问题:

This is the reverse of the usual expanding short URLs question.

For a given Long URL, how can I find which short URLs link to it?

If this needs to go through the APIs of the shorteners, apointers ot the ones which support such a query would be appreciated.

回答1:

Simple answer: submit the URL to each URL shortener that you're interested in.

If the URL has been shortened before you'll be given the same short URL that anyone else submitting your URL got back.
Otherwise, you now have a new short URL! No harm in this really.

回答2:

I do not think that there is a direct way to do this. For example, I could write my own URL shortener tomorrow - and since the shortURL->longURL mapping is private, on my server, I would need to provide you with a way to access that information.

So if you have control of the website, you might be able to glean information from looking at the server logs - the REFERER header, in specific.

I know that for bit.ly, it would be easy for you to shorten the URL there, and that would give you its corresponding shortURL. This same short url is used for anyone who uses bit.ly, unless someone has registered an account.