Introduction

PayPal’s Instant Payment Notification system is a very useful tool for developers.  It can help automate tasks and manage sales in a number of ways.

I’ve written a few articles in the past that covered using IPN in different ways and testing it thoroughly, but nothing about how to setup a basic IPN solution using PHP.  That’s what I’d like to here.

In part 1 of this 2-part series, we’ll go step by step through the procedures used to build a simple IPN listener script that receives the data from PayPal and prepares it for use.  We’ll build our script in a basic, linear fashion so it’s easy to follow for most PHP developers. Advanced developers can then take these steps and build them into custom class libraries if you prefer.

In part 2 we’ll extend our simple IPN script to automatically deliver eBook purchases to buyers.  We’ll also add some code to automatically mark the item as paid and shipped on eBay if the purchase did indeed come from eBay, and we’ll also set feedback for the buyer on eBay at the same time.

Step 1

The first thing we should do is setup a directory structure for our IPN project.  If I’m building this into a website or an application of some sort, I personally like to start with a /paypal directory.  This is where I would keep all of my code that interacts with PayPal in some fashion.  Within that, I like to create an /ipn directory to keep it nice and organized, and within that we’ll create our index.php file to receive the IPN data from PayPal.  This figure represents our structure:

Directory Structure

Step 2

Now we’re ready to start coding our IPN script.  What we’ll do right away is validate the data the script is receiving by sending the same data back to PayPal with the _notify-validate command attached.  The PayPal system will return a result that lets us know whether or not the data actually originated from their system or not and allows us to avoid processing fraudulent data.

Let’s take a quick look at how this is done and then we’ll break it down.

$validate_request = 'cmd=_notify-validate';
foreach ($_POST as $key => $value)
{
  $validate_request .= "&" . $key . "=" . urlencode(stripslashes($value));
}

First, we create a PHP variable to store our request string in that we need to pass to PayPal.  Here, we’ve called this $validate_request, and we’ve pre-populated it with a single request parameter: cmd=_notify-validate.  This parameter is what notifies the PayPal system that we’re requesting validation of IPN data.

With our $validate_request variable prepared, we need to add parameters for all of the data that PayPal originally sent us.  PayPal sends the data to us using the POST method, which is accessible in PHP using a $_POST[‘varname’] syntax.  As such, we simply loop through all of the $_POST data available to the script in order to generate the remainder of our request string.

Step 3

Now that we have our request string ready to send back to PayPal for validation we need to go ahead and complete that step.  We can do this with PHP very easily using CURL.  Again, let’s take a look at this first and then we’ll break it down.

// Validate PayPal data to ensure it actually originated from PayPal
$curl_result = '';
$curl_err = '';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,'www.sandbox.paypal.com/cgi-bin/webscr');
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $validate_request);
curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/x-www-form-urlencoded", "Content-Length: " . strlen($validate_request)));
curl_setopt($ch, CURLOPT_HEADER , 0);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_TIMEOUT, 30);

$curl_result = curl_exec($ch);
$curl_err = curl_error($ch);
curl_close($ch);

First, we’ve prepared two PHP variables for use within our CURL code to store the result and any error information we might get back.  To start, we’ve simply created them and set them to empty values so they’re ready for us later.

Then, we create another PHP variable to store our CURL object.  In this case I’ve named it $ch, and its value, curl_init(), loads CURL for us to use accordingly.

CURL has a number of optional settings that can be specified using the curl_setopt() function.  You may refer to the linked documentation for an in depth review of these options, but I’ll quickly summarize the options we’re utilizing here.

