=head1 NAME
XML::LibXML::Parser - Parsing XML Data with XML::LibXML
=head1 SYNOPSIS
use XML::LibXML;
my $parser = XML::LibXML->new();
my $doc = $parser->parse_string(<<'EOT');
<some-xml/>
EOT
my $fdoc = $parser->parse_file( $xmlfile );
my $fhdoc = $parser->parse_fh( $xmlstream );
my $fragment = $parser->parse_xml_chunk( $xml_wb_chunk );
$parser = XML::LibXML->new();
$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 );
$fragment = $parser->parse_balanced_chunk( $wbxmlstring );
$fragment = $parser->parse_xml_chunk( $wbxmlstring );
$parser->process_xincludes( $doc );
$parser->processXIncludes( $doc );
$parser->parse_chunk($string, $terminate);
$parser->start_push();
$parser->push(@data);
$doc = $parser->finish_push( $recover );
$parser->validation(1);
$parser->recover(1);
$parser->recover_silently(1);
$parser->expand_entities(0);
$parser->keep_blanks(0);
$parser->pedantic_parser(1);
$parser->line_numbers(1);
$parser->load_ext_dtd(1);
$parser->complete_attributes(1);
$parser->expand_xinclude(1);
$parser->load_catalog( $catalog_file );
$parser->base_uri( $your_base_uri );
$parser->gdome_dom(1);
$parser->clean_namespaces( 1 );
$parser->no_network(1);
=head1 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:
=over 4
=item *
A DOM Pull-Parser
=item *
A DOM Push-Parser
=item *
A SAX Parser
=item *
A DOM based SAX Parser.
=back
=head2 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.
=over 4
=item new
$parser = XML::LibXML->new();
There is nothing much to say about the constructor. It simply creates a new
parser instance.
Although libxml2 uses mainly global flags to alter the behaviour of the parser,
each XML::LibXML parser instance has its own flags or callbacks and does not
interfere with other instances.
=back
=head2 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 L<<<<<< 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
=over 4
=item 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().
=item 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 );
=item 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 );
=item 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. Possible options are: Possible options are: encoding and
URI, and with libxml2 > 2.6.27 additionally: recover, suppress_errors,
suppress_warnings, pedantic_parser, no_blanks, and no_network.
=item 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. Possible options are: encoding and URI, and with libxml2 >
2.6.27 additionally: recover, suppress_errors, suppress_warnings,
pedantic_parser, no_blanks, and no_network. 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.
=item 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. Possible options are: encoding and URI, and with libxml2 >
2.6.27 additionally: recover, suppress_errors, suppress_warnings,
pedantic_parser, no_blanks, and no_network.
=back
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 I<<<<<< 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.
=over 4
=item parse_balanced_chunk
$fragment = $parser->parse_balanced_chunk( $wbxmlstring );
This function parses a well balanced XML string into a L<<<<<< XML::LibXML::DocumentFragment >>>>>>.
=item parse_xml_chunk
$fragment = $parser->parse_xml_chunk( $wbxmlstring );
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.
=back
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.
=over 4
=item 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.
=item processXIncludes
$parser->processXIncludes( $doc );
This is an alias to process_xincludes, but through a JAVA like function name.
=back
=head2 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:
=over 4
=item 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
=back
Internally XML::LibXML provides three functions that control the push parser
process:
=over 4
=item start_push
$parser->start_push();
Initializes the push parser.
=item 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!
=item 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.
=back
=head2 DOM based SAX Parser
XML::LibXML 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.
I<<<<<< 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 L<<<<<< XML::LibXML::SAX >>>>>> man page
=head1 SERIALIZATION
XML::LibXML provides some functions to serialize nodes and documents. The
serialization functions are described on the L<<<<<< XML::LibXML::Node >>>>>> manpage or the L<<<<<< XML::LibXML::Document >>>>>> manpage. XML::LibXML checks three global flags that alter the serialization
process:
=over 4
=item *
skipXMLDeclaration
=item *
skipDTD
=item *
setTagCompression
=back
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 I<<<<<< foo >>>>>> will be rendered as I<<<<<< <foo></foo> >>>>>> rather than I<<<<<< <foo/> >>>>>>.
=head1 PARSER OPTIONS
LibXML options are global (unfortunately this is a limitation of the underlying
implementation, not this interface). They can either be set using
$parser->option(...), or XML::LibXML->option(...), both are treated in the same
manner. Note that even two parser processes will share some of the same
options, so be careful out there!
Every option returns the previous value, and can be called without parameters
to get the current value.
