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/ Mojolicious::Guides::Rendering

NAME

Mojolicious::Guides::Rendering - Rendering

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 name.format.handler scheme, with name defaulting to controller/action or the route name, format defaulting to html and handler to ep.

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

All templates should be in the templates directories of the application or the DATA section of the class main.

__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 allows the embedding of Perl code right into actual content using a small set of special tags and line start characters.

<% 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 =%>"
%= Perl expression line, treated as "<%= line %>"
%== Perl expression line, treated as "<%== line %>"
%# Comment line, treated as "<%# line =%>"
%% 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 .= 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.

<%= 'lalala' %>
<%== '<p>test</p>' %>

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

<%= b('<p>test</p>') %>

You can also add an additional equal sign to the end of a tag to have it automatically remove all surrounding whitespace, this allows free indenting without ruining the result.

<% for (1 .. 3) { %>
  <%= $foo =%>
<% } %>

Stash values that don't have invalid characters in their name get automatically initialized as normal variables in the template, and the controller object as $self.

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

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

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 render controller method, but that's usually not necessary, because it will get automatically called if nothing has been rendered after the routes dispatcher finished its work. This also means you can have routes pointing only to templates without actual actions.

$self->render;

There is one big difference though, by calling render manually you can make sure that templates use the current controller object and not the default controller specified in the controller_class attribute of the application class.

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.

$self->render(template => 'foo/bar');

Choosing a specific format and handler is just as easy.

$self->render(template => 'foo/bar', format => 'txt', handler => 'epl');

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

$self->render('foo/bar');

All values passed to the render call are only temporarily assigned to the stash and get reset again once rendering is finished.

Rendering inline templates

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

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

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

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

Rendering text

Perl characters can be rendered with the text stash value, the given content will be automatically encoded to bytes.

$self->render(text => 'Hello Wörld!');

Rendering data

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

$self->render(data => $octets);

Rendering JSON

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

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

Partial rendering

Sometimes you might want to access the rendered result, for example to generate emails, this can be done using the partial stash value.

my $html = $self->render('mail', partial => 1);

Status code

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

$self->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.

$self->render(text => 'Hello.', format => 'txt');

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

# Application
package MyApp;
use Mojo::Base 'Mojolicious';

sub startup {
  my $self = shift;

  # Add new MIME type
  $self->types->type(txt => 'text/plain; charset=utf-8');
}

1;

Stash data

Data can be passed to templates through the stash in any of the native Perl data types.

$self->stash(author     => 'Sebastian');
$self->stash(frameworks => ['Catalyst', 'Mojolicious']);
$self->stash(examples   => {tweetylicious => 'a microblogging app'});

%= $author
%= $frameworks->[1]
%= $examples->{tweetylicious}

Since everything is just Perl normal control structures just work.

% for my $framework (@$frameworks) {
  <%= $framework %> was written by <%= $author %>.
% }

% while (my ($app, $description) = each %$examples) {
  <%= $app %> is a <%= $description %>.
% }

Content negotiation

For resources with different representations and that require truly RESTful content negotiation you can also use respond_to instead of render.

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

The best possible representation will be automatically selected from the Accept request header, format stash value or format GET/POST parameter.

$self->respond_to(
  json => {json => {hello => 'world'}},
  html => sub {
    $self->content_for(head => '<meta name="author" content="sri" />');
    $self->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"
$self->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.

Helpers

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

%= dumper [1, 2, 3]

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

The dumper helper for example will use Data::Dumper to serialize whatever data structure you pass it, this can be very useful for debugging. We differentiate between default helpers which are more general purpose like dumper and tag helpers, which are template specific and mostly used to generate HTML tags.

%= javascript '/script.js'

%= javascript begin
  var a = 'b';
% end

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

Layouts

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

@@ 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 layout helper and place the result of the current template with the content helper. You can also pass along normal stash values to the layout helper.

@@ 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 with the layout argument.

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

To set a layout stash value application wide you can use defaults.

# Application
package MyApp;
use Mojo::Base 'Mojolicious';

sub startup {
  my $self = shift;

  # Default layout
  $self->defaults(layout => 'mylayout');
}

1;

Including partial templates

Like most helpers the include helper is just a shortcut to make your life a little easier.

@@ foo/bar.html.ep
<!DOCTYPE html>
<html>
  %= include 'header'
  <body>Bar</body>
</html>

@@ header.html.ep
<head><title>Howdy</title></head>

Instead of include you could also just call render with the partial argument.

@@ foo/bar.html.ep
<!DOCTYPE html>
<html>
  %= $self->render('header', partial => 1)
  <body>Bar</body>
</html>

@@ header.html.ep
<head><title>Howdy</title></head>

But there is one small difference between the two, if you pass stash values to include, they will get localized automatically and are only available in the partial template.

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

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

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 normal Perl functions.

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

Blocks are always delimited by the begin and end keywords.

