Provided by: libdancer2-perl_0.11+dfsg-1_all 
NAME
Dancer2::Manual - A gentle introduction to Dancer2
VERSION
version 0.11
DESCRIPTION
Dancer2 is a free and open source web application framework written in Perl.
It's a complete rewrite of Dancer, based on Moo and using a more robust and extensible fully-OO design.
It's designed to be powerful and flexible, but also easy to use - getting up and running with your web
app is trivial, and an ecosystem of adaptors for common template engines, session storage, logging
methods and plugins to make common tasks easy mean you can do what you want to do, your way, easily.
INSTALL
Installation of Dancer2 is simple:
perl -MCPAN -e 'install Dancer2'
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 - Dancer2
(If you don't have root access, omit the 'sudo', and cpanminus will install Dancer2 and prereqs into
"~/perl5".)
BOOTSTRAPPING A NEW APP
Create a web application using the dancer script:
dancer2 -a MyApp && cd MyApp
And voila! You can now run the web application:
bin/app.pl
View the web application at:
http://localhost:3000
Note that as Dancer2 supports the PSGI specification, you can also use the "plackup" tool (provided by
Plack) for launching the application:
plackup ./bin/app.pl -p 5000
USAGE
When Dancer2 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 Dancer2.
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, and is the most common
GET requests should be used for typical "fetch" requests - retrieving information. They should
not be used for requests which change data on the server or have other effects.
When defining a route handler for the GET method, Dancer2 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 replace an existing resource.
To define a PUT action, use the put keyword.
a PUT request should replace the existing resource with that specified - for instance - if you
wanted to just update an email address for a user, you'd have to specify all attributes of the
user again; to make a partial update, a "PATCH" request is used.
PATCH The PATCH method updates some attributes of an existing resource.
To define a PATCH action, use the patch 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 Dancer2::Core::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 {
defined param('name') ? "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 Dancer2 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 $name";
};
Conditional Matching
Routes may include some matching conditions (on the useragent and the hostname at the moment):
get '/foo', {agent => 'Songbird (\d\.\d)[\d\/]*?'} => sub {
'foo method for songbird'
}
get '/foo' => sub {
'all browsers except songbird'
}
Prefix
A prefix can be defined for each route handler, like this:
prefix '/home';
From here, any route handler is defined to /home/*
get '/page1' => sub {}; # will match '/home/page1'
You can unset the prefix value
prefix '/'; # or: prefix undef;
get '/page1' => sub {}; will match /page1
Alternatively, to prevent you from ever forgetting to undef the prefix, you can use lexical prefix like
this:
prefix '/home' => sub {
get '/page1' => sub {}; # will match '/home/page1'
}; ## prefix reset to previous value on exit
get '/page1' => sub {}; will match /page1
Action Skipping
An action can choose not to serve the current request and ask Dancer2 to process the request with the
next matching route.
This is done with the pass keyword, like in the following example
get '/say/:word' => sub {
return pass if (params->{word} =~ /^\d+$/);
"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), Dancer2 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, Dancer2 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
Hooks are code references (or anonymous subroutines) that are triggered at specific moments during the
resolution of a request.
Many of them are supported by the core but plugins and engines can also define their own.
Request workflow
"before" hooks are evaluated before each request within the context of the request and receives as
argument the context (a Dancer2::Core::Context object).
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';
};
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->dispatch_path !~ m{^/login}) {
# Pass the original path requested along to the handler:
forward '/login', { requested_path => request->dispatch_path };
}
};
The request keyword returns the current Dancer2::Core::Request object representing the incoming request.
"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.
This hook runs after a request has been processed, but before the response is sent.
It receives a Dancer2::Core::Response object, which it can modify if it needs to make changes to the
response which is about to be sent.
The filter is given the response object as its first argument:
hook after => sub {
my $response = shift;
$response->(content, 'after filter got here!');
};
Templates
"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 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.
