The Log Package

1.1   Creating a Log Object

There are three ways to create Log objects:

• Using the Log::factory() method
• Using the Log::singleton() method
• Direct instantiation

require_once 'Log.php';

$console = Log::factory('console', '', 'TEST');
$console->log('Logging to the console.');

$file = Log::factory('file', 'out.log', 'TEST');
$file->log('Logging to out.log.');

require_once 'Log.php';

/* Same construction parameters */
$a = Log::singleton('console', '', 'TEST');
$b = Log::singleton('console', '', 'TEST');

if ($a === $b) {
    echo '$a and $b point to the same Log instance.' . "\n";
}

/* Different construction parameters */
$c = Log::singleton('console', '', 'TEST1');
$d = Log::singleton('console', '', 'TEST2');

if ($c !== $d) {
    echo '$c and $d point to different Log instances.' . "\n";
}

1.2   Configuring a Handler

A log handler's configuration is determined by the arguments used in its construction. Here's an overview of those parameters:

/* Using the factory method ... */
Log::factory($handler, $name, $ident, $conf, $maxLevel);

/* Using the singleton method ... */
Log::singleton($handler, $name, $ident, $conf, $maxLevel);

/* Using direct instantiation ... */
new Log_handler($name, $ident, $conf, $maxLevel);

1.3   Logging an Event

Events are logged using the log() method:

$logger->log('Message', PEAR_LOG_NOTICE);

The first argument contains the log event's message. Even though the event is always logged as a string, it is possible to pass an object to the log() method. If the object implements a getString() method, a toString() method or Zend Engine 2's special __toString() casting method, it will be used to determine the object's string representation. Otherwise, the serialized form of the object will be logged.

The second, optional argument specifies the log event's priority. See the Log Levels table for the complete list of priorities. The default priority is PEAR_LOG_INFO.

The log() method will return true if the event was successfully logged.

"Shortcut" methods are also available for logging an event at a specific log level. See the Log Levels table for the complete list.

1.4   Log Levels

This table is ordered by highest priority (PEAR_LOG_EMERG) to lowest priority (PEAR_LOG_DEBUG).

1.5   Log Level Masks

Defining a log level mask allows you to include and/or exclude specific levels of events from being logged. The $level construction parameter (see Configuring a Handler) uses this mechanism to exclude log events below a certain priority, and it's possible to define more complex masks once the Log object has been constructed.

Each priority has a specific mask associated with it. To compute a priority's mask, use the static Log::MASK() method:

$mask = Log::MASK(PEAR_LOG_INFO);

To compute the mask for all priorities up to, and including, a certain level, use the Log::MAX() static method:

$mask = Log::MAX(PEAR_LOG_INFO);

To compute the mask for all priorities greater than or equal to a certain level, use the Log::MIN() static method:

$mask = Log::MIN(PEAR_LOG_INFO);

The apply the mask, use the setMask() method:

$logger->setMask($mask);

Masks can be be combined using bitwise operations. To restrict logging to only those events marked as PEAR_LOG_NOTICE or PEAR_LOG_DEBUG:

$mask = Log::MASK(PEAR_LOG_NOTICE) | Log::MASK(PEAR_LOG_DEBUG);
$logger->setMask($mask);

For convenience, two special masks are predefined: PEAR_LOG_NONE and PEAR_LOG_ALL. PEAR_LOG_ALL is especially useful for excluding only specific priorities:

$mask = PEAR_LOG_ALL ^ Log::MASK(PEAR_LOG_NOTICE);
$logger->setMask($mask);

It is also possible to retrieve and modify a Log object's existing mask:

$mask = $logger->getMask() | Log::MASK(PEAR_LOG_INFO);
$logger->setMask($mask);

1.6   Log Line Format

Most log handlers support configurable line formats. The following is a list of special tokens that will be expanded at runtime with contextual information related to the log event. Each token has an alternate shorthand notation, as well.

1.7   Flushing Log Events

Some log handlers (such as the console handler) support explicit "buffering". When buffering is enabled, log events won't actually be written to the output stream until the handler is closed. Other handlers (such as the file handler) support implicit buffering because they use the operating system's IO routines, which may buffer the output.

It's possible to force these handlers to flush their output, however, by calling their flush() method:

$conf = ['buffering' => true];
$logger = Log::singleton('console', '', 'test', $conf);

for ($i = 0; $i < 10; $i++) {
    $logger->log('This event will be buffered.');
}

/* Flush all of the buffered log events. */
$logger->flush();

for ($i = 0; $i < 10; $i++) {
    $logger->log('This event will be buffered.');
}

/* Implicitly flush the buffered events on close. */
$logger->close();

At this time, the flush() method is only implemented by the console handler, the file handler, the Firebug handler, and the mail handler.

2.1   The Console Handler

The Console handler outputs log events directly to the console. It supports output buffering and configurable string formats.

