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NAME ^

Dancer2::Cookbook - Example-driven quick-start to the Dancer2 web framework

VERSION ^

version 0.154000

DESCRIPTION ^

A quick-start guide with examples to get you up and running with the Dancer2 web framework.

BEGINNER'S DANCE ^

A simple Dancer2 web app

Dancer2 has been designed to be easy to work with - it's trivial to write a simple web app, but still has the power to work with larger projects. To start with, let's make an incredibly simple "Hello World" example:

    #!/usr/bin/perl

    use Dancer2;

    get '/hello/:name' => sub {
        return "Why, hello there " . params->{name};
    };

    dance;

Yes - the above is a fully-functioning web app; running that script will launch a webserver listening on the default port (3000). Now you can make a request:

    $ curl http://localhost:3000/hello/Bob
    Why, hello there Bob

and it will say hello. The :name part is a named parameter within the route specification, whose value is made available through params.

Note that you don't need to use the strict and warnings pragmas; they are already loaded by Dancer2.

Starting a Dancer2 project

The above simple example is fine for trivial projects, but for anything more complex, you'll want a more maintainable solution - enter the dancer2 helper script, which will build the framework of your application with a single command:

    $ dancer2 -a mywebapp
    + mywebapp
    + mywebapp/config.yml
    + mywebapp/MANIFEST.SKIP
    + mywebapp/Makefile.PL
    + mywebapp/lib
    + mywebapp/lib/mywebapp.pm
    + mywebapp/public
    + mywebapp/public/500.html
    + mywebapp/public/favicon.ico
    + mywebapp/public/dispatch.cgi
    + mywebapp/public/404.html
    + mywebapp/public/dispatch.fcgi
    + mywebapp/public/images
    + mywebapp/public/images/perldancer.jpg
    + mywebapp/public/images/perldancer-bg.jpg
    + mywebapp/public/css
    + mywebapp/public/css/error.css
    + mywebapp/public/css/style.css
    + mywebapp/public/javascripts
    + mywebapp/public/javascripts/jquery.js
    + mywebapp/t
    + mywebapp/t/001_base.t
    + mywebapp/t/002_index_route.t
    + mywebapp/bin
    + mywebapp/bin/app.pl
    + mywebapp/views
    + mywebapp/views/index.tt
    + mywebapp/views/layouts
    + mywebapp/views/layouts/main.tt
    + mywebapp/environments
    + mywebapp/environments/development.yml
    + mywebapp/environments/production.yml

As you can see, it creates a directory named after the name of the app, along with a configuration file, a views directory (where your templates and layouts will live), an environments directory (where environment-specific settings live), a module containing the actual guts of your application, and a script to start it - or to run your web app via Plack (see: plackup).

DANCE ROUTINES: ROUTES ^

Declaring routes

To control what happens when a web request is received by your webapp, you'll need to declare routes. A route declaration indicates which HTTP method(s) it is valid for, the path it matches (e.g. /foo/bar), and a coderef to execute, which returns the response.

    get '/hello/:name' => sub {
        return "Hi there " . params->{name};
    };

The above route specifies that, for GET requests to /hello/..., the code block provided should be executed.

Handling multiple HTTP request methods

Routes can use any to match all, or a specified list of HTTP methods.

The following will match any HTTP request to the path /myaction:

    any '/myaction' => sub {
        # code
    }

The following will match GET or POST requests to /myaction:

    any ['get', 'post'] => '/myaction' => sub {
        # code
    };

For convenience, any route which matches GET requests will also match HEAD requests.

Retrieving request parameters

The params keyword returns a hashref of request parameters; these will be parameters supplied on the query string within the path itself (with named placeholders) and, for HTTTP POST requests, the content of the POST body.

Named parameters in route path declarations

As seen above, you can use :somename in a route's path to capture part of the path; this will become available by calling params.

So, for a web app where you want to display information on a company, you might use something like:

    get '/company/view/:companyid' => sub {
        my $company_id = params->{companyid};
        # Look up the company and return appropriate page
    };

Wildcard path matching and splat

You can also declare wildcards in a path and retrieve the values they matched with the splat keyword:

    get '/*/*' => sub {
        my ($action, $id) = splat;
        if (my $action eq 'view') {
            return display_item($id);
        } elsif ($action eq 'delete') {
            return delete_item($id);
        } else {
            status 'not_found';
            return "What?";
        }
    };

Before filters - processed before a request

A before filter declares code which should be handled before a request is passed to the appropriate route.

    hook before => sub {
        forward '/foo/oversee', { note => 'Hi there' };
    };

    get '/foo/*' => sub {
        my ($match) = splat; # 'oversee';
        params->{note};      # 'Hi there'
    };

The above declares a before filter which uses forward to do an internal redirect to /foo/oversee with an additional parameter note.

