Dancer(3) User Contributed Perl Documentation Dancer(3)NAMEDancer - lightweight yet powerful web application framework
SYNOPSIS
#!/usr/bin/perl
use Dancer;
get '/hello/:name' => sub {
return "Why, hello there " . param('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::Introduction and the Dancer::Cookbook. For examples on
deploying your Dancer applications, see Dancer::Deployment.
DESCRIPTIONDancer 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.
MORE DOCUMENTATION
This documentation describes all the exported symbols of Dancer. If you
want a quick start guide to discover the framework, you should look at
Dancer::Introduction, or Dancer::Tutorial to learn by example.
If you want to have specific examples of code for real-life problems,
see the Dancer::Cookbook.
If you want to see configuration examples of different deployment
solutions involving Dancer and Plack, see Dancer::Deployment.
You can find out more about the many useful plugins available for
Dancer in Dancer::Plugins.
EXPORTS
By default, "use Dancer" exports all the functions below plus sets up
your app. You can control the exporting through the normal Exporter
mechanism. For example:
# Just export the route controllers
use Dancer qw(before after get post);
# Export everything but pass to avoid clashing with Test::More
use Test::More;
use Dancer qw(!pass);
There are also some special tags to control exports and behaviour.
:moose
This will export everything except functions which clash with Moose.
Currently these are "after" and "before".
:syntax
This tells Dancer to just export symbols and not set up your app. This
is most useful for writing Dancer code outside of your main route
handler.
:tests
This will export everything except functions which clash with commonly
used testing modules. Currently these are "pass".
It can be combined with other export pragmas. For example, while
testing...
use Test::More;
use Dancer qw(:syntax :tests);
# Test::Most also exports "set" and "any"
use Test::Most;
use Dancer qw(:syntax :tests !set !any);
# Alternatively, if you want to use Dancer's set and any...
use Test::Most qw(!set !any);
use Dancer qw(:syntax :tests);
:script
This will export all the keywords, and will also load the
configuration.
This is useful when you want to use your Dancer application from a
script.
use MyApp;
use Dancer ':script';
MyApp::schema('DBSchema')->deploy();
FUNCTIONS
after
Add a hook at the after position:
after sub {
my $response = shift;
# do something with request
};
The anonymous function which is given to "after" will be executed after
having executed a route.
You can define multiple after filters, using the "after" helper as many
times as you wish; each filter will be executed, in the order you added
them.
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
};
before
Defines a before filter:
before sub {
# do something with request, vars or params
};
The anonymous function given to "before" will be executed before
executing a route handler to handle the request.
If the function modifies the request's "path_info" or "method", a new
search for a matching route is performed and the filter is re-executed.
Considering that this can lead to an infinite loop, this mechanism is
stopped after 10 times with an exception.
The before filter can set a response with a redirection code (either
301 or 302): in this case the matched route (if any) will be ignored
and the redirection will be performed immediately.
You can define multiple before filters, using the "before" helper as
many times as you wish; each filter will be executed in the order you
added them.
before_template
Defines a before_template filter:
before_template sub {
my $tokens = shift;
# do something with request, vars or params
# for example, adding a token to the template
$tokens->{token_name} = "some value";
};
The anonymous function which is given to "before_template" will be
executed before sending data and tokens to the template. Receives a
HashRef of the tokens that will be inserted into the template.
This filter works as the "before" and "after" filter.
Now the preferred way for this is to use "hook"s (namely, the
"before_template" one). Check "hook" documentation bellow.
cookies
Accesses cookies values, it returns a HashRef of Dancer::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.
debug
Logs a message of debug level:
debug "This is a debug message";
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";
false
Constant that returns a false value (0).
forward
Runs an internal redirect of the current request to another request.
This helps you avoid having to redirect the user using HTTP and set
another request to your application.
It effectively lets you chain routes together in a clean manner.
get qr{ /demo/articles/(.+) }x => sub {
my ($article_id) = splat;
# you'll have to implement this next sub yourself :)
change_the_main_database_to_demo();
forward '/articles/$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.
