NAME

Kelp::Manual - Reference to web development with Kelp

SYNOPSIS

First ...

# lib/MyApp.pm
package MyApp;
use parent 'Kelp';

sub build {
    my $self = shift;
    my $r = $self->routes;
    $r->add( "/hello", sub { "Hello, world!" } );
    $r->add( '/hello/:name', 'greet' );
}

sub greet {
    my ( $self, $name ) = @_;
    "Hello, $name!";
}

1;

Then ...

# app.psgi
use lib 'lib';
use MyApp;
my $app = MyApp->new;
$app->run;

Finally ...

> plackup app.psgi

Or, for quick prototyping use Kelp::Less:

# app.psgi
use Kelp::Less;

get '/hello/?name' => sub {
    my ( $self, $name ) = @_;
    "Hello " . $name // 'world';
};

run;

DESCRIPTION

If you're going to be deploying a Perl based web application, chances are that you will be using Plack. Plack has almost all necessary tools to create and maintain a healthy web app. Tons of middleware is written for it, and there are several very well tested high performance preforking servers, such as Gazelle.

Plack, however, is not a web framework, hence its creators have intentionally omitted adding certain components. This is where Kelp gets to shine. It provides a layer on top of Plack and puts everything together into a complete web framework.

New Kelp versions and backward compatibility

Major version 2 of Kelp introduced some breaking changes, especially when it comes to how requests are decoded and how the errors are rendered. If you are affected and don't want to modify your code, you are welcome to use a fixed version 1.07 (before the big changes). You will be missing on a lot of improvements though.

Kelp values backward compatibility, but at the same time it will not be hesitant to fix bugs, security issues or major inconveniences where it sees necessary. From 2.01 forward, non-bugfix breaking changes will only be introduced after a 3-month deprecation period. Changelog will list them under [Deprecations] section.

CREATING A NEW WEB APP

Quick development using Kelp::Less

For writing quick experimental web apps and to reduce the boiler plate, one could use Kelp::Less. In this case all of the code can be put in app.psgi: Look up the POD for Kelp::Less for many examples, but to get you started off, here is a quick one:

# app.psgi
use Kelp::Less;

module 'JSON';

get '/api/:user/?action' => sub {
    my ( $self, $user, $action ) = @_;
    my $json = {
        success => \1,
        user    => $user,
        action  => $action // 'ask'
    };
    return $json;
};

run;

Using the `Kelp` script

The easiest way to create the directory structure and a general application skeleton is by using the Kelp script, which comes with this package.

> Kelp MyApp

This will create lib/MyApp.pm, app.psgi and some other files (explained below).

To create a Kelp::Less app file, use:

> Kelp --type=less MyApp

Get help by typing:

> Kelp --help

Directory structure

Before you begin writing the internals of your app, you need to create the directory structure either by hand, or by using the above described Kelp utility script.

.
|--/lib
|   |--MyApp.pm
|   |--/MyApp
|
|--/conf
|   |--config.pl
|   |--test.pl
|   |--development.pl
|   |--deployment.pl
|
|--/views
|--/log
|--/t
|--app.psgi

/lib

The lib folder contains your application modules and any local modules that you want your app to use.

/conf

The conf folder is where Kelp will look for configuration files. You need one main file, named config.pl. You can also add other files that define different running environments, if you name them environment.pl. Replace environment with the actual name of the environment. To change the running environment, you can specify the app mode, or you can set the PLACK_ENV environment variable.

my $app = MyApp->new( mode => 'development' );

> PLACK_ENV=development plackup app.psgi

/views

This is where the Template module will look for template files.

/log

This is where the Logger module will create error.log, debug.log and any other log files that were defined in the configuration.

/t

The t folder is traditionally used to hold test files. It is up to you to use it or not, although we strongly recommend that you write some automated test units for your web app.

app.psgi

This is the PSGI file, of the app, which you will deploy. In it's most basic form it should look like this:

use lib './lib';
use MyApp;

my $app = MyApp->new;
$app->run;

The application classes

Your application's classes should be put in the lib/ folder. The main class, in our example MyApp.pm, initializes any modules and variables that your app will use. Here is an example that uses Moose to create lazy attributes and initialize a database connection:

package MyApp;

use parent Kelp;
use Moose;

has dbh => (
    is      => 'ro',
    isa     => 'DBI',
    lazy    => 1,
    default => sub {
        my $self   = shift;
        my @config = @{ $self->config('dbi') };
        return DBI->connect(@config);
    }
);

sub build {
    my $self = shift;
    $self->routes->add("/read/:id", "read");
}

sub read {
    my ( $self, $id ) = @_;
    $self->dbh->selectrow_array(q[
        SELECT * FROM problems
        WHERE id = ?
    ], $id);
}

1;

What is happening here?

