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XML::LibXML::Parser(3)User Contributed Perl DocumentatioXML::LibXML::Parser(3)

NAME
       XML::LibXML::Parser - Parsing XML Data with XML::LibXML

SYNOPSIS
         use XML::LibXML 1.70;

         # Parser constructor

         $parser = XML::LibXML->new();
         $parser = XML::LibXML->new(option=>value, ...);
         $parser = XML::LibXML->new({option=>value, ...});

         # Parsing XML

         $dom = XML::LibXML->load_xml(
             location => $file_or_url
             # parser options ...
           );
         $dom = XML::LibXML->load_xml(
             string => $xml_string
             # parser options ...
           );
         $dom = XML::LibXML->load_xml({
             IO => $perl_file_handle
             # parser options ...
           );
         $dom = $parser->load_xml(...);

         # Parsing HTML

         $dom = XML::LibXML->load_html(...);
         $dom = $parser->load_html(...);

         # Parsing well-balanced XML chunks

         $fragment = $parser->parse_balanced_chunk( $wbxmlstring, $encoding );

         # Processing XInclude

         $parser->process_xincludes( $doc );
         $parser->processXIncludes( $doc );

         # Old-style parser interfaces

         $doc = $parser->parse_file( $xmlfilename );
         $doc = $parser->parse_fh( $io_fh );
         $doc = $parser->parse_string( $xmlstring);
         $doc = $parser->parse_html_file( $htmlfile, \%opts );
         $doc = $parser->parse_html_fh( $io_fh, \%opts );
         $doc = $parser->parse_html_string( $htmlstring, \%opts );

         # Push parser

         $parser->parse_chunk($string, $terminate);
         $parser->init_push();
         $parser->push(@data);
         $doc = $parser->finish_push( $recover );

         # Set/query parser options

         $parser->option_exists($name);
         $parser->get_option($name);
         $parser->set_option($name,$value);
         $parser->set_options({$name=>$value,...});

         # XML catalogs

         $parser->load_catalog( $catalog_file );

PARSING
       A XML document is read into a data structure such as a DOM tree by a
       piece of software, called a parser. XML::LibXML currently provides four
       different parser interfaces:

       o   A DOM Pull-Parser

       o   A DOM Push-Parser

       o   A SAX Parser

       o   A DOM based SAX Parser.

   Creating a Parser Instance
       XML::LibXML provides an OO interface to the libxml2 parser functions.
       Thus you have to create a parser instance before you can parse any XML
       data.

       new
             $parser = XML::LibXML->new();
             $parser = XML::LibXML->new(option=>value, ...);
             $parser = XML::LibXML->new({option=>value, ...});

           Create a new XML and HTML parser instance. Each parser instance
           holds default values for various parser options. Optionally, one
           can pass a hash reference or a list of option => value pairs to set
           a different default set of options.  Unless specified otherwise,
           the options "load_ext_dtd", "expand_entities", and "huge" are set
           to 1. See "Parser Options" for a list of libxml2 parser's options.

   DOM Parser
       One of the common parser interfaces of XML::LibXML is the DOM parser.
       This parser reads XML data into a DOM like data structure, so each tag
       can get accessed and transformed.

       XML::LibXML's DOM parser is not only capable to parse XML data, but
       also (strict) HTML files. There are three ways to parse documents - as
       a string, as a Perl filehandle, or as a filename/URL. The return value
       from each is a XML::LibXML::Document object, which is a DOM object.

       All of the functions listed below will throw an exception if the
       document is invalid. To prevent this causing your program exiting, wrap
       the call in an eval{} block

       load_xml
             $dom = XML::LibXML->load_xml(
                 location => $file_or_url
                 # parser options ...
               );
             $dom = XML::LibXML->load_xml(
                 string => $xml_string
                 # parser options ...
               );
             $dom = XML::LibXML->load_xml({
                 IO => $perl_file_handle
                 # parser options ...
               );
             $dom = $parser->load_xml(...);

           This function is available since XML::LibXML 1.70. It provides easy
           to use interface to the XML parser that parses given file (or URL),
           string, or input stream to a DOM tree. The arguments can be passed
           in a HASH reference or as name => value pairs. The function can be
           called as a class method or an object method. In both cases it
           internally creates a new parser instance passing the specified
           parser options; if called as an object method, it clones the
           original parser (preserving its settings) and additionally applies
           the specified options to the new parser. See the constructor "new"
           and "Parser Options" for more information.

       load_xml
             $dom = XML::LibXML->load_html(...);
             $dom = $parser->load_html(...);

           This function is available since XML::LibXML 1.70. It has the same
           usage as "load_xml", providing interface to the HTML parser. See
           "load_xml" for more information.

