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3 PAUSE users
5 non-PAUSE users.

Stevan Little


Plack::Debugger - Debugging tool for Plack web applications


version 0.03


  use Plack::Builder;
  use JSON;
  use Plack::Debugger;
  use Plack::Debugger::Storage;
  use Plack::App::Debugger;
  use Plack::Debugger::Panel::Timer;
  use Plack::Debugger::Panel::AJAX;
  use Plack::Debugger::Panel::Memory;
  use Plack::Debugger::Panel::Warnings;
  my $debugger = Plack::Debugger->new(
      storage => Plack::Debugger::Storage->new(
          data_dir     => '/tmp/debugger_panel',
          serializer   => sub { encode_json( shift ) },
          deserializer => sub { decode_json( shift ) },
          filename_fmt => "%s.json",
      panels => [
  my $debugger_app = Plack::App::Debugger->new( debugger => $debugger );
  builder {
      mount $debugger_app->base_url => $debugger_app->to_app;
      mount '/' => builder {
          enable $debugger_app->make_injector_middleware;
          enable $debugger->make_collector_middleware;


This is a rethinking of the excellent Plack::Middleware::Debug module, with the specific intent of providing more flexibility and supporting capture of debugging data in as many places as possible. Specifically we support the following features not easily handled in the previous module.

Capturing AJAX requests

This module is able to capture AJAX requests that are performed on a page and then associate them with the current request.

NOTE: This is currently done using jQuery's global AJAX handlers which means it will only capture AJAX requests made through jQuery. This is not a limitation, it is possible to capture non-jQuery AJAX requests too, but given the ubiquity of jQuery it is unlikely that will be needed. That said, patches are most welcome :)

Capturing post-request data

Not all debugging data may be available during the normal lifecycle of a request, some data is better captured and collated in some kind of post-request cleanup phase. This module allows you to specify that code can be run in the psgix.cleanup phase, which - if your server supports it - will happens after the request has been sent to the browser.

Just capturing data

This module has been designed such that it is possible to just collect debugging data and not use the provided javascript UI. This will allow data to be collected and viewed using some other type of mechanism, for instance it would be possible to collect data on a web browsing session and view it in aggregate instead of just per-page.

NOTE: While we currently do not provide any code to do this, the possibilities are pretty endless if you think about it.



This is the main component of this system, just about every other component either uses information from this component or uses the actual component itself as a delegate.

The primary responsibilities of this component are to coordinate the capture of data using the Plack::Debugger::Panel objects and to store this data using Plack::Debugger::Storage.


This is a simple middleware that wraps your Plack application and runs all the phases of the Plack::Debugger to collect data upon the current request.


This is middleware that attempts to sensibly inject a single HTML <script> tag into the body of a web request. It analyzes a combination of the HTTP status code, headers and the response content-type to try and make a sensible decision about injecting or not. See the documentation in the module for a more detailed description.


This is a small web-service which has two basic responsibilities. The first is to supply the necessary javascript and CSS for the debugging UI. The second is to provide a small REST style JSON web-service that serves up the debugging data.


This is the javascript end of this application which powers the UI for the debugger. This component uses jQuery heavily and so if there is not already a jQuery instance loaded it will pull in its own copy and use that.

Note about jQuery usage

This module ships with the latest jQuery (2.1.1), but the javascript code used by the Plack.Debugger object has been tested against very old versions of jQuery (~1.2.6) to insure that it still functions. If you need to support older versions of jQuery, patches are welcome, but the author reserves the right to draw a line as to how old is too old.


This module was originally developed for Booking.com. With approval from Booking.com, this module was generalized and published on CPAN, for which the authors would like to express their gratitude.


Stevan Little <stevan@cpan.org>


This software is copyright (c) 2014 by Stevan Little.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.