"after_template_render" hooks are called after the view has been rendered. They receive as their first
argument the reference to the content that has been produced. This can be used to post-process the
content rendered by the template engine.
hook after_template_render => sub {
my $ref_content = shift;
my $content = $$ref_content;
# do something with $content
$ref_content = \$content;
};
"before_layout_render" hooks are called whenever the layout is going to be applied to the current
content. The arguments received by the hook are the current tokens hashref and a reference to the current
content.
hook before_layout_render => sub {
my ($tokens, $ref_content) = @_;
$tokens->{new_stuff} = 42;
$ref_conent = \"new content";
};
"after_layout_render" hooks are called once the complete content of the view has been produced, after the
layout has been applied to the content. The argument received by the hook is a reference to the complete
content string.
hook after_layout_render => sub {
my $ref_content = shift;
...
};
Error handling
When an error is caught by Dancer2's core, an exception object is built (of the class
Dancer2::Core::Error). This class provides hook to let the user alter the error work-flow if needed.
"init_error" hooks are called whenever an error object is built, the object is passed to the hook.
hook init_error => sub {
my $error = shift;
# do something with $error
};
This hook was named before_error_init in Dancer, and is now aliased to this hook.
"before_error" hooks are called whenever an error is going to be thrown, it receives the error object as
its first and unique argument.
hook before_error => sub {
my $error = shift;
# do something with $error
};
This hook was named before_error_render in Dancer, and is now aliased to this hook.
"after_error" hooks are called whenever an error object has been thrown, it receives a
Dancer2::Core::Response object as the first argument.
hook after_error => sub {
my $response = shift;
};
This hook was named <after_error_render in Dancer, and is now aliased to this hook.>
"on_route_exception" is called when an exception has been caught, at the route level, just before
rethrowing it higher. This hook receives a Dancer2::Core::Context and the error as arguments.
hook on_route_exception => sub {
my ($context, $error) = @_;
};
File rendering
Whenever a content is produced out of the parsing of a static file, the Dancer2::Handler::File component
is used. This component provides two hooks, "before_file_render" and "after_file_render".
"before_file_render" hooks are called just before starting to parse the file, the hook receives as its
first argument the file path that is going to be processed.
hook before_file_render => sub {
my $path = shift;
};
"after_file_render" are called after the file has been parsed and the response content produced. It
receives the response object (Dancer2::Core::Response) produced.
hook after_file_render => sub {
my $response = shift;
};
Serializers
"before_serializer" is called before serializing the content, and receives as argument the content to
serialize.
hook before_serializer => sub {
my $content = shift;
...
};
"after_serializer" is called after the payload was serialized, and receives the serialized content as an
argument.
hook after_serializer => sub {
my $content = shift;
...
};
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. You could write all your setting calls in the file `appdir/config.yml'. You
would, of course, have write the conffile in YAML.
While better than the first option, it's still not perfect. You can't easily switch from an environment
to another (for example, from development to production) without rewriting the config.yml file. The best
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,
'development' is assumed).
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
Please note that you are not limited to writing configuration files in YAML. Dancer2 supports any file
format that is supported by Config::Any, such as JSON, XML, INI files, and Apache-style config files.
Accessing configuration data
A Dancer2 application can access the information from its config file easily with the config keyword:
get '/appname' => sub {
return "This is " . config->{appname};
};
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 configuration file. Environment-specific settings can also
be defined in environment-specific files (for instance, you do not want to show error stacktraces in
production, and might want extra logging in development). See the cookbook for examples.
Serializers
When writing a webservice, data serialization/deserialization is a common issue to deal with. Dancer2 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 Dancer2;
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 -
Dancer2 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.
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 file:
logger: 'file'
Then you can choose which kind of messages you want to actually log:
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
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 methods, 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 (Dancer2::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
Dancer2::Template::TemplateToolkit. If you do so, you'll also have to import the Template module in your
application code.
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 Dancer2;
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 Dancer2;
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 Dancer2;
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'
};
DSL KEYWORDS
Dancer2 provides you with a DSL (Domain-Specific Language) which makes implementing your web application
trivial.
For example, take the following example:
use Dancer2;
get '/hello/:name' => sub {
my $name = params->{name};
};
dance;
"get" and "params" are keywords provided by Dancer2.
