Tatsuhiko Miyagawa > Plack-0.99_05 > Plack



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Module Version: 0.99_05   Source   Latest Release: Plack-1.0040-TRIAL


Plack - Perl Superglue for Web frameworks and Web Servers (PSGI toolkit)


Plack is a set of tools for using PSGI stack. It contains middleware components, a reference server and utilities for Web application frameworks. Plack is like Ruby's Rack or Python's Paste for WSGI.

See PSGI for the PSGI specification and PSGI::FAQ to know what PSGI and Plack are and why we need them.



Plack::Handler and its subclasses contains adapters for web servers. We have adapters for Standalone, CGI, FCGI, Apache, AnyEvent, Coro, Danga::Socket and many server environments that you can run PSGI applications on.

See Plack::Handler how to write your own adapters.


Plack::Loader is a loader to load one of Plack::Server adapters and run PSGI application code reference with it.


Plack::Util contains a lot of utility functions for server implementors as well as middleware authors.

.psgi files

PSGI application is a code reference but it's not easy to pass code reference in the command line or configuration files, so Plack uses a convention that you need a file named app.psgi or alike, which would be loaded (via perl's core function do) to return the PSGI application code reference.

  # Hello.psgi
  my $app = sub {
      my $env = shift;
      # ...
      return [ $status, $headers, $body ];

If you use a web framework, chances are that they provide a helper utility to automatically generate these .psgi files for you, such as:

  # MyApp.psgi
  use MyApp;
  my $app = sub { MyApp->run_psgi(@_) };

It's important that the return value of .psgi file is the code reference. See eg/dot-psgi directory for more examples of .psgi files.

plackup, Plack::Runner

plackup is a command line launcher to run PSGI applications from command line using Plack::Loader to load PSGI backends. It can be used to run standalone servers and FastCGI daemon processes. Other server backends like Apache2 needs a separate configuration but .psgi application file can still be the same.

If you want to write your own frontend that replaces, or adds functionalities to plackup, take a look at Plack::Runner module.


PSGI middleware is a PSGI application that wraps existent PSGI application and plays both side of application and servers. From the servers the wrapped code reference still looks like and behaves exactly the same as PSGI applications.

Plack::Middleware gives you an easy way to wrap PSGI applications with a clean API, and compatibility with Plack::Builder DSL.


Plack::Builder gives you a DSL that you can enable Middleware in .psgi files to wrap existent PSGI applications.

Plack::Request, Plack::Response

Plack::Request gives you a nice wrapper API around PSGI $env hash to get headers, cookies and query parameters much like Apache::Request in mod_perl.

Plack::Response does the same to construct the response array reference.


Plack::Test is an unified interface to test your PSGI application using standard HTTP::Request and HTTP::Response pair with simple callbacks.


Plack::Test::Suite is a test suite to test a new PSGI server backend.


Patches and Bug Fixes

Small patches and bug fixes can be either submitted via nopaste on IRC irc://irc.perl.org/#plack or email. You could also fork on github (http://github.com/miyagawa/Plack) to make larger fixes.

Module Namespaces

Modules added to the Plack:: sub-namespaces should be reasonably generic components which are useful as building blocks and not just simply using Plack.

Middleware authors are free to use the Plack::Middleware:: namespace for their middleware components. Middleware must be written in the pipeline style such that they can chained together with other middleware components. The Plack::Middleware:: modules in the core distribution are good examples of such modules. It is recommended that you inherit from Plack::Middleware for these types of modules.

Not all middleware components are wrappers, but instead are more like endpoints in a middleware chain. These types of components should use the Plack::App:: namespace. Again, look in the core modules to see excellent examples of these (Plack::App::File, Plack::App::Directory, etc.). It is recommended that you inherit from Plack::Component for these types of modules.

DO NOT USE Plack:: namespace to build a new web application or a framework. It's like naming your application under CGI:: namespace if it's supposed to run on CGI and that is a really bad choice and confuse people.


Copyright 2009- Tatsuhiko Miyagawa


Tatsuhiko Miyagawa


Yuval Kogman (nothingmuch)

Tokuhiro Matsuno (tokuhirom)

Kazuhiro Osawa (Yappo)

Kzzuho Oku

Florian Ragwitz (rafl)

Chia-liang Kao (clkao)

Masahiro Honma (hiratara)

Daisuke Murase (typester)

John Beppu

Matt S Trout (mst)

Shawn M Moore (Sartak)

Stevan Little

Hans Dieter Pearcey (confound)

Tomas Doran (t0m)


Mark Stosberg

Aaron Trevena


PSGI http://plackperl.org/


This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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