libdancer2-perl 0.11+dfsg-1 / usr / share / perl5 / Dancer2 / Manual.pod

# ABSTRACT: A gentle introduction to Dancer2
package Dancer2::Manual;

__END__

=pod

=head1 NAME

Dancer2::Manual - A gentle introduction to Dancer2

=head1 VERSION

version 0.11

=head1 DESCRIPTION

Dancer2 is a free and open source web application framework written in Perl.

It's a complete rewrite of L<Dancer>, based on L<Moo> and using a more robust
and extensible fully-OO design.

It's designed to be powerful and flexible, but also easy to use - getting up and
running with your web app is trivial, and an ecosystem of adaptors for common
template engines, session storage, logging methods and plugins to make
common tasks easy mean you can do what you want to do, your way, easily.

=encoding utf8

=head1 INSTALL

Installation of Dancer2 is simple:

    perl -MCPAN -e 'install Dancer2'

Thanks to the magic of cpanminus, if you do not have CPAN.pm configured, or just
want a quickfire way to get running, the following should work, at least on
Unix-like systems:

    wget -O - http://cpanmin.us | sudo perl - Dancer2

(If you don't have root access, omit the 'sudo', and cpanminus will install
Dancer2 and prereqs into C<~/perl5>.)

=head1 BOOTSTRAPPING A NEW APP

Create a web application using the dancer script:

    dancer2 -a MyApp && cd MyApp

And voilà! You can now run the web application:

    bin/app.pl

View the web application at:

    http://localhost:3000

Note that as Dancer2 supports the L<PSGI> specification, you can also use the C<plackup> tool
(provided by L<Plack>) for launching the application:

    plackup ./bin/app.pl -p 5000

=head1 USAGE

When Dancer2 is imported to a script, that script becomes a webapp, and at this
point, all the script has to do is declare a list of B<routes>.  A route
handler is composed by an HTTP method, a path pattern and a code block.
C<strict> and C<warnings> pragmas are also imported with Dancer2.

The code block given to the route handler has to return a string which will be
used as the content to render to the client.

Routes are defined for a given HTTP method. For each method
supported, a keyword is exported by the module.

The following is an example of a route definition. The route is defined for the
method 'get', so only GET requests will be honoured by that route:

    get '/hello/:name' => sub {
        # do something

        return "Hello ".param('name');
    };

=head2 HTTP Methods

Here are some of the standard HTTP methods which you can use to define your
route handlers.

=over 8

=item B<GET> The GET method retrieves information, and is the most common

GET requests should be used for typical "fetch" requests - retrieving
information.  They should not be used for requests which change data on the
server or have other effects.

When defining a route handler for the GET method, Dancer2 automatically defines
a route handler for the HEAD method (in order to honour HEAD requests for each
of your GET route handlers).

To define a GET action, use the L<get|Dancer2::Manual/get> keyword.

=item B<POST> The POST method is used to create a resource on the server.

To define a POST action, use the L<post|Dancer2::Manual/post> keyword.

=item B<PUT> The PUT method is used to replace an existing resource.

To define a PUT action, use the L<put|Dancer2::Manual/put> keyword.

a PUT request should replace the existing resource with that specified - for
instance - if you wanted to just update an email address for a user, you'd have
to specify all attributes of the user again; to make a partial update, a
C<PATCH> request is used.

=item B<PATCH> The PATCH method updates some attributes of an existing resource.

To define a PATCH action, use the L<patch|Dancer2::Manual/patch>
keyword.

=item B<DELETE> The DELETE method requests that the origin server delete the
resource identified by the Request-URI.

To define a DELETE action, use the L<del|Dancer2::Manual/del> keyword.

=back

To define a route for multiple methods you can also use the special keyword
B<any>. This example illustrates how to define a route for both GET and
POST methods:

    any ['get', 'post'] => '/myaction' => sub {
        # code
    };

Or even, a route handler that would match any HTTP methods:

    any '/myaction' => sub {
        # code
    };

=head2 Route Handlers

The route action is the code reference declared. It can access parameters
through the C<params> keyword, which returns a hashref.
This hashref is a merge of the route pattern matches and the request params.

You can have more details about how params are built and how to access them in
the L<Dancer2::Core::Request> documentation.

=head3 Named Matching

A route pattern can contain one or more tokens (a word prefixed with ':'). Each
token found in a route pattern is used as a named-pattern match. Any match will
be set in the params hashref.

    get '/hello/:name' => sub {
        "Hey ".param('name').", welcome here!";
    };

Tokens can be optional, for example:

    get '/hello/:name?' => sub {
        defined param('name') ? "Hello there ".param('name') : "whoever you are!";
    };

=head3 Wildcards Matching

A route can contain a wildcard (represented by a C<*>). Each wildcard match will
be returned in an arrayref, accessible via the C<splat> keyword.

    get '/download/*.*' => sub {
        my ($file, $ext) = splat;
        # do something with $file.$ext here
    };

=head3 Regular Expression Matching

A route can be defined with a Perl regular expression.

