529 530<p>The latest versions of libxml can be found on <a 531href="ftp://xmlsoft.org/">xmlsoft.org</a> (<a 532href="ftp://speakeasy.rpmfind.net/pub/libxml/">Seattle</a>, <a 533href="ftp://fr.rpmfind.net/pub/libxml/">France</a>) or on the <a 534href="ftp://ftp.gnome.org/pub/GNOME/MIRRORS.html">Gnome FTP server</a> either 535as a <a href="ftp://ftp.gnome.org/pub/GNOME/sources/libxml2/2.4/">source 536archive</a><!-- commenting this out because they seem to have disappeared or <a 537href="ftp://ftp.gnome.org/pub/GNOME/stable/redhat/i386/libxml/">RPM 538packages</a> --> 539 , Antonin Sprinzl also provide <a href="ftp://gd.tuwien.ac.at/pub/libxml/">a 540mirror in Austria</a>. (NOTE that you need both the <a 541href="http://rpmfind.net/linux/RPM/libxml2.html">libxml(2)</a> and <a 542href="http://rpmfind.net/linux/RPM/libxml2-devel.html">libxml(2)-devel</a> 543packages installed to compile applications using libxml.) <a 544href="mailto:igor@stud.fh-frankfurt.de">Igor Zlatkovic</a> is now the 545maintainer of the Windows port, <a 546href="http://www.fh-frankfurt.de/~igor/projects/libxml/index.html">he 547provides binaries</a>. <a href="mailto:Gary.Pennington@sun.com">Gary 548Pennington</a> provides <a href="http://garypennington.net/libxml2/">Solaris 549binaries</a>. <a href="mailto:Steve.Ball@zveno.com">Steve Ball</a> provides 550<a href="http://www.zveno.com/open_source/libxml2xslt.html">Mac Os X 551binaries</a>.</p> 552 553<p><a name="Snapshot">Snapshot:</a></p> 554<ul> 555 <li>Code from the W3C cvs base libxml <a 556 href="ftp://xmlsoft.org/cvs-snapshot.tar.gz">cvs-snapshot.tar.gz</a>.</li> 557 <li>Docs, content of the web site, the list archive included <a 558 href="ftp://xmlsoft.org/libxml-docs.tar.gz">libxml-docs.tar.gz</a>.</li> 559</ul> 560 561<p><a name="Contribs">Contributions:</a></p> 562 563<p>I do accept external contributions, especially if compiling on another 564platform, get in touch with me to upload the package, wrappers for various 565languages have been provided, and can be found in the <a 566href="contribs.html">contrib section</a></p> 567 568<p>Libxml is also available from CVS:</p> 569<ul> 570 <li><p>The <a 571 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gnome-xml">Gnome 572 CVS base</a>. Check the <a 573 href="http://developer.gnome.org/tools/cvs.html">Gnome CVS Tools</a> 574 page; the CVS module is <b>gnome-xml</b>.</p> 575 </li> 576 <li>The <strong>libxslt</strong> module is also present there</li> 577</ul> 578 579<h2><a name="News">News</a></h2> 580 581<h3>CVS only : check the <a 582href="http://cvs.gnome.org/lxr/source/gnome-xml/ChangeLog">Changelog</a> file 583for a really accurate description</h3> 584 585<p>Items not finished and worked on, get in touch with the list if you want 586to test those</p> 587<ul> 588 <li>Finishing up <a href="http://www.w3.org/TR/xmlschema-1/">XML 589 Schemas</a> and <a href="http://www.w3.org/TR/xinclude">XInclude</a></li> 590</ul> 591 592<h3>2.4.30: Dec 12 2002</h3> 593<ul> 594 <li>2.4.29 broke the python bindings, rereleasing</li> 595 <li>Improvement/fixes of the XML API generator, and couple of minor code 596 fixes.</li> 597</ul> 598 599<h3>2.4.29: Dec 11 2002</h3> 600<ul> 601 <li>Windows fixes (Igor): Windows CE port, pthread linking, python bindings 602 (St�phane Bidoul), Mingw (Magnus Henoch), and export list updates</li> 603 <li>Fix for prev in python bindings (ERDI Gergo)</li> 604 <li>Fix for entities handling (Marcus Clarke)</li> 605 <li>Refactored the XML and HTML dumps to a single code path, fixed XHTML1 606 dump</li> 607 <li>Fix for URI parsing when handling URNs with fragment identifiers</li> 608 <li>Fix for HTTP URL escaping problem</li> 609 <li>added an TextXmlReader (C#) like API (work in progress)</li> 610 <li>Rewrote the API in XML generation script, includes a C parser and saves 611 more informations needed for C# bindings</li> 612</ul> 613 614<h3>2.4.28: Nov 22 2002</h3> 615<ul> 616 <li>a couple of python binding fixes</li> 617 <li>2 bug fixes in the XML push parser</li> 618 <li>potential memory leak removed (Martin Stoilov)</li> 619 <li>fix to the configure script for Unix (Dimitri Papadopoulos)</li> 620 <li>added encoding support for XInclude parse="text"</li> 621 <li>autodetection of XHTML1 and specific serialization rules added</li> 622 <li>nasty threading bug fixed (William Brack)</li> 623</ul> 624 625<h3>2.4.27: Nov 17 2002</h3> 626<ul> 627 <li>fixes for the Python bindings</li> 628 <li>a number of bug fixes: SGML catalogs, xmlParseBalancedChunkMemory(), 629 HTML parser, Schemas (Charles Bozeman), document fragment support 630 (Christian Glahn), xmlReconciliateNs (Brian Stafford), XPointer, 631 xmlFreeNode(), xmlSAXParseMemory (Peter Jones), xmlGetNodePath (Petr 632 Pajas), entities processing</li> 633 <li>added grep to xmllint --shell</li> 634 <li>VMS update patch from Craig A. Berry</li> 635 <li>cleanup of the Windows build with support for more compilers (Igor), 636 better thread support on Windows</li> 637 <li>cleanup of Unix Makefiles and spec file</li> 638 <li>Improvements to the documentation (John Fleck)</li> 639</ul> 640 641<h3>2.4.26: Oct 18 2002</h3> 642<ul> 643 <li>Patches for Windows CE port, improvements on Windows paths handling</li> 644 <li>Fixes to the validation code (DTD and Schemas), xmlNodeGetPath() , 645 HTML serialization, Namespace compliance, and a number of small 646 problems</li> 647</ul> 648 649<h3>2.4.25: Sep 26 2002</h3> 650<ul> 651 <li>A number of bug fixes: XPath, validation, Python bindings, DOM and 652 tree, xmlI/O, Html</li> 653 <li>Serious rewrite of XInclude</li> 654 <li>Made XML Schemas regexp part of the default build and APIs, small fix 655 and improvement of the regexp core</li> 656 <li>Changed the validation code to reuse XML Schemas regexp APIs</li> 657 <li>Better handling of Windows file paths, improvement of Makefiles (Igor, 658 Daniel Gehriger, Mark Vakoc)</li> 659 <li>Improved the python I/O bindings, the tests, added resolver and regexp 660 APIs</li> 661 <li>New logos from Marc Liyanage</li> 662 <li>Tutorial improvements: John Fleck, Christopher Harris</li> 663 <li>Makefile: Fixes for AMD x86_64 (Mandrake), DESTDIR (Christophe 664 Merlet)</li> 665 <li>removal of all stderr/perror use for error reporting</li> 666 <li>Better error reporting: XPath and DTD validation</li> 667 <li>update of the trio portability layer (Bjorn Reese)</li> 668</ul> 669 670<p><strong>2.4.24: Aug 22 2002</strong></p> 671<ul> 672 <li>XPath fixes (William), xf:escape-uri() (Wesley Terpstra)</li> 673 <li>Python binding fixes: makefiles (William), generator, rpm build, x86-64 674 (fcrozat)</li> 675 <li>HTML <style> and boolean attributes serializer fixes</li> 676 <li>C14N improvements by Aleksey</li> 677 <li>doc cleanups: Rick Jones</li> 678 <li>Windows compiler makefile updates: Igor and Elizabeth Barham</li> 679 <li>XInclude: implementation of fallback and xml:base fixup added</li> 680</ul> 681 682<h3>2.4.23: July 6 2002</h3> 683<ul> 684 <li>performances patches: Peter Jacobi</li> 685 <li>c14n fixes, testsuite and performances: Aleksey Sanin</li> 686 <li>added xmlDocFormatDump: Chema Celorio</li> 687 <li>new tutorial: John Fleck</li> 688 <li>new hash functions and performances: Sander Vesik, portability fix from 689 Peter Jacobi</li> 690 <li>a number of bug fixes: XPath (William Brack, Richard Jinks), XML and 691 HTML parsers, ID lookup function</li> 692 <li>removal of all remaining sprintf: Aleksey Sanin</li> 693</ul> 694 695<h3>2.4.22: May 27 2002</h3> 696<ul> 697 <li>a number of bug fixes: configure scripts, base handling, parser, memory 698 usage, HTML parser, XPath, documentation (Christian Cornelssen), 699 indentation, URI parsing</li> 700 <li>Optimizations for XMLSec, fixing and making public some of the network 701 protocol handlers (Aleksey)</li> 702 <li>performance patch from Gary Pennington</li> 703 <li>Charles Bozeman provided date and time support for XML Schemas 704 datatypes</li> 705</ul> 706 707<h3>2.4.21: Apr 29 2002</h3> 708 709<p>This release is both a bug fix release and also contains the early XML 710Schemas <a href="http://www.w3.org/TR/xmlschema-1/">structures</a> and <a 711href="http://www.w3.org/TR/xmlschema-2/">datatypes</a> code, beware, all 712interfaces are likely to change, there is huge holes, it is clearly a work in 713progress and don't even think of putting this code in a production system, 714it's actually not compiled in by default. The real fixes are:</p> 715<ul> 716 <li>a couple of bugs or limitations introduced in 2.4.20</li> 717 <li>patches for Borland C++ and MSC by Igor</li> 718 <li>some fixes on XPath strings and conformance patches by Richard 719 Jinks</li> 720 <li>patch from Aleksey for the ExcC14N specification</li> 721 <li>OSF/1 bug fix by Bjorn</li> 722</ul> 723 724<h3>2.4.20: Apr 15 2002</h3> 725<ul> 726 <li>bug fixes: file descriptor leak, XPath, HTML output, DTD validation</li> 727 <li>XPath conformance testing by Richard Jinks</li> 728 <li>Portability fixes: Solaris, MPE/iX, Windows, OSF/1, python bindings, 729 libxml.m4</li> 730</ul> 731 732<h3>2.4.19: Mar 25 2002</h3> 733<ul> 734 <li>bug fixes: half a dozen XPath bugs, Validation, ISO-Latin to UTF8 735 encoder</li> 736 <li>portability fixes in the HTTP code</li> 737 <li>memory allocation checks using valgrind, and profiling tests</li> 738 <li>revamp of the Windows build and Makefiles</li> 739</ul> 740 741<h3>2.4.18: Mar 18 2002</h3> 742<ul> 743 <li>bug fixes: tree, SAX, canonicalization, validation, portability, 744 XPath</li> 745 <li>removed the --with-buffer option it was becoming unmaintainable</li> 746 <li>serious cleanup of the Python makefiles</li> 747 <li>speedup patch to XPath very effective for DocBook stylesheets</li> 748 <li>Fixes for Windows build, cleanup of the documentation</li> 749</ul> 750 751<h3>2.4.17: Mar 8 2002</h3> 752<ul> 753 <li>a lot of bug fixes, including "namespace nodes have no parents in 754 XPath"</li> 755 <li>fixed/improved the Python wrappers, added more examples and more 756 regression tests, XPath extension functions can now return node-sets</li> 757 <li>added the XML Canonicalization support from Aleksey Sanin</li> 758</ul> 759 760<h3>2.4.16: Feb 20 2002</h3> 761<ul> 762 <li>a lot of bug fixes, most of them were triggered by the XML Testsuite 763 from OASIS and W3C. Compliance has been significantly improved.</li> 764 <li>a couple of portability fixes too.</li> 765</ul> 766 767<h3>2.4.15: Feb 11 2002</h3> 768<ul> 769 <li>Fixed the Makefiles, especially the python module ones</li> 770 <li>A few bug fixes and cleanup</li> 771 <li>Includes cleanup</li> 772</ul> 773 774<h3>2.4.14: Feb 8 2002</h3> 775<ul> 776 <li>Change of License to the <a 777 href="http://www.opensource.org/licenses/mit-license.html">MIT 778 License</a> basically for integration in XFree86 codebase, and removing 779 confusion around the previous dual-licensing</li> 780 <li>added Python bindings, beta software but should already be quite 781 complete</li> 782 <li>a large number of fixes and cleanups, especially for all tree 783 manipulations</li> 784 <li>cleanup of the headers, generation of a reference API definition in 785 XML</li> 786</ul> 787 788<h3>2.4.13: Jan 14 2002</h3> 789<ul> 790 <li>update of the documentation: John Fleck and Charlie Bozeman</li> 791 <li>cleanup of timing code from Justin Fletcher</li> 792 <li>fixes for Windows and initial thread support on Win32: Igor and Serguei 793 Narojnyi</li> 794 <li>Cygwin patch from Robert Collins</li> 795 <li>added xmlSetEntityReferenceFunc() for Keith Isdale work on xsldbg</li> 796</ul> 797 798<h3>2.4.12: Dec 7 2001</h3> 799<ul> 800 <li>a few bug fixes: thread (Gary Pennington), xmllint (Geert Kloosterman), 801 XML parser (Robin Berjon), XPointer (Danny Jamshy), I/O cleanups 802 (robert)</li> 803 <li>Eric Lavigne contributed project files for MacOS</li> 804 <li>some makefiles cleanups</li> 805</ul> 806 807<h3>2.4.11: Nov 26 2001</h3> 808<ul> 809 <li>fixed a couple of errors in the includes, fixed a few bugs, some code 810 cleanups</li> 811 <li>xmllint man pages improvement by Heiko Rupp</li> 812 <li>updated VMS build instructions from John A Fotheringham</li> 813 <li>Windows Makefiles updates from Igor</li> 814</ul> 815 816<h3>2.4.10: Nov 10 2001</h3> 817<ul> 818 <li>URI escaping fix (Joel Young)</li> 819 <li>added xmlGetNodePath() (for paths or XPointers generation)</li> 820 <li>Fixes namespace handling problems when using DTD and validation</li> 821 <li>improvements on xmllint: Morus Walter patches for --format and 822 --encode, Stefan Kost and Heiko Rupp improvements on the --shell</li> 823 <li>fixes for xmlcatalog linking pointed by Weiqi Gao</li> 824 <li>fixes to the HTML parser</li> 825</ul> 826 827<h3>2.4.9: Nov 6 2001</h3> 828<ul> 829 <li>fixes more catalog bugs</li> 830 <li>avoid a compilation problem, improve xmlGetLineNo()</li> 831</ul> 832 833<h3>2.4.8: Nov 4 2001</h3> 834<ul> 835 <li>fixed SGML catalogs broken in previous release, updated xmlcatalog 836 tool</li> 837 <li>fixed a compile errors and some includes troubles.</li> 838</ul> 839 840<h3>2.4.7: Oct 30 2001</h3> 841<ul> 842 <li>exported some debugging interfaces</li> 843 <li>serious rewrite of the catalog code</li> 844 <li>integrated Gary Pennington thread safety patch, added configure option 845 and regression tests</li> 846 <li>removed an HTML parser bug</li> 847 <li>fixed a couple of potentially serious validation bugs</li> 848 <li>integrated the SGML DocBook support in xmllint</li> 849 <li>changed the nanoftp anonymous login passwd</li> 850 <li>some I/O cleanup and a couple of interfaces for Perl wrapper</li> 851 <li>general bug fixes</li> 852 <li>updated xmllint man page by John Fleck</li> 853 <li>some VMS and Windows updates</li> 854</ul> 855 856<h3>2.4.6: Oct 10 2001</h3> 857<ul> 858 <li>added an updated man pages by John Fleck</li> 859 <li>portability and configure fixes</li> 860 <li>an infinite loop on the HTML parser was removed (William)</li> 861 <li>Windows makefile patches from Igor</li> 862 <li>fixed half a dozen bugs reported for libxml or libxslt</li> 863 <li>updated xmlcatalog to be able to modify SGML super catalogs</li> 864</ul> 865 866<h3>2.4.5: Sep 14 2001</h3> 867<ul> 868 <li>Remove a few annoying bugs in 2.4.4</li> 869 <li>forces the HTML serializer to output decimal charrefs since some 870 version of Netscape can't handle hexadecimal ones</li> 871</ul> 872 873<h3>1.8.16: Sep 14 2001</h3> 874<ul> 875 <li>maintenance release of the old libxml1 branch, couple of bug and 876 portability fixes</li> 877</ul> 878 879<h3>2.4.4: Sep 12 2001</h3> 880<ul> 881 <li>added --convert to xmlcatalog, bug fixes and cleanups of XML 882 Catalog</li> 883 <li>a few bug fixes and some portability changes</li> 884 <li>some documentation cleanups</li> 885</ul> 886 887<h3>2.4.3: Aug 23 2001</h3> 888<ul> 889 <li>XML Catalog support see the doc</li> 890 <li>New NaN/Infinity floating point code</li> 891 <li>A few bug fixes</li> 892</ul> 893 894<h3>2.4.2: Aug 15 2001</h3> 895<ul> 896 <li>adds xmlLineNumbersDefault() to control line number generation</li> 897 <li>lot of bug fixes</li> 898 <li>the Microsoft MSC projects files should now be up to date</li> 899 <li>inheritance of namespaces from DTD defaulted attributes</li> 900 <li>fixes a serious potential security bug</li> 901 <li>added a --format option to xmllint</li> 902</ul> 903 904<h3>2.4.1: July 24 2001</h3> 905<ul> 906 <li>possibility to keep line numbers in the tree</li> 907 <li>some computation NaN fixes</li> 908 <li>extension of the XPath API</li> 909 <li>cleanup for alpha and ia64 targets</li> 910 <li>patch to allow saving through HTTP PUT or POST</li> 911</ul> 912 913<h3>2.4.0: July 10 2001</h3> 914<ul> 915 <li>Fixed a few bugs in XPath, validation, and tree handling.</li> 916 <li>Fixed XML Base implementation, added a couple of examples to the 917 regression tests</li> 918 <li>A bit of cleanup</li> 919</ul> 920 921<h3>2.3.14: July 5 2001</h3> 922<ul> 923 <li>fixed some entities problems and reduce memory requirement when 924 substituting them</li> 925 <li>lots of improvements in the XPath queries interpreter can be 926 substantially faster</li> 927 <li>Makefiles and configure cleanups</li> 928 <li>Fixes to XPath variable eval, and compare on empty node set</li> 929 <li>HTML tag closing bug fixed</li> 930 <li>Fixed an URI reference computation problem when validating</li> 931</ul> 932 933<h3>2.3.13: June 28 2001</h3> 934<ul> 935 <li>2.3.12 configure.in was broken as well as the push mode XML parser</li> 936 <li>a few more fixes for compilation on Windows MSC by Yon Derek</li> 937</ul> 938 939<h3>1.8.14: June 28 2001</h3> 940<ul> 941 <li>Zbigniew Chyla gave a patch to use the old XML parser in push mode</li> 942 <li>Small Makefile fix</li> 943</ul> 944 945<h3>2.3.12: June 26 2001</h3> 946<ul> 947 <li>lots of cleanup</li> 948 <li>a couple of validation fix</li> 949 <li>fixed line number counting</li> 950 <li>fixed serious problems in the XInclude processing</li> 951 <li>added support for UTF8 BOM at beginning of entities</li> 952 <li>fixed a strange gcc optimizer bugs in xpath handling of float, gcc-3.0 953 miscompile uri.c (William), Thomas Leitner provided a fix for the 954 optimizer on Tru64</li> 955 <li>incorporated Yon Derek and Igor Zlatkovic fixes and improvements for 956 compilation on Windows MSC</li> 957 <li>update of libxml-doc.el (Felix Natter)</li> 958 <li>fixed 2 bugs in URI normalization code</li> 959</ul> 960 961<h3>2.3.11: June 17 2001</h3> 962<ul> 963 <li>updates to trio, Makefiles and configure should fix some portability 964 problems (alpha)</li> 965 <li>fixed some HTML serialization problems (pre, script, and block/inline 966 handling), added encoding aware APIs, cleanup of this code</li> 967 <li>added xmlHasNsProp()</li> 968 <li>implemented a specific PI for encoding support in the DocBook SGML 969 parser</li> 970 <li>some XPath fixes (-Infinity, / as a function parameter and namespaces 971 node selection)</li> 972 <li>fixed a performance problem and an error in the validation code</li> 973 <li>fixed XInclude routine to implement the recursive behaviour</li> 974 <li>fixed xmlFreeNode problem when libxml is included statically twice</li> 975 <li>added --version to xmllint for bug reports</li> 976</ul> 977 978<h3>2.3.10: June 1 2001</h3> 979<ul> 980 <li>fixed the SGML catalog support</li> 981 <li>a number of reported bugs got fixed, in XPath, iconv detection, 982 XInclude processing</li> 983 <li>XPath string function should now handle unicode correctly</li> 984</ul> 985 986<h3>2.3.9: May 19 2001</h3> 987 988<p>Lots of bugfixes, and added a basic SGML catalog support:</p> 989<ul> 990 <li>HTML push bugfix #54891 and another patch from Jonas Borgstr�m</li> 991 <li>some serious speed optimization again</li> 992 <li>some documentation cleanups</li> 993 <li>trying to get better linking on Solaris (-R)</li> 994 <li>XPath API cleanup from Thomas Broyer</li> 995 <li>Validation bug fixed #54631, added a patch from Gary Pennington, fixed 996 xmlValidGetValidElements()</li> 997 <li>Added an INSTALL file</li> 998 <li>Attribute removal added to API: #54433</li> 999 <li>added a basic support for SGML catalogs</li> 1000 <li>fixed xmlKeepBlanksDefault(0) API</li> 1001 <li>bugfix in xmlNodeGetLang()</li> 1002 <li>fixed a small configure portability problem</li> 1003 <li>fixed an inversion of SYSTEM and PUBLIC identifier in HTML document</li> 1004</ul> 1005 1006<h3>1.8.13: May 14 2001</h3> 1007<ul> 1008 <li>bugfixes release of the old libxml1 branch used by Gnome</li> 1009</ul> 1010 1011<h3>2.3.8: May 3 2001</h3> 1012<ul> 1013 <li>Integrated an SGML DocBook parser for the Gnome project</li> 1014 <li>Fixed a few things in the HTML parser</li> 1015 <li>Fixed some XPath bugs raised by XSLT use, tried to fix the floating 1016 point portability issue</li> 1017 <li>Speed improvement (8M/s for SAX, 3M/s for DOM, 1.5M/s for 1018 DOM+validation using the XML REC as input and a 700MHz celeron).