Full Code of Quixotix/PHP-PayPal-IPN for AI

Repository: Quixotix/PHP-PayPal-IPN
Branch: master
Commit: 9e7df79fb50f
Files: 6
Total size: 24.4 KB

Directory structure:
gitextract_rvzawjgx/

├── LICENSE
├── README.md
├── cert/
│   └── api_cert_chain.crt
├── example/
│   ├── ipn.php
│   └── ipn_errors.log
└── ipnlistener.php

================================================
FILE CONTENTS
================================================

================================================
FILE: LICENSE
================================================
Copyright (c) 2012, Micah Carrick
All rights reserved.

Redistribution and use in source and binary forms, with or without modification, 
are permitted provided that the following conditions are met:

    * Redistributions of source code must retain the above copyright notice, 
      this list of conditions and the following disclaimer.
      
    * Redistributions in binary form must reproduce the above copyright notice, 
    this list of conditions and the following disclaimer in the documentation 
    and/or other materials provided with the distribution.
    
    * Neither the name of Quixotix, LLC nor the names of its 
    contributors may be used to endorse or promote products derived from this 
    software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND 
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR 
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON 
ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


================================================
FILE: README.md
================================================
PHP-PayPal-IPN
==============

__This code is over a decade old and no longer relevant. Please consult Paypal developer documentation instead.__

A PayPal Instant Payment Notification (IPN) class for PHP 5. 

Use the `IpnListener` class in your PHP IPN script to handle the encoding 
of POST data, post back to PayPal, and parsing of the response from PayPal.


Features
--------

* Switch between live and sandbox by setting the `use_sandbox` property.
* Supports both secure SSL and plain HTTP transactions by setting the `use_ssl`
  property (SSL is recommended).
* Supports both cURL and fsockopen network libraries by setting the `use_curl`
  property (cURL is recommended).
* Verifies an HTTP "200" response status code from the PayPal server.
* Get detailed plain text reports of the entire IPN using the `getTextReport()` 
  method for use in emails and logs to administrators.
* Throws various exceptions to differentiate between common errors in code or
  server configuration versus invalid IPN responses.


Getting Started
---------------

This code is intended for web developers. You should understand how the IPN
process works conceptually and you should understand when and why you would be
using IPN. Reading the [PayPal Instant Payment Notification Guide][1] is a good
place to start.

You should also have a [PayPal Sandbox Account][2] with a test buyer account and
a test seller account. When logged into your sandbox account there is an IPN
simulator under the 'Test Tools' menu which you can used to test your IPN 
listener.

[1]: https://cms.paypal.com/cms_content/US/en_US/files/developer/IPNGuide.pdf
[2]: https://developer.paypal.com

Once you have your sandbox account setup, you simply create a PHP script that
will be your IPN listener. In that script, use the `IpnListener()` class as shown
below. For a more thoroughly documented example, take a look at the 
`example/ipn.php` script in the source code.

    <?php

    include('ipnlistener.php');

    $listener = new IpnListener();
    $listener->use_sandbox = true;

    try {
        $verified = $listener->processIpn();
    } catch (Exception $e) {
        // fatal error trying to process IPN.
        exit(0);
    }

    if ($verified) {
        // IPN response was "VERIFIED"
    } else {
        // IPN response was "INVALID"
    }

    ?>


Documentation
-------------

Documentation has not been generated yet, but, there are phpDocumentor style
docstrings (comments) throughout `ipnlistener.php` which explain the important
public properties and methods.

I have also written a more in-depth IPN tutorial on my blog: [PayPal IPN with PHP][3]

[3]: http://www.micahcarrick.com/paypal-ipn-with-php.html


Known Issues
------------

__Problem__

The `processIpn()` method throws the following exception:

    cURL error: [52] GnuTLS recv error (-9): A TLS packet with unexpected length was received.

__Solution__

When cURL is compiled with GnuTLS the call to PayPal will fail if the SSL version
is not explicitly set as a cURL option. Set the `force_ssl_v3` property to force 
SSL 3:

    $listener = new IpnListener();
    $listener->force_ssl_v3 = true;

_Note: force_ssl_v3 is now true by default_



__Problem__

     PHP Warning: curl_setopt() [function.curl-setopt]: CURLOPT_FOLLOWLOCATION 
     cannot be activated when in safe_mode or an open_basedir is set in ...

__Solution__

If you need PHP safe mode, you can disable CURLOPT_FOLLOWLOCATION using the
`follow_location` property.

    $listener = new IpnListener();
    $listener->follow_location = false;

_Note: follow_location is now false enabled by default_


Example Report
--------------

Here is an example of a report returned by the `getTextReport()` method. Create
your own reports by extending the `IpnListener()` class or by accessing the data
directly in your ipn script.

