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.\" ========================================================================
.\"
.IX Title "HTTP::LRDD 3pm"
.TH HTTP::LRDD 3pm "2021-09-11" "perl v5.32.1" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
HTTP::LRDD \- link\-based resource descriptor discovery
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& use HTTP::LRDD;
\& 
\& my $lrdd        = HTTP::LRDD\->new;
\& my @descriptors = $lrdd\->discover($resource);
\& foreach my $descriptor (@descriptors)
\& {
\&   my $description = $lrdd\->parse($descriptor);
\&   # $description is an RDF::Trine::Model
\& }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Note: the \s-1LRDD\s0 specification has ceased to be, with some parts being merged into
the host-meta Internet Draft. This \s-1CPAN\s0 module will go in its own direction,
bundling up best-practice techniques for discovering links and descriptors for a
given \s-1URI.\s0
.SS "Import Routine"
.IX Subsection "Import Routine"
.ie n .IP """use HTTP::LRDD (@predicates)""" 4
.el .IP "\f(CWuse HTTP::LRDD (@predicates)\fR" 4
.IX Item "use HTTP::LRDD (@predicates)"
When importing \s-1HTTP::LRDD,\s0 you can optionally provide a list of
predicate URIs (i.e. the URIs which rel values expand to). This
may also include IANA-registered link types, which are short tokens
rather than full URIs. If you do not provide a list of predicate
URIs, then a sensible default set is used.
.Sp
Because this configuration is global in nature, it is not recommended.
It is better to supply a list of predicates to the constructor
instead, or rely on the defaults. This feature should be regarded
as deprecated.
.SS "Constructors"
.IX Subsection "Constructors"
.ie n .IP """HTTP::LRDD\->new(@predicates)""" 4
.el .IP "\f(CWHTTP::LRDD\->new(@predicates)\fR" 4
.IX Item "HTTP::LRDD->new(@predicates)"
Create a new \s-1LRDD\s0 discovery object using the given predicate URIs.
If \f(CW@predicates\fR is omitted, then the predicates passed to the import
routine are used instead.
.ie n .IP """HTTP::LRDD\->new_strict""" 4
.el .IP "\f(CWHTTP::LRDD\->new_strict\fR" 4
.IX Item "HTTP::LRDD->new_strict"
Create a new \s-1LRDD\s0 discovery object using the 'describedby' and
\&'lrdd' IANA-registered predicates.
.ie n .IP """HTTP::LRDD\->new_default""" 4
.el .IP "\f(CWHTTP::LRDD\->new_default\fR" 4
.IX Item "HTTP::LRDD->new_default"
Create a new \s-1LRDD\s0 discovery object using the default set of
predicates ('describedby', 'lrdd', 'wdrs:describedby', 'xhv:meta'
and 'rdfs:seeAlso').
.SS "Public Methods"
.IX Subsection "Public Methods"
.ie n .IP """$lrdd\->discover($resource_uri)""" 4
.el .IP "\f(CW$lrdd\->discover($resource_uri)\fR" 4
.IX Item "$lrdd->discover($resource_uri)"
Discovers a descriptor for the given resource; or if called in a list
context, a list of descriptors.
.Sp
A descriptor is a resource that provides a description for something.
So, if the given resource \s-1URI\s0 was the web address for an image, then
the descriptor might be the web address for a metadata file about the
image. If the given \s-1URI\s0 was an e\-mail address, then the descriptor
might be a profile document for the person to whom the address belongs.
.Sp
The following sources are checked (in order) to find links to
descriptors.
.RS 4
.IP "\(bu" 4
\&\s-1HTTP\s0 response headers (\*(L"Link\*(R" header; \*(L"303 See Other\*(R" status)
.IP "\(bu" 4
\&\s-1HTTP\s0 response message (\s-1RDF\s0 or RDFa)
.IP "\(bu" 4
https://HOSTNAME/.well\-known/host\-meta
.IP "\(bu" 4
http://HOSTNAME/.well\-known/host\-meta
.RE
.RS 4
.Sp
If none of the above is able to yield a link to a descriptor, then
the resource \s-1URI\s0 itself may be returned if it is in a self-describing
format (e.g. \s-1RDF\s0).
.Sp
There is no guaranteed file format for the descriptor, but it is
usually \s-1RDF, POWDER XML\s0 or \s-1XRD.\s0
.Sp
This method can also be called without an object (as a class method)
in which case, a temporary object is created automatically using
\&\f(CW\*(C`new\*(C'\fR.
.RE
.ie n .IP """$lrdd\->parse($descriptor_uri)""" 4
.el .IP "\f(CW$lrdd\->parse($descriptor_uri)\fR" 4
.IX Item "$lrdd->parse($descriptor_uri)"
Parses a descriptor in \s-1XRD\s0 or \s-1RDF\s0 (\s-1RDF/XML,\s0 RDFa, Turtle, etc).
.Sp
Returns an RDF::Trine::Model or undef if unable to process.
