Mojolicious::Guides::Growing(3)

NAME
Mojolicious::Guides::Growing - Growing

OVERVIEW
This document explains the process of 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 interface 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://mojolicio.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: 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.

  Set-Cookie: session=hmac-sha1(base64(json($session)))

In Mojolicious however we are taking this concept one step further by storing everything "JSON" serialized and "Base64" encoded in "HMAC-SHA1" 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, that's 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 myapp.pl
  $ mojo generate app MyApp

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

  $ morbo myapp.pl
  Server available at http://127.0.0.1:3000.

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 usernames 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 undef;
  }

  1;

A simple helper can be registered with the function "helper" in Mojolicious::Lite to make our "model" available to all actions and templates.

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

  use lib 'lib';
  use MyUsers;

  # Helper to lazy initialize and store our model object
  helper users => sub { state $users = MyUsers->new };

  # /?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 method "param" in Mojolicious::Controller is used to access query parameters, POST parameters, file uploads 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 CSS selectors based on Mojo::DOM.

  use Test::More;
  use Test::Mojo;

  # Include application
  use FindBin;
  require "$FindBin::Bin/../myapp.pl";

  # Allow 302 redirect responses
  my $t = Test::Mojo->new;
  $t->ua->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_ok('/' => form => {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"]');

  done_testing();

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

  $ ./myapp.pl test
  $ ./myapp.pl test t/login.t
  $ ./myapp.pl test -v t/login.t

Or perform quick requests right from the command line.

  $ ./myapp.pl get /
  Wrong username or password.

  $ ./myapp.pl get -v '/?user=sri&pass=secr3t'
  GET /?user=sri&pass=secr3t HTTP/1.1
  User-Agent: Mojolicious (Perl)
  Connection: keep-alive
  Accept-Encoding: gzip
  Content-Length: 0
  Host: localhost:59472

  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 once you start using the method "session" in Mojolicious::Controller, there is no setup required, but we suggest setting a more secure passphrase with "secrets" in Mojolicious.

  app->secrets(['Mojolicious rocks']);

This passphrase is used by the "HMAC-SHA1" 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, for more control you can use the "expiration" session value to set an expiration date in seconds from now.

  $self->session(expiration => 3600);

And the whole session can be deleted by using the "expires" session value to set an absolute 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, accessible through the method "flash" in Mojolicious::Controller.

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

Just remember that all session data gets serialized with Mojo::JSON and stored in "HMAC-SHA1" signed cookies, which usually have a 4096 byte limit, depending on 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->secrets(['Mojolicious rocks']);

  helper users => sub { state $users = MyUsers->new };

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

    # Store username 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';

  # Make sure user is logged in for actions in this group
  group {
    under sub {
      my $self = shift;

      # Redirect to main page with a 302 response if user is not logged in
      return 1 if $self->session('user');
      $self->redirect_to('index');
      return undef;
    };

    # A protected page auto rendering "protected.html.ep"
    get '/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');
  };

  app->start;
  __DATA__

  @@ 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 $msg = flash 'message') {
    <b><%= $msg %></b><br>
  % }
  Welcome <%= session 'user' %>.<br>
  %= link_to Logout => 'logout'

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

A list of all built-in 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 Mojo::Base 'Mojolicious';

  use MyUsers;

  sub startup {
    my $self = shift;

    $self->secrets(['Mojolicious rocks']);
    $self->helper(users => sub { state $users = MyUsers->new });

    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');

    my $logged_in = $r->under(sub {
      my $self = shift;
      return 1 if $self->session('user');
      $self->redirect_to('index');
      return undef;
    });
    $logged_in->get('/protected');

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

  1;

The "startup" method gets called right after instantiation and is the place where the whole application gets set up. Since full Mojolicious applications can use nested routes they have no need for "group" blocks.

  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;

  use lib 'lib';
  use Mojolicious::Commands;

  # Start command line interface for application
  Mojolicious::Commands->start_app('MyApp');

  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 Mojo::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 logged_in {
    my $self = shift;
    return 1 if $self->session('user');
    $self->redirect_to('index');
    return undef;
  }

  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 Mojo::Base 'Mojolicious';

  use MyUsers;

  sub startup {
    my $self = shift;

    $self->secrets(['Mojolicious rocks']);
    $self->helper(users => sub { state $users = MyUsers->new });

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

Only a few small details change, since installable scripts can't use lib without breaking updated dual-life modules.

  #!/usr/bin/env perl

  use strict;
  use warnings;

  use FindBin;
  BEGIN { unshift @INC, "$FindBin::Bin/../lib" }

  # Start command line interface for application
  require Mojolicious::Commands;
  Mojolicious::Commands->start_app('MyApp');

  Simplified tests
Normal Mojolicious applications are a little easier to test, so "t/login.t" can be simplified.

  use Test::More;
  use Test::Mojo;

  # Load application class
  my $t = Test::Mojo->new('MyApp');
  $t->ua->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_ok('/' => form => {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"]');

  done_testing();

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

MORE
You can continue with Mojolicious::Guides now or take a look at the Mojolicious wiki <http://github.com/kraih/mojo/wiki>, which contains a lot more documentation and examples by many different authors.

SUPPORT
If you have any questions the documentation might not yet answer, don't hesitate to ask on the mailing-list <http://groups.google.com/group/mojolicious> or the official IRC channel "#mojo" on "irc.perl.org".