$logger = Log::singleton('console', '', 'ident');
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

2.2   The Display Handler

The Display handler simply prints the log events back to the browser. It respects the error_prepend_string and error_append_string error handling values and is useful when logging from standard error handlers.

$conf = ['error_prepend' => '<font color="#ff0000"><tt>',
              'error_append'  => '</tt></font>'];
$logger = Log::singleton('display', '', '', $conf, PEAR_LOG_DEBUG);
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

2.3   The Error_Log Handler

The Error_Log handler sends log events to PHP's error_log() function.

$logger = Log::singleton('error_log', PEAR_LOG_TYPE_SYSTEM, 'ident');
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

2.4   The File Handler

The File handler writes log events to a text file using configurable string formats.

$conf = ['mode' => 0600, 'timeFormat' => '%X %x'];
$logger = Log::singleton('file', 'out.log', 'ident', $conf);
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

2.5   The Firebug Handler

The Firebug handler outputs log events to the Firebug console. It supports output buffering and configurable string formats.

$logger = Log::singleton('firebug', '', 'ident');
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

2.6   The Mail Handler

The Mail handler aggregates a session's log events and sends them in the body of an email message using either the PEAR Mail package or PHP's native mail() function.

If an empty mailBackend value is specified, the mail() function will be used instead of the PEAR Mail package.

Multiple recipients can be specified by separating their email addresses with commas in the $name construction parameter.

$conf = ['subject' => 'Important Log Events'];
$logger = Log::singleton('mail', 'webmaster@example.com', 'ident', $conf);
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

2.7   The MDB2 Handler

The MDB2 handler is similar to the SQL (DB) handler, but instead of using the PEAR DB package, it uses the MDB2 database abstraction package.

2.8   The Null Handler

The Null handler simply consumes log events (akin to sending them to /dev/null). Log level masks are respected, and the event will still be sent to any registered log observers.

$logger = Log::singleton('null');
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

2.9   The SQL (DB) Handler

The SQL handler sends log events to a database using PEAR's DB abstraction layer.

Note: Due to the constraints of the default database schema, the SQL handler limits the length of the $ident string to sixteen (16) characters. This limit can be adjusted using the identLimit configuration parameter.

CREATE TABLE log_table (
    id          INT NOT NULL,
    logtime     TIMESTAMP NOT NULL,
    ident       CHAR(16) NOT NULL,
    priority    INT NOT NULL,
    message     VARCHAR(200),
    PRIMARY KEY (id)
);

$conf = ['dsn' => 'pgsql://jon@localhost+unix/logs'];
$logger = Log::singleton('sql', 'log_table', 'ident', $conf);
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

require_once 'DB.php';
$db = &DB::connect('pgsql://jon@localhost+unix/logs');

$conf['db'] = $db;
$logger = Log::singleton('sql', 'log_table', 'ident', $conf);
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

2.10   The Sqlite Handler

The Sqlite handler sends log events to an Sqlite database using the native PHP sqlite functions.

It is faster than the SQL (DB) handler because requests are made directly to the database without using an abstraction layer. It is also interesting to note that Sqlite database files can be moved, copied, and deleted on your system just like any other files, which makes log management easier. Last but not least, using a database to log your events allows you to use SQL queries to create reports and statistics.

When using a database and logging a lot of events, it is recommended to split the database into smaller databases. This is allowed by Sqlite, and you can later use the Sqlite ATTACH statement to query your log database files globally.

If the database does not exist when the log is opened, sqlite will try to create it automatically. If the log table does not exist, it will also be automatically created. The table creation uses the following SQL request:

CREATE TABLE log_table (
    id          INTEGER PRIMARY KEY NOT NULL,
    logtime     NOT NULL,
    ident       CHAR(16) NOT NULL,
    priority    INT NOT NULL,
    message
);

$conf = ['filename' => 'log.db', 'mode' => 0666, 'persistent' => true];
$logger = Log::factory('sqlite', 'log_table', 'ident', $conf);
$logger->log('logging an event', PEAR_LOG_WARNING);

$db = sqlite_open('log.db', 0666, $error);
$logger = Log::factory('sqlite', 'log_table', 'ident', $db);
$logger->log('logging an event', PEAR_LOG_WARNING);
sqlite_close($db);

2.11   The Syslog Handler

The Syslog handler sends log events to the system logging service (syslog on Unix-like environments or the Event Log on Windows systems). The events are sent using PHP's syslog() function.

$logger = Log::singleton('syslog', LOG_LOCAL0, 'ident');
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

2.12   The Window Handler

The Window handler sends log events to a separate browser window. The original idea for this handler was inspired by Craig Davis' Zend.com article entitled "JavaScript Power PHP Debugging".

$conf = ['title' => 'Sample Log Output'];
$logger = Log::singleton('win', 'LogWindow', 'ident', $conf);
for ($i = 0; $i < 10; $i++) {
    $logger->log("Log entry $i");
}

5.1   Logging PHP Errors

PHP's default error handler can be overridden using the set_error_handler() function. The custom error handling function can use a global Log instance to log the PHP errors.

Note: Fatal PHP errors cannot be handled by a custom error handler at this time.

function errorHandler($code, $message, $file, $line)
{
    global $logger;

    /* Map the PHP error to a Log priority. */
    switch ($code) {
    case E_WARNING:
    case E_USER_WARNING:
        $priority = PEAR_LOG_WARNING;
        break;
    case E_NOTICE:
    case E_USER_NOTICE:
        $priority = PEAR_LOG_NOTICE;
        break;
    case E_ERROR:
    case E_USER_ERROR:
        $priority = PEAR_LOG_ERR;
        break;
    default:
        $priority = PEAR_LOG_INFO;
    }

    $logger->log($message . ' in ' . $file . ' at line ' . $line,
                 $priority);
}

set_error_handler('errorHandler');
trigger_error('This is an information log message.', E_USER_NOTICE);

5.2   Logging PHP Assertions

PHP allows user-defined assert() callback handlers. The assertion callback is configured using the assert_options() function.

function assertCallback($file, $line, $message)
{
    global $logger;

    $logger->log($message . ' in ' . $file . ' at line ' . $line,
                 PEAR_LOG_ALERT);
}

assert_options(ASSERT_CALLBACK, 'assertCallback');
assert(false);

5.3   Logging PHP Exceptions

PHP 5 and later support the concept of exceptions. A custom exception handler can be assigned using the set_exception_handler() function.

function exceptionHandler($exception)
{
    global $logger;

    $logger->log($exception->getMessage(), PEAR_LOG_ALERT);
}

set_exception_handler('exceptionHandler');
throw new Exception('Uncaught Exception');

5.4   Logging PEAR Errors

The Log package can be used with PEAR::setErrorHandling()'s PEAR_ERROR_CALLBACK mechanism by writing an error handling function that uses a global Log instance. Here's an example:

function errorHandler($error)
{
    global $logger;

    $message = $error->getMessage();

    if (!empty($error->backtrace[1]['file'])) {
        $message .= ' (' . $error->backtrace[1]['file'];
        if (!empty($error->backtrace[1]['line'])) {
            $message .= ' at line ' . $error->backtrace[1]['line'];
        }
        $message .= ')';
    }

    $logger->log($message, $error->code);
}

PEAR::setErrorHandling(PEAR_ERROR_CALLBACK, 'errorHandler');
PEAR::raiseError('This is an information log message.', PEAR_LOG_INFO);

6.1   Using a Custom Handler

Using a custom Log handler is very simple. Once written (see Writing New Handlers and Extending Existing Handlers below), you have the choice of placing the file in your PEAR installation's main Log/ directory (usually something like /usr/local/lib/php/Log or C:\php\pear\Log), where it can be found and use by any PHP application on the system, or placing the file somewhere in your application's local hierarchy and including it before the the custom Log object is constructed.

require_once 'Log.php';

$logger = Log::factory('custom', '', 'CUSTOM');

require_once 'Log.php';
require_once 'LocalHandlers/custom.php';

$logger = Log::factory('custom', '', 'CUSTOM');

6.2   Writing New Handlers

Writing a new Log handler is as simple as authoring a new class that extends the Log class and that implements a relatively small set of standard methods.

Every handler's class name must start with Log_ in order for it to be recognized by the Log package.

class Log_custom extends Log

The handler's constructor will be called with four parameters. These values are discussed in detail in the Configuring a Handler section.

Log_custom($name, $ident = '', $conf = [], $level = PEAR_LOG_DEBUG)

The constructor is responsible for configuring the handler based on these values. Handler-specific parameters are passed as part of the $conf array. At a minimum, the handler's constructor must set the following values defined by the Log base class:

$this->id = md5(microtime().rand());
$this->name = $name;
$this->ident = $ident;
$this->mask = Log::MAX($level);

The Handler Methods section below details the various standard methods that can be implemented by a log handler. The Utility Methods section describes some useful utility methods provided by the Log base class which may be useful when implementing a log handler.

6.3   Extending Existing Handlers

Extending existing handlers is very similar to writing new handlers with the exception that, instead of inheriting from the Log base class directly, the handler extends an existing handler's class. This is a useful way of adding some custom behavior to an existing handler without writing an entirely new class (in the spirit of object-oriented programming).

For example, the mail handler could be extended to support sending messages with MIME-encoded attachments simply by authoring a new Log_mail_mime class with a compliant constructor and a custom log() method. The rest of the standard methods would fall back on the Log_mail base class's implementations.

Obviously, the specific details involved in extending an existing handler require a good working understanding of that handler's implementation.

6.4   Handler Methods

6.5   Utility Methods

These utility methods are provided by the Log base class and provide common, useful functionality to handler implementations.

['priority' => $priority, 'message' => $message]