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Editing: 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);
  }

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.