All about Mojolicious – interview of Sebastian Riedel part 2

 

NV: Does the dependency free nature of Mojolicious act as an invitation to people familiar with other frameworks (i.e. Ruby on Rails) and languages (i.e. PHP)? That aside, what other factors/features would lure such developers to the framework?

SR: The dependency free nature of Mojolicious is actually more of a myth, the truth is that installing Mojolicious is simply a very fast and pleasant experience.

One of the ways in which we’ve done this, is to make hard to install 3rd party modules like IO::Socket::SSL and Net::DNS::Native optional.

I think what makes Mojolicious special is best explained with an example application:

 use Mojolicious::Lite;
 use 5.20.0;
 use experimental 'signatures';

    # Render template "index.html.ep" from the DATA section
    get '/' => {template => 'index'};

    # WebSocket service used by the template to extract the title from a web site
    websocket '/title' => sub ($c) {
      $c->on(message => sub ($c, $msg) {
        my $title = $c->ua->get($msg)->res->dom->at('title')->text;
        $c->send($title);
      });
    };

    app->start;
    __DATA__

    @@ index.html.ep
    % my $url = url_for 'title';
    <script>
      var ws = new WebSocket('<%= $url->to_abs %>');
      ws.onmessage = function (event) { document.body.innerHTML += event.data };
      ws.onopen    = function (event) { ws.send('http://mojolicio.us') };
    </script>
   

This is actually the first example application you encounter on our website (http://mojolicio.us).
It doesn’t look very complicated at all. But once you start digging a little deeper, you’ll quickly realize how crazy (in a good way) it really is, and how hard it would be to replicate with any other web framework, in any language.

To give you a very quick summary:

1. There’s an EP (Embedded Perl) template, in the DATA section of a single-file web application. That template generates an HTML file, containing JavaScript, which opens a WebSocket connection, to a dynamically generated URL (ws://127.0.0.1:3000/title), based on the name of a route.
2. Then sends another URL (http://mojolicio.us) through the WebSocket as a text message, which results in a message event being emitted by the server.
3. Our server then uses a full featured HTTP user agent, to issue a GET request to this URL, and uses an HTML DOM parser to extract the title from the resulting document with CSS selectors.
4. Before finally returning it through the WebSocket to the browser, which then displays it in the body of our original HTML file.

Next year at Mojoconf 2015, I’ll be giving a whole talk about this one application, exploring it in much greater detail.

NV: It’s a framework that you use in pure Perl. Why not go for a DSL like Dancer does?

SR: There are actually two kinds of web framework DSLs, and they differ by scope.

First, you have your routing DSL, which usually runs during server start-up and modifies application state. (application scope)

    get '/foo' => sub {...};

Second, there is what I would call the content generation DSL, which modifies request/response state. (request scope)

    get '/foo' => sub {
      header 'Content-Type' => 'text/plain';
      render 'some_template';
    };

Mojolicious does have the first kind, and we’ve already used it in the examples above, but not the second. And the reason for this, is that the second kind does not work very well, when you plan on handling multiple requests concurrently in the same process, which involves a lot of context switching. It’s a trade-off between making your framework more approachable for beginners, that might not know Object-Oriented Perl yet, and supporting modern real-time web features.

Which object system is Mojolicious using and which can I use in my code?

Mojolicious uses plain old hash-based Perl objects, and we take special care to allow for Moose and Moo to be used in applications as well.

NV: With Dancer you can easily integrate jQuery and Bootstrap with the templating system. How does Mojolicious approach this integration?

Mojolicious is completely JavaScript/HTML/CSS framework agnostic, and will work with all of them. Some frameworks, including jQuery and Bootstrap, do have plugins on CPAN, but we don’t discriminate.

NV: Mojolicious vs Mojolicious::Lite. When to use each?

SR: I usually start exploring ideas with a single-file Mojolicious::Lite prototype, like we’ve seen above, and slowly grow it into a well-structured Mojolicious web application, which looks more like your average CPAN distribution.

This is a rather simple process, because Mojolicious::Lite is only a tiny wrapper around Mojolicious, and both share like 99% of the same code.

NV: What can we expect in the future and what is the greater vision for the project’s evolution?

Mojolicious has an amazing community, and I hope we can expand on that to reach more people from outside the Perl community in the future. Not a day goes by where I don’t receive requests for a Mojolicious book, so that’s a pretty big priority too.

Feature wise, with the release of the final RFC, I expect HTTP/2 to be a very big topic in 2015.
And hopefully we will get to play more with new Perl features such as signatures, I can’t wait for a polyfill CPAN module to bring signatures to older versions of Perl.

NV: Finally, prompted by the news that Perl 6 will officially launch for production use by 2015, I’d like to hear your thoughts on Perl 6 and if it could or would be used, with or as part, of Mojolicious.

SR: I’ve had the pleasure to see Jonathan Worthington talk about concurrency and parallelism in Perl6 at Mojoconf 2014, and to say that it was quite inspiring would be an understatement.

But “production use” can mean a lot of different things to a lot of people. Is it feature complete? Is it as fast as Perl5? Would you bet the future of your company on it?

I love Perl6 the language, it solves all the problems I have with Perl5, and if there’s an implementation that’s good enough, you bet there will be a Mojolicious port!

Nikos Vaggalis has a BSc in Computer Science and a MSc in Interactive Multimedia. He works as a Database Developer with Linux and Ingres, and programs in both Perl and C#. As a journalist he writes articles, conducts interviews and reviews technical IT books