---
name: "Plack::Middleware::Conditional"
section: "3pm"
platform: "linux"
package: "libplack-perl"
version: "1.0051-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/Plack::Middleware::Conditional"
---

# Plack::Middleware::Conditional(3pm)

Conditional wrapper for Plack middleware

## NAME

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

## SYNOPSIS

```
  use Plack::Builder;
  builder {
      enable_if { $_[0]->{REMOTE_ADDR} eq '127.0.0.1' } 'StackTrace', force => 1;
      $app;
  };
  # or using the OO interface:
  $app = Plack::Middleware::Conditional->wrap(
      $app,
      condition  => sub { $_[0]->{REMOTE_ADDR} eq '127.0.0.1' },
      builder => sub { Plack::Middleware::StackTrace->wrap($_[0], force => 1) },
  );
```

## DESCRIPTION

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.

## EXAMPLES

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;
      $app;
  };
```

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.

## AUTHOR

Tatsuhiko Miyagawa

Steve Cook

## SEE ALSO

Plack::Builder