This document lists all keywords provided by Dancer2. It does not cover additional keywords which may be
provided by loaded plugins; see the documentation for plugins you use to see which additional keywords
they make available to you.
any
Defines a route for multiple HTTP methods at once:
any ['get', 'post'] => '/myaction' => sub {
# code
};
Or even, a route handler that would match any HTTP methods:
any '/myaction' => sub {
# code
};
cookies
Accesses cookies values, it returns a HashRef of Dancer2::Core::Cookie objects:
get '/some_action' => sub {
my $cookie = cookies->{name};
return $cookie->value;
};
In the case you have stored something else than a Scalar in your cookie:
get '/some_action' => sub {
my $cookie = cookies->{oauth};
my %values = $cookie->value;
return ($values{token}, $values{token_secret});
};
cookie
Accesses a cookie value (or sets it). Note that this method will eventually be preferred over
"set_cookie".
cookie lang => "fr-FR"; # set a cookie and return its value
cookie lang => "fr-FR", expires => "2 hours"; # extra cookie info
cookie "lang" # return a cookie value
If your cookie value is a key/value URI string, like
token=ABC&user=foo
"cookie" will only return the first part ("token=ABC") if called in scalar context. Use list context to
fetch them all:
my @values = cookie "name";
config
Accesses the configuration of the application:
get '/appname' => sub {
return "This is " . config->{appname};
};
content_type
Sets the content-type rendered, for the current route handler:
get '/cat/:txtfile' => sub {
content_type 'text/plain';
# here we can dump the contents of param('txtfile')
};
You can use abbreviations for content types. For instance:
get '/svg/:id' => sub {
content_type 'svg';
# here we can dump the image with id param('id')
};
Note that if you want to change the default content-type for every route, you have to change the
"content_type" setting instead.
dance
Alias for the "start" keyword.
dancer_version
Returns the version of Dancer. If you need the major version, do something like:
int(dancer_version);
debug
Logs a message of debug level:
debug "This is a debug message";
See Dancer2::Core::Role::Logger for details on how to configure where log messages go.
dirname
Returns the dirname of the path given:
my $dir = dirname($some_path);
engine
Given a namespace, returns the current engine object
my $template_engine = engine 'template';
my $html = $template_engine->apply_renderer(...);
$template_engine->apply_layout($html);
error
Logs a message of error level:
error "This is an error message";
See Dancer2::Core::Role::Logger for details on how to configure where log messages go.
false
Constant that returns a false value (0).
forward
Runs an "internal redirect" of the current request to another request. More formally; when the "forward"
is executed, the current dispatch of the request is aborted, the request is modified (altering query
params or request method), and the modified request is dispatched again. Any remaining code (route and
hooks) from the current dispatch will never be run and the modified request's dispatch will execute hooks
for the new request normally.
It effectively lets you chain routes together in a clean manner.
get '/demo/articles/:article_id' => sub {
# you'll have to implement this next sub yourself :)
change_the_main_database_to_demo();
forward "/articles/" . params->{article_id};
};
In the above example, the users that reach /demo/articles/30 will actually reach /articles/30 but we've
changed the database to demo before.
This is pretty cool because it lets us retain our paths and offer a demo database by merely going to
/demo/....
You'll notice that in the example we didn't indicate whether it was GET or POST. That is because
"forward" chains the same type of route the user reached. If it was a GET, it will remain a GET (but if
you do need to change the method, you can do so; read on below for details.)
WARNING : Any code after a c<forward> is ignored, until the end of the route. It's not necessary to use
"return" with c<forward> anymore.
get '/foo/:article_id' => sub {
if ($condition) {
forward "/articles/" . params->{article_id};
# The following code WILL NOT BE executed
do_stuff();
}
more_stuff();
};
Note that c<forward> doesn't parse GET arguments. So, you can't use something like:
forward '/home?authorized=1';
But "forward" supports an optional HashRef with parameters to be added to the actual parameters:
forward '/home', { authorized => 1 };
Finally, you can add some more options to the c<forward> method, in a third argument, also as a HashRef.