  • CURLOPT_URLThis option sets the value of the URL that we’ll be sending (POSTing) our request string to.  For testing purposes we’re using www.sandbox.paypal.com/cgi-bin/webscr.  When moving to production you’ll need to remove sandbox from this value.
  • CURLOPT_RETURNTRANSFERThis option has been set to a 1, or true, so that the response returned from PayPal is received as a data string instead of outputting it directly to the screen.  This allows us to store the result in our $curl_result variable.
  • CURLOPT_POSTThis option is set to a 1, or true, so that the data sent to PayPal will be sent using the POST method.
  • CURLOPT_POSTFIELDSThis option is where we store the post fields that we’re sending to PayPal.  In our case, we’ve stored all of these post fields in our request string that we stored in $validate_request, so that’s what we’re passing into this option.
  • CURLOPT_HTTPHEADERThis option creates the header information that needs to be included for the servers to understand how to communicate with each other.  The value of this option is an array consisting of header values.  Here, we’ve set the content type and the content length accordingly.
  • CURLOPT_HEADERThis option allows us to specify within our code whether or not we’d like the header information to be output when the communication takes place.  This is typically only used for debugging purposes and can actually interfere with our data parsing.  As such, we set this to a 0, or false, to disable this feature.
  • CURLOPT_SSL_VERIFYPEERThis option allows you to specify whether or not you want CURL to verify SSL scripts used on the server.  As we’re working with non-critical data, I’ve set this to false to avoid any conflicts that could arise from invalid certificates.
  • CURLOPT_TIMEOUTThis option sets the amount of the time the script should wait for a response back from PayPal before it quits.  The value should be passed as seconds, so in this case we’ve set the timeout to 30 seconds.

With all of our options set we set our $curl_result variable to curl_exec($ch), which peforms the CURL action and stores the PayPal response in our variable.

Finally, we check for any error by setting our $curl_err variable to curl_error($ch), and we officially close our CURL session using curl_close($ch).

Again, this code sends the request string consisting of the original IPN data back to PayPal and stores PayPal’s response in the $curl_result variable.  If the data is valid, PayPal’s response will include the word VERIFIED in it.  As such, we can set a $valid flag for use throughout script like this:

// Set $valid flag true/false based on whether PayPal was able to verify the data or not.

if (strpos($curl_result, "VERIFIED")!==false)
{
	$valid = true;
}
else
{
	$valid = false;
}

From this point on, if we need to do something based on whether or not the data was valid we can use our $valid flag as a Boolean (true/false) option.

Step 4

Now that we know whether or not our data is valid we’re ready to do something with it.  At this point, your data is ready to go if you’d like to use $_POST[‘variable_name’] within your application.  PayPal provides a list of IPN variables so you can get an idea of what should be available to you within the $_POST array.

Not all IPN variables will be available in every IPN you receive.  The data included depends on the type of the IPN that was sent ($_POST[‘txn_type’]).  Personally, I like to prepare all possible in PHP variables so it’s easily used throughout my IPN script.  If the data was not included in the $_POST array I set the PHP variable to an empty value.  The following code snippet is very long, but has proven very useful for me, personally.  It prepares all of our IPN data into PHP variables, and if the value was not included in the IPN post the PHP variable is simply set to an empty value using shorthand if/then syntax.

// Buyer Information

$address_city = isset($_POST['address_city']) ? $_POST['address_city'] : '';
$address_country = isset($_POST['address_country']) ? $_POST['address_country'] : '';
$address_country_code = isset($_POST['address_country_code']) ? $_POST['address_country_code'] : '';
$address_name = isset($_POST['address_name']) ? $_POST['address_name'] : '';
$address_state = isset($_POST['address_state']) ? $_POST['address_state'] : '';
$address_status = isset($_POST['address_status']) ? $_POST['address_status'] : '';
$address_street = isset($_POST['address_street']) ? $_POST['address_street'] : '';
$address_zip = isset($_POST['address_zip']) ? $_POST['address_zip'] : '';
$first_name = isset($_POST['first_name']) ? $_POST['first_name'] : '';
$last_name = isset($_POST['last_name']) ? $_POST['last_name'] : '';
$payer_business_name = isset($_POST['payer_business_name']) ? $_POST['payer_business_name'] : '';
$payer_email = isset($_POST['payer_email']) ? $_POST['payer_email'] : '';
$payer_id = isset($_POST['payer_id']) ? $_POST['payer_id'] : '';
$payer_status = isset($_POST['payer_status']) ? $_POST['payer_status'] : '';
$contact_phone = isset($_POST['contact_phone']) ? $_POST['contact_phone'] : '';
$residence_country = isset($_POST['residence_country']) ? $_POST['residence_country'] : '';

