LibXML(3pm) User Contributed Perl Documentation LibXML(3pm)NAMEXML::LibXML - Perl Binding for libxml2
SYNOPSIS
use XML::LibXML;
my $dom = XML::LibXML->load_xml(string => <<'EOT');
<some-xml/>
EOT
$Version_String = XML::LibXML::LIBXML_DOTTED_VERSION;
$Version_ID = XML::LibXML::LIBXML_VERSION;
$DLL_Version = XML::LibXML::LIBXML_RUNTIME_VERSION;
$libxmlnode = XML::LibXML->import_GDOME( $node, $deep );
$gdomenode = XML::LibXML->export_GDOME( $node, $deep );
DESCRIPTION
This module is an interface to libxml2, providing XML and HTML parsers
with DOM, SAX and XMLReader interfaces, a large subset of DOM Layer 3
interface and a XML::XPath-like interface to XPath API of libxml2. The
module is split into several packages which are not described in this
section; unless stated otherwise, you only need to "use XML::LibXML;"
in your programs.
For further information, please check the following documentation:
XML::LibXML::Parser
Parsing XML files with XML::LibXML
XML::LibXML::DOM
XML::LibXML Document Object Model (DOM) Implementation
XML::LibXML::SAX
XML::LibXML direct SAX parser
XML::LibXML::Reader
Reading XML with a pull-parser
XML::LibXML::Dtd
XML::LibXML frontend for DTD validation
XML::LibXML::RelaxNG
XML::LibXML frontend for RelaxNG schema validation
XML::LibXML::Schema
XML::LibXML frontend for W3C Schema schema validation
XML::LibXML::XPathContext
API for evaluating XPath expressions with enhanced support for the
evaluation context
XML::LibXML::InputCallback
Implementing custom URI Resolver and input callbacks
XML::LibXML::Common
Common functions for XML::LibXML related Classes
The nodes in the Document Object Model (DOM) are represented by the
following classes (most of which "inherit" from XML::LibXML::Node):
XML::LibXML::Document
XML::LibXML class for DOM document nodes
XML::LibXML::Node
Abstract base class for XML::LibXML DOM nodes
XML::LibXML::Element
XML::LibXML class for DOM element nodes
XML::LibXML::Text
XML::LibXML class for DOM text nodes
XML::LibXML::Comment
XML::LibXML class for comment DOM nodes
XML::LibXML::CDATASection
XML::LibXML class for DOM CDATA sections
XML::LibXML::Attr
XML::LibXML DOM attribute class
XML::LibXML::DocumentFragment
XML::LibXML's DOM L2 Document Fragment implementation
XML::LibXML::Namespace
XML::LibXML DOM namespace nodes
XML::LibXML::PI
XML::LibXML DOM processing instruction nodes
ENCODINGS SUPPORT IN XML::LIBXML
Recall that since version 5.6.1, Perl distinguishes between character
strings (internally encoded in UTF-8) and so called binary data and,
accordingly, applies either character or byte semantics to them. A
scalar representing a character string is distinguished from a byte
string by special flag (UTF8). Please refer to perlunicode for
details.
XML::LibXML's API is designed to deal with many encodings of XML
documents completely transparently, so that the application using
XML::LibXML can be completely ignorant about the encoding of the XML
documents it works with. On the other hand, functions like
"XML::LibXML::Document->setEncoding" give the user control over the
document encoding.
To ensure the aforementioned transparency and uniformity, most
functions of XML::LibXML that work with in-memory trees accept and
return data as character strings (i.e. UTF-8 encoded with the UTF8 flag
on) regardless of the original document encoding; however, the
functions related to I/O operations (i.e. parsing and saving) operate
with binary data (in the original document encoding) obeying the
encoding declaration of the XML documents.
Below we summarize basic rules and principles regarding encoding:
1. Do NOT apply any encoding-related PerlIO layers (":utf8" or
":encoding(...)") to file handles that are an input for the parses
or an output for a serializer of (full) XML documents. This is
because the conversion of the data to/from the internal character
representation is provided by libxml2 itself which must be able to
enforce the encoding specified by the "<?xml version="1.0"
encoding="..."?>" declaration. Here is an example to follow:
use XML::LibXML;
# load
open my $fh, '<', 'file.xml';
binmode $fh; # drop all PerlIO layers possibly created by a use open pragma
$doc = XML::LibXML->load_xml(IO => $fh);
# save
open my $out, '>', 'out.xml';
binmode $out; # as above
$doc->toFH($out);
# or
print {$out} $doc->toString();
2. All functions working with DOM accept and return character strings
(UTF-8 encoded with UTF8 flag on). E.g.
my $doc = XML::LibXML::Document->new('1.0',$some_encoding);
my $element = $doc->createElement($name);
$element->appendText($text);
$xml_fragment = $element->toString(); # returns a character string
$xml_document = $doc->toString(); # returns a byte string
where $some_encoding is the document encoding that will be used
when saving the document, and $name and $text contain character
strings (UTF-8 encoded with UTF8 flag on). Note that the method
"toString" returns XML as a character string if applied to other
node than the Document node and a byte string containing the
appropriate
<?xml version="1.0" encoding="..."?>
declaration if applied to a XML::LibXML::Document.
