Provided by: libdancer-perl_1.3202+dfsg-1_all 
NAME
Dancer::Cookbook - a quick-start guide to the Dancer web framework
VERSION
version 1.3202
DESCRIPTION
A quick-start guide with examples to get you up and running with the Dancer web framework.
BEGINNER'S DANCE
Your first Dancer web app
Dancer has been designed to be easy to work with. It's trivial to write a simple web app,
but still has the power to work with larger projects. To start with, let's make an
incredibly simple "Hello World" example:
#!/usr/bin/perl
use Dancer;
get '/hello/:name' => sub {
return "Why, hello there " . params->{name};
};
dance;
Yes, the above is a fully-functioning web app; running that script will launch a webserver
listening on the default port (3000). Now you can make a request
$ curl http://localhost:3000/hello/Bob
Why, hello there Bob
(or the name of the machine you ran it on, if it's not your local system), and it will say
hello. The ":name" part is a named parameter within the route specification whose value
is made available through "params" - more on that later.
Note that you don't need to use the "strict" and "warnings" pragma, they are already
loaded by Dancer. (If you don't want the "warnings" pragma (which can lead to undesired
warnings about use of undef values, for example), then set the import_warnings setting to
a false value.
Starting a Dancer project
The first simple example is fine for trivial projects, but for anything more complex
you'll want a more maintainable solution - enter the "dancer" helper script, which will
build the framework of your application with a single command:
$ dancer -a mywebapp
+ mywebapp
+ mywebapp/bin
+ mywebapp/bin/app.pl
+ mywebapp/config.yml
+ mywebapp/environments
+ mywebapp/environments/development.yml
+ mywebapp/environments/production.yml
+ mywebapp/views
+ mywebapp/views/index.tt
+ mywebapp/views/layouts
+ mywebapp/views/layouts/main.tt
+ mywebapp/MANIFEST.SKIP
+ mywebapp/lib
+ mywebapp/lib/mywebapp.pm
+ mywebapp/public
+ mywebapp/public/css
+ mywebapp/public/css/style.css
+ mywebapp/public/css/error.css
+ mywebapp/public/images
+ mywebapp/public/500.html
+ mywebapp/public/404.html
+ mywebapp/public/dispatch.fcgi
+ mywebapp/public/dispatch.cgi
+ mywebapp/public/javascripts
+ mywebapp/public/javascripts/jquery.min.js
+ mywebapp/t
+ mywebapp/t/002_index_route.t
+ mywebapp/t/001_base.t
+ mywebapp/Makefile.PL
As you can see, it creates a directory named after the name of the app, along with a
configuration file, a views directory (where your templates and layouts will live), an
environments directory (where environment-specific settings live), a module containing the
actual guts of your application, a script to start it - or to run your web app via
Plack/PSGI - more on that later.
DANCE ROUTINES: ROUTES
Declaring routes
To control what happens when a web request is received by your webapp, you'll need to
declare "routes". A route declaration indicates for which HTTP method(s) it is valid, the
path it matches (e.g. /foo/bar), and a coderef to execute, which returns the response.
get '/hello/:name' => sub {
return "Hi there " . params->{name};
};
The above route specifies that, for GET requests to '/hello/...', the code block provided
should be executed.
Handling multiple HTTP request methods
Routes can use "any" to match all, or a specified list of HTTP methods.
The following will match any HTTP request to the path /myaction:
any '/myaction' => sub {
# code
}
The following will match GET or POST requests to /myaction:
any ['get', 'post'] => '/myaction' => sub {
# code
};
For convenience, any route which matches GET requests will also match HEAD requests.
Retrieving request parameters
The params keyword returns a hashref of request parameters; these will be parameters
supplied on the query string, within the path itself (with named placeholders), and, for
HTTP POST requests, the content of the POST body.
Named parameters in route path declarations
As seen above, you can use ":somename" in a route's path to capture part of the path; this
will become available by calling params.