That option is currently only used to change the method of your request. Use with caution.
forward '/home', { auth => 1 }, { method => 'POST' };
from_dumper ($structure)
Deserializes a Data::Dumper structure.
from_json ($structure, \%options)
Deserializes a JSON structure. Can receive optional arguments. Those arguments are valid JSON arguments
to change the behaviour of the default "JSON::from_json" function.
from_yaml ($structure)
Deserializes a YAML structure.
get
Defines a route for HTTP GET requests to the given path:
get '/' => sub {
return "Hello world";
}
Note that a route to match HEAD requests is automatically created as well.
halt
Sets a response object with the content given.
When used as a return value from a filter, this breaks the execution flow and renders the response
immediately:
hook before => sub {
if ($some_condition) {
halt("Unauthorized");
# This code is not executed :
do_stuff();
}
};
get '/' => sub {
"hello there";
};
WARNING : Issuing a halt immediately exits the current route, and perform the halt. Thus, any code after
a halt is ignored, until the end of the route. So it's not necessary anymore to use "return" with halt.
headers
Adds custom headers to responses:
get '/send/headers', sub {
headers 'X-Foo' => 'bar', X-Bar => 'foo';
}
header
adds a custom header to response:
get '/send/header', sub {
header 'x-my-header' => 'shazam!';
}
Note that it will overwrite the old value of the header, if any. To avoid that, see "push_header".
push_header
Do the same as "header", but allow for multiple headers with the same name.
get '/send/header', sub {
push_header 'x-my-header' => '1';
push_header 'x-my-header' => '2';
will result in two headers "x-my-header" in the response
}
hook
Adds a hook at some position. For example :
hook before_serializer => sub {
my $content = shift;
...
};
There can be multiple hooks assigned to a given position, and each will be executed in order.
info
Logs a message of info level:
info "This is a info message";
See Dancer2::Core::Role::Logger for details on how to configure where log messages go.
load
Loads one or more perl scripts in the current application's namespace. Syntactic sugar around Perl's
"require":
load 'UserActions.pl', 'AdminActions.pl';
mime
Shortcut to access the instance object of Dancer2::Core::MIME. You should read the Dancer2::Core::MIME
documentation for full details, but the most commonly-used methods are summarized below:
# set a new mime type
mime->add_type( foo => 'text/foo' );
# set a mime type alias
mime->add_alias( f => 'foo' );
# get mime type for an alias
my $m = mime->for_name( 'f' );
# get mime type for a file (based on extension)
my $m = mime->for_file( "foo.bar" );
# get current defined default mime type
my $d = mime->default;
# set the default mime type using config.yml
# or using the set keyword
set default_mime_type => 'text/plain';
params
This method should be called from a route handler. It's an alias for the Dancer2::Core::Request params
accessor. It returns an hash reference to all defined parameters. Check "param" below to access quickly
to a single parameter value.
param
This method should be called from a route handler. This method is an accessor to the parameters hash
table.
post '/login' => sub {
my $username = param "user";
my $password = param "pass";
# ...
}
pass
This method should be called from a route handler. Tells Dancer to pass the processing of the request to
the next matching route.
WARNING : Issuing a pass immediately exits the current route, and perform the pass. Thus, any code after
a pass is ignored, until the end of the route. So it's not necessary anymore to use "return" with pass.
get '/some/route' => sub {
if (...) {
# we want to let the next matching route handler process this one
pass(...);
# This code will be ignored
do_stuff();
}
};
patch
Defines a route for HTTP PATCH requests to the given URL:
patch '/resource' => sub { ... };
("PATCH" is a relatively new and not-yet-common HTTP verb, which is intended to work as a "partial-PUT",
transferring just the changes; please see <http://tools.ietf.org/html/rfc5789|RFC5789> for further
details.)