First, we create a lazy attribute and instruct it to connect to DBI. Notice that we have access to the current app and all of its internals via the $self variable. Notice also that the reason we define dbh as a lazy attribute is that config will not yet be initialized. All modules are initialized upon the creation of the object instance, e.g. when we call MyApp->new;
Then, we override Kelp's "build" in Kelp subroutine to create a single route /read/:id, which is assigned to the subroutine read in the current class.
The read subroutine, takes $self and $id (the named placeholder from the path), and uses $self->dbh to retrieve data.

A note about object managers: The above example uses Moose. It is entirely up to you to use Moose, another object manager, or no object manager at all. The above example will be just as successful if you used our own little Kelp::Base:

package MyApp;
use Kelp::Base 'Kelp';

attr dbi => sub {
    ...
};

1;

FRAMEWORK BASICS

Routing

Kelp uses a powerful and very flexible router. Traditionally, it is also light and consists of less than 300 lines of code (comments included). You are encouraged to read Kelp::Routes, but here are some key points. All examples are assumed to be inside the "build" in Kelp method and $r is equal to $self->routes:

Destinations

You can direct HTTP paths to subroutines in your classes or, you can use inline code.

$r->add( "/home", "home" );  # goes to sub home
$r->add( "/legal", "Legal::view" ); # goes to MyApp::Legal::view
$r->add( "/about", sub { "Content for about" }); # inline

Restrict HTTP methods

Make a route only catch a specific HTTP method:

$r->add( [ POST => '/update' ], "update_user" );

Nesting Plack apps

It's easy to have a Plack app nested in Kelp:

$r->add( '/app', {
    to => $plack_app->to_app,
    psgi => 1,
});

See "PLACK APPS" in Kelp::Routes for details.

Named captures

Using regular expressions is so Perl. Sometimes, however, it gets a little overwhelming. Use named paths if you anticipate that you or someone else will ever want to maintain your code.

Explicit

$r->add( "/update/:id", "update" );

# Later
sub update {
    my ( $self, $id ) = @_;
    # Do something with $id
}

Optional

$r->add( "/person/?name", sub {
    my ( $self, $name ) = @_;
    return "I am " . $name // "nobody";
});

This will handle /person, /person/ and /person/jack.

Wildcards

$r->add( '/*article/:id', 'Articles::view' );

This will handle /bar/foo/baz/500 and send it to MyApp::Articles::view with parameters $article equal to bar/foo/baz and $id equal to 500.

Wildcards can also be used without a label:

# FIXME: will match both /actions/create and /actions_and_stuff
$r->add( '/actions*' => sub { ... } );

NOTE: matched contents from an unlabelled wildcard will be discarded if your route also contains named placeholders. Name it to prevent that from happening.

Slurpy

$r->add( '/other-app/>rest' => sub {
    my ( $self, $rest ) = @_;
    return "other-app called with path: " . ($rest // '<none>');
} );

This is a mix of "Wildcards" and "Optional". It works like optional placeholders but will by default also match slashes.

The use case of this is to have something that hijacks all possibilities under that path, but also matches for that base path, for example the above will match all of these:

/other-app/>rest matches:
    /other-app
    /other-app/
    /other-app/home
    /other-app/article/1

/other-app/*rest matches:
    /other-app/home
    /other-app/article/1

/other-app/?rest matches:
    /other-app
    /other-app/
    /other-app/home

Just like wildcards, slurpy placeholders can be used without a label:

# all user actions and their index in one route
$r->add( '/user/actions/>' => sub { ... } );

NOTE: matched contents from an unlabelled slurpy will be discarded if your route also contains named placeholders. Name it to prevent that from happening.

Placeholder restrictions

Paths' named placeholders can be restricted by providing regular expressions.

$r->add( '/user/:id', {
    check => { id => '\d+' },
    to    => "Users::get"
});

# Matches /user/1000, but not /user/abc

Placeholder defaults

This only applies to optional placeholders, or those prefixed with a question mark. If a default value is provided for any of them, it will be used in case the placeholder value is missing.

$r->add( '/:id/?other', defaults => { other => 'info' } );

# GET /100;
# { id => 100, other => 'info' }

# GET /100/delete;
# { id => 100, other => 'delete' }

Bridges

A bridge is a route that has to return a true value in order for the next route in line to be processed.

