How to get the hostname or entire url of the visitor website in Ruby on Rails

If the user clicks a link on http://ift.tt/2CduF4e that points to http://example.com/ the value of request.domain will be example.com

But in my case, I would like to get the visitor's host name facebook.com and entire url http://ift.tt/2CduF4e

How to get that? Any help would be appreciated. Thanks!