Mojolicious::Guides::Rendering - Rendering content

OVERVIEW
CONCEPTS
1. Renderer
2. Embedded Perl
BASICS
ADVANCED
MORE
SUPPORT

OVERVIEW

This document explains content generation with the Mojolicious renderer.

CONCEPTS

Essentials every Mojolicious developer should know.

Renderer

The renderer is a tiny black box turning stash data into actual responses utilizing multiple template systems and data encoding modules.

{text => 'Hello.'}                 -> 200 OK, text/html, 'Hello.'
{json => {x => 3}}                 -> 200 OK, application/json, '{"x":3}'
{text => 'Oops.', status => '410'} -> 410 Gone, text/html, 'Oops.'

Templates can be automatically detected if enough information is provided by the developer or routes. Template names are expected to follow the template.format.handler scheme, with template defaulting to controller/action or the route name, format defaulting to html and handler to ep.

{controller => 'users', action => 'list'} -> 'users/list.html.ep'
{template => 'foo', format => 'txt'}      -> 'foo.txt.ep'
{template => 'foo', handler => 'epl'}     -> 'foo.html.epl'

The controller value gets converted from CamelCase to snake_case using "decamelize" in Mojo::Util and - characters replaced with /.

{controller => 'My::Users', action => 'add'} -> 'my/users/add.html.ep'
{controller => 'my-users', action => 'show'} -> 'my/users/show.html.ep'

All templates should be in the templates directories of the application, which can be customized with "paths" in Mojolicious::Renderer, or one of the the DATA sections from "classes" in Mojolicious::Renderer.

__DATA__

@@ time.html.ep
% use Time::Piece;
% my $now = localtime;
<!DOCTYPE html>
<html>
  <head><title>Time</title></head>
  <body>The time is <%= $now->hms %>.</body>
</html>

@@ hello.txt.ep
...

The renderer can be easily extended to support additional template systems with plugins, but more about that later.

Embedded Perl

Mojolicious includes a minimalistic but very powerful template system out of the box called Embedded Perl or ep for short. It is based on Mojo::Template and allows the embedding of Perl code right into actual content using a small set of special tags and line start characters. For all templates strict, warnings, utf8 and Perl 5.16 features are automatically enabled.

<% Perl code %>
<%= Perl expression, replaced with XML escaped result %>
<%== Perl expression, replaced with result %>
<%# Comment, useful for debugging %>
<%% Replaced with "<%", useful for generating templates %>
% Perl code line, treated as "<% line =%>" (explained later)
%= Perl expression line, treated as "<%= line %>"
%== Perl expression line, treated as "<%== line %>"
%# Comment line, useful for debugging
%% Replaced with "%", useful for generating templates

Tags and lines work pretty much the same, but depending on context one will usually look a bit better. Semicolons get automatically appended to all expressions.

<% my $i = 10; %>
<ul>
  <% for my $j (1 .. $i) { %>
    <li>
      <%= $j %>
    </li>
  <% } %>
</ul>

% my $i = 10;
<ul>
  % for my $j (1 .. $i) {
    <li>
      %= $j
    </li>
  % }
</ul>

Aside from differences in whitespace handling, both examples generate similar Perl code, a naive translation could look like this.

my $output = '';
my $i = 10;
$output .= '<ul>';
for my $j (1 .. $i) {
  $output .= '<li>';
  $output .= xml_escape scalar + $j;
  $output .= '</li>';
}
$output .= '</ul>';
return $output;

An additional equal sign can be used to disable escaping of the characters <, >, &, ' and " in results from Perl expressions, which is the default to prevent XSS attacks against your application.

<%= 'I ♥ Mojolicious!' %>
<%== '<p>I ♥ Mojolicious!</p>' %>

Only Mojo::ByteStream objects are excluded from automatic escaping.

<%= b('<p>I ♥ Mojolicious!</p>') %>

Whitespace characters around tags can be trimmed by adding an additional equal sign to the end of a tag.

<% for (1 .. 3) { %>
  <%= 'Trim all whitespace characters around this expression' =%>
<% } %>

Newline characters can be escaped with a backslash.

This is <%= 1 + 1 %> a\
single line

And a backslash in front of a newline character can be escaped with another backslash.

This will <%= 1 + 1 %> result\\
in multiple\\
lines

A newline character gets appended automatically to every template, unless the last character is a backslash. And empty lines at the end of a template are ignored.

There is <%= 1 + 1 %> no newline at the end here\

At the beginning of the template, stash values that don't have invalid characters in their name get automatically initialized as normal variables, and the controller object as both $self and $c.

$c->stash(name => 'tester');

Hello <%= $name %> from <%= $c->tx->remote_address %>.

A prefix like myapp.* is commonly used for stash values that you don't want to expose in templates.

$c->stash('myapp.name' => 'tester');

There are also many helper functions available, but more about that later.

<%= dumper {foo => 'bar'} %>

BASICS

Most commonly used features every Mojolicious developer should know about.

Automatic rendering

The renderer can be manually started by calling the method "render" in Mojolicious::Controller, but that's usually not necessary, because it will get automatically called if nothing has been rendered after the router finished its work. This also means you can have routes pointing only to templates without actual actions.

$c->render;

There is one big difference though, by calling it manually you can make sure that templates use the current controller object, and not the default controller specified with the attribute "controller_class" in Mojolicious.

$c->render_later;

You can also disable automatic rendering with the method "render_later" in Mojolicious::Controller, which can be very useful to delay rendering when a non-blocking operation has to be performed first.

