Repeated URL post parameters issue - php

Question

Hi can anyone help why URL string parameters post again and again?
HTTP://127.0.0.1/ab/1936.html?cart=yes?cart=yes
i m using this parameter to open mini cart when we added product into cart in magneto 1.9
Please help me how to protect this?
i am using this code-
<?php
if ($_GET['cart']=='yes') {
echo "<script type='text/javascript'>
jQuery('.minicart_open').show();
</script>";
}
?>
cartController.php
protected function _goBack()
{
$returnUrl = $this->getRequest()->getParam('return_url');
// print_r($returnUrl);exit;
if ($returnUrl) {
if (!$this->_isUrlInternal($returnUrl)) {
throw new Mage_Exception('External urls redirect to "' . $returnUrl . '" denied!');
}
$this->_getSession()->getMessages(true);
$this->getResponse()->setRedirect($returnUrl);
} elseif (!Mage::getStoreConfig('checkout/cart/redirect_to_cart')
&& !$this->getRequest()->getParam('in_cart')
&& $backUrl = $this->_getRefererUrl()
) {
$this->getResponse()->setRedirect($backUrl.'?cart=yes');
} else {
if (
(strtolower($this->getRequest()->getActionName()) == 'add')
&& !$this->getRequest()->getParam('in_cart')
) {
$this->_getSession()->setContinueShoppingUrl($this->_getRefererUrl());
}
$this->_redirect('checkout/cart');
}
return $this;
}

Answer 1

i got the answer
Just replace below line
$this->getResponse()->setRedirect($backUrl.'?cart=yes');
To
$url = $backUrl;
// Search substring
if (strpos($url, $key) == false) {
$this->getResponse()->setRedirect($backUrl.'?cart=yes');
}
else {
$this->getResponse()->setRedirect($backUrl);
}
//exit;
its working for me...Hope its helpful for you...