Please be aware that, if you run your app in standalone mode, "PATCH" requests will not reach your app
unless you have a new version of HTTP::Server::Simple which accepts "PATCH" as a valid verb. The current
version at time of writing, 0.44, does not. A pull request has been submitted to add this support, which
you can find at:
<https://github.com/bestpractical/http-server-simple/pull/1>
path
Concatenates multiple paths together, without worrying about the underlying operating system:
my $path = path(dirname($0), 'lib', 'File.pm');
It also normalizes (cleans) the path aesthetically. It does not verify the path exists.
post
Defines a route for HTTP POST requests to the given URL:
post '/' => sub {
return "Hello world";
}
prefix
Defines a prefix 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
For a safer alternative you can use lexical prefix like this:
prefix '/home' => sub {
## Prefix is set to '/home' here
get ...;
get ...;
};
## prefix reset to the previous version here
This makes it possible to nest prefixes:
prefix '/home' => sub {
## some routes
prefix '/private' => sub {
## here we are under /home/private...
## some more routes
};
## back to /home
};
## back to the root
Notice: once you have a prefix set, do not add a caret to the regex:
prefix '/foo';
get qr{^/bar} => sub { ... } # BAD BAD BAD
get qr{/bar} => sub { ... } # Good!
del
Defines a route for HTTP DELETE requests to the given URL:
del '/resource' => sub { ... };
options
Defines a route for HTTP OPTIONS requests to the given URL:
options '/resource' => sub { ... };
put
Defines a route for HTTP PUT requests to the given URL:
put '/resource' => sub { ... };
redirect
Generates a HTTP redirect (302). You can either redirect to a complete different site or within the
application:
get '/twitter', sub {
redirect 'http://twitter.com/me';
# Any code after the redirect will not be executed.
};
WARNING : Issuing a c<redirect> immediately exits the current route. Thus, any code after a c<redirect>
is ignored, until the end of the route. So it's not necessary anymore to use "return" with c<redirect>.
You can also force Dancer to return a specific 300-ish HTTP response code:
get '/old/:resource', sub {
redirect '/new/'.params->{resource}, 301;
};
request
Returns a Dancer2::Core::Request object representing the current request.
See the Dancer2::Core::Request documentation for the methods you can call, for example:
request->referer; # value of the HTTP referer header
request->remote_address; # user's IP address
request->user_agent; # User-Agent header value
send_error
Returns a HTTP error. By default the HTTP code returned is 500:
get '/photo/:id' => sub {
if (...) {
send_error("Not allowed", 403);
} else {
# return content
}
}
WARNING : Issuing a send_error immediately exits the current route, and perform the send_error. Thus, any
code after a send_error is ignored, until the end of the route. So it's not necessary anymore to use
"return" with send_error.
get '/some/route' => sub {
if (...) {
# we want to let the next matching route handler process this one
send_error(..);
# This code will be ignored
do_stuff();
}
};
send_file
Lets the current route handler send a file to the client. Note that the path of the file must be relative
to the public directory unless you use the "system_path" option (see below).
get '/download/:file' => sub {
return send_file(params->{file});
}
WARNING : Issuing a send_file immediately exits the current route, and perform the send_file. Thus, any
code after a send_file is ignored, until the end of the route. So it's not necessary anymore to use
"return" with send_file.
get '/some/route' => sub {
if (...) {
# we want to let the next matching route handler process this one
send_file(...);
# This code will be ignored
do_stuff();
}
};
Send file supports streaming possibility using PSGI streaming. The server should support it but normal
streaming is supported on most, if not all.
get '/download/:file' => sub {
return send_file( params->{file}, streaming => 1 );
}
You can control what happens using callbacks.
First, "around_content" allows you to get the writer object and the chunk of content read, and then
decide what to do with each chunk:
get '/download/:file' => sub {
return send_file(
params->{file},
streaming => 1,
callbacks => {
around_content => sub {
my ( $writer, $chunk ) = @_;
$writer->write("* $chunk");
},
},
);
}
You can use "around" to all get all the content (whether a filehandle if it's a regular file or a full
string if it's a scalar ref) and decide what to do with it:
get '/download/:file' => sub {
return send_file(
params->{file},
streaming => 1,
callbacks => {
around => sub {
my ( $writer, $content ) = @_;
# we know it's a text file, so we'll just stream
# line by line
while ( my $line = <$content> ) {
$writer->write($line);
}
},
},
);
}
Or you could use "override" to control the entire streaming callback request:
get '/download/:file' => sub {
return send_file(
params->{file},
streaming => 1,
callbacks => {
override => sub {
my ( $respond, $response ) = @_;
my $writer = $respond->( [ $newstatus, $newheaders ] );
$writer->write("some line");
},
},
);
}
You can also set the number of bytes that will be read at a time (default being 42K bytes) using "bytes":
get '/download/:file' => sub {
return send_file(
params->{file},
streaming => 1,
bytes => 524288, # 512K
);
};
The content-type will be set depending on the current MIME types definition (see "mime" if you want to
define your own).
