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Squatting-0.52
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/ Squatting::Cookbook

NAME

Squatting::Cookbook - Web Development Techniques for Squatting

INTRODUCTION

Squatting exists because I fell in love with Camping's API, and I couldn't bear the thought of building another site using some other API. When I decided that the next site I wanted to build would be implemented in Perl, I had no choice but to port Camping to Perl, and that's how Squatting was born.

My hope is that other Perl programmers will be able to appreciate how concise this API is, and I hope they'll see just how far a little bit of code can go.

Anatomy of a Squatting Application

Make a Subclass of Squatting

package App;
use base 'Squatting';
our %CONFIG = ();

Make a Package for Your Controllers

If your app is called App, then:

Your controllers must be defined in a package called App::Controllers.
You must say use Squatting ':controllers'.
You must put your controllers in a package variable named @C.
package App::Controllers;
use Squatting ':controllers';
our @C = (
  C(
    Home => [ '/' ],
    get  => sub {
      my ($self) = @_;
      $self->render('home');
    }
  ),
  C(
    Profile => [ '/~(\w+)' ],
    get => sub {
      my ($self, $name) = @_;
      my $v = $self->v;
      $v->{name} = $name;
      $self->render('profile');
    }
  )
);

Anatomy of a Controller

Make a Package for Your Views

If your app is called App, then:

Your views must be defined in a package called App::Views.
You must say use Squatting ':views'.
You must put your views in a package variable named @V.
package App::Views;
use Squatting ':views';
our @V = (
  V(
    'html',
    layout => sub {
    },
    home => sub {
    },
    profile => sub {
    },
  )
);

Anatomy of a View

PROGRAMMING TECHNIQUES

COMET

Event Architecture

RESTless Controllers

How to Set Up Sessions

Continuity and Process Memory

Pure Continuity apps typically don't use persistent session storage, because they can use lexically scoped variables instead. However, Squatting apps are RESTful and stateless by default, so you can't count on the lexical scope of a controller to stick around between requests. Luckily, package variables *will* stick around, so that's what we'll use to implement persistent sessions.

package App;
our %state;
sub service {
  my ($app, $c, @args) = @_;
  my $cr  = $c->cr;
  my $sid = $cr->{session_id};
  if (defined $sid) {
    $c->state = $state{$sid} ||= {};
  } 
  $app->next::method($c, @args);
}

Here, we override service() in the main module of our app so that $c->state will provide a hashref whose values will persist between requests.

Note that instead of writing $app->SUPER::service, we have to write $app->next::method, because Squatting is a sublcass of Class::C3::Componentised.

When Squatting::On::Catalyst

When squatting on top of Catalyst, the Catalyst session becomes $self->state in Squatting. The session storage code in Catalyst is very mature, so it is highly recommended that all the session setup be done on the Catalyst side.

Sessions From Scratch

The challenge is to find a way to assign unique session ids to each visitor and use that session id as a key into a persistent store. TMTOWTDI

How to Use Various Templating Systems With Squatting

HTML::AsSubs

I like HTML::AsSubs for the following reasons:

  • It works as advertised.

  • The implementation is really small.

  • It seems to be widely deployed (even though no one uses it).

  • And generating HTML with code eliminates the need to install templates.

The documentation is up-front about some of the module's shortcomings which I appreciate. However, the docs go a bit too far and recommend that this module not even be used! It says that there are "cleaner" alternatives, but when I looked at them, I came straight back to HTML::AsSubs.

I think the module works just fine, and I'd like to show you how I use it.

Addressing HTML::AsSubs Shortcomings (Alleged and Otherwise)

The exported link() function overrides the builtin link() function.

Noted. You shouldn't be calling the builtin link() in view code anyway, so it's not a big deal.

The exported tr() function must be called using &tr(...) syntax.

This is because it clashes with the builtin tr/../../ operator. I can live with this.

Problem: exports so damned much. (from the code comments)

The funny thing is, it's actually not exporting enough. It's missing a sub for the span tag. (Did that tag even exist in 1994 when this module was written?) Luckily, this is easy to fix.

sub span { HTML::AsSubs::_elem('span', @_) }

If there are any other missing tags, you know what to do.