3. DOM methods also accept binary strings in the original encoding of
the document to which the node belongs (UTF-8 is assumed if the
node is not attached to any document). Exploiting this feature is
NOT RECOMMENDED since it is considered bad practice.
my $doc = XML::LibXML::Document->new('1.0','iso-8859-2');
my $text = $doc->createTextNode($some_latin2_encoded_byte_string);
# WORKS, BUT NOT RECOMMENDED!
NOTE: libxml2 support for many encodings is based on the iconv library.
The actual list of supported encodings may vary from platform to
platform. To test if your platform works correctly with your language
encoding, build a simple document in the particular encoding and try to
parse it with XML::LibXML to see if the parser produces any errors.
Occasional crashes were reported on rare platforms that ship with a
broken version of iconv.
THREAD SUPPORTXML::LibXML since 1.67 partially supports Perl threads in Perl >=
5.8.8. XML::LibXML can be used with threads in two ways:
By default, all XML::LibXML classes use CLONE_SKIP class method to
prevent Perl from copying XML::LibXML::* objects when a new thread is
spawn. In this mode, all XML::LibXML::* objects are thread specific.
This is the safest way to work with XML::LibXML in threads.
Alternatively, one may use
use threads;
use XML::LibXML qw(:threads_shared);
to indicate, that all XML::LibXML node and parser objects should be
shared between the main thread and any thread spawn from there. For
example, in
my $doc = XML::LibXML->load_xml(location => $filename);
my $thr = threads->new(sub{
# code working with $doc
1;
});
$thr->join;
the variable $doc refers to the exact same XML::LibXML::Document in the
spawned thread as in the main thread.
Without using mutex locks, parallel threads may read the same document
(i.e. any node that belongs to the document), parse files, and modify
different documents.
However, if there is a chance that some of the threads will attempt to
modify a document (or even create new nodes based on that document,
e.g. with "$doc->createElement") that other threads may be reading at
the same time, the user is responsible for creating a mutex lock and
using it in both in the thread that modifies and the thread that reads:
my $doc = XML::LibXML->load_xml(location => $filename);
my $mutex : shared;
my $thr = threads->new(sub{
lock $mutex;
my $el = $doc->createElement('foo');
# ...
1;
});
{
lock $mutex;
my $root = $doc->documentElement;
say $root->name;
}
$thr->join;
Note that libxml2 uses dictionaries to store short strings and these
dictionaries are kept on a document node. Without mutex locks, it could
happen in the previous example that the thread modifies the dictionary
while other threads attempt to read from it, which could easily lead to
a crash.
VERSION INFORMATION
Sometimes it is useful to figure out, for which version XML::LibXML was
compiled for. In most cases this is for debugging or to check if a
given installation meets all functionality for the package. The
functions XML::LibXML::LIBXML_DOTTED_VERSION and
XML::LibXML::LIBXML_VERSION provide this version information. Both
functions simply pass through the values of the similar named macros of
libxml2. Similarly, XML::LibXML::LIBXML_RUNTIME_VERSION returns the
version of the (usually dynamically) linked libxml2.
XML::LibXML::LIBXML_DOTTED_VERSION
$Version_String = XML::LibXML::LIBXML_DOTTED_VERSION;
Returns the version string of the libxml2 version XML::LibXML was
compiled for. This will be "2.6.2" for "libxml2 2.6.2".
XML::LibXML::LIBXML_VERSION
$Version_ID = XML::LibXML::LIBXML_VERSION;
Returns the version id of the libxml2 version XML::LibXML was
compiled for. This will be "20602" for "libxml2 2.6.2". Don't mix
this version id with $XML::LibXML::VERSION. The latter contains the
version of XML::LibXML itself while the first contains the version
of libxml2 XML::LibXML was compiled for.
XML::LibXML::LIBXML_RUNTIME_VERSION
$DLL_Version = XML::LibXML::LIBXML_RUNTIME_VERSION;
Returns a version string of the libxml2 which is (usually
dynamically) linked by XML::LibXML. This will be "20602" for
libxml2 released as "2.6.2" and something like "20602-CVS2032" for
a CVS build of libxml2.
