Provided by: libdancer2-perl_0.11+dfsg-1_all 
NAME
Dancer2::Cookbook - Example-driven quick-start to the Dancer2 web framework
VERSION
version 0.11
DESCRIPTION
A quick-start guide with examples to get you up and running with the Dancer2 web framework.
BEGINNER'S DANCE
Your first Dancer2 web app
Dancer2 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 Dancer2;
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 Dancer2.
If you really do not want the "warnings" pragma (for example, due to an undesired warning about use of
undef values), add a "no warnings" pragma to the appropriate block in your module or psgi file.
Starting a Dancer2 project
The first simple example is fine for trivial projects, but for anything more complex, you'll want a more
maintainable solution - enter the "dancer2" helper script, which will build the framework of your
application with a single command:
$ dancer2 -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/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.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 which HTTP method(s) it is valid for, 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 HTTTP 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 filters - processed before a request
A before filter declares code which should be handled before a request is passed to the appropriate
route.
hook before => sub {
forward '/foo/oversee', { note => 'Hi there' };
};
get '/foo/*' => sub {
my ($match) = splat; # 'oversee';
params->{note}; # 'Hi there'
};
The above declares a before filter which uses "forward" to do an internal redirect to "/foo/oversee" with
an additional parameter "note".
See also the hook hook keyword.
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", Dancer2 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 a 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 Dancer2::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 a 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 Dancer2;
use myapp::admin;
prefix undef;
get '/' => sub {...};
1;
package myapp::admin;
use Dancer2;
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 like this:
session: Simple
The Dancer2::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 Dancer2::Session::YAML backend included with Dancer2, 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 Dancer2::Session::YAML. There are other session backends you may
wish to use, for instance Dancer2::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->read("varname")
Controlling where sessions are stored
For disc-based session back ends like Dancer2::Session::YAML, Dancer2::Session::Storable etc, session
files are written to the session dir specified by the "session_dir" setting, which defaults to
"./sessions" if not specifically set.
If you need to control where session files are created, you can do so quickly and easily within your
config file, for example:
session: YAML
engines:
session:
YAML:
session_dir: /tmp/dancer-sessions
If the directory you specify does not exist, Dancer2 will attempt to create it for you.
Destroying a session
When you're done with your session, you can destroy it:
context->destroy_session
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 filter to check their session:
use Dancer2;
set session => "Simple";
hook before => sub {
if (!session('user') && request->dispatch_path !~ m{^/login}) {
forward '/login', { requested_path => request->dispatch_path };
}
};
get '/' => sub { return "Home Page"; };
get '/secret' => sub { return "Top Secret Stuff here"; };
get '/login' => sub {
# Display a login page; the original URL they requested is available as
# param('requested_path'), so could be put in a hidden field in the form
template 'login', { path => param('requested_path') };
};
post '/login' => sub {
# Validate the username and password they supplied
if (param('user') eq 'bob' && param('pass') eq 'letmein') {
session user => param('user');
redirect param('path') || '/';
} else {
redirect '/login?failed=1';
}
};
dance();
Here is what the corresponding "login.tt" file should look like. You should place it in a directory
called views:
<html>
<head>
<title>Session and logging in</title>
</head>
<body>
<form action='/login' method='POST'>
User Name : <input type='text' name='user'/>
Password: <input type='password' name='pass' />
<!-- Put the original path requested into a hidden
field so it's sent back in the POST and can be
used to redirect to the right page after login -->
<input type='hidden' name='path' value='[% path %]'/>
<input type='submit' value='Login' />
</form>
</body>
</html>
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
Dancer2::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: TEMPLATES 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. Dancer2 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 Dancer2::Template::Simple is used, but you may want to upgrade
to Template Toolkit <http://www.template-toolkit.org/>. If you do so, you have to enable this engine in
your settings as explained in Dancer2::Template::TemplateToolkit and 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 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 %]</p>
[% 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 Dancer2::Core::Role::Template).
