Developing a simple Zend_Log_Filter

In the new Zend_Log component of the Zend Framework Beta 0.9.2 release there are currently two log Filter available. The Zend_Log_Filter_Priority object can be used to filter out log Events having a log Priority greater than a specified log Priority value. The other Filter named Zend_Log_Filter_Message might be used to filter out specific log messages matching a Regular expression. The realization of a own Filter can be achieved quick and easy by implementing the Zend_Log_Filter_Interface interface.

The following code snippet shows a custom Filter for filtering out log Events lower to a specific log Priority value. This emerged from an use case that in an audit log the basic log Priorities are not required and shouldn't be allowed due to possible developer mistakes. The custom Filter has to be located in the applications custom library directory i.e. recordshelf/libary/Recordshelf/Log/Filter/Priority.

<?php   

require_once 'Zend/Log/Filter/Interface.php';

class Recordshelf_Log_Filter_Priority_Minimum implements Zend_Log_Filter_Interface
{
    /**
     * @var integer
     */
    protected $_priority;

    /**
     * Filter out any log messages lower than $priority.
     *
     * @param  integer  $priority  Minimum priority to pass through the filter
     * @throws Zend_Log_Exception
     */
    public function __construct($priority)
    {
        if (! is_integer($priority)) {
            throw new Zend_Log_Exception('Priority must be an integer');
        }
        
        $this->_priority = $priority;
    } 

    /**
     * Returns TRUE to accept the message, FALSE to block it.
     *
     * @param  array    $event    event data
     * @return boolean            accepted?
     */
    public function accept($event)
    {
        return $event['priority'] >= $this->_priority;
    }
   
}

I admit this isn't quite a hard one, but it shows the stepz needed to implement a custom filter. As you can the see the minimum conditional for the filter is set via the constructor and is validated through the accept method.

The next code snippet shows how the filter is added to the audit logger and configured to only let pass log Events beyond the log Priority audit. Currently there is no method like getPriorityNumber('audit') in Zend_Log available to retrieve the Priority number of a custom log Priority.

<?php 

  $auditWriter = new Zend_Log_Writer_Stream('/path/to/auditfile');

  /* Use a customized Formatting and add custom log Events */
  $formatter = new Zend_Log_Formatter_Xml('audit', array('msg' => 'message', 
                                                         'level' => 'priorityName',
                                                         'ip-visitor' => 'visitorIp',
                                                         'host-visitor' => 'visitorHost'));
  $auditWriter->setFormatter($formatter); 
  $auditLogger = new Zend_Log($auditWriter);

  /* Add a custom log Priority to the audit logger */
  $auditLogger->addPriority('audit', 8); 

  /* Add some custom log Events to the audit logger */
  $auditLogger->setEventItem('visitorIp', $_SERVER['REMOTE_ADDR']);
  $auditLogger->setEventItem('visitorHost', $_SERVER['REMOTE_HOST']);

  /* Add the custom Filter for all following log Events */
  $filter = new Recordshelf_Log_Filter_Priority_Minimum(8);
  $auditLogger->addFilter($filter);

  /* Gets blocked by filter */
  $auditLogger->info('Informational message');

  /* Passes filter and gets logged */
  $auditLogger->audit('Auditional message');

?>