path: root/lib/XML/LibXML/Reader.pod

=head1 NAME

XML::LibXML::Reader - XML::LibXML::Reader - interface to libxml2 pull parser

=head1 SYNOPSIS



  use XML::LibXML::Reader;



  my $reader = XML::LibXML::Reader->new(location => "file.xml")
         or die "cannot read file.xml\n";
  while ($reader->read) {
    processNode($reader);
  }



  sub processNode {
      my $reader = shift;
      printf "%d %d %s %d\n", ($reader->depth,
                               $reader->nodeType,
                               $reader->name,
                               $reader->isEmptyElement);
  }

or



  my $reader = XML::LibXML::Reader->new(location => "file.xml")
         or die "cannot read file.xml\n";
    $reader->preservePattern('//table/tr');
    $reader->finish;
    print $reader->document->toString(1);


=head1 DESCRIPTION

This is a perl interface to libxml2's pull-parser implementation xmlTextReader I<<<<<< http://xmlsoft.org/html/libxml-xmlreader.html >>>>>>. This feature requires at least libxml2-2.6.21. Pull-parsers (such as StAX in
Java, or XmlReader in C#) use an iterator approach to parse XML documents. They
are easier to program than event-based parser (SAX) and much more lightweight
than tree-based parser (DOM), which load the complete tree into memory.

The Reader acts as a cursor going forward on the document stream and stopping
at each node on the way. At every point, the DOM-like methods of the Reader
object allow one to examine the current node (name, namespace, attributes,
etc.)

The user's code keeps control of the progress and simply calls the C<<<<<< read() >>>>>> function repeatedly to progress to the next node in the document order. Other
functions provide means for skipping complete sub-trees, or nodes until a
specific element, etc.

At every time, only a very limited portion of the document is kept in the
memory, which makes the API more memory-efficient than using DOM. However, it
is also possible to mix Reader with DOM. At every point the user may copy the
current node (optionally expanded into a complete sub-tree) from the processed
document to another DOM tree, or to instruct the Reader to collect sub-document
in form of a DOM tree consisting of selected nodes.

Reader API also supports namespaces, xml:base, entity handling, and DTD
validation. Schema and RelaxNG validation support will probably be added in
some later revision of the Perl interface.

The naming of methods compared to libxml2 and C# XmlTextReader has been changed
slightly to match the conventions of XML::LibXML. Some functions have been
changed or added with respect to the C interface.


=head1 CONSTRUCTOR

Depending on the XML source, the Reader object can be created with either of:



  my $reader = XML::LibXML::Reader->new( location => "file.xml", ... );
    my $reader = XML::LibXML::Reader->new( string => $xml_string, ... );
    my $reader = XML::LibXML::Reader->new( IO => $file_handle, ... );
    my $reader = XML::LibXML::Reader->new( FD => fileno(STDIN), ... );
    my $reader = XML::LibXML::Reader->new( DOM => $dom, ... );

where ... are (optional) reader options described below in L<<<<<< Reader options >>>>>> or various parser options described in L<<<<<< XML::LibXML::Parser >>>>>>. The constructor recognizes the following XML sources:


=head2 Source specification

=over 4

=item location

Read XML from a local file or (non-HTTPS) URL.


=item string

Read XML from a string.


=item IO

Read XML a Perl IO filehandle.


=item FD

Read XML from a file descriptor (bypasses Perl I/O layer, only applicable to
filehandles for regular files or pipes). Possibly faster than IO.


=item DOM

Use reader API to walk through a pre-parsed L<<<<<< XML::LibXML::Document >>>>>>.



=back


=head2 Reader options

=over 4

=item encoding => $encoding

override document encoding.


=item RelaxNG => $rng_schema

can be used to pass either a L<<<<<< XML::LibXML::RelaxNG >>>>>> object or a filename or (non-HTTPS) URL of a RelaxNG schema to the constructor.
The schema is then used to validate the document as it is processed.


=item Schema => $xsd_schema

can be used to pass either a L<<<<<< XML::LibXML::Schema >>>>>> object or a filename or (non-HTTPS) URL of a W3C XSD schema to the constructor.
The schema is then used to validate the document as it is processed.