See also the hook keyword.

Default route

In case you want to avoid a 404 error, or handle multiple routes in the same way and you don't feel like configuring all of them, you can set up a default route handler.

The default route handler will handle any request that doesn't get served by any other route.

All you need to do is set up the following route as the last route:

    any qr{.*} => sub {
        status 'not_found';
        template 'special_404', { path => request->path };
    };

Then you can set up the template like so:

    You tried to reach [% path %], but it is unavailable at the moment.

    Please try again or contact us at <contact@example.com>.

Using the auto_page feature for automatic route creation

For simple "static" pages you can simply enable the auto_page config setting; this means you don't need to declare a route handler for those pages; if a request is for /foo/bar, Dancer2 will check for a matching view (e.g. /foo/bar.tt and render it with the default layout etc. if found. For full details, see the documentation for the auto_page setting.

Simplifying Ajax queries with the Ajax plugin

As an Ajax query is just an HTTP query, it's similar to a GET or POST route. You may ask yourself why you may want to use the ajax keyword (from the Dancer2::Plugin::Ajax plugin) instead of a simple get.

Let's say you have a path like /user/:user in your application. You may want to be able to serve this page with a layout and HTML content. But you may also want to be able to call this same url from a javascript query using Ajax.

So, instead of having the following code:

    get '/user/:user' => sub {
         if (request->is_ajax) {
             # create xml, set headers to text/xml, blablabla
              header('Content-Type' => 'text/xml');
              header('Cache-Control' =>  'no-store, no-cache, must-revalidate');
              to_xml({...})
         }else{
             template users, {....}
         }
    };

you can have

    get '/user/:user' => sub {
        template users, {...}
    }

and

    ajax '/user/:user' => sub {
         to_xml({...}, RootName => undef);
    }

Because it's an Ajax query, you know you need to return XML content, so the content type of the response is set for you.

Using the prefix feature to split your application

For better maintainability, you may want to separate some of your application components into different packages. Let's say we have a simple web app with an admin section and want to maintain this in a different package:

    package myapp;
    use Dancer2;
    use myapp::admin;

    prefix undef;

    get '/' => sub {...};

    1;

    package myapp::admin;
    use Dancer2 appname => 'myapp';

    prefix '/admin';

    get '/' => sub {...};

    1;

The following routes will be generated for us:

    - get /
    - get /admin/
    - head /
    - head /admin/

By default, a separate application is created for every package that uses Dancer2. The appname tag is used to collect routes and hooks into a single Dancer2 application. In the above example, appname => 'myapp' adds the routes from myapp::admin to the routes of the app myapp.

When using multiple applications please ensure that your path definitions do not overlap. For example, if using a default route as described above, once a request is matched to the default route then no further routes (or applications) would be reached.

MUSCLE MEMORY: STORING DATA ^

Handling sessions

It's common to want to use sessions to give your web applications state; for instance, allowing a user to log in, creating a session, and checking that session on subsequent requests.

To make use of sessions, you must first enable the session engine - pick the session engine you want to use, then declare it in your config file like this:

    session: Simple

The Dancer2::Session::Simple backend implements very simple in-memory session storage. This will be fast and useful for testing, but such sessions will not persist between restarts of your app.

You can also use the Dancer2::Session::YAML backend included with Dancer2, which stores session data on disc in YAML files (since YAML is a nice human-readable format, it makes inspecting the contents of sessions a breeze):

    session: YAML

Or, to enable session support from within your code,

    set session => 'YAML';

However, controlling settings is best done from your config file.

'YAML' in the example is the session backend to use; this is shorthand for Dancer2::Session::YAML. There are other session backends - for instance Dancer2::Session::Memcached - but the YAML backend is simple and easy to use.

You can then use the session keyword to manipulate the session:

Storing data in the session

Storing data in the session is as easy as:

    session varname => 'value';

Retrieving data from the session

Retrieving data from the session is as easy as:

    session('varname')

Or, alternatively,

    session->read("varname")

Controlling where sessions are stored

For disc-based session backends like Dancer2::Session::YAML, Dancer2::Session::Storable etc., session files are written to the session dir specified by the session_dir setting, which defaults to ./sessions if not specifically set.

If you need to control where session files are created, you can do so quickly and easily within your config file, for example:

    session: YAML
    engines:
      session:
        YAML:
          session_dir: /tmp/dancer-sessions

If the directory you specify does not exist, Dancer2 will attempt to create it for you.