.Sp
This method can also be called without an object (as a class method)
in which case, a temporary object is created automatically using
\&\f(CW\*(C`new\*(C'\fR.
.ie n .IP """$lrdd\->process($resource_uri)""" 4
.el .IP "\f(CW$lrdd\->process($resource_uri)\fR" 4
.IX Item "$lrdd->process($resource_uri)"
Performs the equivalent of \f(CW\*(C`discover\*(C'\fR and \f(CW\*(C`parse\*(C'\fR in one easy step.
.Sp
Calls \f(CW\*(C`discover\*(C'\fR in a non-list context, so only the first descriptor
is used.
.ie n .IP """$lrdd\->process_all($resource_uri)""" 4
.el .IP "\f(CW$lrdd\->process_all($resource_uri)\fR" 4
.IX Item "$lrdd->process_all($resource_uri)"
Performs the equivalent of \f(CW\*(C`discover\*(C'\fR and \f(CW\*(C`parse\*(C'\fR in one easy step.
.Sp
Calls \f(CW\*(C`discover\*(C'\fR in a list context, so multiple descriptors are
combined into the resulting graph.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Discover the hub address (PubSubHubub) for a feed:
.PP
.Vb 2
\& my $lrdd = HTTP::LRDD\->new(\*(Aqhub\*(Aq);
\& my $hub  = $lrdd\->discover(\*(Aqhttp://example.net/feed.atom\*(Aq);
.Ve
.PP
Discover an author link (rel=\*(L"author\*(R") from an \s-1HTML\s0 page:
.PP
.Vb 2
\& my $lrdd   = HTTP::LRDD\->new(\*(Aqauthor\*(Aq);
\& my $author = $lrdd\->discover(\*(Aqhttp://example.com/page.html\*(Aq);
.Ve
.PP
(For \s-1RDF\s0 people, you should note that rel=\*(L"author\*(R" is not semantically
equivalent to the \*(L"foaf:maker\*(R" property but closer to the 
\&\*(L"foaf:maker/foaf:homepage\*(R" \s-1SPARQL 1.1\s0 property path \- i.e. the rel=\*(L"author\*(R"
link destination is not a \s-1URI\s0 for the author themselves, but a page about
the author.)
.PP
If that author resource is in a machine-readable format (e.g. \s-1RDF\s0), then
parse the data:
.PP
.Vb 1
\& my $author_data = $lrdd\->parse($author);
.Ve
.PP
Or, you can combine \f(CW\*(C`discover\*(C'\fR and \f(CW\*(C`parse\*(C'\fR:
.PP
.Vb 2
\& my $lrdd        = HTTP::LRDD\->new(\*(Aqauthor\*(Aq);
\& my $author_data = $lrdd\->process(\*(Aqhttp://example.com/page.html\*(Aq);
.Ve
.PP
Get metadata for an image:
.PP
.Vb 2
\& my $lrdd = HTTP::LRDD\->new;
\& my $data = $lrdd\->process_all(\*(Aqhttp://example.org/flower.jpeg\*(Aq);
.Ve
.PP
As we're not passing any arguments to the constructor, we can use a shortcut:
.PP
.Vb 1
\& my $data = HTTP::LRDD\->process_all(\*(Aqhttp://example.org/flower.jpeg\*(Aq);
.Ve
.PP
Find the title of the image:
.PP
.Vb 1
\& use RDF::QueryX::Lazy;
\& 
\& my $image   = q<http://example.org/flower.jpeg>;
\& my $results = RDF::QueryX::Lazy
\&   \-> new("SELECT * WHERE { <$image> dc:title ?t }")
\&   \-> execute( HTTP::LRDD\->process_all($image) );
.Ve
.SH "BUGS"
.IX Header "BUGS"
Please report any bugs to <http://rt.cpan.org/>.
.PP
\&\fBNote\fR: many problems can stem from servers that send incorrect
\&\f(CW\*(C`Content\-Type\*(C'\fR headers. If you send an \s-1XRD\s0 file as \*(L"text/html\*(R",
then this module will not guess what you're doing \- it will assume
the file is really \s-1HTML,\s0 and inspect it for RDFa. For host-meta
files, this module is slightly more relaxed, as there's a strong
assumption that they are \s-1XRD...\s0 but \s-1YOU SHOULD NOT RELY ON THIS.\s0
If you're running a server, use the correct media type.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
HTTP::Link::Parser, XRD::Parser, XML::Atom::OWL
WWW::Finger.
.PP
<http://www.perlrdf.org/>.
.SH "AUTHOR"
.IX Header "AUTHOR"
Toby Inkster <tobyink@cpan.org>.
.SH "COPYRIGHT AND LICENCE"
.IX Header "COPYRIGHT AND LICENCE"
Copyright 2010\-2012 Toby Inkster
.PP
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
.SH "DISCLAIMER OF WARRANTIES"
.IX Header "DISCLAIMER OF WARRANTIES"
\&\s-1THIS PACKAGE IS PROVIDED \*(L"AS IS\*(R" AND WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.\s0