libdancer-perl 1.3091+dfsg-1 / usr / share / perl5 / Dancer / Introduction.pod

=head1 NAME

Dancer::Introduction - A gentle introduction to Dancer

=head1 DESCRIPTION

Dancer is a free and open source micro web application framework written in
Perl.

=head1 INSTALL

Installation of Dancer is simple:

    perl -MCPAN -e 'install Dancer'

Thanks to the magic of cpanminus, if you do not have CPAN.pm configured, or just
want a quickfire way to get running, the following should work, at least on
Unix-like systems:

    wget -O - http://cpanmin.us | sudo perl - Dancer

(If you don't have root access, omit the 'sudo', and cpanminus will install
Dancer and prereqs into C<~/perl5>.)

=head1 SETUP

Create a web application using the dancer script:

    dancer -a MyApp

Run the web application:

    cd MyApp
    bin/app.pl

You can read the output of C<bin/app.pl --help> to change any settings such as
the port number.

View the web application at:

    http://localhost:3000

=head1 USAGE

When Dancer is imported to a script, that script becomes a webapp, and at this
point, all the script has to do is declare a list of B<routes>.  A route
handler is composed by an HTTP method, a path pattern and a code block.
C<strict> and C<warnings> pragmas are also imported with Dancer.

The code block given to the route handler has to return a string which will be
used as the content to render to the client.

Routes are defined for a given HTTP method. For each method
supported, a keyword is exported by the module.

The following is an example of a route definition. The route is defined for the
method 'get', so only GET requests will be honoured by that route:

    get '/hello/:name' => sub {
        # do something

        return "Hello ".param('name');
    };


=head2 HTTP METHODS

Here are some of the standard HTTP methods which you can use to define your
route handlers.

=over 8

=item B<GET>        The GET method retrieves information (when defining a route
                    handler for the GET method, Dancer automatically defines a
                    route handler for the HEAD method, in order to honour HEAD
                    requests for each of your GET route handlers).
                    To define a GET action, use the B<get> keyword.

=item B<POST>       The POST method is used to create a resource on the
                    server.
                    To define a POST action, use the B<post> keyword.

=item B<PUT>        The PUT method is used to update an existing resource.
                    To define a PUT action, use the B<put> keyword.

=item B<DELETE>     The DELETE method requests that the origin server delete
                    the resource identified by the Request-URI.
                    To define a DELETE action, use the B<del> keyword.

=back

To define a route for multiple methods you can also use the special keyword
B<any>. This example illustrates how to define a route for both GET and
POST methods:

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

Or even, a route handler that would match any HTTP methods:

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


=head2 ROUTE HANDLERS

The route action is the code reference declared. It can access parameters
through the `params' keyword, which returns a hashref.
This hashref is a merge of the route pattern matches and the request params.

You can have more details about how params are built and how to access them in
the L<Dancer::Request> documentation.

=head2 NAMED MATCHING

A route pattern can contain one or more tokens (a word prefixed with ':'). Each
token found in a route pattern is used as a named-pattern match. Any match will
be set in the params hashref.


    get '/hello/:name' => sub {
        "Hey ".param('name').", welcome here!";
    };

Tokens can be optional, for example:

    get '/hello/:name?' => sub {
        "Hello there " . param('name') || "whoever you are!";
    };


=head2 WILDCARDS MATCHING

A route can contain a wildcard (represented by a '*'). Each wildcard match will
be returned in an arrayref, accessible via the `splat' keyword.

    get '/download/*.*' => sub {
        my ($file, $ext) = splat;
        # do something with $file.$ext here
    };

=head2 REGULAR EXPRESSION MATCHING

A route can be defined with a Perl regular expression.

In order to tell Dancer to consider the route as a real regexp, the route must
be defined explicitly with C<qr{}>, like the following:

    get qr{/hello/([\w]+)} => sub {
        my ($name) = splat;
        return "Hello $name";
    };

=head2 CONDITIONAL MATCHING

Routes may include some matching conditions (on the useragent and the hostname
at the moment):

    get '/foo', {agent => 'Songbird (\d\.\d)[\d\/]*?'} => sub {
      'foo method for songbird'
    }

    get '/foo' => sub {
      'all browsers except songbird'
    }

=head2 PREFIX

A prefix can be defined for each route handler, like this:

    prefix '/home';

From here, any route handler is defined to /home/*

    get '/page1' => sub {}; # will match '/home/page1'

You can unset the prefix value

    prefix '/'; # or: prefix undef;
    get '/page1' => sub {}; will match /page1

Alternatively, to prevent you from ever forgetting to undef the prefix,
you can use lexical prefix like this:

    prefix '/home' => sub {
      get '/page1' => sub {}; # will match '/home/page1'
    }; ## prefix reset to previous value on exit
    
    get '/page1' => sub {}; will match /page1

=head1 ACTION SKIPPING

An action can choose not to serve the current request and ask Dancer to process
the request with the next matching route.