In order to tell Dancer2 to consider the route as a real regexp, the route must
be defined explicitly with C<qr{}>, like the following:

    get qr{/hello/([\w]+)} => sub {
        my ($name) = splat;
        return "Hello $name";
    };

=head3 Conditional Matching

Routes may include some matching conditions (on the useragent and the hostname
at the moment):

    get '/foo', {agent => 'Songbird (\d\.\d)[\d\/]*?'} => sub {
      'foo method for songbird'
    }

    get '/foo' => sub {
      'all browsers except songbird'
    }

=head2 Prefix

A prefix can be defined for each route handler, like this:

    prefix '/home';

From here, any route handler is defined to /home/*

    get '/page1' => sub {}; # will match '/home/page1'

You can unset the prefix value

    prefix '/'; # or: prefix undef;
    get '/page1' => sub {}; will match /page1

Alternatively, to prevent you from ever forgetting to undef the prefix,
you can use lexical prefix like this:

    prefix '/home' => sub {
      get '/page1' => sub {}; # will match '/home/page1'
    }; ## prefix reset to previous value on exit

    get '/page1' => sub {}; will match /page1

=head2 Action Skipping

An action can choose not to serve the current request and ask Dancer2 to process
the request with the next matching route.

This is done with the B<pass> keyword, like in the following example

    get '/say/:word' => sub {
        return pass if (params->{word} =~ /^\d+$/);
        "I say a word: ".params->{word};
    };

    get '/say/:number' => sub {
        "I say a number: ".params->{number};
    };

=head2 Default Error Pages

When an error is rendered (the action responded with a status code different
than 200), Dancer2 first looks in the public directory for an HTML file matching
the error code (eg: 500.html or 404.html).

If such a file exists, it's used to render the error, otherwise, a default
error page will be rendered on the fly.

=head2 Execution Errors

When an error occurs during the route execution, Dancer2 will render an error
page with the HTTP status code 500.

It's possible either to display the content of the error message or to hide it
with a generic error page.

This is a choice left to the end-user and can be set with the
B<show_errors> setting.

Note that you can also choose to consider all warnings in your route handlers
as errors when the setting B<warnings> is set to 1.

=head1 HOOKS

Hooks are code references (or anonymous subroutines) that are triggered at
specific moments during the resolution of a request.

Many of them are supported by the core but plugins and engines can also
define their own.

=head2 Request workflow

C<before> hooks are evaluated before each request within the context of the
request and receives as argument the context (a L<Dancer2::Core::Context>
object).

It's possible to define variables which will be accessible in the action blocks
with the keyword 'var'.

    hook before => sub {
        var note => 'Hi there';
    };

    get '/foo/*' => sub {
        my ($match) = splat; # 'oversee';
        vars->{note}; # 'Hi there'
    };

For another example, this can be used along with session support to easily
give non-logged-in users a login page:

    hook before => sub {
        if (!session('user') && request->dispatch_path !~ m{^/login}) {
            # Pass the original path requested along to the handler:
            forward '/login', { requested_path => request->dispatch_path };
        }
    };

The request keyword returns the current L<Dancer2::Core::Request> object
representing the incoming request.

C<after> hooks are evaluated after the response has been built by a route
handler, and can alter the response itself, just before it's sent to the
client.

This hook runs after a request has been processed, but before the response is
sent.

It receives a L<Dancer2::Core::Response> object, which it can modify
if it needs to make changes to the response which is about to be sent.

The filter is given the response object as its first argument:

    hook after => sub {
        my $response = shift;
        $response->(content, 'after filter got here!');
    };

=head2 Templates

C<before_template_render> hooks are called whenever a template is going to be
processed, they are passed the tokens hash which they can alter.

    hook before_template_render => sub {
        my $tokens = shift;
        $tokens->{foo} = 'bar';
    }

The tokens hash will then be passed to the template with all the modifications
performed by the filter. This is a good way to setup some global vars you like
to have in all your templates, like the name of the user logged in or a
section name.