Rendering templates

The renderer will always try to detect the right template, but you can also use the template stash value to render a specific one. Everything before the last slash will be interpreted as the subdirectory path in which to find the template.

# foo/bar/baz.*.*
$c->render(template => 'foo/bar/baz');

Choosing a specific format and handler is just as easy.

# foo/bar/baz.txt.epl
$c->render(template => 'foo/bar/baz', format => 'txt', handler => 'epl');

Because rendering a specific template is the most common task it also has a shortcut.

$c->render('foo/bar/baz');

If you're not sure in advance if a template actually exists, you can also use the method "render_maybe" in Mojolicious::Controller to try multiple alternatives.

$c->render_maybe('localized/baz') or $c->render('foo/bar/baz');

Rendering to strings

Sometimes you might want to use the rendered result directly instead of generating a response, for example, to send emails, this can be done with "render_to_string" in Mojolicious::Controller.

my $html = $c->render_to_string('mail');

No encoding will be performed, making it easy to reuse the result in other templates or to generate binary data.

my $pdf = $c->render_to_string('invoice', format => 'pdf');
$c->render(data => $pdf, format => 'pdf');

All arguments passed will get localized automatically and are only available during this render operation.

Template variants

To make your application look great on many different devices you can also use the variant stash value to choose between different variants of your templates.

# foo/bar/baz.html+phone.ep
# foo/bar/baz.html.ep
$c->render('foo/bar/baz', variant => 'phone');

This can be done very liberally since it only applies when a template with the correct name actually exists and falls back to the generic one otherwise.

Rendering inline templates

Some renderers such as ep allow templates to be passed inline.

$c->render(inline => 'The result is <%= 1 + 1 %>.');

Since auto-detection depends on a path you might have to supply a handler too.

$c->render(inline => "<%= shift->param('foo') %>", handler => 'epl');

Rendering text

Characters can be rendered to bytes with the text stash value, the given content will be automatically encoded with "encoding" in Mojolicious::Renderer.

$c->render(text => 'I ♥ Mojolicious!');

Rendering data

Bytes can be rendered with the data stash value, no encoding will be performed.

$c->render(data => $bytes);

Rendering JSON

The json stash value allows you to pass Perl data structures to the renderer which get directly encoded to JSON with Mojo::JSON.

$c->render(json => {foo => [1, 'test', 3]});

Status code

Response status codes can be changed with the status stash value.

$c->render(text => 'Oops.', status => 500);

Content type

The Content-Type header of the response is actually based on the MIME type mapping of the format stash value.

# Content-Type: text/plain
$c->render(text => 'Hello.', format => 'txt');

# Content-Type: image/png
$c->render(data => $bytes, format => 'png');

These mappings can be easily extended or changed with "types" in Mojolicious.

# Add new MIME type
$app->types->type(md => 'text/markdown');

Stash data

Any of the native Perl data types can be passed to templates as references through the "stash" in Mojolicious::Controller.

$c->stash(description => 'web framework');
$c->stash(frameworks  => ['Catalyst', 'Mojolicious', 'mojo.js']);
$c->stash(spinoffs    => {minion => 'job queue'});

%= $description
%= $frameworks->[1]
%= $spinoffs->{minion}

Since everything is just Perl normal control structures just work.

% for my $framework (@$frameworks) {
  <%= $framework %> is a <%= $description %>.
% }

% if (my $description = $spinoffs->{minion}) {
  Minion is a <%= $description %>.
% }

For templates that might get rendered in different ways and where you're not sure if a stash value will actually be set, you can just use the helper "stash" in Mojolicious::Plugin::DefaultHelpers.

% if (my $spinoffs = stash 'spinoffs') {
  Minion is a <%= $spinoffs->{minion} %>.
% }

Helpers

Helpers are little functions you can use in templates as well as application and controller code.

# Template
%= dumper [1, 2, 3]

# Application
my $serialized = $app->dumper([1, 2, 3]);

# Controller
my $serialized = $c->dumper([1, 2, 3]);

We differentiate between default helpers, which are more general purpose like "dumper" in Mojolicious::Plugin::DefaultHelpers, and tag helpers like "link_to" in Mojolicious::Plugin::TagHelpers, which are template specific and mostly used to generate HTML tags.

%= link_to Mojolicious => 'https://mojolicious.org'

In controllers you can also use the method "helpers" in Mojolicious::Controller to fully qualify helper calls and ensure that they don't conflict with existing methods you may already have.

my $serialized = $c->helpers->dumper([1, 2, 3]);

A list of all built-in helpers can be found in Mojolicious::Plugin::DefaultHelpers and Mojolicious::Plugin::TagHelpers.

Static files

Static files are automatically served from the public directories of the application, which can be customized with "paths" in Mojolicious::Static, or one of the DATA sections from "classes" in Mojolicious::Static. And if that's not enough you can also serve them manually with "reply->static" in Mojolicious::Plugin::DefaultHelpers and "reply->file" in Mojolicious::Plugin::DefaultHelpers.

use Mojolicious::Lite -signatures;

get '/' => sub ($c) {
  $c->reply->static('index.html');
};

get '/some_download' => sub ($c) {
  $c->res->headers->content_disposition('attachment; filename=bar.png;');
  $c->reply->static('foo/bar.png');
};

get '/leak' => sub ($c) {
  $c->reply->file('/etc/passwd');
};

app->start;

By default static files do not use a prefix and are simply served with a higher precedence than routes. This can be changed with "prefix" in Mojolicious::Static.

