XML::LibXML::Parser(3)User Contributed Perl DocumentatioXML::LibXML::Parser(3)NAMEXML::LibXML::Parser - Parsing XML Data with XML::LibXML
SYNOPSIS
$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);
DESCRIPTIONSYNOPSIS
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 );
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();
There is nothing much to say about the constructor. It simply cre-
ates 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.
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 docu-
ment is invalid. To prevent this causing your program exiting, wrap the
call in an eval{} block
parse_file
$doc = $parser->parse_file( $xmlfilename );
This function parses an XML document from a file or network; $xml-
filename 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 docu-
ment 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; $html-
file 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 for libxml2 < 2.6.27, and for later
versions of libxml2 additionally: recover, suppress_errors, sup-
press_warnings, pedantic_parser, no_blanks, and no_network.
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 for libxml2 < 2.6.27, and for later versions of libxml2 addi-
tionally: recover, suppress_errors, suppress_warnings, pedan-
tic_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.
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 for libxml2 < 2.6.27, and for later versions of libxml2 addi-
tionally: recover, suppress_errors, suppress_warnings, pedan-
tic_parser, no_blanks, and no_network.
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 doc-
uments. 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 frag-
ments.
parse_balanced_chunk
$fragment = $parser->parse_balanced_chunk( $wbxmlstring );
This function parses a well balanced XML string into a
XML::LibXML::DocumentFragment.
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 be used anymore.
By default XML::LibXML does not process XInclude tags within a XML Doc-
ument (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 pro-
cessing 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 XIn-
clude 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.
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 bound-
aries).
While XML::LibXML parse_*() functions force the data to be a well-
formed XML, the push parser will take any arbitrary string that con-
tains 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:
start_push
$parser->start_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!
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.
DOM based SAX Parser
XML::LibXML provides a DOM based SAX parser. The SAX parser is defined
in 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 man-
page 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 serial-
ized 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
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.
validation
$parser->validation(1);
Turn validation on (or off). Defaults to off.
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 vali-
dation 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 for-
gets to close the document tag (or any other tag inside the docu-
ment). The recover mode of XML::LibXML has problems restoring docu-
ments 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).
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.
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.
keep_blanks
$parser->keep_blanks(0);
Allows you to turn off XML::LibXML's default behaviour of maintain-
ing white-space in the document.
pedantic_parser
$parser->pedantic_parser(1);
You can make XML::LibXML more pedantic if you want to.
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())
By default line numbering is switched off (0).
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)
complete_attributes
$parser->complete_attributes(1);
Complete the elements attributes lists with the ones defaulted from
the DTDs. By default, this option is enabled.
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.
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 han-
dler was specified. At the current state it is not possible to make
use of both types of resolving systems at the same time.
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 refer-
ences such as XIncludes work, one has to set a separate base URI,
that is then used for the parsed documents.
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 com-
plete 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 con-
figure XML::LibXML to use this library. For this you need to
rebuild XML::LibXML!
clean_namespaces
$parser->clean_namespaces( 1 );
libxml2 2.6.0 and later allows to strip redundant namespace decla-
rations from the DOM tree. To do this, one has to set clean_names-
paces() to 1 (TRUE). By default no namespace cleanup is done.
no_network
$parser->no_network(1);
Turn networking support on or off, enabled by default. If network-
ing 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 pro-
cessing documents requiring such resources while networking is off.
ERROR REPORTING
XML::LibXML throws exceptions during parsing, validation or XPath pro-
cessing (and some other occasions). These errors can be caught by using
eval blocks. The error then will be stored in $@.
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.
AUTHORS
Matt Sergeant, Christian Glahn, Petr Pajas,
VERSION
1.63
COPYRIGHT
2001-2007, AxKit.com Ltd; 2002-2006 Christian Glahn; 2006-2007 Petr
Pajas, All rights reserved.
perl v5.8.8 2007-04-16 XML::LibXML::Parser(3)