So, for a web app where you want to display information on a company, you might use
something like:
get '/company/view/:companyid' => sub {
my $company_id = params->{companyid};
# Look up the company and return appropriate page
};
Wildcard path matching and splat
You can also declare wildcards in a path, and retrieve the values they matched with the
splat keyword:
get '/*/*' => sub {
my ($action, $id) = splat;
if (my $action eq 'view') {
return display_item($id);
} elsif ($action eq 'delete') {
return delete_item($id);
} else {
status 'not_found';
return "What?";
}
};
Before hooks - processed before a request
A before hook declares code which should be handled before a request is passed to the
appropriate route.
hook 'before' => sub {
var note => 'Hi there';
request->path_info('/foo/oversee')
};
get '/foo/*' => sub {
my ($match) = splat; # 'oversee';
vars->{note}; # 'Hi there'
};
The above declares a before hook which uses "var" to set a variable which will later be
available within the route handler, then amends the path of the request to "/foo/oversee";
this means that, whatever path was requested, it will be treated as though the path
requested was "/foo/oversee".
Default route
In case you want to avoid a 404 error, or handle multiple routes in the same way and you
don't feel like configuring all of them, you can set up a default route handler.
The default route handler will handle any request that doesn't get served by any other
route.
All you need to do is set up the following route as the last route:
any qr{.*} => sub {
status 'not_found';
template 'special_404', { path => request->path };
};
Then you can set up the template as such:
You tried to reach <% path %>, but it is unavailable at the moment.
Please try again or contact us at our email at <...>.
Using the auto_page feature for automatic route creation
For simple "static" pages, you can simply enable the "auto_page" config setting; this
means that you need not declare a route handler for those pages; if a request is for
"/foo/bar", Dancer will check for a matching view (e.g. "/foo/bar.tt" and render it with
the default layout etc if found. For full details, see the documentation for the
auto_page setting.
Why should I use the Ajax plugin
As an Ajax query is just an HTTP query, it's similar to a GET or POST route. You may ask
yourself why you may want to use the "ajax" keyword (from the Dancer::Plugin::Ajax plugin)
instead of a simple "get".
Let's say you have a path like '/user/:user' in your application. You may want to be able
to serve this page, with a layout and HTML content. But you may also want to be able to
call this same url from a javascript query using Ajax.
So, instead of having the following code:
get '/user/:user' => sub {
if (request->is_ajax) {
# create xml, set headers to text/xml, blablabla
header('Content-Type' => 'text/xml');
header('Cache-Control' => 'no-store, no-cache, must-revalidate');
to_xml({...})
}else{
template users, {....}
}
};
you can have
get '/user/:user' => sub {
template users, {...}
}
and
ajax '/user/:user' => sub {
to_xml({...}, RootName => undef);
}
Because it's an Ajax query you know you need to return XML content, so the content type of
the response is set for you.
Using the prefix feature to split your application
For better maintainability you may want to separate some of your application components to
different packages. Let's say we have a simple web app with an admin section, and want to
maintain this in a different package:
package myapp;
use Dancer ':syntax';
use myapp::admin;
prefix undef;
get '/' => sub {...};
1;
package myapp::admin;
use Dancer ':syntax';
prefix '/admin';
get '/' => sub {...};
1;
The following routes will be generated for us:
- get /
- get /admin/
- head /
- head /admin/
MUSCLE MEMORY: STORING DATA
Handling sessions
It's common to want to use sessions to give your web applications state; for instance,
allowing a user to log in, creating a session, and checking that session on subsequent
requests.
To make use of sessions you must first enable the session engine. Pick the session engine
you want to use, then declare it in your config file:
session: Simple
The Dancer::Session::Simple backend implements very simple in-memory session storage.
This will be fast and useful for testing, but sessions do not persist between restarts of
your app.
You can also use the Dancer::Session::YAML backend included with Dancer, which stores
session data on disc in YAML files (since YAML is a nice human-readable format, it makes
inspecting the contents of sessions a breeze):
session: YAML
Or, to enable session support from within your code,
set session => 'YAML';
(Controlling settings is best done from your config file, though). 'YAML' in the example
is the session backend to use; this is shorthand for Dancer::Session::YAML. There are
other session backends you may wish to use, for instance Dancer::Session::Memcache, but
the YAML backend is a simple and easy to use example which stores session data in a YAML
file in sessions).