# Serve static files only with a "/static" prefix
$app->static->prefix('/static');

To allow for the prefix to be configured dynamically, you can use "url_for_file" in Mojolicious::Controller to generate URLs with it. Many tag helpers will also use the prefix automatically when it makes sense.

Static assets

While Mojolicious does not have any special support for frontend frameworks like Vue.js and React, the public/assets directory is reserved for static assets created by bundlers like Webpack and Rollup.js ahead of time. Asset files can be of any type, they just have to follow the [name].[checksum].[extensions] naming scheme, like myapp.ab1234cd5678ef.js. You can then use "url_for_asset" in Mojolicious::Controller or "asset_tag" in Mojolicious::Plugin::TagHelpers to generate URLs without having to know the checksum.

# "/assets/myapp.ab1234cd5678ef.js"
$c->url_for_asset('/myapp.js');

# "<script src="/assets/myapp.ab1234cd5678ef.js"></script>"
$c->asset_tag('/myapp.js');

If your application runs in development mode, all assets will be served with a Cache-Control: no-cache header, to speed up development by preventing browser caching. Additionally all assets following the [name].development.[extensions] naming scheme, like myapp.development.js, have a higher precedence than assets with checksums. That way you can just overwrite your assets during development, instead of having to manually delete them each time they are rebuilt with a different checksum.

# "/assets/foo/bar.development.js"
$c->url_for_asset('/foo/bar.js');

Webpack configuration example (webpack.config.js):

import Path from '@mojojs/path';

const isDev = process.env.MOJO_MODE === 'development';

export default {
  output: {
    filename: isDev ? '[name].development.js' : '[name].[chunkhash].js',
    path: Path.currentFile().sibling('public', 'assets').toString(),
    publicPath: ''
  },

  // Add your own rules and entry point here
};

Rollup configuration example (rollup.config.js):

import Path from '@mojojs/path';

const isDev = process.env.MOJO_MODE === 'development';

export default {
  output: {
    entryFileNames: isDev ? '[name].development.[ext]' : '[name].[hash].[ext]',
    dir: Path.currentFile().sibling('public', 'assets').toString(),
    format: 'iife'
  },

  // Add your own rules and entry point here
};

Everything else is up to your bundler of choice, so you need to consult its documentation for further information. And where you keep your asset sources, such as .vue and .jsx files, is not important, as long as your bundler can find them. Using a directory named assets or frontend in your application root directory is a good best practice though.

Content negotiation

For resources with different representations and that require truly RESTful content negotiation you can also use "respond_to" in Mojolicious::Plugin::DefaultHelpers instead of "render" in Mojolicious::Controller.

# /hello (Accept: application/json) -> "json"
# /hello (Accept: application/xml)  -> "xml"
# /hello.json                       -> "json"
# /hello.xml                        -> "xml"
# /hello?_format=json               -> "json"
# /hello?_format=xml                -> "xml"
$c->respond_to(
  json => {json => {hello => 'world'}},
  xml  => {text => '<hello>world</hello>'}
);

The best possible representation will be automatically selected from the _format GET/POST parameter, format stash value or Accept request header and stored in the format stash value. To change MIME type mappings for the Accept request header or the Content-Type response header you can use "types" in Mojolicious.

$c->respond_to(
  json => {json => {hello => 'world'}},
  html => sub {
    $c->content_for(head => '<meta name="author" content="sri">');
    $c->render(template => 'hello', message => 'world')
  }
);

Callbacks can be used for representations that are too complex to fit into a single render call.

# /hello (Accept: application/json) -> "json"
# /hello (Accept: text/html)        -> "html"
# /hello (Accept: image/png)        -> "any"
# /hello.json                       -> "json"
# /hello.html                       -> "html"
# /hello.png                        -> "any"
# /hello?_format=json                -> "json"
# /hello?_format=html                -> "html"
# /hello?_format=png                 -> "any"
$c->respond_to(
  json => {json => {hello => 'world'}},
  html => {template => 'hello', message => 'world'},
  any  => {text => '', status => 204}
);

And if no viable representation could be found, the any fallback will be used or an empty 204 response rendered automatically.

# /hello                      -> "html"
# /hello (Accept: text/html)  -> "html"
# /hello (Accept: text/xml)   -> "xml"
# /hello (Accept: text/plain) -> undef
# /hello.html                 -> "html"
# /hello.xml                  -> "xml"
# /hello.txt                  -> undef
# /hello?_format=html          -> "html"
# /hello?_format=xml           -> "xml"
# /hello?_format=txt           -> undef
if (my $format = $c->accepts('html', 'xml')) {
  ...
}

For even more advanced negotiation logic you can also use the helper "accepts" in Mojolicious::Plugin::DefaultHelpers.

