NAME

XML::Parser::GlobEvents - event driven XML parser, filtered on tag path, with element tree for parameter

SYNOPSIS

 use XML::Parser::GlobEvents qw(parse);
 parse(\*DATA,
     item => sub {  # for each tag with name 'item':
         my($node) = @_;
         print "$node->{title}{-text} ($node->{-attr}{id}): $node->{description}{-text}\n";
     }
 );

 __DATA__
 <root>
   <item id="1">
     <title>Floor Wax</title>
     <description>Is it a floor wax?</description>
   </item>
   <item id="2">
     <title>Dessert Topping</title>
     <description>Is it a dessert topping?</description>
   </item>
 </root>

DESCRIPTION

XML::Parser::GlobEvents is a module aimed to parse data from XML files that have a predictable, repetitive structure, in a "process as you parse" manner. It lets you to specify event handlers that get invoked when start and/or end tags are being parsed. They are filtered on a pattern specifying which tag, and where it should appear in the document. As it parses, it builds a complete tree for the element, that gets passed to the End handler.

Afterwards, if there are no more pending End handlers for an element or any of its enclosing elements, then it is automatically discarded - usually before the rest of the document is even parsed.

Note that this module is only a parser, it does not produce XML. But parsing XML is the hard part, producing XML is easy.

FUNCTIONS

The core API of this module is a single function: "parse", which you can choose to import under its alias "parse_xml". There are no objects, there is no need for subclassing.

parse

 parse($file,  # file name, filehandle, or ref to scalar containing the XML
     pattern => {
         Start => sub { my($node) = @_; ... },  # Start handler, optional
         End => sub { my($node) = @_; ... },    # End handler, optional
         Other => 1, ...                        # other specifiers, optional
      },
      pattern2 = > { ... },                     # repeatable
      pattern2 => sub { my($code) = @_; ... },  # End handler only
 );

The first parameter you have to pass it is the file name, filehandle, or a ref to a scalar containing the XML data.

Next follow any number of pattern+specifier pairs:

 "pattern" => \%spec

If you pass a code ref instead of a hashref as the specifier, it is taken to mean an End handler.

 "pattern" => sub { ... }   # End handler

PATHS AND PATTERNS

These are inspired by XPath, but absolutely minimal. Even if you're new to this, you can most likely pick it up in minutes.

paths

A path is written just like a Unix file path, where the directory names are replaced by tag names. The reason why this can even work reliably is because a "/" character is not allowed in a tag name.

For example, in the following XML, the path to the element with tag name "gamma" is "/alpha/beta/gamma".

 <alpha>
   <beta>
     <gamma>HERE</gamma>
   </beta>
 </alpha>

patterns

The rules to specify path patterns are like this:

foo

matches if the current tag has the name "foo", on any depth

alpha/foo

matches if the current tag is "foo" and its parent is "alpha"

*

matches any tag

alpha/*

matches any child tag under "alpha"

alpha//foo

matches any tag "foo" that is somewhere under "alpha" (AKA a descendant), either directly (a child) or at any depth: i.e. it will match for all of "alpha/foo", "alpha/beta/foo" and "alpha/beta/gamma/foo".

alpha//*

matches any descendant tag under "alpha"

/alpha/beta

is an absolute path, anchored to the root. Note that "alpha/beta" is equivalent to "//alpha/beta", i.e. not anchored.

That's about it. I'm not planning to ever implement more of XPath, simply because we don't need it: why should I emulate silly functions when it's so much easier and faster to deal with them, in the handlers, in Perl? This includes expressions and comparisons, and filtering on attributes. Simply return early from the handler.

HANDLERS

There are 2 types of handlers:

Start tag handler

This one is invoked when the pattern matches as the start tag is parsed, and before any of the child elements.

The properties passed to the callback in the first parameter include the path, the tag name, and the attributes hash.

You cannot get at the element's contents, because the contents haven't been parsed yet.

End tag handler

It is invoked when the end tag is parsed (and the pattern matches). It is in general much more useful than the Start handler, because in addition to the above properties as passed to the Start handler (including attributes from the start tag, as these are actually properties of the element of which this tag is the closing tag), you also get a tree for the parsed content.

If you have more than one handler matching for one tag, they will be invoked in sequence, from the most specific pattern first (meaning: more fixed parts, and fewer wildcards) to the least specific one.

The first parameter to these handlers is the "node", which represents the contents for the current tag/element.

Note that restrictions on well-formedness of XML by the underlying parser enforces the fact that these events always come in pairs: a Start event is always complemented by an associated End event - whether you have set a handler on it, or not.