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, 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 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
Templates and unicode
If you use Plack and have some unicode problem with your Dancer2 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 file will look like this:
charset: UTF-8
engines:
template:
template_toolkit:
ENCODING: utf8
TT's WRAPPER directive in Dancer2
Dancer2 already provides a WRAPPER-like ability, which we call a "layout". The reason we do not use TT's
WRAPPER (which also makes us incompatible with it) 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 Dancer2
You can do this by simply commenting (or removing) the "layout" configuration in the config 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:
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 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 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 an
environment to another without rewriting the config file.
An even solution 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 inside your application
A Dancer2 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 :)
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 Dancer2 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 Dancer2;
print "template:".config->{template}."\n"; #simple
print "log:".config->{log}."\n"; #undef
Note that "config->{log}" should result 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 Dancer2 where to look for it. One way to do so, is
to tell Dancer2 where the webapp lives. From there Dancer2 deduces where the config.yml file is
(typically "$webapp/config.yml").
# bin/script2.pl
use FindBin;
use Cwd qw/realpath/;
use Dancer2;
#tell the Dancer2 where the app lives
my $appdir=realpath( "$FindBin::Bin/..");
Dancer2::Config::setting('appdir',$appdir);
Dancer2::Config::load();
#getter
print "environment:".config->{environment}."\n"; #development
print "log:".config->{log}."\n"; #value from development environment
By default Dancer2 loads development environment (typically "$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 Dancer2 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.:
Dancer2::Config::setting('appdir','/path/to/app/dir');
If you want to load an environment other than the default, try this:
# bin/script2.pl
use Dancer2;
#tell the Dancer2 where the app lives
Dancer2::Config::setting('appdir','/path/to/app/dir');
#which environment to load
config->{environment}='production';
Dancer2::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 Dancer2 itself.
To start logging, select the logging engine you wish to use with the "logger" setting; Dancer2 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 file:
logger: 'file'
Then you can choose which kind of messages you want to actually log:
log: 'core' # will log debug, warnings, errors,
# and messages from Dancer2 itself
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
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, info, warning or error with your message:
debug "This is a debug message from my app.";
RESTING
Writing a REST application
With Dancer2, it's easy to write REST applications. Dancer2 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 file:
serializer: JSON
Or right in your code:
set serializer => 'JSON';
From now, all hash ref or array ref 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 want 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 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.
DANCER ON THE STAGE: DEPLOYMENT
Running stand-alone
At the simplest, your Dancer2 app can run standalone, operating as its own webserver using
HTTP::Server::Simple::PSGI.
Simply fire up your app:
$ perl bin/app.pl
>> Listening on 0.0.0.0:3000
== Entering the dance floor ...
Point your browser at it, and away you go!
This option can be useful for small personal web apps or internal apps, but if you want to make your app
available to the world, it probably won't suit you.
Auto Reloading with Plack and Shotgun
To edit your files without the need to restart the webserver on each file change, simply start your
Dancer2 app using plackup and Plack::Loader::Shotgun:
$ plackup -L Shotgun bin/app.pl
HTTP::Server::PSGI: Accepting connections at http://0:5000/
Point your browser at it. Files can now be changed in your favorite editor and the browser needs to be
refreshed to see the saved changes.
Please note that this is not recommended for production for performance reasons. This is the Dancer2
replacement solution of the old Dancer experimental "auto_reload" option.
On Windows, Shotgun loader is known to cause huge memory leaks in a fork-emulation layer. If you are
aware of this and still want to run the loader, please use the following command:
> set PLACK_SHOTGUN_MEMORY_LEAK=1 && plackup -L Shotgun bin\app.pl
HTTP::Server::PSGI: Accepting connections at http://0:5000/
CGI and Fast-CGI
In providing ultimate flexibility in terms of deployment, your Dancer2 app can be run as a simple cgi-
script out-of-the-box. No additional web-server configuration needed. Your web server should recognize
.cgi files and be able to serve Perl scripts. The Perl module Plack::Runner is required.