C<after_template_render> hooks are called after the view has been rendered. They
receive as their first argument the reference to the content that has been
produced. This can be used to post-process the content rendered by the template
engine.

    hook after_template_render => sub {
        my $ref_content = shift;
        my $content = $$ref_content;
        # do something with $content
        $ref_content = \$content;
    };

C<before_layout_render> hooks are called whenever the layout is going to be
applied to the current content. The arguments received by the hook are the
current tokens hashref and a reference to the current content.

    hook before_layout_render => sub {
        my ($tokens, $ref_content) = @_;
        $tokens->{new_stuff} = 42;
        $ref_conent = \"new content";
    };

C<after_layout_render> hooks are called once the complete content of the view
has been produced, after the layout has been applied to the content. The
argument received by the hook is a reference to the complete content string.

    hook after_layout_render => sub {
        my $ref_content = shift;
        ...
    };

=head2 Error handling

When an error is caught by Dancer2's core, an exception object is built (of the
class L<Dancer2::Core::Error>). This class provides hook to let the user alter
the error work-flow if needed.

C<init_error> hooks are called whenever an error object is built, the object is
passed to the hook.

    hook init_error => sub {
        my $error = shift;
        # do something with $error
    };

I<This hook was named B<before_error_init> in Dancer, and is now aliased to
this hook.>

C<before_error> hooks are called whenever an error is going to be thrown, it
receives the error object as its first and unique argument.

    hook before_error => sub {
        my $error = shift;
        # do something with $error
    };

I<This hook was named B<before_error_render> in Dancer, and is now aliased to
this hook.>

C<after_error> hooks are called whenever an error object has been thrown, it
receives a L<Dancer2::Core::Response> object as the first argument.

    hook after_error => sub {
        my $response = shift;
    };

I<This hook was named <after_error_render> in Dancer, and is now aliased to
this hook.>

C<on_route_exception> is called when an exception has been caught, at the
route level, just before rethrowing it higher. This hook receives a
L<Dancer2::Core::Context> and the error as arguments.

  hook on_route_exception => sub {
    my ($context, $error) = @_;
  };

=head2 File rendering

Whenever a content is produced out of the parsing of a static file, the
L<Dancer2::Handler::File> component is used. This component provides two hooks,
C<before_file_render> and C<after_file_render>.

C<before_file_render> hooks are called just before starting to parse the file,
the hook receives as its first argument the file path that is going to be
processed.

    hook before_file_render => sub {
        my $path = shift;
    };

C<after_file_render> are called after the file has been parsed and the response
content produced. It receives the response object (L<Dancer2::Core::Response>)
produced.

    hook after_file_render => sub {
       my $response = shift;
    };

=head2 Serializers

C<before_serializer> is called before serializing the content, and receives as
argument the content to serialize.

  hook before_serializer => sub {
    my $content = shift;
    ...
  };

C<after_serializer> is called after the payload was serialized, and receives
the serialized content as an argument.

  hook after_serializer => sub {
    my $content = shift;
    ...
  };

=head1 CONFIGURATION AND ENVIRONMENTS

Configuring a Dancer2 application can be done in many ways. The easiest one (and
maybe the dirtiest) is to put all your settings statements at the top of
your script, before calling the dance() method.

Other ways are possible.  You could write all your setting calls in the file
`appdir/config.yml'. You would, of course, have write the conffile in YAML.

While better than the first option, it's still not perfect.  You can't easily
switch from an environment to another (for example, from development to
production) without rewriting the config.yml file.  The best way is to have
one config.yml file with default global settings, like the following:

    # appdir/config.yml
    logger: 'file'
    layout: 'main'

And then write as many environment files as you like in appdir/environments.
That way, the appropriate environment config file will be loaded according to
the running environment (if none is specified, 'development' is assumed).

Note that you can change the running environment using the --environment
commandline switch.

Typically, you'll want to set the following values in a development config
file:

    # appdir/environments/development.yml
    log: 'debug'
    startup_info: 1
    show_errors:  1

And in a production one:

    # appdir/environments/production.yml
    log: 'warning'
    startup_info: 0
    show_errors:  0

Please note that you are not limited to writing configuration files in YAML.
Dancer2 supports any file format that is supported by L<Config::Any>, such as
JSON, XML, INI files, and Apache-style config files.

=head2 Accessing configuration data

A Dancer2 application can access the information from its config file easily with
the config keyword:

    get '/appname' => sub {
        return "This is " . config->{appname};
    };

=head2 Settings

It's possible to change quite every parameter of the application via the
settings mechanism.

A setting is key/value pair assigned by the keyword B<set>:

    set setting_name => 'setting_value';

More usefully, settings can be defined in a configuration file.
Environment-specific settings can also be defined in environment-specific files
(for instance, you do not want to show error stacktraces in production, and might want extra
logging in development).  See the cookbook for examples.

