Provided by: libdancer2-perl_1.1.0+dfsg-1_all 
NAME
Dancer2::Plugin - base class for Dancer2 plugins
VERSION
version 1.1.0
SYNOPSIS
The plugin itself:
package Dancer2::Plugin::Polite;
use strict;
use warnings;
use Dancer2::Plugin;
has smiley => (
is => 'ro',
default => sub {
$_[0]->config->{smiley} || ':-)'
}
);
plugin_keywords 'add_smileys';
sub BUILD {
my $plugin = shift;
$plugin->app->add_hook( Dancer2::Core::Hook->new(
name => 'after',
code => sub { $_[0]->content( $_[0]->content . " ... please?" ) }
));
$plugin->app->add_route(
method => 'get',
regexp => '/goodbye',
code => sub {
my $app = shift;
'farewell, ' . $app->request->params->{name};
},
);
}
sub add_smileys {
my( $plugin, $text ) = @_;
$text =~ s/ (?<= \. ) / $plugin->smiley /xeg;
return $text;
}
1;
then to load into the app:
package MyApp;
use strict;
use warnings;
use Dancer2;
BEGIN { # would usually be in config.yml
set plugins => {
Polite => {
smiley => '8-D',
},
};
}
use Dancer2::Plugin::Polite;
get '/' => sub {
add_smileys( 'make me a sandwich.' );
};
1;
DESCRIPTION
Writing the plugin
"use Dancer2::Plugin"
The plugin must begin with
use Dancer2::Plugin;
which will turn the package into a Moo class that inherits from Dancer2::Plugin. The base
class provides the plugin with two attributes: "app", which is populated with the Dancer2
app object for which the plugin is being initialized for, and "config" which holds the
plugin section of the application configuration.
Modifying the app at building time
If the plugin needs to tinker with the application -- add routes or hooks, for example --
it can do so within its "BUILD()" function.
sub BUILD {
my $plugin = shift;
$plugin->app->add_route( ... );
}
Adding keywords
Via "plugin_keywords"
Keywords that the plugin wishes to export to the Dancer2 app can be defined via the
"plugin_keywords" keyword:
plugin_keywords qw/
add_smileys
add_sad_kitten
/;
Each of the keyword will resolve to the class method of the same name. When invoked as
keyword, it'll be passed the plugin object as its first argument.
sub add_smileys {
my( $plugin, $text ) = @_;
return join ' ', $text, $plugin->smiley;
}
# and then in the app
get '/' => sub {
add_smileys( "Hi there!" );
};
You can also pass the functions directly to "plugin_keywords".
plugin_keywords
add_smileys => sub {
my( $plugin, $text ) = @_;
$text =~ s/ (?<= \. ) / $plugin->smiley /xeg;
return $text;
},
add_sad_kitten => sub { ... };
Or a mix of both styles. We're easy that way:
plugin_keywords
add_smileys => sub {
my( $plugin, $text ) = @_;
$text =~ s/ (?<= \. ) / $plugin->smiley /xeg;
return $text;
},
'add_sad_kitten';
sub add_sad_kitten {
...;
}
If you want several keywords to be synonyms calling the same function, you can list them
in an arrayref. The first function of the list is taken to be the "real" method to link to
the keywords.
plugin_keywords [qw/ add_smileys add_happy_face /];
sub add_smileys { ... }
Calls to "plugin_keywords" are cumulative.
Via the ":PluginKeyword" function attribute
For perl 5.12 and higher, keywords can also be defined by adding the ":PluginKeyword"
attribute to the function you wish to export.
For Perl 5.10, the export triggered by the sub attribute comes too late in the game, and
the keywords won't be exported in the application namespace.
sub foo :PluginKeyword { ... }
sub bar :PluginKeyword( baz quux ) { ... }
# equivalent to
sub foo { ... }
sub bar { ... }
plugin_keywords 'foo', [ qw/ baz quux / ] => \&bar;
For an attribute
You can also turn an attribute of the plugin into a keyword.
has foo => (
is => 'ro',
plugin_keyword => 1, # keyword will be 'foo'
);
has bar => (
is => 'ro',
plugin_keyword => 'quux', # keyword will be 'quux'
);
has baz => (
is => 'ro',
plugin_keyword => [ 'baz', 'bazz' ], # keywords will be 'baz' and 'bazz'
);
Accessing the plugin configuration
The plugin configuration is available via the "config()" method.
sub BUILD {
my $plugin = shift;
if ( $plugin->config->{feeling_polite} ) {
$plugin->app->add_hook( Dancer2::Core::Hook->new(
name => 'after',
code => sub { $_[0]->content( $_[0]->content . " ... please?" ) }
));
}
}
Getting default values from config file
Since initializing a plugin with either a default or a value passed via the configuration
file, like
has smiley => (
is => 'ro',
default => sub {
$_[0]->config->{smiley} || ':-)'
}
);
"Dancer2::Plugin" allows for a "from_config" key in the attribute definition. Its value
is the plugin configuration key that will be used to initialize the attribute.