Running on Apache (CGI and FCGI)
Start by adding the following to your apache configuration ("httpd.conf" or "sites-available/*site*"):
<VirtualHost *:80>
ServerName www.example.com
DocumentRoot /srv/www.example.com/public
ServerAdmin you@example.com
<Directory "/srv/www.example.com/public">
AllowOverride None
Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
Order allow,deny
Allow from all
AddHandler cgi-script .cgi
</Directory>
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ /dispatch.cgi$1 [QSA,L]
ErrorLog /var/log/apache2/www.example.com-error.log
CustomLog /var/log/apache2/www.example.com-access_log common
</VirtualHost>
Note that when using fast-cgi your rewrite rule should be:
RewriteRule ^(.*)$ /dispatch.fcgi$1 [QSA,L]
Here, the mod_rewrite magic for Pretty-URLs is directly put in Apache's configuration. But if your web
server supports .htaccess files, you can drop those lines in a .htaccess file.
To check if your server supports mod_rewrite type "apache2 -l" to list modules. To enable mod_rewrite
(Debian), run "a2enmod rewrite". Place following code in a file called .htaccess in your application's
root folder:
# BEGIN dancer application htaccess
RewriteEngine On
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteCond %{SCRIPT_FILENAME} !-f
RewriteRule (.*) /dispatch.cgi$1 [L]
# END dancer application htaccess
Now you can access your dancer application URLs as if you were using the embedded web server.
http://localhost/
This option is a no-brainer, easy to setup, low maintenance but serves requests slower than all other
options.
You can use the same technique to deploy with FastCGI, by just changing the line:
AddHandler cgi-script .cgi
By:
AddHandler fastcgi-script .fcgi
Of course remember to update your rewrite rules, if you have set any:
RewriteRule (.*) /dispatch.fcgi$1 [L]
Running under an appdir
If you want to deploy multiple applications under the same VirtualHost, using one application per
directory for example, you can do the following.
This example uses the FastCGI dispatcher that comes with Dancer2, but you should be able to adapt this to
use any other way of deployment described in this guide. The only purpose of this example is to show how
to deploy multiple applications under the same base directory/virtualhost.
<VirtualHost *:80>
ServerName localhost
DocumentRoot "/path/to/rootdir"
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
<Directory "/path/to/rootdir">
AllowOverride None
Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
Order allow,deny
Allow from all
AddHandler fastcgi-script .fcgi
</Directory>
RewriteRule /App1(.*)$ /App1/public/dispatch.fcgi$1 [QSA,L]
RewriteRule /App2(.*)$ /App2/public/dispatch.fcgi$1 [QSA,L]
...
RewriteRule /AppN(.*)$ /AppN/public/dispatch.fcgi$1 [QSA,L]
</VirtualHost>
Of course, if your Apache configuration allows that, you can put the RewriteRules in a .htaccess file
directly within the application's directory, which lets you add a new application without changing the
Apache configuration.
Running on lighttpd (CGI)
To run as a CGI app on lighttpd, just create a soft link to the dispatch.cgi script (created when you run
dancer -a MyApp) inside your system's cgi-bin folder. Make sure mod_cgi is enabled.
ln -s /path/to/MyApp/public/dispatch.cgi /usr/lib/cgi-bin/mycoolapp.cgi
Running on lighttpd (FastCGI)
Make sure mod_fcgi is enabled. You also must have FCGI installed.
This example configuration uses TCP/IP:
$HTTP["url"] == "^/app" {
fastcgi.server += (
"/app" => (
"" => (
"host" => "127.0.0.1",
"port" => "5000",
"check-local" => "disable",
)
)
)
}
Launch your application:
plackup -s FCGI --port 5000 bin/app.pl
This example configuration uses a socket:
$HTTP["url"] =~ "^/app" {
fastcgi.server += (
"/app" => (
"" => (
"socket" => "/tmp/fcgi.sock",
"check-local" => "disable",
)
)
)
}
Launch your application:
plackup -s FCGI --listen /tmp/fcgi.sock bin/app.pl
Plack middlewares
If you want to use Plack middlewares, you need to enable them using Plack::Builder as such:
# in app.psgi or any other handler
use Dancer2;
use MyWebApp;
use Plack::Builder;
builder {
enable 'Deflater';
enable 'Session', store => 'File';
enable 'Debug', panels => [ qw<DBITrace Memory Timer> ];
dance;
};
The nice thing about this setup is that it will work seamlessly through Plack or through the internal web
server.
# load dev web server (without middlewares)
perl -Ilib app.psgi
# load plack web server (with middlewares)
plackup -I lib app.psgi
You do not need to provide different files for either server.
