Rickrolling with mod_rewrite

Comic Credit:XKCD

Rickrolling is one of the latest goofy internet pranks, memes, or whatever you want to call it. By strictest definition, to rickroll someone is to send them a link that seems to be for something interesting, but actually takes them to a video of Rick Astley's "Never gonna give you up". These can be via e-mail, instant message, or even discussion forums.

Example of rickroll bait:

Did you see the video of the new spy plane the military is working on?!

Fast forward to today. I find out that some morons have planned to have a little fun with one of the websites that I help with. It's not my site, but run by a client and friend of mine. Not too big of a deal, just some bored teenagers, probably. Not sure what they were up to, but it probably involved lots of forum trolling, trash talking, or spamming. Who knows? I figured I would rickroll these twerps. If they click on the URL they posted in their little forum, they won't get the site they wanted. They will get Rick Astley instead. Meanwhile, the site works fine for everyone else.

In order to do this, I used Mod_Rewrite for apache, and added this to my .htaccess file. In this example, people who click on a link to my site from anywhere on http://www.evil.net will get rickrolled:

RewriteEngine on
RewriteCond %{HTTP_REFERER} ^http://www\.evil\.net [NC]
RewriteRule .* http://www.youtube.com/watch?v=eBGIQ7ZuuiU [R]

The first line just initializes the rewrite engine.

The second line checks the HTTP_REFERER server variable to see if it starts with "http://www.evil.net" (It's a regular expression, "^" means "starts with" and the periods have to be escaped with a backslash or else they're treated as wildcard characters) The [NC] simply means "no case" so that the referer URL is case-insensitive.

The third line tells apache what to do. In this case, it replaces the entire url (.*) with a link to the video on YouTube. The code at the end specifies what kind of rewrite. In this case, [R] means that the web server passes an HTTP 302 status, telling the browser that the URL has been temporarily moved. And you just got rickrolled.

This can be tweaked to keep certain sites from deep-linking your image/media files as well. Keeping EVERYONE from deep-linking requires a different recipe, but in short, you ALLOW only your site to link to the images and media files. Everyone else sees something else of your choosing.

Related Links:
Mod_Rewrite Tips site
Regular-Expressions.info (for forming good RegEx rules)
XKCD.com