Dancer2::Plugin::Mason - What's old is new again!

This year, Retro Santa paid us a visit and gave us a new gift of something old - an HTML::Mason plugin for Dancer2!

But Santa, why? WHY?

Before we start, one thing to clarify. Not unlike Dancer, the Mason framework underwent a total rewrite at some point. And, like Dancer, the two versions of the framework adopted different namespaces (HTML::Mason and Mason, for v1 and v2 respectively) such that the breaking changes of the new version wouldn't break old applications. In this article we are specifically talking about using the templating engine of the original Mason, HTML::Mason.

Mason as a framework is a templating engine and controller logic that is tightly coupled to the Apache web server that was meant to power it. Something that, at the time, made all the sense in the world. But since then... well, the world moved on a little bit. But while the controller layer of Mason got superceded by other mechanisms, its templating engine remains a strong and solid one. So it's not surprising that a lot of projects (such as Request Tracker (RT)) kept using it, pairing it with their own controller layer. Likewise, most Perl web frameworks provide a way to use it.

Catalyst? Check.

Mojolicious? Check.

Dancer1? Check.

Dancer2? ... uh oh.

Well, uh oh no more!

Dancer2::Template::Mason is a template adapter for HTML::Mason. If HTML::Mason is your favorite template system, you can now use it in your favorite web framework. If you have legacy Mason applications that would benefit from having a Dancer-powered controller, or a general refresh with some a more modern design, Dancer2 has your back.

Still talking about Mason in 2023? Does this mean I'm on the Naughty List?

Not at all! It's actually a pretty good gift, combining two powerful tools that are already in the toolbox of a lot of Perl developers. Go ahead, you can thank Retro Santa now. I'll wait.

How do I use it?

First, create your layout (views/layouts/main.m):

<html lang="en">
        <title><% $title %></title>

        <% $content %>

$title => "It's HTML::Mason... in Dancer2!"

That pile of variables in %args? As with its other template adapters, Dancer2 gives you those automatically. HTML::Mason, unlike some other template engines (Template::Toolkit for example) prefers you to explicitly declare variables before using them. But, and don't tell anybody I told you this, if you don't wanna declare them, you can reference them all via the %ARGS hash too.

Next, create your page template (views/index.m):

<p>Hello, <% $ARGS{ name } %>!</p>

And finally, add a route that uses your Mason template:

get '/:name?' => sub {
    my $name = body_paramaters->get( 'name' ) // 'Mystery Visitor';
    template 'index', { name => $name };

and Bob's your uncle! Seriously! Now, when you go to http://localhost:5000/Uncle%20Bob you'll see:

Hello, Uncle Bob!

And if you go to http://localhost/:5000 you get:

Hello, Mystery Visitor!

Care and feeding of your Mason templates

Off the shelf, the engine will re-compile the templates each time they are accessed, which is what one wants when developing. When the time comes for production and a little more ooomph is desired, the templates can be easily cached by adding the following to environments/production.yml:

template: "mason"
      extension: m
      data_dir: "/path/to/your/app/var/"
      use_object_files: 1
      static_source: 1

You'll need to clear the cache when templates change, however:

rm -rf /path/to/your/app/var/obj

Ok, where did this gift really come from? Retro Santa my %^$!!!

There are actually two mischievous elves hiding behind the beard and Santa suit. Yanick reworked his original Dancer1 Mason plugin, thanks to CromeDome's relentless poking, prodding, agitating, encouraging, testing, troubleshooting, and patch submitting.


I'd like to thank Jonathan Swartz for the shout-out in the Mason documentation, and for contributing a Mason (v2) template adapter for Dancer(1), and Yanick for putting up with my endless shenanigans.


This article has been written by Jason Crome for the Twelve Days of Dancer.


No copyright retained. Enjoy.

Jason A. Crome / CromeDome