doc/upgrade.html - third_party/libxml2 - Git at Google

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
                       "http://www.w3.org/TR/REC-html40/loose.dtd">
 <html>
 <head>
   <title>Upgrading libxml client code from 1.x to 2.x</title>
   <meta name="GENERATOR" content="amaya V2.1">
   <meta http-equiv="Content-Type" content="text/html">
 </head>

 <body bgcolor="#ffffff">
 <h1 align="center">Upgrading libxml client code from 1.x to 2.x</h1>

 <h2>Incompatible changes:</h2>

 <p>Version 2 of libxml is the first version introducing serious backward
 incompatible changes. The main goals were:</p>
 <ul>
   <li>a general cleanup. A number of mistakes inherited from the very early
     versions couldn't be changed due to compatibility constraints. Example the
     "childs" element in the nodes.</li>
   <li>Uniformization of the various nodes, at least for their header and link
     parts (doc, parent, children, prev, next), the goal is a simpler
     programming model and simplifying the task of the DOM implementors.</li>
   <li>better conformances to the XML specification, for example version 1.x
     had an heuristic to try to detect ignorable white spaces. As a result the
     SAX event generated were ignorableWhitespace() while the spec requires
     character() in that case. This also mean that a number of DOM node
     containing blank text may populate the DOM tree which were not present
     before.</li>
 </ul>

 <h2>How to fix libxml-1.x code:</h2>

 <p>So client code of libxml designed to run with version 1.x may have to be
 changed to compile against version 2.x of libxml. Here is a list of changes
 that I have collected, they may not be sufficient, so in case you find other
 change which are required, <a href="mailto:Daniel.Ïeillardw3.org">drop me a
 mail</a>:</p>
 <ol>
   <li>Node <strong>childs</strong> field has been renamed
     <strong>children</strong> so s/childs/children/g should be  applied
     (probablility of having "childs" anywere else is close to 0+</li>
   <li>The document don't have anymore a <strong>root</strong> element it has
     been replaced by <strong>children</strong> and usually you will get a list
     of element here. For example a Dtd element for the internal subset and
     it's declaration may be found in that list, as well as processing
     instructions or comments found before or after the document root element.
     Use <strong>xmlDocGetRootElement(doc)</strong> to get the root element of
     a document. Alternatively if you are sure to not reference Dtds nor have
     PIs or comments before or after the root element s/->root/->children/g
     will probably do it.</li>
   <li>The white space issue, this one is more complex, unless special case of
     validating parsing, the line breaks and spaces usually used for indenting
     and formatting the document content becomes significant. So they are
     reported by SAX and if your using the DOM tree, corresponding nodes are
     generated. Too approach can be taken:
     <ol>
       <li>lazy one, use the compatibility call
         <strong>xmlKeepBlanksDefault(0)</strong> but be aware that you are
         relying on a special (and possibly broken) set of heuristics of libxml
         to detect ignorable blanks. Don't complain if it breaks or make your
         application not 100% clean w.r.t. to it's input.</li>
       <li>the Right Way: change you code to accept possibly unsignificant
         blanks characters, or have your tree populated with weird blank text
         nodes. You can spot them using the comodity function
         <strong>xmlIsBlankNode(node)</strong> returning 1 for such blank
         nodes.</li>
     </ol>
     <p>Note also that with the new default the output functions don't add any
     extra indentation when saving a tree in order to be able to round trip
     (read and save) without inflating the document with extra formatting
     chars.</p>
   </li>
   <li>The include path has changed to $prefix/libxml/ and the includes
     themselves uses this new prefix in includes instructions... If you are
     using (as expected) the
     <pre>xml-config --cflags</pre>
     <p>output to generate you compile commands this will probably work out of
     the box</p>
   </li>
 </ol>

 <h2>Ensuring both libxml-1.x and libxml-2.x compatibility</h2>

 <p>Two new version of libxml (1.8.8) and libxml2 (2.1.0) have been released to
 allow smoth upgrade of existing libxml v1code while retaining compatibility.
 They offers the following:</p>
 <ol>
   <li>similar include naming, one should use
     <strong>#include&lt;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 be
     inserted once in the client code</li>
 </ol>

 <p>So the roadmap to upgrade your existing libxml applications is the
 following:</p>
 <ol>
   <li>install the  libxml-1.8.8 (and libxml-devel-1.8.8) packages</li>
   <li>find all occurences where the xmlDoc <strong>root</strong> field is used
     and change it to <strong>xmlRootNode</strong></li>
   <li>similary find all occurences 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>install libxml2-2.1.0, remove libxml-devel-1.8.8 and install
     libxml2-devel-2.1.0 (libxml-1.8.8 can be kept installed for legacy
   stuff)</li>
   <li>remove your config.cache, relaunch your configuration mechanism, and
     recompile, 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 may
     be due to extra empty nodes due to formating spaces being kept in libxml2
     contrary to libxml1, in that case insert xmlKeepBlanksDefault(1) in your
     code 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 from
 libxml 1.x to 2.x than the ones you may have to patch for. The overall code
 has been considerably improved and the conformance to the XML specification
 has been drastically improve. Don't take those changes as an excuse to not
 upgrade, it may cost a lot on the long term ...</p>

