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{

// save the affiliate ID

$_SESSION[‘aff_id’] = $_REQUEST[‘aff_id’];

// obtain the URL with no affiliate ID

$clean_url = SITE_DOMAIN . remove_query_param($_SERVER[‘REQUEST_URI’], ‘aff_id’);

// 301 redirect to the new URL

header(‘HTTP/1.1 301 Moved Permanently’);

header(‘Location: ‘ . $clean_url);

}

Finally,

aff_test.php

checks whether there’s a session parameter named

aff_id

set. In case it is, your

user got to the page through an affiliate link, and you’ll need to take this into account when dealing with

this particular user. For the purposes of this simple exercise, you’re simply displaying the affiliate ID, or

(no affiliate)

in case the page was first loaded without an

aff_id

parameter.

// display affiliate details

echo ‘You got here through affiliate: ‘;

if (!isset($_SESSION[‘aff_id’]))

{

echo ‘(no affiliate)‘;

}

else

{

echo $_SESSION[‘aff_id’];

}

?>

It’s also worth analyzing what happens inside the

remove_query_param()

function from

url_utils

.inc.php

. The strategy you took for removing one query string parameter is to transform the existing

query string to an associative array, and then compose the associative array back to a query string, after

removing the

aff_id

element.

To keep the code cleaner, you have a separate function that transforms a query string to an associative

array. This function is named

parse_query_string()

, and receives as parameter a query string, such

as

a=1&aff_id=34&b=2

, and returns an associative array with these elements:

‘a’ => ‘1’

‘aff_id’ => ‘34’

‘b’ => ‘2’

The function starts by using

explode()

to split the query string on the

&

character:

// transforms a query string into an associative array

function parse_query_string($query_string)

{

// split the query string into individual name-value pairs

$items = explode(‘&‘, $query_string);

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Chapter 5: Duplicate Content

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