</li> 1019 <li>incorporated more Windows cleanup</li> 1020 <li>added xmlSaveFormatFile()</li> 1021 <li>fixed problems in copying nodes with entities references (gdome)</li> 1022 <li>removed some troubles surrounding the new validation module</li> 1023</ul> 1024 1025<h3>2.3.7: April 22 2001</h3> 1026<ul> 1027 <li>lots of small bug fixes, corrected XPointer</li> 1028 <li>Non deterministic content model validation support</li> 1029 <li>added xmlDocCopyNode for gdome2</li> 1030 <li>revamped the way the HTML parser handles end of tags</li> 1031 <li>XPath: corrections of namespaces support and number formatting</li> 1032 <li>Windows: Igor Zlatkovic patches for MSC compilation</li> 1033 <li>HTML output fixes from P C Chow and William M. Brack</li> 1034 <li>Improved validation speed sensible for DocBook</li> 1035 <li>fixed a big bug with ID declared in external parsed entities</li> 1036 <li>portability fixes, update of Trio from Bjorn Reese</li> 1037</ul> 1038 1039<h3>2.3.6: April 8 2001</h3> 1040<ul> 1041 <li>Code cleanup using extreme gcc compiler warning options, found and 1042 cleared half a dozen potential problem</li> 1043 <li>the Eazel team found an XML parser bug</li> 1044 <li>cleaned up the user of some of the string formatting function. used the 1045 trio library code to provide the one needed when the platform is missing 1046 them</li> 1047 <li>xpath: removed a memory leak and fixed the predicate evaluation 1048 problem, extended the testsuite and cleaned up the result. XPointer seems 1049 broken ...</li> 1050</ul> 1051 1052<h3>2.3.5: Mar 23 2001</h3> 1053<ul> 1054 <li>Biggest change is separate parsing and evaluation of XPath expressions, 1055 there is some new APIs for this too</li> 1056 <li>included a number of bug fixes(XML push parser, 51876, notations, 1057 52299)</li> 1058 <li>Fixed some portability issues</li> 1059</ul> 1060 1061<h3>2.3.4: Mar 10 2001</h3> 1062<ul> 1063 <li>Fixed bugs #51860 and #51861</li> 1064 <li>Added a global variable xmlDefaultBufferSize to allow default buffer 1065 size to be application tunable.</li> 1066 <li>Some cleanup in the validation code, still a bug left and this part 1067 should probably be rewritten to support ambiguous content model :-\</li> 1068 <li>Fix a couple of serious bugs introduced or raised by changes in 2.3.3 1069 parser</li> 1070 <li>Fixed another bug in xmlNodeGetContent()</li> 1071 <li>Bjorn fixed XPath node collection and Number formatting</li> 1072 <li>Fixed a loop reported in the HTML parsing</li> 1073 <li>blank space are reported even if the Dtd content model proves that they 1074 are formatting spaces, this is for XML conformance</li> 1075</ul> 1076 1077<h3>2.3.3: Mar 1 2001</h3> 1078<ul> 1079 <li>small change in XPath for XSLT</li> 1080 <li>documentation cleanups</li> 1081 <li>fix in validation by Gary Pennington</li> 1082 <li>serious parsing performances improvements</li> 1083</ul> 1084 1085<h3>2.3.2: Feb 24 2001</h3> 1086<ul> 1087 <li>chasing XPath bugs, found a bunch, completed some TODO</li> 1088 <li>fixed a Dtd parsing bug</li> 1089 <li>fixed a bug in xmlNodeGetContent</li> 1090 <li>ID/IDREF support partly rewritten by Gary Pennington</li> 1091</ul> 1092 1093<h3>2.3.1: Feb 15 2001</h3> 1094<ul> 1095 <li>some XPath and HTML bug fixes for XSLT</li> 1096 <li>small extension of the hash table interfaces for DOM gdome2 1097 implementation</li> 1098 <li>A few bug fixes</li> 1099</ul> 1100 1101<h3>2.3.0: Feb 8 2001 (2.2.12 was on 25 Jan but I didn't kept track)</h3> 1102<ul> 1103 <li>Lots of XPath bug fixes</li> 1104 <li>Add a mode with Dtd lookup but without validation error reporting for 1105 XSLT</li> 1106 <li>Add support for text node without escaping (XSLT)</li> 1107 <li>bug fixes for xmlCheckFilename</li> 1108 <li>validation code bug fixes from Gary Pennington</li> 1109 <li>Patch from Paul D. Smith correcting URI path normalization</li> 1110 <li>Patch to allow simultaneous install of libxml-devel and 1111 libxml2-devel</li> 1112 <li>the example Makefile is now fixed</li> 1113 <li>added HTML to the RPM packages</li> 1114 <li>tree copying bugfixes</li> 1115 <li>updates to Windows makefiles</li> 1116 <li>optimization patch from Bjorn Reese</li> 1117</ul> 1118 1119<h3>2.2.11: Jan 4 2001</h3> 1120<ul> 1121 <li>bunch of bug fixes (memory I/O, xpath, ftp/http, ...)</li> 1122 <li>added htmlHandleOmittedElem()</li> 1123 <li>Applied Bjorn Reese's IPV6 first patch</li> 1124 <li>Applied Paul D. Smith patches for validation of XInclude results</li> 1125 <li>added XPointer xmlns() new scheme support</li> 1126</ul> 1127 1128<h3>2.2.10: Nov 25 2000</h3> 1129<ul> 1130 <li>Fix the Windows problems of 2.2.8</li> 1131 <li>integrate OpenVMS patches</li> 1132 <li>better handling of some nasty HTML input</li> 1133 <li>Improved the XPointer implementation</li> 1134 <li>integrate a number of provided patches</li> 1135</ul> 1136 1137<h3>2.2.9: Nov 25 2000</h3> 1138<ul> 1139 <li>erroneous release :-(</li> 1140</ul> 1141 1142<h3>2.2.8: Nov 13 2000</h3> 1143<ul> 1144 <li>First version of <a href="http://www.w3.org/TR/xinclude">XInclude</a> 1145 support</li> 1146 <li>Patch in conditional section handling</li> 1147 <li>updated MS compiler project</li> 1148 <li>fixed some XPath problems</li> 1149 <li>added an URI escaping function</li> 1150 <li>some other bug fixes</li> 1151</ul> 1152 1153<h3>2.2.7: Oct 31 2000</h3> 1154<ul> 1155 <li>added message redirection</li> 1156 <li>XPath improvements (thanks TOM !)</li> 1157 <li>xmlIOParseDTD() added</li> 1158 <li>various small fixes in the HTML, URI, HTTP and XPointer support</li> 1159 <li>some cleanup of the Makefile, autoconf and the distribution content</li> 1160</ul> 1161 1162<h3>2.2.6: Oct 25 2000:</h3> 1163<ul> 1164 <li>Added an hash table module, migrated a number of internal structure to 1165 those</li> 1166 <li>Fixed a posteriori validation problems</li> 1167 <li>HTTP module cleanups</li> 1168 <li>HTML parser improvements (tag errors, script/style handling, attribute 1169 normalization)</li> 1170 <li>coalescing of adjacent text nodes</li> 1171 <li>couple of XPath bug fixes, exported the internal API</li> 1172</ul> 1173 1174<h3>2.2.5: Oct 15 2000:</h3> 1175<ul> 1176 <li>XPointer implementation and testsuite</li> 1177 <li>Lot of XPath fixes, added variable and functions registration, more 1178 tests</li> 1179 <li>Portability fixes, lots of enhancements toward an easy Windows build 1180 and release</li> 1181 <li>Late validation fixes</li> 1182 <li>Integrated a lot of contributed patches</li> 1183 <li>added memory management docs</li> 1184 <li>a performance problem when using large buffer seems fixed</li> 1185</ul> 1186 1187<h3>2.2.4: Oct 1 2000:</h3> 1188<ul> 1189 <li>main XPath problem fixed</li> 1190 <li>Integrated portability patches for Windows</li> 1191 <li>Serious bug fixes on the URI and HTML code</li> 1192</ul> 1193 1194<h3>2.2.3: Sep 17 2000</h3> 1195<ul> 1196 <li>bug fixes</li> 1197 <li>cleanup of entity handling code</li> 1198 <li>overall review of all loops in the parsers, all sprintf usage has been 1199 checked too</li> 1200 <li>Far better handling of larges Dtd. Validating against DocBook XML Dtd 1201 works smoothly now.</li> 1202</ul> 1203 1204<h3>1.8.10: Sep 6 2000</h3> 1205<ul> 1206 <li>bug fix release for some Gnome projects</li> 1207</ul> 1208 1209<h3>2.2.2: August 12 2000</h3> 1210<ul> 1211 <li>mostly bug fixes</li> 1212 <li>started adding routines to access xml parser context options</li> 1213</ul> 1214 1215<h3>2.2.1: July 21 2000</h3> 1216<ul> 1217 <li>a purely bug fixes release</li> 1218 <li>fixed an encoding support problem when parsing from a memory block</li> 1219 <li>fixed a DOCTYPE parsing problem</li> 1220 <li>removed a bug in the function allowing to override the memory 1221 allocation routines</li> 1222</ul> 1223 1224<h3>2.2.0: July 14 2000</h3> 1225<ul> 1226 <li>applied a lot of portability fixes</li> 1227 <li>better encoding support/cleanup and saving (content is now always 1228 encoded in UTF-8)</li> 1229 <li>the HTML parser now correctly handles encodings</li> 1230 <li>added xmlHasProp()</li> 1231 <li>fixed a serious problem with &#38;</li> 1232 <li>propagated the fix to FTP client</li> 1233 <li>cleanup, bugfixes, etc ...</li> 1234 <li>Added a page about <a href="encoding.html">libxml Internationalization 1235 support</a></li> 1236</ul> 1237 1238<h3>1.8.9: July 9 2000</h3> 1239<ul> 1240 <li>fixed the spec the RPMs should be better</li> 1241 <li>fixed a serious bug in the FTP implementation, released 1.8.9 to solve 1242 rpmfind users problem</li> 1243</ul> 1244 1245<h3>2.1.1: July 1 2000</h3> 1246<ul> 1247 <li>fixes a couple of bugs in the 2.1.0 packaging</li> 1248 <li>improvements on the HTML parser</li> 1249</ul> 1250 1251<h3>2.1.0 and 1.8.8: June 29 2000</h3> 1252<ul> 1253 <li>1.8.8 is mostly a commodity package for upgrading to libxml2 according 1254 to <a href="upgrade.html">new instructions</a>. It fixes a nasty problem 1255 about &#38; charref parsing</li> 1256 <li>2.1.0 also ease the upgrade from libxml v1 to the recent version. it 1257 also contains numerous fixes and enhancements: 1258 <ul> 1259 <li>added xmlStopParser() to stop parsing</li> 1260 <li>improved a lot parsing speed when there is large CDATA blocs</li> 1261 <li>includes XPath patches provided by Picdar Technology</li> 1262 <li>tried to fix as much as possible DTD validation and namespace 1263 related problems</li> 1264 <li>output to a given encoding has been added/tested</li> 1265 <li>lot of various fixes</li> 1266 </ul> 1267 </li> 1268</ul> 1269 1270<h3>2.0.0: Apr 12 2000</h3> 1271<ul> 1272 <li>First public release of libxml2. If you are using libxml, it's a good 1273 idea to check the 1.x to 2.x upgrade instructions. NOTE: while initially 1274 scheduled for Apr 3 the release occurred only on Apr 12 due to massive 1275 workload.</li> 1276 <li>The include are now located under $prefix/include/libxml (instead of 1277 $prefix/include/gnome-xml), they also are referenced by 1278 <pre>#include <libxml/xxx.h></pre> 1279 <p>instead of</p> 1280 <pre>#include "xxx.h"</pre> 1281 </li> 1282 <li>a new URI module for parsing URIs and following strictly RFC 2396</li> 1283 <li>the memory allocation routines used by libxml can now be overloaded 1284 dynamically by using xmlMemSetup()</li> 1285 <li>The previously CVS only tool tester has been renamed 1286 <strong>xmllint</strong> and is now installed as part of the libxml2 1287 package</li> 1288 <li>The I/O interface has been revamped. There is now ways to plug in 1289 specific I/O modules, either at the URI scheme detection level using 1290 xmlRegisterInputCallbacks() or by passing I/O functions when creating a 1291 parser context using xmlCreateIOParserCtxt()</li> 1292 <li>there is a C preprocessor macro LIBXML_VERSION providing the version 1293 number of the libxml module in use</li> 1294 <li>a number of optional features of libxml can now be excluded at 1295 configure time (FTP/HTTP/HTML/XPath/Debug)</li> 1296</ul> 1297 1298<h3>2.0.0beta: Mar 14 2000</h3> 1299<ul> 1300 <li>This is a first Beta release of libxml version 2</li> 1301 <li>It's available only from<a href="ftp://xmlsoft.org/">xmlsoft.org 1302 FTP</a>, it's packaged as libxml2-2.0.0beta and available as tar and 1303 RPMs</li> 1304 <li>This version is now the head in the Gnome CVS base, the old one is 1305 available under the tag LIB_XML_1_X</li> 1306 <li>This includes a very large set of changes. From a programmatic point 1307 of view applications should not have to be modified too much, check the 1308 <a href="upgrade.html">upgrade page</a></li> 1309 <li>Some interfaces may changes (especially a bit about encoding).</li> 1310 <li>the updates includes: 1311 <ul> 1312 <li>fix I18N support. ISO-Latin-x/UTF-8/UTF-16 (nearly) seems correctly 1313 handled now</li> 1314 <li>Better handling of entities, especially well-formedness checking 1315 and proper PEref extensions in external subsets</li> 1316 <li>DTD conditional sections</li> 1317 <li>Validation now correctly handle entities content</li> 1318 <li><a href="http://rpmfind.net/tools/gdome/messages/0039.html">change 1319 structures to accommodate DOM</a></li> 1320 </ul> 1321 </li> 1322 <li>Serious progress were made toward compliance, <a 1323 href="conf/result.html">here are the result of the test</a> against the 1324 OASIS testsuite (except the Japanese tests since I don't support that 1325 encoding yet). This URL is rebuilt every couple of hours using the CVS 1326 head version.</li> 1327</ul> 1328 1329<h3>1.8.7: Mar 6 2000</h3> 1330<ul> 1331 <li>This is a bug fix release:</li> 1332 <li>It is possible to disable the ignorable blanks heuristic used by 1333 libxml-1.x, a new function xmlKeepBlanksDefault(0) will allow this. Note 1334 that for adherence to XML spec, this behaviour will be disabled by 1335 default in 2.x . The same function will allow to keep compatibility for 1336 old code.</li> 1337 <li>Blanks in <a> </a> constructs are not ignored anymore, 1338 avoiding heuristic is really the Right Way :-\</li> 1339 <li>The unchecked use of snprintf which was breaking libxml-1.8.6 1340 compilation on some platforms has been fixed</li> 1341 <li>nanoftp.c nanohttp.c: Fixed '#' and '?' stripping when processing 1342 URIs</li> 1343</ul> 1344 1345<h3>1.8.6: Jan 31 2000</h3> 1346<ul> 1347 <li>added a nanoFTP transport module, debugged until the new version of <a 1348 href="http://rpmfind.net/linux/rpm2html/rpmfind.html">rpmfind</a> can use 1349 it without troubles</li> 1350</ul> 1351 1352<h3>1.8.5: Jan 21 2000</h3> 1353<ul> 1354 <li>adding APIs to parse a well balanced chunk of XML (production <a 1355 href="http://www.w3.org/TR/REC-xml#NT-content">[43] content</a> of the 1356 XML spec)</li> 1357 <li>fixed a hideous bug in xmlGetProp pointed by Rune.Djurhuus@fast.no</li> 1358 <li>Jody Goldberg <jgoldberg@home.com> provided another patch trying 1359 to solve the zlib checks problems</li> 1360 <li>The current state in gnome CVS base is expected to ship as 1.8.5 with 1361 gnumeric soon</li> 1362</ul> 1363 1364<h3>1.8.4: Jan 13 2000</h3> 1365<ul> 1366 <li>bug fixes, reintroduced xmlNewGlobalNs(), fixed xmlNewNs()</li> 1367 <li>all exit() call should have been removed from libxml</li> 1368 <li>fixed a problem with INCLUDE_WINSOCK on WIN32 platform</li> 1369 <li>added newDocFragment()</li> 1370</ul> 1371 1372<h3>1.8.3: Jan 5 2000</h3> 1373<ul> 1374 <li>a Push interface for the XML and HTML parsers</li> 1375 <li>a shell-like interface to the document tree (try tester --shell :-)</li> 1376 <li>lots of bug fixes and improvement added over XMas holidays</li> 1377 <li>fixed the DTD parsing code to work with the xhtml DTD</li> 1378 <li>added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()</li> 1379 <li>Fixed bugs in xmlNewNs()</li> 1380 <li>External entity loading code has been revamped, now it uses 1381 xmlLoadExternalEntity(), some fix on entities processing were added</li> 1382 <li>cleaned up WIN32 includes of socket stuff</li> 1383</ul> 1384 1385<h3>1.8.2: Dec 21 1999</h3> 1386<ul> 1387 <li>I got another problem with includes and C++, I hope this issue is fixed 1388 for good this time</li> 1389 <li>Added a few tree modification functions: xmlReplaceNode, 1390 xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and 1391 xmlDocSetRootElement</li> 1392 <li>Tried to improve the HTML output with help from <a 1393 href="mailto:clahey@umich.edu">Chris Lahey</a></li> 1394</ul> 1395 1396<h3>1.8.1: Dec 18 1999</h3> 1397<ul> 1398 <li>various patches to avoid troubles when using libxml with C++ compilers 1399 the "namespace" keyword and C escaping in include files</li> 1400 <li>a problem in one of the core macros IS_CHAR was corrected</li> 1401 <li>fixed a bug introduced in 1.8.0 breaking default namespace processing, 1402 and more specifically the Dia application</li> 1403 <li>fixed a posteriori validation (validation after parsing, or by using a 1404 Dtd not specified in the original document)</li> 1405 <li>fixed a bug in</li> 1406</ul> 1407 1408<h3>1.8.0: Dec 12 1999</h3> 1409<ul> 1410 <li>cleanup, especially memory wise</li> 1411 <li>the parser should be more reliable, especially the HTML one, it should 1412 not crash, whatever the input !</li> 1413 <li>Integrated various patches, especially a speedup improvement for large 1414 dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>, 1415 configure with --with-buffers to enable them.</li> 1416 <li>attribute normalization, oops should have been added long ago !</li> 1417 <li>attributes defaulted from DTDs should be available, xmlSetProp() now 1418 does entities escaping by default.</li> 1419</ul> 1420 1421<h3>1.7.4: Oct 25 1999</h3> 1422<ul> 1423 <li>Lots of HTML improvement</li> 1424 <li>Fixed some errors when saving both XML and HTML</li> 1425 <li>More examples, the regression tests should now look clean</li> 1426 <li>Fixed a bug with contiguous charref</li> 1427</ul> 1428 1429<h3>1.7.3: Sep 29 1999</h3> 1430<ul> 1431 <li>portability problems fixed</li> 1432 <li>snprintf was used unconditionally, leading to link problems on system 1433 were it's not available, fixed</li> 1434</ul> 1435 1436<h3>1.7.1: Sep 24 1999</h3> 1437<ul> 1438 <li>The basic type for strings manipulated by libxml has been renamed in 1439 1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason 1440 is that CHAR was conflicting with a predefined type on Windows. However 1441 on non WIN32 environment, compatibility is provided by the way of a 1442 <strong>#define </strong>.