           Parsing HTML may cause problems, especially if the ampersand ('&')
           is used.  This is a common problem if HTML code is parsed that
           contains links to CGI-scripts. Such links cause the parser to throw
           errors. In such cases libxml2 still parses the entire document as
           there was no error, but the error causes XML::LibXML to stop the
           parsing process. However, the document is not lost.  Such HTML
           documents should be parsed using the recover flag. By default
           recovering is deactivated.

           The functions described above are implemented to parse well formed
           documents.  In some cases a program gets well balanced XML instead
           of well formed documents (e.g. a XML fragment from a Database).
           With XML::LibXML it is not required to wrap such fragments in the
           code, because XML::LibXML is capable even to parse well balanced
           XML fragments.

           parse_balanced_chunk
                 $fragment = $parser->parse_balanced_chunk( $wbxmlstring, $encoding );

               This function parses a well balanced XML string into a
               XML::LibXML::DocumentFragment. The first arguments contains the
               input string, the optional second argument can be used to
               specify character encoding of the input (UTF-8 is assumed by
               default).

           parse_xml_chunk
               This is the old name of parse_balanced_chunk(). Because it may
               causes confusion with the push parser interface, this function
               should not be used anymore.

           By default XML::LibXML does not process XInclude tags within a XML
           Document (see options section below). XML::LibXML allows to post
           process a document to expand XInclude tags.

           process_xincludes
                 $parser->process_xincludes( $doc );

               After a document is parsed into a DOM structure, you may want
               to expand the documents XInclude tags. This function processes
               the given document structure and expands all XInclude tags (or
               throws an error) by using the flags and callbacks of the given
               parser instance.

               Note that the resulting Tree contains some extra nodes (of type
               XML_XINCLUDE_START and XML_XINCLUDE_END) after successfully
               processing the document. These nodes indicate where data was
               included into the original tree.  if the document is
               serialized, these extra nodes will not show up.

               Remember: A Document with processed XIncludes differs from the
               original document after serialization, because the original
               XInclude tags will not get restored!

               If the parser flag "expand_xincludes" is set to 1, you need not
               to post process the parsed document.

           processXIncludes
                 $parser->processXIncludes( $doc );

               This is an alias to process_xincludes, but through a JAVA like
               function name.

           parse_file
                 $doc = $parser->parse_file( $xmlfilename );

               This function parses an XML document from a file or network;
               $xmlfilename can be either a filename or an URL. Note that for
               parsing files, this function is the fastest choice, about 6-8
               times faster then parse_fh().

           parse_fh
                 $doc = $parser->parse_fh( $io_fh );

               parse_fh() parses a IOREF or a subclass of IO::Handle.

               Because the data comes from an open handle, libxml2's parser
               does not know about the base URI of the document. To set the
               base URI one should use parse_fh() as follows:

                 my $doc = $parser->parse_fh( $io_fh, $baseuri );

           parse_string
                 $doc = $parser->parse_string( $xmlstring);

               This function is similar to parse_fh(), but it parses a XML
               document that is available as a single string in memory. Again,
               you can pass an optional base URI to the function.

                 my $doc = $parser->parse_string( $xmlstring, $baseuri );

           parse_html_file
                 $doc = $parser->parse_html_file( $htmlfile, \%opts );

               Similar to parse_file() but parses HTML (strict) documents;
               $htmlfile can be filename or URL.

               An optional second argument can be used to pass some options to
               the HTML parser as a HASH reference. See options labeled with
               HTML in "Parser Options".

           parse_html_fh
                 $doc = $parser->parse_html_fh( $io_fh, \%opts );

               Similar to parse_fh() but parses HTML (strict) streams.