Rendering `exception` and `not_found` pages

By now you've probably already encountered the built-in 404 (Not Found) and 500 (Server Error) pages, that get rendered automatically when you make a mistake. Those are fallbacks for when your own exception handling fails, which can be especially helpful during development. You can also render them manually with the helpers "reply->exception" in Mojolicious::Plugin::DefaultHelpers and "reply->not_found" in Mojolicious::Plugin::DefaultHelpers.

use Mojolicious::Lite -signatures;
use Scalar::Util qw(looks_like_number);

get '/divide/:dividend/by/:divisor' => sub ($c) {

  my $dividend = $c->param('dividend');
  my $divisor  = $c->param('divisor');

  # 404
  return $c->reply->not_found unless looks_like_number $dividend && looks_like_number $divisor;

  # 500
  return $c->reply->exception('Division by zero!') if $divisor == 0;

  # 200
  $c->render(text => $dividend / $divisor);
};

app->start;

To change the HTTP status code of the exception, you can use "rendered" in Mojolicious::Controller.

return $c->reply->exception('Division by zero!')->rendered(400) if $divisor == 0;

You can also change the templates of those pages, since you most likely want to show your users something more closely related to your application in production. The renderer will always try to find exception.$mode.$format.* or not_found.$mode.$format.* before falling back to the built-in default templates.

use Mojolicious::Lite;

get '/dies' => sub { die 'Intentional error' };

app->start;
__DATA__

@@ exception.production.html.ep
<!DOCTYPE html>
<html>
  <head><title>Server error</title></head>
  <body>
    <h1>Exception</h1>
    <p><%= $exception->message %></p>
    <h1>Stash</h1>
    <pre><%= dumper $snapshot %></pre>
  </body>
</html>

The default exception format is html, but that can be changed at application and controller level. By default there are handlers for html, txt and json available. There are also various exception helpers in Mojolicious::Plugin::DefaultHelpers for you to overload to change the default behavior.

use Mojolicious::Lite -signatures;

app->exception_format('json');

get '/json' => sub ($c) {
  die 'Just a test';
};

get '/txt' => sub ($c) {
  $c->exception_format('txt');
  die 'Just a test';
};

app->start;

The hook "before_render" in Mojolicious makes even more advanced customizations possible by allowing you to intercept and modify the arguments passed to the renderer.

use Mojolicious::Lite -signatures;

hook before_render => sub ($c, $args) {

  # Make sure we are rendering the exception template
  return unless my $template = $args->{template};
  return unless $template eq 'exception';

  # Switch to JSON rendering if content negotiation allows it
  return unless $c->accepts('json');
  $args->{json} = {exception => $c->stash('exception')};
};

get '/' => sub { die "This sho...ALL GLORY TO THE HYPNOTOAD!\n" };

app->start;

Layouts

Most of the time when using ep templates you will want to wrap your generated content in an HTML skeleton, thanks to layouts that's absolutely trivial.

use Mojolicious::Lite;

get '/' => {template => 'foo/bar'};

app->start;
__DATA__

@@ foo/bar.html.ep
% layout 'mylayout';
Hello World!

@@ layouts/mylayout.html.ep
<!DOCTYPE html>
<html>
  <head><title>MyApp</title></head>
  <body><%= content %></body>
</html>

You just select the right layout template with the helper "layout" in Mojolicious::Plugin::DefaultHelpers and place the result of the current template with the helper "content" in Mojolicious::Plugin::DefaultHelpers. You can also pass along normal stash values to the layout helper.

use Mojolicious::Lite;

get '/' => {template => 'foo/bar'};

app->start;
__DATA__

@@ foo/bar.html.ep
% layout 'mylayout', title => 'Hi there';
Hello World!

@@ layouts/mylayout.html.ep
<!DOCTYPE html>
<html>
  <head><title><%= $title %></title></head>
  <body><%= content %></body>
</html>

Instead of the layout helper you could also just use the layout stash value, or call "render" in Mojolicious::Controller with the layout argument.

$c->render(template => 'mytemplate', layout => 'mylayout');

To set a layout stash value application-wide you can use "defaults" in Mojolicious.

$app->defaults(layout => 'mylayout');

Layouts can also be used with "render_to_string" in Mojolicious::Controller, but the layout value needs to be passed as a render argument (not a stash value).

my $html = $c->render_to_string('reminder', layout => 'mail');

Partial templates

You can break up bigger templates into smaller, more manageable chunks. These partial templates can also be shared with other templates. Just use the helper "include" in Mojolicious::Plugin::DefaultHelpers to include one template into another.

use Mojolicious::Lite;

get '/' => {template => 'foo/bar'};

app->start;
__DATA__

@@ foo/bar.html.ep
<!DOCTYPE html>
<html>
  %= include '_header', title => 'Howdy'
  <body>Bar</body>
</html>

@@ _header.html.ep
<head><title><%= $title %></title></head>

You can name partial templates however you like, but a leading underscore is a commonly used naming convention.

Reusable template blocks

It's never fun to repeat yourself, that's why you can build reusable template blocks in ep that work very similar to normal Perl functions, with the begin and end keywords. Just be aware that both keywords are part of the surrounding tag and not actual Perl code, so there can only be whitespace after begin and before end.

use Mojolicious::Lite;

get '/' => 'welcome';

app->start;
__DATA__

@@ welcome.html.ep
<% my $block = begin %>
  % my $name = shift;
  Hello <%= $name %>.
<% end %>
<%= $block->('Wolfgang') %>
<%= $block->('Baerbel') %>

A naive translation of the template to Perl code could look like this.

my $output = '';
my $block  = sub ($name) {
  my $output = '';
  $output .= 'Hello ';
  $output .= xml_escape scalar + $name;
  $output .= '.';
  return Mojo::ByteStream->new($output);
};
$output .= xml_escape scalar + $block->('Wolfgang');
$output .= xml_escape scalar + $block->('Baerbel');
return $output;

While template blocks cannot be shared between templates, they are most commonly used to pass parts of a template to helpers.

