Plack::Middleware::Conditional - Conditional wrapper for Plack middleware


  use Plack::Builder;

  builder {
      enable_if { $_[0]->{REMOTE_ADDR} eq '' } 'StackTrace', force => 1;

  # or using the OO interface:
  $app = Plack::Middleware::Conditional->wrap(
      condition  => sub { $_[0]->{REMOTE_ADDR} eq '' },
      builder => sub { Plack::Middleware::StackTrace->wrap($_[0], force => 1) },


Plack::Middleware::Conditional is a piece of meta-middleware, to run a specific middleware component under runtime conditions. The goal of this middleware is to avoid baking runtime configuration options in individual middleware components, and rather share them as another middleware component.


Note that some of the middleware component names are just made up for the explanation and might not exist.

  # Minify JavaScript if the browser is Firefox
  enable_if { $_[0]->{HTTP_USER_AGENT} =~ /Firefox/ } 'JavaScriptMinifier';

  # Enable Stacktrace when being accessed from the local network
  enable_if { $_[0]->{REMOTE_ADDR} =~ /^10\.0\.1\.*/ } 'StackTrace';

  # Work with other conditional setter middleware:
  # Transcode Jpeg on the fly for mobile clients
  builder {
      enable 'MobileDetector';
      enable_if { $_[0]->{'plack.mobile_detected'} }
        'TranscodeJpeg', max_size => 30_000;

Note that in the last example MobileDetector should come first because the conditional check runs in pre-run conditions, which is from outer to inner: that is, from the top to the bottom in the Builder DSL code.


Tatsuhiko Miyagawa

Steve Cook