               An optional second argument can be used to pass some options to
               the HTML parser as a HASH reference. See options labeled with
               HTML in "Parser Options".

               Note: encoding option may not work correctly with this function
               in libxml2 < 2.6.27 if the HTML file declares charset using a
               META tag.

           parse_html_string
                 $doc = $parser->parse_html_string( $htmlstring, \%opts );

               Similar to parse_string() but parses HTML (strict) strings.

               An optional second argument can be used to pass some options to
               the HTML parser as a HASH reference. See options labeled with
               HTML in "Parser Options".

   Push Parser
       XML::LibXML provides a push parser interface. Rather than pulling the
       data from a given source the push parser waits for the data to be
       pushed into it.

       This allows one to parse large documents without waiting for the parser
       to finish. The interface is especially useful if a program needs to
       pre-process the incoming pieces of XML (e.g. to detect document
       boundaries).

       While XML::LibXML parse_*() functions force the data to be a well-
       formed XML, the push parser will take any arbitrary string that
       contains some XML data. The only requirement is that all the pushed
       strings are together a well formed document. With the push parser
       interface a program can interrupt the parsing process as required,
       where the parse_*() functions give not enough flexibility.

       Different to the pull parser implemented in parse_fh() or parse_file(),
       the push parser is not able to find out about the documents end itself.
       Thus the calling program needs to indicate explicitly when the parsing
       is done.

       In XML::LibXML this is done by a single function:

       parse_chunk
             $parser->parse_chunk($string, $terminate);

           parse_chunk() tries to parse a given chunk of data, which isn't
           necessarily well balanced data. The function takes two parameters:
           The chunk of data as a string and optional a termination flag. If
           the termination flag is set to a true value (e.g. 1), the parsing
           will be stopped and the resulting document will be returned as the
           following example describes:

             my $parser = XML::LibXML->new;
             for my $string ( "<", "foo", ' bar="hello world"', "/>") {
                  $parser->parse_chunk( $string );
             }
             my $doc = $parser->parse_chunk("", 1); # terminate the parsing

       Internally XML::LibXML provides three functions that control the push
       parser process:

       init_push
             $parser->init_push();

           Initializes the push parser.

       push
             $parser->push(@data);

           This function pushes the data stored inside the array to libxml2's
           parser. Each entry in @data must be a normal scalar! This method
           can be called repeatedly.

       finish_push
             $doc = $parser->finish_push( $recover );

           This function returns the result of the parsing process. If this
           function is called without a parameter it will complain about non
           well-formed documents. If $restore is 1, the push parser can be
           used to restore broken or non well formed (XML) documents as the
           following example shows:

             eval {
                 $parser->push( "<foo>", "bar" );
                 $doc = $parser->finish_push();    # will report broken XML
             };
             if ( $@ ) {
                # ...
             }

           This can be annoying if the closing tag is missed by accident. The
           following code will restore the document:

             eval {
                 $parser->push( "<foo>", "bar" );
                 $doc = $parser->finish_push(1);   # will return the data parsed
                                                   # unless an error happened
             };

             print $doc->toString(); # returns "<foo>bar</foo>"

           Of course finish_push() will return nothing if there was no data
           pushed to the parser before.

   Pull Parser (Reader)
       XML::LibXML also provides a pull-parser interface similar to the
       XmlReader interface in .NET. This interface is almost streaming, and is
       usually faster and simpler to use than SAX. See XML::LibXML::Reader.

   Direct SAX Parser
       XML::LibXML provides a direct SAX parser in the XML::LibXML::SAX
       module.

   DOM based SAX Parser
       XML::LibXML also provides a DOM based SAX parser. The SAX parser is
       defined in the module XML::LibXML::SAX::Parser. As it is not a stream
       based parser, it parses documents into a DOM and traverses the DOM tree
       instead.

       The API of this parser is exactly the same as any other Perl SAX2
       parser. See XML::SAX::Intro for details.

       Aside from the regular parsing methods, you can access the DOM tree
       traverser directly, using the generate() method:

         my $doc = build_yourself_a_document();
         my $saxparser = $XML::LibXML::SAX::Parser->new( ... );
         $parser->generate( $doc );

       This is useful for serializing DOM trees, for example that you might
       have done prior processing on, or that you have as a result of XSLT
       processing.

