Franck Cuny @franckcuny

Software and Operation engineer.

A simple feed aggregator with modern Perl - part 4

We have the model, the aggregator (and some tests), now we can do a basic frontend to read our feed. For this I will create a webapp using Catalyst.

Catalyst::Devel is required for developping catalyst application, so we will install it first:

% cpan Catalyst::Devel

Now we can create our catalyst application using the helper:

% catalyst.pl MyFeedReader

This command initialise the framework for our application MyFeedReader. A number of files are created, like the structure of the MVC directory, some tests, helpers, ...

We start by creating a view, using TTSite. TTSite generate some templates for us, and the configuration for this template. We will also have a basic CSS, a header, footer, etc.

cd MyFeedReader
perl script/myfeedreader_create.pl view TT TTSite

TTSite files are under root/src and root/lib. A MyAggregator/View/TT.pm file is also created. We edit it to make it look like this:

__PACKAGE__->config({
    INCLUDE_PATH => [
        MyFeedReader->path_to( 'root', 'src' ),
        MyFeedReader->path_to( 'root', 'lib' )
    ],
    PRE_PROCESS  => 'config/main',
    WRAPPER      => 'site/wrapper',
    ERROR        => 'error.tt2',
    TIMER        => 0,
    TEMPLATE_EXTENSION => '.tt2',
});

Now we create our first template, in root/src/index.tt2

to <a href="/feed/">your feeds</a>

If you start the application (using perl script/myfeedreader_server.pl) and point your browser on http://localhost:3000/, this template will be rendered.

We need two models, one for KiokuDB and another one for MyModel:

lib/MyFeedReader/Model/KiokuDB.pm

package MyFeedReader::Model::KiokuDB;
use Moose;
BEGIN { extends qw(Catalyst::Model::KiokuDB) }
1;

we edit the configuration file (**myfeedreader.conf**), and set the dsn for our kiokudb backend

    <Model KiokuDB>
        dsn dbi:SQLite:../MyAggregator/foo.db
    </Model>

lib/MyFeedReader/Model/MyModel.pm

package MyFeedReader::Model::MyModel;
use base qw/Catalyst::Model::DBIC::Schema/;
1;

and the configuration:

<Model MyModel>
    connect_info dbi:SQLite:../MyModel/model.db
    schema_class MyModel
</Model>

We got our view and our model, we can do the code for the controller. We need 2 controller, one for the feed, and one for the entries. The Feed controller will list them and display entries titles for a given feed. The Entry controller will just display them.

lib/MyFeedReader/Controller/Feed.pm

package MyFeedReader::Controller::Feed;
use strict;
use warnings;
use parent 'Catalyst::Controller';

__PACKAGE__->config->{namespace} = 'feed';

sub index : Path : Args(0) {
    my ( $self, $c ) = @_;
    $c->stash->{feeds}
        = [ $c->model('MyModel')->resultset('Feed')->search() ];
}

sub view : Chained('/') : PathPart('feed/view') : Args(1) {
    my ( $self, $c, $id ) = @_;
    $c->stash->{feed}
        = $c->model('MyModel')->resultset('Feed')->find($id);
}

1;

The function index list the feeds, while the function view list the entries for a give feed. We use the chained action mechanism to dispatch this url, so we can have urls like this /feed/\*

We create our 2 templates (for index and view):

root/src/feed/index.tt2

<ul>
    [% FOREACH feed IN feeds %]
        <li><a href="/feed/view/[% feed.id %]">[% feed.url %]</a></li>
    [% END %]
</ul>

root/src/feed/vew.tt2

<h1>[% feed.url %]</h1>

<h3>entries</h3>
<ul>
    [% FOREACH entry IN feed.entries %]
        <li><a href="/entry/[% entry.id %]">[% entry.permalink %]</a></li>
    [% END %]
</ul>

If you point your browser to http://localhost:3000/feed/ you will see this:

list feeds

Now the controller for displaying the entries:

package MyFeedReader::Controller::Entry;
use strict;
use warnings;
use MyAggregator::Entry;
use parent 'Catalyst::Controller';

__PACKAGE__->config->{namespace} = 'entry';

sub view : Chained('/') : PathPart('entry') : Args(1) {
    my ( $self, $c, $id ) = @_;
    $c->stash->{entry} = $c->model('KiokuDB')->lookup($id);
}

1;

The function view fetch an entry from the kiokudb backend, and store it in the stash, so we can use it in our template.

root/src/entry/view.tt2

<h1><a href="[% entry.permalink %]">[% entry.title %]</a></h1>
<span>Posted [% entry.date %] by [% entry.author %]</span>
<div id="content">
    [% entry.content %]
</div>

If you point your browser to an entry (something like http://localhost:3000/entry/somesha256value), you will see an entry:

show entry

Et voila, we are done with a really basic feed reader. You can add methods to add or delete feed, mark an entry as read, ...

The code is available on my git server.