Destroying a session

When you're done with your session, you can destroy it:

    app->destroy_session

Sessions and logging in

Note! The following example will in this form prevent the application from returning static content (files inside the public/ directory, like CSS, javascript files etc.) when the user is not logged in, because the before hook is executed on the static files as well. A simple way to prevent this is using Plack::Middleware::Static for serving static files. An example can be found here.

A common requirement is to check the user is logged in, and, if not, require them to log in before continuing.

This can easily be handled with a before filter to check their session:

    use Dancer2;
    set session => "Simple";

    hook before => sub {
        if (!session('user') && request->dispatch_path !~ m{^/login}) {
            forward '/login', { requested_path => request->dispatch_path };
        }
    };

    get '/' => sub { return "Home Page"; };

    get '/secret' => sub { return "Top Secret Stuff here"; };

    get '/login' => sub {
        # Display a login page; the original URL they requested is available as
        # param('requested_path'), so could be put in a hidden field in the form
        template 'login', { path => param('requested_path') };
    };

    post '/login' => sub {
        # Validate the username and password they supplied
        if (param('user') eq 'bob' && param('pass') eq 'letmein') {
            session user => param('user');
            redirect param('path') || '/';
        } else {
            redirect '/login?failed=1';
        }
    };

    dance();

Here is what the corresponding login.tt file should look like. You should place it in a directory called views/:

    <html>
      <head>
        <title>Session and logging in</title>
      </head>
      <body>
        <form action='/login' method='POST'>
            User Name : <input type='text' name='user'/>
            Password: <input type='password' name='pass' />

            <!-- Put the original path requested into a hidden
                       field so it's sent back in the POST and can be
                       used to redirect to the right page after login -->
            <input type='hidden' name='path' value='[% path %]'/>

            <input type='submit' value='Login' />
        </form>
      </body>
    </html>

Of course, you'll probably want to validate your users against a database table, or maybe via IMAP/LDAP/SSH/POP3/local system accounts via PAM etc. Authen::Simple is probably a good starting point here!

A simple working example of handling authentication against a database table yourself (using Dancer2::Plugin::Database which provides the database keyword, and Crypt::SaltedHash to handle salted hashed passwords (well, you wouldn't store your users passwords in the clear, would you?)) follows:

    post '/login' => sub {
        my $user = database->quick_select('users',
            { username => params->{user} }
        );
        if (!$user) {
            warning "Failed login for unrecognised user " . params->{user};
            redirect '/login?failed=1';
        } else {
            if (Crypt::SaltedHash->validate($user->{password}, params->{pass}))
            {
                debug "Password correct";
                # Logged in successfully
                session user => $user;
                redirect params->{path} || '/';
            } else {
                debug("Login failed - password incorrect for " . params->{user});
                redirect '/login?failed=1';
            }
        }
    };

Retrieve complete hash stored in session

Get complete hash stored in session:

    my $hash = session;

APPEARANCE: TEMPLATES AND LAYOUTS ^

Returning plain content is all well and good for examples or trivial apps, but soon you'll want to use templates to maintain separation between your code and your content. Dancer2 makes this easy.

Your route handlers can use the template keyword to render templates.

Views

It's possible to render the action's content with a template, this is called a view. The appdir/views directory is the place where views are located.

You can change this location by changing the setting 'views'.

By default, the internal template engine Dancer2::Template::Simple is used, but you may want to upgrade to Template Toolkit. If you do so, you have to enable this engine in your settings as explained in Dancer2::Template::TemplateToolkit and you'll also have to import the Template module in your application code.

Views use a .tt extension by convention. This can be overridden by setting the extension attribute in the template engine configuration. See the Using Templates section in the manual for details.

In order to render a view, just call the template keyword at the end of the action by giving the view name and the HASHREF of tokens to interpolate in the view (note that for convenience, the request, session, params and vars are automatically accessible in the view, named request, session, params and vars) - for example:

    hook before => sub { var time => scalar(localtime) };

    get '/hello/:name' => sub {
        my $name = params->{name};
        template 'hello.tt', { name => $name };
    };

The template hello.tt could contain, for example:

    <p>Hi there, [% name %]!</p>
    <p>You're using [% request.user_agent %]</p>
    [% IF session.username %]
        <p>You're logged in as [% session.username %]</p>
    [% END %]
    It's currently [% vars.time %]

For a full list of the tokens automatically added to your template (like session, request and vars, refer to Dancer2::Core::Role::Template).