Adding helpers

You should always try to keep your actions small and reuse as much code as possible. Helpers make this very easy, they get passed the current controller object as first argument, and you can use them to do pretty much anything an action could do.

use Mojolicious::Lite -signatures;

helper debug => sub ($c, $str) {
  $c->app->log->debug($str);
};

get '/' => sub ($c) {
  $c->debug('Hello from an action!');
} => 'index';

app->start;
__DATA__

@@ index.html.ep
% debug 'Hello from a template!';

Helpers can also accept template blocks as last argument, this for example, allows very pleasant to use tag helpers and filters. Wrapping the helper result into a Mojo::ByteStream object can prevent accidental double escaping.

use Mojolicious::Lite -signatures;
use Mojo::ByteStream;

helper trim_newline => sub ($c, $block) {
  my $result = $block->();
  $result =~ s/\n//g;
  return Mojo::ByteStream->new($result);
};

get '/' => 'index';

app->start;
__DATA__

@@ index.html.ep
%= trim_newline begin
  Some text.
  %= 1 + 1
  More text.
% end

Similar to stash values, you can use a prefix like myapp.* to keep helpers from getting exposed in templates as functions, and to organize them into namespaces as your application grows. Every prefix automatically becomes a helper that returns a proxy object containing the current controller object and on which you can call the nested helpers.

use Mojolicious::Lite -signatures;

helper 'cache_control.no_caching'   => sub ($c) { $c->res->headers->cache_control('private, max-age=0, no-cache') };
helper 'cache_control.five_minutes' => sub ($c) { $c->res->headers->cache_control('public, max-age=300') };

get '/news' => sub ($c) {
  $c->cache_control->no_caching;
  $c->render(text => 'Always up to date.');
};

get '/some_older_story' => sub ($c) {
  $c->cache_control->five_minutes;
  $c->render(text => 'This one can be cached for a bit.');
};

app->start;

While helpers can also be redefined, this should only be done very carefully to avoid conflicts.

Content blocks

The helper "content_for" in Mojolicious::Plugin::DefaultHelpers allows you to pass whole blocks of content from one template to another. This can be very useful when your layout has distinct sections, such as sidebars, where content should be inserted by the template.

use Mojolicious::Lite;

get '/' => 'foo';

app->start;
__DATA__

@@ foo.html.ep
% layout 'mylayout';
% content_for header => begin
  <meta http-equiv="Content-Type" content="text/html">
% end
<div>Hello World!</div>
% content_for header => begin
  <meta http-equiv="Pragma" content="no-cache">
% end

@@ layouts/mylayout.html.ep
<!DOCTYPE html>
<html>
  <head><%= content 'header' %></head>
  <body><%= content %></body>
</html>

Forms

To build HTML forms more efficiently you can use tag helpers like "form_for" in Mojolicious::Plugin::TagHelpers, which can automatically select a request method for you if a route name is provided. And since most browsers only allow forms to be submitted with GET and POST, but not request methods like PUT or DELETE, they are spoofed with an _method query parameter.

use Mojolicious::Lite -signatures;

get '/' => 'form';

# PUT  /nothing
# POST /nothing?_method=PUT
put '/nothing' => sub ($c) {

  # Prevent double form submission with redirect
  my $value = $c->param('whatever');
  $c->flash(confirmation => "We did nothing with your value ($value).");
  $c->redirect_to('form');
};

app->start;
__DATA__

@@ form.html.ep
<!DOCTYPE html>
<html>
  <body>
    % if (my $confirmation = flash 'confirmation') {
      <p><%= $confirmation %></p>
    % }
    %= form_for nothing => begin
      %= text_field whatever => 'I ♥ Mojolicious!'
      %= submit_button
    % end
  </body>
</html>

The helpers "flash" in Mojolicious::Plugin::DefaultHelpers and "redirect_to" in Mojolicious::Plugin::DefaultHelpers are often used together to prevent double form submission, allowing users to receive a confirmation message that will vanish if they decide to reload the page they've been redirected to.

Form validation

You can use "validation" in Mojolicious::Plugin::DefaultHelpers to validate GET and POST parameters submitted to your application. All unknown fields will be ignored by default, so you have to decide which should be required or optional before you can perform checks on their values. Every check is performed right away, so you can use the results immediately to build more advanced validation logic with methods like "is_valid" in Mojolicious::Validator::Validation.

use Mojolicious::Lite -signatures;

get '/' => sub ($c) {

  # Check if parameters have been submitted
  my $v = $c->validation;
  return $c->render('index') unless $v->has_data;

  # Validate parameters ("pass_again" depends on "pass")
  $v->required('user')->size(1, 20)->like(qr/^[a-z0-9]+$/);
  $v->required('pass_again')->equal_to('pass') if $v->optional('pass')->size(7, 500)->is_valid;

  # Check if validation failed
  return $c->render('index') if $v->has_error;

  # Render confirmation
  $c->render('thanks');
};

app->start;
__DATA__

@@ index.html.ep
<!DOCTYPE html>
<html>
  <head>
    <style>
      label.field-with-error { color: #dd7e5e }
      input.field-with-error { background-color: #fd9e7e }
    </style>
  </head>
  <body>
    %= form_for index => begin
      %= label_for user => 'Username (required, 1-20 characters, a-z/0-9)'
      <br>
      %= text_field 'user', id => 'user'
      %= submit_button
      <br>
      %= label_for pass => 'Password (optional, 7-500 characters)'
      <br>
      %= password_field 'pass', id => 'pass'
      <br>
      %= label_for pass_again => 'Password again (equal to the value above)'
      <br>
      %= password_field 'pass_again', id => 'pass_again'
    % end
  </body>
</html>

@@ thanks.html.ep
<!DOCTYPE html>
<html><body>Thank you <%= validation->param('user') %>.</body></html>

Form elements generated with tag helpers from Mojolicious::Plugin::TagHelpers will automatically remember their previous values and add the class field-with-error for fields that failed validation to make styling with CSS easier.