</li> 1443 <li>Changed another error : the use of a structure field called errno, and 1444 leading to troubles on platforms where it's a macro</li> 1445</ul> 1446 1447<h3>1.7.0: Sep 23 1999</h3> 1448<ul> 1449 <li>Added the ability to fetch remote DTD or parsed entities, see the <a 1450 href="html/libxml-nanohttp.html">nanohttp</a> module.</li> 1451 <li>Added an errno to report errors by another mean than a simple printf 1452 like callback</li> 1453 <li>Finished ID/IDREF support and checking when validation</li> 1454 <li>Serious memory leaks fixed (there is now a <a 1455 href="html/libxml-xmlmemory.html">memory wrapper</a> module)</li> 1456 <li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a> 1457 implementation</li> 1458 <li>Added an HTML parser front-end</li> 1459</ul> 1460 1461<h2><a name="XML">XML</a></h2> 1462 1463<p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for 1464markup-based structured documents. Here is <a name="example">an example XML 1465document</a>:</p> 1466<pre><?xml version="1.0"?> 1467<EXAMPLE prop1="gnome is great" prop2="&amp; linux too"> 1468 <head> 1469 <title>Welcome to Gnome</title> 1470 </head> 1471 <chapter> 1472 <title>The Linux adventure</title> 1473 <p>bla bla bla ...</p> 1474 <image href="linus.gif"/> 1475 <p>...</p> 1476 </chapter> 1477</EXAMPLE></pre> 1478 1479<p>The first line specifies that it is an XML document and gives useful 1480information about its encoding. Then the rest of the document is a text 1481format whose structure is specified by tags between brackets. <strong>Each 1482tag opened has to be closed</strong>. XML is pedantic about this. However, if 1483a tag is empty (no content), a single tag can serve as both the opening and 1484closing tag if it ends with <code>/></code> rather than with 1485<code>></code>. Note that, for example, the image tag has no content (just 1486an attribute) and is closed by ending the tag with <code>/></code>.</p> 1487 1488<p>XML can be applied successfully to a wide range of tasks, ranging from 1489long term structured document maintenance (where it follows the steps of 1490SGML) to simple data encoding mechanisms like configuration file formatting 1491(glade), spreadsheets (gnumeric), or even shorter lived documents such as 1492WebDAV where it is used to encode remote calls between a client and a 1493server.</p> 1494 1495<h2><a name="XSLT">XSLT</a></h2> 1496 1497<p>Check <a href="http://xmlsoft.org/XSLT">the separate libxslt page</a></p> 1498 1499<p><a href="http://www.w3.org/TR/xslt">XSL Transformations</a>, is a 1500language for transforming XML documents into other XML documents (or 1501HTML/textual output).</p> 1502 1503<p>A separate library called libxslt is being developed on top of libxml2. 1504This module "libxslt" too can be found in the Gnome CVS base.</p> 1505 1506<p>You can check the <a 1507href="http://cvs.gnome.org/lxr/source/libxslt/FEATURES">features</a> 1508supported and the progresses on the <a 1509href="http://cvs.gnome.org/lxr/source/libxslt/ChangeLog" 1510name="Changelog">Changelog</a>.</p> 1511 1512<h2><a name="Python">Python and bindings</a></h2> 1513 1514<p>There are a number of language bindings and wrappers available for 1515libxml2, the list below is not exhaustive. Please contact the <a 1516href="http://mail.gnome.org/mailman/listinfo/xml-bindings">xml-bindings@gnome.org</a> 1517(<a href="http://mail.gnome.org/archives/xml-bindings/">archives</a>) in 1518order to get updates to this list or to discuss the specific topic of libxml2 1519or libxslt wrappers or bindings:</p> 1520<ul> 1521 <li><a href="http://libxmlplusplus.sourceforge.net/">Libxml++</a> seems the 1522 most up-to-date C++ bindings for libxml2, check the <a 1523 href="http://libxmlplusplus.sourceforge.net/reference/html/hierarchy.html">documentation</a> 1524 and the <a 1525 href="http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/libxmlplusplus/libxml%2b%2b/examples/">examples</a>.</li> 1526 <li>There is another <a href="http://libgdome-cpp.berlios.de/">C++ wrapper 1527 based on the gdome2 bindings</a> maintained by Tobias Peters.</li> 1528 <li>and a third C++ wrapper by Peter Jones <pjones@pmade.org> 1529 <p>Website: <a 1530 href="http://pmade.org/pjones/software/xmlwrapp/">http://pmade.org/pjones/software/xmlwrapp/</a></p> 1531 </li> 1532 <li><a 1533 href="http://mail.gnome.org/archives/xml/2001-March/msg00014.html">Matt 1534 Sergeant</a> developed <a 1535 href="http://axkit.org/download/">XML::LibXSLT</a>, a Perl wrapper for 1536 libxml2/libxslt as part of the <a href="http://axkit.com/">AxKit XML 1537 application server</a>.</li> 1538 <li><a href="mailto:dkuhlman@cutter.rexx.com">Dave Kuhlman</a> provides an 1539 earlier version of the libxml/libxslt <a 1540 href="http://www.rexx.com/~dkuhlman">wrappers for Python</a>.</li> 1541 <li>Gopal.V and Peter Minten develop <a 1542 href="http://savannah.gnu.org/projects/libxmlsharp">libxml#</a>, a set of 1543 C# libxml2 bindings.</li> 1544 <li>Petr Kozelka provides <a 1545 href="http://sourceforge.net/projects/libxml2-pas">Pascal units to glue 1546 libxml2</a> with Kylix, Delphi and other Pascal compilers.</li> 1547 <li>Uwe Fechner also provides <a 1548 href="http://sourceforge.net/projects/idom2-pas/">idom2</a>, a DOM2 1549 implementation for Kylix2/D5/D6 from Borland.</li> 1550 <li>Wai-Sun "Squidster" Chia provides <a 1551 href="http://www.rubycolor.org/arc/redist/">bindings for Ruby</a> and 1552 libxml2 bindings are also available in Ruby through the <a 1553 href="http://libgdome-ruby.berlios.de/">libgdome-ruby</a> module 1554 maintained by Tobias Peters.</li> 1555 <li>Steve Ball and contributors maintains <a 1556 href="http://tclxml.sourceforge.net/">libxml2 and libxslt bindings for 1557 Tcl</a>.</li> 1558 <li>There is support for libxml2 in the DOM module of PHP.</li> 1559</ul> 1560 1561<p>The distribution includes a set of Python bindings, which are guaranteed 1562to be maintained as part of the library in the future, though the Python 1563interface have not yet reached the maturity of the C API.</p> 1564 1565<p>To install the Python bindings there are 2 options:</p> 1566<ul> 1567 <li>If you use an RPM based distribution, simply install the <a 1568 href="http://rpmfind.net/linux/rpm2html/search.php?query=libxml2-python">libxml2-python 1569 RPM</a> (and if needed the <a 1570 href="http://rpmfind.net/linux/rpm2html/search.php?query=libxslt-python">libxslt-python 1571 RPM</a>).</li> 1572 <li>Otherwise use the <a href="ftp://xmlsoft.org/python/">libxml2-python 1573 module distribution</a> corresponding to your installed version of 1574 libxml2 and libxslt. Note that to install it you will need both libxml2 1575 and libxslt installed and run "python setup.py build install" in the 1576 module tree.</li> 1577</ul> 1578 1579<p>The distribution includes a set of examples and regression tests for the 1580python bindings in the <code>python/tests</code> directory. Here are some 1581excerpts from those tests:</p> 1582 1583<h3>tst.py:</h3> 1584 1585<p>This is a basic test of the file interface and DOM navigation:</p> 1586<pre>import libxml2 1587 1588doc = libxml2.parseFile("tst.xml") 1589if doc.name != "tst.xml": 1590 print "doc.name failed" 1591 sys.exit(1) 1592root = doc.children 1593if root.name != "doc": 1594 print "root.name failed" 1595 sys.exit(1) 1596child = root.children 1597if child.name != "foo": 1598 print "child.name failed" 1599 sys.exit(1) 1600doc.freeDoc()</pre> 1601 1602<p>The Python module is called libxml2; parseFile is the equivalent of 1603xmlParseFile (most of the bindings are automatically generated, and the xml 1604prefix is removed and the casing convention are kept). All node seen at the 1605binding level share the same subset of accessors:</p> 1606<ul> 1607 <li><code>name</code> : returns the node name</li> 1608 <li><code>type</code> : returns a string indicating the node type</li> 1609 <li><code>content</code> : returns the content of the node, it is based on 1610 xmlNodeGetContent() and hence is recursive.</li> 1611 <li><code>parent</code> , <code>children</code>, <code>last</code>, 1612 <code>next</code>, <code>prev</code>, <code>doc</code>, 1613 <code>properties</code>: pointing to the associated element in the tree, 1614 those may return None in case no such link exists.</li> 1615</ul> 1616 1617<p>Also note the need to explicitly deallocate documents with freeDoc() . 1618Reference counting for libxml2 trees would need quite a lot of work to 1619function properly, and rather than risk memory leaks if not implemented 1620correctly it sounds safer to have an explicit function to free a tree. The 1621wrapper python objects like doc, root or child are them automatically garbage 1622collected.</p> 1623 1624<h3>validate.py:</h3> 1625 1626<p>This test check the validation interfaces and redirection of error 1627messages:</p> 1628<pre>import libxml2 1629 1630#deactivate error messages from the validation 1631def noerr(ctx, str): 1632 pass 1633 1634libxml2.registerErrorHandler(noerr, None) 1635 1636ctxt = libxml2.createFileParserCtxt("invalid.xml") 1637ctxt.validate(1) 1638ctxt.parseDocument() 1639doc = ctxt.doc() 1640valid = ctxt.isValid() 1641doc.freeDoc() 1642if valid != 0: 1643 print "validity check failed"</pre> 1644 1645<p>The first thing to notice is the call to registerErrorHandler(), it 1646defines a new error handler global to the library. It is used to avoid seeing 1647the error messages when trying to validate the invalid document.</p> 1648 1649<p>The main interest of that test is the creation of a parser context with 1650createFileParserCtxt() and how the behaviour can be changed before calling 1651parseDocument() . Similarly the informations resulting from the parsing phase 1652are also available using context methods.</p> 1653 1654<p>Contexts like nodes are defined as class and the libxml2 wrappers maps the 1655C function interfaces in terms of objects method as much as possible. The 1656best to get a complete view of what methods are supported is to look at the 1657libxml2.py module containing all the wrappers.</p> 1658 1659<h3>push.py:</h3> 1660 1661<p>This test show how to activate the push parser interface:</p> 1662<pre>import libxml2 1663 1664ctxt = libxml2.createPushParser(None, "<foo", 4, "test.xml") 1665ctxt.parseChunk("/>", 2, 1) 1666doc = ctxt.doc() 1667 1668doc.freeDoc()</pre> 1669 1670<p>The context is created with a special call based on the 1671xmlCreatePushParser() from the C library. The first argument is an optional 1672SAX callback object, then the initial set of data, the length and the name of 1673the resource in case URI-References need to be computed by the parser.</p> 1674 1675<p>Then the data are pushed using the parseChunk() method, the last call 1676setting the third argument terminate to 1.</p> 1677 1678<h3>pushSAX.py:</h3> 1679 1680<p>this test show the use of the event based parsing interfaces. In this case 1681the parser does not build a document, but provides callback information as 1682the parser makes progresses analyzing the data being provided:</p> 1683<pre>import libxml2 1684log = "" 1685 1686class callback: 1687 def startDocument(self): 1688 global log 1689 log = log + "startDocument:" 1690 1691 def endDocument(self): 1692 global log 1693 log = log + "endDocument:" 1694 1695 def startElement(self, tag, attrs): 1696 global log 1697 log = log + "startElement %s %s:" % (tag, attrs) 1698 1699 def endElement(self, tag): 1700 global log 1701 log = log + "endElement %s:" % (tag) 1702 1703 def characters(self, data): 1704 global log 1705 log = log + "characters: %s:" % (data) 1706 1707 def warning(self, msg): 1708 global log 1709 log = log + "warning: %s:" % (msg) 1710 1711 def error(self, msg): 1712 global log 1713 log = log + "error: %s:" % (msg) 1714 1715 def fatalError(self, msg): 1716 global log 1717 log = log + "fatalError: %s:" % (msg) 1718 1719handler = callback() 1720 1721ctxt = libxml2.createPushParser(handler, "<foo", 4, "test.xml") 1722chunk = " url='tst'>b" 1723ctxt.parseChunk(chunk, len(chunk), 0) 1724chunk = "ar</foo>" 1725ctxt.parseChunk(chunk, len(chunk), 1) 1726 1727reference = "startDocument:startElement foo {'url': 'tst'}:" + \ 1728 "characters: bar:endElement foo:endDocument:" 1729if log != reference: 1730 print "Error got: %s" % log 1731 print "Expected: %s" % reference</pre> 1732 1733<p>The key object in that test is the handler, it provides a number of entry 1734points which can be called by the parser as it makes progresses to indicate 1735the information set obtained. The full set of callback is larger than what 1736the callback class in that specific example implements (see the SAX 1737definition for a complete list). The wrapper will only call those supplied by 1738the object when activated. The startElement receives the names of the element 1739and a dictionary containing the attributes carried by this element.</p> 1740 1741<p>Also note that the reference string generated from the callback shows a 1742single character call even though the string "bar" is passed to the parser 1743from 2 different call to parseChunk()</p> 1744 1745<h3>xpath.py:</h3> 1746 1747<p>This is a basic test of XPath wrappers support</p> 1748<pre>import libxml2 1749 1750doc = libxml2.parseFile("tst.xml") 1751ctxt = doc.xpathNewContext() 1752res = ctxt.xpathEval("//*") 1753if len(res) != 2: 1754 print "xpath query: wrong node set size" 1755 sys.exit(1) 1756if res[0].name != "doc" or res[1].name != "foo": 1757 print "xpath query: wrong node set value" 1758 sys.exit(1) 1759doc.freeDoc() 1760ctxt.xpathFreeContext()</pre> 1761 1762<p>This test parses a file, then create an XPath context to evaluate XPath 1763expression on it. The xpathEval() method execute an XPath query and returns 1764the result mapped in a Python way. String and numbers are natively converted, 1765and node sets are returned as a tuple of libxml2 Python nodes wrappers. Like 1766the document, the XPath context need to be freed explicitly, also not that 1767the result of the XPath query may point back to the document tree and hence 1768the document must be freed after the result of the query is used.</p> 1769 1770<h3>xpathext.py:</h3> 1771 1772<p>This test shows how to extend the XPath engine with functions written in 1773python:</p> 1774<pre>import libxml2 1775 1776def foo(ctx, x): 1777 return x + 1 1778 1779doc = libxml2.parseFile("tst.xml") 1780ctxt = doc.xpathNewContext() 1781libxml2.registerXPathFunction(ctxt._o, "foo", None, foo) 1782res = ctxt.xpathEval("foo(1)") 1783if res != 2: 1784 print "xpath extension failure" 1785doc.freeDoc() 1786ctxt.xpathFreeContext()</pre> 1787 1788<p>Note how the extension function is registered with the context (but that 1789part is not yet finalized, this may change slightly in the future).</p> 1790 1791<h3>tstxpath.py:</h3> 1792 1793<p>This test is similar to the previous one but shows how the extension 1794function can access the XPath evaluation context:</p> 1795<pre>def foo(ctx, x): 1796 global called 1797 1798 # 1799 # test that access to the XPath evaluation contexts 1800 # 1801 pctxt = libxml2.xpathParserContext(_obj=ctx) 1802 ctxt = pctxt.context() 1803 called = ctxt.function() 1804 return x + 1</pre> 1805 1806<p>All the interfaces around the XPath parser(or rather evaluation) context 1807are not finalized, but it should be sufficient to do contextual work at the 1808evaluation point.</p> 1809 1810<h3>Memory debugging:</h3> 1811 1812<p>last but not least, all tests starts with the following prologue:</p> 1813<pre>#memory debug specific 1814libxml2.debugMemory(1)</pre> 1815 1816<p>and ends with the following epilogue:</p> 1817<pre>#memory debug specific 1818libxml2.cleanupParser() 1819if libxml2.debugMemory(1) == 0: 1820 print "OK" 1821else: 1822 print "Memory leak %d bytes" % (libxml2.debugMemory(1)) 1823 libxml2.dumpMemory()</pre> 1824 1825<p>Those activate the memory debugging interface of libxml2 where all 1826allocated block in the library are tracked. The prologue then cleans up the 1827library state and checks that all allocated memory has been freed. If not it 1828calls dumpMemory() which saves that list in a <code>.memdump</code> file.</p> 1829 1830<h2><a name="architecture">libxml architecture</a></h2> 1831 1832<p>Libxml is made of multiple components; some of them are optional, and most 1833of the block interfaces are public. The main components are:</p> 1834<ul> 1835 <li>an Input/Output layer</li> 1836 <li>FTP and HTTP client layers (optional)</li> 1837 <li>an Internationalization layer managing the encodings support</li> 1838 <li>a URI module</li> 1839 <li>the XML parser and its basic SAX interface</li> 1840 <li>an HTML parser using the same SAX interface (optional)</li> 1841 <li>a SAX tree module to build an in-memory DOM representation</li> 1842 <li>a tree module to manipulate the DOM representation</li> 1843 <li>a validation module using the DOM representation (optional)</li> 1844 <li>an XPath module for global lookup in a DOM representation 1845 (optional)</li> 1846 <li>a debug module (optional)</li> 1847</ul> 1848 1849<p>Graphically this gives the following:</p> 1850 1851<p><img src="libxml.gif" alt="a graphical view of the various"></p> 1852 1853<p></p> 1854 1855<h2><a name="tree">The tree output</a></h2> 1856 1857<p>The parser returns a tree built during the document analysis. The value 1858returned is an <strong>xmlDocPtr</strong> (i.e., a pointer to an 1859<strong>xmlDoc</strong> structure). This structure contains information such 1860as the file name, the document type, and a <strong>children</strong> pointer 1861which is the root of the document (or more exactly the first child under the 1862root which is the document). The tree is made of <strong>xmlNode</strong>s, 1863chained in double-linked lists of siblings and with a children<->parent 1864relationship. An xmlNode can also carry properties (a chain of xmlAttr 1865structures). An attribute may have a value which is a list of TEXT or 1866ENTITY_REF nodes.</p> 1867 1868<p>Here is an example (erroneous with respect to the XML spec since there 1869should be only one ELEMENT under the root):</p> 1870 1871<p><img src="structure.gif" alt=" structure.gif "></p> 1872 1873<p>In the source package there is a small program (not installed by default) 1874called <strong>xmllint</strong> which parses XML files given as argument and 1875prints them back as parsed. This is useful for detecting errors both in XML 1876code and in the XML parser itself. It has an option <strong>--debug</strong> 1877which prints the actual in-memory structure of the document; here is the 1878result with the <a href="#example">example</a> given before:</p> 1879<pre>DOCUMENT 1880version=1.0 1881standalone=true 1882 ELEMENT EXAMPLE 1883 ATTRIBUTE prop1 1884 TEXT 1885 content=gnome is great 1886 ATTRIBUTE prop2 1887 ENTITY_REF 1888 TEXT 1889 content= linux too 1890 ELEMENT head 1891 ELEMENT title 1892 TEXT 1893 content=Welcome to Gnome 1894 ELEMENT chapter 1895 ELEMENT title 1896 TEXT 1897 content=The Linux adventure 1898 ELEMENT p 1899 TEXT 1900 content=bla bla bla ... 