Path-based middlewares
If you want to setup a middleware for a specific path, you can do that using Plack::Builder which uses
Plack::App::URLMap:
# in your app.psgi or any other handler
use Dancer2;
use MyWebApp;
use Plack::Builder;
my $special_handler = sub { ... };
builder {
mount '/' => dance;
mount '/special' => $special_handler;
};
Running on Perl webservers with plackup
A number of Perl web servers supporting PSGI are available on cpan:
Starman
"Starman" is a high performance web server, with support for preforking, signals, ...
Twiggy
"Twiggy" is an "AnyEvent" web server, it's light and fast.
Corona
"Corona" is a "Coro" based web server.
To start your application, just run plackup (see Plack and specific servers above for all available
options):
$ plackup bin/app.pl
$ plackup -E deployment -s Starman --workers=10 -p 5001 -a bin/app.pl
As you can see, the scaffolded Perl script for your app can be used as a PSGI startup file.
Enabling content compression
Content compression (gzip, deflate) can be easily enabled via a Plack middleware (see "Plack::Middleware"
in Plack): Plack::Middleware::Deflater. It's a middleware to encode the response body in gzip or
deflate, based on Accept-Encoding HTTP request header.
Enable it as you would enable any Plack middleware. First you need to install
Plack::Middleware::Deflater, then in the handler (usually app.psgi) edit it to use Plack::Builder, as
described above:
use Dancer2;
use MyWebApp;
use Plack::Builder;
builder {
enable 'Deflater';
dance;
};
To test if content compression works, trace the HTTP request and response before and after enabling this
middleware. Among other things, you should notice that the response is gzip or deflate encoded, and
contains a header "Content-Encoding" set to "gzip" or "deflate"
Running multiple apps with Plack::Builder
You can use Plack::Builder to mount multiple Dancer2 applications on a PSGI webserver like Starman.
Start by creating a simple app.psgi file:
use OurWiki; # first app
use OurForum; # second app
use Plack::Builder;
builder {
mount '/wiki' => OurWiki->dance;
mount '/forum' => OurForum->dance;
};
and now use Starman
plackup -a app.psgi -s Starman
Currently this still demands the same appdir for both (default circumstance) but in a future version this
will be easier to change while staying very simple to mount.
Running from Apache with Plack
You can run your app from Apache using PSGI (Plack), with a config like the following:
<VirtualHost myapp.example.com>
ServerName www.myapp.example.com
ServerAlias myapp.example.com
DocumentRoot /websites/myapp.example.com
<Directory /home/myapp/myapp>
AllowOverride None
Order allow,deny
Allow from all
</Directory>
<Location />
SetHandler perl-script
PerlHandler Plack::Handler::Apache2
PerlSetVar psgi_app /websites/myapp.example.com/app.pl
</Location>
ErrorLog /websites/myapp.example.com/logs/error_log
CustomLog /websites/myapp.example.com/logs/access_log common
</VirtualHost>
To set the environment you want to use for your application (production or development), you can set it
this way:
<VirtualHost>
...
SetEnv DANCER_ENVIRONMENT "production"
...
</VirtualHost>
Creating a service
You can turn your app into proper service running in background using one of the following examples:
Using Ubic
Ubic is an extensible perlish service manager. You can use it to start and stop any services,
automatically start them on reboots or daemon failures, and implement custom status checks.
A basic PSGI service description (usually in /etc/ubic/service/application):
use parent qw(Ubic::Service::Plack);
# if your application is not installed in @INC path:
sub start {
my $self = shift;
$ENV{PERL5LIB} = '/path/to/your/application/lib';
$self->SUPER::start(@_);
}
__PACKAGE__->new(
server => 'Starman',
app => '/path/to/your/application/app.pl',
port => 5000,
user => 'www-data',
);
Run "ubic start application" to start the service.
Using daemontools
daemontools is a collection of tools for managing UNIX services. You can use it to easily
start/restart/stop services.