// Basic Information

$notify_version = isset($_POST['notify_version']) ? $_POST['notify_version'] : '';
$verify_sign = isset($_POST['verify_sign']) ? $_POST['verify_sign'] : '';
$charset = isset($_POST['charset']) ? $_POST['charset'] : '';
$ipn_track_id = isset($_POST['ipn_track_id']) ? $_POST['ipn_track_id'] : '';
$btn_id = isset($_POST['btn_id']) ? $_POST['btn_id'] : '';
$business = isset($_POST['business']) ? $_POST['business'] : '';
$item_name = isset($_POST['item_name']) ? $_POST['item_name'] : '';
$item_number = isset($_POST['item_number']) ? $_POST['item_number'] : '';
$quantity = isset($_POST['quantity']) ? $_POST['quantity'] : 0;
$receiver_email = isset($_POST['receiver_email']) ? $_POST['receiver_email'] : '';
$receiver_id = isset($_POST['receiver_id']) ? $_POST['receiver_id'] : '';
$transaction_subject = isset($_POST['transaction_subject']) ? $_POST['transaction_subject'] : '';

// Cart Items

$num_cart_items = isset($_POST['num_cart_items']) ? $_POST['num_cart_items'] : '';

$i = 1;
$cart_items = array();
while(isset($_POST['item_number' . $i]))
{
	$item_number = isset($_POST['item_number' . $i]) ? $_POST['item_number' . $i] : '';
	$item_name = isset($_POST['item_name' . $i]) ? $_POST['item_name' . $i] : '';
	$quantity = isset($_POST['quantity' . $i]) ? $_POST['quantity' . $i] : '';
	$mc_gross = isset($_POST['mc_gross_' . $i]) ? $_POST['mc_gross_' . $i] : 0;
	$mc_handling = isset($_POST['mc_handling' . $i]) ? $_POST['mc_handling' . $i] : 0;
	$mc_shipping = isset($_POST['mc_shipping' . $i]) ? $_POST['mc_shipping' . $i] : 0;
	$custom = isset($_POST['custom' . $i]) ? $_POST['custom' . $i] : '';
	$option_name1 = isset($_POST['option_name1_' . $i]) ? $_POST['option_name1_' . $i] : '';
	$option_selection1 = isset($_POST['option_selection1_' . $i]) ? $_POST['option_selection1_' . $i] : '';
	$option_name2 = isset($_POST['option_name2_' . $i]) ? $_POST['option_name2_' . $i] : '';
	$option_selection2 = isset($_POST['option_selection2_' . $i]) ? $_POST['option_selection2_' . $i] : '';
	$option_name3 = isset($_POST['option_name3_' . $i]) ? $_POST['option_name3_' . $i] : '';
	$option_selection3 = isset($_POST['option_selection3_' . $i]) ? $_POST['option_selection3_' . $i] : '';
	$option_name4 = isset($_POST['option_name4_' . $i]) ? $_POST['option_name4_' . $i] : '';
	$option_selection4 = isset($_POST['option_selection4_' . $i]) ? $_POST['option_selection4_' . $i] : '';
	$option_name5 = isset($_POST['option_name5_' . $i]) ? $_POST['option_name5_' . $i] : '';
	$option_selection5 = isset($_POST['option_selection5_' . $i]) ? $_POST['option_selection5_' . $i] : '';
	$option_name6 = isset($_POST['option_name6_' . $i]) ? $_POST['option_name6_' . $i] : '';
	$option_selection6 = isset($_POST['option_selection6_' . $i]) ? $_POST['option_selection6_' . $i] : '';
	$option_name7 = isset($_POST['option_name7_' . $i]) ? $_POST['option_name7_' . $i] : '';
	$option_selection7 = isset($_POST['option_selection7_' . $i]) ? $_POST['option_selection7_' . $i] : '';
	$option_name8 = isset($_POST['option_name8_' . $i]) ? $_POST['option_name8_' . $i] : '';
	$option_selection8 = isset($_POST['option_selection8_' . $i]) ? $_POST['option_selection8_' . $i] : '';
	$option_name9 = isset($_POST['option_name9_' . $i]) ? $_POST['option_name9_' . $i] : '';
	$option_selection9 = isset($_POST['option_selection9_' . $i]) ? $_POST['option_selection9_' . $i] : '';