Broader functionality might be added in the future.
It is important to note that issuing a forward by itself does not exit
and forward immediately, forwarding is deferred until after the current
route or filter has been processed. To exit and forward immediately,
use the return function, e.g.
get '/some/path => sub {
if ($condition) {
return forward '/articles/$article_id';
}
more_stuff();
};
You probably always want to use "return" with forward.
Note that forward doesn't parse GET arguments. So, you can't use
something like:
return forward '/home?authorized=1';
But "forward" supports an optional HashRef with parameters to be added
to the actual parameters:
return forward '/home', { authorized => 1 };
Finally, you can add some more options to the 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.
return 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 ($structure)
Deserializes a YAML structure.
from_xml ($structure, %options)
Deserializes a XML structure. Can receive optional arguments. These
arguments are valid XML::Simple arguments to change the behaviour of
the default "XML::Simple::XMLin" function.
get
Defines a route for HTTP GET requests to the given path:
get '/' => sub {
return "Hello world";
}
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:
before sub {
if ($some_condition) {
return halt("Unauthorized");
}
};
get '/' => sub {
"hello there";
};
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_serialization => sub {
my $response = shift;
$response->content->{generated_at} = localtime();
};
Supported before hooks (in order of execution):
before_deserializer
This hook receives no arguments.
hook before_deserializer => sub {
...
};
before_file_render
This hook receives as argument the path of the file to render.
hook before_file_render => sub {
my $path = shift;
...
};
before_error_init
This hook receives as argument a Dancer::Error object.
hook before_error_init => sub {
my $error = shift;
...
};
before_error_render
This hook receives as argument a Dancer::Error object.
hook before_error_render => sub {
my $error = shift;
};
before
This is an alias to "before".
This hook receives no arguments.
before sub {
...
};
is equivalent to
hook before => sub {
...
};
before_template_render
This is an alias to 'before_template'.
This hook receives as argument a HashRef, containing the tokens
that will be passed to the template. You can use it to add more
tokens, or delete some specific token.
hook before_template_render => sub {
my $tokens = shift;
delete $tokens->{user};
$tokens->{time} = localtime;
};
is equivalent to
hook before_template => sub {
my $tokens = shift;
delete $tokens->{user};
$tokens->{time} = localtime;
};
before_layout_render
This hook receives two arguments. The first one is a HashRef
containing the tokens. The second is a ScalarRef representing the
content of the template.
hook before_layout_render => sub {
my ($tokens, $html_ref) = @_;
...
};
before_serialization
This hook receives as argument a Dancer::Response object.
hook before_serializer => sub {
my $response = shift;
$response->content->{start_time} = time();
};
Supported after hooks (in order of execution):
after_deserializer
This hook receives no arguments.
hook after_deserializer => sub {
...
};
after_file_render
This hook receives as argument a Dancer::Response object.
hook after_file_render => sub {
my $response = shift;
};
after_template_render
This hook receives as argument a ScalarRef representing the content
generated by the template.
hook after_template_render => sub {
my $html_ref = shift;
};
after_layout_render
This hook receives as argument a ScalarRef representing the content
generated by the layout
hook after_layout_render => sub {
my $html_ref = shift;
};
after
This is an alias for 'after'.
This hook receives as argument a Dancer::Response object.
hook after => sub {
my $response = shift;
};
This is equivalent to
after sub {
my $response = shift;
};
after_error_render
This hook receives as argument a Dancer::Response object.
hook after_error_render => sub {
my $response = shift;
};
layout
This method is deprecated. Use "set":
set layout => 'user';
logger
Deprecated. Use "<set logger =" 'console'>> to change current logger
engine.
load
Loads one or more perl scripts in the current application's namespace.