    --------------------------------------------------------------------------------
    [09/09/2011 8:35 AM] - https://www.sandbox.paypal.com/cgi-bin/webscr (curl)
    --------------------------------------------------------------------------------
    HTTP/1.1 200 OK
    Date: Fri, 09 Sep 2011 13:35:39 GMT
    Server: Apache
    X-Frame-Options: SAMEORIGIN
    Set-Cookie: c9MWDuvPtT9GIMyPc3jwol1VSlO=Ch-NORlHUjlmbEm__KG9LupR4mfMfQTkx1QQ6hHDyc0RImWr88NY_ILeICENiwtVX3iw4jEnT1-1gccYjQafWrQCkDmiykNT8TeDUg7R7L0D9bQm47PTG8MafmrpyrUAxQfst0%7c_jG1ZL6CffJgwrC-stQeqni04tKaYSIZqyqhFU7tKnV520wiYOw0hwk5Ehrh3hLDvBxkpm%7cYTFdl0w0YpEqxu0D1jDTVTlEGXlmLs4wob2Glu9htpZkFV9O2aCyfQ4CvA2kLJmlI6YiXm%7c1315575340; domain=.paypal.com; path=/; Secure; HttpOnly
    Set-Cookie: cookie_check=yes; expires=Mon, 06-Sep-2021 13:35:40 GMT; domain=.paypal.com; path=/; Secure; HttpOnly
    Set-Cookie: navcmd=_notify-validate; domain=.paypal.com; path=/; Secure; HttpOnly
    Set-Cookie: navlns=0.0; expires=Thu, 04-Sep-2031 13:35:40 GMT; domain=.paypal.com; path=/; Secure; HttpOnly
    Set-Cookie: Apache=10.72.109.11.1315575339707456; path=/; expires=Sun, 01-Sep-41 13:35:39 GMT
    X-Cnection: close
    Transfer-Encoding: chunked
    Content-Type: text/html; charset=UTF-8

    VERIFIED
    --------------------------------------------------------------------------------
    test_ipn                 1
    payment_type             instant
    payment_date             06:34:51 Sep 09, 2011 PDT
    payment_status           Completed
    address_status           confirmed
    payer_status             verified
    first_name               John
    last_name                Smith
    payer_email              buyer@paypalsandbox.com
    payer_id                 TESTBUYERID01
    address_name             John Smith
    address_country          United States
    address_country_code     US
    address_zip              95131
    address_state            CA
    address_city             San Jose
    address_street           123, any street
    business                 seller@paypalsandbox.com
    receiver_email           seller@paypalsandbox.com
    receiver_id              TESTSELLERID1
    residence_country        US
    item_name                something
    item_number              AK-1234
    quantity                 1
    shipping                 3.04
    tax                      2.02
    mc_currency              USD
    mc_fee                   0.44
    mc_gross                 12.34
    mc_gross_1               9.34
    txn_type                 web_accept
    txn_id                   51991334
    notify_version           2.1
    custom                   xyz123
    charset                  windows-1252
    verify_sign              Ah5rOpfPGo5g6FNg95DMPybP51J5AUEdXS1hqyRAP6WYYwaixKNDgQRR


================================================
FILE: cert/api_cert_chain.crt
================================================
-----BEGIN CERTIFICATE-----
MIIDgzCCAuygAwIBAgIQJUuKhThCzONY+MXdriJupDANBgkqhkiG9w0BAQUFADBf
MQswCQYDVQQGEwJVUzEXMBUGA1UEChMOVmVyaVNpZ24sIEluYy4xNzA1BgNVBAsT
LkNsYXNzIDMgUHVibGljIFByaW1hcnkgQ2VydGlmaWNhdGlvbiBBdXRob3JpdHkw
HhcNOTcwNDE3MDAwMDAwWhcNMTExMDI0MjM1OTU5WjCBujEfMB0GA1UEChMWVmVy
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MzFJMEcGA1UECxNAd3d3LnZlcmlzaWduLmNvbS9DUFMgSW5jb3JwLmJ5IFJlZi4g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-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
MIICPDCCAaUCEHC65B0Q2Sk0tjjKewPMur8wDQYJKoZIhvcNAQECBQAwXzELMAkG
A1UEBhMCVVMxFzAVBgNVBAoTDlZlcmlTaWduLCBJbmMuMTcwNQYDVQQLEy5DbGFz
cyAzIFB1YmxpYyBQcmltYXJ5IENlcnRpZmljYXRpb24gQXV0aG9yaXR5MB4XDTk2
MDEyOTAwMDAwMFoXDTI4MDgwMTIzNTk1OVowXzELMAkGA1UEBhMCVVMxFzAVBgNV
BAoTDlZlcmlTaWduLCBJbmMuMTcwNQYDVQQLEy5DbGFzcyAzIFB1YmxpYyBQcmlt
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BarsAx94f56TuZoAqiN91qyFomNFx3InzPRMxnVx0jnvT0Lwdd8KkMaOIG+YD/is
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AA9WjQKZ7aKQRUzkuxCkPfAyAw7xzvjoyVGM5mKf5p/AfbdynMk2OmufTqj/ZA1k
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
MIIDAjCCAmsCEH3Z/gfPqB63EHln+6eJNMYwDQYJKoZIhvcNAQEFBQAwgcExCzAJ
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-----END CERTIFICATE-----