$r->add( '/users', { to => 'Users::auth', bridge => 1 } );
$r->add( '/users/:action' => 'Users::dispatch' );

See "BRIDGES" in Kelp::Routes for more information.

URL building

Each path can be given a name and later a URL can be built using that name and the necessary arguments.

$r->add( "/update/:id", { name => 'update', to => 'User::update' } );

# Later

my $url = $self->route->url('update', id => 1000); # /update/1000

Reading a HTTP request

All input data comes nicely packed inside Kelp::Request, which inherits Plack::Request. It has a coulpe convenience methods and handles charset decoding automatically.

Input data charsets

All request methods showcased below will try to decode request data with either charset from the Content-Type header (if present and supported by Encode module) or with application charset otherwise.

There are a couple methods starting with raw_ which return encoded data. See "ENCODING" in Kelp::Request for details.

`param` and friends

The request class has a couple of param methods, which allow quick and easy access to request parameters.

sub fetch_params {
    my $self = shift;
    my $key = 'parameter_name';

    # fetch parameters from query form, body form or JSON body
    my $json_or_body_or_query = $self->param($key);
    my $always_query = $self->res->query_param($key);
    my $always_body = $self->res->body_param($key);
    my $always_json = $self->res->json_param($key);
}

These param methods return a single value with a $key or a list of available keys with no arguments.

`parameters` and friends

These methods return a Hash::MultiValue object with parameters:

sub fetch_parameters {
    my $self = shift;

    # fetch parameters from query form or body form
    my $body_or_query = $self->res->parameters($key);
    my $always_query = $self->res->query_parameters($key);
    my $always_body = $self->res->body_parameters($key);
}

They may be more useful to get a lot of parameters in one go.

`content`, `raw_body` and `json_content`

These methods return the body of the request.

content returns the body properly decoded.

json_content tries to decode the content as json and return a Perl structure or undef on error or if it isn't a json request.

raw_body is same as content, but it has the original request encoding.

File uploads

The request object has a uploads|Plack::Request/uploads property. The uploads property returns a reference to a hash containing all uploads.

sub upload {
    my $self = shift;
    my $uploads  = $self->req->uploads;

    # Now $uploads is a hashref to all uploads
    ...
}

For Kelp::Less, then you can use the req reserved word:

get '/upload' => sub {
    my $uploads = req->uploads;
};

Other request data

See Kelp::Request and Plack::Request to see how to fetch some other data you may find useful.

Building an HTTP response

Kelp contains an elegant module, called Kelp::Response, which extends Plack::Response with several useful methods. Most methods return $self after they do the required job. For the sake of the examples below, let's assume that all of the code is located inside a route definition.

Automatic content type

Your routes don't always have to set the response object. You could just return a simple scalar value or a reference to a hash, array or anything that can be converted to JSON.

# Content-type automatically set to "text/html"
sub text_route {
    return "There, there ...";
}

# Content-type automatically set to "application/json"
sub json_route {
    return { error => 1,  message => "Fail" };
}

Automatic charset encoding

With Kelp, you don't have to worry about the encoding of the response - most of the methods will automatically encode the response into configured application's charset. Plaintext and HTML content types will by default have charset part added. To make it all work flawlessly, remember to use utf8; at the top of your files.

If you'd like to instead take charset into your own hands, you will have to use "render_binary" in Kelp::Response and manually set content types and charsets.

Rendering text

# Render simple text
$self->res->text->render("It works!");

Rendering HTML

$self->res->html->render("<h1>It works!</h1>");

Custom content type

$self->res->set_content_type('image/png');

Return 404 or 500 errors

sub some_route {
    my $self = shift;
    if ($missing) {
        return $self->res->render_404;
    }
    if ($broken) {
        return $self->res->render_500;
    }
}

Templates

sub hello {
    my ( $self, $name ) = @_;
    $self->res->template( 'hello.tt', { name => $name } );
}

The above example will render the contents of hello.tt, and it will set the content-type to text/html. To set a different content-type, use set_content_type or any of its aliases:

sub hello_txt {
    my ( $self, $name ) = @_;
    $self->res->text->template( 'hello_txt.tt', { name => $name } );
}

Headers

$self->set_header( "X-Framework", "Kelp" )->render( { success => \1 } );

Serving static files

If you want to serve static pages, you can use the Plack::Middleware::Static middleware that comes with Plack. Here is an example configuration that serves files in your public folder (under the Kelp root folder) from URLs that begin with /public:

# conf/config.pl
{
    middleware      => [qw/Static/],
    middleware_init => {
        Static => {
            path => qr{^/public/},
            root => '.',
        }
    }
};

Delayed responses

To send a delayed response, have your route return a subroutine.

sub delayed {
    my $self = shift;
    return sub {
        my $responder = shift;
        $self->res->code(200);
        $self->res->text->body("Better late than never.");
        $responder->($self->res->finalize);
    };
}

See the PSGI pod for more information and examples.

