URL Shortening - Techniques

Techniques

In URL shortening, every long URL is associated with a unique key, which is the part after http://top-level domain name/, for example http://tinyurl.com/m3q2xt has a key of m3q2xt. Not all redirection is treated equally; the redirection instruction sent to a browser can contain in its header the HTTP status 301 (permanent redirect) or 307 (temporary redirect).

There are several techniques to implement a URL shortening. Keys can be generated in base 36, assuming 26 letters and 10 numbers. In this case, each character in the sequence will be 0, 1, 2, ..., 9, a, b, c, ..., y, z. Alternatively, if uppercase and lowercase letters are differentiated, then each character can represent a single digit within a number of base 62 (26 + 26 + 10). In order to form the key, a hash function can be made, or a random number generated so that key sequence is not predictable. Or users may propose their own keys. For example, http://en.wikipedia.org/w/index.php?title=TinyURL&diff=283621022&oldid=283308287 can be shortened to http://bit.ly/tinyurlwiki.

Not all protocols are capable of being shortened, as of 2011, although protocols such as http, https, ftp, ftps, mailto, news, mms, rtmp, rtmpt, e2dk, pop, imap, nntp, news, ldap, gopher, dict and dns are being addressed by such services as URL Shortener. Typically, data: and javascript: URLs are not supported for security reasons. Some URL shortening services support the forwarding of mailto URLs, as an alternative to address munging, to avoid unwanted harvest by web crawlers or bots. This may sometimes be done using short, CAPTCHA-protected URLs, but this is not common.

Tinyarro.ws, urlrace.com, and qoiob.com use Unicode characters to achieve the shortest URLs possible, since more condensed URLs are possible with a given number of characters compared to those using a standard Latin alphabet.