http occurring twice in a URL

Question

I ran into a website today that had two URLs and im completely stunned. The website, not to be specific, has a full address of http://example/cat/http://example/dog. I will say that the first part is a randomly generated ad that pops up, but regardless isn't going to two addresses the equivalent of being at two different houses at the same time i.e. impossible? Anyhow, I just wanted some clarification on how it works.

And before you ask, the site is not exactly something that i would paste on an affluent forum thus the reason I have left it out.

Answer 1

Your example URL, http://example/cat/http://example/dog, points to a page accessed with the http protocol, on the host example, with the path cat/http://example/dog. It's perfectly valid for the path part of a URL to contain elements that look like the protocol and hostname parts of another URL.

One relatively prominent example of a legit site using such URLs is archive.org's Wayback Machine. For example, to see what http://webmasters.stackexchange.com/ looked like in late 2010, you can go to http://web.archive.org/web/2010/http://webmasters.stackexchange.com/.

Answer 2

The second one can simply be a parameter in the URL.

Answer 3

People also often see "http" in their access logs when the forget the colon in a link to an external site. For example on the page http://example.com/finder/findstuff is the following HTML:

<a href="http//www.google.com/">Search Google</a>

Due to the missing colon, this will result in the visitor being sent to http://example.com/finder/http//www.google.com/ when clicking on the link.