CONFIGURING THE APPLICATION

Adding middleware

Kelp, being Plack-centric, will let you easily add middleware. There are three possible ways to add middleware to your application, and all three ways can be used separately or together.

Using the configuration

Adding middleware in your configuration is probably the easiest and best way for you. This way you can load different middleware for each running mode, e.g. Debug in development only.

Add middleware names to the middleware array in your configuration file and the corresponding initializing arguments in the middleware_init hash:

# conf/development.pl
{
    middleware      => [qw/Session Debug/],
    middleware_init => {
        Session => { store => 'File' }
    }
}

The middleware will be added in the order you specify in the middleware array.

In `app.psgi`:

# app.psgi
use MyApp;
use Plack::Builder;

my $app = MyApp->new();

builder {
    enable "Plack::Middleware::ContentLength";
    $app->run;
};

By overriding the "run" in Kelp subroutine in `lib/MyApp.pm`:

Make sure you call SUPER first, and then wrap new middleware around the returned app.

# lib/MyApp.pm
sub run {
    my $self = shift;
    my $app = $self->SUPER::run(@_);
    $app = Plack::Middleware::ContentLength->wrap($app);
    return $app;
}

Note that any middleware defined in your config file will be added first.

Pluggable modules

How to load modules using the config

Kelp can be extended using custom modules. There are two modules that are always loaded by each application instance. Those are Config and Routes. The reason behind this is that each and every application always needs a router and configuration. All other modules must be loaded either using the "load_module" in Kelp method, or using the modules key in the configuration. The default configuration already loads these modules: Template, Logger and JSON. Your configuration can remove some and/or add others. The configuration key modules_init may contain hashes with initialization arguments. See Kelp::Module for configuration examples.

Creating your own module

Each new module must be a subclass of the Kelp::Module class. Modules' job is to initialize and register new methods into the web application class. Here is a simple module which initializes an extremely simple cache:

package Kelp::Module::ExampleCache;

use Kelp::Base 'Kelp::Module';

sub build {
    my ($self, %args) = @_;

    my $case_sensitive = !$args{case_insensitive};
    my %cache;

    $self->register(cache_set => sub {
        my ($app, $key, $value) = @_;
        $cache{$case_sensitive ? $key : lc $key} = $value;
    });

    $self->register(cache_get => sub {
        my ($app, $key) = @_;
        return $cache{$case_sensitive ? $key : lc $key};
    });

}

1;

What is happening here?

First we create a class Kelp::Module::ExampleCache which inherits Kelp::Module.
Then, we override the build method (of Kelp::Module), we fetch the case_insensitive value from the configuration (configured under modules_init.ExampleCache.case_insensitive).
Last step is to initialize the hash which will store the keys and register two methods into the web application via the register method. They will be ready to use in the main application class.

See more examples and POD at Kelp::Module.

Reblessing into controller classes

All of the examples here show routes which take a instance of the web application as a first parameter. This is true even if those routes live in another class.

To rebless the app instance into the controller class instance, the controller class must extend the class specified in base configuration field. The default value of that field is the application class, so your application class is by default your main controller class. All other controllers must (directly or indirectly) inherit from your application class.

Step 1: Configure the controller

It is a good practice to set up a different base, so that you separate general app code from request-handling code.

# config.pl
{
    modules_init => {
        Routes => {
            rebless => 1, # the app instance will be reblessed
            base => 'MyApp::Controller',
        }
    }
}

Step 2: Create a main controller class

This step is only required if you've changed the base.

# lib/MyApp/Controller.pm
package MyApp::Controller;
use Kelp::Base 'MyApp';

# Now $self is an instance of 'MyApp::Controller';
sub service_method {
    my $self = shift;
    ...;
}

1;

Step 3: Create any number of controller classes

They all must inherit from your main controller class.

# lib/MyApp/Controller/Users.pm
package MyApp::Controller::Users;
use Kelp::Base 'MyApp::Controller';

# Now $self is an instance of 'MyApp::Controller::Users'
sub authenticate {
    my $self = shift;
    ...;
}

1;

Step 4: Add routes with shorter class names

You no longer have to prefix destinations with the base controller class name.

