URL Shorten: how is this achieved?

Question

Possible Duplicate:
How do short URLs services work?

I often see shortened urls from bitly.com such as http://bit.ly/abcd. How is this "bit.ly" realized at server side? Is it some DNS trick inside?

Answer 1

Yes.. actually if you go to https://bitly.com/ you will notice that it provides this URL shortening service.

Going to http://bit.ly/abcd just redirects it to a URL of your choice. You can figure it by looking at the HTTP request and response headers

Request URL:http://bit.ly/abcd
Request Method:GET
Status Code:301 Moved
Request Headersview source
Accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Connection:keep-alive
Host:bit.ly
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.24 Safari/535.1
Response Headersview source
Cache-control:private; max-age=90
Connection:keep-alive
Content-Length:145
Content-Type:text/html; charset=utf-8
Date:Thu, 16 Jun 2011 21:14:04 GMT
Location:http://macthemes2.net/forum/viewtopic.php?id=16786044
MIME-Version:1.0
Server:nginx
Set-Cookie:_bit=4dfa721c-001f7-011f8-c8ac8fa8;domain=.bit.ly;expires=Tue Dec 13 16:14:04 2011;path=/; HttpOnly

http://www.w3.org/Protocols/HTTP/HTRESP.html talks about status codes and 301 is what you should be looking for

Answer 2

No, it's just an HTTP server that looks up abcd in a database, finds http://example.com/long/url, and sends an HTTP redirect answer, like

HTTP/1.1 301 Moved Permanently
Location: http://example.com/long/url

Answer 3

Have you gone to http://bit.ly/? The url shortener stores the long url in a database, then when the short url is used, the url shortener service performs an http redirect to the long url.

Answer 4

LY is the top-level domain for Libya, which is distinct from bitly.com.

Answer 5

bit.ly is just a domain like any other (ie: .com, .net. .fr)

In this case .ly belongs to Libya.

Answer 6

It looks like they use A-Za-z0-9 for generating their URLs, and if my calculations are right, this means at any one time they can probably store a database of 61,474,519 of those codes mapped onto the long URLs. Assuming certain links can expire, or people can delete links they have made, it's safe to assume they won't run out of possibilities soon...and hey if they do, just make the links up to 8 characters- then you get 3,381,098,545 possibilities =P