	$btn_id = isset($_POST['btn_id' . $i]) ? $_POST['btn_id' . $i] : '';

	$current_item = array(
		'item_number' => $item_number,
		'item_name' => $item_name,
		'quantity' => $quantity,
		'mc_gross' => $mc_gross,
		'mc_handling' => $mc_handling,
		'mc_shipping' => $mc_shipping,
		'custom' => $custom,
		'option_name1' => $option_name1,
		'option_selection1' => $option_selection1,
		'option_name2' => $option_name2,
		'option_selection2' => $option_selection2,
		'option_name3' => $option_name3,
		'option_selection3' => $option_selection3,
		'option_name4' => $option_name4,
		'option_selection4' => $option_selection4,
		'option_name5' => $option_name5,
		'option_selection5' => $option_selection5,
		'option_name6' => $option_name6,
		'option_selection6' => $option_selection6,
		'option_name7' => $option_name7,
		'option_selection7' => $option_selection7,
		'option_name8' => $option_name8,
		'option_selection8' => $option_selection8,
		'option_name9' => $option_name9,
		'option_selection9' => $option_selection9,
		'btn_id' => $btn_id
	);

	array_push($cart_items, $current_item);
	$i++;
}

// Advanced and Custom Information

$custom = isset($_POST['custom']) ? $_POST['custom'] : '';
$invoice = isset($_POST['invoice']) ? $_POST['invoice'] : '';
$memo = isset($_POST['memo']) ? $_POST['memo'] : '';
$option_name1 = isset($_POST['option_name1']) ? $_POST['option_name1'] : '';
$option_selection1 = isset($_POST['option_selection1']) ? $_POST['option_selection1'] : '';
$option_name2 = isset($_POST['option_name2']) ? $_POST['option_name2'] : '';
$option_selection2 = isset($_POST['option_selection2']) ? $_POST['option_selection2'] : '';
$option_name3 = isset($_POST['option_name3']) ? $_POST['option_name3'] : '';
$option_selection3 = isset($_POST['option_selection3']) ? $_POST['option_selection3'] : '';
$option_name4 = isset($_POST['option_name4']) ? $_POST['option_name4'] : '';
$option_selection4 = isset($_POST['option_selection2']) ? $_POST['option_selection4'] : '';
$option_name5 = isset($_POST['option_name5']) ? $_POST['option_name5'] : '';
$option_selection5 = isset($_POST['option_selection2']) ? $_POST['option_selection5'] : '';
$option_name6 = isset($_POST['option_name6']) ? $_POST['option_name6'] : '';
$option_selection6 = isset($_POST['option_selection2']) ? $_POST['option_selection6'] : '';
$option_name7 = isset($_POST['option_name7']) ? $_POST['option_name7'] : '';
$option_selection7 = isset($_POST['option_selection2']) ? $_POST['option_selection7'] : '';
$option_name8 = isset($_POST['option_name8']) ? $_POST['option_name8'] : '';
$option_selection8 = isset($_POST['option_selection2']) ? $_POST['option_selection8'] : '';
$option_name9 = isset($_POST['option_name9']) ? $_POST['option_name9'] : '';
$option_selection9 = isset($_POST['option_selection2']) ? $_POST['option_selection9'] : '';

