NAME¶
Catalyst::PSGI - How Catalyst and PSGI work together
SYNOPSIS¶
The PSGI specification defines an interface between web servers and Perl-based
web applications and frameworks. It supports the writing of portable
applications that can be run using various methods (as a standalone server, or
using mod_perl, FastCGI, etc.). Plack is an implementation of the PSGI
specification for running Perl applications.
Catalyst used to contain an entire set of "Catalyst::Engine::XXXX"
classes to handle various web servers and environments (e.g. CGI, FastCGI,
mod_perl) etc.
This has been changed in Catalyst 5.9 so that all of that work is done by
Catalyst implementing the PSGI specification, using Plack's adaptors to
implement that functionality.
This means that we can share common code, and share fixes for specific web
servers.
I already have an application¶
If you already have a Catalyst application, then you should be able to upgrade
to the latest release with little or no trouble (see the notes in
Catalyst::Upgrading for specifics about your web server deployment).
Writing your own PSGI file.¶
What is a .psgi file?¶
A ".psgi" file lets you control how your application code reference is
built. Catalyst will automatically handle this for you, but it's possible to
do it manually by creating a "myapp.psgi" file in the root of your
application.
Why would I want to write my own .psgi file?¶
Writing your own .psgi file allows you to use the alternate plackup command to
start your application, and allows you to add classes and extensions that
implement Plack::Middleware, such as Plack::Middleware::ErrorDocument or
Plack::Middleware::AccessLog.
The simplest ".psgi" file for an application called
"TestApp" would be:
use strict;
use warnings;
use TestApp;
my $app = TestApp->psgi_app(@_);
Note that Catalyst will apply a number of middleware components for you
automatically, and these
will not be applied if you manually create a
psgi file yourself. Details of these components can be found below.
Additional information about psgi files can be found at:
<
http://search.cpan.org/dist/Plack/lib/Plack.pm#.psgi_files>
What is in the .psgi file Catalyst generates by default?¶
Catalyst generates an application which, if the "using_frontend_proxy"
setting is on, is wrapped in Plack::Middleware::ReverseProxy, and contains
some engine-specific fixes for uniform behaviour, as contained in:
- Plack::Middleware::LighttpdScriptNameFix
- Plack::Middleware::IIS6ScriptNameFix
If you override the default by providing your own ".psgi" file, then
none of these things will be done automatically for you by the PSGI
application returned when you call "MyApp->psgi_app". Thus, if
you need any of this functionality, you'll need to implement this in your
".psgi" file yourself.
An apply_default_middlewares method is supplied to wrap your application in the
default middlewares if you want this behaviour and you are providing your own
.psgi file.
This means that the auto-generated (no .psgi file) code looks something like
this:
use strict;
use warnings;
use TestApp;
my $app = TestApp->apply_default_middlewares(TestApp->psgi_app(@_));
SEE ALSO¶
Catalyst::Upgrading, Plack, PSGI::FAQ, PSGI.
AUTHORS¶
Catalyst Contributors, see Catalyst.pm
COPYRIGHT¶
This library is free software. You can redistribute it and/or modify it under
the same terms as Perl itself.