<label class="field-with-error" for="user">
  Username (required, only characters e-t)
</label>
<input class="field-with-error" type="text" name="user" value="sri">

For a full list of available checks see also "CHECKS" in Mojolicious::Validator.

Adding form validation checks

Validation checks can be registered with "add_check" in Mojolicious::Validator and return a false value if they were successful. A true value may be used to pass along additional information which can then be retrieved with "error" in Mojolicious::Validator::Validation.

use Mojolicious::Lite -signatures;

# Add "range" check
app->validator->add_check(range => sub ($v, $name, $value, $min, $max) {
  return $value < $min || $value > $max;
});

get '/' => 'form';

post '/test' => sub ($c) {

  # Validate parameters with custom check
  my $v = $c->validation;
  $v->required('number')->range(3, 23);

  # Render form again if validation failed
  return $c->render('form') if $v->has_error;

  # Prevent double form submission with redirect
  $c->flash(number => $v->param('number'));
  $c->redirect_to('form');
};

app->start;
__DATA__

@@ form.html.ep
<!DOCTYPE html>
<html>
  <body>
    % if (my $number = flash 'number') {
      <p>Thanks, the number <%= $number %> was valid.</p>
    % }
    %= form_for test => begin
      % if (my $err = validation->error('number')) {
        <p>
          %= 'Value is required.' if $err->[0] eq 'required'
          %= 'Value needs to be between 3 and 23.' if $err->[0] eq 'range'
        </p>
      % }
      %= text_field 'number'
      %= submit_button
    % end
  </body>
</html>

Cross-site request forgery

CSRF is a very common attack on web applications that trick your logged in users to submit forms they did not intend to send, with something as mundane as a link. All you have to do, to protect your users from this, is to add an additional hidden field to your forms with "csrf_field" in Mojolicious::Plugin::TagHelpers, and validate it with "csrf_protect" in Mojolicious::Validator::Validation.

use Mojolicious::Lite -signatures;

get '/' => {template => 'target'};

post '/' => sub ($c) {

  # Check CSRF token
  my $v = $c->validation;
  return $c->render(text => 'Bad CSRF token!', status => 403) if $v->csrf_protect->has_error('csrf_token');

  my $city = $v->required('city')->param('city');
  $c->render(text => "Low orbit ion cannon pointed at $city!") unless $v->has_error;
} => 'target';

app->start;
__DATA__

@@ target.html.ep
<!DOCTYPE html>
<html>
  <body>
    %= form_for target => begin
      %= csrf_field
      %= label_for city => 'Which city to point low orbit ion cannon at?'
      %= text_field 'city', id => 'city'
      %= submit_button
    %= end
  </body>
</html>

For Ajax requests and the like, you can also generate a token directly with the helper "csrf_token" in Mojolicious::Plugin::DefaultHelpers, and then pass it along with the X-CSRF-Token request header.

ADVANCED

Less commonly used and more powerful features.

Template inheritance

Inheritance takes the layout concept above one step further, the helpers "content" in Mojolicious::Plugin::DefaultHelpers and "extends" in Mojolicious::Plugin::DefaultHelpers allow you to build skeleton templates with named blocks that child templates can override.

use Mojolicious::Lite;

# first > mylayout
get '/first' => {template => 'first', layout => 'mylayout'};

# third > second > first > mylayout
get '/third' => {template => 'third', layout => 'mylayout'};

app->start;
__DATA__

@@ layouts/mylayout.html.ep
<!DOCTYPE html>
<html>
  <head><title>Hello</title></head>
  <body><%= content %></body>
</html>

@@ first.html.ep
%= content header => begin
  Default header
% end
<div>Hello World!</div>
%= content footer => begin
  Default footer
% end

@@ second.html.ep
% extends 'first';
% content header => begin
  New header
% end

@@ third.html.ep
% extends 'second';
% content footer => begin
  New footer
% end

This chain could go on and on to allow a very high level of template reuse.

Custom responses

Most response content, static as well as dynamic, gets served through Mojo::Asset::File and Mojo::Asset::Memory objects. For somewhat static content, like cached JSON data or temporary files, you can create your own and use the helper "reply->asset" in Mojolicious::Plugin::DefaultHelpers to serve them while allowing content negotiation to be performed with Range, If-Modified-Since and If-None-Match headers.

use Mojolicious::Lite -signatures;
use Mojo::Asset::File;

get '/leak' => sub ($c) {
  $c->res->headers->content_type('text/plain');
  $c->reply->asset(Mojo::Asset::File->new(path => '/etc/passwd'));
};

app->start;

For even more control you can also just skip the helper and use "rendered" in Mojolicious::Controller to tell the renderer when you're done generating a response.

use Mojolicious::Lite -signatures;
use Mojo::Asset::File;

get '/leak' => sub ($c) {
  $c->res->headers->content_type('text/plain');
  $c->res->content->asset(Mojo::Asset::File->new(path => '/etc/passwd'));
  $c->rendered(200);
};

app->start;

Helper plugins

Some helpers might be useful enough for you to share them between multiple applications, plugins make that very simple.

package Mojolicious::Plugin::DebugHelper;
use Mojo::Base 'Mojolicious::Plugin', -signatures;

sub register ($self, $app, $conf) {
  $app->helper(debug => sub ($c, $str) {
    $c->app->log->debug($str);
  });
}

1;

The register method will be called when you load the plugin. And to add your helper to the application, you can use "helper" in Mojolicious.

use Mojolicious::Lite -signatures;

plugin 'DebugHelper';

get '/' => sub ($c) {
  $c->debug('It works!');
  $c->render(text => 'Hello!');
};

app->start;

A skeleton for a full CPAN compatible plugin distribution can be automatically generated.