================================================
FILE: example/ipn.php
================================================
<?php
/**
 *  PHP-PayPal-IPN Example
 *
 *  This shows a basic example of how to use the IpnListener() PHP class to 
 *  implement a PayPal Instant Payment Notification (IPN) listener script.
 *
 *  For a more in depth tutorial, see my blog post:
 *  http://www.micahcarrick.com/paypal-ipn-with-php.html
 *
 *  This code is available at github:
 *  https://github.com/Quixotix/PHP-PayPal-IPN
 *
 *  @package    PHP-PayPal-IPN
 *  @author     Micah Carrick
 *  @copyright  (c) 2011 - Micah Carrick
 *  @license    http://opensource.org/licenses/gpl-3.0.html
 */
 
 
/*
Since this script is executed on the back end between the PayPal server and this
script, you will want to log errors to a file or email. Do not try to use echo
or print--it will not work! 

Here I am turning on PHP error logging to a file called "ipn_errors.log". Make
sure your web server has permissions to write to that file. In a production 
environment it is better to have that log file outside of the web root.
*/
ini_set('log_errors', true);
ini_set('error_log', dirname(__FILE__).'/ipn_errors.log');


// instantiate the IpnListener class
include('../ipnlistener.php');
$listener = new IpnListener();


/*
When you are testing your IPN script you should be using a PayPal "Sandbox"
account: https://developer.paypal.com
When you are ready to go live change use_sandbox to false.
*/
$listener->use_sandbox = true;

/*
By default the IpnListener object is going  going to post the data back to PayPal
using cURL over a secure SSL connection. This is the recommended way to post
the data back, however, some people may have connections problems using this
method. 

To post over standard HTTP connection, use:
$listener->use_ssl = false;

To post using the fsockopen() function rather than cURL, use:
$listener->use_curl = false;
*/

/*
The processIpn() method will encode the POST variables sent by PayPal and then
POST them back to the PayPal server. An exception will be thrown if there is 
a fatal error (cannot connect, your server is not configured properly, etc.).
Use a try/catch block to catch these fatal errors and log to the ipn_errors.log
file we setup at the top of this file.

The processIpn() method will send the raw data on 'php://input' to PayPal. You
can optionally pass the data to processIpn() yourself:
$verified = $listener->processIpn($my_post_data);
*/
try {
    $listener->requirePostMethod();
    $verified = $listener->processIpn();
} catch (Exception $e) {
    error_log($e->getMessage());
    exit(0);
}


/*
The processIpn() method returned true if the IPN was "VERIFIED" and false if it
was "INVALID".
*/
if ($verified) {
    /*
    Once you have a verified IPN you need to do a few more checks on the POST
    fields--typically against data you stored in your database during when the
    end user made a purchase (such as in the "success" page on a web payments
    standard button). The fields PayPal recommends checking are:
    
        1. Check the $_POST['payment_status'] is "Completed"
	    2. Check that $_POST['txn_id'] has not been previously processed 
	    3. Check that $_POST['receiver_email'] is your Primary PayPal email 
	    4. Check that $_POST['payment_amount'] and $_POST['payment_currency'] 
	       are correct
    
    Since implementations on this varies, I will leave these checks out of this
    example and just send an email using the getTextReport() method to get all
    of the details about the IPN.  
    */
    mail('YOUR EMAIL ADDRESS', 'Verified IPN', $listener->getTextReport());

} else {
    /*
    An Invalid IPN *may* be caused by a fraudulent transaction attempt. It's
    a good idea to have a developer or sys admin manually investigate any 
    invalid IPN.
    */
    mail('YOUR EMAIL ADDRESS', 'Invalid IPN', $listener->getTextReport());
}

?>


================================================
FILE: example/ipn_errors.log
================================================