Layouts

A layout is a special view, located in the 'layouts' directory (inside the views directory) which must have a token named content. That token marks the place where to render the action view. This lets you define a global layout for your actions, and have each individual view contain only specific content. This is a good thing to avoid lots of needless duplication of HTML :)

Here is an example of a layout: views/layouts/main.tt :

    <html>
        <head>...</head>
        <body>
        <div id="header">
        ...
        </div>

        <div id="content">
        [% content %]
        </div>

        </body>
    </html>

You can tell your app which layout to use with layout: name in the config file, or within your code:

    set layout => 'main';

You can control which layout to use (or whether to use a layout at all) for a specific request without altering the layout setting by passing an options hashref as the third param to the template keyword:

    template 'index.tt', {}, { layout => undef };

If your application is not mounted under root (/), you can use a before_template hook instead of hardcoding the path into your application for your CSS, images and JavaScript:

    hook before_template_render => sub {
        my $tokens = shift;
        $tokens->{uri_base} = request->base->path;
    };

Then in your layout, modify your CSS inclusion as follows:

    <link rel="stylesheet" href="[% uri_base %]/css/style.css" />

From now on you can mount your application wherever you want, without any further modification of the CSS inclusion.

Templates and unicode

If you use Plack and have a unicode problem with your Dancer2 application, don't forget to check if you have set your template engine to use unicode, and set the default charset to UTF-8. So, if you are using template toolkit, your config file will look like this:

    charset: UTF-8
    engines:
      template:
        template_toolkit:
          ENCODING: utf8

Template Toolkit's WRAPPER directive in Dancer2

Dancer2 already provides a WRAPPER-like ability, which we call a "layout". The reason we don't use Template Toolkit's WRAPPER (which also makes us incompatible with it) is because not all template systems support it. Actually, most don't.

However, you might want to use it, and be able to define META variables and regular Template::Toolkit variables.

These few steps will get you there:

Done! Everything will work fine out of the box, including variables and META variables.

SETTING THE STAGE: CONFIGURATION AND LOGGING ^

Configuration and environments

Configuring a Dancer2 application can be done in many ways. The easiest one (and maybe the dirtiest) is to put all your settings statements at the top of your script, before calling the dance() method.

Other ways are possible: for example, you can define all your settings in the file appdir/config.yml. For this, you must have installed the YAML module, and of course, write the config file in YAML.

That's better than the first option, but it's still not perfect as you can't switch easily from an environment to another without rewriting the config file.

A better solution is to have one config.yml file with default global settings, like the following:

    # appdir/config.yml
    logger: 'file'
    layout: 'main'

And then write as many environment files as you like in appdir/environments. That way, the appropriate environment config file will be loaded according to the running environment (if none is specified, it will be 'development').

Note that you can change the running environment using the --environment command line switch.

Typically, you'll want to set the following values in a development config file:

    # appdir/environments/development.yml
    log: 'debug'
    startup_info: 1
    show_errors:  1

And in a production one:

    # appdir/environments/production.yml
    log: 'warning'
    startup_info: 0
    show_errors:  0

Accessing configuration information

From inside your application

A Dancer2 application can use the config keyword to easily access the settings within its config file, for instance:

    get '/appname' => sub {
        return "This is " . config->{appname};
    };

This makes keeping your application's settings all in one place simple and easy - you shouldn't need to worry about implementing all that yourself :)

From a separate script

You may want to access your webapp's configuration from outside your webapp. You could, of course, use the YAML module of your choice and load your webapps's config.yml, but chances are that this is not convenient.

Use Dancer2 instead. You can simply use the values from config.yml and some additional default values:

    # bin/show_app_config.pl
    use Dancer2;
    print "template:".config->{template}."\n"; # simple
    print "log:".config->{log}."\n"; # undef

Note that config->{log} should result in an uninitialized warning on a default scaffold since the environment isn't loaded and log is defined in the environment and not in config.yml. Hence undef.

Dancer2 will load your config.yml configuration file along with the correct environment file located in your environments directory.

The environment is determined by two environment variables in the following order:

If neither of those is set, it will default to loading the development environment (typically $webapp/environment/development.yml).

If you wish to load a different environment, you need to override these variables.

You can call your script with the environment changed:

    $ PLACK_ENV=production perl bin/show_app_config.pl

Or you can override them directly in the script (less recommended):

    BEGIN { $ENV{'DANCER_ENVIRONMENT'} = 'production' }
    use Dancer2;

    ...

Logging

Configuring logging

It's possible to log messages generated by the application and by Dancer2 itself.

To start logging, select the logging engine you wish to use with the logger setting; Dancer2 includes built-in log engines named file and console, which log to a logfile and to the console respectively.