=item ...

the reader further supports various parser options described in L<<<<<< XML::LibXML::Parser >>>>>> (specifically those labeled by /reader/).



=back


=head1 METHODS CONTROLLING PARSING PROGRESS

=over 4

=item read ()

Moves the position to the next node in the stream, exposing its properties.

Returns 1 if the node was read successfully, 0 if there is no more nodes to
read, or -1 in case of error


=item readAttributeValue ()

Parses an attribute value into one or more Text and EntityReference nodes.

Returns 1 in case of success, 0 if the reader was not positioned on an
attribute node or all the attribute values have been read, or -1 in case of
error.


=item readState ()

Gets the read state of the reader. Returns the state value, or -1 in case of
error. The module exports constants for the Reader states, see STATES below.


=item depth ()

The depth of the node in the tree, starts at 0 for the root node.


=item next ()

Skip to the node following the current one in the document order while avoiding
the sub-tree if any. Returns 1 if the node was read successfully, 0 if there is
no more nodes to read, or -1 in case of error.


=item nextElement (localname?,nsURI?)

Skip nodes following the current one in the document order until a specific
element is reached. The element's name must be equal to a given localname if
defined, and its namespace must equal to a given nsURI if defined. Either of
the arguments can be undefined (or omitted, in case of the latter or both).

Returns 1 if the element was found, 0 if there is no more nodes to read, or -1
in case of error.


=item nextPatternMatch (compiled_pattern)

Skip nodes following the current one in the document order until an element
matching a given compiled pattern is reached. See L<<<<<< XML::LibXML::Pattern >>>>>> for information on compiled patterns. See also the C<<<<<< matchesPattern >>>>>> method.

Returns 1 if the element was found, 0 if there is no more nodes to read, or -1
in case of error.


=item skipSiblings ()

Skip all nodes on the same or lower level until the first node on a higher
level is reached. In particular, if the current node occurs in an element, the
reader stops at the end tag of the parent element, otherwise it stops at a node
immediately following the parent node.

Returns 1 if successful, 0 if end of the document is reached, or -1 in case of
error.


=item nextSibling ()

It skips to the node following the current one in the document order while
avoiding the sub-tree if any.

Returns 1 if the node was read successfully, 0 if there is no more nodes to
read, or -1 in case of error


=item nextSiblingElement (name?,nsURI?)

Like nextElement but only processes sibling elements of the current node
(moving forward using C<<<<<< nextSibling () >>>>>> rather than C<<<<<< read () >>>>>>, internally).

Returns 1 if the element was found, 0 if there is no more sibling nodes, or -1
in case of error.


=item finish ()

Skip all remaining nodes in the document, reaching end of the document.

Returns 1 if successful, 0 in case of error.


=item close ()

This method releases any resources allocated by the current instance and closes
any underlying input. It returns 0 on failure and 1 on success. This method is
automatically called by the destructor when the reader is forgotten, therefore
you do not have to call it directly.



=back


=head1 METHODS EXTRACTING INFORMATION

=over 4

=item name ()

Returns the qualified name of the current node, equal to (Prefix:)LocalName.


=item nodeType ()

Returns the type of the current node. See NODE TYPES below.


=item localName ()

Returns the local name of the node.


=item prefix ()

Returns the prefix of the namespace associated with the node.


=item namespaceURI ()

Returns the URI defining the namespace associated with the node.


=item isEmptyElement ()

Check if the current node is empty, this is a bit bizarre in the sense that
<a/> will be considered empty while <a></a> will not.


=item hasValue ()

Returns true if the node can have a text value.


=item value ()

Provides the text value of the node if present or undef if not available.


=item readInnerXml ()

Reads the contents of the current node, including child nodes and markup.
Returns a string containing the XML of the node's content, or undef if the
current node is neither an element nor attribute, or has no child nodes.


=item readOuterXml ()

Reads the contents of the current node, including child nodes and markup.

Returns a string containing the XML of the node including its content, or undef
if the current node is neither an element nor attribute.


=item nodePath()

Returns a canonical location path to the current element from the root node to
the current node. Namespaced elements are matched by '*', because there is no
way to declare prefixes within XPath patterns. Unlike C<<<<<< XML::LibXML::Node::nodePath() >>>>>>, this function does not provide sibling counts (i.e. instead of e.g. '/a/b[1]'
and '/a/b[2]' you get '/a/b' for both matches).


