The Endpoint Resolver is a simple library that takes a URL and returns the final destination of that URL. It tries to follow a Location:
header.
Given the URL, it gets passes to a server side resolver that hits the URL to get the headers. If a Location:
header appears it is a redirect (ignoring 301, 302 for now, so a 200 + Location would count).
Since this happens via JSONP, it happens asynchronously via appending the script to the DOM. This is why you pass in a callback that will be passed the new URL, and the original one.
If the URL has been changed they will of course be different, and a simple helper Endpoint.isRedirecting(url, orig)
will do that test for you.
The reason I built this was for a Twitter client. Seeing tinyurl / snurl / is.gd / twurl / .... URLs is ugly, and it can be scary not knowing where you are going, so wouldn't it be nice to convert them back to the real URL?
I built a Twitter Resolve URL Greasemonkey script to do just that.
// Simplest version Endpoint.resolve('http://snurl.com/2luj3', function(url) { alert(url); }); // Used in the form below Endpoint.resolve( document.getElementById('testurl').value, function(url) { alert(url); } ); // Using the original URL to work out if it has changed Endpoint.resolve( document.getElementById('testurl').value, function(url, orig) { alert(url); alert(Endpoint.isRedirecting(url, orig)); } ); // How it is used in the Twitter Endpoint Resolver Endpoint.resolve(url, function(resulturl, originalurl) { if (!Endpoint.isRedirecting(resulturl, originalurl)) return; newtext = newtext.replace(originalurl, resulturl, "g"); jQuery(el).html(newtext); });
All of the code (JavaScript / PHP) is available thanks to Google Code. I wanted to host this service on App Engine, but couldn't find a way to get the correct headers from the fetch() as it seems to automatically follow the redirects so you end up with the final page.