Provided by: libdancer-perl_1.3120+dfsg-1_all bug

NAME

       Dancer::Introduction - A gentle introduction to Dancer

DESCRIPTION

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

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 "~/perl5".)

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 "bin/app.pl --help" to change any settings such as the port
       number.

       View the web application at:

           http://localhost:3000

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 routes.  A route handler is composed by an HTTP
       method, a path pattern and a code block.  "strict" and "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');
           };

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

       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 get keyword.
       POST       The POST method is used to create a resource on the server. To define a POST
       action, use the post keyword.
       PUT        The PUT method is used to update an existing resource. To define a PUT action,
       use the put keyword.
       DELETE     The DELETE method requests that the origin server delete the resource
       identified by the Request-URI. To define a DELETE action, use the del keyword.

       To define a route for multiple methods you can also use the special keyword 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
           };

   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
       Dancer::Request documentation.

   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!");
           };

   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
           };

   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 "qr{}", like the following:

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

   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'
           }

   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'

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 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};
           };

   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.

   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 show_errors setting.

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

HOOKS

   Before hooks
       Before hooks 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'.

           hook '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:

           hook '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 Dancer::Request module for details.

   After hooks
       "after" hooks 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 hook is given the response object as its first argument:

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

   Before template hook
       "before_template_render" hooks are called whenever a template is going to be processed,
       they are passed the tokens hash which they can alter.

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

       The tokens hash will then be passed to the template with all the modifications performed
       by the hook. 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.

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

   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?';
           };

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

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

   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};
           };

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 {
               ...
           };

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, error and info messages
           log: 'info'      # will log info, warning and error messages
           log: 'warning'   # will log warning and error messages
           log: 'error'     # will log error messages

       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, info, warning and error functions. For instance:

           debug "This is a debug message";

USING 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', 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 (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 Dancer::Template::TemplateToolkit. If you do so, you'll also have
       to import the 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>

   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 };
           };

STATIC FILES

   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.

   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'
           };

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 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 Dancer::Config for complete details about supported settings.

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 response that is a reference 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 a reference - 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.

       JSON
           requires JSON

       YAML
           requires YAML

       XML requires XML::Simple

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

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;