If your filename does not have an extension, or you need to force a specific mime type, you can pass it
to "send_file" as follows:
return send_file(params->{file}, content_type => 'image/png');
Also, you can use your aliases or file extension names on "content_type", like this:
return send_file(params->{file}, content_type => 'png');
For files outside your public folder, you can use the "system_path" switch. Just bear in mind that its
use needs caution as it can be dangerous.
return send_file('/etc/passwd', system_path => 1);
If you have your data in a scalar variable, "send_file" can be useful as well. Pass a reference to that
scalar, and "send_file" will behave as if there was a file with that contents:
return send_file( \$data, content_type => 'image/png' );
Note that Dancer is unable to guess the content type from the data contents. Therefore you might need to
set the "content_type" properly. For this kind of usage an attribute named "filename" can be useful. It
is used as the Content-Disposition header, to hint the browser about the filename it should use.
return send_file( \$data, content_type => 'image/png'
filename => 'onion.png' );
Note that you should always use "return send_file ..." to stop execution of your route handler at that
point.
set
Defines a setting:
set something => 'value';
You can set more than one value at once:
set something => 'value', otherthing => 'othervalue';
setting
Returns the value of a given setting:
setting('something'); # 'value'
session
Provides access to all data stored in the user's session (if any).
It can also be used as a setter to store data in the session:
# getter example
get '/user' => sub {
if (session('user')) {
return "Hello, ".session('user')->name;
}
};
# setter example
post '/user/login' => sub {
...
if ($logged_in) {
session user => $user;
}
...
};
You may also need to clear a session:
# destroy session
get '/logout' => sub {
...
context->destroy_session;
...
};
If you need to fetch the session ID being used for any reason:
my $id = session->id;
splat
Returns the list of captures made from a route handler with a route pattern which includes wildcards:
get '/file/*.*' => sub {
my ($file, $extension) = splat;
...
};
There is also the extensive splat (A.K.A. "megasplat"), which allows extensive greedier matching,
available using two asterisks. The additional path is broken down and returned as an ArrayRef:
get '/entry/*/tags/**' => sub {
my ( $entry_id, $tags ) = splat;
my @tags = @{$tags};
};
This helps with chained actions:
get '/team/*/**' => sub {
my ($team) = splat;
var team => $team;
pass;
};
prefix '/team/*';
get '/player/*' => sub {
my ($player) = splat;
# etc...
};
get '/score' => sub {
return score_for( vars->{'team'} );
};
start
Starts the application or the standalone server (depending on the deployment choices).
This keyword should be called at the very end of the script, once all routes are defined. At this point,
Dancer takes over control.
status
Changes the status code provided by an action. By default, an action will produce an "HTTP 200 OK"
status code, meaning everything is OK:
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 either a numeric status code or its name in lower case, with underscores as a
separator for blanks - see the list in "HTTP CODES" in Dancer2::Core::HTTP.
template
Returns the response of processing the given template with the given parameters (and optional settings),
wrapping it in the default or specified layout too, if layouts are in use.
An example of a route handler which returns the result of using template to build a response with the
current template engine:
get '/' => sub {
...
return template 'some_view', { token => 'value'};
};
Note that "template" simply returns the content, so when you use it in a route handler, if execution of
the route handler should stop at that point, make sure you use 'return' to ensure your route handler
returns the content.