# lib/MyApp.pm

...

sub build {
    my $self = shift;

    # if 'base' was not changed, this would have to be written as:
    # => 'Controller::Users::authenticate'
    $self->add_route('/login' => 'Users::authenticate');

}

NEXT STEPS

Testing

Kelp provides a test class called Kelp::Test. It is object oriented, and all methods return the Kelp::Test object, so they can be chained together. Testing is done by sending HTTP requests to an already built application and analyzing the response. Therefore, each test usually begins with the "request" in Kelp::Test method, which takes a single HTTP::Request parameter. It sends the request to the web app and saves the response as an HTTP::Response object.

# file t/test.t
use MyApp;
use Kelp::Test;
use Test::More;
use HTTP::Request::Common;

my $app = MyApp->new( mode => 'test' );
my $t = Kelp::Test->new( app => $app );

$t->request( GET '/path' )
  ->code_is(200)
  ->content_is("It works");

$t->request( POST '/api' )
  ->json_cmp({auth => 1});

done_testing;

What is happening here?

First, we create an instance of the web application class, which we have previously built and placed in the lib/ folder. We set the mode of the app to test, so that file conf/test.pl overrides the main configuration. The test configuration can contain anything you see fit. Perhaps you want to disable certain modules, or maybe you want to make DBI connect to a different database.
Second, we create an instance of the Kelp::Test class and tell it that it will perform all tests using our $app instance.
At this point we are ready to send requests to the app via the request method. It takes only one argument, an HTTP::Request object. It is very convenient to use the HTTP::Request::Common module here, because you can create common requests using abridged syntax, i.e. GET, POST, etc. The line $t->request( GET '/path' ) first creates a HTTP::Request GET object, and then passes it to the request method.
After we send the request, we can test the response using any of the Test:: modules, or via the methods provided by Kelp::Test. In the above example, we test if we got a code 200 back from /path and if the returned content was It works.

Run the rest as usual, using prove:

> prove -l t/test.t

Take a look at the Kelp::Test for details and more examples.

Common problems and solutions

You may want to take a look at our Kelp::Manual::Cookbook.

SUPPORT

GitHub: https://github.com/Kelp-framework/Kelp
Mailing list: https://groups.google.com/g/perl-kelp

AUTHOR

Stefan Geneshky - minimal <at> cpan.org

Currently maintained by Bartosz Jarzyna - bbrtj.pro <at> gmail.com

CONTRIBUTORS

In no particular order:

Julio Fraire

Maurice Aubrey

David Steinbrunner

Gurunandan Bhat

Perlover

Ruslan Zakirov

Christian Froemmel (senfomat)

Ivan Baidakou (basiliscos)

roy-tate

Konstantin Yakunin (@yakunink)

Benjamin Hengst (notbenh)

Nikolay Mishin (@mishin)

Bartosz Jarzyna (bbrtj)

LICENSE

This module and all the modules in this package are governed by the same license as Perl itself.

To install Kelp, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Kelp

CPAN shell

perl -MCPAN -e shell
install Kelp

For more information on module installation, please visit the detailed CPAN module installation guide.

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NAME

SYNOPSIS

DESCRIPTION

New Kelp versions and backward compatibility

CREATING A NEW WEB APP

Quick development using Kelp::Less

Using the Kelp script

Directory structure

The application classes

FRAMEWORK BASICS

Routing

Destinations

Restrict HTTP methods

Nesting Plack apps

Named captures

Explicit

Optional

Wildcards

Slurpy

Placeholder restrictions

Placeholder defaults

Bridges

URL building

Reading a HTTP request

Input data charsets

param and friends

parameters and friends

content, raw_body and json_content

File uploads

Other request data

Building an HTTP response

Automatic content type

Automatic charset encoding

Rendering text

Rendering HTML

Custom content type

Return 404 or 500 errors

Templates

Headers

Serving static files

Delayed responses

CONFIGURING THE APPLICATION

Adding middleware

Using the configuration

In app.psgi:

By overriding the "run" in Kelp subroutine in lib/MyApp.pm:

Pluggable modules

How to load modules using the config

Creating your own module

Reblessing into controller classes

Step 1: Configure the controller

Step 2: Create a main controller class

Step 3: Create any number of controller classes

Step 4: Add routes with shorter class names

NEXT STEPS

Testing

Common problems and solutions

SUPPORT

AUTHOR

CONTRIBUTORS

LICENSE

Module Install Instructions

Using the `Kelp` script

`param` and friends

`parameters` and friends

`content`, `raw_body` and `json_content`

In `app.psgi`:

By overriding the "run" in Kelp subroutine in `lib/MyApp.pm`: