How to Add extra Data to Log Messages via a Processor

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How to Add extra Data to Log Messages via a Processor

Monolog allows you to process every record before logging it by adding some extra data. This is the role of a processor, which can be applied for the whole handler stack or only for a specific handler or channel.

A processor is a callable receiving the record as its first argument. Processors are configured using the monolog.processor DIC tag. See the reference about it.

Adding a Session/Request Token

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:

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        // src/Logger/SessionRequestProcessor.php
namespace App\Logger;

use Monolog\LogRecord;
use Symfony\Component\HttpFoundation\Exception\SessionNotFoundException;
use Symfony\Component\HttpFoundation\RequestStack;

class SessionRequestProcessor
{
    public function __construct(
        private RequestStack $requestStack
    ) {
    }

    // this method is called for each log record; optimize it to not hurt performance
    public function __invoke(LogRecord $record): LogRecord
    {
        try {
            $session = $this->requestStack->getSession();
        } catch (SessionNotFoundException $e) {
            return;
        }
        if (!$session->isStarted()) {
            return $record;
        }

        $sessionId = substr($session->getId(), 0, 8) ?: '????????';

        $record->extra['token'] = $sessionId.'-'.substr(uniqid('', true), -8);

        return $record;
    }
}
    

Next, register your class as a service, as well as a formatter that uses the extra information:

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        # config/services.yaml
services:
    monolog.formatter.session_request:
        class: Monolog\Formatter\LineFormatter
        arguments:
            - "[%%datetime%%] [%%extra.token%%] %%channel%%.%%level_name%%: %%message%% %%context%% %%extra%%\n"

    App\Logger\SessionRequestProcessor:
        tags:
            - { name: monolog.processor }
    

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        <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<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
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/monolog
        https://symfony.com/schema/dic/monolog/monolog-1.0.xsd">

    <services>
        <service id="monolog.formatter.session_request"
            class="Monolog\Formatter\LineFormatter">

            <argument>[%%datetime%%] [%%extra.token%%] %%channel%%.%%level_name%%: %%message%% %%context%% %%extra%%&#xA;</argument>
        </service>

        <service id="App\Logger\SessionRequestProcessor">
            <tag name="monolog.processor"/>
        </service>
    </services>
</container>
    

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        // config/services.php
use App\Logger\SessionRequestProcessor;
use Monolog\Formatter\LineFormatter;

$container
    ->register('monolog.formatter.session_request', LineFormatter::class)
    ->addArgument('[%%datetime%%] [%%extra.token%%] %%channel%%.%%level_name%%: %%message%% %%context%% %%extra%%\n');

$container
    ->register(SessionRequestProcessor::class)
    ->addTag('monolog.processor');
    

Finally, set the formatter to be used on whatever handler you want:

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        # config/packages/prod/monolog.yaml
monolog:
    handlers:
        main:
            type: stream
            path: '%kernel.logs_dir%/%kernel.environment%.log'
            level: debug
            formatter: monolog.formatter.session_request
    

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        <!-- config/packages/prod/monolog.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<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
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/monolog
        https://symfony.com/schema/dic/monolog/monolog-1.0.xsd">

    <monolog:config>
        <monolog:handler
            name="main"
            type="stream"
            path="%kernel.logs_dir%/%kernel.environment%.log"
            level="debug"
            formatter="monolog.formatter.session_request"
        />
    </monolog:config>
</container>
    

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        // config/packages/prod/monolog.php
use Symfony\Config\MonologConfig;

return static function (MonologConfig $monolog) {
    $monolog->handler('main')
        ->type('stream')
        ->path('%kernel.logs_dir%/%kernel.environment%.log')
        ->level('debug')
        ->formatter('monolog.formatter.session_request')
    ;
};
    

If you use several handlers, you can also register a processor at the handler level or at the channel level instead of registering it globally (see the following sections).

When registering a new processor, instead of adding the tag manually in your configuration files, you can use the #[AsMonologProcessor] attribute to apply it on the processor class:

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        // src/Logger/SessionRequestProcessor.php
namespace App\Logger;

use Monolog\Attribute\AsMonologProcessor;

#[AsMonologProcessor]
class SessionRequestProcessor
{
    // ...
}
    

The #[AsMonologProcessor] attribute takes these optional arguments:

channel: the logging channel the processor should be pushed to;
handler: the handler the processor should be pushed to;
method: the method that processes the records (useful when applying the attribute to the entire class instead of a single method).

3.8

The #[AsMonologProcessor] attribute was introduced in MonologBundle 3.8.

Symfony's MonologBridge provides processors that can be registered inside your application.

DebugProcessor: Adds additional information useful for debugging like a timestamp or an error message to the record.
TokenProcessor: Adds information from the current user's token to the record namely username, roles and whether the user is authenticated.
SwitchUserTokenProcessor: Adds information about the user who is impersonating the logged in user, namely username, roles and whether the user is authenticated.
WebProcessor: Overrides data from the request using the data inside Symfony's request object.
RouteProcessor: Adds information about current route (controller, action, route parameters).
ConsoleCommandProcessor: Adds information about the current console command.

Registering Processors per Handler

You can register a processor per handler using the handler option of the monolog.processor tag:

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        # config/services.yaml
services:
    App\Logger\SessionRequestProcessor:
        tags:
            - { name: monolog.processor, handler: main }
    

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        <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<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
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/monolog
        https://symfony.com/schema/dic/monolog/monolog-1.0.xsd">

    <services>
        <service id="App\Logger\SessionRequestProcessor">
            <tag name="monolog.processor" handler="main"/>
        </service>
    </services>
</container>
    

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        // config/services.php

// ...
$container
    ->register(SessionRequestProcessor::class)
    ->addTag('monolog.processor', ['handler' => 'main']);
    

Registering Processors per Channel

You can register a processor per channel using the channel option of the monolog.processor tag:

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        # config/services.yaml
services:
    App\Logger\SessionRequestProcessor:
        tags:
            - { name: monolog.processor, channel: main }
    

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        <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<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
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/monolog
        https://symfony.com/schema/dic/monolog/monolog-1.0.xsd">

    <services>
        <service id="App\Logger\SessionRequestProcessor">
            <tag name="monolog.processor" channel="main"/>
        </service>
    </services>
</container>
    

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        // config/services.php

// ...
$container
    ->register(SessionRequestProcessor::class)
    ->addTag('monolog.processor', ['channel' => 'main']);
    

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.

How to Add extra Data to Log Messages via a Processor

How to Add extra Data to Log Messages via a Processor

Adding a Session/Request Token

Registering Processors per Handler

Registering Processors per Channel

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