If it's given the value 1, the name of the attribute will be taken as the configuration
key.
Nested hash keys can also be referred to using a dot notation.
If the plugin configuration has no value for the given key, the attribute default, if
specified, will be honored.
If the key is given a coderef as value, it's considered to be a "default" value combo:
has foo => (
is => 'ro',
from_config => sub { 'my default' },
);
# equivalent to
has foo => (
is => 'ro',
from_config => 'foo',
default => sub { 'my default' },
);
For example:
# in config.yml
plugins:
Polite:
smiley: ':-)'
greeting:
casual: Hi!
formal: How do you do?
# in the plugin
has smiley => ( # will be ':-)'
is => 'ro',
from_config => 1,
default => sub { ':-(' },
);
has casual_greeting => ( # will be 'Hi!'
is => 'ro',
from_config => 'greeting.casual',
);
has apology => ( # will be 'sorry'
is => 'ro',
from_config => 'apology',
default => sub { 'sorry' },
)
has closing => ( # will be 'See ya!'
is => 'ro',
from_config => sub { 'See ya!' },
);
Config becomes immutable
The plugin's "config" attribute is loaded lazily on the first call to "config". After this
first call "config" becomes immutable so you cannot do the following in a test:
use Dancer2;
use Dancer2::Plugin::FooBar;
set plugins => {
FooBar => {
wibble => 1, # this is OK
},
};
flibble(45); # plugin keyword called which causes config read
set plugins => {
FooBar => {
wibble => 0, # this will NOT change plugin config
},
};
Accessing the parent Dancer app
If the plugin is instantiated within a Dancer app, it'll be accessible via the method
"app()".
sub BUILD {
my $plugin = shift;
$plugin->app->add_route( ... );
}
To use Dancer's DSL in your plugin:
$self->dsl->debug( “Hi! I’m logging from your plugin!” );
See "DSL KEYWORDS" in Dancer2::Manual for a full list of Dancer2 DSL.
Using the plugin within the app
A plugin is loaded via
use Dancer2::Plugin::Polite;
The plugin will assume that it's loading within a Dancer module and will automatically
register itself against its "app()" and export its keywords to the local namespace. If you
don't want this to happen, specify that you don't want anything imported via empty
parentheses when "use"ing the module:
use Dancer2::Plugin::Polite ();
Plugins using plugins
It's easy to use plugins from within a plugin:
package Dancer2::Plugin::SourPuss;
use Dancer2::Plugin;
use Dancer2::Plugin::Polite;
sub my_keyword { my $smiley = smiley(); }
1;
This does not export "smiley()" into your application - it is only available from within
your plugin. However, from the example above, you can wrap DSL from other plugins and make
it available from your plugin.
Utilizing other plugins
You can use the "find_plugin" to locate other plugins loaded by the user, in order to use
them, or their information, directly:
# MyApp.pm
use Dancer2;
use Dancer2::Plugin::Foo;
use Dancer2::Plugin::Bar;
# Dancer2::Plugin::Bar;
...
sub my_keyword {
my $self = shift;
my $foo = $self->find_plugin('Dancer2::Plugin::Foo')
or $self->dsl->send_error('Could not find Foo');
return $foo->foo_keyword(...);
}
Hooks
New plugin hooks are declared via "plugin_hooks".
plugin_hooks 'my_hook', 'my_other_hook';
Hooks are prefixed with "plugin.plugin_name". So the plugin "my_hook" coming from the
plugin "Dancer2::Plugin::MyPlugin" will have the hook name "plugin.myplugin.my_hook".
Hooks are executed within the plugin by calling them via the associated app.
$plugin->execute_plugin_hook( 'my_hook' );
You can also call any other hook if you provide the full name using the "execute_hook"
method:
$plugin->app->execute_hook( 'core.app.route_exception' );
Or using their alias:
$plugin->app->execute_hook( 'on_route_exception' );
Note: If your plugin consumes a plugin that declares any hooks, those hooks are added to
your application, even though DSL is not.
Writing Test Gotchas
Constructor for Dancer2::Plugin::Foo has been inlined and cannot be updated
You'll usually get this one because you are defining both the plugin and app in your test
file, and the runtime creation of Moo's attributes happens after the compile-time import
voodoo dance.
To get around this nightmare, wrap your plugin definition in a "BEGIN" block.
BEGIN {
package Dancer2::Plugin::Foo;
use Dancer2::Plugin;
has bar => (
is => 'ro',
from_config => 1,
);
plugin_keywords qw/ bar /;
}
{
package MyApp;
use Dancer2;
use Dancer2::Plugin::Foo;
bar();
}
You cannot overwrite a locally defined method (bar) with a reader
If you set an object attribute of your plugin to be a keyword as well, you need to call
"plugin_keywords" after the attribute definition.
package Dancer2::Plugin::Foo;
use Dancer2::Plugin;
has bar => (
is => 'ro',
);
plugin_keywords 'bar';
AUTHOR
Dancer Core Developers
COPYRIGHT AND LICENSE
This software is copyright (c) 2023 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.