There's one more pseudo-tag that I like to add for practical reasons.

sub x { map { HTML::Element->new('~literal', text => $_) } @_ }

Normally, HTML::AsSubs will entity escape all the text that you give it. However, there are many times when you legitimately don't want text to be entity escaped, so that's what x() is for.

An Example View That Uses HTML::AsSubs

package App::Views;
use strict;
use warnings;
use Squatting ':views';
use HTML::AsSubs;

sub span { HTML::AsSubs::_elem('span', @_) }
sub x    { map { HTML::Element->new('~literal', text => $_) } @_ }

our @V = (
  V(
    'html',
    layout => sub {
      my ($self, $v, $content) = @_;
      html(
        head(
          title( $v->{title} ),
          style(x( $self->_css )),
        ),
        body(
          x( $content )
        )
      )->as_HTML;
    },
    _css => sub {qq|
      body {
        background : #000;
        color      : #f5deb3;
      }
    |},
    home => sub {
      my ($self, $v) = @_;
      h1( $v->{message} )->as_HTML;
    },
  ),
);
1;

Again, the nicest part about generating HTML from code is that you don't have to worry about installing template files. The templates are in memory as perl expressions. When building web apps that are designed to be embedded, this is a really nice feature to have as it makes deployment that much easier.

If HTML::AsSubs is a bit too low tech for you, there are more modern expressions of the code-to-html idea on CPAN. For example, Template::Declare looks like it may be worth looking into. I'm happy with HTML::AsSubs, though.

Tenjin

Tenjin is the fastest templating system that no one outside of Japan seems to know about. It's really unfortunate that this module isn't on CPAN, but hopefully this will be rectified in the near future. Until then, you can download it from http://kuwata-lab.com/.

An Example View That Uses Tenjin

First, make sure your template_path is configurable for deployment purposes.

package App;
our %CONFIG = (
  template_path => './www'
);

And here is the actual view:

package App::Views;
use strict;
use warnings;
no  warnings 'once';
use Squatting ':views';
use Tenjin;

# make functions defined in this package available to templates
use base 'Tenjin::Context';
eval $Tenjin::Context::defun;
$Tenjin::CONTEXT_CLASS = 'App::Views';

our @V = (
  V(
    'html',
    tenjin => Tenjin::Engine->new({ 
      path => [ $App::CONFIG{template_path} ], postfix => '.html' 
    }),
    layout => sub {
      my ($self, $v, $content) = @_;
      my $tenjin = $self->{tenjin};
      $v->{content} = $content;
      $tenjin->render(":layout", $v);
    },
    _ => sub {
      my ($self, $v) = @_;
      my $tenjin = $self->{tenjin};
      $v->{self} = $self;
      $tenjin->render(":$self->{template}", $v);
    }
  ),
);
1;

That's all there is too it. Views for other file-based templating systems will follow a similar pattern where the special _ template is used to map method names to filenames.

Template Toolkit

TODO

HTML::Mason

TODO

HTML::Template

TODO

How to Internationalize and Localize Squatting Apps

Using Subdomains For Maximum Flexibility

I'm a fan of the way Wikipedia uses subdomains in its localization strategy.

Locale::Maketext

How to be an OpenID Consumer

TODO - go into much more detail and clean up the code.

helper function for making a Net::OpenID::Consumer object

sub csr {
  my ($self) = @_;
  return Net::OpenID::Consumer->new(
    ua    => LWPx::ParanoidAgent->new,
    cache => Cache::File->new(cache_root => '/tmp/openid-consumer-cache'),
    args  => $self->input,
    consumer_secret => '...',
    required_root   => 'http://work:4234/'
  );
}

Login controller; form is provided somewhere else; POST is the entry point; GET is where the sequence finishes.