To enable logging to a file, add the following to your config file:

    logger: 'file'

Then you can choose which kind of messages you want to actually log:

    log: 'core'      # will log debug, warnings, errors,
                     # and messages from Dancer2 itself
    log: 'debug'     # will log debug, info, warning and errors
    log: 'info'      # will log info, warning and errors
    log: 'warning'   # will log warning and errors
    log: 'error'     # will log only errors

If you're using the file logging engine, a directory appdir/logs will be created and will host one logfile per environment. The log message contains the time it was written, the PID of the current process, the message and the caller information (file and line).

Logging your own messages

Just call debug, info, warning or error with your message:

    debug "This is a debug message from my app.";

RESTING ^

Writing a REST application

With Dancer2, it's easy to write REST applications. Dancer2 provides helpers to serialize and deserialize for the following data formats:

JSON
YAML
XML
Data::Dumper

To activate this feature, you only have to set the serializer setting to the format you require, for instance in your config file:

   serializer: JSON

Or directly in your code:

   set serializer => 'JSON';

From now, all hashrefs or arrayrefs returned by a route will be serialized to the format you chose, and all data received from POST or PUT requests will be automatically deserialized.

    get '/hello/:name' => sub {
        # this structure will be returned to the client as
        # {"name":"$name"}
        return {name => params->{name}};
    };

It's possible to let the client choose which serializer to use. For this, use the mutable serializer, and an appropriate serializer will be chosen from the Content-Type header.

It's also possible to return a custom error using the send_error keyword. When you don't use a serializer, the send_error function will take a string as first parameter (the message), and an optional HTTP code. When using a serializer, the message can be a string, an arrayref or a hashref:

    get '/hello/:name' => sub {
        if (...) {
           send_error("you can't do that");
           # or
           send_error({reason => 'access denied', message => "no"});
        }
    };

The content of the error will be serialized using the appropriate serializer.

DANCER ON THE STAGE: DEPLOYMENT ^

Running stand-alone

At the simplest, your Dancer2 app can run standalone, operating as its own webserver using HTTP::Server::PSGI.

Simply fire up your app:

    $ perl bin/app.pl
    >> Listening on 0.0.0.0:3000
    == Entering the dance floor ...

Point your browser at it, and away you go!

This option can be useful for small personal web apps or internal apps, but if you want to make your app available to the world, it probably won't suit you.

Auto Reloading with Plack and Shotgun

To edit your files without the need to restart the webserver on each file change, simply start your Dancer2 app using plackup and Plack::Loader::Shotgun:

    $ plackup -L Shotgun bin/app.pl
    HTTP::Server::PSGI: Accepting connections at http://0:5000/

Point your browser at it. Files can now be changed in your favorite editor and the browser needs to be refreshed to see the saved changes.

Please note that this is not recommended for production for performance reasons. This is the Dancer2 replacement solution of the old Dancer experimental auto_reload option.

On Windows, Shotgun loader is known to cause huge memory leaks in a fork-emulation layer. If you are aware of this and still want to run the loader, please use the following command:

    > set PLACK_SHOTGUN_MEMORY_LEAK=1 && plackup -L Shotgun bin\app.pl
    HTTP::Server::PSGI: Accepting connections at http://0:5000/

CGI and Fast-CGI

In providing ultimate flexibility in terms of deployment, your Dancer2 app can be run as a simple cgi-script out-of-the-box. No additional web-server configuration needed. Your web server should recognize .cgi files and be able to serve Perl scripts. The Perl module Plack::Runner is required.

Running on Apache (CGI and FCGI)

Start by adding the following to your apache configuration (httpd.conf or sites-available/*site*):

    <VirtualHost *:80>
        ServerName www.example.com
        DocumentRoot /srv/www.example.com/public
        ServerAdmin you@example.com

        <Directory "/srv/www.example.com/public">
           AllowOverride None
           Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
           Order allow,deny
           Allow from all
           AddHandler cgi-script .cgi
        </Directory>

        RewriteEngine On
        RewriteCond %{REQUEST_FILENAME} !-f
        RewriteRule ^(.*)$ /dispatch.cgi$1 [QSA,L]

        ErrorLog  /var/log/apache2/www.example.com-error.log
        CustomLog /var/log/apache2/www.example.com-access_log common
    </VirtualHost>

Note that when using fast-cgi your rewrite rule should be:

        RewriteRule ^(.*)$ /dispatch.fcgi$1 [QSA,L]

Here, the mod_rewrite magic for Pretty-URLs is directly put in Apache's configuration. But if your web server supports .htaccess files, you can drop those lines in a .htaccess file.

