How to use paypal IPN for membership website ( PHP )

Question

Using a PayPal button for recurring payments for my website's subscription service. I have created a log in system using emails and passwords. Once logged in the user can pay for the subscription ( A PayPal button appears ) Once they have paid for the subscription they get redirected to my ipn page, here I somehow want to update the users membership_status = 1 in my database, and if the user cancelled their payment I want it so the IPN will message the server and set the membership_status = 0 for example. I'm unsure as to the safest way to do this.

This is the php code given by paypal for the IPN page

<?php

// CONFIG: Enable debug mode. This means we'll log requests into 'ipn.log' in the same directory.
// Especially useful if you encounter network errors or other intermittent problems with IPN (validation).
// Set this to 0 once you go live or don't require logging.
define("DEBUG", 1);

// Set to 0 once you're ready to go live
define("USE_SANDBOX", 1);


define("LOG_FILE", "./ipn.log");


// Read POST data
// reading posted data directly from $_POST causes serialization
// issues with array data in POST. Reading raw POST data from input stream instead.
$raw_post_data = file_get_contents('php://input');
$raw_post_array = explode('&', $raw_post_data);
$myPost = array();
foreach ($raw_post_array as $keyval) {
    $keyval = explode ('=', $keyval);
    if (count($keyval) == 2)
        $myPost[$keyval[0]] = urldecode($keyval[1]);
}
// read the post from PayPal system and add 'cmd'
$req = 'cmd=_notify-validate';
if(function_exists('get_magic_quotes_gpc')) {
    $get_magic_quotes_exists = true;
}
foreach ($myPost as $key => $value) {
    if($get_magic_quotes_exists == true && get_magic_quotes_gpc() == 1) {
        $value = urlencode(stripslashes($value));
    } else {
        $value = urlencode($value);
    }
    $req .= "&$key=$value";
}

// Post IPN data back to PayPal to validate the IPN data is genuine
// Without this step anyone can fake IPN data

if(USE_SANDBOX == true) {
    $paypal_url = "https://www.sandbox.paypal.com/cgi-bin/webscr";
} else {
    $paypal_url = "https://www.paypal.com/cgi-bin/webscr";
}

$ch = curl_init($paypal_url);
if ($ch == FALSE) {
    return FALSE;
}

curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $req);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 1);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
curl_setopt($ch, CURLOPT_FORBID_REUSE, 1);

if(DEBUG == true) {
    curl_setopt($ch, CURLOPT_HEADER, 1);
    curl_setopt($ch, CURLINFO_HEADER_OUT, 1);
}

// CONFIG: Optional proxy configuration
//curl_setopt($ch, CURLOPT_PROXY, $proxy);
//curl_setopt($ch, CURLOPT_HTTPPROXYTUNNEL, 1);

// Set TCP timeout to 30 seconds
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 30);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Connection: Close'));

// CONFIG: Please download 'cacert.pem' from "http://curl.haxx.se/docs/caextract.html" and set the directory path
// of the certificate as shown below. Ensure the file is readable by the webserver.
// This is mandatory for some environments.

//$cert = __DIR__ . "./cacert.pem";
//curl_setopt($ch, CURLOPT_CAINFO, $cert);

$res = curl_exec($ch);
if (curl_errno($ch) != 0) // cURL error
    {
    if(DEBUG == true) { 
        error_log(date('[Y-m-d H:i e] '). "Can't connect to PayPal to validate IPN message: " . curl_error($ch) . PHP_EOL, 3, LOG_FILE);
    }
    curl_close($ch);
    exit;

} else {
        // Log the entire HTTP response if debug is switched on.
        if(DEBUG == true) {
            error_log(date('[Y-m-d H:i e] '). "HTTP request of validation request:". curl_getinfo($ch, CURLINFO_HEADER_OUT) ." for IPN payload: $req" . PHP_EOL, 3, LOG_FILE);
            error_log(date('[Y-m-d H:i e] '). "HTTP response of validation request: $res" . PHP_EOL, 3, LOG_FILE);
        }
        curl_close($ch);
}

// Inspect IPN validation result and act accordingly

// Split response headers and payload, a better way for strcmp
$tokens = explode("\r\n\r\n", trim($res));
$res = trim(end($tokens));

if (strcmp ($res, "VERIFIED") == 0) {
    // check whether the payment_status is Completed
    // check that txn_id has not been previously processed
    // check that receiver_email is your PayPal email
    // check that payment_amount/payment_currency are correct
    // process payment and mark item as paid.

    // assign posted variables to local variables
    //$item_name = $_POST['item_name'];
    //$item_number = $_POST['item_number'];
    //$payment_status = $_POST['payment_status'];
    //$payment_amount = $_POST['mc_gross'];
    //$payment_currency = $_POST['mc_currency'];
    //$txn_id = $_POST['txn_id'];
    //$receiver_email = $_POST['receiver_email'];
    //$payer_email = $_POST['payer_email'];

    if(DEBUG == true) {
        error_log(date('[Y-m-d H:i e] '). "Verified IPN: $req ". PHP_EOL, 3, LOG_FILE);
    }
} else if (strcmp ($res, "INVALID") == 0) {
    // log for manual investigation
    // Add business logic here which deals with invalid IPN messages
    if(DEBUG == true) {
        error_log(date('[Y-m-d H:i e] '). "Invalid IPN: $req" . PHP_EOL, 3, LOG_FILE);
    }
}

?>

Answer 1

Once they have paid for the subscription they get redirected to my ipn page

Really bad choice, redirecting users to IPN page, use Auto Return URL to bring back customer from Paypal to your website. More Information

here I somehow want to update the users membership_status = 1 in my database

Instant Payment Notification (IPN) is a message service that automatically notifies merchants of events related to PayPal transactions. Merchants can use it to automate back-office and administrative functions, like automatically fulfilling orders and providing customers with order status.

More Info

You can update the users membership_status in database according to payment status you receive in IPN from paypal, payment status e.g Completed, Pending, etc

if the user cancelled their payment I want it so the IPN will message the server and set the membership_status = 0

If user cancel payment, bring back the customer to website use Cancel URL more information but as there is no payment activity on Paypal if user cancelled so you will not receive any response through IPN

But as you are using recurring payments you can receive payment notification through IPN only in the case if your subscribed member cancelled existing membership.

More information