how to detect - where did the user came from?

Question

Let's say I have google'd for digital photography school

http://www.google.com/search?q=digital+photography+school&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

I get few results.

And from the results if I click "Photography Tips & Tutorials" under subsection of first result "Digital Photography Tips: Digital Photography School"

On the digital photography school page I see something like this. -

Google Search Results

You arrived here after searching for the following phrases:

• digital
• photography
• school

How does dps know that we came from google even with search terms?

Answer 1

They can get the URL by reading the HTTP Referrer, and then they can parse the query string appropriately.

Answer 2

The referring url is sent in the request headers. They parsed it to get your search terms.

Answer 3

I suppose they just parse Referer :) http://en.wikipedia.org/wiki/Referer

Answer 4

It will probaby look at the HTTP Referrer and then analyse the querystring.

Answer 5

They can simply check the referrer. Most web browsers have them enabled, only a few people disable them.

Answer 6

Parse the referrer to get the query. Here's a PHP example:

<?php
    $referrer = parse_url($_SERVER['HTTP_REFERER']);
    if(strpos($referrer['host'], 'google') !== FALSE){
        parse_str($referrer['query'], $query);
        $words = explode('+', $query['q']);
    }
?>

The variable $words should now be an array containing all search terms. This could be improved upon to handle quotes and other special cases.