// Website Payments Standard, Website Payments Pro, and Refund Information
$auth_id = isset($_POST['auth_id']) ? $_POST['auth_id'] : '';
$auth_exp = isset($_POST['auth_exp']) ? $_POST['auth_exp'] : '';
$auth_amount = isset($_POST['auth_amount']) ? $_POST['auth_amount'] : '';
$auth_status = isset($_POST['auth_status']) ? $_POST['auth_status'] : '';

// Fraud Management Filters
$i = 1;
$fraud_management_filters = array();

while(isset($_POST['fraud_management_filters_' . $i]))
{
	$filter_name = isset($_POST['fraud_management_filter_' . $i]) ? $_POST['fraud_management_filter_' . $i] : '';

	array_push($fraud_management_filters, $filter_name);
	$i++;
}

$mc_gross = isset($_POST['mc_gross']) ? $_POST['mc_gross'] : 0;
$mc_handling = isset($_POST['mc_handling']) ? $_POST['mc_handling'] : 0;
$mc_shipping = isset($_POST['mc_shipping']) ? $_POST['mc_shipping'] : 0;
$mc_fee = isset($_POST['mc_fee']) ? $_POST['mc_fee'] : 0;
$num_cart_items = isset($_POST['num_cart_items']) ? $_POST['num_cart_items'] : 0;
$parent_txn_id = isset($_POST['parent_txn_id']) ? $_POST['parent_txn_id'] : '';
$payment_date = isset($_POST['payment_date']) ? $_POST['payment_date'] : '';
$payment_status = isset($_POST['payment_status']) ? $_POST['payment_status'] : '';
$payment_type = isset($_POST['payment_type']) ? $_POST['payment_type'] : '';
$pending_reason = isset($_POST['pending_reason']) ? $_POST['pending_reason'] : '';
$protection_eligibility = isset($_POST['protection_eligibility']) ? $_POST['protection_eligibility'] : '';
$reason_code = isset($_POST['reason_code']) ? $_POST['reason_code'] : '';
$remaining_settle = isset($_POST['remaining_settle']) ? $_POST['remaining_settle'] : '';
$shipping_method = isset($_POST['shipping_method']) ? $_POST['shipping_method'] : '';
$shipping = isset($_POST['shipping']) ? $_POST['shipping'] : 0;
$tax = isset($_POST['tax']) ? $_POST['tax'] : 0;
$transaction_entity = isset($_POST['transaction_entity']) ? $_POST['transaction_entity'] : '';
$txn_id = isset($_POST['txn_id']) ? $_POST['txn_id'] : '';
$txn_type = isset($_POST['txn_type']) ? $_POST['txn_type'] : '';

// Currency and Currency Exchange Information

$exchange_rate = isset($_POST['exchange_rate']) ? $_POST['exchange_rate'] : '';
$mc_currency = isset($_POST['mc_currency']) ? $_POST['mc_currency'] : '';
$settle_amount = isset($_POST['settle_amount']) ? $_POST['settle_amount'] : 0;
$settle_currency = isset($_POST['settle_currency']) ? $_POST['settle_currency'] : '';

// Auction Variables

$auction_buyer_id = isset($_POST['auction_buyer_id']) ? $_POST['auction_buyer_id'] : '';
$auction_closing_date = isset($_POST['auction_closing_date']) ? $_POST['auction_closing_date'] : '';
$auction_multi_item = isset($_POST['auction_multi_item']) ? $_POST['auction_multi_item'] : 0;
$for_auction = isset($_POST['for_auction']) ? 1 : 0;
$handling_amount = isset($_POST['handling_amount']) ? $_POST['handling_amount'] : 0;
$shipping_discount = isset($_POST['shipping_discount']) ? $_POST['shipping_discount'] : 0;
$insurance_amount = isset($_POST['insurance_amount']) ? $_POST['insurance_amount'] : 0;