NODE

A node is a hash ref, plain and simple. That hash contains generic properties, such as the tag name and the attributes, and, in case of an End handler, references to its text contents, and to child nodes, which are similar hash refs. They represent a tree for the element and its decendants.

node properties

Generic node properties have a name that starts with a "-" sign, which will not ever clash with the name of any tag.

Thanks to the special syntax rules of Perl, you don't have to quote them: $node->{-name} means exactly the same thing as $node->{'-name'}.

-name

the tag name

-path

the element's path, in the form /alpha/beta/gamma where 'alpha' is the root element and 'gamma' is the current tag's name, plus every other tag in between.

-attr

a hash ref with the attributes, entities decoded and converted to UTF8

-position

the number of the current tag among its siblings (under the same parent) with the same name. The first item has number 1.

-contents

an array ref containing all top level texts as plain strings, and child nodes as hash refs, in the order as in the document.

-text

the plain text contents from the top level, excluding text in nested tags, as a plain string. Entities are decoded and the whole text is converted to UTF8.

Accessing child nodes

There is more than one way to access a child node. They are:

$node->{TAG}

(replace "TAG" with the actual name of the tag)

This is the direct access to a child node for an element with that tag name. In case there's more than one such element, then it'll be the last one in the document.

Because, even though tag names may contain "-" characters, they cannot ever start with one, this will not clash with our ordinary node properties.

$node->{'TAG[]'}

(replace "TAG" with the actual name of the tag)

This will be an array ref with all child elements with this tag name, in the order of the document.

$node->{-contents}

An array ref that contains plain text (simple strings) and child nodes (hashrefs), in the order of the document.

Text

Accessing text can be done through the node property "-text": $node->{-text}

This includes only text immediately at the top level of the current element; text in child elements is ignored.

Entities are decoded and the text is converted to UTF8.

Whitespace

Whitespace is trimmed and normalized (meaning: any sequence of whitespace is replaced by a single space) by default. To prevent this, you can specify

    Whitespace => $mode

in the specifier for this pattern, in the hash, alongside the Start and/or End handler. The values for mode are:

normalize

default behaviour: trim and collapse

trim

trim only, to prevent collapse

collapse

no trim, collapse only

keep

no trim, no collapse

CDATA

CDATA sections in the document are also included as plain text.

DEPENDENCIES

Expat

This module is built on top of XML::Parser::Expat, which is part of the XML::Parser distro, but without all the unnecessary fluff that the latter layer module adds.

Text

It is Expat that decodes the entities and converts text to UTF-8, for text contents and for attributes. If your XML file uses a character encoding that your instance of XML::Parser::Expat doesn't currently handle, you can most likely add it, for example using XML-Encoding.

Namespace Support

Expat has a primitive but workable take on namespaces: a tag with a namespace like "RDF:rdf" is just taken as is: the tag's name is simply "RDF:rdf".

Although the original idea behind namespaces was that the URI was the real identifier of the namespace, and the namespace prefix before the colon was just a temporary abbreviation, people ended up remembering the prefix as the namespace name, while nobody remembers the namespace URI.

In short: those namespace prefixes are very unlikely to ever change between files from the same source, although theoretically, they can.

I may at one time add support to associate a namespace prefix with the URI specified in the document, and have the patterns automatically adapt to them, but at this time, it looks very unlikely that I ever will need it.

CDATA

Expat treats CDATA sections, although parsed differently, as plain text. So that's where they end up.

Other XML document contents

This module does not include a handler for processing instructions nor for comments, so they're just ignored.

RELEASE NOTES

This is a historical release. It's pretty much the module as I wrote it in 2000-2001. It's one of the modules I have always been the most proud of. Whenever I think of parsing XML, this module is still the module I think of first...

I have changed very little to this module, it is for most parts the same as I have used so often, a long long time ago. There are bugs, and I do have more plans for future development, but I prefer to release it now and let you get to know it, rather than keeping it in the cellar for another year in the hope to get it up to snuff.

There's a few things that don't quote work the way I think they ought to. I'll probably get around them sometime. But I had to release this module some time, and sooner rather than later...

But: there is room for growth.

AUTHOR

Bart Lateur, bart.lateur@pandora.be (mailto:bart.lateur@pandora.be)

COPYRIGHT AND LICENSE

Copyright (c) 2000-2009 by Bart Lateur

This library is free software; you can redistribute it and/or modify it under the same terms as any version of Perl 5 you may have available.

SEE ALSO

SAX
DOM
XPath
XSLT
XML::Twig as an alternative module (allegedly)

I understood that XML::Twig is supposed to work in a similar way. When I started out looking at various XML parsers, I did have a good long look at it. After 1 to 2 days of intensive study, I gave up and decided to write my own parsing module instead. That was easier...

http://www.xml.com/lpt/a/1564

XML Namespaces Don't Need URIs

XML::Encoding

for adding support for more character encodings to your XML parser