=head2 Serializers

When writing a webservice, data serialization/deserialization is a common issue
to deal with. Dancer2 can automatically handle that for you, via a serializer.

When setting up a serializer, a new behaviour is authorized for any route
handler you define: any non-scalar response will be rendered as a serialized
string, via the current serializer.

Here is an example of a route handler that will return a HashRef

    use Dancer2;
    set serializer => 'JSON';

    get '/user/:id/' => sub {
        { foo => 42,
          number => 100234,
          list => [qw(one two three)],
        }
    };

As soon as the content is not a scalar - and a serializer is set, which is not
the case by default - Dancer2 renders the response via the current
serializer.

Hence, with the JSON serializer set, the route handler above would result in a
content like the following:

    {"number":100234,"foo":42,"list":["one","two","three"]}

The following serializers are available, be aware they dynamically depend on
Perl modules you may not have on your system.

=over 4

=item B<JSON>

requires L<JSON>

=item B<YAML>

requires L<YAML>

=item B<XML>

requires L<XML::Simple>

=item B<Mutable>

will try to find the appropriate serializer using the B<Content-Type> and
B<Accept-type> header of the request.

=back

=head2 Logging

It's possible to log messages sent by the application. In the current version,
only one method is possible for logging messages but future releases may add
additional logging methods, for instance logging to syslog.

In order to enable the logging system for your application, you first have to
start the logger engine in your config file:

    logger: 'file'

Then you can choose which kind of messages you want to actually log:

    log: 'debug'     # will log debug, info, warning and errors
    log: 'info'      # will log info, warning and errors
    log: 'warning'   # will log warning and errors
    log: 'error'     # will log only errors

A directory appdir/logs will be created and will host one logfile per
environment. The log message contains the time it was written, the PID of the
current process, the message and the caller information (file and line).

To log messages, use the debug, info, warning and error methods, for instance:

    debug "This is a debug message";

=head2 Using Templates

=head3 Views

It's possible to render the action's content with a template; this is called a
view. The `appdir/views' directory is the place where views are located.

You can change this location by changing the setting 'views', for instance if
your templates are located in the 'templates' directory, do the following:

    set views => path(dirname(__FILE__), 'templates');

By default, the internal template engine is used (L<Dancer2::Template::Simple>)
but you may want to upgrade to Template::Toolkit. If you do so, you have to
enable this engine in your settings as explained in
L<Dancer2::Template::TemplateToolkit>. If you do so, you'll also have to import
the L<Template> module in your application code.

All views must have a '.tt' extension. This may change in the future.

In order to render a view, just call the 'template' keyword at the end of the
action by giving the view name and the HASHREF of tokens to interpolate in the
view (note that the request, session and route params are automatically
accessible in the view, named request, session and params):

    use Dancer2;
    use Template;

    get '/hello/:name' => sub {
        template 'hello' => { number => 42 };
    };

And the appdir/views/hello.tt view can contain the following code:

   <html>
    <head></head>
    <body>
        <h1>Hello [% params.name %]</h1>
        <p>Your lucky number is [% number %]</p>
        <p>You are using [% request.user_agent %]</p>
        [% IF session.user %]
            <p>You're logged in as [% session.user %]</p>
        [% END %]
    </body>
   </html>

=head3 Layouts

A layout is a special view, located in the 'layouts' directory (inside the
views directory) which must have a token named `content'. That token marks the
place where to render the action view. This lets you define a global layout
for your actions. Any tokens that you defined when you called the 'template'
keyword are available in the layouts, as well as the standard session,
request, and params tokens. This allows you to insert per-page content into
the HTML boilerplate, such as page titles, current-page tags for navigation,
etc.

Here is an example of a layout: views/layouts/main.tt:

    <html>
        <head>[% page_title %]</head>
        <body>
        <div id="header">
        ...
        </div>

        <div id="content">
        [% content %]
        </div>

        </body>
    </html>

This layout can be used like the following:

    use Dancer2;
    set layout => 'main';

    get '/' => sub {
        template 'index' => { page_title => "Your website Homepage" };
    };

Of course, if a layout is set, it can also be disabled for a specific action,
like the following:

    use Dancer2;
    set layout => 'main';

    get '/nolayout' => sub {
        template 'some_ajax_view',
            { tokens_var => "42" },
            { layout => 0 };
    };

=head2 Static Files

=head3 Static Directory

Static files are served from the ./public directory. You can specify a
different location by setting the 'public' option:

    set public => path(dirname(__FILE__), 'static');

Note that the public directory name is not included in the URL. A file
./public/css/style.css is made available as example.com/css/style.css.