       WARNING

       This is NOT a streaming SAX parser. As I said above, this parser reads
       the entire document into a DOM and serialises it. Some people couldn't
       read that in the paragraph above so I've added this warning. If you
       want a streaming SAX parser look at the XML::LibXML::SAX man page

SERIALIZATION
       XML::LibXML provides some functions to serialize nodes and documents.
       The serialization functions are described on the XML::LibXML::Node
       manpage or the XML::LibXML::Document manpage. XML::LibXML checks three
       global flags that alter the serialization process:

       o   skipXMLDeclaration

       o   skipDTD

       o   setTagCompression

       of that three functions only setTagCompression is available for all
       serialization functions.

       Because XML::LibXML does these flags not itself, one has to define them
       locally as the following example shows:

         local $XML::LibXML::skipXMLDeclaration = 1;
         local $XML::LibXML::skipDTD = 1;
         local $XML::LibXML::setTagCompression = 1;

       If skipXMLDeclaration is defined and not '0', the XML declaration is
       omitted during serialization.

       If skipDTD is defined and not '0', an existing DTD would not be
       serialized with the document.

       If setTagCompression is defined and not '0' empty tags are displayed as
       open and closing tags rather than the shortcut. For example the empty
       tag foo will be rendered as <foo></foo> rather than <foo/>.

PARSER OPTIONS
       Handling of libxml2 parser options has been unified and improved in
       XML::LibXML 1.70. You can now set default options for a particular
       parser instance by passing them to the constructor as
       "XML::LibXML->new({name=>value, ...})" or
       "XML::LibXML->new(name=>value,...)". The options can be queried and
       changed using the following methods (pre-1.70 interfaces such as
       "$parser->load_ext_dtd(0)" also exist, see below):

       option_exists
             $parser->option_exists($name);

           Returns 1 if the current XML::LibXML version supports the option
           $name, otherwise returns 0 (note that this does not necessarily
           mean that the option is supported by the underlying libxml2
           library).

       get_option
             $parser->get_option($name);

           Returns the current value of the parser option $name.

       set_option
             $parser->set_option($name,$value);

           Sets option $name to value $value.

       set_options
             $parser->set_options({$name=>$value,...});

           Sets multiple parsing options at once.

       IMPORTANT NOTE: This documentation reflects the parser flags available
       in libxml2 2.7.3. Some options have no effect if an older version of
       libxml2 is used.

       Each of the flags listed below is labeled labeled

       /parser/
           if it can be used with a "XML::LibXML" parser object (i.e. passed
           to "XML::LibXML->new", "XML::LibXML->set_option", etc.)

       /html/
           if it can be used passed to the "parse_html_*" methods

       /reader/
           if it can be used with the "XML::LibXML::Reader".

       Unless specified otherwise, the default for boolean valued options is 0
       (false).

       The available options are:

       URI /parser, html, reader/

           In case of parsing strings or file handles, XML::LibXML doesn't
           know about the base uri of the document. To make relative
           references such as XIncludes work, one has to set a base URI, that
           is then used for the parsed document.

       line_numbers
           /parser, html, reader/

           If this option is activated, libxml2 will store the line number of
           each element node in the parsed document. The line number can be
           obtained using the "line_number()" method of the
           "XML::LibXML::Node" class (for non-element nodes this may report
           the line number of the containing element). The line numbers are
           also used for reporting positions of validation errors.

           IMPORTANT: Due to limitations in the libxml2 library line numbers
           greater than 65535 will be returned as 65535. Unfortunatelly, this
           is a long and sad story, please see
           <http://bugzilla.gnome.org/show_bug.cgi?id=325533> for more
           details.

       encoding
           /html/

           character encoding of the input

       recover
           /parser, html, reader/

           recover from errors; possible values are 0, 1, and 2

           A true value turns on recovery mode which allows one to parse
           broken XML or HTML data. The recovery mode allows the parser to
           return the successfully parsed portion of the input document. This
           is useful for almost well-formed documents, where for example a
           closing tag is missing somewhere. Still, XML::LibXML will only
           parse until the first fatal (non-recoverable) error occurs,
           reporting recoverable parsing errors as warnings. To suppress even
           these warnings, use recover=>2.

