I get a lot of ideas. Most of them wander aimlessly in my head until they become obsolete, but once in a while I’ll get an idea that seems useful and simple enough to do in my free time.<\/p>\n
If you’ve used Twitter, you’ve seen the myriad of url shortening services like TinyUrl and Bit.ly. Url shortening services are a kludge<\/a> and they break one useful, built-in feature of the web, which is the ability to know where you’re going when you click a link<\/a>.<\/p>\n So I thought, this is something that I could fix in an hour or so with a Greasemonkey script. If you have no idea what I’m talking about, Greasemonkey is a Firefox Plugin that runs in your browser and lets you run your own Javascript on pages you load. Greasemonkey comes with a handy-dandy AJAX function called GM_xmlhttpRequest.<\/p>\n I figured all I have to do is grab all the anchors on the page, see if they match a list of shortener urls, do an xmlhttpRequest for each one and grab the final location (after the service finishes with it’s redirecting) from the headers.<\/p>\n Something along these lines: <\/code><\/p>\n <\/p>\n As you can see, it should just be a matter of plucking the location header<\/a> from responseDetails.responseHeaders. <\/p>\n But every time I fetched a url, even though Firefox theoretically handles GET redirects correctly<\/a>, I never found a location in the headers returned.<\/p>\n If you can’t do an AJAX call, you can do things the old-fashioned way with hidden iframes.<\/p>\n <\/code><\/p>\n The problem there is that although I can easily create the iframe, it’s hard to get the final location. If I get the value of the src attribute, it’s still set to whatever I set it to in the first place. I tried using the location of the contentWindow:<\/p>\n <\/code><\/p>\n …but that gives me “about:blank” since my GM script runs before the iframes are loaded.<\/p>\n I played around a bit adding and event listener to the iframe but got access errors. Then it got late so I gave up. It turns out lots of other people have already had the same idea<\/a>. <\/p>\n
\n<\/p>\n\r\nfunction getTargetUrl(short_url) {\r\n\r\n GM_log('Getting '+short_url);\r\n\r\n GM_xmlhttpRequest({\r\n method: 'GET',\r\n url: short_url,\r\n headers: {\r\n 'User-agent': 'Mozilla\/4.0 (compatible) Greasemonkey',\r\n 'Accept': 'text\/html'\r\n },\r\n onload: function(responseDetails) {\r\n GM_log('Done. Status ' + responseDetails.status +\r\n ' Text ' + responseDetails.statusText + '\\n\\n' +\r\n ' Headers:\\n' + responseDetails.responseHeaders);\r\n }\r\n });\r\n}<\/pre>\n<\/p>\n\r\n var the_iframe = document.createElement('iframe');\r\n the_iframe.setAttribute('style', 'height:10px;width:10px;');\r\n the_iframe.setAttribute('src', short_url);\r\n document.body.appendChild(the_iframe);\r\n<\/pre>\n<\/p>\n\r\nGM_log('Current href: '+\r\n document.getElementById('embiggen'+num).contentWindow.location.href);\r\n<\/pre>\n