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/ Mojolicious::Guides::Growing

NAME

Mojolicious::Guides::Growing - Growing

OVERVIEW

Starting a Mojolicious::Lite prototype from scratch and growing it into a well structured Mojolicious application.

CONCEPTS

Essentials every Mojolicious developer should know.

Model View Controller

MVC is a software architectural pattern for graphical user iterface programming originating in Smalltalk-80, that separates application logic, presentation and input.

         .------------.    .-------.    .------.
Input -> | Controller | -> | Model | -> | View | -> Output
         '------------'    '-------'    '------'

A slightly modified version of the pattern moving some application logic into the controller is the foundation of pretty much every web framework these days, including Mojolicious.

            .----------------.     .-------.
Request  -> |                | <-> | Model |
            |                |     '-------'
            |   Controller   |
            |                |     .-------.
Response <- |                | <-> | View  |
            '----------------'     '-------'

The controller receives a request from a user, passes incoming data to the model and retrieves data from it, which then gets turned into an actual response by the view. But note that this pattern is just a guideline that most of the time results in cleaner more maintainable code, not a rule that should be followed at all costs.

Representational State Transfer

REST is a software architectural style for distributed hypermedia systems such as the web. While it can be applied to many protocols it is most commonly used with HTTP these days. In REST terms, when you are opening a URL like http://mojolicio.us/foo with your browser, you are basically asking the web server for the HTML representation of the http://mojolicio.us/foo resource.

.--------.                                .--------.
|        | ->  http://mojolici.us/foo  -> |        |
| Client |                                | Server |
|        | <- <html>Mojo rocks!</html> <- |        |
'--------'                                '--------'

The fundamental idea here is that all resources are uniquely addressable with URLs and every resource can have different representations such as HTML, RSS or JSON. User interface concerns are separated from data storage concerns and all session state is kept client side.

.---------.                        .------------.
|         | ->    PUT /foo      -> |            |
|         | ->    Hello world!  -> |            |
|         |                        |            |
|         | <-    201 CREATED   <- |            |
|         |                        |            |
|         | ->    GET /foo      -> |            |
| Browser |                        | Web Server |
|         | <-    200 OK        <- |            |
|         | <-    Hello world!  <- |            |
|         |                        |            |
|         | ->    DELETE /foo   -> |            |
|         |                        |            |
|         | <-    200 OK        <- |            |
'---------'                        '------------'

While HTTP methods such as PUT, GET and DELETE are not directly part of REST they go very well with it and are commonly used to manipulate resources.

Sessions

HTTP was designed as a stateless protocol, web servers don't know anything about previous requests, which makes user friendly login systems very tricky. Sessions solve this problem by allowing web applications to keep stateful information across several HTTP requests.

GET /login?user=sri&pass=s3cret HTTP/1.1
Host: mojolicio.us

HTTP/1.1 200 OK
Set-Cookie: sessionid=987654321
Content-Length: 10
Hello sri!

GET /protected HTTP/1.1
Host: mojolicio.us
Cookie: $Version=1; sessionid=987654321

HTTP/1.1 200 OK
Set-Cookie: sessionid=987654321
Content-Length: 16
Hello again sri!

Traditionally all session data was stored on the server side and only session ids were exchanged between browser and web server in the form of cookies.

HTTP/1.1 200 OK
Set-Cookie: session=base64(hmac-md5(storable($session)))

In Mojolicious however we are taking this concept one step further by storing everything in HMAC-MD5 signed cookies, which is more compatible with the REST philosophy and reduces infrastructure requirements.

Test Driven Development

TDD is a software development process where the developer starts writing failing test cases that define the desired functionality and then moves on to producing code that passes these tests. There are many advantages such as always having good test coverage and code being designed for testability, which will in turn often prevent future changes from breaking old code. Most of Mojolicious was developed using TDD.

PROTOTYPE

One of the main differences between Mojolicious and other web frameworks is that it also includes Mojolicious::Lite, a micro web framework optimized for rapid prototyping.

