NAME
WWW::Blog::Metadata - Extract common metadata from weblogs
SYNOPSIS
use WWW::Blog::Metadata;
use Data::Dumper;
my $uri;
my $meta = WWW::Blog::Metadata->extract_from_uri($uri)
or die WWW::Blog::Metadata->errstr;
print Dumper $meta;
DESCRIPTION
*WWW::Blog::Metadata* extracts common metadata from weblogs: syndication
feed URIs, FOAF URIs, locative information, etc. Some benefits of using
*WWW::Blog::Metadata*:
* The extraction makes only one parsing pass over the HTML, rather
than one for each type of metadata. It also attempts to be
intelligent about only parsing as much of the HTML document as is
required to give you the metadata that you need.
* Many of the types of metadata that *WWW::Blog::Metadata* extracts
can be found in multiple places in an HTML document. This module
does the work for you, and abstracts it all behind an API.
USAGE
WWW::Blog::Metadata->extract_from_uri($uri)
Given a URI *$uri* pointing to a weblog, fetches the page contents, and
attempts to extract common metadata from that weblog.
On error, returns "undef", and the error message can be obtained by
calling *WWW::Blog::Metadata->errstr*.
On success, returns a *WWW::Blog::Metadata* object.
WWW::Blog::Metadata->extract_from_html($html [, $base_uri ])
Uses the same extraction mechanism as *extract_from_uri*, but assumes
that you've already fetched the HTML document and will provide it in
*$html*, which should be a reference to a scalar containing the HTML.
If you know the base URI of the document, you should provide it in
*$base_uri*. *WWW::Blog::Metadata* will attempt to find the base URI of
the document if it's specified in the HTML itself, but you can give it a
head start by passing in *$base_uri*.
This method has the same return value as *extract_from_uri*.
$meta->feeds
A reference to a hash of syndication feed URIs.
(Note: these are currently extracted using *Feed::Find*, which requires
a separate parsing step, and sort of renders the above benefit #1
somewhat of a lie. This is done for maximum correctness, but it's
possible it could change at some point.)
$meta->foaf_uri
The URI for a FOAF file, specified in the standard manner used for FOAF
auto-discovery.
$meta->lat
$meta->lon
The latitude and longitude specified for the weblog, from either *icbm*
or *geo.position* *<meta />* tags.
$meta->generator
The tool that generated the weblog, from a *generator* *<meta />* tag.
PLUGINS
There are endless amounts of metadata that you might want to extract
from a weblog, and the methods above are only what are provided by
default. If you'd like to extract more information, you can use
*WWW::Blog::Metadata*'s plugin architecture to build access to the
metadata that you want, while while making only one parsing pass over
the HTML document.
The plugin architecture uses *Module::Pluggable::Ordered*, and it
provides 2 pluggable events:
* on_got_html
This event is fired before the HTML document is parsed, so you
should use it for extracting metadata after the page has been
fetched (if you're using *extract_from_uri*), but before it's been
parsed.
Your method will receive 4 parameters: the class name; the
*WWW::Blog::Metadata* object; a reference to a string containing the
HTML document; and the base URI of the document.
You could use this event to run heuristics on either the HTML or the
URI, or both. The following example uses *WWW::Blog::Identify* to
attempt to identify the true generator of the weblog:
package WWW::Blog::Metadata::Flavor;
use strict;
use WWW::Blog::Identify qw( identify );
use WWW::Blog::Metadata;
WWW::Blog::Metadata->mk_accessors(qw( flavor ));
sub on_got_html {
my $class = shift;
my($meta, $html, $base_uri) = @_;
$meta->flavor( identify($base_uri, $$html) );
}
sub on_got_html_order { 99 }
1;
This automatically adds a new accessor to the *$meta* object that is
returned from the *extract_from_** methods, so you can call
my $meta = WWW::Blog::Metadata->extract_from_uri($uri);
print $meta->flavor;
to retrieve the name of the identified weblogging tool.
* on_got_tag
This event is fired for each HTML tag found in the document during
the parsing phase.
Your method will receive 5 parameters: the class name; the
*WWW::Blog::Metadata* object; the tag name; a reference to a hash
containing the tag attributes; and the base URI.
The following example looks for the specific tag identifying the URI
for the RSD (Really Simple Discoverability) file identifying the
editing APIs that the weblog supports.
package WWW::Blog::Metadata::RSD;
use strict;
use WWW::Blog::Metadata;
WWW::Blog::Metadata->mk_accessors(qw( rsd_uri ));
sub on_got_tag {
my $class = shift;
my($meta, $tag, $attr, $base_uri) = @_;
if ($tag eq 'link' && $attr->{rel} =~ /\bEditURI\b/i &&
$attr->{type} eq 'application/rsd+xml') {
$meta->rsd_uri(URI->new_abs($attr->{href}, $base_uri)->as_string);
}
}
sub on_got_tag_order { 99 }
1;
This automatically adds a new accessor to the *$meta* object that is
returned from the *extract_from_** methods, so you can call
my $meta = WWW::Blog::Metadata->extract_from_uri($uri);
print $meta->rsd_uri;
to retrieve the URI for the RSD file.
* on_finished
This event is fired at the end of the extraction process.
Your method will receive 2 parameters: the class name, and the
*WWW::Blog::Metadata* object.
LICENSE
*WWW::Blog::Metadata* is free software; you may redistribute it and/or
modify it under the same terms as Perl itself.
AUTHOR & COPYRIGHT
Except where otherwise noted, *WWW::Blog::Metadata* is Copyright 2005
Benjamin Trott, ben+cpan@stupidfool.org. All rights reserved.