To check if your server supports mod_rewrite type apache2 -l to list modules. To enable mod_rewrite on Debian or Ubuntu, run a2enmod rewrite. Place following code in a file called .htaccess in your application's root folder:

    # BEGIN dancer application htaccess
    RewriteEngine On
    RewriteCond %{SCRIPT_FILENAME} !-d
    RewriteCond %{SCRIPT_FILENAME} !-f
    RewriteRule (.*) /dispatch.cgi$1 [L]
    # END dancer application htaccess

Now you can access your Dancer2 application URLs as if you were using the embedded web server:

    http://localhost/

This option is a no-brainer, easy to setup, low maintenance but serves requests slower than all other options.

You can use the same technique to deploy with FastCGI, by just changing the line:

    AddHandler cgi-script .cgi

to:

    AddHandler fastcgi-script .fcgi

Of course remember to update your rewrite rules, if you have set any:

    RewriteRule (.*) /dispatch.fcgi$1 [L]

Running under an appdir

If you want to deploy multiple applications under the same VirtualHost (using one application per directory, for example) you can use the following example Apache configuration.

This example uses the FastCGI dispatcher that comes with Dancer2, but you should be able to adapt this to use any other way of deployment described in this guide. The only purpose of this example is to show how to deploy multiple applications under the same base directory/VirtualHost.

    <VirtualHost *:80>
        ServerName localhost
        DocumentRoot "/path/to/rootdir"
        RewriteEngine On
        RewriteCond %{REQUEST_FILENAME} !-f

        <Directory "/path/to/rootdir">
            AllowOverride None
            Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
            Order allow,deny
            Allow from all
            AddHandler fastcgi-script .fcgi
        </Directory>

        RewriteRule /App1(.*)$ /App1/public/dispatch.fcgi$1 [QSA,L]
        RewriteRule /App2(.*)$ /App2/public/dispatch.fcgi$1 [QSA,L]
        ...
        RewriteRule /AppN(.*)$ /AppN/public/dispatch.fcgi$1 [QSA,L]
    </VirtualHost>

Of course, if your Apache configuration allows that, you can put the RewriteRules in a .htaccess file directly within the application's directory, which lets you add a new application without changing the Apache configuration.

Running on lighttpd (CGI)

To run as a CGI app on lighttpd, just create a soft link to the dispatch.cgi script (created when you run dancer -a MyApp) inside your system's cgi-bin folder. Make sure mod_cgi is enabled.

    ln -s /path/to/MyApp/public/dispatch.cgi /usr/lib/cgi-bin/mycoolapp.cgi

Running on lighttpd (FastCGI)

Make sure mod_fcgi is enabled. You also must have FCGI installed.

This example configuration uses TCP/IP:

    $HTTP["url"] == "^/app" {
        fastcgi.server += (
            "/app" => (
                "" => (
                    "host" => "127.0.0.1",
                    "port" => "5000",
                    "check-local" => "disable",
                )
            )
        )
    }

Launch your application:

    plackup -s FCGI --port 5000 bin/app.pl

This example configuration uses a socket:

    $HTTP["url"] =~ "^/app" {
        fastcgi.server += (
            "/app" => (
                "" => (
                    "socket" => "/tmp/fcgi.sock",
                    "check-local" => "disable",
                )
            )
        )
    }

Launch your application:

    plackup -s FCGI --listen /tmp/fcgi.sock bin/app.pl

Plack middlewares

If you want to use Plack middlewares, you need to enable them using Plack::Builder as such:

    # in app.psgi or any other handler
    use Dancer2;
    use MyWebApp;
    use Plack::Builder;

    builder {
        enable 'Deflater';
        enable 'Session', store => 'File';
        enable 'Debug', panels => [ qw<DBITrace Memory Timer> ];
        dance;
    };

The nice thing about this setup is that it will work seamlessly through Plack or through the internal web server.

    # load dev web server (without middlewares)
    perl -Ilib app.psgi

    # load plack web server (with middlewares)
    plackup -I lib app.psgi

You do not need to provide different files for either server.

Path-based middlewares

If you want to set up a middleware for a specific path, you can do that using Plack::Builder which uses Plack::App::URLMap:

    # in your app.psgi or any other handler
    use Dancer2;
    use MyWebApp;
    use Plack::Builder;

    my $special_handler = sub { ... };

    builder {
        mount '/'        => dance;
        mount '/special' => $special_handler;
    };

Running on Perl web servers with plackup

A number of Perl web servers supporting PSGI are available on CPAN:

Starman

Starman is a high performance web server, with support for preforking, signals, multiple interfaces, graceful restarts and dynamic worker pool configuration.

Twiggy

Twiggy is an AnyEvent web server, it's light and fast.

