Getting request's source site

[Guy Tamir]

On Monday, August 26, 2013 5:25:49 PM UTC+3, Steven D'Aprano wrote:
> On Mon, 26 Aug 2013 06:10:41 -0700, Guy Tamir wrote:
> 
> 
> 
> > Hi all,
> 
> > 
> 
> > I was wondering how i can get the source from which the request came
> 
> > from. If a user posted a link that directs to my server on facebook i'd
> 
> > like to know that a specific click was from facebook or twitter etc..
> 
> 
> 
> That would be the "referer" header in the HTTP request. (Note that it is 
> 
> an accidental misspelling of "referrer".) Including a referrer is not 
> 
> compulsory, so be prepared for it not to be available.
> 
> 
> 
> 
> 
> 
> 
> -- 
> 
> Steven

Thanks for reply,
In what cases will i have this header? is there something i can do to enforce having it?
Are there any other ways?