=over 4
=item validation
$parser->validation(1);
Turn validation on (or off). Defaults to off.
=item recover
$parser->recover(1);
Turn the parsers recover mode on (or off). Defaults to off.
This allows one to parse broken XML data into memory. This switch will only
work with XML data rather than HTML data. Also the validation will be switched
off automatically.
The recover mode helps to recover documents that are almost well-formed very
efficiently. That is for example a document that forgets to close the document
tag (or any other tag inside the document). The recover mode of XML::LibXML has
problems restoring documents that are more like well balanced chunks.
XML::LibXML will only parse until the first fatal error occurs, reporting
recoverable parsing errors as warnings. To suppress these warnings use
$parser->recover_silently(1); or, equivalently, $parser->recover(2).
=item recover_silently
$parser->recover_silently(1);
Turns the parser warnings off (or on). Defaults to on.
This allows to switch off warnings printed to STDERR when parsing documents
with recover(1).
Please note that calling recover_silently(0) also turns the parser recover mode
off and calling recover_silently(1) automatically activates the parser recover
mode.
=item expand_entities
$parser->expand_entities(0);
Turn entity expansion on or off, enabled by default. If entity expansion is
off, any external parsed entities in the document are left as entities.
Probably not very useful for most purposes.
=item keep_blanks
$parser->keep_blanks(0);
Allows you to turn off XML::LibXML's default behaviour of maintaining
white-space in the document.
=item pedantic_parser
$parser->pedantic_parser(1);
You can make XML::LibXML more pedantic if you want to.
=item line_numbers
$parser->line_numbers(1);
If this option is activated XML::LibXML will store the line number of a node.
This gives more information where a validation error occurred. It could be also
used to find out about the position of a node after parsing (see also
XML::LibXML::Node::line_number()).
IMPORTANT: Due to limitations in the libxml2 library line numbers greater than
65535 will be returned as 65535. Please see L<<<<<< http://bugzilla.gnome.org/show_bug.cgi?id=325533 >>>>>> for more details.
By default line numbering is switched off (0).
=item load_ext_dtd
$parser->load_ext_dtd(1);
Load external DTD subsets while parsing.
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.
If you leave this parser flag untouched, everything will work, because the
default is 1 (activated)
=item complete_attributes
$parser->complete_attributes(1);
Complete the elements attributes lists with the ones defaulted from the DTDs.
By default, this option is enabled.
=item expand_xinclude
$parser->expand_xinclude(1);
Expands XIinclude tags immediately while parsing the document. This flag
assures that the parser callbacks are used while parsing the included document.
=item load_catalog
$parser->load_catalog( $catalog_file );
Will use $catalog_file as a catalog during all parsing processes. Using a
catalog will significantly speed up parsing processes if many external
resources are loaded into the parsed documents (such as DTDs or XIncludes).
Note that catalogs will not be available if an external entity handler was
specified. At the current state it is not possible to make use of both types of
resolving systems at the same time.
=item base_uri
$parser->base_uri( $your_base_uri );
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 separate base URI, that is then used for the parsed documents.
=item gdome_dom
$parser->gdome_dom(1);
THIS FLAG IS EXPERIMENTAL!
Although quite powerful XML:LibXML's DOM implementation is limited if one needs
or wants full DOM level 2 or level 3 support. XML::GDOME is based on libxml2 as
well but provides a rather complete DOM implementation by wrapping libgdome.
This 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!
=item clean_namespaces
$parser->clean_namespaces( 1 );
libxml2 2.6.0 and later allows to strip redundant namespace declarations from
the DOM tree. To do this, one has to set clean_namespaces() to 1 (TRUE). By
default no namespace cleanup is done.
=item no_network
$parser->no_network(1);
Turn networking support on or off, enabled by default. If networking is off,
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
$parser->recover(1) for processing documents requiring such resources while
networking is off.
=back
=head1 ERROR REPORTING
XML::LibXML throws exceptions during parsing, validation or XPath processing
(and some other occasions). These errors can be caught by using I<<<<<< eval >>>>>> blocks. The error then will be stored in I<<<<<< $@ >>>>>>. There are two implementations: the old one throws $@ which is a flat 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 occurs and does not wait if a user test for
them. 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. 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.
=head1 AUTHORS
Matt Sergeant,
Christian Glahn,
Petr Pajas
=head1 VERSION
1.66
=head1 COPYRIGHT
2001-2007, AxKit.com Ltd; 2002-2006 Christian Glahn; 2006-2008 Petr Pajas, All rights reserved.
=cut