A basic script to start an application: (in /service/application/run)
#!/bin/sh
# if your application is not installed in @INC path:
export PERL5LIB='/path/to/your/application/lib'
exec 2>&1 \
/usr/local/bin/plackup -s Starman -a /path/to/your/application/app.pl -p 5000
Running stand-alone behind a proxy / load balancer
Another option would be to run your app stand-alone as described above, but then use a proxy or load
balancer to accept incoming requests (on the standard port 80, say) and feed them to your Dancer2 app.
This could be achieved using various software; examples would include:
Using Apache's mod_proxy
You could set up a VirtualHost for your web app, and proxy all requests through to it:
<VirtualHost mywebapp.example.com:80>
ProxyPass / http://localhost:3000/
ProxyPassReverse / http://localhost:3000/
</VirtualHost>
Or, if you want your webapp to share an existing VirtualHost, you could have it under a specified dir:
ProxyPass /mywebapp/ http://localhost:3000/
ProxyPassReverse /mywebapp/ http://localhost:3000/
It is important for you to note that the Apache2 modules "mod_proxy" and "mod_proxy_http" must be
enabled.
a2enmod proxy
a2enmod proxy_http
It is also important to set permissions for proxying for security purposes, below is an example.
<Proxy *>
Order allow,deny
Allow from all
</Proxy>
Using perlbal
"perlbal" is a single-threaded event-based server written in Perl supporting HTTP load balancing, web
serving, and a mix of the two, available from <http://www.danga.com/perlbal/>
It processes hundreds of millions of requests a day just for LiveJournal, Vox and TypePad and dozens of
other "Web 2.0" applications.
It can also provide a management interface to let you see various information on requests handled etc.
It could easily be used to handle requests for your Dancer2 apps, too.
It can be easily installed from CPAN:
perl -MCPAN -e 'install Perlbal'
Once installed, you'll need to write a configuration file. See the examples provided with perlbal, but
you'll probably want something like:
CREATE POOL my_dancers
POOL my_dancers ADD 10.0.0.10:3030
POOL my_dancers ADD 10.0.0.11:3030
POOL my_dancers ADD 10.0.0.12:3030
POOL my_dancers ADD 10.0.0.13:3030
CREATE SERVICE my_webapp
SET listen = 0.0.0.0:80
SET role = reverse_proxy
SET pool = my_dancers
SET persist_client = on
SET persist_backend = on
SET verify_backend = on
ENABLE my_webapp
Using balance
"balance" is a simple load-balancer from Inlab Software, available from
<http://www.inlab.de/balance.html>.
It could be used simply to hand requests to a standalone Dancer2 app. You could even run several
instances of your Dancer2 app, on the same machine or on several machines, and use a machine running
balance to distribute the requests between them, for some serious heavy traffic handling!
To listen on port 80, and send requests to a Dancer2 app on port 3000:
balance http localhost:3000
To listen on a specified IP only on port 80, and distribute requests between multiple Dancer2 apps on
multiple other machines:
balance -b 10.0.0.1 80 10.0.0.2:3000 10.0.0.3:3000 10.0.0.4:3000
Using Lighttpd
You can use Lighttp's mod_proxy:
$HTTP["url"] =~ "/application" {
proxy.server = (
"/" => (
"application" => ( "host" => "127.0.0.1", "port" => 3000 )
)
)
}
This configuration will proxy all request to the /application path to the path / on localhost:3000.
Using Nginx
with Nginx:
upstream backendurl {
server unix:THE_PATH_OF_YOUR_PLACKUP_SOCKET_HERE.sock;
}
server {
listen 80;
server_name YOUR_HOST_HERE;
access_log /var/log/YOUR_ACCESS_LOG_HERE.log;
error_log /var/log/YOUR_ERROR_LOG_HERE.log info;
root YOUR_ROOT_PROJECT/public;
location / {
try_files $uri @proxy;
access_log off;
expires max;
}
location @proxy {
proxy_set_header Host $http_host;
proxy_set_header X-Forwarded-Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://backendurl;
}
}
You will need plackup to start a worker listening on a socket :
cd YOUR_PROJECT_PATH
sudo -u www plackup -E production -s Starman --workers=2 -l THE_PATH_OF_YOUR_PLACKUP_SOCKET_HERE.sock -a bin/app.pl
A good way to start this is to use "daemontools" and place this line with all environments variables in
the "run" file.
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::Cookbook(3pm)