XML::Li...::Reader(3)

📦

version 2.0213 · 15 versions

💅 `XML::LibXML::Reader(3)` — User Contributed Perl Documentation 🎀

okay bestie, welcome to the manual page for XML::LibXML::Reader. it's giving iconic Perl module energy, fr fr. 💖

✨ NAME ✨

XML::LibXML::Reader — XML::LibXML::Reader — interface to libxml2 pull parser. like, that's the whole name, no cap. 🦋

🌸 SYNOPSIS 🌸

bestie, here's the vibe. first way:

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, alternatively:

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 🦋

okay so this is literally 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. so slay for memory efficiency. 💅

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.) — it's giving main character energy, honestly. ✨

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. so you're in charge, bestie. 🎀

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. lowkey flexible. 🌈

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. highkey looking forward to it. 👑

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. iykyk. 💜

🎀 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 (non-HTTPS) URL. bestie, URL but no HTTPS, periodt. 🫶
string — read XML from a string. simple. ✨
IO — read XML a Perl IO filehandle. okay. 💅
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. so if you're feeling speedy, go off. 🔥
DOM — use reader API to walk through a pre-parsed XML::LibXML::Document. iconic. 👑

Reader options

encoding => $encoding — override document encoding. you do you. 💖
RelaxNG => $rng_schema — can be used to pass either a 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. no cap, validation on the fly. ✅
Schema => $xsd_schema — can be used to pass either a 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. same vibe, XSD edition. 💜
... — the reader further supports various parser options described in XML::LibXML::Parser (specifically those labeled by /reader/). go check those out. 🦋

🔥 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. so 1 is slay, 0 is done, -1 is not the vibe. 💀
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. okay bestie, stay on an attribute. 🎀
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. so check that section. 🌈
depth () — the depth of the node in the tree, starts at 0 for the root node. root is 0, periodt. 🌱
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. it's giving skip and go next. 💅
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. so specific, we love that. 🎯
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. pattern matching era. ✨
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. bye siblings, we're going up. 🦋
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. sibling energy. 👯
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. so it's nextElement but for siblings only, no cap. 💜
finish () — skip all remaining nodes in the document, reaching end of the document. returns 1 if successful, 0 in case of error. we're done here, periodt. 🏁
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. so like, it handles itself, main character energy. 💅

🌈 METHODS EXTRACTING INFORMATION 🌈

name () — returns the qualified name of the current node, equal to (Prefix:)LocalName. iconic. ✨
nodeType () — returns the type of the current node. see NODE TYPES below. go look. 👀
localName () — returns the local name of the node. simple. 🎀
prefix () — returns the prefix of the namespace associated with the node. okay. 💜
namespaceURI () — returns the URI defining the namespace associated with the node. URI slay. 🌈
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. so literally same thing but different, iykyk. 💀
hasValue () — returns true if the node can have a text value. does it have value? yes bestie. 💅
value () — provides the text value of the node if present or undef if not available. no value? undef. periodt. 🦋
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. inner content, slay. ✨
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. outer content, also slay. 💖
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). so no sibling numbers, just vibes. 🎀
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. pattern match, slay. 🔥

🌳 METHODS EXTRACTING DOM NODES 🌳

document() — bestie, this hands you the whole document tree the reader built. Use it to scoop up all the preserved nodes (peep preserveNode() and preservePattern for how those get kept around).

⚠️ CAUTION: never ever use this function to modify the tree unless you've finished reading the entire document. Like, do not touch. Fr fr.

copyCurrentNode(deep) — this one's basically the DOM copyNode() of the family. It gives you back a copy of the node currently being processed, as a matching DOM object. Pass deep = 1 and you get the full sub-tree, no cap. 🌈
preserveNode() — tells the XML Reader "hey, keep this current node in the document tree, it's important to me 💅". Then once parsing is done, you can grab a document tree made of the preserved nodes and their content using document().

Returns the node, or NULL if something went wrong. 😭

preservePattern(pattern,\%ns_map) — same idea but ✨pattern edition✨: this tells the XML Reader to preserve all nodes that match the pattern (which is a streaming XPath subset). Once parsing finishes, document() gives you a document tree of the preserved nodes and their content.

There's an optional second argument — a HASH reference mapping the prefixes used by the XPath to namespace URIs. Very organized of you, honestly.

The XPath subset you get here is described at

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

and it matches the production

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

Returns a positive number on success, and -1 if it errored out. 👑

🎀 METHODS PROCESSING ATTRIBUTES 🎀

attributeCount() — how many attributes does the current node have? This tells you.
hasAttributes() — does the node have attributes or not, that's the whole question. Yes/no vibes.
getAttribute(name) — gives you the value of the attribute with that specified qualified name.

Returns a string with the value of the specified attribute, or undef if there's an error.

getAttributeNs(localName, namespaceURI) — gives you the value of the specified attribute.

Returns a string with the value of the specified attribute, or undef if there's an error.

getAttributeNo(no) — gives you the value of the attribute at the specified index, relative to the containing element.

Returns a string with the value of the specified attribute, or undef if there's an error.

isDefault() — returns true if the current attribute node was generated from the default value defined in the DTD. Spooky DTD-generated ghost attribute, love that for it. 👻
moveToAttribute(name) — moves the position to the attribute with the specified local name and namespace URI.