$ mojo generate plugin DebugHelper

And if you have a PAUSE account (which can be requested at http://pause.perl.org), you are only a few commands away from releasing it to CPAN.

$ perl Makefile.PL
$ make test
$ make manifest
$ make dist
$ mojo cpanify -u USER -p PASS Mojolicious-Plugin-DebugHelper-0.01.tar.gz

Bundling assets with plugins

Assets such as templates and static files can be easily bundled with your plugins, even if you plan to release them to CPAN.

$ mojo generate plugin AlertAssets
$ mkdir Mojolicious-Plugin-AlertAssets/lib/Mojolicious/Plugin/AlertAssets
$ cd Mojolicious-Plugin-AlertAssets/lib/Mojolicious/Plugin/AlertAssets
$ mkdir public
$ echo 'alert("Hello World!");' > public/alertassets.js
$ mkdir templates
$ echo '%= javascript "/alertassets.js"' > templates/alertassets.html.ep

Just give them reasonably unique names, ideally based on the name of your plugin, and append their respective directories to the list of search paths when register is called.

package Mojolicious::Plugin::AlertAssets;
use Mojo::Base 'Mojolicious::Plugin', -signatures;

use Mojo::File qw(curfile);

sub register ($self, $app, $conf) {

  # Append "templates" and "public" directories
  my $base = curfile->sibling('AlertAssets');
  push @{$app->renderer->paths}, $base->child('templates')->to_string;
  push @{$app->static->paths},   $base->child('public')->to_string;
}

1;

Both will work just like normal templates and public directories once you've installed and loaded the plugin, with slightly lower precedence.

use Mojolicious::Lite;

plugin 'AlertAssets';

get '/alert_me';

app->start;
__DATA__

@@ alert_me.html.ep
<!DOCTYPE html>
<html>
  <head>
    <title>Alert me!</title>
    %= include 'alertassets'
  </head>
  <body>You've been alerted.</body>
</html>

And it works just the same for assets bundled in the DATA section of your plugin.

package Mojolicious::Plugin::AlertAssets;
use Mojo::Base 'Mojolicious::Plugin', -signatures;

sub register ($self, $app, $conf) {

  # Append class
  push @{$app->renderer->classes}, __PACKAGE__;
  push @{$app->static->classes},   __PACKAGE__;
}

1;
__DATA__

@@ alertassets.js
alert("Hello World!");

@@ alertassets.html.ep
%= javascript "/alertassets.js"

Post-processing dynamic content

While post-processing tasks are generally very easy with the hook "after_dispatch" in Mojolicious, for content generated by the renderer it is a lot more efficient to use "after_render" in Mojolicious.

use Mojolicious::Lite -signatures;
use IO::Compress::Gzip qw(gzip);

hook after_render => sub ($c, $output, $format) {

  # Check if "gzip => 1" has been set in the stash
  return unless $c->stash->{gzip};

  # Check if user agent accepts gzip compression
  return unless ($c->req->headers->accept_encoding // '') =~ /gzip/i;
  $c->res->headers->append(Vary => 'Accept-Encoding');

  # Compress content with gzip
  $c->res->headers->content_encoding('gzip');
  gzip $output, \my $compressed;
  $$output = $compressed;
};

get '/' => {template => 'hello', title => 'Hello', gzip => 1};

app->start;
__DATA__

@@ hello.html.ep
<!DOCTYPE html>
<html>
  <head><title><%= title %></title></head>
  <body>Compressed content.</body>
</html>

If you want to compress all dynamically generated content you can also activate "compress" in Mojolicious::Renderer.

Streaming

You don't have to render all content at once, the method "write" in Mojolicious::Controller can also be used to stream a series of smaller chunks.

use Mojolicious::Lite -signatures;

get '/' => sub ($c) {

  # Prepare body
  my $body = 'Hello World!';
  $c->res->headers->content_length(length $body);

  # Start writing directly with a drain callback
  my $drain = sub ($c) {
    my $chunk = substr $body, 0, 1, '';
    $c->write($chunk, length $body ? __SUB__ : undef);
  };
  $c->$drain;
};

app->start;

The drain callback will be executed whenever the entire previous chunk of data has actually been written.

HTTP/1.1 200 OK
Date: Sat, 13 Sep 2014 16:48:29 GMT
Content-Length: 12
Server: Mojolicious (Perl)

Hello World!

Instead of providing a Content-Length header you can also call "finish" in Mojolicious::Controller and close the connection manually once you are done.

use Mojolicious::Lite -signatures;

get '/' => sub ($c) {

  # Prepare body
  my $body = 'Hello World!';

  # Start writing directly with a drain callback
  my $drain = sub ($c) {
    my $chunk = substr $body, 0, 1, '';
    length $chunk ? $c->write($chunk, __SUB__) : $c->finish;
  };
  $c->$drain;
};

app->start;

While this is rather inefficient, as it prevents keep-alive, it is sometimes necessary for EventSource and similar applications.

