Paypal IPN - Check if payment status is completed?

Question

I have an ebooks selling website, where a user can download a book after he had made a purchase. I receive an IPN from Paypal and as far as I understand, sometimes the payment status comes as "In-Progress" or "Processing" if the user has chosen Credit Card as the payment method. Since Paypal then will resend the IPN when the payment is completed, what is the best way to check if the payment status is completed in order to avoid duplicates in your database?

Solution

These are the possible statuses that Paypal return to your IPN listener

Canceled_Reversal
Completed
Denied
Failed
Refunded
Reversed
Voided
In-Progress
Pending
Processed

You should check for Completed status in order to make sure the payment was completed. Below is an example of the IPN Listener that check for different statuses

<?php
    //Build the data to post back to Paypal
    $postback = 'cmd=_notify-validate'; 

    // go through each of the posted vars and add them to the postback variable
    foreach ($_POST as $key => $value) {
    $value = urlencode(stripslashes($value));
    $postback .= "&$key=$value";
    }


    // build the header string to post back to PayPal system to validate
    $header = "POST /cgi-bin/webscr HTTP/1.0\r\n";
    $header .= "Content-Type: application/x-www-form-urlencoded\r\n";
    $header .= "Content-Length: " . strlen($postback) . "\r\n\r\n";

    // Send to paypal or the sandbox depending on whether you're live or developing
    // comment out one of the following lines
    //$fp = fsockopen ('ssl://www.sandbox.paypal.com', 443, $errno, $errstr, 30);//open the connection
    $fp = fsockopen ('ssl://www.paypal.com', 443, $errno, $errstr, 30);
    // or use port 443 for an SSL connection
    //$fp = fsockopen ('ssl://www.paypal.com', 443, $errno, $errstr, 30);

    if (!$fp) 
    {
        // HTTP ERROR Failed to connect
        //error handling or email here
    }
    else // if we've connected OK
    {
        fputs ($fp, $header . $postback);//post the data back
        while (!feof($fp)) 
        {
            $response = fgets ($fp, 1024);

            if (strcmp ($response, "VERIFIED") == 0) //It's verified
            {
                // assign posted variables to local variables, apply urldecode to them all at this point as well, makes things simpler later
                $payment_status = $_POST['payment_status'];//read the payment details and the account holder

                if($payment_status == 'Completed')
                {
                    //Do something
                }
                else if($payment_status == 'Denied' || $payment_status == 'Failed' || $payment_status == 'Refunded' || $payment_status == 'Reversed' || $payment_status == 'Voided')
                {
                    //Do something
                }
                else if($payment_status == 'In-Progress' || $payment_status == 'Pending' || $payment_status == 'Processed')
                {
                    //Do something
                }
                else if($payment_status == 'Canceled_Reversal')
                {
                    //Do something
                }
            }
            else if (strcmp ($response, "INVALID") == 0) 
            { 
                //the Paypal response is INVALID, not VERIFIED
            }
        } //end of while
        fclose ($fp);
    }
?>