=item matchesPattern(compiled_pattern)

Returns a true value if the current node matches a compiled pattern. See L<<<<<< XML::LibXML::Pattern >>>>>> for information on compiled patterns. See also the C<<<<<< nextPatternMatch >>>>>> method.



=back


=head1 METHODS EXTRACTING DOM NODES

=over 4

=item document ()

Provides access to the document tree built by the reader. This function can be
used to collect the preserved nodes (see C<<<<<< preserveNode() >>>>>> and preservePattern).

CAUTION: Never use this function to modify the tree unless reading of the whole
document is completed!


=item copyCurrentNode (deep)

This function is similar a DOM function C<<<<<< copyNode() >>>>>>. It returns a copy of the currently processed node as a corresponding DOM
object. Use deep = 1 to obtain the full sub-tree.


=item preserveNode ()

This tells the XML Reader to preserve the current node in the document tree. A
document tree consisting of the preserved nodes and their content can be
obtained using the method C<<<<<< document() >>>>>> once parsing is finished.

Returns the node or NULL in case of error.


=item preservePattern (pattern,\%ns_map)

This tells the XML Reader to preserve all nodes matched by the pattern (which
is a streaming XPath subset). A document tree consisting of the preserved nodes
and their content can be obtained using the method C<<<<<< document() >>>>>> once parsing is finished.

An optional second argument can be used to provide a HASH reference mapping
prefixes used by the XPath to namespace URIs.

The XPath subset available with this function is described at



  http://www.w3.org/TR/xmlschema-1/#Selector

and matches the production



  Path ::= ('.//')? ( Step '/' )* ( Step | '@' NameTest )

Returns a positive number in case of success and -1 in case of error



=back


=head1 METHODS PROCESSING ATTRIBUTES

=over 4

=item attributeCount ()

Provides the number of attributes of the current node.


=item hasAttributes ()

Whether the node has attributes.


=item getAttribute (name)

Provides the value of the attribute with the specified qualified name.

Returns a string containing the value of the specified attribute, or undef in
case of error.


=item getAttributeNs (localName, namespaceURI)

Provides the value of the specified attribute.

Returns a string containing the value of the specified attribute, or undef in
case of error.


=item getAttributeNo (no)

Provides the value of the attribute with the specified index relative to the
containing element.

Returns a string containing the value of the specified attribute, or undef in
case of error.


=item isDefault ()

Returns true if the current attribute node was generated from the default value
defined in the DTD.


=item moveToAttribute (name)

Moves the position to the attribute with the specified local name and namespace
URI.

Returns 1 in case of success, -1 in case of error, 0 if not found


=item moveToAttributeNo (no)

Moves the position to the attribute with the specified index relative to the
containing element.

Returns 1 in case of success, -1 in case of error, 0 if not found


=item moveToAttributeNs (localName,namespaceURI)

Moves the position to the attribute with the specified local name and namespace
URI.

Returns 1 in case of success, -1 in case of error, 0 if not found


=item moveToFirstAttribute ()

Moves the position to the first attribute associated with the current node.

Returns 1 in case of success, -1 in case of error, 0 if not found


=item moveToNextAttribute ()

Moves the position to the next attribute associated with the current node.

Returns 1 in case of success, -1 in case of error, 0 if not found


=item moveToElement ()

Moves the position to the node that contains the current attribute node.

Returns 1 in case of success, -1 in case of error, 0 if not moved


=item isNamespaceDecl ()

Determine whether the current node is a namespace declaration rather than a
regular attribute.

Returns 1 if the current node is a namespace declaration, 0 if it is a regular
attribute or other type of node, or -1 in case of error.



=back


=head1 OTHER METHODS

=over 4

=item lookupNamespace (prefix)

Resolves a namespace prefix in the scope of the current element.

Returns a string containing the namespace URI to which the prefix maps or undef
in case of error.


=item encoding ()

Returns a string containing the encoding of the document or undef in case of
error.


=item standalone ()

Determine the standalone status of the document being read. Returns 1 if the
document was declared to be standalone, 0 if it was declared to be not
standalone, or -1 if the document did not specify its standalone status or in
case of error.


