Mojolicious::Guides::Rendering(3p)

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 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.

  $self->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.

  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');

  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 Woerld!');

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

  $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" in Mojolicious::Controller instead of "render" in Mojolicious::Controller.

  # /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 helper "dumper" in Mojolicious::Plugin::DefaultHelpers 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 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.

  @@ 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.

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

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

  # 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 "include" in Mojolicious::Plugin::DefaultHelpers 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" in Mojolicious::Controller 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 helper "content_for" in Mojolicious::Plugin::DefaultHelpers 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, the helpers "content" in Mojolicious::Plugin::DefaultHelpers and "extends" in Mojolicious::Plugin::DefaultHelpersallow you to build a skeleton template with named 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 helper "memorize" in Mojolicious::Plugin::DefaultHelpers 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>

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';

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

    # 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"

  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.

  Internationalization
Thanks to Locale::Maketext all you need for basic internationalization support in your application is the plugin Mojolicious::Plugin::I18N and a few lexicon classes.

  package MyApp::I18N::de;
  use Mojo::Base -strict;
  use base 'MyApp::I18N';

  our %Lexicon = ('Hello World' => 'Hallo Welt');

  package main;
  use Mojolicious::Lite;

  plugin I18N => {namespace => 'MyApp::I18N'};

  get '/' => 'hello';

  app->start;
  __DATA__

  @@ hello.html.ep
  <%=l 'Hello World' %>!

Preferred languages will be automatically detected from the "Accept-Language" header or can be manually changed with the helper "languages" in Mojolicious::Plugin::I18N.

  $ ./myapp.pl get -H 'Accept-Language: de' /

  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 call to "finish" in Mojolicious::Controller 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 X 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.