XML::LibXML issues a warning if the version of libxml2 dynamically
linked to it is less than the version of libxml2 which it was
compiled against.
EXPORTS
By default the module exports all constants and functions listed in the
:all tag, described below.
EXPORT TAGS
":all"
Includes the tags ":libxml", ":encoding", and ":ns" described
below.
":libxml"
Exports integer constants for DOM node types.
XML_ELEMENT_NODE => 1
XML_ATTRIBUTE_NODE => 2
XML_TEXT_NODE => 3
XML_CDATA_SECTION_NODE => 4
XML_ENTITY_REF_NODE => 5
XML_ENTITY_NODE => 6
XML_PI_NODE => 7
XML_COMMENT_NODE => 8
XML_DOCUMENT_NODE => 9
XML_DOCUMENT_TYPE_NODE => 10
XML_DOCUMENT_FRAG_NODE => 11
XML_NOTATION_NODE => 12
XML_HTML_DOCUMENT_NODE => 13
XML_DTD_NODE => 14
XML_ELEMENT_DECL => 15
XML_ATTRIBUTE_DECL => 16
XML_ENTITY_DECL => 17
XML_NAMESPACE_DECL => 18
XML_XINCLUDE_START => 19
XML_XINCLUDE_END => 20
":encoding"
Exports two encoding conversion functions from XML::LibXML::Common.
encodeToUTF8()decodeFromUTF8()
":ns"
Exports two convenience constants: the implicit namespace of the
reserved "xml:" prefix, and the implicit namespace for the reserved
"xmlns:" prefix.
XML_XML_NS => 'http://www.w3.org/XML/1998/namespace'
XML_XMLNS_NS => 'http://www.w3.org/2000/xmlns/'
RELATED MODULES
The modules described in this section are not part of the XML::LibXML
package itself. As they support some additional features, they are
mentioned here.
XML::LibXSLT
XSLT 1.0 Processor using libxslt and XML::LibXML
XML::LibXML::Iterator
XML::LibXML Implementation of the DOM Traversal Specification
XML::CompactTree::XS
Uses XML::LibXML::Reader to very efficiently to parse XML document
or element into native Perl data structures, which are less
flexible but significantly faster to process then DOM.
XML::LIBXML AND XML::GDOME
Note: THE FUNCTIONS DESCRIBED HERE ARE STILL EXPERIMENTAL
Although both modules make use of libxml2's XML capabilities, the DOM
implementation of both modules are not compatible. But still it is
possible to exchange nodes from one DOM to the other. The concept of
this exchange is pretty similar to the function cloneNode(): The
particular node is copied on the low-level to the opposite DOM
implementation.
Since the DOM implementations cannot coexist within one document, one
is forced to copy each node that should be used. Because you are always
keeping two nodes this may cause quite an impact on a machines memory
usage.
XML::LibXML provides two functions to export or import GDOME nodes:
import_GDOME() and export_GDOME(). Both function have two parameters:
the node and a flag for recursive import. The flag works as in
cloneNode().
The two functions allow to export and import XML::GDOME nodes
explicitly, however, XML::LibXML allows also the transparent import of
XML::GDOME nodes in functions such as appendChild(), insertAfter() and
so on. While native nodes are automatically adopted in most functions
XML::GDOME nodes are always cloned in advance. Thus if the original
node is modified after the operation, the node in the XML::LibXML
document will not have this information.
import_GDOME
$libxmlnode = XML::LibXML->import_GDOME( $node, $deep );
This clones an XML::GDOME node to an XML::LibXML node explicitly.
export_GDOME
$gdomenode = XML::LibXML->export_GDOME( $node, $deep );
Allows one to clone an XML::LibXML node into an XML::GDOME node.
CONTACTS
For bug reports, please use the CPAN request tracker on
http://rt.cpan.org/NoAuth/Bugs.html?Dist=XML-LibXML
For suggestions etc., and other issues related to XML::LibXML you may
use the perl XML mailing list ("perl-xml@listserv.ActiveState.com"),
where most XML-related Perl modules are discussed. In case of problems
you should check the archives of that list first. Many problems are
already discussed there. You can find the list's archives and
subscription options at
<http://aspn.activestate.com/ASPN/Mail/Browse/Threaded/perl-xml>.
AUTHORS
Matt Sergeant, Christian Glahn, Petr Pajas
VERSION
2.0108
COPYRIGHT
2001-2007, AxKit.com Ltd.
2002-2006, Christian Glahn.
2006-2009, Petr Pajas.
perl v5.18.1 2013-12-17 LibXML(3pm)
