[php] Get the client IP address using PHP

It also works fine for internal IP addresses:

 function get_client_ip()
 {
      $ipaddress = '';
      if (getenv('HTTP_CLIENT_IP'))
          $ipaddress = getenv('HTTP_CLIENT_IP');
      else if(getenv('HTTP_X_FORWARDED_FOR'))
          $ipaddress = getenv('HTTP_X_FORWARDED_FOR');
      else if(getenv('HTTP_X_FORWARDED'))
          $ipaddress = getenv('HTTP_X_FORWARDED');
      else if(getenv('HTTP_FORWARDED_FOR'))
          $ipaddress = getenv('HTTP_FORWARDED_FOR');
      else if(getenv('HTTP_FORWARDED'))
          $ipaddress = getenv('HTTP_FORWARDED');
      else if(getenv('REMOTE_ADDR'))
          $ipaddress = getenv('REMOTE_ADDR');
      else
          $ipaddress = 'UNKNOWN';

      return $ipaddress;
 }