           Note that validation is switched off automatically in recovery
           mode.

       expand_entities
           /parser, reader/

           substitute entities; possible values are 0 and 1; default is 1

           Note that although this flag disables entity substitution, it does
           not prevent the parser from loading external entities; when
           substitution of an external entity is disabled, the entity will be
           represented in the document tree by a XML_ENTITY_REF_NODE node
           whose subtree will be the content obtained by parsing the external
           resource; Although this is level of nesting is visible from the DOM
           it is transparent to XPath data model, so it is possible to match
           nodes in an unexpanded entity by the same XPath expression as if
           the entity was expanded. See also ext_ent_handler.

       ext_ent_handler
           /parser/

           Provide a custom external entity handler to be used when
           expand_entities is set to 1. Possible value is a subroutine
           reference.

           This feature does not work properly in libxml2 < 2.6.27!

           The subroutine provided is called whenever the parser needs to
           retrieve the content of an external entity. It is called with two
           arguments: the system ID (URI) and the public ID. The value
           returned by the subroutine is parsed as the content of the entity.

           This method can be used to completely disable entity loading, e.g.
           to prevent exploits of the type described at
           (<http://searchsecuritychannel.techtarget.com/generic/0,295582,sid97_gci1304703,00.html>),
           where a service is tricked to expose its private data by letting it
           parse a remote file (RSS feed) that contains an entity reference to
           a local file (e.g. "/etc/fstab").

           A more granular solution to this problem, however, is provided by
           custom URL resolvers, as in

             my $c = XML::LibXML::InputCallback->new();
             sub match {   # accept file:/ URIs except for XML catalogs in /etc/xml/
               my ($uri) = @_;
               return ($uri=~m{^file:/}
                       and $uri !~ m{^file:///etc/xml/})
                      ? 1 : 0;
             }
             $c->register_callbacks([ \&match, sub{}, sub{}, sub{} ]);
             $parser->input_callbacks($c);

       load_ext_dtd
           /parser, reader/

           load the external DTD subset while parsing; possible values are 0
           and 1. Unless specified, XML::LibXML sets this option to 1.

           This flag is also required for DTD Validation, to provide complete
           attribute, and to expand entities, regardless if the document has
           an internal subset. Thus switching off external DTD loading, will
           disable entity expansion, validation, and complete attributes on
           internal subsets as well.

       complete_attributes
           /parser, reader/

           create default DTD attributes; possible values are 0 and 1

       validation
           /parser, reader/

           validate with the DTD; possible values are 0 and 1

       suppress_errors
           /parser, html, reader/

           suppress error reports; possible values are 0 and 1

       suppress_warnings
           /parser, html, reader/

           suppress warning reports; possible values are 0 and 1

       pedantic_parser
           /parser, html, reader/

           pedantic error reporting; possible values are 0 and 1

       no_blanks
           /parser, html, reader/

           remove blank nodes; possible values are 0 and 1

       expand_xinclude or xinclude
           /parser, reader/

           Implement XInclude substitution; possible values are 0 and 1

           Expands XIinclude tags immediately while parsing the document. Note
           that the parser will use the URI resolvers installed via
           "XML::LibXML::InputCallback" to parse the included document (if
           any).

       no_xinclude_nodes
           /parser, reader/

           do not generate XINCLUDE START/END nodes; possible values are 0 and
           1

       no_network
           /parser, html, reader/

           Forbid network access; possible values are 0 and 1

           If set to true, all attempts to fetch non-local resources (such as
           DTD or external entities) will fail (unless custom callbacks are
           defined).

           It may be necessary to use the flag "recover" for processing
           documents requiring such resources while networking is off.

       clean_namespaces
           /parser, reader/

           remove redundant namespaces declarations during parsing; possible
           values are 0 and 1.

       no_cdata
           /parser, html, reader/

           merge CDATA as text nodes; possible values are 0 and 1

       no_basefix
           /parser, reader/

           not fixup XINCLUDE xml#base URIS; possible values are 0 and 1

       huge
           /parser, html, reader/

           relax any hardcoded limit from the parser; possible values are 0
           and 1. Unless specified, XML::LibXML sets this option to 1.

       gdome
           /parser/

           THIS OPTION IS EXPERIMENTAL!

