PHP Paypal IPN Integration Class not logging IPN results

I'm using开发者_JS百科 Micah Carrick's PHP Paypal IPN Integration Class and have code in paypal.class.php as:

   function __construct() {
      // initialization constructor.  Called when class is created.
      $this->paypal_url = 'https://www.paypal.com/cgi-bin/webscr';
      $this->last_error = '';
      $this->ipn_log_file = '.ipn_results.log';
      $this->ipn_log = true; 
      $this->ipn_response = '';

However, this file is not being created. Do I need to do something special to get it to work?

If I need to set permissions, do I set permissions on this or the calling php script (which includes the above file)?

Note that the dot in .ipn_results.log will hide the file on Unix/Linux systems. You probably mean

$this->ipn_log_file = './ipn_results.log';

but it is preferable to specify a full path here to avoid confusion.