 <p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>

 <p>$Id: upgrade.html,v 1.6 2000/06/29 00:43:26 veillard Exp $</p>
 </body>
 </html>
	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
	"http://www.w3.org/TR/REC-html40/loose.dtd">
	<html>
	<head>
	<title>Upgrading libxml client code from 1.x to 2.x</title>
	<meta name="GENERATOR" content="amaya V2.1">
	<meta http-equiv="Content-Type" content="text/html">
	</head>

	<body bgcolor="#ffffff">
	<h1 align="center">Upgrading libxml client code from 1.x to 2.x</h1>

	<h2>Incompatible changes:</h2>

	<p>Version 2 of libxml is the first version introducing serious backward
	incompatible changes. The main goals were:</p>
	<ul>
	<li>a general cleanup. A number of mistakes inherited from the very early
	versions couldn't be changed due to compatibility constraints. Example the
	"childs" element in the nodes.</li>
	<li>Uniformization of the various nodes, at least for their header and link
	parts (doc, parent, children, prev, next), the goal is a simpler
	programming model and simplifying the task of the DOM implementors.</li>
	<li>better conformances to the XML specification, for example version 1.x
	had an heuristic to try to detect ignorable white spaces. As a result the
	SAX event generated were ignorableWhitespace() while the spec requires
	character() in that case. This also mean that a number of DOM node
	containing blank text may populate the DOM tree which were not present
	before.</li>
	</ul>

	<h2>How to fix libxml-1.x code:</h2>

	<p>So client code of libxml designed to run with version 1.x may have to be
	changed to compile against version 2.x of libxml. Here is a list of changes
	that I have collected, they may not be sufficient, so in case you find other
	change which are required, <a href="mailto:Daniel.Ïeillardw3.org">drop me a
	mail</a>:</p>
	<ol>
	<li>Node <strong>childs</strong> field has been renamed
	<strong>children</strong> so s/childs/children/g should be applied
	(probablility of having "childs" anywere else is close to 0+</li>
	<li>The document don't have anymore a <strong>root</strong> element it has
	been replaced by <strong>children</strong> and usually you will get a list
	of element here. For example a Dtd element for the internal subset and
	it's declaration may be found in that list, as well as processing
	instructions or comments found before or after the document root element.
	Use <strong>xmlDocGetRootElement(doc)</strong> to get the root element of
	a document. Alternatively if you are sure to not reference Dtds nor have
	PIs or comments before or after the root element s/->root/->children/g
	will probably do it.</li>
	<li>The white space issue, this one is more complex, unless special case of
	validating parsing, the line breaks and spaces usually used for indenting
	and formatting the document content becomes significant. So they are
	reported by SAX and if your using the DOM tree, corresponding nodes are
	generated. Too approach can be taken:
	<ol>
	<li>lazy one, use the compatibility call
	<strong>xmlKeepBlanksDefault(0)</strong> but be aware that you are
	relying on a special (and possibly broken) set of heuristics of libxml
	to detect ignorable blanks. Don't complain if it breaks or make your
	application not 100% clean w.r.t. to it's input.</li>
	<li>the Right Way: change you code to accept possibly unsignificant
	blanks characters, or have your tree populated with weird blank text
	nodes. You can spot them using the comodity function
	<strong>xmlIsBlankNode(node)</strong> returning 1 for such blank
	nodes.</li>
	</ol>
	<p>Note also that with the new default the output functions don't add any
	extra indentation when saving a tree in order to be able to round trip
	(read and save) without inflating the document with extra formatting
	chars.</p>
	</li>
	<li>The include path has changed to $prefix/libxml/ and the includes
	themselves uses this new prefix in includes instructions... If you are
	using (as expected) the
	<pre>xml-config --cflags</pre>
	<p>output to generate you compile commands this will probably work out of
	the box</p>
	</li>
	</ol>

	<h2>Ensuring both libxml-1.x and libxml-2.x compatibility</h2>

	<p>Two new version of libxml (1.8.8) and libxml2 (2.1.0) have been released to
	allow smoth upgrade of existing libxml v1code while retaining compatibility.
	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 be
	inserted once in the client code</li>
	</ol>

	<p>So the roadmap to upgrade your existing libxml applications is the
	following:</p>
	<ol>
	<li>install the libxml-1.8.8 (and libxml-devel-1.8.8) packages</li>
	<li>find all occurences where the xmlDoc <strong>root</strong> field is used
	and change it to <strong>xmlRootNode</strong></li>
	<li>similary find all occurences 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>install libxml2-2.1.0, remove libxml-devel-1.8.8 and install
	libxml2-devel-2.1.0 (libxml-1.8.8 can be kept installed for legacy
	stuff)</li>
	<li>remove your config.cache, relaunch your configuration mechanism, and
	recompile, 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 may
	be due to extra empty nodes due to formating spaces being kept in libxml2
	contrary to libxml1, in that case insert xmlKeepBlanksDefault(1) in your
	code 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 from
	libxml 1.x to 2.x than the ones you may have to patch for. The overall code
	has been considerably improved and the conformance to the XML specification
	has been drastically improve. Don't take those changes as an excuse to not
	upgrade, it may cost a lot on the long term ...</p>

	<p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>

	<p>$Id: upgrade.html,v 1.6 2000/06/29 00:43:26 veillard Exp $</p>
	</body>
	</html>