XML::LibXML::Reader(3pUser Contributed Perl DocumentatXML::LibXML::Reader(3pm)NAMEXML::LibXML::Reader - XML::LibXML::Reader - interface to libxml2 pull
parser
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);
DESCRIPTION
This is a perl interface to libxml2's pull-parser implementation
xmlTextReader 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 in the way. At every point DOM-like methods of
the Reader object allow to examine the current node (name, namespace,
attributes, etc.)
The user's code keeps control of the progress and simply calls the
"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.
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 "Reader
options" or various parser options described in XML::LibXML::Parser.
The constructor recognizes the following XML sources:
Source specification
location
Read XML from a local file or URL.
string
Read XML from a string.
IO Read XML a Perl IO filehandle.
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.
DOM Use reader API to walk through a pre-parsed XML::LibXML::Document.
Reader options
encoding => $encoding
override document encoding.
RelaxNG => $rng_schema
can be used to pass either a XML::LibXML::RelaxNG object or a
filename or URL of a RelaxNG schema to the constructor. The schema
is then used to validate the document as it is processed.
Schema => $xsd_schema
can be used to pass either a XML::LibXML::Schema object or a
filename or URL of a W3C XSD schema to the constructor. The schema
is then used to validate the document as it is processed.
... the reader further supports various parser options described in
XML::LibXML::Parser (specifically those labeled by /reader/).
METHODS CONTROLLING PARSING PROGRESS
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
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.
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.
depth ()
The depth of the node in the tree, starts at 0 for the root node.
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.
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.
nextPatternMatch (compiled_pattern)
Skip nodes following the current one in the document order until an
element matching a given compiled pattern is reached. See
XML::LibXML::Pattern for information on compiled patterns. See also
the "matchesPattern" method.
Returns 1 if the element was found, 0 if there is no more nodes to
read, or -1 in case of error.
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.
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
nextSiblingElement (name?,nsURI?)
Like nextElement but only processes sibling elements of the current
node (moving forward using "nextSibling ()" rather than "read ()",
internally).
Returns 1 if the element was found, 0 if there is no more sibling
nodes, or -1 in case of error.
finish ()
Skip all remaining nodes in the document, reaching end of the
document.
Returns 1 if successful, 0 in case of error.
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.
METHODS EXTRACTING INFORMATION
name ()
Returns the qualified name of the current node, equal to
(Prefix:)LocalName.
nodeType ()
Returns the type of the current node. See NODE TYPES below.
localName ()
Returns the local name of the node.
prefix ()
Returns the prefix of the namespace associated with the node.
namespaceURI ()
Returns the URI defining the namespace associated with the node.
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.
hasValue ()
Returns true if the node can have a text value.
value ()
Provides the text value of the node if present or undef if not
available.
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.
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.
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 "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).
matchesPattern(compiled_pattern)
Returns a true value if the current node matches a compiled
pattern. See XML::LibXML::Pattern for information on compiled
patterns. See also the "nextPatternMatch" method.
METHODS EXTRACTING DOM NODES
document ()
Provides access to the document tree built by the reader. This
function can be used to collect the preserved nodes (see
"preserveNode()" and preservePattern).
CAUTION: Never use this function to modify the tree unless reading
of the whole document is completed!
copyCurrentNode (deep)
This function is similar a DOM function "copyNode()". It returns a
copy of the currently processed node as a corresponding DOM object.
Use deep = 1 to obtain the full sub-tree.
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 "document()"
once parsing is finished.
Returns the node or NULL in case of error.
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 "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
METHODS PROCESSING ATTRIBUTES
attributeCount ()
Provides the number of attributes of the current node.
hasAttributes ()
Whether the node has attributes.
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.
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.
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.
isDefault ()
Returns true if the current attribute node was generated from the
default value defined in the DTD.
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
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
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
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
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
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
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.
OTHER METHODS
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.
encoding ()
Returns a string containing the encoding of the document or undef
in case of error.
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.
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.
baseURI ()
Returns the base URI of a given node.
isValid ()
Retrieve the validity status from the parser.
Returns 1 if valid, 0 if no, and -1 in case of error.
xmlLang ()
The xml:lang scope within which the node resides.
lineNumber ()
Provide the line number of the current parsing point.
columnNumber ()
Provide the column number of the current parsing point.
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.
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
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.
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.
NODE TYPES
The reader interface provides the following constants for node types
(the constant symbols are exported by default or if tag ":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
STATES
The following constants represent the values returned by "readState()".
They are exported by default, or if tag ":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
SEE ALSO
XML::LibXML::Pattern for information about compiled patterns.
http://xmlsoft.org/html/libxml-xmlreader.html
http://dotgnu.org/pnetlib-doc/System/Xml/XmlTextReader.html
ORIGINAL IMPLEMENTATION
Heiko Klein, <H.Klein@gmx.net<gt> and Petr Pajas
AUTHORS
Matt Sergeant, Christian Glahn, Petr Pajas
VERSION
2.0108
COPYRIGHT
2001-2007, AxKit.com Ltd.
2002-2006, Christian Glahn.
2006-2009, Petr Pajas.
perl v5.18.1 2013-12-17 XML::LibXML::Reader(3pm)