1901 ELEMENT image 1902 ATTRIBUTE href 1903 TEXT 1904 content=linus.gif 1905 ELEMENT p 1906 TEXT 1907 content=...</pre> 1908 1909<p>This should be useful for learning the internal representation model.</p> 1910 1911<h2><a name="interface">The SAX interface</a></h2> 1912 1913<p>Sometimes the DOM tree output is just too large to fit reasonably into 1914memory. In that case (and if you don't expect to save back the XML document 1915loaded using libxml), it's better to use the SAX interface of libxml. SAX is 1916a <strong>callback-based interface</strong> to the parser. Before parsing, 1917the application layer registers a customized set of callbacks which are 1918called by the library as it progresses through the XML input.</p> 1919 1920<p>To get more detailed step-by-step guidance on using the SAX interface of 1921libxml, see the <a 1922href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">nice 1923documentation</a>.written by <a href="mailto:james@daa.com.au">James 1924Henstridge</a>.</p> 1925 1926<p>You can debug the SAX behaviour by using the <strong>testSAX</strong> 1927program located in the gnome-xml module (it's usually not shipped in the 1928binary packages of libxml, but you can find it in the tar source 1929distribution). Here is the sequence of callbacks that would be reported by 1930testSAX when parsing the example XML document shown earlier:</p> 1931<pre>SAX.setDocumentLocator() 1932SAX.startDocument() 1933SAX.getEntity(amp) 1934SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp; linux too') 1935SAX.characters( , 3) 1936SAX.startElement(head) 1937SAX.characters( , 4) 1938SAX.startElement(title) 1939SAX.characters(Welcome to Gnome, 16) 1940SAX.endElement(title) 1941SAX.characters( , 3) 1942SAX.endElement(head) 1943SAX.characters( , 3) 1944SAX.startElement(chapter) 1945SAX.characters( , 4) 1946SAX.startElement(title) 1947SAX.characters(The Linux adventure, 19) 1948SAX.endElement(title) 1949SAX.characters( , 4) 1950SAX.startElement(p) 1951SAX.characters(bla bla bla ..., 15) 1952SAX.endElement(p) 1953SAX.characters( , 4) 1954SAX.startElement(image, href='linus.gif') 1955SAX.endElement(image) 1956SAX.characters( , 4) 1957SAX.startElement(p) 1958SAX.characters(..., 3) 1959SAX.endElement(p) 1960SAX.characters( , 3) 1961SAX.endElement(chapter) 1962SAX.characters( , 1) 1963SAX.endElement(EXAMPLE) 1964SAX.endDocument()</pre> 1965 1966<p>Most of the other interfaces of libxml are based on the DOM tree-building 1967facility, so nearly everything up to the end of this document presupposes the 1968use of the standard DOM tree build. Note that the DOM tree itself is built by 1969a set of registered default callbacks, without internal specific 1970interface.</p> 1971 1972<h2><a name="Validation">Validation & DTDs</a></h2> 1973 1974<p>Table of Content:</p> 1975<ol> 1976 <li><a href="#General5">General overview</a></li> 1977 <li><a href="#definition">The definition</a></li> 1978 <li><a href="#Simple">Simple rules</a> 1979 <ol> 1980 <li><a href="#reference">How to reference a DTD from a document</a></li> 1981 <li><a href="#Declaring">Declaring elements</a></li> 1982 <li><a href="#Declaring1">Declaring attributes</a></li> 1983 </ol> 1984 </li> 1985 <li><a href="#Some">Some examples</a></li> 1986 <li><a href="#validate">How to validate</a></li> 1987 <li><a href="#Other">Other resources</a></li> 1988</ol> 1989 1990<h3><a name="General5">General overview</a></h3> 1991 1992<p>Well what is validation and what is a DTD ?</p> 1993 1994<p>DTD is the acronym for Document Type Definition. This is a description of 1995the content for a family of XML files. This is part of the XML 1.0 1996specification, and allows one to describe and verify that a given document 1997instance conforms to the set of rules detailing its structure and content.</p> 1998 1999<p>Validation is the process of checking a document against a DTD (more 2000generally against a set of construction rules).</p> 2001 2002<p>The validation process and building DTDs are the two most difficult parts 2003of the XML life cycle. Briefly a DTD defines all the possible elements to be 2004found within your document, what is the formal shape of your document tree 2005(by defining the allowed content of an element; either text, a regular 2006expression for the allowed list of children, or mixed content i.e. both text 2007and children). The DTD also defines the valid attributes for all elements and 2008the types of those attributes.</p> 2009 2010<h3><a name="definition1">The definition</a></h3> 2011 2012<p>The <a href="http://www.w3.org/TR/REC-xml">W3C XML Recommendation</a> (<a 2013href="http://www.xml.com/axml/axml.html">Tim Bray's annotated version of 2014Rev1</a>):</p> 2015<ul> 2016 <li><a href="http://www.w3.org/TR/REC-xml#elemdecls">Declaring 2017 elements</a></li> 2018 <li><a href="http://www.w3.org/TR/REC-xml#attdecls">Declaring 2019 attributes</a></li> 2020</ul> 2021 2022<p>(unfortunately) all this is inherited from the SGML world, the syntax is 2023ancient...</p> 2024 2025<h3><a name="Simple1">Simple rules</a></h3> 2026 2027<p>Writing DTDs can be done in many ways. The rules to build them if you need 2028something permanent or something which can evolve over time can be radically 2029different. Really complex DTDs like DocBook ones are flexible but quite 2030harder to design. I will just focus on DTDs for a formats with a fixed simple 2031structure. It is just a set of basic rules, and definitely not exhaustive nor 2032usable for complex DTD design.</p> 2033 2034<h4><a name="reference1">How to reference a DTD from a document</a>:</h4> 2035 2036<p>Assuming the top element of the document is <code>spec</code> and the dtd 2037is placed in the file <code>mydtd</code> in the subdirectory 2038<code>dtds</code> of the directory from where the document were loaded:</p> 2039 2040<p><code><!DOCTYPE spec SYSTEM "dtds/mydtd"></code></p> 2041 2042<p>Notes:</p> 2043<ul> 2044 <li>The system string is actually an URI-Reference (as defined in <a 2045 href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>) so you can use a 2046 full URL string indicating the location of your DTD on the Web. This is a 2047 really good thing to do if you want others to validate your document.</li> 2048 <li>It is also possible to associate a <code>PUBLIC</code> identifier (a 2049 magic string) so that the DTD is looked up in catalogs on the client side 2050 without having to locate it on the web.</li> 2051 <li>A DTD contains a set of element and attribute declarations, but they 2052 don't define what the root of the document should be. This is explicitly 2053 told to the parser/validator as the first element of the 2054 <code>DOCTYPE</code> declaration.</li> 2055</ul> 2056 2057<h4><a name="Declaring2">Declaring elements</a>:</h4> 2058 2059<p>The following declares an element <code>spec</code>:</p> 2060 2061<p><code><!ELEMENT spec (front, body, back?)></code></p> 2062 2063<p>It also expresses that the spec element contains one <code>front</code>, 2064one <code>body</code> and one optional <code>back</code> children elements in 2065this order. The declaration of one element of the structure and its content 2066are done in a single declaration. Similarly the following declares 2067<code>div1</code> elements:</p> 2068 2069<p><code><!ELEMENT div1 (head, (p | list | note)*, div2?)></code></p> 2070 2071<p>which means div1 contains one <code>head</code> then a series of optional 2072<code>p</code>, <code>list</code>s and <code>note</code>s and then an 2073optional <code>div2</code>. And last but not least an element can contain 2074text:</p> 2075 2076<p><code><!ELEMENT b (#PCDATA)></code></p> 2077 2078<p><code>b</code> contains text or being of mixed content (text and elements 2079in no particular order):</p> 2080 2081<p><code><!ELEMENT p (#PCDATA|a|ul|b|i|em)*></code></p> 2082 2083<p><code>p </code>can contain text or <code>a</code>, <code>ul</code>, 2084<code>b</code>, <code>i </code>or <code>em</code> elements in no particular 2085order.</p> 2086 2087<h4><a name="Declaring1">Declaring attributes</a>:</h4> 2088 2089<p>Again the attributes declaration includes their content definition:</p> 2090 2091<p><code><!ATTLIST termdef name CDATA #IMPLIED></code></p> 2092 2093<p>means that the element <code>termdef</code> can have a <code>name</code> 2094attribute containing text (<code>CDATA</code>) and which is optional 2095(<code>#IMPLIED</code>). The attribute value can also be defined within a 2096set:</p> 2097 2098<p><code><!ATTLIST list type (bullets|ordered|glossary) 2099"ordered"></code></p> 2100 2101<p>means <code>list</code> element have a <code>type</code> attribute with 3 2102allowed values "bullets", "ordered" or "glossary" and which default to 2103"ordered" if the attribute is not explicitly specified.</p> 2104 2105<p>The content type of an attribute can be text (<code>CDATA</code>), 2106anchor/reference/references 2107(<code>ID</code>/<code>IDREF</code>/<code>IDREFS</code>), entity(ies) 2108(<code>ENTITY</code>/<code>ENTITIES</code>) or name(s) 2109(<code>NMTOKEN</code>/<code>NMTOKENS</code>). The following defines that a 2110<code>chapter</code> element can have an optional <code>id</code> attribute 2111of type <code>ID</code>, usable for reference from attribute of type 2112IDREF:</p> 2113 2114<p><code><!ATTLIST chapter id ID #IMPLIED></code></p> 2115 2116<p>The last value of an attribute definition can be <code>#REQUIRED 2117</code>meaning that the attribute has to be given, <code>#IMPLIED</code> 2118meaning that it is optional, or the default value (possibly prefixed by 2119<code>#FIXED</code> if it is the only allowed).</p> 2120 2121<p>Notes:</p> 2122<ul> 2123 <li>Usually the attributes pertaining to a given element are declared in a 2124 single expression, but it is just a convention adopted by a lot of DTD 2125 writers: 2126 <pre><!ATTLIST termdef 2127 id ID #REQUIRED 2128 name CDATA #IMPLIED></pre> 2129 <p>The previous construct defines both <code>id</code> and 2130 <code>name</code> attributes for the element <code>termdef</code>.</p> 2131 </li> 2132</ul> 2133 2134<h3><a name="Some1">Some examples</a></h3> 2135 2136<p>The directory <code>test/valid/dtds/</code> in the libxml distribution 2137contains some complex DTD examples. The example in the file 2138<code>test/valid/dia.xml</code> shows an XML file where the simple DTD is 2139directly included within the document.</p> 2140 2141<h3><a name="validate1">How to validate</a></h3> 2142 2143<p>The simplest way is to use the xmllint program included with libxml. The 2144<code>--valid</code> option turns-on validation of the files given as input. 2145For example the following validates a copy of the first revision of the XML 21461.0 specification:</p> 2147 2148<p><code>xmllint --valid --noout test/valid/REC-xml-19980210.xml</code></p> 2149 2150<p>the -- noout is used to disable output of the resulting tree.</p> 2151 2152<p>The <code>--dtdvalid dtd</code> allows validation of the document(s) 2153against a given DTD.</p> 2154 2155<p>Libxml exports an API to handle DTDs and validation, check the <a 2156href="http://xmlsoft.org/html/libxml-valid.html">associated 2157description</a>.</p> 2158 2159<h3><a name="Other1">Other resources</a></h3> 2160 2161<p>DTDs are as old as SGML. So there may be a number of examples on-line, I 2162will just list one for now, others pointers welcome:</p> 2163<ul> 2164 <li><a href="http://www.xml101.com:8081/dtd/">XML-101 DTD</a></li> 2165</ul> 2166 2167<p>I suggest looking at the examples found under test/valid/dtd and any of 2168the large number of books available on XML. The dia example in test/valid 2169should be both simple and complete enough to allow you to build your own.</p> 2170 2171<p></p> 2172 2173<h2><a name="Memory">Memory Management</a></h2> 2174 2175<p>Table of Content:</p> 2176<ol> 2177 <li><a href="#General3">General overview</a></li> 2178 <li><a href="#setting">Setting libxml set of memory routines</a></li> 2179 <li><a href="#cleanup">Cleaning up after parsing</a></li> 2180 <li><a href="#Debugging">Debugging routines</a></li> 2181 <li><a href="#General4">General memory requirements</a></li> 2182</ol> 2183 2184<h3><a name="General3">General overview</a></h3> 2185 2186<p>The module <code><a 2187href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlmemory.h</a></code> 2188provides the interfaces to the libxml memory system:</p> 2189<ul> 2190 <li>libxml does not use the libc memory allocator directly but xmlFree(), 2191 xmlMalloc() and xmlRealloc()</li> 2192 <li>those routines can be reallocated to a specific set of routine, by 2193 default the libc ones i.e. free(), malloc() and realloc()</li> 2194 <li>the xmlmemory.c module includes a set of debugging routine</li> 2195</ul> 2196 2197<h3><a name="setting">Setting libxml set of memory routines</a></h3> 2198 2199<p>It is sometimes useful to not use the default memory allocator, either for 2200debugging, analysis or to implement a specific behaviour on memory management 2201(like on embedded systems). Two function calls are available to do so:</p> 2202<ul> 2203 <li><a href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemGet 2204 ()</a> which return the current set of functions in use by the parser</li> 2205 <li><a 2206 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemSetup()</a> 2207 which allow to set up a new set of memory allocation functions</li> 2208</ul> 2209 2210<p>Of course a call to xmlMemSetup() should probably be done before calling 2211any other libxml routines (unless you are sure your allocations routines are 2212compatibles).</p> 2213 2214<h3><a name="cleanup">Cleaning up after parsing</a></h3> 2215 2216<p>Libxml is not stateless, there is a few set of memory structures needing 2217allocation before the parser is fully functional (some encoding structures 2218for example). This also mean that once parsing is finished there is a tiny 2219amount of memory (a few hundred bytes) which can be recollected if you don't 2220reuse the parser immediately:</p> 2221<ul> 2222 <li><a href="http://xmlsoft.org/html/libxml-parser.html">xmlCleanupParser 2223 ()</a> is a centralized routine to free the parsing states. Note that it 2224 won't deallocate any produced tree if any (use the xmlFreeDoc() and 2225 related routines for this).</li> 2226 <li><a href="http://xmlsoft.org/html/libxml-parser.html">xmlInitParser 2227 ()</a> is the dual routine allowing to preallocate the parsing state 2228 which can be useful for example to avoid initialization reentrancy 2229 problems when using libxml in multithreaded applications</li> 2230</ul> 2231 2232<p>Generally xmlCleanupParser() is safe, if needed the state will be rebuild 2233at the next invocation of parser routines, but be careful of the consequences 2234in multithreaded applications.</p> 2235 2236<h3><a name="Debugging">Debugging routines</a></h3> 2237 2238<p>When configured using --with-mem-debug flag (off by default), libxml uses 2239a set of memory allocation debugging routines keeping track of all allocated 2240blocks and the location in the code where the routine was called. A couple of 2241other debugging routines allow to dump the memory allocated infos to a file 2242or call a specific routine when a given block number is allocated:</p> 2243<ul> 2244 <li><a 2245 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMallocLoc()</a> 2246 <a 2247 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlReallocLoc()</a> 2248 and <a 2249 href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemStrdupLoc()</a> 2250 are the memory debugging replacement allocation routines</li> 2251 <li><a href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlMemoryDump 2252 ()</a> dumps all the informations about the allocated memory block lefts 2253 in the <code>.memdump</code> file</li> 2254</ul> 2255 2256<p>When developing libxml memory debug is enabled, the tests programs call 2257xmlMemoryDump () and the "make test" regression tests will check for any 2258memory leak during the full regression test sequence, this helps a lot 2259ensuring that libxml does not leak memory and bullet proof memory 2260allocations use (some libc implementations are known to be far too permissive 2261resulting in major portability problems!).</p> 2262 2263<p>If the .memdump reports a leak, it displays the allocation function and 2264also tries to give some informations about the content and structure of the 2265allocated blocks left. This is sufficient in most cases to find the culprit, 2266but not always. Assuming the allocation problem is reproducible, it is 2267possible to find more easily:</p> 2268<ol> 2269 <li>write down the block number xxxx not allocated</li> 2270 <li>export the environment variable XML_MEM_BREAKPOINT=xxxx , the easiest 2271 when using GDB is to simply give the command 2272 <p><code>set environment XML_MEM_BREAKPOINT xxxx</code></p> 2273 <p>before running the program.</p> 2274 </li> 2275 <li>run the program under a debugger and set a breakpoint on 2276 xmlMallocBreakpoint() a specific function called when this precise block 2277 is allocated</li> 2278 <li>when the breakpoint is reached you can then do a fine analysis of the 2279 allocation an step to see the condition resulting in the missing 2280 deallocation.</li> 2281</ol> 2282 2283<p>I used to use a commercial tool to debug libxml memory problems but after 2284noticing that it was not detecting memory leaks that simple mechanism was 2285used and proved extremely efficient until now. Lately I have also used <a 2286href="http://developer.kde.org/~sewardj/">valgrind</a> with quite some 2287success, it is tied to the i386 architecture since it works by emulating the 2288processor and instruction set, it is slow but extremely efficient, i.e. it 2289spot memory usage errors in a very precise way.</p> 2290 2291<h3><a name="General4">General memory requirements</a></h3> 2292 2293<p>How much libxml memory require ? It's hard to tell in average it depends 2294of a number of things:</p> 2295<ul> 2296 <li>the parser itself should work in a fixed amount of memory, except for 2297 information maintained about the stacks of names and entities locations. 2298 The I/O and encoding handlers will probably account for a few KBytes. 2299 This is true for both the XML and HTML parser (though the HTML parser 2300 need more state).