Tag Archives: Greasemonkey

Adblock Ajax bit.ly debugging firefox firefox add-on HTML iframe Javascript kludge redirects tinyurl troubleshooting Twitter url shorteners web-development xmlhttprequest

TinyUrl Trouble: Greasemonkey drops the location header in GM_xmlhttpRequest

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.

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 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.

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.

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.

Something along these lines:

function getTargetUrl(short_url) {

  GM_log('Getting '+short_url);

      method: 'GET',
      url: short_url,
      headers: {
          'User-agent': 'Mozilla/4.0 (compatible) Greasemonkey',
          'Accept': 'text/html'
      onload: function(responseDetails) {
          GM_log('Done.  Status ' + responseDetails.status +
                ' Text ' + responseDetails.statusText + '\n\n' +
                ' Headers:\n' + responseDetails.responseHeaders);

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An interesting use of Greasemonkey – Troubleshooting other people’s sites

Detriot-Superior and Center Street Bridge I’ve played around with Firefox’s Greasemonkey add-on here and there but never really delved into it until recently.  I found most of the common uses for it to be either too specific to someone else’s use habits or already covered by other extensions.  For example, there are probably a million ad blocking scripts out there, but I already have Adblock.

I’ve grown to appreciate Greasemonkey a lot more since I learned that you can make AJAX calls in scripts – now we can do some real damage.  But this post is not about that, it’s about a totally different use case that I hadn’t thought of before.

If you’re a web developer with any friends or family you’ve probably heard this one before:

“Something’s wrong with my web site, can you take a look?”

Often, though, you won’t have access to a dev server, database, or even a copy of the server-side code.  All you can see is the HTML and Javascript source and the HTTP transactions going back and forth.

Greasemonkey can’t rewrite PHP code on someone else’s server but it does make it really, really easy for you to alter forms, delete and change cookie values, and patch and debug Javascript on the site you’re looking at, without changing any other variables.

This can be really, really useful in some situations.  So now it’s officially added to my volunteer/web-developer/brother-in-law toolbelt.