Syntactic sugar around Perl's "require":
load 'UserActions.pl', 'AdminActions.pl';
load_app
Loads a Dancer package. This method sets the libdir to the current
"./lib" directory:
# if we have lib/Webapp.pm, we can load it like:
load_app 'Webapp';
# or with options
load_app 'Forum', prefix => '/forum', settings => {foo => 'bar'};
Note that the package loaded using load_app must import Dancer with the
":syntax" option.
To load multiple apps repeat load_app:
load_app 'one';
load_app 'two';
The old way of loading multiple apps in one go (load_app 'one', 'two';)
is deprecated.
mime_type
Deprecated. See "mime".
mime
Shortcut to access the instance object of Dancer::MIME. You should read
the Dancer::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 Dancer::Request params accessor. It returns an hash reference to
all defined parameters. Check "param" bellow 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.
You should always "return" after calling "pass":
get '/some/route' => sub {
if (...) {
# we want to let the next matching route handler process this one
return pass();
}
};
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';
};
You can also force Dancer to return a specific 300-ish HTTP response
code:
get '/old/:resource', sub {
redirect '/new/'.params->{resource}, 301;
};
It is important to note that issuing a redirect by itself does not exit
and redirect immediately, redirection is deferred until after the
current route or filter has been processed. To exit and redirect
immediately, use the return function, e.g.
get '/restricted', sub {
return redirect '/login' if accessDenied();
return 'Welcome to the restricted section';
};
render_with_layout
Allows a handler to provide plain HTML (or other content), but have it
rendered within the layout still.
This method is DEPRECATED, and will be removed soon. Instead, you
should be using the "engine" keyword:
get '/foo' => sub {
# Do something which generates HTML directly (maybe using
# HTML::Table::FromDatabase or something)
my $content = ...;
# get the template engine
my $template_engine = engine 'template';
# apply the layout (not the renderer), and return the result
$template_engine->apply_layout($content)
};
It works very similarly to "template" in that you can pass tokens to be
used in the layout, and/or options to control the way the layout is
rendered. For instance, to use a custom layout:
render_with_layout $content, {}, { layout => 'layoutname' };
request
Returns a Dancer::Request object representing the current request.
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
}
}
This will not cause your route handler to return immediately, so be
careful that your route handler doesn't then override the error. You
can avoid that by saying "return send_error(...)" instead.
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 {
send_file(params->{file});
}
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:
send_file(params->{file}, content_type => 'image/png');
Also, you can use your aliases or file extension names on
"content_type", like this:
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.
send_file('/etc/passwd', system_path => 1);
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'
set_cookie
Creates or updates cookie values:
get '/some_action' => sub {
set_cookie name => 'value',
expires => (time + 3600),
domain => '.foo.com';
};
In the example above, only 'name' and 'value' are mandatory.
You can also store more complex structure in your cookies:
get '/some_auth' => sub {
set_cookie oauth => {
token => $twitter->request_token,
token_secret => $twitter->secret_token,
...
};
};
You can't store more complex structure than this. All keys in the
HashRef should be Scalars; storing references will not work.
See Dancer::Cookie for further options when creating your cookie.
Note that this method will be eventually deprecated in favor of the new
"cookie" method.
session
Provides access to all data stored in the user's session (if any).
It can also be used as a setter to store data in the session:
# getter example
get '/user' => sub {
if (session('user')) {
return "Hello, ".session('user')->name;
}
};
# setter example
post '/user/login' => sub {
...
if ($logged_in) {
session user => $user;
}
...
};
You may also need to clear a session:
# destroy session
get '/logout' => sub {
...
session->destroy;
...