// Mass Payments

$i = 1;
$mass_payments = array();
while(isset($_POST['masspay_txn_id_' . $i]))
{
	$masspay_txn_id = isset($_POST['masspay_txn_id_' . $i]) ? $_POST['masspay_txn_id_' . $i] : '';
	$mc_currency = isset($_POST['mc_currency_' . $i]) ? $_POST['mc_currency_' . $i] : '';
	$mc_fee = isset($_POST['mc_fee_' . $i]) ? $_POST['mc_fee_' . $i] : 0;
	$mc_gross = isset($_POST['mc_gross_' . $i]) ? $_POST['mc_gross_' . $i] : 0;
	$receiver_email = isset($_POST['receiver_email_' . $i]) ? $_POST['receiver_email_' . $i] : '';
	$status = isset($_POST['status_' . $i]) ? $_POST['status_' . $i] : '';
	$unique_id = isset($_POST['unique_id_' . $i]) ? $_POST['unique_id_' . $i] : '';

	$current_payment_data_set = array(
		'masspay_txn_id' => $masspay_txn_id,
		'mc_currency' => $mc_currency,
		'mc_fee' => $mc_fee,
		'mc_gross' => $mc_gross,
		'receiver_email' => $receiver_email,
		'status' => $status,
		'unique_id' => $unique_id
	);

	array_push($mass_payments, $current_payment_data_set);
	$i++;
}

// Recurring Payments Information

$initial_payment_status = isset($_POST['initial_payment_status']) ? $_POST['initial_payment_status'] : '';
$initial_payment_txn_id = isset($_POST['initial_payment_txn_id']) ? $_POST['initial_payment_txn_id'] : '';
$recurring_payment_id = isset($_POST['recurring_payment_id']) ? $_POST['recurring_payment_id'] : '';
$product_name = isset($_POST['product_name']) ? $_POST['product_name'] : '';
$product_type = isset($_POST['product_type']) ? $_POST['product_type'] : '';
$period_type = isset($_POST['period_type']) ? $_POST['period_type'] : '';
$payment_cycle = isset($_POST['payment_cycle']) ? $_POST['payment_cycle'] : '';
$outstanding_balance = isset($_POST['outstanding_balance']) ? $_POST['outstanding_balance'] : '';
$amount_per_cycle = isset($_POST['amount_per_cycle']) ? $_POST['amount_per_cycle'] : 0;
$initial_payment_amount = isset($_POST['initial_payment_amount']) ? $_POST['initial_payment_amount'] : '';
$profile_status = isset($_POST['profile_status']) ? $_POST['profile_status'] : '';
$amount = isset($_POST['amount']) ? $_POST['amount'] : '';
$time_created = isset($_POST['time_created']) ? $_POST['time_created'] : '';
$next_payment_date = isset($_POST['next_payment_date']) ? $_POST['next_payment_date'] : '';
$rp_invoice_id = isset($_POST['rp_invoice_id']) ? $_POST['rp_invoice_id'] : '';

// Subscription Variables

$subscr_date = isset($_POST['subscr_date']) ? $_POST['subscr_date'] : '';
$subscr_effective = isset($_POST['subscr_effective']) ? $_POST['subscr_effective'] : '';
$period1 = isset($_POST['period1']) ? $_POST['period1'] : '';
$period2 = isset($_POST['period2']) ? $_POST['period2'] : '';
$period3 = isset($_POST['period3']) ? $_POST['period3'] : '';
$amount1 = isset($_POST['amount1']) ? $_POST['amount1'] : 0;
$amount2 = isset($_POST['amount2']) ? $_POST['amount2'] : 0;
$amount3 = isset($_POST['amount3']) ? $_POST['amount3'] : 0;
$mc_amount1 = isset($_POST['mc_amount1']) ? $_POST['mc_amount1'] : 0;
$mc_amount2 = isset($_POST['mc_amount2']) ? $_POST['mc_amount2'] : 0;
$mc_amount3 = isset($_POST['mc_amount3']) ? $_POST['mc_amount3'] : 0;
$mc_currency = isset($_POST['mc_currency']) ? $_POST['mc_currency'] : '';
$recurring = isset($_POST['recurring']) ? $_POST['recurring'] : '';
$reattempt = isset($_POST['reattempt']) ? $_POST['reattempt'] : '';
$retry_at = isset($_POST['retry_at']) ? $_POST['retry_at'] : '';
$recur_times = isset($_POST['recur_times']) ? $_POST['recur_times'] : '';
$username = isset($_POST['username']) ? $_POST['username'] : '';
$password = isset($_POST['password']) ? $_POST['password'] : '';
$subscr_id = isset($_POST['subscr_id']) ? $_POST['subscr_id'] : '';