</li> 2301 <li>If you are generating the DOM tree then memory requirements will grow 2302 nearly linear with the size of the data. In general for a balanced 2303 textual document the internal memory requirement is about 4 times the 2304 size of the UTF8 serialization of this document (example the XML-1.0 2305 recommendation is a bit more of 150KBytes and takes 650KBytes of main 2306 memory when parsed). Validation will add a amount of memory required for 2307 maintaining the external Dtd state which should be linear with the 2308 complexity of the content model defined by the Dtd</li> 2309 <li>If you don't care about the advanced features of libxml like 2310 validation, DOM, XPath or XPointer, but really need to work fixed memory 2311 requirements, then the SAX interface should be used.</li> 2312</ul> 2313 2314<p></p> 2315 2316<h2><a name="Encodings">Encodings support</a></h2> 2317 2318<p>Table of Content:</p> 2319<ol> 2320 <li><a href="encoding.html#What">What does internationalization support 2321 mean ?</a></li> 2322 <li><a href="encoding.html#internal">The internal encoding, how and 2323 why</a></li> 2324 <li><a href="encoding.html#implemente">How is it implemented ?</a></li> 2325 <li><a href="encoding.html#Default">Default supported encodings</a></li> 2326 <li><a href="encoding.html#extend">How to extend the existing 2327 support</a></li> 2328</ol> 2329 2330<h3><a name="What">What does internationalization support mean ?</a></h3> 2331 2332<p>XML was designed from the start to allow the support of any character set 2333by using Unicode. Any conformant XML parser has to support the UTF-8 and 2334UTF-16 default encodings which can both express the full unicode ranges. UTF8 2335is a variable length encoding whose greatest points are to reuse the same 2336encoding for ASCII and to save space for Western encodings, but it is a bit 2337more complex to handle in practice. UTF-16 use 2 bytes per characters (and 2338sometimes combines two pairs), it makes implementation easier, but looks a 2339bit overkill for Western languages encoding. Moreover the XML specification 2340allows document to be encoded in other encodings at the condition that they 2341are clearly labeled as such. For example the following is a wellformed XML 2342document encoded in ISO-8859 1 and using accentuated letter that we French 2343likes for both markup and content:</p> 2344<pre><?xml version="1.0" encoding="ISO-8859-1"?> 2345<tr�s>l�</tr�s></pre> 2346 2347<p>Having internationalization support in libxml means the following:</p> 2348<ul> 2349 <li>the document is properly parsed</li> 2350 <li>informations about it's encoding are saved</li> 2351 <li>it can be modified</li> 2352 <li>it can be saved in its original encoding</li> 2353 <li>it can also be saved in another encoding supported by libxml (for 2354 example straight UTF8 or even an ASCII form)</li> 2355</ul> 2356 2357<p>Another very important point is that the whole libxml API, with the 2358exception of a few routines to read with a specific encoding or save to a 2359specific encoding, is completely agnostic about the original encoding of the 2360document.</p> 2361 2362<p>It should be noted too that the HTML parser embedded in libxml now obey 2363the same rules too, the following document will be (as of 2.2.2) handled in 2364an internationalized fashion by libxml too:</p> 2365<pre><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" 2366 "http://www.w3.org/TR/REC-html40/loose.dtd"> 2367<html lang="fr"> 2368<head> 2369 <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"> 2370</head> 2371<body> 2372<p>W3C cr�e des standards pour le Web.</body> 2373</html></pre> 2374 2375<h3><a name="internal">The internal encoding, how and why</a></h3> 2376 2377<p>One of the core decision was to force all documents to be converted to a 2378default internal encoding, and that encoding to be UTF-8, here are the 2379rationale for those choices:</p> 2380<ul> 2381 <li>keeping the native encoding in the internal form would force the libxml 2382 users (or the code associated) to be fully aware of the encoding of the 2383 original document, for examples when adding a text node to a document, 2384 the content would have to be provided in the document encoding, i.e. the 2385 client code would have to check it before hand, make sure it's conformant 2386 to the encoding, etc ... Very hard in practice, though in some specific 2387 cases this may make sense.</li> 2388 <li>the second decision was which encoding. From the XML spec only UTF8 and 2389 UTF16 really makes sense as being the two only encodings for which there 2390 is mandatory support. UCS-4 (32 bits fixed size encoding) could be 2391 considered an intelligent choice too since it's a direct Unicode mapping 2392 support. I selected UTF-8 on the basis of efficiency and compatibility 2393 with surrounding software: 2394 <ul> 2395 <li>UTF-8 while a bit more complex to convert from/to (i.e. slightly 2396 more costly to import and export CPU wise) is also far more compact 2397 than UTF-16 (and UCS-4) for a majority of the documents I see it used 2398 for right now (RPM RDF catalogs, advogato data, various configuration 2399 file formats, etc.) and the key point for today's computer 2400 architecture is efficient uses of caches. If one nearly double the 2401 memory requirement to store the same amount of data, this will trash 2402 caches (main memory/external caches/internal caches) and my take is 2403 that this harms the system far more than the CPU requirements needed 2404 for the conversion to UTF-8</li> 2405 <li>Most of libxml version 1 users were using it with straight ASCII 2406 most of the time, doing the conversion with an internal encoding 2407 requiring all their code to be rewritten was a serious show-stopper 2408 for using UTF-16 or UCS-4.</li> 2409 <li>UTF-8 is being used as the de-facto internal encoding standard for 2410 related code like the <a href="http://www.pango.org/">pango</a> 2411 upcoming Gnome text widget, and a lot of Unix code (yep another place 2412 where Unix programmer base takes a different approach from Microsoft 2413 - they are using UTF-16)</li> 2414 </ul> 2415 </li> 2416</ul> 2417 2418<p>What does this mean in practice for the libxml user:</p> 2419<ul> 2420 <li>xmlChar, the libxml data type is a byte, those bytes must be assembled 2421 as UTF-8 valid strings. The proper way to terminate an xmlChar * string 2422 is simply to append 0 byte, as usual.</li> 2423 <li>One just need to make sure that when using chars outside the ASCII set, 2424 the values has been properly converted to UTF-8</li> 2425</ul> 2426 2427<h3><a name="implemente">How is it implemented ?</a></h3> 2428 2429<p>Let's describe how all this works within libxml, basically the I18N 2430(internationalization) support get triggered only during I/O operation, i.e. 2431when reading a document or saving one. Let's look first at the reading 2432sequence:</p> 2433<ol> 2434 <li>when a document is processed, we usually don't know the encoding, a 2435 simple heuristic allows to detect UTF-18 and UCS-4 from whose where the 2436 ASCII range (0-0x7F) maps with ASCII</li> 2437 <li>the xml declaration if available is parsed, including the encoding 2438 declaration. At that point, if the autodetected encoding is different 2439 from the one declared a call to xmlSwitchEncoding() is issued.</li> 2440 <li>If there is no encoding declaration, then the input has to be in either 2441 UTF-8 or UTF-16, if it is not then at some point when processing the 2442 input, the converter/checker of UTF-8 form will raise an encoding error. 2443 You may end-up with a garbled document, or no document at all ! Example: 2444 <pre>~/XML -> /xmllint err.xml 2445err.xml:1: error: Input is not proper UTF-8, indicate encoding ! 2446<tr�s>l�</tr�s> 2447 ^ 2448err.xml:1: error: Bytes: 0xE8 0x73 0x3E 0x6C 2449<tr�s>l�</tr�s> 2450 ^</pre> 2451 </li> 2452 <li>xmlSwitchEncoding() does an encoding name lookup, canonicalize it, and 2453 then search the default registered encoding converters for that encoding. 2454 If it's not within the default set and iconv() support has been compiled 2455 it, it will ask iconv for such an encoder. If this fails then the parser 2456 will report an error and stops processing: 2457 <pre>~/XML -> /xmllint err2.xml 2458err2.xml:1: error: Unsupported encoding UnsupportedEnc 2459<?xml version="1.0" encoding="UnsupportedEnc"?> 2460 ^</pre> 2461 </li> 2462 <li>From that point the encoder processes progressively the input (it is 2463 plugged as a front-end to the I/O module) for that entity. It captures 2464 and convert on-the-fly the document to be parsed to UTF-8. The parser 2465 itself just does UTF-8 checking of this input and process it 2466 transparently. The only difference is that the encoding information has 2467 been added to the parsing context (more precisely to the input 2468 corresponding to this entity).</li> 2469 <li>The result (when using DOM) is an internal form completely in UTF-8 2470 with just an encoding information on the document node.</li> 2471</ol> 2472 2473<p>Ok then what happens when saving the document (assuming you 2474collected/built an xmlDoc DOM like structure) ? It depends on the function 2475called, xmlSaveFile() will just try to save in the original encoding, while 2476xmlSaveFileTo() and xmlSaveFileEnc() can optionally save to a given 2477encoding:</p> 2478<ol> 2479 <li>if no encoding is given, libxml will look for an encoding value 2480 associated to the document and if it exists will try to save to that 2481 encoding, 2482 <p>otherwise everything is written in the internal form, i.e. UTF-8</p> 2483 </li> 2484 <li>so if an encoding was specified, either at the API level or on the 2485 document, libxml will again canonicalize the encoding name, lookup for a 2486 converter in the registered set or through iconv. If not found the 2487 function will return an error code</li> 2488 <li>the converter is placed before the I/O buffer layer, as another kind of 2489 buffer, then libxml will simply push the UTF-8 serialization to through 2490 that buffer, which will then progressively be converted and pushed onto 2491 the I/O layer.</li> 2492 <li>It is possible that the converter code fails on some input, for example 2493 trying to push an UTF-8 encoded Chinese character through the UTF-8 to 2494 ISO-8859-1 converter won't work. Since the encoders are progressive they 2495 will just report the error and the number of bytes converted, at that 2496 point libxml will decode the offending character, remove it from the 2497 buffer and replace it with the associated charRef encoding &#123; and 2498 resume the conversion. This guarantees that any document will be saved 2499 without losses (except for markup names where this is not legal, this is 2500 a problem in the current version, in practice avoid using non-ascii 2501 characters for tags or attributes names @@). A special "ascii" encoding 2502 name is used to save documents to a pure ascii form can be used when 2503 portability is really crucial</li> 2504</ol> 2505 2506<p>Here is a few examples based on the same test document:</p> 2507<pre>~/XML -> /xmllint isolat1 2508<?xml version="1.0" encoding="ISO-8859-1"?> 2509<tr�s>l�</tr�s> 2510~/XML -> /xmllint --encode UTF-8 isolat1 2511<?xml version="1.0" encoding="UTF-8"?> 2512<très>l� �</très> 2513~/XML -> </pre> 2514 2515<p>The same processing is applied (and reuse most of the code) for HTML I18N 2516processing. Looking up and modifying the content encoding is a bit more 2517difficult since it is located in a <meta> tag under the <head>, 2518so a couple of functions htmlGetMetaEncoding() and htmlSetMetaEncoding() have 2519been provided. The parser also attempts to switch encoding on the fly when 2520detecting such a tag on input. Except for that the processing is the same 2521(and again reuses the same code).</p> 2522 2523<h3><a name="Default">Default supported encodings</a></h3> 2524 2525<p>libxml has a set of default converters for the following encodings 2526(located in encoding.c):</p> 2527<ol> 2528 <li>UTF-8 is supported by default (null handlers)</li> 2529 <li>UTF-16, both little and big endian</li> 2530 <li>ISO-Latin-1 (ISO-8859-1) covering most western languages</li> 2531 <li>ASCII, useful mostly for saving</li> 2532 <li>HTML, a specific handler for the conversion of UTF-8 to ASCII with HTML 2533 predefined entities like &copy; for the Copyright sign.</li> 2534</ol> 2535 2536<p>More over when compiled on an Unix platform with iconv support the full 2537set of encodings supported by iconv can be instantly be used by libxml. On a 2538linux machine with glibc-2.1 the list of supported encodings and aliases fill 25393 full pages, and include UCS-4, the full set of ISO-Latin encodings, and the 2540various Japanese ones.</p> 2541 2542<h4>Encoding aliases</h4> 2543 2544<p>From 2.2.3, libxml has support to register encoding names aliases. The 2545goal is to be able to parse document whose encoding is supported but where 2546the name differs (for example from the default set of names accepted by 2547iconv). The following functions allow to register and handle new aliases for 2548existing encodings. Once registered libxml will automatically lookup the 2549aliases when handling a document:</p> 2550<ul> 2551 <li>int xmlAddEncodingAlias(const char *name, const char *alias);</li> 2552 <li>int xmlDelEncodingAlias(const char *alias);</li> 2553 <li>const char * xmlGetEncodingAlias(const char *alias);</li> 2554 <li>void xmlCleanupEncodingAliases(void);</li> 2555</ul> 2556 2557<h3><a name="extend">How to extend the existing support</a></h3> 2558 2559<p>Well adding support for new encoding, or overriding one of the encoders 2560(assuming it is buggy) should not be hard, just write an input and output 2561conversion routines to/from UTF-8, and register them using 2562xmlNewCharEncodingHandler(name, xxxToUTF8, UTF8Toxxx), and they will be 2563called automatically if the parser(s) encounter such an encoding name 2564(register it uppercase, this will help). The description of the encoders, 2565their arguments and expected return values are described in the encoding.h 2566header.</p> 2567 2568<p>A quick note on the topic of subverting the parser to use a different 2569internal encoding than UTF-8, in some case people will absolutely want to 2570keep the internal encoding different, I think it's still possible (but the 2571encoding must be compliant with ASCII on the same subrange) though I didn't 2572tried it. The key is to override the default conversion routines (by 2573registering null encoders/decoders for your charsets), and bypass the UTF-8 2574checking of the parser by setting the parser context charset 2575(ctxt->charset) to something different than XML_CHAR_ENCODING_UTF8, but 2576there is no guarantee that this will work. You may also have some troubles 2577saving back.</p> 2578 2579<p>Basically proper I18N support is important, this requires at least 2580libxml-2.0.0, but a lot of features and corrections are really available only 2581starting 2.2.</p> 2582 2583<h2><a name="IO">I/O Interfaces</a></h2> 2584 2585<p>Table of Content:</p> 2586<ol> 2587 <li><a href="#General1">General overview</a></li> 2588 <li><a href="#basic">The basic buffer type</a></li> 2589 <li><a href="#Input">Input I/O handlers</a></li> 2590 <li><a href="#Output">Output I/O handlers</a></li> 2591 <li><a href="#entities">The entities loader</a></li> 2592 <li><a href="#Example2">Example of customized I/O</a></li> 2593</ol> 2594 2595<h3><a name="General1">General overview</a></h3> 2596 2597<p>The module <code><a 2598href="http://xmlsoft.org/html/libxml-xmlio.html">xmlIO.h</a></code> provides 2599the interfaces to the libxml I/O system. This consists of 4 main parts:</p> 2600<ul> 2601 <li>Entities loader, this is a routine which tries to fetch the entities 2602 (files) based on their PUBLIC and SYSTEM identifiers. The default loader 2603 don't look at the public identifier since libxml do not maintain a 2604 catalog. You can redefine you own entity loader by using 2605 <code>xmlGetExternalEntityLoader()</code> and 2606 <code>xmlSetExternalEntityLoader()</code>. <a href="#entities">Check the 2607 example</a>.</li> 2608 <li>Input I/O buffers which are a commodity structure used by the parser(s) 2609 input layer to handle fetching the informations to feed the parser. This 2610 provides buffering and is also a placeholder where the encoding 2611 converters to UTF8 are piggy-backed.</li> 2612 <li>Output I/O buffers are similar to the Input ones and fulfill similar 2613 task but when generating a serialization from a tree.</li> 2614 <li>A mechanism to register sets of I/O callbacks and associate them with 2615 specific naming schemes like the protocol part of the URIs. 2616 <p>This affect the default I/O operations and allows to use specific I/O 2617 handlers for certain names.</p> 2618 </li> 2619</ul> 2620 2621<p>The general mechanism used when loading http://rpmfind.net/xml.html for 2622example in the HTML parser is the following:</p> 2623<ol> 2624 <li>The default entity loader calls <code>xmlNewInputFromFile()</code> with 2625 the parsing context and the URI string.</li> 2626 <li>the URI string is checked against the existing registered handlers 2627 using their match() callback function, if the HTTP module was compiled 2628 in, it is registered and its match() function will succeeds</li> 2629 <li>the open() function of the handler is called and if successful will 2630 return an I/O Input buffer</li> 2631 <li>the parser will the start reading from this buffer and progressively 2632 fetch information from the resource, calling the read() function of the 2633 handler until the resource is exhausted</li> 2634 <li>if an encoding change is detected it will be installed on the input 2635 buffer, providing buffering and efficient use of the conversion 2636 routines</li> 2637 <li>once the parser has finished, the close() function of the handler is 2638 called once and the Input buffer and associated resources are 2639 deallocated.</li> 2640</ol> 2641 2642<p>The user defined callbacks are checked first to allow overriding of the 2643default libxml I/O routines.</p> 2644 2645<h3><a name="basic">The basic buffer type</a></h3> 2646 2647<p>All the buffer manipulation handling is done using the 2648<code>xmlBuffer</code> type define in <code><a 2649href="http://xmlsoft.org/html/libxml-tree.html">tree.h</a> </code>which is a 2650resizable memory buffer. The buffer allocation strategy can be selected to be 2651either best-fit or use an exponential doubling one (CPU vs. memory use 2652trade-off). The values are <code>XML_BUFFER_ALLOC_EXACT</code> and 2653<code>XML_BUFFER_ALLOC_DOUBLEIT</code>, and can be set individually or on a 2654system wide basis using <code>xmlBufferSetAllocationScheme()</code>. A number 2655of functions allows to manipulate buffers with names starting with the 2656<code>xmlBuffer...</code> prefix.