HTTP/1.1 200 OK
Date: Sat, 13 Sep 2014 16:48:29 GMT
Connection: close
Server: Mojolicious (Perl)

Hello World!

Chunked transfer encoding

For very dynamic content you might not know the response content length in advance, that's where the chunked transfer encoding and "write_chunk" in Mojolicious::Controller come in handy. A common use would be to send the head section of an HTML document to the browser in advance and speed up preloading of referenced images and stylesheets.

use Mojolicious::Lite -signatures;

get '/' => sub ($c) {
  $c->write_chunk('<html><head><title>Example</title></head>' => sub ($c) {
    $c->finish('<body>Example</body></html>');
  });
};

app->start;

The optional drain callback ensures that all previous chunks have been written before processing continues. To end the stream you can call "finish" in Mojolicious::Controller or write an empty chunk of data.

HTTP/1.1 200 OK
Date: Sat, 13 Sep 2014 16:48:29 GMT
Transfer-Encoding: chunked
Server: Mojolicious (Perl)

29
<html><head><title>Example</title></head>
1b
<body>Example</body></html>
0

Especially in combination with long inactivity timeouts this can be very useful for Comet (long polling). Due to limitations in some web servers this might not work perfectly in all deployment environments.

Encoding

Templates stored in files are expected to be UTF-8 by default, but that can be easily changed with "encoding" in Mojolicious::Renderer.

$app->renderer->encoding('koi8-r');

All templates from the DATA section are bound to the encoding of the Perl script.

use Mojolicious::Lite;

get '/heart';

app->start;
__DATA__

@@ heart.html.ep
I ♥ Mojolicious!

Base64 encoded DATA files

Base64 encoded static files such as images can be easily stored in the DATA section of your application, similar to templates.

use Mojolicious::Lite;

get '/' => {text => 'I ♥ Mojolicious!'};

app->start;
__DATA__

@@ favicon.ico (base64)
...base64 encoded image...

Inflating DATA templates

Templates stored in files get preferred over files from the DATA section, this allows you to include a default set of templates in your application that the user can later customize. The command Mojolicious::Command::Author::inflate will write all templates and static files from the DATA section into actual files in the templates and public directories.

$ ./myapp.pl inflate

Customizing the template syntax

You can easily change the whole template syntax by loading Mojolicious::Plugin::EPRenderer with a custom configuration.

use Mojolicious::Lite;

plugin EPRenderer => {
  name     => 'mustache',
  template => {
    tag_start => '{{',
    tag_end   => '}}'
  }
};

get '/:name' => {name => 'Anonymous'} => 'index';

app->start;
__DATA__

@@ index.html.mustache
Hello {{= $name }}.

Mojo::Template contains the whole list of available options.

Adding your favorite template system

Maybe you would prefer a different template system than ep, which is provided by Mojolicious::Plugin::EPRenderer, and there is not already a plugin on CPAN for your favorite one. All you have to do, is to add a new handler with "add_handler" in Mojolicious::Renderer when register is called.

package Mojolicious::Plugin::MyRenderer;
use Mojo::Base 'Mojolicious::Plugin', -signatures;

sub register ($self, $app, $conf) {

  # Add "mine" handler
  $app->renderer->add_handler(mine => sub ($renderer, $c, $output, $options) {

    # Check for one-time use inline template
    my $inline_template = $options->{inline};

    # Check for appropriate template in "templates" directories
    my $template_path = $renderer->template_path($options);

    # Check for appropriate template in DATA sections
    my $data_template = $renderer->get_data_template($options);

    # This part is up to you and your template system :)
    ...

    # Pass the rendered result back to the renderer
    $$output = 'Hello World!';

    # Or just die if an error occurs
    die 'Something went wrong with the template';
  });
}

1;

An inline template, if provided by the user, will be passed along with the options. You can use "template_path" in Mojolicious::Renderer to search the templates directories of the application, and "get_data_template" in Mojolicious::Renderer to search the DATA sections.

use Mojolicious::Lite;

plugin 'MyRenderer';

# Render an inline template
get '/inline' => {inline => '...', handler => 'mine'};

# Render a template from the DATA section
get '/data' => {template => 'test'};

app->start;
__DATA__

@@ test.html.mine
...

Adding a handler to generate binary data

By default the renderer assumes that every handler generates characters that need to be automatically encoded, but this can be easily disabled if you're generating bytes instead.

use Mojolicious::Lite -signatures;
use Storable qw(nfreeze);

# Add "storable" handler
app->renderer->add_handler(storable => sub ($renderer, $c, $output, $options) {

  # Disable automatic encoding
  delete $options->{encoding};

  # Encode data from stash value
  $$output = nfreeze delete $c->stash->{storable};
});

# Set "handler" value automatically if "storable" value is set already
app->hook(before_render => sub ($c, $args) {
  $args->{handler} = 'storable' if exists $args->{storable} || exists $c->stash->{storable};
});

get '/' => {storable => {i => '♥ mojolicious'}};

app->start;

The hook "before_render" in Mojolicious can be used to make stash values like storable special, so that they no longer require a handler value to be set explicitly.

# Explicit "handler" value
$c->render(storable => {i => '♥ mojolicious'}, handler => 'storable');

# Implicit "handler" value (with "before_render" hook)
$c->render(storable => {i => '♥ mojolicious'});

You can continue with Mojolicious::Guides now or take a look at the Mojolicious 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 in the Forum, on IRC, or Matrix.