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 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" 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 } );
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 => '.',
}
}
};
Uploading files
File uploads are handled by Kelp::Request, which inherits Plack::Request
and has its "uploads|Plack::Request/uploads" property. The uploads
propery 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;
};
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.
loaded_modules
A hashref containing the names and instances of all loaded modules. For
example, if you have these two modules loaded: Template and JSON, then a
dump of the "loaded_modules" hash will look like this:
{
Template => Kelp::Module::Template=HASH(0x208f6e8),
JSON => Kelp::Module::JSON=HASH(0x209d454)
}
This can come handy if your module does more than just registering a new
method into the application. Then, you can use its object instance to do
access that additional functionality.
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.
long_error
When a route dies, Kelp will by default display a short error message.
Set this attribute to a true value, if you need to see a full stack
trace of the error. The "KELP_LONG_ERROR" environment variable can also
set this attribute.
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
$r->add("/one", "one");
...
}
load_module
"load_module($name, %options)"
Used to load a module. All modules must be under the "Kelp::Module::"
namespace.
$self->load_module("Redis", server => '127.0.0.1');
# Will look for and load Kelp::Module::Redis
Options for the module may be specified after its name, or in the
"modules_init" hash in the config. The precedence is given to the inline
options. 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 an instance of Kelp::Request, initialized with the current
request's 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_finalize
Override this method, to modify the response object just before it gets
finalized.
package MyApp;
sub before_finalize {
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 ) {
$self->can_watch_south_path(1);
}
}
See Kelp::Request for more information and examples.
session
A shortcut to "$self->req->session". Take a look at "session" in
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( $url_for_name );
}
SUPPORT
* GitHub: https://github.com/naturalist/kelp
* Mailing list:
https://groups.google.com/forum/?fromgroups#!forum/perl-kelp
AUTHOR
Stefan Geneshky - minimal@cpan.org
CONTRIBUTORS
Gurunandan Bhat - gbhat@pobox.com
LICENSE
This module and all the modules in this package are governed by the same
license as Perl itself.