================================================
FILE: ipnlistener.php
================================================
<?php
/**
 *  PayPal IPN Listener
 *
 *  A class to listen for and handle Instant Payment Notifications (IPN) from 
 *  the PayPal server.
 *
 *  https://github.com/Quixotix/PHP-PayPal-IPN
 *
 *  @package    PHP-PayPal-IPN
 *  @author     Micah Carrick
 *  @copyright  (c) 2012 - Micah Carrick
 *  @version    2.1.0
 */
class IpnListener {
    
    /**
     *  If true, the recommended cURL PHP library is used to send the post back 
     *  to PayPal. If flase then fsockopen() is used. Default true.
     *
     *  @var boolean
     */
    public $use_curl = true;     
    
    /**
     *  If true, explicitly sets cURL to use SSL version 3. Use this if cURL
     *  is compiled with GnuTLS SSL.
     *
     *  @var boolean
     */
    public $force_ssl_v3 = true;     
   
    /**
     *  If true, cURL will use the CURLOPT_FOLLOWLOCATION to follow any 
     *  "Location: ..." headers in the response.
     *
     *  @var boolean
     */
    public $follow_location = false;     
    
    /**
     *  If true, an SSL secure connection (port 443) is used for the post back 
     *  as recommended by PayPal. If false, a standard HTTP (port 80) connection
     *  is used. Default true.
     *
     *  @var boolean
     */
    public $use_ssl = true;      
    
    /**
     *  If true, the paypal sandbox URI www.sandbox.paypal.com is used for the
     *  post back. If false, the live URI www.paypal.com is used. Default false.
     *
     *  @var boolean
     */
    public $use_sandbox = false; 
    
    /**
     *  The amount of time, in seconds, to wait for the PayPal server to respond
     *  before timing out. Default 30 seconds.
     *
     *  @var int
     */
    public $timeout = 30;       
    
    private $post_data = array();
    private $post_uri = '';     
    private $response_status = '';
    private $response = '';

    const PAYPAL_HOST = 'www.paypal.com';
    const SANDBOX_HOST = 'www.sandbox.paypal.com';
    
    /**
     *  Post Back Using cURL
     *
     *  Sends the post back to PayPal using the cURL library. Called by
     *  the processIpn() method if the use_curl property is true. Throws an
     *  exception if the post fails. Populates the response, response_status,
     *  and post_uri properties on success.
     *
     *  @param  string  The post data as a URL encoded string
     */
    protected function curlPost($encoded_data) {

        if ($this->use_ssl) {
            $uri = 'https://'.$this->getPaypalHost().'/cgi-bin/webscr';
            $this->post_uri = $uri;
        } else {
            $uri = 'http://'.$this->getPaypalHost().'/cgi-bin/webscr';
            $this->post_uri = $uri;
        }
        
        $ch = curl_init();

		curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, true);
		curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
		curl_setopt($ch, CURLOPT_CAINFO, 
		            dirname(__FILE__)."/cert/api_cert_chain.crt");
        curl_setopt($ch, CURLOPT_URL, $uri);
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $encoded_data);
        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, $this->follow_location);
        curl_setopt($ch, CURLOPT_TIMEOUT, $this->timeout);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_HEADER, true);
        
        if ($this->force_ssl_v3) {
            curl_setopt($ch, CURLOPT_SSLVERSION, 3);
        }
        
        $this->response = curl_exec($ch);
        $this->response_status = strval(curl_getinfo($ch, CURLINFO_HTTP_CODE));
        
        if ($this->response === false || $this->response_status == '0') {
            $errno = curl_errno($ch);
            $errstr = curl_error($ch);
            throw new Exception("cURL error: [$errno] $errstr");
        }
    }
    
    /**
     *  Post Back Using fsockopen()
     *
     *  Sends the post back to PayPal using the fsockopen() function. Called by
     *  the processIpn() method if the use_curl property is false. Throws an
     *  exception if the post fails. Populates the response, response_status,
     *  and post_uri properties on success.
     *
     *  @param  string  The post data as a URL encoded string
     */
    protected function fsockPost($encoded_data) {
    
        if ($this->use_ssl) {
            $uri = 'ssl://'.$this->getPaypalHost();
            $port = '443';
            $this->post_uri = $uri.'/cgi-bin/webscr';
        } else {
            $uri = $this->getPaypalHost(); // no "http://" in call to fsockopen()
            $port = '80';
            $this->post_uri = 'http://'.$uri.'/cgi-bin/webscr';
        }

        $fp = fsockopen($uri, $port, $errno, $errstr, $this->timeout);
        
        if (!$fp) { 
            // fsockopen error
            throw new Exception("fsockopen error: [$errno] $errstr");
        } 

