.. index:: single: Logging
Monolog is a logging library for PHP 5.3 used by Symfony2. It is inspired by the Python LogBook library.
In Monolog each logger defines a logging channel. Each channel has a stack of handlers to write the logs (the handlers can be shared).
Tip
When injecting the logger in a service you can :ref:`use a custom channel<dic_tags-monolog>` to see easily which part of the application logged the message.
The basic handler is the StreamHandler which writes logs in a stream
(by default in the app/logs/prod.log in the prod environment and
app/logs/dev.log in the dev environment).
Monolog comes also with a powerful built-in handler for the logging in
prod environment: FingersCrossedHandler. It allows you to store the
messages in a buffer and to log them only if a message reaches the
action level (ERROR in the configuration provided in the standard
edition) by forwarding the messages to another handler.
To log a message simply get the logger service from the container in your controller:
$logger = $this->get('logger');
$logger->info('We just got the logger');
$logger->err('An error occurred');
Tip
Using only the methods of the :class:`Symfony\\Component\\HttpKernel\\Log\\LoggerInterface` interface allows to change the logger implementation without changing your code.
The logger uses a stack of handlers which are called successively. This allows you to log the messages in several ways easily.
.. configuration-block::
.. code-block:: yaml
monolog:
handlers:
syslog:
type: stream
path: /var/log/symfony.log
level: error
main:
type: fingerscrossed
action_level: warning
handler: file
file:
type: stream
level: debug
.. code-block:: xml
<container xmlns="http://symfony.com/schema/dic/services"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:monolog="http://symfony.com/schema/dic/monolog"
xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd
http://symfony.com/schema/dic/monolog http://symfony.com/schema/dic/monolog/monolog-1.0.xsd">
<monolog:config>
<monolog:handler
name="syslog"
type="stream"
path="/var/log/symfony.log"
level="error"
/>
<monolog:handler
name="main"
type="fingerscrossed"
action-level="warning"
handler="file"
/>
<monolog:handler
name="file"
type="stream"
level="debug"
/>
</monolog:config>
</container>
The above configuration defines a stack of handlers which will be called in the order where they are defined.
Tip
The handler named "file" will not be included in the stack itself as it is used as a nested handler of the fingerscrossed handler.
Note
If you want to change the config of MonologBundle in another config file you need to redefine the whole stack. It cannot be merged because the order matters and a merge does not allow to control the order.
The handler uses a Formatter to format the record before logging
it. All Monolog handlers use an instance of
Monolog\Formatter\LineFormatter by default but you can replace it
easily. Your formatter must implement
Monolog\Formatter\FormatterInterface.
.. configuration-block::
.. code-block:: yaml
services:
my_formatter:
class: Monolog\Formatter\JsonFormatter
monolog:
handlers:
file:
type: stream
level: debug
formatter: my_formatter
.. code-block:: xml
<container xmlns="http://symfony.com/schema/dic/services"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:monolog="http://symfony.com/schema/dic/monolog"
xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd
http://symfony.com/schema/dic/monolog http://symfony.com/schema/dic/monolog/monolog-1.0.xsd">
<services>
<service id="my_formatter" class="Monolog\Formatter\JsonFormatter" />
</services>
<monolog:config>
<monolog:handler
name="file"
type="stream"
level="debug"
formatter="my_formatter"
/>
</monolog:config>
</container>
Monolog allows to process the record before logging it to add some extra data. A processor can be applied for the whole handler stack or only for a specific handler.
A processor is simply a callable receiving the record as it's first argument.
Processors are configured using the monolog.processor DIC tag. See the
:ref:`reference about it<dic_tags-monolog-processor>`.
Sometimes it is hard to tell which entries in the log belong to which session and/or request. The following example will add a unique token for each request using a processor.
namespace Acme\MyBundle;
use Symfony\Component\HttpFoundation\Session;
class SessionRequestProcessor
{
private $session;
private $token;
public function __construct(Session $session)
{
$this->session = $session;
}
public function processRecord(array $record)
{
if (null === $this->token) {
try {
$this->token = substr($this->session->getId(), 0, 8);
} catch (\RuntimeException $e) {
$this->token = '????????';
}
$this->token .= '-' . substr(uniqid(), -8);
}
$record['extra']['token'] = $this->token;
return $record;
}
}.. configuration-block::
.. code-block:: yaml
services:
monolog.formatter.session_request:
class: Monolog\Formatter\LineFormatter
arguments:
- "[%%datetime%%] [%%extra.token%%] %%channel%%.%%level_name%%: %%message%%\n"
monolog.processor.session_request:
class: Acme\MyBundle\SessionRequestProcessor
arguments: [ @session ]
tags:
- { name: monolog.processor, method: processRecord }
monolog:
handlers:
main:
type: stream
path: %kernel.logs_dir%/%kernel.environment%.log
level: debug
formatter: monolog.formatter.session_request
Note
If you use several handlers, you can also register the processor at the handler level instead of globally.