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.\"
.IX Title "Plack::Component 3pm"
.TH Plack::Component 3pm 2024-01-20 "perl v5.38.2" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH NAME
Plack::Component \- Base class for PSGI endpoints
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\&  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 $res;
\&  }
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Plack::Component is the base class shared between Plack::Middleware
and \f(CW\*(C`Plack::App::*\*(C'\fR modules. If you are writing middleware, you should
inherit from Plack::Middleware, but if you are writing a
Plack::App::* you should inherit from this directly.
.SH "REQUIRED METHOD"
.IX Header "REQUIRED METHOD"
.IP "call ($env)" 4
.IX Item "call ($env)"
You are expected to implement a \f(CW\*(C`call\*(C'\fR method in your component. This
is where all the work gets done. It receives the PSGI \f(CW$env\fR hash-ref
as an argument and is expected to return a proper PSGI response value.
.SH METHODS
.IX Header "METHODS"
.IP "new (%opts | \e%opts)" 4
.IX Item "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.
.IP prepare_app 4
.IX Item "prepare_app"
This method is called by \f(CW\*(C`to_app\*(C'\fR and is meant as a hook to be used to
prepare your component before it is packaged as a PSGI \f(CW$app\fR.
.IP to_app 4
.IX Item "to_app"
This is the method used in several parts of the Plack infrastructure to
convert your component into a PSGI \f(CW$app\fR. You should not ever need to
override this method; it is recommended to use \f(CW\*(C`prepare_app\*(C'\fR and \f(CW\*(C`call\*(C'\fR
instead.
.IP response_cb 4
.IX Item "response_cb"
This is a wrapper for \f(CW\*(C`response_cb\*(C'\fR in Plack::Util. See
"RESPONSE CALLBACK" in Plack::Middleware for details.
.SH "OBJECT LIFECYCLE"
.IX Header "OBJECT LIFECYCLE"
Objects for the derived classes (Plack::App::* or
Plack::Middleware::*) are created at the PSGI application compile
phase using \f(CW\*(C`new\*(C'\fR, \f(CW\*(C`prepare_app\*(C'\fR and \f(CW\*(C`to_app\*(C'\fR, and the created
object persists during the web server lifecycle, unless it is running
on the non-persistent environment like CGI. \f(CW\*(C`call\*(C'\fR is invoked against
the same object whenever a new request comes in.
.PP
You can check if it is running in a persistent environment by checking
\&\f(CW\*(C`psgi.run_once\*(C'\fR key in the \f(CW$env\fR being true (non-persistent) or
false (persistent), but it is best for you to write your middleware
safely for a persistent environment. To accomplish that, you should
avoid saving per-request data like \f(CW$env\fR in your object.
.SH "BACKWARDS COMPATIBILITY"
.IX Header "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:
.PP
.Vb 1
\&  use Plack::Util::Accessor qw( foo bar baz );
.Ve
.PP
However, in order to keep backwards compatibility this module provides a
\&\f(CW\*(C`mk_accessors\*(C'\fR method similar to Class::Accessor::Fast. New code should
not use this and use Plack::Util::Accessor instead.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Plack Plack::Builder Plack::Middleware