Corona

Corona is a Coro based web server.

To start your application, just run plackup (see Plack and specific servers above for all available options):

   $ plackup bin/app.pl
   $ plackup -E deployment -s Starman --workers=10 -p 5001 -a bin/app.pl

As you can see, the scaffolded Perl script for your app can be used as a PSGI startup file.

Enabling content compression

Content compression (gzip, deflate) can be easily enabled via a Plack middleware (see "Plack::Middleware" in Plack): Plack::Middleware::Deflater. It's a middleware to encode the response body in gzip or deflate, based on the Accept-Encoding HTTP request header.

Enable it as you would enable any Plack middleware. First you need to install Plack::Middleware::Deflater, then in the handler (usually app.psgi) edit it to use Plack::Builder, as described above:

    use Dancer2;
    use MyWebApp;
    use Plack::Builder;

    builder {
        enable 'Deflater';
        dance;
    };

To test if content compression works, trace the HTTP request and response before and after enabling this middleware. Among other things, you should notice that the response is gzip or deflate encoded, and contains a header Content-Encoding set to gzip or deflate.

Running multiple apps with Plack::Builder

You can use Plack::Builder to mount multiple Dancer2 applications on a PSGI webserver like Starman.

Start by creating a simple app.psgi file:

    use OurWiki;  # first app
    use OurForum; # second app
    use Plack::Builder;

    builder {
        mount '/wiki'  => OurWiki->psgi_app;
        mount '/forum' => OurForum->psgi_app;
    };

and now use Starman

    plackup -a app.psgi -s Starman

Currently this still demands the same appdir for both (default circumstance) but in a future version this will be easier to change while staying very simple to mount.

Running from Apache with Plack

You can run your app from Apache using PSGI (Plack), with a config like the following:

    <VirtualHost myapp.example.com>
        ServerName www.myapp.example.com
        ServerAlias myapp.example.com
        DocumentRoot /websites/myapp.example.com

        <Directory /home/myapp/myapp>
            AllowOverride None
            Order allow,deny
            Allow from all
        </Directory>

        <Location />
            SetHandler perl-script
            PerlResponseHandler Plack::Handler::Apache2
            PerlSetVar psgi_app /websites/myapp.example.com/app.pl
        </Location>

        ErrorLog  /websites/myapp.example.com/logs/error_log
        CustomLog /websites/myapp.example.com/logs/access_log common
    </VirtualHost>

To set the environment you want to use for your application (production or development), you can set it this way:

    <VirtualHost>
        ...
        SetEnv DANCER_ENVIRONMENT "production"
        ...
    </VirtualHost>

Serving static files using Plack::Middleware::Static

You can use Plack::Middleware::Static to serve your static files instead of Dancer2::Handler::File. That way before hooks will not be executed for them. This is required to make the example in Sessions and logging-in work.

First, we have to disable Dancer2::Handler::File in the config:

    route_handlers: []

Next, our bin/app.pl should look similar to this:

    #!/usr/bin/env perl
    use Plack::Builder;
    use Dancer2::FileUtils qw[ path ];
    use MyApp;

    builder {
        enable "Plack::Middleware::Static",
                path => sub { -f path('public', shift) },
                root => 'public';
        dance;
    };

The path option returns true if the requested file exists inside the public/ directory. For example the file /css/default.css is searched for at public/css/default.css. When the file is found, Plack::Middleware::Static returns the requested file from the 'root' directory, which is in this example the public/ folder.

Creating a service

You can turn your app into a proper service running in the background using one of the following examples.

Using Ubic

Ubic is an extensible perlish service manager. You can use it to start and stop any services, automatically start them on reboots or daemon failures, and implement custom status checks.

A basic PSGI service description (usually in /etc/ubic/service/application):

    use parent qw(Ubic::Service::Plack);

    # if your application is not installed in @INC path:
    sub start {
        my $self = shift;
        $ENV{PERL5LIB} = '/path/to/your/application/lib';
        $self->SUPER::start(@_);
    }

    __PACKAGE__->new(
        server => 'Starman',
        app => '/path/to/your/application/app.pl',
        port => 5000,
        user => 'www-data',
    );

Run ubic start application to start the service.

Using daemontools

daemontools is a collection of tools for managing UNIX services. You can use it to easily start/restart/stop services.

A basic script to start an application: (in /service/application/run)

    #!/bin/sh

    # if your application is not installed in @INC path:
    export PERL5LIB='/path/to/your/application/lib'

    exec 2>&1 \
    /usr/local/bin/plackup -s Starman -a /path/to/your/application/app.pl -p 5000

Running stand-alone behind a proxy / load balancer

Another option would be to run your app stand-alone as described above, but then use a proxy or load balancer to accept incoming requests (on the standard port 80, say) and feed them to your Dancer2 app.

