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


    Plack is a set of tools for using the 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

    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 the built-in standalone web server
    HTTP::Server::PSGI, CGI, FCGI, Apache1, Apache2 and
    HTTP::Server::Simple included in the core Plack distribution.

    There are also many HTTP server implementations on CPAN that have Plack

    See Plack::Handler when writing your own adapters.


    Plack::Loader is a loader to load one Plack::Handler adapter and run a
    PSGI application code reference with it.


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

 .psgi files

    A PSGI application is a code reference but it's not easy to pass code
    reference via the command line or configuration files, so Plack uses a
    convention that you need a file named app.psgi or similar, 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 the Plack::Runner module.


    PSGI middleware is a PSGI application that wraps an existing 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

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


    Plack::Test is a 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:// or the github issue tracker
    <>. Forking on github is another
    good way if you intend to make larger fixes.

    See also when you think this
    document is terribly outdated.

 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 would
    confuse people badly.


    Tatsuhiko Miyagawa


    The following copyright notice applies to all the files provided in
    this distribution, including binary files, unless explicitly noted

    Copyright 2009-2013 Tatsuhiko Miyagawa


    Tatsuhiko Miyagawa (miyagawa)

    Tokuhiro Matsuno (tokuhirom)

    Jesse Luehrs (doy)

    Tomas Doran (bobtfish)

    Graham Knop (haarg)


    Yuval Kogman (nothingmuch)

    Kazuhiro Osawa (Yappo)

    Kazuho 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)


    Mark Stosberg

    Aaron Trevena


    The PSGI specification upon which Plack is based.

    The Plack wiki:

    The Plack FAQ:


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