=item xmlVersion ()

Determine the XML version of the document being read. Returns a string
containing the XML version of the document or undef in case of error.


=item baseURI ()

Returns the base URI of a given node.


=item isValid ()

Retrieve the validity status from the parser.

Returns 1 if valid, 0 if no, and -1 in case of error.


=item xmlLang ()

The xml:lang scope within which the node resides.


=item lineNumber ()

Provide the line number of the current parsing point.


=item columnNumber ()

Provide the column number of the current parsing point.


=item byteConsumed ()

This function provides the current index of the parser relative to the start of
the current entity. This function is computed in bytes from the beginning
starting at zero and finishing at the size in bytes of the file if parsing a
file. The function is of constant cost if the input is UTF-8 but can be costly
if run on non-UTF-8 input.


=item setParserProp (prop => value, ...)

Change the parser processing behaviour by changing some of its internal
properties. The following properties are available with this function:
``load_ext_dtd'', ``complete_attributes'', ``validation'', ``expand_entities''.

Since some of the properties can only be changed before any read has been done,
it is best to set the parsing properties at the constructor.

Returns 0 if the call was successful, or -1 in case of error


=item getParserProp (prop)

Get value of an parser internal property. The following property names can be
used: ``load_ext_dtd'', ``complete_attributes'', ``validation'',
``expand_entities''.

Returns the value, usually 0 or 1, or -1 in case of error.



=back


=head1 DESTRUCTION

XML::LibXML takes care of the reader object destruction when the last reference
to the reader object goes out of scope. The document tree is preserved, though,
if either of $reader->document or $reader->preserveNode was used and references
to the document tree exist.


=head1 NODE TYPES

The reader interface provides the following constants for node types (the
constant symbols are exported by default or if tag C<<<<<< :types >>>>>> is used).



  XML_READER_TYPE_NONE                    => 0
  XML_READER_TYPE_ELEMENT                 => 1
  XML_READER_TYPE_ATTRIBUTE               => 2
  XML_READER_TYPE_TEXT                    => 3
  XML_READER_TYPE_CDATA                   => 4
  XML_READER_TYPE_ENTITY_REFERENCE        => 5
  XML_READER_TYPE_ENTITY                  => 6
  XML_READER_TYPE_PROCESSING_INSTRUCTION  => 7
  XML_READER_TYPE_COMMENT                 => 8
  XML_READER_TYPE_DOCUMENT                => 9
  XML_READER_TYPE_DOCUMENT_TYPE           => 10
  XML_READER_TYPE_DOCUMENT_FRAGMENT       => 11
  XML_READER_TYPE_NOTATION                => 12
  XML_READER_TYPE_WHITESPACE              => 13
  XML_READER_TYPE_SIGNIFICANT_WHITESPACE  => 14
  XML_READER_TYPE_END_ELEMENT             => 15
  XML_READER_TYPE_END_ENTITY              => 16
  XML_READER_TYPE_XML_DECLARATION         => 17


=head1 STATES

The following constants represent the values returned by C<<<<<< readState() >>>>>>. They are exported by default, or if tag C<<<<<< :states >>>>>> is used:



  XML_READER_NONE      => -1
  XML_READER_START     =>  0
  XML_READER_ELEMENT   =>  1
  XML_READER_END       =>  2
  XML_READER_EMPTY     =>  3
  XML_READER_BACKTRACK =>  4
  XML_READER_DONE      =>  5
  XML_READER_ERROR     =>  6


=head1 SEE ALSO

L<<<<<< XML::LibXML::Pattern >>>>>> for information about compiled patterns.

http://xmlsoft.org/html/libxml-xmlreader.html

http://dotgnu.org/pnetlib-doc/System/Xml/XmlTextReader.html


=head1 ORIGINAL IMPLEMENTATION

Heiko Klein, <H.Klein@gmx.net<gt> and Petr Pajas

=head1 AUTHORS

Matt Sergeant,
Christian Glahn,
Petr Pajas


=head1 VERSION

2.0207

=head1 COPYRIGHT

2001-2007, AxKit.com Ltd.

2002-2006, Christian Glahn.

2006-2009, Petr Pajas.

=cut


=head1 LICENSE

This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.