};
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 Dancer::HTTP.
template
Tells the route handler to build a response with the current template
engine:
get '/' => sub {
...
template 'some_view', { token => 'value'};
};
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.tt', {}, { layout => undef };
};
Some tokens are automatically added to your template ("perl_version",
"dancer_version", "settings", "request", "params", "vars" and, if you
have sessions enabled, "session"). Check Dancer::Template::Abstract
for further details.
to_dumper ($structure)
Serializes a structure with Data::Dumper.
to_json ($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.
to_yaml ($structure)
Serializes a structure to YAML.
to_xml ($structure, %options)
Serializes a structure to XML. Can receive optional arguments. Thoses
arguments are valid XML::Simple arguments to change the behaviour of
the default "XML::Simple::XMLout" function.
true
Constant that returns a true value (1).
upload
Provides access to file uploads. Any uploaded file is accessible as a
Dancer::Request::Upload object. You can access all parsed uploads via:
post '/some/route' => sub {
my $file = upload('file_input_foo');
# file is a Dancer::Request::Upload object
};
If you named multiple input of type "file" with the same name, the
upload keyword will return an Array of Dancer::Request::Upload objects:
post '/some/route' => sub {
my ($file1, $file2) = upload('files_input');
# $file1 and $file2 are Dancer::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 Dancer::Request::Upload object
# $all_uploads->{'files_input'} is an ArrayRef of Dancer::Request::Upload objects
};
Note that you can also access the filename of the upload received via
the params keyword:
post '/some/route' => sub {
# params->{'files_input'} is the filename of the file uploaded
};
See Dancer::Request::Upload for details about the interface provided.
uri_for
Returns a fully-qualified URI for the given path:
get '/' => sub {
redirect uri_for('/path');
# can be something like: http://localhost:3000/path
};
captures
Returns a reference to a copy of "%+", if there are named captures in
the route Regexp.
Named captures are a feature of Perl 5.10, and are not supported in
earlier versions:
get qr{
/ (?<object> user | ticket | comment )
/ (?<action> delete | find )
/ (?<id> \d+ )
/?$
}x
, sub {
my $value_for = captures;
"i don't want to $$value_for{action} the $$value_for{object} $$value_for{id} !"
};
var
Defines a variable shared between filters and route handlers.
before sub {
var foo => 42;
};
Route handlers and other filters will be able to read that variable
with the "vars" keyword.
vars
Returns the HashRef of all shared variables set during the filter/route
chain:
get '/path' => sub {
if (vars->{foo} eq 42) {
...
}
};
warning
Logs a warning message through the current logger engine.
AUTHOR
This module has been written by Alexis Sukrieh <sukria@cpan.org> and
others, see the AUTHORS file that comes with this distribution for
details.
SOURCE CODE
The source code for this module is hosted on GitHub
<http://github.com/sukria/Dancer>. Feel free to fork the repository
and submit pull requests! (See Dancer::Development for details on how
to contribute).
Also, why not watch the repo
<https://github.com/sukria/Dancer/toggle_watch> to keep up to date with
the latest upcoming changes?
GETTING HELP / CONTRIBUTING
The Dancer development team can be found on #dancer on irc.perl.org:
<irc://irc.perl.org/dancer>
If you don't have an IRC client installed/configured, there is a simple
web chat client at <http://www.perldancer.org/irc> for you.
There is also a Dancer users mailing list available - subscribe at:
http://lists.perldancer.org/cgi-bin/listinfo/dancer-users
<http://lists.perldancer.org/cgi-bin/listinfo/dancer-users>
If you'd like to contribute to the Dancer project, please see
<http://www.perldancer.org/contribute> for all the ways you can help!
DEPENDENCIES
The following modules are mandatory (Dancer cannot run without them):
HTTP::Server::Simple::PSGI
HTTP::Body
LWP
MIME::Types
URI
The following modules are optional:
JSON : needed to use JSON serializer
Plack : in order to use PSGI
Template : in order to use TT for rendering views
XML::Simple and XML:SAX <XML:SAX> or <XML:Parser> for XML serialization
YAML : needed for configuration file support
LICENSE
This module is free software and is published under the same terms as
Perl itself.
SEE ALSO
Main Dancer web site: <http://perldancer.org/>.
The concept behind this module comes from the Sinatra ruby project, see
<http://www.sinatrarb.com/> for details.
perl v5.14.1 2011-07-26 Dancer(3)