Differences

You likely know the feeling, you've got a really cool idea and want to try it as quickly as possible, thats exactly why Mojolicious::Lite applications don't need more than a single file.

myapp.pl   # Templates and even static files can be inlined

Full Mojolicious applications on the other hand are much closer to a well organized CPAN distribution to maximize maintainability.

myapp                      # Application directory
|- script                  # Script directory
|  `- myapp                # Application script
|- lib                     # Library directory
|  |- MyApp.pm             # Application class
|  `- MyApp                # Application namespace
|     `- Example.pm        # Controller class
|- t                       # Test directory
|  `- basic.t              # Random test
|- log                     # Log directory
|  `- development.log      # Development mode log file
|- public                  # Static file directory (served automatically)
|  `- index.html           # Static HTML file
`- templates               # Template directory
   |- layouts              # Template directory for layouts
   |  `- default.html.ep   # Layout template
   `- example              # Template directory for "Example" controller
      `- welcome.html.ep   # Template for "welcome" action

Both application skeletons can be automatically generated.

% mojo generate lite_app
...

% mojo generate app
...

Foundation

We start our new application with a single executable Perl script.

% mkdir myapp
% cd myapp
% touch myapp.pl
% chmod 744 myapp.pl

This will be the foundation for our login manager example application.

#!/usr/bin/env perl
use Mojolicious::Lite;

get '/' => sub {
    my $self = shift;
    $self->render(text => 'Hello world!');
};

app->start;

The built in web server makes working on your application a lot of fun thanks to automatic reloading.

% ./myapp.pl daemon --reload
Server available at http://*:3000.

Just save your changes and they will be automatically in effect the next time you refresh your browser.

Model

In Mojolicious we consider web applications simple frontends for existing business logic, that means Mojolicious is by design entirely model layer agnostic and you just use whatever Perl modules you like most.

% mkdir lib
% touch lib/MyUsers.pm
% chmod 644 lib/MyUsers.pm

Our login manager will simply use a plain old Perl module abstracting away all logic related to matching user names and passwords.

package MyUsers;

use strict;
use warnings;

my $USERS = {
    sri    => 'secr3t',
    marcus => 'lulz',
    yko    => 'zeecaptain'
};

sub new { bless {}, shift }

sub check {
    my ($self, $user, $pass) = @_;

    # Success
    return 1 if $USERS->{$user} && $USERS->{$user} eq $pass;

    # Fail
    return;
}

1;

A simple helper function can be registered with the helper method of Mojolicious to make our model available to all actions and templates.

#!/usr/bin/env perl
use Mojolicious::Lite;

use lib 'lib';
use MyUsers;

# Model instance
my $users = MyUsers->new;

# Helper function returning our model instance
app->helper(users => sub { return $users });

# /?user=sri&pass=secr3t
any '/' => sub {
    my $self = shift;

    # Query parameters
    my $user = $self->param('user') || '';
    my $pass = $self->param('pass') || '';

    # Check password
    return $self->render(text => "Welcome $user!")
      if $self->users->check($user, $pass);

    # Failed
    $self->render(text => 'Wrong username or password!');
};

app->start;

The param method of our Mojolicious::Controller instance is used to access query parameters, POST parameters and route placeholders, all at once.

Testing

In Mojolicious we take test driven development very serious and try to promote it wherever we can.

% mkdir t
% touch t/login.t
% chmod 644 t/login.t

Test::Mojo is a scriptable HTTP user agent designed specifically for testing, with many fun state of the art features such as CSS3 selectors based on Mojo::DOM.

use Test::More tests => 16;
use Test::Mojo;

# Include application and help with home directory detection
use FindBin;
$ENV{MOJO_HOME} = "$FindBin::Bin/../";
require "$ENV{MOJO_HOME}/myapp.pl";

# Allow 302 redirect responses
my $t = Test::Mojo->new(max_redirects => 1);

# Test if the HTML login form exists
$t->get_ok('/')->status_is(200)
  ->element_exists('form input[name="user"]')
  ->element_exists('form input[name="pass"]')
  ->element_exists('form input[type="submit"]');

# Test login with valid credentials
$t->post_form_ok('/' => {user => 'sri', pass => 'secr3t'})
  ->status_is(200)->text_like('html body' => qr/Welcome sri/);

# Test accessing a protected page
$t->get_ok('/protected')->status_is(200)->text_like('a' => qr/Logout/);

# Test if HTML login form shows up again after logout
$t->get_ok('/logout')->status_is(200)
  ->element_exists('form input[name="user"]')
  ->element_exists('form input[name="pass"]')
  ->element_exists('form input[type="submit"]');

From now on you can always check your progress by running these unit tests against your application.

% ./myapp.pl test
...
% perl t/login.t
...

To make the tests less noisy and limit log output to just error messages you can also add a line like this.

$t->app->log->level('error');

Quick GET requests can be performed right from the command line.

% ./myapp.pl get /
Wrong username or password!