You can then use the session keyword to manipulate the session:
Storing data in the session
Storing data in the session is as easy as:
session varname => 'value';
Retrieving data from the session
Retrieving data from the session is as easy as:
session('varname')
Or, alternatively,
session->{varname}
Controlling where sessions are stored
For disc-based session back ends like Dancer::Session::YAML, Dancer::Session::Storable
etc, session files are written to the session dir specified by the "session_dir" setting,
which defaults to "appdir/sessions".
If you need to control where session files are created, you can do so quickly and easily
within your config file. For example:
session_dir: /tmp/dancer-sessions
If the directory you specify does not exist, Dancer will attempt to create it for you.
Destroying a session
When you're done with your session, you can destroy it:
session->destroy
Sessions and logging in
A common requirement is to check the user is logged in, and, if not, require them to log
in before continuing.
This can easily be handled with a before hook to check their session:
hook 'before' => sub {
if (! session('user') && request->path_info !~ m{^/login}) {
var requested_path => request->path_info;
request->path_info('/login');
}
};
get '/login' => sub {
# Display a login page; the original URL they requested is available as
# vars->{requested_path}, so could be put in a hidden field in the form
template 'login', { path => vars->{requested_path} };
};
post '/login' => sub {
# Validate the username and password they supplied
if (params->{user} eq 'bob' && params->{pass} eq 'letmein') {
session user => params->{user};
redirect params->{path} || '/';
} else {
redirect '/login?failed=1';
}
};
In your login page template, you'll want a text field named user, a password field named
pass, and a hidden field named path, which will be populated with the path originally
requested, so that it's sent back in the POST submission, and can be used by the post
route to redirect onwards to the page originally requested once you're logged in.
Of course you'll probably want to validate your users against a database table, or maybe
via IMAP/LDAP/SSH/POP3/local system accounts via PAM etc. Authen::Simple is probably a
good starting point here!
A simple working example of handling authentication against a database table yourself
(using Dancer::Plugin::Database which provides the "database" keyword, and
Crypt::SaltedHash to handle salted hashed passwords (well, you wouldn't store your users'
passwords in the clear, would you?)) follows:
post '/login' => sub {
my $user = database->quick_select('users',
{ username => params->{user} }
);
if (!$user) {
warning "Failed login for unrecognised user " . params->{user};
redirect '/login?failed=1';
} else {
if (Crypt::SaltedHash->validate($user->{password}, params->{pass}))
{
debug "Password correct";
# Logged in successfully
session user => $user;
redirect params->{path} || '/';
} else {
debug("Login failed - password incorrect for " . params->{user});
redirect '/login?failed=1';
}
}
};
Retrieve complete hash stored in session
Get complete hash stored in session:
my $hash = session;
APPEARANCE
Using templates - views and layouts
Returning plain content is all well and good for examples or trivial apps, but soon you'll
want to use templates to maintain separation between your code and your content. Dancer
makes this easy.
Your route handlers can use the template keyword to render 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'.
By default, the internal template engine Dancer::Template::Simple is used, 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, by default, Dancer configures the Template::Toolkit engine to use "<% %">
brackets instead of its default "[% %]" brackets. You can change this by using the
following in your config file:
template: template_toolkit
engines:
template_toolkit:
start_tag: '[%'
stop_tag: '%]'
All views must have a '.tt' extension. This may change in the future.
To render a view just call the "template|Dancer/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
for convenience, the request, session, params and vars are automatically accessible in the
view, named "request", "session", "params" and "vars"). For example:
hook 'before' => sub { var time => scalar(localtime) };
get '/hello/:name' => sub {
my $name = params->{name};
template 'hello.tt', { name => $name };
};
The template 'hello.tt' could contain, for example:
<p>Hi there, <% name %>!</p>
<p>You're using <% request.user_agent %></p>
<% IF session.username %>
<p>You're logged in as <% session.username %>
<% END %>
It's currently <% vars.time %>
For a full list of the tokens automatically added to your template (like "session",
"request" and "vars", refer to Dancer::Template::Abstract).