</p> 2657 2658<h3><a name="Input">Input I/O handlers</a></h3> 2659 2660<p>An Input I/O handler is a simple structure 2661<code>xmlParserInputBuffer</code> containing a context associated to the 2662resource (file descriptor, or pointer to a protocol handler), the read() and 2663close() callbacks to use and an xmlBuffer. And extra xmlBuffer and a charset 2664encoding handler are also present to support charset conversion when 2665needed.</p> 2666 2667<h3><a name="Output">Output I/O handlers</a></h3> 2668 2669<p>An Output handler <code>xmlOutputBuffer</code> is completely similar to an 2670Input one except the callbacks are write() and close().</p> 2671 2672<h3><a name="entities">The entities loader</a></h3> 2673 2674<p>The entity loader resolves requests for new entities and create inputs for 2675the parser. Creating an input from a filename or an URI string is done 2676through the xmlNewInputFromFile() routine. The default entity loader do not 2677handle the PUBLIC identifier associated with an entity (if any). So it just 2678calls xmlNewInputFromFile() with the SYSTEM identifier (which is mandatory in 2679XML).</p> 2680 2681<p>If you want to hook up a catalog mechanism then you simply need to 2682override the default entity loader, here is an example:</p> 2683<pre>#include <libxml/xmlIO.h> 2684 2685xmlExternalEntityLoader defaultLoader = NULL; 2686 2687xmlParserInputPtr 2688xmlMyExternalEntityLoader(const char *URL, const char *ID, 2689 xmlParserCtxtPtr ctxt) { 2690 xmlParserInputPtr ret; 2691 const char *fileID = NULL; 2692 /* lookup for the fileID depending on ID */ 2693 2694 ret = xmlNewInputFromFile(ctxt, fileID); 2695 if (ret != NULL) 2696 return(ret); 2697 if (defaultLoader != NULL) 2698 ret = defaultLoader(URL, ID, ctxt); 2699 return(ret); 2700} 2701 2702int main(..) { 2703 ... 2704 2705 /* 2706 * Install our own entity loader 2707 */ 2708 defaultLoader = xmlGetExternalEntityLoader(); 2709 xmlSetExternalEntityLoader(xmlMyExternalEntityLoader); 2710 2711 ... 2712}</pre> 2713 2714<h3><a name="Example2">Example of customized I/O</a></h3> 2715 2716<p>This example come from <a href="http://xmlsoft.org/messages/0708.html">a 2717real use case</a>, xmlDocDump() closes the FILE * passed by the application 2718and this was a problem. The <a 2719href="http://xmlsoft.org/messages/0711.html">solution</a> was to redefine a 2720new output handler with the closing call deactivated:</p> 2721<ol> 2722 <li>First define a new I/O output allocator where the output don't close 2723 the file: 2724 <pre>xmlOutputBufferPtr 2725xmlOutputBufferCreateOwn(FILE *file, xmlCharEncodingHandlerPtr encoder) { 2726����xmlOutputBufferPtr ret; 2727���� 2728����if (xmlOutputCallbackInitialized == 0) 2729��������xmlRegisterDefaultOutputCallbacks(); 2730 2731����if (file == NULL) return(NULL); 2732����ret = xmlAllocOutputBuffer(encoder); 2733����if (ret != NULL) { 2734��������ret->context = file; 2735��������ret->writecallback = xmlFileWrite; 2736��������ret->closecallback = NULL; /* No close callback */ 2737����} 2738����return(ret); <br> 2739 2740 2741 2742 2743 2744 2745 2746 2747 2748 2749 2750 2751 2752 2753 2754 2755 2756 2757 2758 2759 2760 2761 2762 2763 2764} </pre> 2765 </li> 2766 <li>And then use it to save the document: 2767 <pre>FILE *f; 2768xmlOutputBufferPtr output; 2769xmlDocPtr doc; 2770int res; 2771 2772f = ... 2773doc = .... 2774 2775output = xmlOutputBufferCreateOwn(f, NULL); 2776res = xmlSaveFileTo(output, doc, NULL); 2777 </pre> 2778 </li> 2779</ol> 2780 2781<h2><a name="Catalog">Catalog support</a></h2> 2782 2783<p>Table of Content:</p> 2784<ol> 2785 <li><a href="General2">General overview</a></li> 2786 <li><a href="#definition">The definition</a></li> 2787 <li><a href="#Simple">Using catalogs</a></li> 2788 <li><a href="#Some">Some examples</a></li> 2789 <li><a href="#reference">How to tune catalog usage</a></li> 2790 <li><a href="#validate">How to debug catalog processing</a></li> 2791 <li><a href="#Declaring">How to create and maintain catalogs</a></li> 2792 <li><a href="#implemento">The implementor corner quick review of the 2793 API</a></li> 2794 <li><a href="#Other">Other resources</a></li> 2795</ol> 2796 2797<h3><a name="General2">General overview</a></h3> 2798 2799<p>What is a catalog? Basically it's a lookup mechanism used when an entity 2800(a file or a remote resource) references another entity. The catalog lookup 2801is inserted between the moment the reference is recognized by the software 2802(XML parser, stylesheet processing, or even images referenced for inclusion 2803in a rendering) and the time where loading that resource is actually 2804started.</p> 2805 2806<p>It is basically used for 3 things:</p> 2807<ul> 2808 <li>mapping from "logical" names, the public identifiers and a more 2809 concrete name usable for download (and URI). For example it can associate 2810 the logical name 2811 <p>"-//OASIS//DTD DocBook XML V4.1.2//EN"</p> 2812 <p>of the DocBook 4.1.2 XML DTD with the actual URL where it can be 2813 downloaded</p> 2814 <p>http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd</p> 2815 </li> 2816 <li>remapping from a given URL to another one, like an HTTP indirection 2817 saying that 2818 <p>"http://www.oasis-open.org/committes/tr.xsl"</p> 2819 <p>should really be looked at</p> 2820 <p>"http://www.oasis-open.org/committes/entity/stylesheets/base/tr.xsl"</p> 2821 </li> 2822 <li>providing a local cache mechanism allowing to load the entities 2823 associated to public identifiers or remote resources, this is a really 2824 important feature for any significant deployment of XML or SGML since it 2825 allows to avoid the aleas and delays associated to fetching remote 2826 resources.</li> 2827</ul> 2828 2829<h3><a name="definition">The definitions</a></h3> 2830 2831<p>Libxml, as of 2.4.3 implements 2 kind of catalogs:</p> 2832<ul> 2833 <li>the older SGML catalogs, the official spec is SGML Open Technical 2834 Resolution TR9401:1997, but is better understood by reading <a 2835 href="http://www.jclark.com/sp/catalog.htm">the SP Catalog page</a> from 2836 James Clark. This is relatively old and not the preferred mode of 2837 operation of libxml.</li> 2838 <li><a href="http://www.oasis-open.org/committees/entity/spec.html">XML 2839 Catalogs</a> is far more flexible, more recent, uses an XML syntax and 2840 should scale quite better. This is the default option of libxml.</li> 2841</ul> 2842 2843<p></p> 2844 2845<h3><a name="Simple">Using catalog</a></h3> 2846 2847<p>In a normal environment libxml will by default check the presence of a 2848catalog in /etc/xml/catalog, and assuming it has been correctly populated, 2849the processing is completely transparent to the document user. To take a 2850concrete example, suppose you are authoring a DocBook document, this one 2851starts with the following DOCTYPE definition:</p> 2852<pre><?xml version='1.0'?> 2853<!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN" 2854 "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd"></pre> 2855 2856<p>When validating the document with libxml, the catalog will be 2857automatically consulted to lookup the public identifier "-//Norman Walsh//DTD 2858DocBk XML V3.1.4//EN" and the system identifier 2859"http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd", and if these entities have 2860been installed on your system and the catalogs actually point to them, libxml 2861will fetch them from the local disk.</p> 2862 2863<p style="font-size: 10pt"><strong>Note</strong>: Really don't use this 2864DOCTYPE example it's a really old version, but is fine as an example.</p> 2865 2866<p>Libxml will check the catalog each time that it is requested to load an 2867entity, this includes DTD, external parsed entities, stylesheets, etc ... If 2868your system is correctly configured all the authoring phase and processing 2869should use only local files, even if your document stays portable because it 2870uses the canonical public and system ID, referencing the remote document.</p> 2871 2872<h3><a name="Some">Some examples:</a></h3> 2873 2874<p>Here is a couple of fragments from XML Catalogs used in libxml early 2875regression tests in <code>test/catalogs</code> :</p> 2876<pre><?xml version="1.0"?> 2877<!DOCTYPE catalog PUBLIC 2878 "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" 2879 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 2880<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"> 2881 <public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN" 2882 uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/> 2883...</pre> 2884 2885<p>This is the beginning of a catalog for DocBook 4.1.2, XML Catalogs are 2886written in XML, there is a specific namespace for catalog elements 2887"urn:oasis:names:tc:entity:xmlns:xml:catalog". The first entry in this 2888catalog is a <code>public</code> mapping it allows to associate a Public 2889Identifier with an URI.</p> 2890<pre>... 2891 <rewriteSystem systemIdStartString="http://www.oasis-open.org/docbook/" 2892 rewritePrefix="file:///usr/share/xml/docbook/"/> 2893...</pre> 2894 2895<p>A <code>rewriteSystem</code> is a very powerful instruction, it says that 2896any URI starting with a given prefix should be looked at another URI 2897constructed by replacing the prefix with an new one. In effect this acts like 2898a cache system for a full area of the Web. In practice it is extremely useful 2899with a file prefix if you have installed a copy of those resources on your 2900local system.</p> 2901<pre>... 2902<delegatePublic publicIdStartString="-//OASIS//DTD XML Catalog //" 2903 catalog="file:///usr/share/xml/docbook.xml"/> 2904<delegatePublic publicIdStartString="-//OASIS//ENTITIES DocBook XML" 2905 catalog="file:///usr/share/xml/docbook.xml"/> 2906<delegatePublic publicIdStartString="-//OASIS//DTD DocBook XML" 2907 catalog="file:///usr/share/xml/docbook.xml"/> 2908<delegateSystem systemIdStartString="http://www.oasis-open.org/docbook/" 2909 catalog="file:///usr/share/xml/docbook.xml"/> 2910<delegateURI uriStartString="http://www.oasis-open.org/docbook/" 2911 catalog="file:///usr/share/xml/docbook.xml"/> 2912...</pre> 2913 2914<p>Delegation is the core features which allows to build a tree of catalogs, 2915easier to maintain than a single catalog, based on Public Identifier, System 2916Identifier or URI prefixes it instructs the catalog software to look up 2917entries in another resource. This feature allow to build hierarchies of 2918catalogs, the set of entries presented should be sufficient to redirect the 2919resolution of all DocBook references to the specific catalog in 2920<code>/usr/share/xml/docbook.xml</code> this one in turn could delegate all 2921references for DocBook 4.2.1 to a specific catalog installed at the same time 2922as the DocBook resources on the local machine.</p> 2923 2924<h3><a name="reference">How to tune catalog usage:</a></h3> 2925 2926<p>The user can change the default catalog behaviour by redirecting queries 2927to its own set of catalogs, this can be done by setting the 2928<code>XML_CATALOG_FILES</code> environment variable to a list of catalogs, an 2929empty one should deactivate loading the default <code>/etc/xml/catalog</code> 2930default catalog</p> 2931 2932<h3><a name="validate">How to debug catalog processing:</a></h3> 2933 2934<p>Setting up the <code>XML_DEBUG_CATALOG</code> environment variable will 2935make libxml output debugging informations for each catalog operations, for 2936example:</p> 2937<pre>orchis:~/XML -> xmllint --memory --noout test/ent2 2938warning: failed to load external entity "title.xml" 2939orchis:~/XML -> export XML_DEBUG_CATALOG= 2940orchis:~/XML -> xmllint --memory --noout test/ent2 2941Failed to parse catalog /etc/xml/catalog 2942Failed to parse catalog /etc/xml/catalog 2943warning: failed to load external entity "title.xml" 2944Catalogs cleanup 2945orchis:~/XML -> </pre> 2946 2947<p>The test/ent2 references an entity, running the parser from memory makes 2948the base URI unavailable and the the "title.xml" entity cannot be loaded. 2949Setting up the debug environment variable allows to detect that an attempt is 2950made to load the <code>/etc/xml/catalog</code> but since it's not present the 2951resolution fails.</p> 2952 2953<p>But the most advanced way to debug XML catalog processing is to use the 2954<strong>xmlcatalog</strong> command shipped with libxml2, it allows to load 2955catalogs and make resolution queries to see what is going on. This is also 2956used for the regression tests:</p> 2957<pre>orchis:~/XML -> /xmlcatalog test/catalogs/docbook.xml \ 2958 "-//OASIS//DTD DocBook XML V4.1.2//EN" 2959http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd 2960orchis:~/XML -> </pre> 2961 2962<p>For debugging what is going on, adding one -v flags increase the verbosity 2963level to indicate the processing done (adding a second flag also indicate 2964what elements are recognized at parsing):</p> 2965<pre>orchis:~/XML -> /xmlcatalog -v test/catalogs/docbook.xml \ 2966 "-//OASIS//DTD DocBook XML V4.1.2//EN" 2967Parsing catalog test/catalogs/docbook.xml's content 2968Found public match -//OASIS//DTD DocBook XML V4.1.2//EN 2969http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd 2970Catalogs cleanup 2971orchis:~/XML -> </pre> 2972 2973<p>A shell interface is also available to debug and process multiple queries 2974(and for regression tests):</p> 2975<pre>orchis:~/XML -> /xmlcatalog -shell test/catalogs/docbook.xml \ 2976 "-//OASIS//DTD DocBook XML V4.1.2//EN" 2977> help 2978Commands available: 2979public PublicID: make a PUBLIC identifier lookup 2980system SystemID: make a SYSTEM identifier lookup 2981resolve PublicID SystemID: do a full resolver lookup 2982add 'type' 'orig' 'replace' : add an entry 2983del 'values' : remove values 2984dump: print the current catalog state 2985debug: increase the verbosity level 2986quiet: decrease the verbosity level 2987exit: quit the shell 2988> public "-//OASIS//DTD DocBook XML V4.1.2//EN" 2989http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd 2990> quit 2991orchis:~/XML -> </pre> 2992 2993<p>This should be sufficient for most debugging purpose, this was actually 2994used heavily to debug the XML Catalog implementation itself.</p> 2995 2996<h3><a name="Declaring">How to create and maintain</a> catalogs:</h3> 2997 2998<p>Basically XML Catalogs are XML files, you can either use XML tools to 2999manage them or use <strong>xmlcatalog</strong> for this. The basic step is 3000to create a catalog the -create option provide this facility:</p> 3001<pre>orchis:~/XML -> /xmlcatalog --create tst.xml 3002<?xml version="1.0"?> 3003<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" 3004 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 3005<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/> 3006orchis:~/XML -> </pre> 3007 3008<p>By default xmlcatalog does not overwrite the original catalog and save the 3009result on the standard output, this can be overridden using the -noout 3010option. The <code>-add</code> command allows to add entries in the 3011catalog:</p> 3012<pre>orchis:~/XML -> /xmlcatalog --noout --create --add "public" \ 3013 "-//OASIS//DTD DocBook XML V4.1.2//EN" \ 3014 http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd tst.xml 3015orchis:~/XML -> cat tst.xml 3016<?xml version="1.0"?> 3017<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" \ 3018 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 3019<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"> 3020<public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN" 3021 uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/> 3022</catalog> 3023orchis:~/XML -> </pre> 3024 3025<p>The <code>-add</code> option will always take 3 parameters even if some of 3026the XML Catalog constructs (like nextCatalog) will have only a single 3027argument, just pass a third empty string, it will be ignored.</p> 3028 3029<p>Similarly the <code>-del</code> option remove matching entries from the 3030catalog:</p> 3031<pre>orchis:~/XML -> /xmlcatalog --del \ 3032 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" tst.xml 3033<?xml version="1.0"?> 3034<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" 3035 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"> 3036<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/> 3037orchis:~/XML -> </pre> 3038 3039<p>The catalog is now empty. Note that the matching of <code>-del</code> is 3040exact and would have worked in a similar fashion with the Public ID 3041string.</p> 3042 3043<p>This is rudimentary but should be sufficient to manage a not too complex 3044catalog tree of resources.</p> 3045 3046<h3><a name="implemento">The implementor corner quick review of the 3047API:</a></h3> 3048 3049<p>First, and like for every other module of libxml, there is an 3050automatically generated <a href="html/libxml-catalog.html">API page for 3051catalog support</a>.</p> 3052 3053<p>The header for the catalog interfaces should be included as:</p> 3054<pre>#include <libxml/catalog.h></pre> 3055 3056<p>The API is voluntarily kept very simple. First it is not obvious that 3057applications really need access to it since it is the default behaviour of 3058libxml (Note: it is possible to completely override libxml default catalog by 3059using <a href="html/libxml-parser.html">xmlSetExternalEntityLoader</a> to 3060plug an application specific resolver).</p> 3061 3062<p>Basically libxml support 2 catalog lists:</p> 3063<ul> 3064 <li>the default one, global shared by all the application</li> 3065 <li>a per-document catalog, this one is built if the document uses the 3066 <code>oasis-xml-catalog</code> PIs to specify its own catalog list, it is 3067 associated to the parser context and destroyed when the parsing context 3068 is destroyed.</li> 3069</ul> 3070 3071<p>the document one will be used first if it exists.</p> 3072 3073<h4>Initialization routines:</h4> 3074 3075<p>xmlInitializeCatalog(), xmlLoadCatalog() and xmlLoadCatalogs() should be 3076used at startup to initialize the catalog, if the catalog should be 3077initialized with specific values xmlLoadCatalog() or xmlLoadCatalogs() 3078should be called before xmlInitializeCatalog() which would otherwise do a 3079default initialization first.</p> 3080 3081<p>The xmlCatalogAddLocal() call is used by the parser to grow the document 3082own catalog list if needed.</p> 3083 3084<h4>Preferences setup:</h4> 3085 3086<p>The XML Catalog spec requires the possibility to select default 3087preferences between public and system delegation, 3088xmlCatalogSetDefaultPrefer() allows this, xmlCatalogSetDefaults() and 3089xmlCatalogGetDefaults() allow to control if XML Catalogs resolution should 3090be forbidden, allowed for global catalog, for document catalog or both, the 3091default is to allow both.</p> 3092 3093<p>And of course xmlCatalogSetDebug() allows to generate debug messages 3094(through the xmlGenericError() mechanism).