XML::RSS::LibXML(3) XML::RSS with XML::LibXML

SYNOPSIS


use XML::RSS::LibXML;
my $rss = XML::RSS::LibXML->new;
$rss->parsefile($file);
print "channel: $rss->{channel}->{title}\n";
foreach my $item (@{ $rss->{items} }) {
print " item: $item->{title} ($item->{link})\n";
}
# Add custom modules
$rss->add_module(uri => $uri, prefix => $prefix);
# See docs for XML::RSS for these
$rss->channel(...);
$rss->add_item(...);
$rss->image(...);
$rss->textinput(...);
$rss->save(...);
$rss->as_string($format);
# XML::RSS::LibXML only methods
my $version = $rss->version;
my $base = $rss->base;
my $hash = $rss->namespaces;
my $list = $rss->items;
my $encoding = $rss->encoding;
my $modules = $rss->modules;
my $output = $rss->output;
my $stylesheets = $rss->stylesheets;
my $num_items = $rss->num_items;

DESCRIPTION

XML::RSS::LibXML uses XML::LibXML (libxml2) for parsing RSS instead of XML::RSS' XML::Parser (expat), while trying to keep interface compatibility with XML::RSS.

XML::RSS is an extremely handy tool, but it is unfortunately not exactly the most lean or efficient RSS parser, especially in a long-running process. So for a long time I had been using my own version of RSS parser to get the maximum speed and efficiency - this is the re-packaged version of that module, such that it adheres to the XML::RSS interface.

Use this module when you have severe performance requirements working with RSS files.

VERSION 0.3105

The original XML::RSS has been evolving in fairly rapid manner lately, and that meant that there were a lot of features to keep up with. To keep compatibility, I've had to pretty much rewrite the module from ground up.

Now XML::RSS::LibXML is *almost* compatible with XML::RSS. If there are problems, please send in bug reports (or more preferrably, patches ;)

COMPATIBILITY

There seems to be a bit of confusion as to how compatible XML::RSS::LibXML is with XML::RSS: XML::RSS::LibXML is NOT 100% compatible with XML::RSS. For instance XML::RS::LibXML does not do a complete parsing of the XML document because of the way we deal with XPath and libxml's DOM (see CAVEATS below)

On top of that, I originally wrote XML::RSS::LibXML as sort of a fast replacement for XML::RAI, which looked cool in terms of abstracting the various modules. And therefore versions prior to 0.02 worked more like XML::RAI rather than XML::RSS. That was a mistake in hind sight, so it has been addressed (Since XML::RSS::LibXML version 0.08, it even supports writing RSS :)

From now on XML::RSS::LibXML will try to match XML::RSS's functionality as much as possible in terms of parsing RSS feeds. Please send in patches and any tests that may be useful!

PARSED STRUCTURE

Once parsed the resulting data structure resembles that of XML::RSS. However, as one addition/improvement, XML::RSS::LibXML uses a technique to allow users to access complex data structures that XML::RSS doesn't support as of this writing.

For example, suppose you have a tag like the following: 

  <rss version="2.0" xml:base="http://example.com/">
  ...
    <channel>
      <tag attr1="val1" attr2="val3">foo bar baz</tag>
    </channel>
  </rss>

All of the fields in this construct can be accessed like so: 

  $rss->channel->{tag}        # "foo bar baz"
  $rss->channel->{tag}{attr1} # "val1"
  $rss->channel->{tag}{attr2} # "val2"

See XML::RSS::LibXML::MagicElement for details.

METHODS

new(%args)

Creates a new instance of XML::RSS::LibXML. You may specify a version or an XML base in the constructor args to control which output format as_string() will use. 

  XML::RSS::LibXML->new(version => '1.0', base => 'http://example.com/');

The XML base will be included only in RSS 2.0 output. You can also specify the encoding that you expect this RSS object to use when creating an RSS string 

  XML::RSS::LiBXML->new(encoding => 'euc-jp');

parse($string)

Parse a string containing RSS.

parsefile($filename)

Parse an RSS file specified by $filename

channel(%args)

add_item(%args)

image(%args)

textinput(%args)

These methods are used to generate RSS. See the documentation for XML::RSS for details. Currently RSS version 0.9, 1.0, and 2.0 are supported.

