NAME
    Plack::App::RDF::Files - serve RDF data from files

SYNOPSIS
    Create a file "app.psgi":

        use Plack::App::RDF::Files;
        Plack::App::RDF::Files->new(
            base_dir => '/path/to/rdf/',       # mandatory
            base_uri => 'http://example.org/'  # optional
        )->to_app;

    Run it as web application by calling "plackup". Request URLs are then
    mapped to URIs and directories to return data from RDF files as
    following:

        http://localhost:5000/foo  =>  http://example.org/foo
                                             /path/to/rdf/foo/
                                             /path/to/rdf/foo/*.(nt|ttl|rdfxml)
        http://localhost:5000/x/y  =>  http://example.org/x/y
                                             /path/to/rdf/x/y/
                                             /path/to/rdf/x/y/*.(nt|ttl|rdfxml)

    In short, each subdirectory corresponds to an RDF resource.

DESCRIPTION
    This PSGI application serves RDF from files. Each accessible RDF
    resource corresponds to a (sub)directory, located in a common based
    directory. All RDF files in a directory are merged and returned as RDF
    graph. If no RDF data was found in an existing subdirectory, an
    axiomatic triple is returned:

        $REQUEST_URI <a <http://www.w3.org/2000/01/rdf-schema#Resource> .

    Requesting the base directory, however will result in a HTTP 404 error
    unless option "index_property" is enabled.

    HTTP HEAD and conditional GET requests are supported by ETag and
    Last-Modified-Headers (see Plack::Middleware::ConditionalGET).

CONFIGURATION
    base_dir
        Mandatory base directory that all resource directories are located
        in.

    base_uri
        The base URI of all resources. If no base URI has been specified,
        the base URI is taken from the PSGI request.

    file_types
        An array of RDF file types, given as extensions to look for. Set to
        "['rdfxml','nt','ttl']" by default.

    index_property
        By default a HTTP 404 error is returned if one tries to access the
        base directory. Enable this option by setting it to 1 or to an URI,
        to also serve RDF data from the base directory. By default
        "http://www.w3.org/2000/01/rdf-schema#seeAlso" is used as index
        property, if enabled.

    path_map
        Optional code reference that maps a local part of an URI to a
        relative directory. Set to the identity mapping by default.

    namespaces
        Optional namespaces for serialization, passed to
        RDF::Trine::Serializer.

METHODS
  call( $env )
    Core method of the PSGI application.

    The following PSGI environment variables are read and/or set by the
    application.

    rdf.uri
        The requested URI as string or URI object.

    rdf.iterator
        The RDF::Trine::Iterator that will be used for serializing, if
        "psgi.streaming" is set. One can use this variable to catch the RDF
        data in another post-processing middleware.

    rdf.files
        An hash of source filenames, each with the number of triples (on
        success) as property "size", an error message as "error" if parsing
        failed, and the timestamp of last modification as "mtime". "size"
        and "error" may not be given before parsing, if "rdf.iterator" is
        set.

    negotiate.format
        RDF serialization format (See Plack::Middleware::Negotiate).
        Supported values are "ttl", "nt", "n3", "json", and "rdfxml".

    If an existing resource does not contain triples, the axiomatic triple
    "$uri rdf:type rdfs:Resource" is returned.

  files( $env )
    Get a list of RDF files (as hash reference) that will be read for a
    given request, given as PSGI environment.

    The requested URI is saved in field "rdf.uri" of the request
    environment. On success returns the base directory and a list of files,
    each mapped to its last modification time. Undef is returned if the
    request contained invalid characters (everything but "a-zA-Z0-9:.@/-"
    and the forbidden sequence "../" or a sequence starting with "/"), or if
    called with the base URI and "index_property" not enabled.

  headers( $files )
    Get a response headers object (as provided by Plack::Util::headers) with
    ETag and Last-Modified from a list of RDF files given as returned by the
    files method.

SEE ALSO
    Use Plack::Middleware::Negotiate to add content negotiation based on an
    URL parameter and/or suffix.

    See RDF::LinkedData for a different module to serve RDF as linked data.
    See also RDF::Flow and RDF::Lazy for processing RDF data.

    See <http://foafpress.org/> for a similar approach in PHP.

COPYRIGHT AND LICENSE
    Copyright Jakob Voss, 2014-

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