Mangling CPAN with Plack::App::Proxy

Olaf AldersToronto Perl MongersSeptember 30, 2010

olaf@wundercounter.comtwitter.com/wundercounter

What is PSGI/Plack?

Superglue interface between perl web application frameworks and web servers, just like Perl is the duct tape of the internet.

PSGI is an interface between Perl web applications and web servers, and Plack is a Perl module and toolkit that contains PSGI middleware, helpers and adapters to web servers.

PSGI and Plack are inspired by Python's WSGI and Ruby's Rack.

http://plackperl.org

Plack::App::Proxy

Plack middleware which allows you to map a local url to another local (or remote) url.

Easier to set up than Apache's mod_proxy

Doesn't require Apache

Doesn't appear to have the same security implications

How can we (ab)use this?

search.cpan.org is a great resource

I wish it had syntax highlighting

I don't want to use a Firefox plugin (Greasemonkey)

Using Plack, I will subvert CPAN to my will

I have also enlisted @ioncache to help me out

Introducing cpan-mangler

http://github.com/oalders/cpan-mangler

Install and Run

git clone http://github.com/ioncache/Plack-Middleware-HTMLify.gitgit clone http://github.com/oalders/cpan-mangler.git

cpanm Plack Plack::App::Proxy

cd cpan-manglerplackup -I../Plack-Middleware-HTMLify/lib

Documentation before:

Documentation after:

Is there more?

POD now looks much better

How about the module source?

Module source before:

Module source after:

Looking under the hood

Let's look at how we went about setting up the proxy. It's very easy to set up. You can proxy a site of your choice in just a few minutes.

Set up the proxy

use Plack::App::Proxy;use Plack::Builder;

my $app = builder { mount "/" => builder {; Plack::App::Proxy->new( remote => 'http://search.cpan.org/' )->to_app; };};

$app;

# http://github.com/oalders/cpan-mangler/blob/master/examples/proxy.psgi

Mangle the POD

use Plack::App::Proxy;use Plack::Builder;

my $pod_highlight = q[...]; # insert JavaScript and CSS here

my $app = builder { enable "Debug", panels => [qw(Environment Memory Timer Response)]; mount "/" => builder { enable 'SimpleContentFilter', filter => sub { s{}{$pod_highlight}i; }; Plack::App::Proxy->new( remote => 'http://search.cpan.org/' )->to_app; };};

$app;

# Find full code sample at# http://github.com/oalders/cpan-mangler/blob/master/examples/pod-mangler.psgi

Known Issues

Doesn't perform perfectly

Can slow down page rendering on large pages (e.g. CGI.pm)

Some mangling may happen several times on a big page (chunking)

The Good Parts

Makes proxying dead easy

Improve your CPAN experience (be creative)

Beyond CPAN

can be used for Google ad tracking

proxy an entire site

set up a custom domain name for the proxy

direct all Google ads to this new domain

mangle the pages to add your own analytics code

site's existing functionality should remain the same

you can now replicate a site for tracking without making a copy of it or knowing/caring how it works under the hood