google checkout php callback explained - php

Question

Hi all i don't know if i'm doing this right or not but i can't understand how google checkout works.
I have the php code that sends the XML to the google checkout everything is ok i reach on the checkout process taxes prices shipping is ok.
$_currency = $params['currency'];
$base_domain = 'https://' . (($params['mode'] == 'transaction') ? 'checkout.google.com' : 'sandbox.google.com/checkout');
$base_url = $base_domain . '/cws/v2/Merchant/' . $params['merchantId'] . '/checkout';
// Form XML array with cart items
$_items = '';
$google_products = $this->CI->go_cart->contents();
foreach ($google_products as $k => $v) {
$item_options = '';
if (isset($v['options'])) {
foreach ($v['options'] as $name => $value) {
if (is_array($value)) {
foreach ($value as $item) {
$item_options .= $item;
}
} else {
$item_options .= $value;
}
}
}
$_items .= '<item>' . '<merchant-item-id>' . $v['id'] . '</merchant-item-id>' . '<item-name>' . strip_tags($v['name']) . ' ' . $item_options . '</item-name>' . '<item-description>' . substr(strip_tags($item_options), 0, 299) . '</item-description>' . "<unit-price currency='" . $_currency . "'>" . $v['price'] . '</unit-price>' . '<quantity>' . $v['quantity'] . '</quantity>' . '</item>';
}
$xml_cart = "<?xml version='1.0' encoding='UTF-8'?>
<checkout-shopping-cart xmlns='http://checkout.google.com/schema/2'>
<shopping-cart>
<merchant-private-data>
<additional_data>
<session_id>" . base64_encode($customer['bill_address']["email"] . date('h:i:s')) . "</session_id>
<currency_code>" . $_currency . "</currency_code>
<payment_id>" . base64_encode($customer['bill_address']["email"] . date('h:i:s')) . "</payment_id>
" . $private_ship_data . "
</additional_data>
</merchant-private-data>
<items>" . $_items . "</items>
</shopping-cart>
<checkout-flow-support>
<merchant-checkout-flow-support>
<platform-id>971865505315434</platform-id>
<request-buyer-phone-number>true</request-buyer-phone-number>
<edit-cart-url>" . $edit_cart_url . "</edit-cart-url>
<merchant-calculations>
<merchant-calculations-url>" . $calculation_url . "</merchant-calculations-url>
</merchant-calculations>
<continue-shopping-url>" . $return_url . "</continue-shopping-url>
" . $shippings . $taxes . "
</merchant-checkout-flow-support>
</checkout-flow-support>
</checkout-shopping-cart>";
$signature = $this->fn_calc_hmac_sha1($xml_cart, $params['merchantKey']);
$b64_cart = base64_encode($xml_cart);
$b64_signature = base64_encode($signature);
echo '<form method="post" action="' . $base_url . '" name="BB_BuyButtonForm">
<input type="hidden" name="cart" value="' . $b64_cart . '" />
<input type="hidden" name="signature" value="' . $b64_signature . '" />
<input alt="" src="' . $base_domain . '/buttons/checkout.gif?merchant_id=' . $params['merchantId'] . '&w=160&h=43&style=' . 'white' . '&variant=text&loc=en_US" type="image"/>
</form>';
exit;
}
After i click on submit payment i'm then redirected to a page with successfull message and with a link to return to my website.
I'm wondering how can i check if the payment was or not successfully.
Also there is a callback that i don't know exactly what is supposed to do.
Please help me understand better
I have attached the code below.

Answer 1

Disclaimer: Am not a PHP dev.
Your code above is known as Part 1. Checkout API documented here. It covers how you get your data/cart to Google for Checkout
Part II. Order Processing covers how to get data from Google (into your systems). A tutorial is provided here. This is where you provide a Callback API URL that listens to (waits for) HTTP POSTs from Google and proceed to process the data.