% ./myapp.pl get -v /?user=sri&pass=secr3t
HTTP/1.1 200 OK
Connection: Keep-Alive
Date: Sun, 18 Jul 2010 13:09:58 GMT
Server: Mojolicious (Perl)
Content-Length: 12
Content-Type: text/plain

Welcome sri!

State Keeping

Sessions in Mojolicious pretty much just work out of the box and there is no setup required, but we suggest using a more secure secret passphrase.

app->secret('Mojolicious rocks!');

This passphrase is used by the HMAC-MD5 algorithm to make signed cookies secure and can be changed at any time to invalidate all existing sessions.

$self->session(user => 'sri');
my $user = $self->session('user');

By default all sessions expire after one hour, and the whole session can be deleted by setting an expiration date in the past.

$self->session(expires => 1);

For data that should only be visible on the next request, like a confirmation message after a 302 redirect, you can use the flash.

$self->flash(message => 'Everything is fine!');
$self->redirect_to('goodbye');

Just remember that everything is stored in HMAC-MD5 signed cookies, so there is usually a 4096 byte limit, depending on the browser.

Final Prototype

A final myapp.pl prototype passing all of the unit tests above could look like this.

#!/usr/bin/env perl
use Mojolicious::Lite;

use lib 'lib';
use MyUsers;

# Make signed cookies secure
app->secret('Mojolicious rocks!');

my $users = MyUsers->new;
app->helper(users => sub { return $users });

# Main login action
any '/' => sub {
    my $self = shift;

    # Query or POST parameters
    my $user = $self->param('user') || '';
    my $pass = $self->param('pass') || '';

    # Check password and render "index.html.ep" if neccessary
    return $self->render unless $self->users->check($user, $pass);

    # Store user name in session
    $self->session(user => $user);

    # Store a friendly message for the next page in flash
    $self->flash(message => 'Thanks for logging in!');

    # Redirect to protected page with a 302 response
    $self->redirect_to('protected');
} => 'index';

# A protected page auto rendering "protected.html.ep"
get '/protected' => sub {
    my $self = shift;

    # Redirect to main page with a 302 response if user is not logged in
    return $self->redirect_to('index') unless $self->session('user');
} => 'protected';

# Logout action
get '/logout' => sub {
    my $self = shift;

    # Expire and in turn clear session automatically
    $self->session(expires => 1);

    # Redirect to main page with a 302 response
    $self->redirect_to('index');
} => 'logout';

app->start;
__DATA__

@@ layouts/default.html.ep
<!doctype html><html>
    <head><title>Login Manager</title></head>
    <body><%= content %></body>
</html>

@@ index.html.ep
% layout 'default';
<%= form_for index => begin %>
    <% if (param 'user') { %>
        <b>Wrong name or password, please try again.</b><br>
    <% } %>
    Name:<br>
    <%= text_field 'user' %><br>
    Password:<br>
    <%= password_field 'pass' %><br>
    <%= submit_button 'Login' %>
<% end %>

@@ protected.html.ep
% layout 'default';
<% if (my $message = flash 'message') { %>
    <b><%= $message %></b><br>
<% } %>
Welcome <%= session 'user' %>!<br>
<%= link_to Logout => 'logout' %>

More information about built in template helpers can be found in Mojolicious::Plugin::DefaultHelpers and Mojolicious::Plugin::TagHelpers.

WELL STRUCTURED APPLICATION

Due to the flexibility of Mojolicious there are many variations of the actual growing process, but this should give you a good overview of the possibilities.

Inflating Templates

All templates and static files inlined in the DATA section can be automatically turned into separate files in the templates and public directories.

% ./myapp.pl inflate
...

Those directories always get priority, so inflating can also be a great way to allow your users to customize their applications.

Simplified Application Class

This is the heart of every full Mojolicious application and always gets instantiated during server startup.

% touch lib/MyApp.pm
% chmod 644 lib/MyApp.pm

We will start by extracting all actions from myapp.pl and turn them into simplified hybrid routes in the Mojolicious::Routes router, none of the actual action code needs to be changed.

package MyApp;

use strict;
use warnings;

use base 'Mojolicious';

use MyUsers;

sub startup {
    my $self = shift;

    $self->secret('Mojolicious rocks!');
    my $users = MyUsers->new;
    $self->helper(users => sub { return $users });

    # Router
    my $r = $self->routes;

    $r->any('/' => sub {
        my $self = shift;

        my $user = $self->param('user') || '';
        my $pass = $self->param('pass') || '';

        return $self->render unless $self->users->check($user, $pass);

        $self->session(user => $user);
        $self->flash(message => 'Thanks for logging in!');
        $self->redirect_to('protected');
    } => 'index');

    $r->get('/protected' => sub {
        my $self = shift;
        return $self->redirect_to('index') unless $self->session('user');
    } => 'protected');

    $r->get('/logout' => sub {
        my $self = shift;
        $self->session(expires => 1);
        $self->redirect_to('index');
    } => 'logout');
}

1;

The startup method of Mojolicious gets called right after instantiation and is the place where the whole application gets set up.