</p> 3095 3096<h4>Querying routines:</h4> 3097 3098<p>xmlCatalogResolve(), xmlCatalogResolveSystem(), xmlCatalogResolvePublic() 3099and xmlCatalogResolveURI() are relatively explicit if you read the XML 3100Catalog specification they correspond to section 7 algorithms, they should 3101also work if you have loaded an SGML catalog with a simplified semantic.</p> 3102 3103<p>xmlCatalogLocalResolve() and xmlCatalogLocalResolveURI() are the same but 3104operate on the document catalog list</p> 3105 3106<h4>Cleanup and Miscellaneous:</h4> 3107 3108<p>xmlCatalogCleanup() free-up the global catalog, xmlCatalogFreeLocal() is 3109the per-document equivalent.</p> 3110 3111<p>xmlCatalogAdd() and xmlCatalogRemove() are used to dynamically modify the 3112first catalog in the global list, and xmlCatalogDump() allows to dump a 3113catalog state, those routines are primarily designed for xmlcatalog, I'm not 3114sure that exposing more complex interfaces (like navigation ones) would be 3115really useful.</p> 3116 3117<p>The xmlParseCatalogFile() is a function used to load XML Catalog files, 3118it's similar as xmlParseFile() except it bypass all catalog lookups, it's 3119provided because this functionality may be useful for client tools.</p> 3120 3121<h4>threaded environments:</h4> 3122 3123<p>Since the catalog tree is built progressively, some care has been taken to 3124try to avoid troubles in multithreaded environments. The code is now thread 3125safe assuming that the libxml library has been compiled with threads 3126support.</p> 3127 3128<p></p> 3129 3130<h3><a name="Other">Other resources</a></h3> 3131 3132<p>The XML Catalog specification is relatively recent so there isn't much 3133literature to point at:</p> 3134<ul> 3135 <li>You can find a good rant from Norm Walsh about <a 3136 href="http://www.arbortext.com/Think_Tank/XML_Resources/Issue_Three/issue_three.html">the 3137 need for catalogs</a>, it provides a lot of context informations even if 3138 I don't agree with everything presented. Norm also wrote a more recent 3139 article <a 3140 href="http://wwws.sun.com/software/xml/developers/resolver/article/">XML 3141 entities and URI resolvers</a> describing them.</li> 3142 <li>An <a href="http://home.ccil.org/~cowan/XML/XCatalog.html">old XML 3143 catalog proposal</a> from John Cowan</li> 3144 <li>The <a href="http://www.rddl.org/">Resource Directory Description 3145 Language</a> (RDDL) another catalog system but more oriented toward 3146 providing metadata for XML namespaces.</li> 3147 <li>the page from the OASIS Technical <a 3148 href="http://www.oasis-open.org/committees/entity/">Committee on Entity 3149 Resolution</a> who maintains XML Catalog, you will find pointers to the 3150 specification update, some background and pointers to others tools 3151 providing XML Catalog support</li> 3152 <li>Here is a <a href="buildDocBookCatalog">shell script</a> to generate 3153 XML Catalogs for DocBook 4.1.2 . If it can write to the /etc/xml/ 3154 directory, it will set-up /etc/xml/catalog and /etc/xml/docbook based on 3155 the resources found on the system. Otherwise it will just create 3156 ~/xmlcatalog and ~/dbkxmlcatalog and doing: 3157 <p><code>export XMLCATALOG=$HOME/xmlcatalog</code></p> 3158 <p>should allow to process DocBook documentations without requiring 3159 network accesses for the DTD or stylesheets</p> 3160 </li> 3161 <li>I have uploaded <a href="ftp://xmlsoft.org/test/dbk412catalog.tar.gz">a 3162 small tarball</a> containing XML Catalogs for DocBook 4.1.2 which seems 3163 to work fine for me too</li> 3164 <li>The <a href="http://www.xmlsoft.org/xmlcatalog_man.html">xmlcatalog 3165 manual page</a></li> 3166</ul> 3167 3168<p>If you have suggestions for corrections or additions, simply contact 3169me:</p> 3170 3171<h2><a name="library">The parser interfaces</a></h2> 3172 3173<p>This section is directly intended to help programmers getting bootstrapped 3174using the XML library from the C language. It is not intended to be 3175extensive. I hope the automatically generated documents will provide the 3176completeness required, but as a separate set of documents. The interfaces of 3177the XML library are by principle low level, there is nearly zero abstraction. 3178Those interested in a higher level API should <a href="#DOM">look at 3179DOM</a>.</p> 3180 3181<p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are 3182separated from the <a href="html/libxml-htmlparser.html">HTML parser 3183interfaces</a>. Let's have a look at how the XML parser can be called:</p> 3184 3185<h3><a name="Invoking">Invoking the parser : the pull method</a></h3> 3186 3187<p>Usually, the first thing to do is to read an XML input. The parser accepts 3188documents either from in-memory strings or from files. The functions are 3189defined in "parser.h":</p> 3190<dl> 3191 <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt> 3192 <dd><p>Parse a null-terminated string containing the document.</p> 3193 </dd> 3194</dl> 3195<dl> 3196 <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt> 3197 <dd><p>Parse an XML document contained in a (possibly compressed) 3198 file.</p> 3199 </dd> 3200</dl> 3201 3202<p>The parser returns a pointer to the document structure (or NULL in case of 3203failure).</p> 3204 3205<h3 id="Invoking1">Invoking the parser: the push method</h3> 3206 3207<p>In order for the application to keep the control when the document is 3208being fetched (which is common for GUI based programs) libxml provides a push 3209interface, too, as of version 1.8.3. Here are the interface functions:</p> 3210<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax, 3211 void *user_data, 3212 const char *chunk, 3213 int size, 3214 const char *filename); 3215int xmlParseChunk (xmlParserCtxtPtr ctxt, 3216 const char *chunk, 3217 int size, 3218 int terminate);</pre> 3219 3220<p>and here is a simple example showing how to use the interface:</p> 3221<pre> FILE *f; 3222 3223 f = fopen(filename, "r"); 3224 if (f != NULL) { 3225 int res, size = 1024; 3226 char chars[1024]; 3227 xmlParserCtxtPtr ctxt; 3228 3229 res = fread(chars, 1, 4, f); 3230 if (res > 0) { 3231 ctxt = xmlCreatePushParserCtxt(NULL, NULL, 3232 chars, res, filename); 3233 while ((res = fread(chars, 1, size, f)) > 0) { 3234 xmlParseChunk(ctxt, chars, res, 0); 3235 } 3236 xmlParseChunk(ctxt, chars, 0, 1); 3237 doc = ctxt->myDoc; 3238 xmlFreeParserCtxt(ctxt); 3239 } 3240 }</pre> 3241 3242<p>The HTML parser embedded into libxml also has a push interface; the 3243functions are just prefixed by "html" rather than "xml".</p> 3244 3245<h3 id="Invoking2">Invoking the parser: the SAX interface</h3> 3246 3247<p>The tree-building interface makes the parser memory-hungry, first loading 3248the document in memory and then building the tree itself. Reading a document 3249without building the tree is possible using the SAX interfaces (see SAX.h and 3250<a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James 3251Henstridge's documentation</a>). Note also that the push interface can be 3252limited to SAX: just use the two first arguments of 3253<code>xmlCreatePushParserCtxt()</code>.</p> 3254 3255<h3><a name="Building">Building a tree from scratch</a></h3> 3256 3257<p>The other way to get an XML tree in memory is by building it. Basically 3258there is a set of functions dedicated to building new elements. (These are 3259also described in <libxml/tree.h>.) For example, here is a piece of 3260code that produces the XML document used in the previous examples:</p> 3261<pre> #include <libxml/tree.h> 3262 xmlDocPtr doc; 3263 xmlNodePtr tree, subtree; 3264 3265 doc = xmlNewDoc("1.0"); 3266 doc->children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL); 3267 xmlSetProp(doc->children, "prop1", "gnome is great"); 3268 xmlSetProp(doc->children, "prop2", "& linux too"); 3269 tree = xmlNewChild(doc->children, NULL, "head", NULL); 3270 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome"); 3271 tree = xmlNewChild(doc->children, NULL, "chapter", NULL); 3272 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure"); 3273 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ..."); 3274 subtree = xmlNewChild(tree, NULL, "image", NULL); 3275 xmlSetProp(subtree, "href", "linus.gif");</pre> 3276 3277<p>Not really rocket science ...</p> 3278 3279<h3><a name="Traversing">Traversing the tree</a></h3> 3280 3281<p>Basically by <a href="html/libxml-tree.html">including "tree.h"</a> your 3282code has access to the internal structure of all the elements of the tree. 3283The names should be somewhat simple like <strong>parent</strong>, 3284<strong>children</strong>, <strong>next</strong>, <strong>prev</strong>, 3285<strong>properties</strong>, etc... For example, still with the previous 3286example:</p> 3287<pre><code>doc->children->children->children</code></pre> 3288 3289<p>points to the title element,</p> 3290<pre>doc->children->children->next->children->children</pre> 3291 3292<p>points to the text node containing the chapter title "The Linux 3293adventure".</p> 3294 3295<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be 3296present before the document root, so <code>doc->children</code> may point 3297to an element which is not the document Root Element; a function 3298<code>xmlDocGetRootElement()</code> was added for this purpose.</p> 3299 3300<h3><a name="Modifying">Modifying the tree</a></h3> 3301 3302<p>Functions are provided for reading and writing the document content. Here 3303is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p> 3304<dl> 3305 <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const 3306 xmlChar *value);</code></dt> 3307 <dd><p>This sets (or changes) an attribute carried by an ELEMENT node. 3308 The value can be NULL.</p> 3309 </dd> 3310</dl> 3311<dl> 3312 <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar 3313 *name);</code></dt> 3314 <dd><p>This function returns a pointer to new copy of the property 3315 content. Note that the user must deallocate the result.</p> 3316 </dd> 3317</dl> 3318 3319<p>Two functions are provided for reading and writing the text associated 3320with elements:</p> 3321<dl> 3322 <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar 3323 *value);</code></dt> 3324 <dd><p>This function takes an "external" string and converts it to one 3325 text node or possibly to a list of entity and text nodes. All 3326 non-predefined entity references like &Gnome; will be stored 3327 internally as entity nodes, hence the result of the function may not be 3328 a single node.</p> 3329 </dd> 3330</dl> 3331<dl> 3332 <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int 3333 inLine);</code></dt> 3334 <dd><p>This function is the inverse of 3335 <code>xmlStringGetNodeList()</code>. It generates a new string 3336 containing the content of the text and entity nodes. Note the extra 3337 argument inLine. If this argument is set to 1, the function will expand 3338 entity references. For example, instead of returning the &Gnome; 3339 XML encoding in the string, it will substitute it with its value (say, 3340 "GNU Network Object Model Environment").</p> 3341 </dd> 3342</dl> 3343 3344<h3><a name="Saving">Saving a tree</a></h3> 3345 3346<p>Basically 3 options are possible:</p> 3347<dl> 3348 <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int 3349 *size);</code></dt> 3350 <dd><p>Returns a buffer into which the document has been saved.</p> 3351 </dd> 3352</dl> 3353<dl> 3354 <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt> 3355 <dd><p>Dumps a document to an open file descriptor.</p> 3356 </dd> 3357</dl> 3358<dl> 3359 <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt> 3360 <dd><p>Saves the document to a file. In this case, the compression 3361 interface is triggered if it has been turned on.</p> 3362 </dd> 3363</dl> 3364 3365<h3><a name="Compressio">Compression</a></h3> 3366 3367<p>The library transparently handles compression when doing file-based 3368accesses. The level of compression on saves can be turned on either globally 3369or individually for one file:</p> 3370<dl> 3371 <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt> 3372 <dd><p>Gets the document compression ratio (0-9).</p> 3373 </dd> 3374</dl> 3375<dl> 3376 <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt> 3377 <dd><p>Sets the document compression ratio.</p> 3378 </dd> 3379</dl> 3380<dl> 3381 <dt><code>int xmlGetCompressMode(void);</code></dt> 3382 <dd><p>Gets the default compression ratio.</p> 3383 </dd> 3384</dl> 3385<dl> 3386 <dt><code>void xmlSetCompressMode(int mode);</code></dt> 3387 <dd><p>Sets the default compression ratio.</p> 3388 </dd> 3389</dl> 3390 3391<h2><a name="Entities">Entities or no entities</a></h2> 3392 3393<p>Entities in principle are similar to simple C macros. An entity defines an 3394abbreviation for a given string that you can reuse many times throughout the 3395content of your document. Entities are especially useful when a given string 3396may occur frequently within a document, or to confine the change needed to a 3397document to a restricted area in the internal subset of the document (at the 3398beginning). Example:</p> 3399<pre>1 <?xml version="1.0"?> 34002 <!DOCTYPE EXAMPLE SYSTEM "example.dtd" [ 34013 <!ENTITY xml "Extensible Markup Language"> 34024 ]> 34035 <EXAMPLE> 34046 &xml; 34057 </EXAMPLE></pre> 3406 3407<p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing 3408its name with '&' and following it by ';' without any spaces added. There 3409are 5 predefined entities in libxml allowing you to escape characters with 3410predefined meaning in some parts of the xml document content: 3411<strong>&lt;</strong> for the character '<', <strong>&gt;</strong> 3412for the character '>', <strong>&apos;</strong> for the character ''', 3413<strong>&quot;</strong> for the character '"', and 3414<strong>&amp;</strong> for the character '&'.</p> 3415 3416<p>One of the problems related to entities is that you may want the parser to 3417substitute an entity's content so that you can see the replacement text in 3418your application. Or you may prefer to keep entity references as such in the 3419content to be able to save the document back without losing this usually 3420precious information (if the user went through the pain of explicitly 3421defining entities, he may have a a rather negative attitude if you blindly 3422substitute them as saving time). The <a 3423href="html/libxml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a> 3424function allows you to check and change the behaviour, which is to not 3425substitute entities by default.</p> 3426 3427<p>Here is the DOM tree built by libxml for the previous document in the 3428default case:</p> 3429<pre>/gnome/src/gnome-xml -> /xmllint --debug test/ent1 3430DOCUMENT 3431version=1.0 3432 ELEMENT EXAMPLE 3433 TEXT 3434 content= 3435 ENTITY_REF 3436 INTERNAL_GENERAL_ENTITY xml 3437 content=Extensible Markup Language 3438 TEXT 3439 content=</pre> 3440 3441<p>And here is the result when substituting entities:</p> 3442<pre>/gnome/src/gnome-xml -> /tester --debug --noent test/ent1 3443DOCUMENT 3444version=1.0 3445 ELEMENT EXAMPLE 3446 TEXT 3447 content= Extensible Markup Language</pre> 3448 3449<p>So, entities or no entities? Basically, it depends on your use case. I 3450suggest that you keep the non-substituting default behaviour and avoid using 3451entities in your XML document or data if you are not willing to handle the 3452entity references elements in the DOM tree.</p> 3453 3454<p>Note that at save time libxml enforces the conversion of the predefined 3455entities where necessary to prevent well-formedness problems, and will also 3456transparently replace those with chars (i.e. it will not generate entity 3457reference elements in the DOM tree or call the reference() SAX callback when 3458finding them in the input).</p> 3459 3460<p><span style="background-color: #FF0000">WARNING</span>: handling entities 3461on top of the libxml SAX interface is difficult!!! If you plan to use 3462non-predefined entities in your documents, then the learning curve to handle 3463then using the SAX API may be long. If you plan to use complex documents, I 3464strongly suggest you consider using the DOM interface instead and let libxml 3465deal with the complexity rather than trying to do it yourself.</p> 3466 3467<h2><a name="Namespaces">Namespaces</a></h2> 3468 3469<p>The libxml library implements <a 3470href="http://www.w3.org/TR/REC-xml-names/">XML namespaces</a> support by 3471recognizing namespace constructs in the input, and does namespace lookup 3472automatically when building the DOM tree. A namespace declaration is 3473associated with an in-memory structure and all elements or attributes within 3474that namespace point to it. Hence testing the namespace is a simple and fast 3475equality operation at the user level.</p> 3476 3477<p>I suggest that people using libxml use a namespace, and declare it in the 3478root element of their document as the default namespace. Then they don't need 3479to use the prefix in the content but we will have a basis for future semantic 3480refinement and merging of data from different sources. This doesn't increase 3481the size of the XML output significantly, but significantly increases its 3482value in the long-term. Example:</p> 3483<pre><mydoc xmlns="http://mydoc.example.org/schemas/"> 3484 <elem1>...</elem1> 3485 <elem2>...</elem2> 3486</mydoc></pre> 3487 3488<p>The namespace value has to be an absolute URL, but the URL doesn't have to 3489point to any existing resource on the Web. It will bind all the element and 3490attributes with that URL. I suggest to use an URL within a domain you 3491control, and that the URL should contain some kind of version information if 3492possible. For example, <code>"http://www.gnome.org/gnumeric/1.0/"</code> is a 3493good namespace scheme.</p> 3494 3495<p>Then when you load a file, make sure that a namespace carrying the 3496version-independent prefix is installed on the root element of your document, 3497and if the version information don't match something you know, warn the user 3498and be liberal in what you accept as the input. Also do *not* try to base 3499namespace checking on the prefix value. <foo:text> may be exactly the 3500same as <bar:text> in another document. What really matters is the URI 3501associated with the element or the attribute, not the prefix string (which is 3502just a shortcut for the full URI). In libxml, element and attributes have an 3503<code>ns</code> field pointing to an xmlNs structure detailing the namespace 3504prefix and its URI.</p> 3505 3506<p>@@Interfaces@@</p> 3507 3508<p>@@Examples@@</p> 3509 3510<p>Usually people object to using namespaces together with validity checking. 