        $header = "POST /cgi-bin/webscr HTTP/1.1\r\n";
        $header .= "Host: ".$this->getPaypalHost()."\r\n";
        $header .= "Content-Type: application/x-www-form-urlencoded\r\n";
        $header .= "Content-Length: ".strlen($encoded_data)."\r\n";
        $header .= "Connection: Close\r\n\r\n";
        
        fputs($fp, $header.$encoded_data."\r\n\r\n");
        
        while(!feof($fp)) { 
            if (empty($this->response)) {
                // extract HTTP status from first line
                $this->response .= $status = fgets($fp, 1024); 
                $this->response_status = trim(substr($status, 9, 4));
            } else {
                $this->response .= fgets($fp, 1024); 
            }
        } 
        
        fclose($fp);
    }
    
    private function getPaypalHost() {
        if ($this->use_sandbox) return self::SANDBOX_HOST;
        else return self::PAYPAL_HOST;
    }
    
    /**
     *  Get POST URI
     *
     *  Returns the URI that was used to send the post back to PayPal. This can
     *  be useful for troubleshooting connection problems. The default URI
     *  would be "ssl://www.sandbox.paypal.com:443/cgi-bin/webscr"
     *
     *  @return string
     */
    public function getPostUri() {
        return $this->post_uri;
    }
    
    /**
     *  Get Response
     *
     *  Returns the entire response from PayPal as a string including all the
     *  HTTP headers.
     *
     *  @return string
     */
    public function getResponse() {
        return $this->response;
    }
    
    /**
     *  Get Response Status
     *
     *  Returns the HTTP response status code from PayPal. This should be "200"
     *  if the post back was successful. 
     *
     *  @return string
     */
    public function getResponseStatus() {
        return $this->response_status;
    }
    
    /**
     *  Get Text Report
     *
     *  Returns a report of the IPN transaction in plain text format. This is
     *  useful in emails to order processors and system administrators. Override
     *  this method in your own class to customize the report.
     *
     *  @return string
     */
    public function getTextReport() {
        
        $r = '';
        
        // date and POST url
        for ($i=0; $i<80; $i++) { $r .= '-'; }
        $r .= "\n[".date('m/d/Y g:i A').'] - '.$this->getPostUri();
        if ($this->use_curl) $r .= " (curl)\n";
        else $r .= " (fsockopen)\n";
        
        // HTTP Response
        for ($i=0; $i<80; $i++) { $r .= '-'; }
        $r .= "\n{$this->getResponse()}\n";
        
        // POST vars
        for ($i=0; $i<80; $i++) { $r .= '-'; }
        $r .= "\n";
        
        foreach ($this->post_data as $key => $value) {
            $r .= str_pad($key, 25)."$value\n";
        }
        $r .= "\n\n";
        
        return $r;
    }
    
    /**
     *  Process IPN
     *
     *  Handles the IPN post back to PayPal and parsing the response. Call this
     *  method from your IPN listener script. Returns true if the response came
     *  back as "VERIFIED", false if the response came back "INVALID", and 
     *  throws an exception if there is an error.
     *
     *  @param array
     *
     *  @return boolean
     */    
    public function processIpn($post_data=null) {

        $encoded_data = 'cmd=_notify-validate';
        
        if ($post_data === null) { 
            // use raw POST data 
            if (!empty($_POST)) {
                $this->post_data = $_POST;
                $encoded_data .= '&'.file_get_contents('php://input');
            } else {
                throw new Exception("No POST data found.");
            }
        } else { 
            // use provided data array
            $this->post_data = $post_data;
            
            foreach ($this->post_data as $key => $value) {
                $encoded_data .= "&$key=".urlencode($value);
            }
        }

        if ($this->use_curl) $this->curlPost($encoded_data); 
        else $this->fsockPost($encoded_data);
        
        if (strpos($this->response_status, '200') === false) {
            throw new Exception("Invalid response status: ".$this->response_status);
        }
        
        if (strpos($this->response, "VERIFIED") !== false) {
            return true;
        } elseif (strpos($this->response, "INVALID") !== false) {
            return false;
        } else {
            throw new Exception("Unexpected response from PayPal.");
        }
    }
    
    /**
     *  Require Post Method
     *
     *  Throws an exception and sets a HTTP 405 response header if the request
     *  method was not POST. 
     */    
    public function requirePostMethod() {
        // require POST requests
        if ($_SERVER['REQUEST_METHOD'] && $_SERVER['REQUEST_METHOD'] != 'POST') {
            header('Allow: POST', true, 405);
            throw new Exception("Invalid HTTP request method.");
        }
    }
}