=head3 Static File from a Route Handler

It's possible for a route handler to send a static file, as follows:

    get '/download/*' => sub {
        my $params = shift;
        my ($file) = @{ $params->{splat} };

        send_file $file;
    };

Or even if you want your index page to be a plain old index.html file, just do:

    get '/' => sub {
        send_file '/index.html'
    };

=head1 DSL KEYWORDS

Dancer2 provides you with a DSL (Domain-Specific Language) which makes
implementing your web application trivial.

For example, take the following example:

    use Dancer2;

    get '/hello/:name' => sub {
        my $name = params->{name};
    };
    dance;

C<get> and C<params> are keywords provided by Dancer2.

This document lists all keywords provided by Dancer2.  It does not cover
additional keywords which may be provided by loaded plugins; see the
documentation for plugins you use to see which additional keywords they make
available to you.

=head2 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
    };

=head2 cookies

Accesses cookies values, it returns a HashRef of L<Dancer2::Core::Cookie>
objects:

    get '/some_action' => sub {
        my $cookie = cookies->{name};
        return $cookie->value;
    };

In the case you have stored something else than a Scalar in your cookie:

    get '/some_action' => sub {
        my $cookie = cookies->{oauth};
        my %values = $cookie->value;
        return ($values{token}, $values{token_secret});
    };

=head2 cookie

Accesses a cookie value (or sets it). Note that this method will
eventually be preferred over C<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

C<cookie> will only return the first part (C<token=ABC>) if called in scalar context.
Use list context to fetch them all:

    my @values = cookie "name";

=head2 config

Accesses the configuration of the application:

    get '/appname' => sub {
        return "This is " . config->{appname};
    };

=head2 content_type

Sets the B<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 C<content_type> setting instead.

=head2 dance

Alias for the C<start> keyword.

=head2 dancer_version

Returns the version of Dancer. If you need the major version, do something like:

  int(dancer_version);

=head2 debug

Logs a message of debug level:

    debug "This is a debug message";

See L<Dancer2::Core::Role::Logger> for details on how to configure where log messages go.

=head2 dirname

Returns the dirname of the path given:

    my $dir = dirname($some_path);

=head2 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);

=head2 error

Logs a message of error level:

    error "This is an error message";

See L<Dancer2::Core::Role::Logger> for details on how to configure where log messages go.

=head2 false

Constant that returns a false value (0).

=head2 forward

Runs an "internal redirect" of the current request to another request. More
formally; when the C<forward> is executed, the current dispatch of the request
is aborted, the request is modified (altering query params or request method),
and the modified request is dispatched again. Any remaining code (route and
hooks) from the current dispatch will never be run and the modified request's
dispatch will execute hooks for the new request normally.

It effectively lets you chain routes together in a clean manner.

    get '/demo/articles/:article_id' => sub {

        # you'll have to implement this next sub yourself :)
        change_the_main_database_to_demo();

        forward "/articles/" . params->{article_id};
    };

In the above example, the users that reach I</demo/articles/30> will actually
reach I</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 I</demo/...>.

You'll notice that in the example we didn't indicate whether it was B<GET> or
B<POST>. That is because C<forward> chains the same type of route the user
reached. If it was a B<GET>, it will remain a B<GET> (but if you do need to
change the method, you can do so; read on below for details.)

B<WARNING> : Any code after a c<forward> is ignored, until the end of the route.
It's not necessary to use C<return> with c<forward> anymore.

    get '/foo/:article_id' => sub {
        if ($condition) {
            forward "/articles/" . params->{article_id};
            # The following code WILL NOT BE executed
            do_stuff();
        }

        more_stuff();
    };

Note that c<forward> doesn't parse GET arguments. So, you can't use
something like:

    forward '/home?authorized=1';

But C<forward> supports an optional HashRef with parameters to be added
to the actual parameters:

    forward '/home', { authorized => 1 };

Finally, you can add some more options to the c<forward> method, in a
third argument, also as a HashRef. That option is currently
only used to change the method of your request. Use with caution.

    forward '/home', { auth => 1 }, { method => 'POST' };

=head2 from_dumper ($structure)

Deserializes a Data::Dumper structure.

=head2 from_json ($structure, \%options)

Deserializes a JSON structure. Can receive optional arguments. Those arguments
are valid L<JSON> arguments to change the behaviour of the default
C<JSON::from_json> function.

=head2 from_yaml ($structure)

Deserializes a YAML structure.

=head2 get

Defines a route for HTTP B<GET> requests to the given path:

    get '/' => sub {
        return "Hello world";
    }

Note that a route to match B<HEAD> requests is automatically created as well.

=head2 halt

Sets a response object with the content given.