3511I will try to make sure that using namespaces won't break validity checking, 3512so even if you plan to use or currently are using validation I strongly 3513suggest adding namespaces to your document. A default namespace scheme 3514<code>xmlns="http://...."</code> should not break validity even on less 3515flexible parsers. Using namespaces to mix and differentiate content coming 3516from multiple DTDs will certainly break current validation schemes. I will 3517try to provide ways to do this, but this may not be portable or 3518standardized.</p> 3519 3520<h2><a name="Upgrading">Upgrading 1.x code</a></h2> 3521 3522<p>Incompatible changes:</p> 3523 3524<p>Version 2 of libxml is the first version introducing serious backward 3525incompatible changes. The main goals were:</p> 3526<ul> 3527 <li>a general cleanup. A number of mistakes inherited from the very early 3528 versions couldn't be changed due to compatibility constraints. Example 3529 the "childs" element in the nodes.</li> 3530 <li>Uniformization of the various nodes, at least for their header and link 3531 parts (doc, parent, children, prev, next), the goal is a simpler 3532 programming model and simplifying the task of the DOM implementors.</li> 3533 <li>better conformances to the XML specification, for example version 1.x 3534 had an heuristic to try to detect ignorable white spaces. As a result the 3535 SAX event generated were ignorableWhitespace() while the spec requires 3536 character() in that case. This also mean that a number of DOM node 3537 containing blank text may populate the DOM tree which were not present 3538 before.</li> 3539</ul> 3540 3541<h3>How to fix libxml-1.x code:</h3> 3542 3543<p>So client code of libxml designed to run with version 1.x may have to be 3544changed to compile against version 2.x of libxml. Here is a list of changes 3545that I have collected, they may not be sufficient, so in case you find other 3546change which are required, <a href="mailto:Daniel.�eillardw3.org">drop me a 3547mail</a>:</p> 3548<ol> 3549 <li>The package name have changed from libxml to libxml2, the library name 3550 is now -lxml2 . There is a new xml2-config script which should be used to 3551 select the right parameters libxml2</li> 3552 <li>Node <strong>childs</strong> field has been renamed 3553 <strong>children</strong> so s/childs/children/g should be applied 3554 (probability of having "childs" anywhere else is close to 0+</li> 3555 <li>The document don't have anymore a <strong>root</strong> element it has 3556 been replaced by <strong>children</strong> and usually you will get a 3557 list of element here. For example a Dtd element for the internal subset 3558 and it's declaration may be found in that list, as well as processing 3559 instructions or comments found before or after the document root element. 3560 Use <strong>xmlDocGetRootElement(doc)</strong> to get the root element of 3561 a document. Alternatively if you are sure to not reference DTDs nor have 3562 PIs or comments before or after the root element 3563 s/->root/->children/g will probably do it.</li> 3564 <li>The white space issue, this one is more complex, unless special case of 3565 validating parsing, the line breaks and spaces usually used for indenting 3566 and formatting the document content becomes significant. So they are 3567 reported by SAX and if your using the DOM tree, corresponding nodes are 3568 generated. Too approach can be taken: 3569 <ol> 3570 <li>lazy one, use the compatibility call 3571 <strong>xmlKeepBlanksDefault(0)</strong> but be aware that you are 3572 relying on a special (and possibly broken) set of heuristics of 3573 libxml to detect ignorable blanks. Don't complain if it breaks or 3574 make your application not 100% clean w.r.t. to it's input.</li> 3575 <li>the Right Way: change you code to accept possibly insignificant 3576 blanks characters, or have your tree populated with weird blank text 3577 nodes. You can spot them using the commodity function 3578 <strong>xmlIsBlankNode(node)</strong> returning 1 for such blank 3579 nodes.</li> 3580 </ol> 3581 <p>Note also that with the new default the output functions don't add any 3582 extra indentation when saving a tree in order to be able to round trip 3583 (read and save) without inflating the document with extra formatting 3584 chars.</p> 3585 </li> 3586 <li>The include path has changed to $prefix/libxml/ and the includes 3587 themselves uses this new prefix in includes instructions... If you are 3588 using (as expected) the 3589 <pre>xml2-config --cflags</pre> 3590 <p>output to generate you compile commands this will probably work out of 3591 the box</p> 3592 </li> 3593 <li>xmlDetectCharEncoding takes an extra argument indicating the length in 3594 byte of the head of the document available for character detection.</li> 3595</ol> 3596 3597<h3>Ensuring both libxml-1.x and libxml-2.x compatibility</h3> 3598 3599<p>Two new version of libxml (1.8.11) and libxml2 (2.3.4) have been released 3600to allow smooth upgrade of existing libxml v1code while retaining 3601compatibility. They offers the following:</p> 3602<ol> 3603 <li>similar include naming, one should use 3604 <strong>#include<libxml/...></strong> in both cases.</li> 3605 <li>similar identifiers defined via macros for the child and root fields: 3606 respectively <strong>xmlChildrenNode</strong> and 3607 <strong>xmlRootNode</strong></li> 3608 <li>a new macro <strong>LIBXML_TEST_VERSION</strong> which should be 3609 inserted once in the client code</li> 3610</ol> 3611 3612<p>So the roadmap to upgrade your existing libxml applications is the 3613following:</p> 3614<ol> 3615 <li>install the libxml-1.8.8 (and libxml-devel-1.8.8) packages</li> 3616 <li>find all occurrences where the xmlDoc <strong>root</strong> field is 3617 used and change it to <strong>xmlRootNode</strong></li> 3618 <li>similarly find all occurrences where the xmlNode 3619 <strong>childs</strong> field is used and change it to 3620 <strong>xmlChildrenNode</strong></li> 3621 <li>add a <strong>LIBXML_TEST_VERSION</strong> macro somewhere in your 3622 <strong>main()</strong> or in the library init entry point</li> 3623 <li>Recompile, check compatibility, it should still work</li> 3624 <li>Change your configure script to look first for xml2-config and fall 3625 back using xml-config . Use the --cflags and --libs output of the command 3626 as the Include and Linking parameters needed to use libxml.</li> 3627 <li>install libxml2-2.3.x and libxml2-devel-2.3.x (libxml-1.8.y and 3628 libxml-devel-1.8.y can be kept simultaneously)</li> 3629 <li>remove your config.cache, relaunch your configuration mechanism, and 3630 recompile, if steps 2 and 3 were done right it should compile as-is</li> 3631 <li>Test that your application is still running correctly, if not this may 3632 be due to extra empty nodes due to formating spaces being kept in libxml2 3633 contrary to libxml1, in that case insert xmlKeepBlanksDefault(1) in your 3634 code before calling the parser (next to 3635 <strong>LIBXML_TEST_VERSION</strong> is a fine place).</li> 3636</ol> 3637 3638<p>Following those steps should work. It worked for some of my own code.</p> 3639 3640<p>Let me put some emphasis on the fact that there is far more changes from 3641libxml 1.x to 2.x than the ones you may have to patch for. The overall code 3642has been considerably cleaned up and the conformance to the XML specification 3643has been drastically improved too. Don't take those changes as an excuse to 3644not upgrade, it may cost a lot on the long term ...</p> 3645 3646<h2><a name="Thread">Thread safety</a></h2> 3647 3648<p>Starting with 2.4.7, libxml makes provisions to ensure that concurrent 3649threads can safely work in parallel parsing different documents. There is 3650however a couple of things to do to ensure it:</p> 3651<ul> 3652 <li>configure the library accordingly using the --with-threads options</li> 3653 <li>call xmlInitParser() in the "main" thread before using any of the 3654 libxml API (except possibly selecting a different memory allocator)</li> 3655</ul> 3656 3657<p>Note that the thread safety cannot be ensured for multiple threads sharing 3658the same document, the locking must be done at the application level, libxml 3659exports a basic mutex and reentrant mutexes API in <libxml/threads.h>. 3660The parts of the library checked for thread safety are:</p> 3661<ul> 3662 <li>concurrent loading</li> 3663 <li>file access resolution</li> 3664 <li>catalog access</li> 3665 <li>catalog building</li> 3666 <li>entities lookup/accesses</li> 3667 <li>validation</li> 3668 <li>global variables per-thread override</li> 3669 <li>memory handling</li> 3670</ul> 3671 3672<p>XPath is supposed to be thread safe now, but this wasn't tested 3673seriously.</p> 3674 3675<h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2> 3676 3677<p><a href="http://www.w3.org/DOM/">DOM</a> stands for the <em>Document 3678Object Model</em>; this is an API for accessing XML or HTML structured 3679documents. Native support for DOM in Gnome is on the way (module gnome-dom), 3680and will be based on gnome-xml. This will be a far cleaner interface to 3681manipulate XML files within Gnome since it won't expose the internal 3682structure.</p> 3683 3684<p>The current DOM implementation on top of libxml is the <a 3685href="http://cvs.gnome.org/lxr/source/gdome2/">gdome2 Gnome module</a>, this 3686is a full DOM interface, thanks to Paolo Casarini, check the <a 3687href="http://www.cs.unibo.it/~casarini/gdome2/">Gdome2 homepage</a> for more 3688informations.</p> 3689 3690<h2><a name="Example"></a><a name="real">A real example</a></h2> 3691 3692<p>Here is a real size example, where the actual content of the application 3693data is not kept in the DOM tree but uses internal structures. It is based on 3694a proposal to keep a database of jobs related to Gnome, with an XML based 3695storage structure. Here is an <a href="gjobs.xml">XML encoded jobs 3696base</a>:</p> 3697<pre><?xml version="1.0"?> 3698<gjob:Helping xmlns:gjob="http://www.gnome.org/some-location"> 3699 <gjob:Jobs> 3700 3701 <gjob:Job> 3702 <gjob:Project ID="3"/> 3703 <gjob:Application>GBackup</gjob:Application> 3704 <gjob:Category>Development</gjob:Category> 3705 3706 <gjob:Update> 3707 <gjob:Status>Open</gjob:Status> 3708 <gjob:Modified>Mon, 07 Jun 1999 20:27:45 -0400 MET DST</gjob:Modified> 3709 <gjob:Salary>USD 0.00</gjob:Salary> 3710 </gjob:Update> 3711 3712 <gjob:Developers> 3713 <gjob:Developer> 3714 </gjob:Developer> 3715 </gjob:Developers> 3716 3717 <gjob:Contact> 3718 <gjob:Person>Nathan Clemons</gjob:Person> 3719 <gjob:Email>nathan@windsofstorm.net</gjob:Email> 3720 <gjob:Company> 3721 </gjob:Company> 3722 <gjob:Organisation> 3723 </gjob:Organisation> 3724 <gjob:Webpage> 3725 </gjob:Webpage> 3726 <gjob:Snailmail> 3727 </gjob:Snailmail> 3728 <gjob:Phone> 3729 </gjob:Phone> 3730 </gjob:Contact> 3731 3732 <gjob:Requirements> 3733 The program should be released as free software, under the GPL. 3734 </gjob:Requirements> 3735 3736 <gjob:Skills> 3737 </gjob:Skills> 3738 3739 <gjob:Details> 3740 A GNOME based system that will allow a superuser to configure 3741 compressed and uncompressed files and/or file systems to be backed 3742 up with a supported media in the system. This should be able to 3743 perform via find commands generating a list of files that are passed 3744 to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine 3745 or via operations performed on the filesystem itself. Email 3746 notification and GUI status display very important. 3747 </gjob:Details> 3748 3749 </gjob:Job> 3750 3751 </gjob:Jobs> 3752</gjob:Helping></pre> 3753 3754<p>While loading the XML file into an internal DOM tree is a matter of 3755calling only a couple of functions, browsing the tree to gather the data and 3756generate the internal structures is harder, and more error prone.</p> 3757 3758<p>The suggested principle is to be tolerant with respect to the input 3759structure. For example, the ordering of the attributes is not significant, 3760the XML specification is clear about it. It's also usually a good idea not to 3761depend on the order of the children of a given node, unless it really makes 3762things harder. Here is some code to parse the information for a person:</p> 3763<pre>/* 3764 * A person record 3765 */ 3766typedef struct person { 3767 char *name; 3768 char *email; 3769 char *company; 3770 char *organisation; 3771 char *smail; 3772 char *webPage; 3773 char *phone; 3774} person, *personPtr; 3775 3776/* 3777 * And the code needed to parse it 3778 */ 3779personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) { 3780 personPtr ret = NULL; 3781 3782DEBUG("parsePerson\n"); 3783 /* 3784 * allocate the struct 3785 */ 3786 ret = (personPtr) malloc(sizeof(person)); 3787 if (ret == NULL) { 3788 fprintf(stderr,"out of memory\n"); 3789 return(NULL); 3790 } 3791 memset(ret, 0, sizeof(person)); 3792 3793 /* We don't care what the top level element name is */ 3794 cur = cur->xmlChildrenNode; 3795 while (cur != NULL) { 3796 if ((!strcmp(cur->name, "Person")) && (cur->ns == ns)) 3797 ret->name = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3798 if ((!strcmp(cur->name, "Email")) && (cur->ns == ns)) 3799 ret->email = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3800 cur = cur->next; 3801 } 3802 3803 return(ret); 3804}</pre> 3805 3806<p>Here are a couple of things to notice:</p> 3807<ul> 3808 <li>Usually a recursive parsing style is the more convenient one: XML data 3809 is by nature subject to repetitive constructs and usually exhibits highly 3810 structured patterns.</li> 3811 <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, 3812 i.e. the pointer to the global XML document and the namespace reserved to 3813 the application. Document wide information are needed for example to 3814 decode entities and it's a good coding practice to define a namespace for 3815 your application set of data and test that the element and attributes 3816 you're analyzing actually pertains to your application space. This is 3817 done by a simple equality test (cur->ns == ns).</li> 3818 <li>To retrieve text and attributes value, you can use the function 3819 <em>xmlNodeListGetString</em> to gather all the text and entity reference 3820 nodes generated by the DOM output and produce an single text string.</li> 3821</ul> 3822 3823<p>Here is another piece of code used to parse another level of the 3824structure:</p> 3825<pre>#include <libxml/tree.h> 3826/* 3827 * a Description for a Job 3828 */ 3829typedef struct job { 3830 char *projectID; 3831 char *application; 3832 char *category; 3833 personPtr contact; 3834 int nbDevelopers; 3835 personPtr developers[100]; /* using dynamic alloc is left as an exercise */ 3836} job, *jobPtr; 3837 3838/* 3839 * And the code needed to parse it 3840 */ 3841jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) { 3842 jobPtr ret = NULL; 3843 3844DEBUG("parseJob\n"); 3845 /* 3846 * allocate the struct 3847 */ 3848 ret = (jobPtr) malloc(sizeof(job)); 3849 if (ret == NULL) { 3850 fprintf(stderr,"out of memory\n"); 3851 return(NULL); 3852 } 3853 memset(ret, 0, sizeof(job)); 3854 3855 /* We don't care what the top level element name is */ 3856 cur = cur->xmlChildrenNode; 3857 while (cur != NULL) { 3858 3859 if ((!strcmp(cur->name, "Project")) && (cur->ns == ns)) { 3860 ret->projectID = xmlGetProp(cur, "ID"); 3861 if (ret->projectID == NULL) { 3862 fprintf(stderr, "Project has no ID\n"); 3863 } 3864 } 3865 if ((!strcmp(cur->name, "Application")) && (cur->ns == ns)) 3866 ret->application = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3867 if ((!strcmp(cur->name, "Category")) && (cur->ns == ns)) 3868 ret->category = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); 3869 if ((!strcmp(cur->name, "Contact")) && (cur->ns == ns)) 3870 ret->contact = parsePerson(doc, ns, cur); 3871 cur = cur->next; 3872 } 3873 3874 return(ret); 3875}</pre> 3876 3877<p>Once you are used to it, writing this kind of code is quite simple, but 3878boring. Ultimately, it could be possible to write stubbers taking either C 3879data structure definitions, a set of XML examples or an XML DTD and produce 3880the code needed to import and export the content between C data and XML 3881storage. This is left as an exercise to the reader :-)</p> 3882 3883<p>Feel free to use <a href="example/gjobread.c">the code for the full C 3884parsing example</a> as a template, it is also available with Makefile in the 3885Gnome CVS base under gnome-xml/example</p> 3886 3887<h2><a name="Contributi">Contributions</a></h2> 3888<ul> 3889 <li>Bjorn Reese, William Brack and Thomas Broyer have provided a number of 3890 patches, Gary Pennington worked on the validation API, threading support 3891 and Solaris port.</li> 3892 <li>John Fleck helps maintaining the documentation and man pages.</li> 3893 <li><a href="mailto:igor@stud.fh-frankfurt.de">Igor Zlatkovic</a> is now 3894 the maintainer of the Windows port, <a 3895 href="http://www.fh-frankfurt.de/~igor/projects/libxml/index.html">he 3896 provides binaries</a></li> 3897 <li><a href="mailto:Gary.Pennington@sun.com">Gary Pennington</a> provides 3898 <a href="http://garypennington.net/libxml2/">Solaris binaries</a></li> 3899 <li><a 3900 href="http://mail.gnome.org/archives/xml/2001-March/msg00014.html">Matt 3901 Sergeant</a> developed <a 3902 href="http://axkit.org/download/">XML::LibXSLT</a>, a Perl wrapper for 3903 libxml2/libxslt as part of the <a href="http://axkit.com/">AxKit XML 3904 application server</a></li> 3905 <li><a href="mailto:fnatter@gmx.net">Felix Natter</a> and <a 3906 href="mailto:geertk@ai.rug.nl">Geert Kloosterman</a> provide <a 3907 href="libxml-doc.el">an emacs module</a> to lookup libxml(2) functions 3908 documentation</li> 3909 <li><a href="mailto:sherwin@nlm.nih.gov">Ziying Sherwin</a> provided <a 3910 href="http://xmlsoft.org/messages/0488.html">man pages</a></li> 3911 <li>there is a module for <a 3912 href="http://acs-misc.sourceforge.net/nsxml.html">libxml/libxslt support 3913 in OpenNSD/AOLServer</a></li> 3914 <li><a href="mailto:dkuhlman@cutter.rexx.com">Dave Kuhlman</a> provided the 3915 first version of libxml/libxslt <a 3916 href="http://www.rexx.com/~dkuhlman">wrappers for Python</a></li> 3917 <li>Petr Kozelka provides <a 3918 href="http://sourceforge.net/projects/libxml2-pas">Pascal units to glue 3919 libxml2</a> with Kylix and Delphi and other Pascal compilers</li> 3920 <li><a href="mailto:aleksey@aleksey.com">Aleksey Sanin</a> implemented the 3921 <a href="http://www.w3.org/Signature/">XML Canonicalization and XML 3922 Digital Signature</a> <a 3923 href="http://www.aleksey.com/xmlsec/">implementations for libxml2</a></li> 3924</ul> 3925 3926<p></p> 3927</body> 3928</html> 3929
