NAME

       Plack::Component - Base class for PSGI endpoints

SYNOPSIS

         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;
         }

DESCRIPTION

       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.

REQUIRED METHOD

       call ($env)
           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.

METHODS

       new (%opts | \%opts)
           The constructor accepts either a hash or a hashref and uses that to create the
           instance. It will call no other methods and simply return the instance that is
           created.

       prepare_app
           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
           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.

       response_cb
           This is a wrapper for "response_cb" in Plack::Util. See "RESPONSE CALLBACK" in
           Plack::Middleware for details.

OBJECT LIFECYCLE

       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.

       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.

BACKWARDS COMPATIBILITY

       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.

SEE ALSO

       Plack Plack::Builder Plack::Middleware