NAME

       Plack::Middleware::Debug - display information about the current request/response

SYNOPSIS

         enable "Debug";

DESCRIPTION

       The debug middleware offers a configurable set of panels that displays information about
       the current request and response. The information is generated only for responses with a
       status of 200 ("OK") and a "Content-Type" that contains "text/html" or
       "application/xhtml+xml" and is embedded in the HTML that is sent back to the browser. Also
       the code is injected directly before the "</body>" tag so if there is no such tag, the
       information will not be injected.

       To enable the middleware, just use Plack::Builder as usual in your ".psgi" file:

           use Plack::Builder;

           builder {
               enable 'Debug', panels => [ qw(DBITrace Memory Timer) ];
               $app;
           };

       The "Debug" middleware takes an optional "panels" argument whose value is expected to be a
       reference to an array of panel specifications.  If given, only those panels will be
       enabled. If you don't pass a "panels" argument, the default list of panels -
       "Environment", "Response", "Timer", "Memory", "Session" and "DBITrace" - will be enabled,
       each with their default settings, and automatically disabled if their targer modules or
       middleware components are not loaded.

       Each panel specification can take one of three forms:

       A string
           This is interpreted as the base name of a panel in the "Plack::Middeware::Debug::"
           namespace. The panel class is loaded and a panel object is created with its default
           settings.

       An array reference
           If you need to pass arguments to the panel object as it is created, you may use this
           form (But see below).

           The first element of the array reference has to be the panel base name.  The remaining
           elements are key/value pairs to be passed to the panel.

           For example:

               builder {
                   enable 'Debug', panels =>
                     [ qw(Environment Response Timer Memory),
                       [ 'DBITrace', level => 2 ]
                     ];
                   $app;
               };

           Because each panel is a middleware component, you can write this way as well:

               builder {
                   enable 'Debug'; # load defaults
                   enable 'Debug::DBITrace', level => 2;
                   $app;
               };

           Note that the "<enable 'Debug'"> line should come before other Debug panels because of
           the order middleware components are executed.

       Custom middleware
           You can also pass a Panel middleware component. This might be useful if you have
           custom debug panels in your framework or web application.

HOW TO WRITE YOUR OWN DEBUG PANEL

       The "Debug" middleware is designed to be easily extensible. You might want to write a
       custom debug panel for your framework or for your web application. Each debug panel is
       also a Plack middleware copmonent and is easy to write one.

       Let's look at the anatomy of the "Timer" debug panel. Here is the code from that panel:

         package Plack::Middleware::Debug::Timer;
         use Time::HiRes;

         use parent qw(Plack::Middleware::Debug::Base);

         sub run {
             my($self, $env, $panel) = @_;

             my $start = [ Time::HiRes::gettimeofday ];

             return sub {
                 my $res = shift;

                 my $end = [ Time::HiRes::gettimeofday ];
                 my $elapsed = sprintf '%.6f s', Time::HiRes::tv_interval $start, $end;

                 $panel->nav_subtitle($elapsed);
                 $panel->content(
                     $self->render_list_pairs(
                         [ Start  => $self->format_time($start),
                           End    => $self->format_time($end),
                           Elapsed => $elapsed ],
                     ),
                 );
             };
         }

         sub format_time { ... }

       To write a new debug panel, place it in the "Plack::Middleware::Debug::" namespace. In our
       example, the "Timer" panel lives in the "Plack::Middleware::Debug::Timer" package.

       The only thing your panel should do is to subclass Plack::Middleware::Debug::Base. This
       does most of the things a middleware component should do as a Plack middleware, so you
       only need to override "run" method to profile and create the panel content.

         sub run {
             my($self, $env, $panel) = @_;

             # Do something before the application runs

             return sub {
                 my $res = shift;

                 # Do something after the application returns

             };
         }

       You can create as many lexical variables as you need and reference that in the returned
       callback as a closure, and update the content of of the $panel which is
       Plack::Middleware::Debug::Panel object.

       In our "Timer" example we want to list three key/value pairs: the start time, the end time
       and the elapsed time. We use the "render_list_pairs()" method to place the pairs in the
       order we want. There is also a "render_hash()" and "render_lines()" method, to render a
       hash keys and values, as well as just text lines (e.g. log messages).

BUGS AND LIMITATIONS

       Please report any bugs or feature requests through the web interface at
       <http://rt.cpan.org>.

INSTALLATION

       See perlmodinstall for information and options on installing Perl modules.

AVAILABILITY

       The latest version of this module is available from the Comprehensive Perl Archive Network
       (CPAN). Visit <http://www.perl.com/CPAN/> to find a CPAN site near you. Or see
       <http://search.cpan.org/dist/Plack-Middleware-Debug/>.

       The development version lives at <http://github.com/miyagawa/plack-middleware-debug/>.
       Instead of sending patches, please fork this project using the standard git and github
       infrastructure.

AUTHORS

       Marcel Grunauer, "<marcel@cpan.org>"

       Tatsuhiko Miyagawa, "<miyagawa@bulknews.net>"

COPYRIGHT AND LICENSE

       Copyright 2009 by Marcel Gruenauer

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

SEE ALSO

       The debug middleware is heavily influenced (that is, adapted from) the Django Debug
       Toolbar - see <http://github.com/robhudson/django-debug-toolbar>.