           Although quite powerful, XML:LibXML's DOM implementation is
           incomplete with respect to the DOM level 2 or level 3
           specifications. XML::GDOME is based on libxml2 as well and and
           provides a rather complete DOM implementation by wrapping libgdome.
           This flag allows you to make use of XML::LibXML's full parser
           options and XML::GDOME's DOM implementation at the same time.

           To make use of this function, one has to install libgdome and
           configure XML::LibXML to use this library. For this you need to
           rebuild XML::LibXML!

           Note: this feature was not seriously tested in recent XML::LibXML
           releases.

       For compatibility with XML::LibXML versions prior to 1.70, the
       following methods are also supported for querying and setting the
       corresponding parser options (if called without arguments, the methods
       return the current value of the corresponding parser options; with an
       argument sets the option to a given value):

         $parser->validation();
         $parser->recover();
         $parser->pedantic_parser();
         $parser->line_numbers();
         $parser->load_ext_dtd();
         $parser->complete_attributes();
         $parser->expand_xinclude();
         $parser->gdome_dom();
         $parser->clean_namespaces();
         $parser->no_network();

       The following obsolete methods trigger parser options in some special
       way:

       recover_silently
             $parser->recover_silently(1);;

           If called without an argument, returns true if the current value of
           the "recover" parser option is 2 and returns false otherwise. With
           a true argument sets the "recover" parser option to 2; with a false
           argument sets the "recover" parser option to 0.

       expand_entities
             $parser->expand_entities(0);

           Get/set the "expand_entities" option. If called with a true
           argument, also turns the "load_ext_dtd" option to 1.

       keep_blanks
             $parser->keep_blanks(0);

           This is actually an oposite of the "no_blanks" parser option. If
           used without an argument retrieves negated value of "no_blanks". If
           used with an argument sets "no_blanks" to the oposite value.

       base_uri
             $parser->base_uri( $your_base_uri );

           Get/set the "URI" option.

XML CATALOGS
       "libxml2" supports XML catalogs. Catalogs are used to map remote
       resources to their local copies. Using catalogs can speed up parsing
       processes if many external resources from remote addresses are loaded
       into the parsed documents (such as DTDs or XIncludes).

       Note that libxml2 has a global pool of loaded catalogs, so if you apply
       the method "load_catalog" to one parser instance, all parser instances
       will start using the catalog (in addition to other previously loaded
       catalogs).

       Note also that catalogs are not used when a custom external entity
       handler is specified. At the current state it is not possible to make
       use of both types of resolving systems at the same time.

       load_catalog
             $parser->load_catalog( $catalog_file );

           Loads the XML catalog file $catalog_file.

ERROR REPORTING
       XML::LibXML throws exceptions during parsing, validation or XPath
       processing (and some other occasions). These errors can be caught by
       using eval blocks. The error is stored in $@. There are two
       implementations: the old one throws $@ which is just a message string,
       in the new one $@ is an object from the class XML::LibXML::Error; this
       class overrides the operator "" so that when printed, the object
       flattens to the usual error message.

       XML::LibXML throws errors as they occur. This is a very common
       misunderstanding in the use of XML::LibXML. If the eval is omitted,
       XML::LibXML will always halt your script by "croaking" (see Carp man
       page for details).

       Also note that an increasing number of functions throw errors if bad
       data is passed as arguments. If you cannot assure valid data passed to
       XML::LibXML you should eval these functions.

       Note: since version 1.59, get_last_error() is no longer available in
       XML::LibXML for thread-safety reasons.

AUTHORS
       Matt Sergeant, Christian Glahn, Petr Pajas

VERSION
       1.70

COPYRIGHT
       2001-2007, AxKit.com Ltd.

       2002-2006, Christian Glahn.

       2006-2009, Petr Pajas.

perl v5.12.1                      2009-10-07            XML::LibXML::Parser(3)
 

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