When used as a return value from a filter, this breaks the execution flow and
renders the response immediately:

    hook before => sub {
        if ($some_condition) {
            halt("Unauthorized");
            # This code is not executed :
            do_stuff();
        }
    };

    get '/' => sub {
        "hello there";
    };

B<WARNING> : Issuing a halt immediately exits the current route, and perform
the halt. Thus, any code after a halt is ignored, until the end of the route.
So it's not necessary anymore to use C<return> with halt.

=head2 headers

Adds custom headers to responses:

    get '/send/headers', sub {
        headers 'X-Foo' => 'bar', X-Bar => 'foo';
    }

=head2 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 L</push_header>.

=head2 push_header

Do the same as C<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
    }

=head2 hook

Adds a hook at some position. For example :

  hook before_serializer => sub {
    my $content = shift;
    ...
  };

There can be multiple hooks assigned to a given position, and each will be
executed in order.

=head2 info

Logs a message of info level:

    info "This is a info message";

See L<Dancer2::Core::Role::Logger> for details on how to configure where log
messages go.

=head2 load

Loads one or more perl scripts in the current application's namespace. Syntactic
sugar around Perl's C<require>:

    load 'UserActions.pl', 'AdminActions.pl';

=head2 mime

Shortcut to access the instance object of L<Dancer2::Core::MIME>. You should
read the L<Dancer2::Core::MIME> documentation for full details, but the most
commonly-used methods are summarized below:

    # set a new mime type
    mime->add_type( foo => 'text/foo' );

    # set a mime type alias
    mime->add_alias( f => 'foo' );

    # get mime type for an alias
    my $m = mime->for_name( 'f' );

    # get mime type for a file (based on extension)
    my $m = mime->for_file( "foo.bar" );

    # get current defined default mime type
    my $d = mime->default;

    # set the default mime type using config.yml
    # or using the set keyword
    set default_mime_type => 'text/plain';

=head2 params

I<This method should be called from a route handler>.
It's an alias for the
L<Dancer2::Core::Request params accessor|Dancer2::Core::Request/"params">. It
returns an hash reference to all defined parameters. Check C<param> below to
access quickly to a single parameter value.

=head2 param

I<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";
       # ...
   }

=head2 pass

I<This method should be called from a route handler>.
Tells Dancer to pass the processing of the request to the next
matching route.

B<WARNING> : Issuing a pass immediately exits the current route, and perform
the pass. Thus, any code after a pass is ignored, until the end of the route.
So it's not necessary anymore to use C<return> with pass.

    get '/some/route' => sub {
        if (...) {
            # we want to let the next matching route handler process this one
            pass(...);
            # This code will be ignored
            do_stuff();
        }
    };

=head2 patch

Defines a route for HTTP B<PATCH> requests to the given URL:

    patch '/resource' => sub { ... };

(C<PATCH> is a relatively new and not-yet-common HTTP verb, which is intended to
work as a "partial-PUT", transferring just the changes; please see
L<http://tools.ietf.org/html/rfc5789|RFC5789> for further details.)

Please be aware that, if you run your app in standalone mode, C<PATCH> requests
will not reach your app unless you have a new version of L<HTTP::Server::Simple>
which accepts C<PATCH> as a valid verb.  The current version at time of writing,
C<0.44>, does not.  A pull request has been submitted to add this support, which
you can find at:

L<https://github.com/bestpractical/http-server-simple/pull/1>

=head2 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.

=head2 post

Defines a route for HTTP B<POST> requests to the given URL:

    post '/' => sub {
        return "Hello world";
    }

=head2 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

B<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!

=head2 del

Defines a route for HTTP B<DELETE> requests to the given URL:

    del '/resource' => sub { ... };

=head2 options

Defines a route for HTTP B<OPTIONS> requests to the given URL:

    options '/resource' => sub { ... };

=head2 put

Defines a route for HTTP B<PUT> requests to the given URL:

    put '/resource' => sub { ... };

=head2 redirect

Generates a HTTP redirect (302).  You can either redirect to a complete
different site or within the application:

    get '/twitter', sub {
        redirect 'http://twitter.com/me';
        # Any code after the redirect will not be executed.
    };

B<WARNING> : Issuing a c<redirect> immediately exits the current route.
Thus, any code after a c<redirect> is ignored, until the end of the route.
So it's not necessary anymore to use C<return> with c<redirect>.

You can also force Dancer to return a specific 300-ish HTTP response code:

    get '/old/:resource', sub {
        redirect '/new/'.params->{resource}, 301;
    };

=head2 request

Returns a L<Dancer2::Core::Request> object representing the current request.

