NAME
    Kelp - A web framework light, yet rich in nutrients.

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 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 Starman.

    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.

    Kelp provides:

    *   Advanced Routing. Create intricate, yet simple ways to capture HTTP
        requests and route them to their designated code. Use explicit and
        optional named placeholders, wildcards, or just regular expressions.

    *   Flexible Configuration. Use different configuration file for each
        environment, e.g. development, deployment, etc. Merge a temporary
        configuration into your current one for testing and debugging
        purposes.

    *   Enhanced Logging. Log messages at different levels of emergency. Log
        to a file, screen, or anything supported by Log::Dispatcher.

    *   Powerful Rendering. Use the built-in auto-rendering logic, or the
        template module of your choice to return rich text, html and JSON
        responses.

    *   JSON encoder/decoder. If you're serious about your back-end code.
        Kelp comes with JSON, but you can easily plug in JSON::XS or any
        decoder of your choice.

    *   Extendable Core. Kelp uses pluggable modules for everything. This
        allows anyone to add a module for a custom interface. Writing Kelp
        modules is a pleasant and fulfilling activity.

    *   Sleek Testing. Kelp takes Plack::Test and wraps it in an object
        oriented class of convenience methods. Testing is done via sending
        requests to your routes, then analyzing the response.

WHY KELP?
    What makes Kelp different from the other Perl micro web frameworks?
    There are a number of fine web frameworks on CPAN, and most of them
    provide a complete platform for web app building. Most of them, however,
    bring their deployment code, and aim to write their own processing
    mechanisms. Kelp, on the other hand, is heavily *Plack*-centric. It uses
    Plack as its foundation layer, and it builds the web framework on top of
    it. "Kelp::Request" is an extension of "Plack::Request",
    "Kelp::Response" is an extension of "Plack::Response".

    This approach of extending current CPAN code puts familiar and well
    tested tools in the hands of the application developer, while keeping
    familiar syntax and work flow.

    Kelp is a team player and it uses several popular, trusted CPAN modules
    for its internals. At the same time it doesn't include modules that it
    doesn't need, just because they are considered trendy. It does its best
    to keep a lean profile and a small footprint, and it's completely object
    manager agnostic.

CREATING A NEW WEB APP
  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, use:

        > Kelp --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
         |
         |--/view
         |--/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' );

        or

            > PLACK_ENV=development plackup app.psgi

    /view
        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 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" 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;

  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" 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" );

   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.

   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

  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;

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

        run;

  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" 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 = $self->SUPER::run(@_);
            Plack::Middleware::ContentLength->wrap($app);
        }

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

  Deploying
    Deploying a Kelp application is done the same way any other Plack
    application is deployed:

        > plackup -E deployment -s Starman app.psgi

  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' )" fist
        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.

  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" };
        }

   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 } );

   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.

  Pluggable modules
    Kelp can be extended using custom *modules*. Each new module must be a
    subclass of the "Kelp::Module" namespace. Modules' job is to initialize
    and register new methods into the web application class. The following
    is the full code of the Kelp::Module::JSON for example:

        package Kelp::Module::JSON;

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

        sub build {
            my ( $self, %args ) = @_;
            my $json = JSON->new;
            $json->property( $_ => $args{$_} ) for keys %args;
            $self->register( json => $json );
        }

        1;

    What is happening here?

    *   First we create a class "Kelp::Module::JSON" which inherits
        "Kelp::Module".

    *   Then, we override the "build" method (of "Kelp::Module"), create a
        new JSON object and register it into the web application via the
        "register" method.

    If we instruct our web application to load the "JSON" module, it will
    have a new method "json" which will be a link to the "JSON" object
    initialized in the module.

    See more exampled and POD at Kelp::Module.

   How to load modules using the config
    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" 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.