// Dispute Notification Variables

$receipt_id = isset($_POST['receipt_id']) ? $_POST['receipt_id'] : '';
$case_id = isset($_POST['case_id']) ? $_POST['case_id'] : '';
$case_type = isset($_POST['case_type']) ? $_POST['case_type'] : '';
$case_creation_date = isset($_POST['case_creation_date']) ? $_POST['case_creation_date'] : '';

// Adaptive Payments Fields

$transaction_type = isset($_POST['transaction_type']) ? $_POST['transaction_type'] : '';
$status = isset($_POST['status']) ? $_POST['status'] : '';
$sender_email = isset($_POST['senderEmail']) ? $_POST['senderEmail'] : '';
$action_type = isset($_POST['actionType']) ? $_POST['actionType'] : '';
$payment_request_date = isset($_POST['payment_request_date']) ? $_POST['payment_request_date'] : '';
$reverse_all_parallel_payments_on_error = isset($_POST['reverse_all_parallel_payments_on_error']) ? $_POST['reverse_all_parallel_payments_on_error'] : '';

$adaptive_payment_transactions = array();
$i = 0;
while(isset($_POST['transaction' . $i . '.id']))
{
	$transaction_id = isset($_POST['transaction' . $i . '.id']) ? $_POST['transaction' . $i . '.id'] : '';
	$transaction_status = isset($_POST['transaction' . $i . '.status']) ? $_POST['transaction' . $i . '.status'] : '';
	$transaction_id_for_sender = isset($_POST['transaction' . $i . '.id_for_sender']) ? $_POST['transaction' . $i . '.id_for_sender'] : '';
	$tranasction_status_for_sender_txn = isset($_POST['transaction' . $i . '.status_for_sender_txn']) ? $_POST['transaction' . $i . '.status_for_sender_txn'] : '';
	$transaction_refund_id = isset($_POST['transaction' . $i . '.refund_id']) ? $_POST['transaction' . $i . '.refund_id'] : '';
	$transaction_refund_amount = isset($_POST['transaction' . $i . '.refund_amount']) ? $_POST['transaction' . $i . '.refund_amount'] : '';
	$transaction_refund_account_charged = isset($_POST['transaction' . $i . '.refund_account_charged']) ? $_POST['transaction' . $i . '.refund_account_charged'] : '';
	$transaction_receiver = isset($_POST['transaction' . $i . '.receiver']) ? $_POST['transaction' . $i . '.receiver'] : '';
	$transaction_invoice_id = isset($_POST['transaction' . $i . '.invoiceId']) ? $_POST['transaction' . $i . '.invoiceId'] : '';
	$transaction_amount = isset($_POST['transaction' . $i . '.amount']) ? $_POST['transaction' . $i . '.amount'] : '';
	$transaction_is_primary_receiver = isset($_POST['transaction' . $i . '.is_primary_receiver']) ? $_POST['transaction' . $i . '.is_primary_receiver'] : '';
	$current_transaction = array(
	'transaction_id' => $transaction_id,
	'transaction_status' => $transaction_status,
	'transaction_id_for_sender' => $transaction_id_for_sender,
	'transaction_status_for_sender_txn' => $transaction_status_for_sender_txn,
	'transaction_refund_id' => $transaction_refund_id,
	'transaction_refund_amount' => $transaction_refund_amount,
	'transaction_refund_account_charged' => $transaction_refund_account_charged,
	'transaction_receiver' => $transaction_receiver,
	'transaction_invoice_id' => $transaction_invoice_id,
	'transaction_amount' => $transaction_amount,
	'transaction_is_primary_receiver' => $transaction_is_primary_receiver
	);
	array_push($adaptive_payment_transactions, $current_transaction);
	$i++;
}

