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This function verifies if the REFERER is from the local domain, and if it is, it doesn’t display the naviga-

tion link. If the REFERER is from any other domain, or if it is empty, the navigation link

is

displayed.

The function starts by telling if a REFERER does exist. If it doesn’t, you set a temporary variable, named

$display_nav

, to

true

. The default value of this variable is

false

. At the end of the function you ver-

ify its value and decide whether or not to display the navigation links:

// display popup navigation only when visitor comes from a SERP

function display_popup_navigation()

{

// display navigation?

$disp_nav = false;

// if there is no REFERER (visitor loaded popup directly), display navigation

if (!isset($_SERVER[‘HTTP_REFERER’]))

{

$disp_nav = true;

}

If there is a REFERER, you verify if the host name of the REFERER is the same one as the host of the

SITE_DOMAIN

constant, which you’ve defined in

config.inc.php

. If the host names are different, the

visitor arrived at the popup from an external web site, and you must display the navigation link:

// if the REFERER not from our domain, display navigation

else

{

// parse the REFERER and the local site using parse_url()

$parsed_referer = parse_url($_SERVER[‘HTTP_REFERER’]);

$parsed_local = parse_url(SITE_DOMAIN);

// extract the domain of the referer, and that of the local site

$referer_host = $parsed_referer[‘host’];

$local_host = $parsed_local[‘host’];

// display navigation if the REFERER URL is not from the local domain

if ($referer_host != $local_host)

{

$disp_nav = true;

}

}

In the end, if

$disp_nav

is

true

, you display the navigation link:

// display navigation if necessary

if ($disp_nav == true)

{

echo ‘<a href=”catalog.html”>Visit our catalog page!</a>’;

}

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Chapter 6: SE-Friendly HTML and JavaScript

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