This is done with the B<pass> keyword, like in the following example

    get '/say/:word' => sub {
        return pass if (params->{word} =~ /^\d+$/);
        "I say a word: ".params->{word};
    };

    get '/say/:number' => sub {
        "I say a number: ".params->{number};
    };


=head2 DEFAULT ERROR PAGES

When an error is rendered (the action responded with a status code different
than 200), Dancer first looks in the public directory for an HTML file matching
the error code (eg: 500.html or 404.html).

If such a file exists, it's used to render the error, otherwise, a default
error page will be rendered on the fly.

=head2 EXECUTION ERRORS

When an error occurs during the route execution, Dancer will render an error
page with the HTTP status code 500.

It's possible either to display the content of the error message or to hide it
with a generic error page.

This is a choice left to the end-user and can be set with the
B<show_errors> setting.

Note that you can also choose to consider all warnings in your route handlers
as errors when the setting B<warnings> is set to 1.

=head1 FILTERS

=head2 Before filters

Before filters are evaluated before each request within the context of the
request and can modify the request and response. It's possible to define
variables which will be accessible in the action blocks with the keyword 'var'.

    before sub {
        var note => 'Hi there';
        request->path_info('/foo/oversee')
    };

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


For another example, this can be used along with session support to easily
give non-logged-in users a login page:

    before sub {
        if (!session('user') && request->path_info !~ m{^/login}) {
            # Pass the original path requested along to the handler:
            var requested_path => request->path_info;
            request->path_info('/login');
        }
    };


The request keyword returns the current Dancer::Request object representing the
incoming request. See the documentation of the L<Dancer::Request> module for
details.

=head2 After filters 

C<after> filters are evaluated after the response has been built by a route
handler, and can alter the response itself, just before it's sent to the
client.

The filter is given the response object as its first argument:

    after sub {
        my $response = shift;
        $response->{content} = 'after filter got here!';
    };


=head2 Before template filters

C<before_template> hooks are called whenever a template is going to be
processed, they are passed the tokens hash which they can alter.

    before_template sub {
        my $tokens = shift;
        $tokens->{foo} = 'bar';
    }

The tokens hash will then be passed to the template with all the modifications
performed by the filter. This is a good way to setup some global vars you like
to have in all your templates, like the name of the user logged in or a
section name.

=head1 CONFIGURATION AND ENVIRONMENTS

Configuring a Dancer 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, you can write all your setting calls in the file
`appdir/config.yml'. For this, you must have installed the YAML module, and of
course, write the conffile 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.yml file.

The better way 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
commandline 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

=head2 load

You can use the load method to include additional routes into your application:

    get '/go/:value', sub {
        # foo
    };

    load 'more_routes.pl';

    # then, in the file more_routes.pl:
    get '/yes', sub {
        'orly?';
    };

B<load> is just a wrapper for B<require>, but you can also specify a list of
routes files:

    load 'login_routes.pl', 'session_routes.pl', 'misc_routes.pl';

=head2 Accessing configuration data

A Dancer application can access the information from its config file easily with
the config keyword:

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


=head1 Importing just the syntax

If you want to use more complex file hierarchies, you can import just the
syntax of Dancer.

    package App;

    use Dancer;            # App may contain generic routes
    use App::User::Routes; # user-related routes

Then in App/User/Routes.pm:

    use Dancer ':syntax';

    get '/user/view/:id' => sub {
        ...
    };

=head1 LOGGING

It's possible to log messages sent by the application. In the current version,
only one method is possible for logging messages but future releases may add
additional logging methods, for instance logging to syslog.

In order to enable the logging system for your application, you first have to
start the logger engine in your config.yml

    logger: 'file'

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

    log: 'debug'     # will log debug, warning and errors
    log: 'warning'   # will log warning and errors
    log: 'error'     # will log only errors

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).

