UriBin: A self-replicating paste bin that lives in url shorteners
Today I was looking through old projects, and decided UriBin deserves a nice breakdown. It's crazy, and interesting, and not trivial to grok.
I called UriBin "A self-replicating paste bin that lives in URL shorteners", but what on earth does that mean? I'll try to break it down.
What are Data URIs?
A standard URL is a pointer to a website where your browser can find some data. A data URI acts like a URL, but contains the data encoded within it. Try pasting this in your URL bar:
data:text/html,<h1>Hello World</h1><p>Enjoy my website</p>
Unlike a standard URL, no HTTP request or server is required, the browser simply reads it out of the URI.
What is a link shortener?
Link shortening services like Bit.ly or TinyUrl are essentially public lookup tables that map short URLs to longer URLs. You load the shortened URL and the service sends your browser the longer URL and says "go here instead". This is known as a "redirect". Some of URL shorteners, like TinyUrl, don't distinguish between URLs and data URIs.
See where this is going?
If your data is small enough, you can encode it as a data URI and "shorten" the URI. For example, I've shorted the example URI from above as:
If you click that link it will "redirect" you to the data URI and you will see my "Hello World" website in your browser. Note that rather than sending your browser a new URL, TinyUrl returned the actual data of my website. Essentially I've tricked TinyURL into hosting my web page.
So we can stash arbitrary content in TinyUrl?
Let's build tool to do just that!
But that's not crazy enough!
Okay, it turns out we can make our tool so tiny, that we can encode it as a data URI and host it in a URL shortener itself.
But even that's not crazy enough!
And there you have it. Each little hosted text snippet we generate is a replica of our original tool, but with the user's text embedded within it.
How does it work?
It's actually quite simple. Our tools just grabs a copy of itself from
document.URL, replaces the old text with the text the user has supplied, and
then redirects the user to
<URL> is the URL string it just created.
And... viola, you have a self-replicating paste bin that lives in url shorteners.