Since template just returns the result of rendering the template, you can also use it to perform other
templating tasks, e.g. generating emails:
post '/some/route' => sub {
if (...) {
email {
to => 'someone@example.com',
from => 'foo@example.com',
subject => 'Hello there',
msg => template('emails/foo', { name => params->{name} }),
};
return template 'message_sent';
} else {
return template 'error';
}
};
Compatibility notice: "template" was changed in version 1.3090 to immediately interrupt execution of a
route handler and return the content, as it's typically used at the end of a route handler to return
content. However, this caused issues for some people who were using "template" to generate emails etc,
rather than accessing the template engine directly, so this change has been reverted in 1.3091.
The first parameter should be a template available in the views directory, the second one (optional) is a
HashRef of tokens to interpolate, and the third (again optional) is a HashRef of options.
For example, to disable the layout for a specific request:
get '/' => sub {
template 'index', {}, { layout => undef };
};
Or to request a specific layout, of course:
get '/user' => sub {
template 'user', {}, { layout => 'user' };
};
Some tokens are automatically added to your template ("perl_version", "dancer_version", "settings",
"request", "params", "vars" and, if you have sessions enabled, "session"). Check
Dancer2::Core::Role::Template for further details.
to_dumper ($structure)
Serializes a structure with Data::Dumper.
Calling this function will not trigger the serialization's hooks.
to_json ($structure, \%options)
Serializes a structure to JSON. Can receive optional arguments. Thoses arguments are valid JSON arguments
to change the behaviour of the default "JSON::to_json" function.
Calling this function will not trigger the serialization's hooks.
to_yaml ($structure)
Serializes a structure to YAML.
Calling this function will not trigger the serialization's hooks.
true
Constant that returns a true value (1).
upload
Provides access to file uploads. Any uploaded file is accessible as a Dancer2::Core::Request::Upload
object. You can access all parsed uploads via:
post '/some/route' => sub {
my $file = upload('file_input_foo');
# file is a Dancer2::Core::Request::Upload object
};
If you named multiple input of type "file" with the same name, the upload keyword will return an Array of
Dancer2::Core::Request::Upload objects:
post '/some/route' => sub {
my ($file1, $file2) = upload('files_input');
# $file1 and $file2 are Dancer2::Core::Request::Upload objects
};
You can also access the raw HashRef of parsed uploads via the current request object:
post '/some/route' => sub {
my $all_uploads = request->uploads;
# $all_uploads->{'file_input_foo'} is a Dancer2::Core::Request::Upload object
# $all_uploads->{'files_input'} is an ArrayRef of Dancer2::Core::Request::Upload objects
};
Note that you can also access the filename of the upload received via the params keyword:
post '/some/route' => sub {
# params->{'files_input'} is the filename of the file uploaded
};
See Dancer2::Core::Request::Upload for details about the interface provided.
uri_for
Returns a fully-qualified URI for the given path:
get '/' => sub {
redirect uri_for('/path');
# can be something like: http://localhost:3000/path
};
captures
Returns a reference to a copy of "%+", if there are named captures in the route Regexp.
Named captures are a feature of Perl 5.10, and are not supported in earlier versions:
get qr{
/ (?<object> user | ticket | comment )
/ (?<action> delete | find )
/ (?<id> \d+ )
/?$
}x
, sub {
my $value_for = captures;
"i don't want to $$value_for{action} the $$value_for{object} $$value_for{id} !"
};
var
Provides an accessor for variables shared between filters and route handlers. Given a key/value pair, it
sets a variable:
hook before sub {
var foo => 42;
};
Later, route handlers and other filters will be able to read that variable:
get '/path' => sub {
my $foo = var 'foo';
...
};
vars
Returns the HashRef of all shared variables set during the filter/route chain with the "var" keyword:
get '/path' => sub {
if (vars->{foo} eq 42) {
...
}
};
warning
Logs a warning message through the current logger engine:
warning "This is a warning";
See Dancer2::Core::Role::Logger for details on how to configure where log messages go.
AUTHOR
Dancer Core Developers
COPYRIGHT AND LICENSE
This software is copyright (c) 2013 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.
perl v5.18.1 2013-12-15 Dancer2::Manual(3pm)