Simplified Application Script

myapp.pl itself can now be turned into a simplified application script to allow running unit tests again.

#!/usr/bin/env perl

use strict;
use warnings;

# Load application class
use lib 'lib';
use MyApp;

# Start application
MyApp->start;

Controller Class

Hybrid routes are a nice intermediate step, but to maximize maintainability it makes sense to split our action code from its routing information.

% mkdir lib/MyApp
% touch lib/MyApp/Login.pm
% chmod 644 lib/MyApp/Login.pm

Once again the actual action code does not change at all.

package MyApp::Login;

use strict;
use warnings;

use base 'Mojolicious::Controller';

sub index {
    my $self = shift;

    my $user = $self->param('user') || '';
    my $pass = $self->param('pass') || '';

    return $self->render unless $self->users->check($user, $pass);

    $self->session(user => $user);
    $self->flash(message => 'Thanks for logging in!');
    $self->redirect_to('protected');
}

sub protected {
    my $self = shift;
    return $self->redirect_to('index') unless $self->session('user');
}

sub logout {
    my $self = shift;
    $self->session(expires => 1);
    $self->redirect_to('index');
}

1;

All Mojolicious::Controller controllers are plain old Perl classes and get instantiated on demand.

Application Class

The application class lib/MyApp.pm can now be reduced to model and routing information.

package MyApp;

use strict;
use warnings;

use base 'Mojolicious';

use MyUsers;

sub startup {
    my $self = shift;

    $self->secret('Mojolicious rocks!');
    my $users = MyUsers->new;
    $self->helper(users => sub { return $users });

    my $r = $self->routes;
    $r->any('/')->to('login#index')->name('index');
    $r->get('/protected')->to('login#protected')->name('protected');
    $r->get('/logout')->to('login#logout')->name('logout');
}

1;

Mojolicious::Routes allows many route variations, choose whatever you like most.

Templates

Templates are usually bound to controllers, so they need to be moved into the appropriate directories.

% mkdir templates/login
% mv templates/index.html.ep templates/login/index.html.ep
% mv templates/protected.html.ep templates/login/protected.html.ep

Script

Finally myapp.pl can be replaced with a proper Mojolicious script.

% rm myapp.pl
% mkdir script
% touch script/myapp
% chmod 744 script/myapp

The library detection code was specifically designed for tricky production environments.

#!/usr/bin/env perl

use strict;
use warnings;

use File::Basename 'dirname';
use File::Spec;

use lib join '/', File::Spec->splitdir(dirname(__FILE__)), 'lib';
use lib join '/', File::Spec->splitdir(dirname(__FILE__)), '..', 'lib';

# Check if Mojo is installed
eval 'use Mojolicious::Commands';
die <<EOF if $@;
It looks like you don't have the Mojolicious Framework installed.
Please visit http://mojolicio.us for detailed installation instructions.

EOF

# Application
$ENV{MOJO_APP} ||= 'MyApp';

# Start commands
Mojolicious::Commands->start;

Simplified Tests

Normal Mojolicious applications are a little easier to test and don't need help with home directory detection, so t/login.t can be simplified.

use Test::More tests => 16;
use Test::Mojo;

# Load application class
my $t = Test::Mojo->new(app => 'MyApp', max_redirects => 1);

$t->get_ok('/')->status_is(200)
  ->element_exists('form input[name="user"]')
  ->element_exists('form input[name="pass"]')
  ->element_exists('form input[type="submit"]');

$t->post_form_ok('/' => {user => 'sri', pass => 'secr3t'})
  ->status_is(200)->text_like('html body' => qr/Welcome sri/);

$t->get_ok('/protected')->status_is(200)->text_like('a' => qr/Logout/);

$t->get_ok('/logout')->status_is(200)
  ->element_exists('form input[name="user"]')
  ->element_exists('form input[name="pass"]')
  ->element_exists('form input[type="submit"]');

Test driven development takes a little getting used to, but is very well worth it!