This could be achieved using various software; examples would include:

Using Apache's mod_proxy

You could set up a VirtualHost for your web app, and proxy all requests through to it:

    <VirtualHost mywebapp.example.com:80>
    ProxyPass / http://localhost:3000/
    ProxyPassReverse / http://localhost:3000/
    </VirtualHost>

Or, if you want your webapp to share an existing VirtualHost, you could have it under a specified dir:

    ProxyPass /mywebapp/ http://localhost:3000/
    ProxyPassReverse /mywebapp/ http://localhost:3000/

It is important for you to note that the Apache2 modules mod_proxy and mod_proxy_http must be enabled:

    $ a2enmod proxy
    $ a2enmod proxy_http

It is also important to set permissions for proxying for security purposes, below is an example.

    <Proxy *>
      Order allow,deny
      Allow from all
    </Proxy>

Using perlbal

perlbal is a single-threaded event-based server written in Perl supporting HTTP load balancing, web serving, and a mix of the two, available from http://www.danga.com/perlbal/.

It processes hundreds of millions of requests a day just for LiveJournal, Vox and TypePad and dozens of other "Web 2.0" applications.

It can also provide a management interface to let you see various information on requests handled etc.

It could easily be used to handle requests for your Dancer2 apps, too.

It can be easily installed from CPAN:

    perl -MCPAN -e 'install Perlbal'

Once installed, you'll need to write a configuration file. See the examples provided with perlbal, but you'll probably want something like:

    CREATE POOL my_dancers
    POOL my_dancers ADD 10.0.0.10:3030
    POOL my_dancers ADD 10.0.0.11:3030
    POOL my_dancers ADD 10.0.0.12:3030
    POOL my_dancers ADD 10.0.0.13:3030

    CREATE SERVICE my_webapp
    SET listen          = 0.0.0.0:80
    SET role            = reverse_proxy
    SET pool            = my_dancers
    SET persist_client  = on
    SET persist_backend = on
    SET verify_backend  = on
    ENABLE my_webapp

Using balance

balance is a simple load-balancer from Inlab Software, available from http://www.inlab.de/balance.html.

It could be used simply to hand requests to a standalone Dancer2 app. You could even run several instances of your Dancer2 app, on the same machine or on several machines, and use a machine running balance to distribute the requests between them, for some serious heavy traffic handling!

To listen on port 80, and send requests to a Dancer2 app on port 3000:

    balance http localhost:3000

To listen on a specified IP only on port 80, and distribute requests between multiple Dancer2 apps on multiple other machines:

    balance -b 10.0.0.1 80 10.0.0.2:3000 10.0.0.3:3000 10.0.0.4:3000

Using lighttpd

You can use lighttp's mod_proxy:

    $HTTP["url"] =~ "/application" {
        proxy.server = (
            "/" => (
                "application" => ( "host" => "127.0.0.1", "port" => 3000 )
            )
        )
    }

This configuration will proxy all requests to the /application path to the path / on localhost:3000.

Using Nginx

with Nginx:

    upstream backendurl {
        server unix:THE_PATH_OF_YOUR_PLACKUP_SOCKET_HERE.sock;
    }

    server {
      listen       80;
      server_name YOUR_HOST_HERE;

      access_log /var/log/YOUR_ACCESS_LOG_HERE.log;
      error_log  /var/log/YOUR_ERROR_LOG_HERE.log info;

      root YOUR_ROOT_PROJECT/public;
      location / {
        try_files $uri @proxy;
        access_log off;
        expires max;
      }

      location @proxy {
            proxy_set_header Host $http_host;
            proxy_set_header X-Forwarded-Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_pass       http://backendurl;
      }

    }

You will need plackup to start a worker listening on a socket :

    cd YOUR_PROJECT_PATH
    sudo -u www plackup -E production -s Starman --workers=2 \
        -l THE_PATH_OF_YOUR_PLACKUP_SOCKET_HERE.sock -a bin/app.pl

A good way to start this is to use daemontools and place this line with all environments variables in the "run" file.

NON-STANDARD STEPS ^

Turning off warnings

The warnings pragma is already used when one loads Dancer2. However, if you really do not want the warnings pragma (for example, due to an undesired warning about use of undef values), add a no warnings pragma to the appropriate block in your module or psgi file.

AUTHOR ^

Dancer Core Developers

COPYRIGHT AND LICENSE ^

This software is copyright (c) 2014 by Alexis Sukrieh.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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