@@ welcome.html.ep
% my $block = begin
  % my $name = shift;
  Hello <%= $name %>.
% end
% for (1 .. 10) {
  %= $block->('Sebastian')
% }

A naive translation to Perl code could look like this.

@@ welcome.html.pl
my $output = '';
my $block  = sub {
  my $name   = shift;
  my $output = '';
  $output .= 'Hello ';
  $output .= escape scalar $name;
  $output .= '.';
  return Mojo::ByteStream->new($output);
}
for (1 .. 10) {
  $output .= escape scalar $block->('Sebastian');
}
return $output;

Content blocks

Blocks and the content_for helper can also be used to pass whole sections of the template to the layout.

@@ foo/bar.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_for 'header' %></head>
  <body><%= content %></body>
</html>

Template inheritance

Inheritance takes the layout concept above one step further, it allows you to build a skeleton template with named content blocks that child templates can override.

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

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

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

Memorizing template blocks

Compiled templates are always cached in memory, but with the memorize helper you can go one step further and prevent template blocks from getting executed more than once.

@@ cached.html.ep
% use Time::Piece;
%= memorize begin
  This template was compiled at <%= localtime->hms %>.
% end

Adding helpers

Adding and redefining helpers is very easy, you can use them to do pretty much everything.

use Mojolicious::Lite;

helper debug => sub {
  my ($self, $string) = @_;
  $self->app->log->debug($string);
};

get '/' => sub {
  my $self = shift;
  $self->debug('action');
} => 'index';

app->start;
__DATA__

@@ index.html.ep
% debug 'template';

Helpers can also accept template blocks as last argument, this for example allows very pleasant to use tag helpers and filters.

use Mojolicious::Lite;
use Mojo::ByteStream;

helper trim_newline => sub {
  my ($self, $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

Wrapping the helper result into a Mojo::ByteStream object can prevent accidental double escaping.

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';

sub register {
  my ($self, $app) = @_;
  $app->helper(debug => sub {
    my ($self, $string) = @_;
    $self->app->log->debug($string);
  });
}

1;

The register method will be called when you load the plugin.

use Mojolicious::Lite;

plugin 'DebugHelper';

get '/' => sub {
  my $self = shift;
  $self->debug('It works.');
  $self->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 relasing 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 AlertAssets/lib/Mojolicious/Plugin/AlertAssets
$ cd 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 append their respective directories to the list of search paths when register is called.

package Mojolicious::Plugin::AlertAssets;
use Mojo::Base 'Mojolicious::Plugin';

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

sub register {
  my ($self, $app) = @_;

  # Append "templates" and "public" directories
  my $base = catdir(dirname(__FILE__), 'AlertAssets');
  push @{$app->renderer->paths}, catdir($base, 'templates');
  push @{$app->static->paths},   catdir($base, 'public');
}

1;

Both will work just like normal templates and public direcotries 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>

Custom exception and not_found templates

While the built-in exception and not_found templates are very useful during development, you most likely want to show your users something more related to your application in production. That's why Mojolicious will always try to render exception.$mode.$format.* or not_found.$mode.$format.* before falling back to the built-in default templates.

@@ not_found.production.html.ep
<!DOCTYPE html>
<html>
  <head><title>Page not found</title></head>
  <body>Page does not seem to exist.</body>
</html>

ADVANCED

Less commonly used and more powerful features.

Chunked transfer encoding

For very dynamic content you might not know the response Content-Length in advance, that's where the chunked Transfer-Encoding comes 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.

$self->write_chunk('<html><head><title>Example</title></head>', sub {
  my $self = shift;
  $self->finish('<body>Example</body></html>');
});

The optional drain callback ensures that all previous chunks have been written before processing continues. An empty chunk or finish call marks the end of the stream.

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.

# Application
package MyApp;
use Mojo::Base 'Mojolicious';

sub startup {
  my $self = shift;

  # Different encoding
  $self->renderer->encoding('koi8-r');
}

1;

All templates from the DATA section are bound to the encoding of the Perl script, so don't forget to use the utf8 pragma if necessary.

use Mojolicious::Lite;
use utf8;

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.

@@ 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 inflate command 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 the ep_renderer plugin with a custom configuration.

use Mojolicious::Lite;

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

get '/' => '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, all you have to do is add a new handler.

use Mojolicious::Lite;

app->renderer->add_handler(
  mine => sub {
    my ($r, $c, $output, $options) = @_;

    # One time use inline template
    my $inline = $options->{inline};

    # Generate relative template path
    my $name = $r->template_name($options);

    # Try to find appropriate template in DATA section
    my $content = $r->get_data_template($options, $name);

    # Generate absolute template path
    my $path = $r->template_path($options);

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

    # Pass the rendered result back to the renderer
    $$output = 'The rendered result';

    # Return true if rendering succeeded and false if it didn't
    return 1;
  }
);

get '/' => 'index';

app->start;
__DATA__

@@ index.html.mine
...

Since most template systems don't support templates in the DATA section the renderer provides methods to help you with that.

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.