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| </style><title>Upgrading 1.x code</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"><table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr><td width="120"><a href="http://swpat.ffii.org/"><img src="epatents.png" alt="Action against software patents" /></a></td><td width="180"><a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 Logo" /></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo" /></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo" /></a><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo" /></a></div></td><td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center"><h1>The XML C parser and toolkit of Gnome</h1><h2>Upgrading 1.x code</h2></td></tr></table></td></tr></table></td></tr></table><table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr><td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Developer Menu</b></center></td></tr><tr><td bgcolor="#fffacd"><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="20" value="" /><input name="submit" type="submit" value="Search ..." /></form><ul><li><a href="index.html" style="font-weight:bold">Main Menu</a></li><li><a href="html/index.html" style="font-weight:bold">Reference Manual</a></li><li><a href="examples/index.html" style="font-weight:bold">Code Examples</a></li><li><a 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bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"><p>Incompatible changes:</p><p>Version 2 of libxml2 is the first version introducing serious |
| backwardincompatible changes. The main goals were:</p><ul><li>a general cleanup. A number of mistakes inherited from the very |
| earlyversions couldn't be changed due to compatibility constraints. |
| Examplethe "childs" element in the nodes.</li> |
| <li>Uniformization of the various nodes, at least for their header and |
| linkparts (doc, parent, children, prev, next), the goal is a |
| simplerprogramming model and simplifying the task of the DOM |
| implementors.</li> |
| <li>better conformances to the XML specification, for example version |
| 1.xhad an heuristic to try to detect ignorable white spaces. As a result |
| theSAX event generated were ignorableWhitespace() while the spec |
| requirescharacter() in that case. This also mean that a number of DOM |
| nodecontaining blank text may populate the DOM tree which were not |
| presentbefore.</li> |
| </ul><h3>How to fix libxml-1.x code:</h3><p>So client code of libxml designed to run with version 1.x may have to |
| bechanged to compile against version 2.x of libxml. Here is a list of |
| changesthat I have collected, they may not be sufficient, so in case you find |
| otherchange which are required, <a href="mailto:Daniel.Veillard@w3.org">drop |
| me amail</a>:</p><ol><li>The package name have changed from libxml to libxml2, the library |
| nameis now -lxml2 . There is a new xml2-config script which should be |
| used toselect the right parameters libxml2</li> |
| <li>Node <strong>childs</strong>field has been |
| renamed<strong>children</strong>so s/childs/children/g should be |
| applied(probability of having "childs" anywhere else is close to 0+</li> |
| <li>The document don't have anymore a <strong>root</strong>element it |
| hasbeen replaced by <strong>children</strong>and usually you will get |
| alist of element here. For example a Dtd element for the internal |
| subsetand it's declaration may be found in that list, as well as |
| processinginstructions or comments found before or after the document |
| root element.Use <strong>xmlDocGetRootElement(doc)</strong>to get the |
| root element ofa document. Alternatively if you are sure to not reference |
| DTDs nor havePIs or comments before or after the root |
| elements/->root/->children/g will probably do it.</li> |
| <li>The white space issue, this one is more complex, unless special case |
| ofvalidating parsing, the line breaks and spaces usually used for |
| indentingand formatting the document content becomes significant. So they |
| arereported by SAX and if your using the DOM tree, corresponding nodes |
| aregenerated. Too approach can be taken: |
| <ol><li>lazy one, use the compatibility |
| call<strong>xmlKeepBlanksDefault(0)</strong>but be aware that you |
| arerelying on a special (and possibly broken) set of heuristics |
| oflibxml to detect ignorable blanks. Don't complain if it breaks |
| ormake your application not 100% clean w.r.t. to it's input.</li> |
| <li>the Right Way: change you code to accept possibly |
| insignificantblanks characters, or have your tree populated with |
| weird blank textnodes. You can spot them using the commodity |
| function<strong>xmlIsBlankNode(node)</strong>returning 1 for such |
| blanknodes.</li> |
| </ol><p>Note also that with the new default the output functions don't add |
| anyextra indentation when saving a tree in order to be able to round |
| trip(read and save) without inflating the document with extra |
| formattingchars.</p> |
| </li> |
| <li>The include path has changed to $prefix/libxml/ and the |
| includesthemselves uses this new prefix in includes instructions... If |
| you areusing (as expected) the |
| <pre>xml2-config --cflags</pre> |
| <p>output to generate you compile commands this will probably work out |
| ofthe box</p> |
| </li> |
| <li>xmlDetectCharEncoding takes an extra argument indicating the length |
| inbyte of the head of the document available for character detection.</li> |
| </ol><h3>Ensuring both libxml-1.x and libxml-2.x compatibility</h3><p>Two new version of libxml (1.8.11) and libxml2 (2.3.4) have been |
| releasedto allow smooth upgrade of existing libxml v1code while |
| retainingcompatibility. They offers the following:</p><ol><li>similar include naming, one should |
| use<strong>#include<libxml/...></strong>in both cases.</li> |
| <li>similar identifiers defined via macros for the child and root |
| fields:respectively |
| <strong>xmlChildrenNode</strong>and<strong>xmlRootNode</strong></li> |
| <li>a new macro <strong>LIBXML_TEST_VERSION</strong>which should beinserted |
| once in the client code</li> |
| </ol><p>So the roadmap to upgrade your existing libxml applications is |
| thefollowing:</p><ol><li>install the libxml-1.8.8 (and libxml-devel-1.8.8) packages</li> |
| <li>find all occurrences where the xmlDoc <strong>root</strong>field isused |
| and change it to <strong>xmlRootNode</strong></li> |
| <li>similarly find all occurrences where the |
| xmlNode<strong>childs</strong>field is used and change it |
| to<strong>xmlChildrenNode</strong></li> |
| <li>add a <strong>LIBXML_TEST_VERSION</strong>macro somewhere in |
| your<strong>main()</strong>or in the library init entry point</li> |
| <li>Recompile, check compatibility, it should still work</li> |
| <li>Change your configure script to look first for xml2-config and fallback |
| using xml-config . Use the --cflags and --libs output of the commandas |
| the Include and Linking parameters needed to use libxml.</li> |
| <li>install libxml2-2.3.x and libxml2-devel-2.3.x (libxml-1.8.y |
| andlibxml-devel-1.8.y can be kept simultaneously)</li> |
| <li>remove your config.cache, relaunch your configuration mechanism, |
| andrecompile, if steps 2 and 3 were done right it should compile |
| as-is</li> |
| <li>Test that your application is still running correctly, if not this |
| maybe due to extra empty nodes due to formating spaces being kept in |
| libxml2contrary to libxml1, in that case insert xmlKeepBlanksDefault(1) |
| in yourcode before calling the parser (next |
| to<strong>LIBXML_TEST_VERSION</strong>is a fine place).</li> |
| </ol><p>Following those steps should work. It worked for some of my own code.</p><p>Let me put some emphasis on the fact that there is far more changes |
| fromlibxml 1.x to 2.x than the ones you may have to patch for. The overall |
| codehas been considerably cleaned up and the conformance to the XML |
| specificationhas been drastically improved too. Don't take those changes as |
| an excuse tonot upgrade, it may cost a lot on the long term ...</p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html> |
