Plack::Component - Base class for PSGI endpoints
package Plack::App::Foo; use parent qw( Plack::Component ); sub call { my($self, $env) = @_; # Do something with $env my $res = ...; # create a response ... # return the response return $res; }
Plack::Component is the base class shared between Plack::Middleware and Plack::App::* modules. If you are writing middleware, you should inherit from Plack::Middleware, but if you are writing a Plack::App::* you should inherit from this directly.
You are expected to implement a call method in your component. This is where all the work gets done. It receives the PSGI $env hash-ref as an argument and is expected to return a proper PSGI response value.
call
$env
The constructor accepts either a hash or a hash-ref and uses that to create the instance with. It will call no other methods and simply return the instance that is created.
This method is called by to_app and is meant as a hook to be used to prepare your component before it is packaged as a PSGI $app.
to_app
$app
This is the method used in several parts of the Plack infrastructure to convert your component into a PSGI $app. You should not ever need to override this method, it is recommended to use prepare_app and call instead.
prepare_app
This is a wrapper for response_cb in Plack::Util. See "RESPONSE CALLBACK" in Plack::Middleware for details.
response_cb
Objects for the derived classes (Plack::App::* or Plack::Middleware::*) are created at the PSGI application compile phase using new, prepare_app and to_app, and the created object persists during the web server lifecycle, unless it is running on the non-persistent environment like CGI. call is invoked against the same object whenever a new request comes in.
new
You can check if it is running in a persistent environment by checking psgi.run_once key in the $env being true (non-persistent) or false (persistent), but it is best for you to write your middleware safely for a persistent environment. To accomplish that, you should avoid saving per-request data like $env in your object.
psgi.run_once
The Plack::Middleware module used to inherit from Class::Accessor::Fast, which has been removed in favor of the Plack::Util::Accessor module. When developing new components it is recommended to use Plack::Util::Accessor like so:
use Plack::Util::Accessor qw( foo bar baz );
However, in order to keep backwards compatibility this module provides a mk_accessors method similar to Class::Accessor::Fast. New code should not use this and use Plack::Util::Accessor instead.
mk_accessors
Plack Plack::Builder Plack::Middleware
To install Plack, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Plack
CPAN shell
perl -MCPAN -e shell install Plack
For more information on module installation, please visit the detailed CPAN module installation guide.