$return_url = isset($_POST['returnUrl']) ? $_POST['returnUrl'] : '';
$cancel_url = isset($_POST['cancelUrl']) ? $_POST['cancelUrl'] : '';
$ipn_notification_url = isset($_POST['ipnNotificationUrl']) ? $_POST['ipnNotificationUrl'] : '';
$pay_key = isset($_POST['payKey']) ? $_POST['payKey'] : '';
$fees_payer = isset($_POST['feesPayer']) ? $_POST['feesPayer'] : '';
$tracking_id = isset($_POST['trackingId']) ? $_POST['trackingId'] : '';
$preapproval_key = isset($_POST['preapprovalKey']) ? $_POST['preapprovalKey'] : '';
$approved = isset($_POST['approved']) ? $_POST['approved'] : '';
$current_number_of_payments = isset($_POST['current_number_of_payments']) ? $_POST['current_number_of_payments'] : '';
$current_total_amount_of_all_payments = isset($_POST['current_total_amount_of_all_payments']) ? $_POST['current_total_amount_of_all_payments'] : '';
$current_period_attempts = isset($_POST['current_period_attempts']) ? $_POST['current_period_attempts'] : '';
$currency_code = isset($_POST['currencyCode']) ? $_POST['currencyCode'] : '';
$date_of_month = isset($_POST['date_of_month']) ? $_POST['date_of_month'] : '';
$day_of_week = isset($_POST['day_of_week']) ? $_POST['day_of_week'] : '';
$starting_date = isset($_POST['starting_date']) ? $_POST['starting_date'] : '';
$ending_date = isset($_POST['ending_date']) ? $_POST['ending_date'] : '';
$max_total_amount_of_all_payments = isset($_POST['max_total_amount_of_all_payments']) ? $_POST['max_total_amount_of_all_payments'] : '';
$max_amount_per_payment = isset($_POST['max_amount_per_payment']) ? $_POST['max_amount_per_payment'] : '';
$max_number_of_payments = isset($_POST['max_number_of_payments']) ? $_POST['max_number_of_payments'] : '';
$payment_period = isset($_POST['payment_period']) ? $_POST['payment_period'] : '';
$pin_type = isset($_POST['pin_type']) ? $_POST['pin_type'] : '';

// Adaptive Accounts
$account_key = isset($_POST['account_key']) ? $_POST['account_key'] : '';
$confirmation_code = isset($_POST['confirmation_code']) ? $_POST['confirmation_code'] : '';

All of the PHP variable names used are based on the name PayPal uses in the original IPN POST so you can use the variables within your code anywhere you’d like and rest assured that you won’t run into PHP warnings that the data is not available.

As this code is very lengthy, I like to separate it and keep it in an include file.  Let’s create a new file, parse-data.php, and store all of this code there.  Then we can include it in our index.php file.  Our directory structure is now:

Directory Structure 2

And the next step in our index.php file will be:

// Store all IPN data in PHP variables for easy access throughout the rest of the application.

require_once('parse-data.php');

Part 1 Wrap Up

At this point we’ve got an IPN listener that will receive the data from PayPal, validate it accordingly, and prepare all of the data in PHP variables for easy access throughout the application.

As I mentioned before, you may wish to take these steps and build them into your own class for a more structured approach, but this should make sense to any novice – advanced PHP developer so you can make it work best for you.

Stay tuned for part 2 of this series where we’ll extend this solution to automatically deliver an eBook to buyers, and if the item was purchased from an eBay auction, we’ll update the eBay platform to show the item has been delivered.

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