See the L<Dancer2::Core::Request> documentation for the methods you can call, for
example:

    request->referer;         # value of the HTTP referer header
    request->remote_address;  # user's IP address
    request->user_agent;      # User-Agent header value

=head2 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
        }
    }

B<WARNING> : Issuing a send_error immediately exits the current route, and perform
the send_error. Thus, any code after a send_error is ignored, until the end of the route.
So it's not necessary anymore to use C<return> with send_error.

    get '/some/route' => sub {
        if (...) {
            # we want to let the next matching route handler process this one
            send_error(..);
            # This code will be ignored
            do_stuff();
        }
    };

=head2 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 B<public> directory unless you use
the C<system_path> option (see below).

    get '/download/:file' => sub {
        return send_file(params->{file});
    }

B<WARNING> : Issuing a send_file immediately exits the current route, and perform
the send_file. Thus, any code after a send_file is ignored, until the end of the route.
So it's not necessary anymore to use C<return> with send_file.

    get '/some/route' => sub {
        if (...) {
            # we want to let the next matching route handler process this one
            send_file(...);
            # This code will be ignored
            do_stuff();
        }
    };

Send file supports streaming possibility using PSGI streaming. The server should
support it but normal streaming is supported on most, if not all.

    get '/download/:file' => sub {
        return send_file( params->{file}, streaming => 1 );
    }

You can control what happens using callbacks.

First, C<around_content> allows you to get the writer object and the chunk of
content read, and then decide what to do with each chunk:

    get '/download/:file' => sub {
        return send_file(
            params->{file},
            streaming => 1,
            callbacks => {
                around_content => sub {
                    my ( $writer, $chunk ) = @_;
                    $writer->write("* $chunk");
                },
            },
        );
    }

You can use C<around> to all get all the content (whether a filehandle if it's
a regular file or a full string if it's a scalar ref) and decide what to do with
it:

    get '/download/:file' => sub {
        return send_file(
            params->{file},
            streaming => 1,
            callbacks => {
                around => sub {
                    my ( $writer, $content ) = @_;

                    # we know it's a text file, so we'll just stream
                    # line by line
                    while ( my $line = <$content> ) {
                        $writer->write($line);
                    }
                },
            },
        );
    }

Or you could use C<override> to control the entire streaming callback request:

    get '/download/:file' => sub {
        return send_file(
            params->{file},
            streaming => 1,
            callbacks => {
                override => sub {
                    my ( $respond, $response ) = @_;

                    my $writer = $respond->( [ $newstatus, $newheaders ] );
                    $writer->write("some line");
                },
            },
        );
    }

You can also set the number of bytes that will be read at a time (default being
42K bytes) using C<bytes>:

    get '/download/:file' => sub {
        return send_file(
            params->{file},
            streaming => 1,
            bytes     => 524288, # 512K
        );
    };

The content-type will be set depending on the current MIME types definition
(see C<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 C<send_file> as follows:

    return send_file(params->{file}, content_type => 'image/png');

Also, you can use your aliases or file extension names on
C<content_type>, like this:

    return send_file(params->{file}, content_type => 'png');

For files outside your B<public> folder, you can use the C<system_path>
switch. Just bear in mind that its use needs caution as it can be
dangerous.

   return send_file('/etc/passwd', system_path => 1);

If you have your data in a scalar variable, C<send_file> can be useful
as well. Pass a reference to that scalar, and C<send_file> will behave
as if there was a file with that contents:

   return send_file( \$data, content_type => 'image/png' );

Note that Dancer is unable to guess the content type from the data
contents. Therefore you might need to set the C<content_type>
properly. For this kind of usage an attribute named C<filename> can be
useful.  It is used as the Content-Disposition header, to hint the
browser about the filename it should use.

   return send_file( \$data, content_type => 'image/png'
                             filename     => 'onion.png' );

Note that you should always use C<return send_file ...> to stop execution of
your route handler at that point.

=head2 set

Defines a setting:

    set something => 'value';

You can set more than one value at once:

    set something => 'value', otherthing => 'othervalue';

=head2 setting

Returns the value of a given setting:

    setting('something'); # 'value'

=head2 session

Provides access to all data stored in the user's session (if any).

It can also be used as a setter to store data in the session:

    # getter example
    get '/user' => sub {
        if (session('user')) {
            return "Hello, ".session('user')->name;
        }
    };

    # setter example
    post '/user/login' => sub {
        ...
        if ($logged_in) {
            session user => $user;
        }
        ...
    };

You may also need to clear a session:

    # destroy session
    get '/logout' => sub {
        ...
        context->destroy_session;
        ...
    };

If you need to fetch the session ID being used for any reason:

    my $id = session->id;

=head2 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'} );
    };

=head2 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.