ATTRIBUTES
  hostname
    Gets the current hostname.

        sub some_route {
            my $self = shift;
            if ( $self->hostname eq 'prod-host' ) {
                ...
            }
        }

  mode
    Sets or gets the current mode. The mode is important for the app to know
    what configuration file to merge into the main configuration. See
    Kelp::Module::Config for more information.

        my $app = MyApp->new( mode => 'development' );
        # conf/config.pl and conf/development.pl are merged with priority
        # given to the second one.

  config_module
    Sets of gets the class of the configuration module to be loaded on
    startup. The default value is "Config", which will cause the
    "Kelp::Module::Config" to get loaded. See the documentation for
    Kelp::Module::Config for more information and for an example of how to
    create and use other config modules.

  path
    Gets the current path of the application. That would be the path to
    "app.psgi"

  name
    Gets or sets the name of the application. If not set, the name of the
    main class will be used.

        my $app = MyApp->new( name => 'Twittar' );

  charset
    Sets of gets the encoding charset of the app. It will be "UTF-8", if not
    set to anything else. The charset could also be changed in the config
    files.

  req
    This attribute only makes sense if called within a route definition. It
    will contain a reference to the current Kelp::Request instance.

        sub some_route {
            my $self = shift;
            if ( $self->req->is_json ) {
                ...
            }
        }

  res
    This attribute only makes sense if called within a route definition. It
    will contain a reference to the current Kelp::Response instance.

        sub some_route {
            my $self = shift;
            $self->res->json->render( { success => 1 } );
        }

METHODS
  build
    On it's own the "build" method doesn't do anything. It is called by the
    constructor, so it can be overridden to add route destinations and
    initializations.

        package MyApp;

        sub build {
            my $self = shift;
            my $r = $self->routes;

            # Load some modules
            $self->load_module("MongoDB");
            $self->load_module("Validate");

            # Add all route destinations
            $r->add("/one", "one");
            ...

        }

  load_module
    Used to load a module. All modules must be under the "Kelp::Module::"
    namespace.

        $self->load_module("Redis");
        # Will look for an load Kelp::Module::Redis

    See Kelp::Module for more information on making and using modules.

  request
    This method is used to create the request object for each HTTP request.
    It returns and instance of Kelp::Request, initialized with the current
    requests environment. You can override this method to use a custom
    request module.

        package MyApp;
        use MyApp::Request;

        sub request {
            my ( $self, $env ) = @_;
            return MyApp::Requst->new( app => $app, env => $env );
        }

        # Now each request will be handled by MyApp::Request

  before_render
    Override this method, to modify the response object just before it gets
    rendered.

        package MyApp;

        sub before_render {
            my $self = shift;
            $self->res->set_header("X-App-Name", "MyApp");
        }

        ...

    The above is an example of how to insert a custom header into the
    response of every route.

  response
    This method creates the response object, e.g. what an HTTP request will
    return. By default the object created is Kelp::Response. Much like
    "request", the response can also be overridden to use a custom response
    object.

  run
    This method builds and returns the PSGI app. You can override it in
    order to include middleware. See "Adding middleware" for an example.

  param
    A shortcut to "$self->req->param":

        sub some_route {
            my $self = shift;
            if ( $self->param('age') > 18 ) {
                $self->can_watch_south_path(1);
            }
        }

    See Kelp::Request for more information and examples.

  stash
    Provides safe access to "$self->req->stash". When called without
    arguments, it will return the stash hash. If called with a single
    argument, it will return the value of the corresponding key in the
    stash. See "stash" in Kelp::Request for more information and examples.

  named
    Provides safe access to "$self->req->named". When called without
    arguments, it will return the named hash. If called with a single
    argument, it will return the value of the corresponding key in the named
    hash. See "named" in Kelp::Request for more information and examples.

  url_for
    A safe shortcut to "$self->routes->url". Builds a URL from path and
    arguments.

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

        sub check {
            my $self = shift;
            my $url_for_name = $self->url_for('name', name => 'jake', id => 1003);
            $self->res->redirect_to();
        }

SUPPORT
    *   GitHub: https://github.com/naturalist/kelp

    *   Mailing list:
        https://groups.google.com/forum/?fromgroups#!forum/perl-kelp

AUTHOR
    Stefan Geneshky - minimal@cpan.org

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