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 to render
the action view. This lets you define a global layout for your actions, and have each
individual view contain only the specific content. This is a good thing to avoid lots of
needless duplication of HTML :)
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>
You can tell your app which layout to use with "layout: name" in the config file, or
within your code:
set layout => 'main';
You can control which layout to use (or whether to use a layout at all) for a specific
request without altering the layout setting by passing an options hashref as the third
param to the template keyword:
template 'index.tt', {}, { layout => undef };
If your application is not mounted under root (/), you can use a before_template_render
hook instead of hardcoding the path to your application for your css, images and
javascript:
hook 'before_template_render' => sub {
my $tokens = shift;
$tokens->{uri_base} = request->base->path;
};
Then in your layout, modify your css inclusion as follows:
<link rel="stylesheet" href="<% uri_base %>/css/style.css" />
From now on, you can mount your application wherever you want, without any further
modification of the css inclusion
template and unicode
If you use Plack and have some unicode problem with your Dancer application, don't forget
to check if you have set your template engine to use unicode, and set the default charset
to UTF-8. So, if you are using template toolkit, your config.yml will look like this:
charset: UTF-8
engines:
template_toolkit:
ENCODING: utf8
TT's WRAPPER directive in Dancer (META variables, SETs)
Dancer already provides a WRAPPER-like ability, which we call a "layout". The reason we do
not use TT's WRAPPER (which also makes it incompatible with Dancer) is because not all
template systems support it. Actually, most don't.
However, you might want to use it, and be able to define META variables and regular
Template::Toolkit variables.
These few steps will get you there:
• Disable the layout in Dancer
You can do this by simply commenting (or removing) the "layout" configuration in the
config.yml file.
• Use Template Toolkit template engine
Change the configuration of the template to Template Toolkit:
# in config.yml
template: "template_toolkit"
• Tell the Template Toolkit engine who's your wrapper
# in config.yml
# ...
engines:
template_toolkit:
WRAPPER: layouts/main.tt
Done! Everything will work fine out of the box, including variables and META variables.
SETTING THE STAGE: CONFIGURATION AND LOGGING
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 define all your settings in the file `appdir/config.yml'.
For this, you must have installed the YAML module, and of course, write the config file in
YAML.
That's better than the first option, but it's still not perfect as you can't switch easily
from one 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" command line
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
Accessing configuration information from your app
A Dancer application can use the 'config' keyword to easily access the settings within its
config file, for instance:
get '/appname' => sub {
return "This is " . config->{appname};
};
This makes keeping your application's settings all in one place simple and easy. You
shouldn't need to worry about implementing all that yourself :)
Accessing configuration information from a separate script
You may well want to access your webapp's configuration from outside your webapp. You
could, of course, use the YAML module of your choice and load your webapps's config.yml,
but chances are that this is not convenient.
Use Dancer instead. Without any ado, magic or too big jumps, you can use the values from
config.yml and some additional default values:
# bin/script1.pl
use Dancer ':script';
print "template:".config->{template}."\n"; #simple
print "log:".config->{log}."\n"; #undef
Note that config->{log} should result in an undef error on a default scaffold since you
did not load the environment and in the default scaffold log is defined in the environment
and not in config.yml. Hence undef.
If you want to load an environment you need to tell Dancer where to look for it. One way
to do so, is to tell Dancer where the webapp lives. From there Dancer deduces where the
config.yml file is (typically $webapp/config.yml).
# bin/script2.pl
use FindBin;
use Cwd qw/realpath/;
use Dancer ':script';
#tell the Dancer where the app lives
my $appdir=realpath( "$FindBin::Bin/..");
Dancer::Config::setting('appdir',$appdir);
Dancer::Config::load();
#getter
print "environment:".config->{environment}."\n"; #development
print "log:".config->{log}."\n"; #value from development environment
By default Dancer loads development environment (typically
$webapp/environment/development.yml). In contrast to the example before, you do have a
value from the development environment (environment/development.yml) now. Also note that
in the above example Cwd and FindBin are used. They are likely to be already loaded by
Dancer anyways, so it's not a big overhead. You could just as well hand over a simple path
for the app if you like that better, e.g.:
Dancer::Config::setting('appdir','/path/to/app/dir');
If you want to load an environment other than the default, try this:
# bin/script2.pl
use Dancer ':script';
#tell the Dancer where the app lives
Dancer::Config::setting('appdir','/path/to/app/dir');
#which environment to load
config->{environment}='production';
Dancer::Config::load();
#getter
print "log:".config->{log}."\n"; #has value from production environment
By the way, you not only get values, you can also set values straightforward like we do
above with config->{environment}='production'. Of course, this value does not get written
in any file; it only lives in memory and your webapp doesn't have access to it, but you
can use it inside your script.
Logging
Configuring logging
It's possible to log messages generated by the application and by Dancer itself.
To start logging, select the logging engine you wish to use with the "logger" setting;
Dancer includes built-in log engines named "file" and "console", which log to a logfile
and to the console respectively.
To enable logging to a file, add the following to your config.yml:
logger: 'file'
Then you can choose which kind of messages you want to actually log:
log: 'core' # will log all messages, including messages from
# Dancer itself
log: 'debug' # will log debug, info, warning and error messages
log: 'info' # will log info, warning and error messages
log: 'warning' # will log warning and error messages
log: 'error' # will log error messages
If you're using the "file" logging engine, 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).
Logging your own messages
Just call debug, warning, error or info with your message:
debug "This is a debug message from my app.";
RESTING
Writing a REST application
With Dancer, it's easy to write REST applications. Dancer provides helpers to serialize
and deserialize for the following data formats:
JSON
YAML
XML
Data::Dumper
To activate this feature, you only have to set the "serializer" setting to the format you
require, for instance in your config.yml:
serializer: JSON
Or right in your code:
set serializer => 'JSON';
From now, all HashRefs or ArrayRefs returned by a route will be serialized to the format
you chose, and all data received from POST or PUT requests will be automatically
deserialized.
get '/hello/:name' => sub {
# this structure will be returned to the client as
# {"name":"$name"}
return {name => params->{name}};
};
It's possible to let the client choose which serializer he wants to use. For this, use the
mutable serializer, and an appropriate serializer will be chosen from the Content-Type
header.
It's also possible to return a custom error, using the send_error keyword.. When you
don't use a serializer, the "send_error" function will take a string as the first
parameter (the message), and an optional HTTP code. When using a serializer, the message
can be a string, an ArrayRef or a HashRef:
get '/hello/:name' => sub {
if (...) {
send_error("you can't do that");
# or
send_error({reason => 'access denied', message => "no"});
}
};
The content of the error will be serialized using the appropriate serializer.
Deploying your Dancer applications
For examples on deploying your Dancer applications including standalone, behind
proxy/load-balancing software, and using common web servers including Apache to run via
CGI/FastCGI etc, see Dancer::Deployment.
DANCER ON THE STAGE: DEPLOYMENT
Plack middlewares
If you deploy with Plack and use some Plack middlewares, you can enable them directly from
Dancer's configuration files.
Generic middlewares
To enable middlewares in Dancer, you just have to set the plack_middlewares setting like
the following:
set plack_middlewares => [
[ 'SomeMiddleware' => qw(some options for somemiddleware) ],
];
For instance, if you want to enable Plack::Middleware::Debug in your Dancer application,
all you have to do is to set "plack_middlewares" like that:
set plack_middlewares => [
[ 'Debug' => ( 'panels' => [qw(DBITrace Memory Timer)] ) ],
];
Of course, you can also put this configuration into your config.yml file, or even in your
environment configuration files:
# environments/development.yml
...
plack_middlewares:
-
- Debug # first element of the array is the name of the middleware
- panels # following elements are the configuration ofthe middleware
-
- DBITrace
- Memory
- Timer
Path-based middlewares
If you want to set up a middleware for a specific path, you can do that using
"plack_middlewares_map". You'll need Plack::App::URLMap to do that.
plack_middlewares_map:
'/': ['Debug']
'/timer': ['Timer'],
DEVELOPMENT TOOLS
Auto-reloading code
When you are furiously hacking on your Dancer app, it might come in handy to have the
application auto-detect changes in the code and reload itself.
To do that, you can use Plack::Loader::Shotgun, Plack::Middleware::Refresh, or plackup
with the "-r" switch:
plackup -r bin/appl.pl (will restart the app whenever a file in ./bin or ./lib is modified
AUTHOR
Dancer Core Developers
COPYRIGHT AND LICENSE
This software is copyright (c) 2010 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.