=head2 status

Changes the status code provided by an action.  By default, an action will
produce an C<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
L<Dancer2::Core::HTTP/"HTTP CODES">.

=head2 template

Returns the response of processing the given template with the given parameters
(and optional settings), wrapping it in the default or specified layout too, if
layouts are in use.

An example of a  route handler which returns the result of using template to
build a response with the current template engine:

    get '/' => sub {
        ...
        return template 'some_view', { token => 'value'};
    };

Note that C<template> simply returns the content, so when you use it in a route
handler, if execution of the route handler should stop at that point, make
sure you use 'return' to ensure your route handler returns the content.

Since template just returns the result of rendering the template, you can also
use it to perform other templating tasks, e.g. generating emails:

    post '/some/route' => sub {
        if (...) {
            email {
                to      => 'someone@example.com',
                from    => 'foo@example.com',
                subject => 'Hello there',
                msg     => template('emails/foo', { name => params->{name} }),
            };

            return template 'message_sent';
        } else {
            return template 'error';
        }
    };

Compatibility notice: C<template> was changed in version 1.3090 to immediately
interrupt execution of a route handler and return the content, as it's typically
used at the end of a route handler to return content.  However, this caused
issues for some people who were using C<template> to generate emails etc, rather
than accessing the template engine directly, so this change has been reverted
in 1.3091.

The first parameter should be a template available in the views directory, the
second one (optional) is a HashRef of tokens to interpolate, and the third
(again optional) is a HashRef of options.

For example, to disable the layout for a specific request:

    get '/' => sub {
        template 'index', {}, { layout => undef };
    };

Or to request a specific layout, of course:

    get '/user' => sub {
        template 'user', {}, { layout => 'user' };
    };

Some tokens are automatically added to your template (C<perl_version>,
C<dancer_version>, C<settings>, C<request>, C<params>, C<vars> and, if
you have sessions enabled, C<session>).  Check
L<Dancer2::Core::Role::Template> for further details.

=head2 to_dumper ($structure)

Serializes a structure with Data::Dumper.

Calling this function will B<not> trigger the serialization's hooks.

=head2 to_json ($structure, \%options)

Serializes a structure to JSON. Can receive optional arguments. Thoses arguments
are valid L<JSON> arguments to change the behaviour of the default
C<JSON::to_json> function.

Calling this function will B<not> trigger the serialization's hooks.

=head2 to_yaml ($structure)

Serializes a structure to YAML.

Calling this function will B<not> trigger the serialization's hooks.

=head2 true

Constant that returns a true value (1).

=head2 upload

Provides access to file uploads.  Any uploaded file is accessible as a
L<Dancer2::Core::Request::Upload> object. You can access all parsed uploads via:

    post '/some/route' => sub {
        my $file = upload('file_input_foo');
        # file is a Dancer2::Core::Request::Upload object
    };

If you named multiple input of type "file" with the same name, the upload
keyword will return an Array of Dancer2::Core::Request::Upload objects:

    post '/some/route' => sub {
        my ($file1, $file2) = upload('files_input');
        # $file1 and $file2 are Dancer2::Core::Request::Upload objects
    };

You can also access the raw HashRef of parsed uploads via the current request
object:

    post '/some/route' => sub {
        my $all_uploads = request->uploads;
        # $all_uploads->{'file_input_foo'} is a Dancer2::Core::Request::Upload object
        # $all_uploads->{'files_input'} is an ArrayRef of Dancer2::Core::Request::Upload objects
    };

Note that you can also access the filename of the upload received via the params
keyword:

    post '/some/route' => sub {
        # params->{'files_input'} is the filename of the file uploaded
    };

See L<Dancer2::Core::Request::Upload> for details about the interface provided.

=head2 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
    };

=head2 captures

Returns a reference to a copy of C<%+>, 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} !"
    };

=head2 var

Provides an accessor for variables shared between filters and route handlers.
Given a key/value pair, it sets a variable:

    hook before sub {
        var foo => 42;
    };

Later, route handlers and other filters will be able to read that variable:

    get '/path' => sub {
        my $foo = var 'foo';
        ...
    };

=head2 vars

Returns the HashRef of all shared variables set during the filter/route
chain with the C<var> keyword:

    get '/path' => sub {
        if (vars->{foo} eq 42) {
            ...
        }
    };

=head2 warning

Logs a warning message through the current logger engine:

    warning "This is a warning";

See L<Dancer2::Core::Role::Logger> for details on how to configure where log messages go.

=head1 AUTHOR

Dancer Core Developers

=head1 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.

=cut