Dancer - Lightweight yet powerful web application framework
#!/usr/bin/perl use Dancer; get '/hello/:name' => sub { return "Why, hello there " . params->{name}; }; dance;
The above is a basic but functional web app created with Dancer. If you want to see more examples and get up and running quickly, check out the Dancer::Cookbook.
Dancer is a web application framework designed to be as effortless as possible for the developer, taking care of the boring bits as easily as possible, yet staying out of your way and letting you get on with writing your code.
Dancer aims to provide the simplest way for writing web applications, and offers the flexibility to scale between a very simple lightweight web service consisting of a few lines of code in a single file, all the way up to a more complex fully-fledged web application with session support, templates for views and layouts, etc.
If you don't want to write CGI scripts by hand, and find Catalyst too big or cumbersome for your project, Dancer is what you need.
Dancer has few pre-requisites, so your Dancer webapps will be easy to deploy.
Dancer apps can be used with a an embedded web server (great for easy testing), and can run under PSGI/Plack for easy deployment in a variety of webserver environments.
As soon as Dancer is imported to a script, that script becomes a webapp. All the script has to do is to declare a list of routes. A route handler is composed by an HTTP method, a path pattern and a code block.
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.
Here is an example of a route definition:
get '/hello/:name' => sub { # do something important here return "Hello ".params->{name}; };
The route is defined for the method 'get', so only GET requests will be honoured by that route.
All existing HTTP methods are defined in the RFC 2616 http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html.
Here are the ones you can use to define your route handlers.
You can also use the special keyword any to define a route for multiple methods at once. For instance, you may want to define a route for both GET and POST methods, this is done like the following:
any ['get', 'post'] => '/myaction' => sub { # code };
Or even, a route handler that would match any HTTP methods:
any '/myaction' => sub { # code };
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.
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 ".params->{name}.", welcome here!"; };
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 };
A route can be defined with a Perl regular expression. The syntax is assumed to be a classic Perl regexp except for the slashes that will be escaped before running the match.
For instance, don't do '\/hello\/(.+)' but rather: '/hello/(.+)'
In order to tell Dancer to consider the route as a real regexp, the route must be defined explicitly with the keyword 'r', like the following:
get r( '/hello/([\w]+)' ) => sub { my ($name) = splat; return "Hello $name"; };
Routes may include some matching conditions (on the useragent and the hostname at the moment):
get '/foo', {agent => 'Songbird (\d\.\d)[\d\/]*?'} => sub { 'foo method for songbird' } get '/foo' => sub { 'all browsers except songbird' }
A prefix can be defined for each route handler, like this:
prefix '/home';
From here, any route handler is defined to /home/*
get '/page1' => sub {}; # will match '/home/page1'
You can unset the prefix value
prefix undef; get '/page1' => sub {}; will match /page1
Once the script is ready, you can run the webserver just by running the script. The following options are supported:
An action can choose not to serve the current request and ask Dancer to process the request with the next matching route.
This is done with the pass keyword, like in the following example
get '/say/:word' => sub { pass if (params->{word} =~ /^\d+$/); "I say a word: ".params->{word}; }; get '/say/:number' => sub { "I say a number: ".params->{number}; };
The action's return value is always considered to be the content to render. So take care to your return value.
In order to change the default behaviour of the rendering of an action, you can use the following keywords.
The redirect action is a helper and shortcut to a common HTTP response code (302). You can either redirect to a complete different site or you can also do it within the application:
get '/twitter', sub { redirect 'http://twitter.com/me'; };
You can also force Dancer to return an specific 300-ish HTTP response code:
get '/old/:resouce', sub { redirect '/new/'.params->{resource}, 301; };
By default, an action will produce an 'HTTP 200 OK' status code, meaning everything is OK. It's possible to change that with the keyword status :
get '/download/:file' => { if (! -f params->{file}) { status 'not_found'; return "File does not exist, unable to download"; } # serving the file... };
In that example, Dancer will notice that the status has changed, and will render the response accordingly.
The status keyword receives the name of the status to render, it can be either an HTTP code or its alias, as defined in Dancer::HTTP.
You can also change the content type rendered in the same maner, with the keyword content_type
get '/cat/:txtfile' => { content_type 'text/plain'; # here we can dump the contents of params->{txtfile} };
It is possible to add custom headers to responses with the header (or headers) keyword:
get '/send/header', sub { header 'X-My-Header' => 'shazam!'; }
or...
get '/send/headers', sub { headers 'X-Foo' => 'bar', X-Bar => 'foo'; }
You can use both undistinctly, they do exactly what you expect them to do.
When an error is renderered (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.
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.
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('/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 Dancer::Request module for details.
Configuring a Dancer application can be done in many ways. The easiest one (and maybe the 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' access_log: 1 show_errors: 1
And in a production one:
# appdir/environments/production.yml log: 'warning' access_log: 0 show_errors: 0
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';
A Dancer application can access the information from its config file easily with the config keyword:
get '/appname' => sub { return "This is " . config->{appname}; };
If you want to use more complex files 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 { ... };
It's possible to log messages sent by the application. In the current version, only one method is possible for logging messages but it may come in future releases new methods.
In order to enable the logging system for your application, you first have to start the logger engine in your config.yml
log: '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";
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.
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>
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.
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>
This layout can be used like the following:
use Dancer; use Template; layout 'main'; get '/' => sub { template 'index'; };
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.
By default, Dancer will automatically detect the mime-types to use for the static files accessed.
It's possible to choose specific mime-type per file extensions. For instance, we can imagine you want to serve *.foo as a text/foo content, instead of text/plain (which would be the content type detected by Dancer if *.foo are text files).
mime_type foo => 'text/foo';
This configures the 'text/foo' content type for any file matching '*.foo'.
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' };
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';
See Dancer::Config for complete details about supported settings.
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 ".params->{name}" }; # run the webserver Dancer->dance;
This module has been written by Alexis Sukrieh <sukria@cpan.org> and others, see the AUTHORS file that comes with this distribution for details.
The source code for this module is hosted on GitHub http://github.com/sukria/Dancer
Dancer depends on the following modules:
The following modules are mandatory (Dancer cannot run without them)
The following modules are optional
This module is free software and is published under the same terms as Perl itself.
The concept behind this module comes from the Sinatra ruby project, see http://www.sinatrarb.com/ for details.
To install Dancer, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Dancer
CPAN shell
perl -MCPAN -e shell install Dancer
For more information on module installation, please visit the detailed CPAN module installation guide.