Additionally, add_item takes an extra parameter, ``mode'', which allows you to add items either in front of the list or at the end of the list: 

   $rss->add_item(
      mode => "append",
      title => "...",
      link  => "...",
   );
   $rss->add_item(
      mode => "insert",
      title => "...",
      link  => "...",
   );

By default, items are appended to the end of the list

as_string($format)

Return the string representation of the parsed RSS. If $format is true, this flag is passed to the underlying XML::LibXML object's toString() method.

By default, $format is true.

add_module(uri => $uri, prefix => $prefix)

Adds a new module. You should do this before parsing the RSS. XML::RSS::LibXML understands a few modules by default: 

    rdf     => "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
    dc      => "http://purl.org/dc/elements/1.1/",
    syn     => "http://purl.org/rss/1.0/modules/syndication/",
    admin   => "http://webns.net/mvcb/",
    content => "http://purl.org/rss/1.0/modules/content/",
    cc      => "http://web.resource.org/cc/",
    taxo    => "http://purl.org/rss/1.0/modules/taxonomy/",

So you do not need to add these explicitly.

save($file)

Saves the RSS to a file

items()

Syntactic sugar to allow statement like this: 

  foreach my $item ($rss->items) {
    ...
  }

Instead of 

  foreach my $item (@{$rss->{items}}) {
    ...
  }

In scalar context, returns the reference to the list of items.

create_libxml()

Creates, configures, and returns an XML::LibXML object. Used by "parse()" to instantiate the parser used to parse the feed.

PERFORMANCE

Here's a simple benchmark using benchmark.pl in this distribution, using XML::RSS 1.29_02 and XML::RSS::LibXML 0.30 

  daisuke@beefcake XML-RSS-LibXML$ perl -Mblib tools/benchmark.pl t/data/rss20.xml 
  XML::RSS -> 1.29_02
  XML::RSS::LibXML -> 0.30
               Rate        rss rss_libxml
  rss        25.6/s         --       -67%
  rss_libxml 78.1/s       205%         --

CAVEATS

- Only first level data under <channel> and <item> tags are examined. So if you have complex data, this module will not pick it up. For most of the cases, this will suffice, though.

- Namespace for namespaced attributes aren't properly parsed as part of the structure. Hopefully your RSS doesn't do something like this: 

  <foo bar:baz="whee">

You won't be able to get at ``bar'' in this case: 

  $xml->{foo}{baz}; # "whee"
  $xml->{foo}{bar}{baz}; # nope

- Some of the structures will need to be handled via XML::RSS::LibXML::MagicElement. For example, XML::RSS's SYNOPSIS shows a snippet like this: 

  $rss->add_item(title => "GTKeyboard 0.85",
     # creates a guid field with permaLink=true
     permaLink  => "http://freshmeat.net/news/1999/06/21/930003829.html",
     # alternately creates a guid field with permaLink=false
     # guid     => "gtkeyboard-0.85
     enclosure   => { url=> 'http://example.com/torrent', type=>"application/x-bittorrent" },
     description => 'blah blah'
  );

However, the enclosure element will need to be an object: 

  enclosure => XML::RSS::LibXML::MagicElement->new(
    attributes => {
       url => 'http://example.com/torrent', 
       type=>"application/x-bittorrent" 
    },
  );

- Some elements such as permaLink elements are not really parsed such that it can be serialized and parsed back and force. I could fix this, but that would break some compatibility with XML::RSS

TODO

Tests. Currently tests are simply stolen from XML::RSS. It would be nice to have tests that do more extensive testing for correctness

COPYRIGHT AND LICENSE

Copyright (c) 2005-2007 Daisuke Maki <[email protected]>, Tatsuhiko Miyagawa <[email protected]>. All rights reserved.

Many tests were shamelessly borrowed from XML::RSS 1.29_02

Development partially funded by Brazil, Ltd. <http://b.razil.jp>

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

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