C(
  Login => [ '/login' ],
  get => sub {
    my ($self) = @_;
    my $csr = csr($self);
    $self->headers->{'Content-Type'} = 'text/plain';
    if (my $setup_url = $csr->user_setup_url) {
      # redirect/link/popup user to $setup_url
      $self->redirect($setup_url);
      return;
    } elsif ($csr->user_cancel) {
      # restore web app state to prior to check_url
      return "user_cancel";
    } elsif (my $vident = $csr->verified_identity) {
       my $verified_url = $vident->url;
       return "verified_url $verified_url !";
    } else {
       return "Error validating identity: " . $csr->err;
    }
  },
  post => sub {
    my ($self) = @_;
    my $input = $self->input;
    my $csr = csr($self);
    my $claimed_identity = $csr->claimed_identity($input->{openid});
    my $check_url = $claimed_identity->check_url(
      return_to  => "http://work:4234/login",
      trust_root => "http://work:4234/",
    );
    $self->redirect($check_url);
  },
),

How to be an OpenID Provider

How to Compose Multiple Squatting Apps Into One App

After you init the app, you can start mounting other apps.

App->mount('OtherApp0' => '/prefix0');
App->mount('OtherApp1' => '/prefix1');
App->mount('OtherApp2' => '/prefix2');

If you need to relocate, do that after you finish mounting. The order is always init, mount, and relocate. Also, remember that an app can only be mounted once, and relocate should only be called once.

How to Embed a Squatting App Into Other Frameworks

In order to embed a Squatting app into an app written in another framework, we need to be able to do the following things.

get incoming CGI parameters
get incoming HTTP request headers
get incoming HTTP method
set outgoing HTTP status
set outgoing HTTP response headers
set outgoing content

If we can do all these things, Squatting can make itself at home. Here are some concrete examples to get you started.

Catalyst

To embed a Squatting app into a Catalyst app, you can add code like this to your Root controller.

use App 'On::Catalyst';
App->init;
App->relocate('/somewhere');
sub somewhere : Local { App->catalyze($_[1]) }

If you want the Squatting app to be completely in charge, you don't even have to relocate() -- just redefine the default() method like this:

use App 'On::Catalyst';
App->init;
sub default : Private { App->catalyze($_[1]) }

Raw mod_perl1

Raw mod_perl2

HTML::Mason

TODO: Implement a dhandler that embeds a Squatting app

CGI

To run a Squatting app in a CGI environment, a script like the following has to be written.

use App 'On::CGI';
my $q = CGI->new;
App->init;
App->relocate('/cgi-bin/app.cgi');
App->cgi($q);

The key to doing this right is to relocate the app correctly. The path that you relocate to should be the same as the REQUEST_PATH for the script. For example, if the URL you use to get to the script is http://localhost/cgi-bin/app.cgi, then you should relocate to /cgi-bin/app.cgi.

How to Replace a Squatting App's Layout

Now that you've embedded or composed some Squatting apps together, the next thing you'll want to do is make the whole system of sites look consistent. To do this, you'll usually get the App's first view object and replace its layout method with your own.

my $view = $App::Views::V[0];
$view->{layout} = sub {
  my ($self, $v, $content) = @_;
  # 
  # make the layout look however you want
  # using any templating system you want
  # ( or none at all )
  # and return a string
  #
};

DEPLOYMENT TECHNIQUES

Let Squatting+Continuity Own Port 80

This is the simplest thing you could possibly do, but it's also somewhat limiting.

Reverse Proxying to Squatting+Continuity w/ Perlbal

Reverse Proxying to Squatting+Continuity w/ nginx

Piggy-Backing on Top of Other Frameworks

If you've embedded a Squatting app into another application, the rules and conventions governing the other application's framework take precedence. Follow their deployment guidelines, and you should be fine.

SCALING TECHNIQUES

This section is for those who wish to scale Squatting apps that are using a Continuity foundation. If any part of your site is RESTless and stateful, and you've suddenly got a lot of traffic to your site, this section is for you.

Session Affinity with Multiple Instances

TODO

Linux and OpenSSI

TODO

DragonFlyBSD Single Image Cluster

This is currently science fiction.