To log messages, use the debug, warning and error methods, for instance:

    debug "This is a debug message";


=head1 USING TEMPLATES

=head1 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', for instance if
your templates are located in the 'templates' directory, do the following:

    set views => path(dirname(__FILE__), 'templates');

By default, the internal template engine is used (L<Dancer::Template::Simple>)
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
L<Dancer::Template::TemplateToolkit>. If you do so, you'll also have to import
the L<Template> module in your application code. Note that Dancer configures
the Template::Toolkit engine to use <% %> brackets instead of its default
[% %] brackets, although you can change this in your config file.

All views must have a '.tt' extension. This may change in the future.

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 the request, session and route params are automatically
accessible in the view, named request, session and params):

    use Dancer;
    use Template;

    get '/hello/:name' => sub {
        template 'hello' => { number => 42 };
    };

And the appdir/views/hello.tt view can contain the following code:

   <html>
    <head></head>
    <body>
        <h1>Hello <% params.name %></h1>
        <p>Your lucky number is <% number %></p>
        <p>You are using <% request.user_agent %></p>
        <% IF session.user %>
            <p>You're logged in as <% session.user %></p>
        <% END %>
    </body>
   </html>

=head2 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. Any tokens that you defined when you called the 'template'
keyword are available in the layouts, as well as the standard session,
request, and params tokens. This allows you to insert per-page content into
the HTML boilerplate, such as page titles, current-page tags for navigation,
etc.

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

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

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

        </body>
    </html>

This layout can be used like the following:

    use Dancer;
    set layout => 'main';

    get '/' => sub {
        template 'index' => { page_title => "Your website Homepage" };
    };

Of course, if a layout is set, it can also be disabled for a specific action,
like the following:

    use Dancer;
    set layout => 'main';

    get '/nolayout' => sub {
        template 'some_ajax_view',
            { tokens_var => "42" },
            { layout => 0 };
    };

=head1 STATIC FILES

=head2 STATIC DIRECTORY

Static files are served from the ./public directory. You can specify a
different location by setting the 'public' option:

    set public => path(dirname(__FILE__), 'static');

Note that the public directory name is not included in the URL. A file
./public/css/style.css is made available as example.com/css/style.css.

=head2 STATIC FILE FROM A ROUTE HANDLER

It's possible for a route handler to send a static file, as follows:

    get '/download/*' => sub {
        my $params = shift;
        my ($file) = @{ $params->{splat} };

        send_file $file;
    };

Or even if you want your index page to be a plain old index.html file, just do:

    get '/' => sub {
        send_file '/index.html'
    };

=head1 SETTINGS

It's possible to change quite every parameter of the application via the
settings mechanism.

A setting is key/value pair assigned by the keyword B<set>:

    set setting_name => 'setting_value';

More usefully, settings can be defined in a YAML configuration file.
Environment-specific settings can also be defined in environment-specific files
(for instance, you don't want auto_reload in production, and might want extra
logging in development).  See the cookbook for examples.

See L<Dancer::Config> for complete details about supported settings.

=head1 SERIALIZERS

When writing a webservice, data serialization/deserialization is a common issue
to deal with. Dancer can automatically handle that for you, via a serializer.

When setting up a serializer, a new behaviour is authorized for any route
handler you define: any non-scalar response will be rendered as a serialized
string, via the current serializer.

Here is an example of a route handler that will return a HashRef

    use Dancer;
    set serializer => 'JSON';

    get '/user/:id/' => sub {
        { foo => 42,
          number => 100234,
          list => [qw(one two three)],
        }
    };

As soon as the content is not a scalar - and a serializer is set, which is not
the case by default - Dancer renders the response via the current
serializer.

Hence, with the JSON serializer set, the route handler above would result in a
content like the following:

    {"number":100234,"foo":42,"list":["one","two","three"]}

The following serializers are available, be aware they dynamically depend on
Perl modules you may not have on your system.

=over 4

=item B<JSON>

requires L<JSON>

=item B<YAML>

requires L<YAML>

=item B<XML>

requires L<XML::Simple>

=item B<Mutable>

will try to find the appropriate serializer using the B<Content-Type> and
B<Accept-type> header of the request.

=back

=head1 EXAMPLE

This is a possible webapp created with Dancer:

    #!/usr/bin/perl

    # make this script a webapp
    use Dancer;

    # declare routes/actions
    get '/' => sub {
        "Hello World";
    };

    get '/hello/:name' => sub {
        "Hello ".param('name');
    };

    # run the webserver
    Dancer->dance;

=cut