NAME

SYNOPSIS

  enable "Debug";

DESCRIPTION

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

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

INSTALLATION

AVAILABILITY

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

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

COPYRIGHT AND LICENSE

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

SEE ALSO