Cookie is set to null when ran - php

Question

Let me give you the code first and explain below it:
<?php
$productID = $_POST['productID'];
$productAmount = $_POST['productAmount'];
//Declare variables
$cartNumItems = 0;
//Check if cookie exists and set variable if it does
if(isset($_COOKIE['cart'])){
if($_COOKIE['cart'] != null && $_COOKIE['cart'] != ''){
$cart = $_COOKIE['cart'];
}
}
//Get array from cookie
if(isset($cart)){
//Decode array from $cart variable and store it
$cartArray = json_decode($cart);
//Count number of items in $cart
$cartAmount = count($cartArray);
for($i = 0; $i < $cartAmount; $i++){
//Check if $cart has the same product in it already
if($productID == $cartArray[$i][0]){
//Add to the amount of that product
$cartArray[$i][1] += $productAmount;
break;
}
//If it does not have the same product already, just add a new one
else if($i == ($cartAmount - 1)){
array_push($cartArray, array($productID, $productAmount));
break;
};
};
//Recount number of items in $cart
for($i = 0; $i < $cartAmount; $i++){
$cartNumItems += $cartArray[$i][1];
};
//Encode $cart so it can be stored in cookie
$cartRaw = json_encode($cartArray);
//Create cookies
setcookie('cart', $cartRaw, time() + (86400 * 7), '/');
setcookie('cartNumItems', $cartNumItems, time() + (86400 * 7), '/');
echo 'true';
}
else{
//Create the info that needs to be put into cookie
$cart = json_encode(
array(
array($productID, $productAmount)
)
);
$cartArray = json_decode($cart);
//Count and store the amount of items in cart array
$cartAmount = count($cartArray);
//Store amount of items in $cartNumItems variable
for($i = 0; $i < $cartAmount; $i++){
$cartNumItems += $cartArray[$i][1];
};
//Create cookies
setcookie('cart', $cart, time() + (86400 * 7), '/');
setcookie('cartNumItems', $cartNumItems, time() + (86400 * 7), '/');
echo 'true';
};
?>
When this code is ran the very first time, the "cart" cookie is not set. So it runs the big else statement when checking if the variable "$cart" is set. The else statement works fine and does what it's supposed to. It creates a 2d array, then creates the cookies with the needed information.
The second time the code runs, the if statement should run. Which I believe it does. The "cart" cookie (aka "$cart" variable) is set to null. Then the "cartNumItems" cookie (aka "$cartNumItems" variable) is set to 0. Which it's not supposed to do. I just can't find where it does this, or why it does this.
In case there is any confusion about what specifically is the problem code, this is the problem code (it would seem):
//Get array from cookie
if(isset($cart)){
//Decode array from $cart variable and store it
$cartArray = json_decode($cart);
//Count number of items in $cart
$cartAmount = count($cartArray);
for($i = 0; $i < $cartAmount; $i++){
//Check if $cart has the same product in it already
if($productID == $cartArray[$i][0]){
//Add to the amount of that product
$cartArray[$i][1] += $productAmount;
break;
}
//If it does not have the same product already, just add a new one
else if($i == ($cartAmount - 1)){
array_push($cartArray, array($productID, $productAmount));
break;
};
};
//Recount number of items in $cart
for($i = 0; $i < $cartAmount; $i++){
$cartNumItems += $cartArray[$i][1];
};
//Encode $cart so it can be stored in cookie
$cartRaw = json_encode($cartArray);
//Create cookies
setcookie('cart', $cartRaw, time() + (86400 * 7), '/');
setcookie('cartNumItems', $cartNumItems, time() + (86400 * 7), '/');
echo 'true';
}
Update:
I've found what resets the cookie, this bit of code in the if statement:
//Decode array from $cart variable and store it
$cartArray = json_decode($cart);
When this is ran, $cartArray is set to null, therefore the rest of the code is working off of a null variable. Now what I don't understand is why it's being set to null. when I var_dump the $cart variable I get string(16) "[[\"21\",\"1\"]]". But when I run...
echo json_decode($cart);
It just comes out blank.

Answer 1

[[\"21\",\"1\"]] is not valid JSON, because of the \ characters. Those should not be there in the first place – times of magic_quotes_gpc are gone, unless your PHP version was really old. Remove them, before you call json_decode on the string.
So since you say it doesn’t occur locally, but on your web hoster’s server, it very likely is the setting magic_quotes_gpc that is responsible here (if your PHP version is <= 5.3). If your hoster doesn‘t provide any means to turn it of (custom php.ini, .htaccess), then you can use get_magic_quotes_gpc() to detect it from within your script, and then use f.e. stripslashes to remove them.
(Also check the user comments on the manual page for get_magic_quotes_gpc(), they offer solutions to remove those extra slashes from all external input data via a few lines of scripting.)