eZ components - EventLog
~~~~~~~~~~~~~~~~~~~~~~~~

.. contents:: Table of Contents

Introduction
============

The EventLog component provides an API to log events and audit trails. These
events and audit trails are written to files or other storage spaces in
various formats. How and where the log messages (events and audit trails) are
written depends on the chosen or customized log writer.

The available log writers are:

- ezcLogUnixFileWriter, which writes log messages to a file in an 'Unix' file
  format.
- ezcLogDatabaseWriter, which writes log messages to the database. Available
  in the EventLogDatabaseTieIn_ component.

Each of these writers can be customized or extended.

An incoming log message can be written to zero or more writers. The writers
that write the log message depends on the variables of the log message itself and the
ezcLogMapper implementation. An implementation of the ezcLogMapper checks the
severity, source, and category from the log message and forwards the message
to the matching writers.


Class overview
==============

The following classes are most important to use, customize, or extend:

ezcLog
  The ezcLog is a singleton, meaning that only one instance to the log can
  exist. This class provides methods to configure and record log messages. The
  recorded log messages are sent to an implementation of the ezcLogMapper,
  deciding which writers should write the log message.

ezcLogMapper
  The ezcLogMapper provides an interface for the log message mapping. Log
  messages are dispatched from the ezcLog to a writer. To which writer a
  message is dispatched is determined in the class that implements
  ezclogMapper and is assigned in the ezcLog.

ezcLogFilterSet
  The ezcLogFilterSet is an implementation of the ezcLogMapper. The
  ezcLogFilterSet contains a set of ezcLogFilterRules. These rules are
  processed sequentially. The rule assigned first will be processed first.
  Each rule determines whether the log message matches with the filter rule. If the
  log message matches, it calls the writer and decide whether the filter set
  stops processing.

  The ezcLogFilterSet is inspired by modern mail applications regarding the
  mail filter settings. Normally these mail filter settings sort the incoming
  mail and stores it in the correct mail folder.

ezcLogWriter
  The ezcLogWriter provides an interface for the writers. An implementation
  of this interface is a valid writer, and can be addressed by the ezcLogMapper.
  The writer itself can determine how and where the log message is stored.

ezcLogUnixFileWriter
  The ezcLogUnixFileWriter writes the log message to a file.

ezcLogFilter
  The ezcLogFilter is a structure to specify which log messages are accepted in
  a filter set.

For more information about these classes, see the class documentation.


Examples
========

Writing a log message to a file
-------------------------------

This example creates a file writer, and assigns it to the default log mapper.

.. include:: tutorial_simple_file_writer.php
   :literal:

First the tutorial_autoload.php is included. The included file loads the
correct php files for the EventLog component.

Hereafter the log is set up, and a message is written to the log file
"default.log" and the file will be placed in the "/tmp/logs" directory.

After execution, the file "/tmp/logs/default.log" contains something like::

    Jan 24 14:39:57 [Warning] [default] [default] Could not connect with the payment server.

Respectively the date, severity, source, category, and message are shown. The
source and category are both set to default, because they were not specified in
the message.


Assigning sources and categories
--------------------------------

The default source and category from the ezcLog can be set via the properties
"source" and "category". The next example demonstrates how the default
properties can be set and how extra variables can be added to the log.

.. include:: tutorial_sources_categories.php
   :literal:

After execution, the file "/tmp/logs/default.log" contains something like::

    Jan 24 15:45:04 [Warning] [Payment module] [Template] Could not find cache file: </var/cache/payment1234.cache>.
    Jan 24 15:45:04 [Error] [Payment module] [SQL] Cannot execute query: <SELECT * FROM Orders WHERE ID = '123'>.
    Jan 24 15:45:04 [Debug] [Payment module] Starting shutdown process. (file: /home/rb/php5/ezcomponents/packages/EventLog/trunk/docs/tutorial_sources_categories.php, line: 25)


Adding log attributes automatically
-----------------------------------

In some cases it is convenient to add automatically log attributes to the log
message. For example:

- Audit trails should include the current user.
- A payment system should always include the order number.

However, the log attributes appended to the log message are static. The
value assigned to the attribute will be the same.

The next example assigns two automatic attributes:

.. include:: tutorial_auto_variables.php
   :literal:

After execution, the file "/tmp/logs/default.log" contains::

    Jan 25 10:15:19 [Failed audit] [security] [login/logoff] Authentication failed (username: John Doe)
    Jan 25 10:15:19 [Debug] [Payment] [external connections] Connecting with the server. (service: Paynet Terminal)
    Jan 25 10:15:19 [Success audit] [Payment] [shop] Payed with creditcard. (username: John Doe, service: Paynet Terminal)


Assigning log messages to different files
-----------------------------------------

Depending on the incoming log message, the message can be stored on different
writers. This example handles the log message as follows:

- Ignore all message with the severity DEBUG.
- Store the audit trails in the "audit_trails.log" file.
- Store the logs with the Payment category in the "payment.log" file.
- Store all the messages, except DEBUG, in the "general.log" file.

The code is as follows:

.. include:: tutorial_multiple_log_files.php
   :literal:


Using trigger_error()
---------------------

The EventLog component is designed that it can be used with trigger_error_ or
stand-alone. Instead of calling the ezcLog::getInstance()->log() method, the
trigger_error() can be called.  Using the trigger_error() method makes your code
less Log package dependent and produces less overhead when logging is disabled.

The function set_error_handler_ should set up a callback function (or method)
that in its turn calls the EventLog. See for more information the
ezcLog::logHandler() method.

.. _trigger_error: http://www.php.net/trigger_error
.. _set_error_handler: http://www.php.net/set_error_handler
.. _EventLogDatabaseTieIn: http://ez.no/doc/components/view/trunk/(file)/introduction_EventLogDatabaseTiein.html



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