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</style><title>Upgrading 1.x code</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"> |    | The XML C parser and toolkit of GnomeUpgrading 1.x code |
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| <center>API Indexes</center> | |
| <center>Related links</center> | |
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| Incompatible changes: Version 2 of libxml2 is the first version introducing serious backward |
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incompatible changes. The main goals were:
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a general cleanup. A number of mistakes inherited from the very early
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versions couldn't be changed due to compatibility constraints. Example
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the "childs" element in the nodes.
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Uniformization of the various nodes, at least for their header and link
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parts (doc, parent, children, prev, next), the goal is a simpler
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programming model and simplifying the task of the DOM implementors.
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better conformances to the XML specification, for example version 1.x
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had an heuristic to try to detect ignorable white spaces. As a result the
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SAX event generated were ignorableWhitespace() while the spec requires
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character() in that case. This also mean that a number of DOM node
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containing blank text may populate the DOM tree which were not present
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before.
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How to fix libxml-1.x code:So client code of libxml designed to run with version 1.x may have to be
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changed to compile against version 2.x of libxml. Here is a list of changes
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that I have collected, they may not be sufficient, so in case you find other
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change which are required, drop me a
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mail:
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The package name have changed from libxml to libxml2, the library name
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is now -lxml2 . There is a new xml2-config script which should be used to
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select the right parameters libxml2
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Node childs field has been renamed
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children so s/childs/children/g should be applied
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(probability of having "childs" anywhere else is close to 0+
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The document don't have anymore a root element it has
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been replaced by children and usually you will get a
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list of element here. For example a Dtd element for the internal subset
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and it's declaration may be found in that list, as well as processing
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instructions or comments found before or after the document root element.
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Use xmlDocGetRootElement(doc) to get the root element of
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a document. Alternatively if you are sure to not reference DTDs nor have
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PIs or comments before or after the root element
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s/->root/->children/g will probably do it.
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The white space issue, this one is more complex, unless special case of
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validating parsing, the line breaks and spaces usually used for indenting
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and formatting the document content becomes significant. So they are
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reported by SAX and if your using the DOM tree, corresponding nodes are
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generated. Too approach can be taken:
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lazy one, use the compatibility call
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xmlKeepBlanksDefault(0) but be aware that you are
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relying on a special (and possibly broken) set of heuristics of
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libxml to detect ignorable blanks. Don't complain if it breaks or
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make your application not 100% clean w.r.t. to it's input.
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the Right Way: change you code to accept possibly insignificant
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blanks characters, or have your tree populated with weird blank text
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nodes. You can spot them using the commodity function
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xmlIsBlankNode(node) returning 1 for such blank
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nodes.
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Note also that with the new default the output functions don't add any
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extra indentation when saving a tree in order to be able to round trip
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(read and save) without inflating the document with extra formatting
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chars.
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The include path has changed to $prefix/libxml/ and the includes
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themselves uses this new prefix in includes instructions... If you are
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using (as expected) the
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xml2-config --cflags
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output to generate you compile commands this will probably work out of
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the box
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xmlDetectCharEncoding takes an extra argument indicating the length in
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byte of the head of the document available for character detection.
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Ensuring both libxml-1.x and libxml-2.x compatibilityTwo new version of libxml (1.8.11) and libxml2 (2.3.4) have been released
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to allow smooth upgrade of existing libxml v1code while retaining
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compatibility. They offers the following:
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similar include naming, one should use
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#include<libxml/...> in both cases.
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similar identifiers defined via macros for the child and root fields:
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respectively xmlChildrenNode and
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xmlRootNode
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a new macro LIBXML_TEST_VERSION which should be
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inserted once in the client code
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So the roadmap to upgrade your existing libxml applications is the
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following:
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install the libxml-1.8.8 (and libxml-devel-1.8.8) packages
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find all occurrences where the xmlDoc root field is
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used and change it to xmlRootNode
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similarly find all occurrences where the xmlNode
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childs field is used and change it to
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xmlChildrenNode
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add a LIBXML_TEST_VERSION macro somewhere in your
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main() or in the library init entry point
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Recompile, check compatibility, it should still work
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Change your configure script to look first for xml2-config and fall
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back using xml-config . Use the --cflags and --libs output of the command
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as the Include and Linking parameters needed to use libxml.
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install libxml2-2.3.x and libxml2-devel-2.3.x (libxml-1.8.y and
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libxml-devel-1.8.y can be kept simultaneously)
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remove your config.cache, relaunch your configuration mechanism, and
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recompile, if steps 2 and 3 were done right it should compile as-is
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Test that your application is still running correctly, if not this may
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be due to extra empty nodes due to formating spaces being kept in libxml2
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contrary to libxml1, in that case insert xmlKeepBlanksDefault(1) in your
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code before calling the parser (next to
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LIBXML_TEST_VERSION is a fine place).
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Following those steps should work. It worked for some of my own code. Let me put some emphasis on the fact that there is far more changes from
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libxml 1.x to 2.x than the ones you may have to patch for. The overall code
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has been considerably cleaned up and the conformance to the XML specification
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has been drastically improved too. Don't take those changes as an excuse to
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not upgrade, it may cost a lot on the long term ...Daniel Veillard </body></html>
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