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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 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 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:

namespace App\Logger;

use Symfony\Component\HttpFoundation\Session\SessionInterface;

class SessionRequestProcessor
{
    private $session;
    private $sessionId;

    public function __construct(SessionInterface $session)
    {
        $this->session = $session;
    }

    public function __invoke(array $record)
    {
        if (!$this->session->isStarted()) {
            return $record;
        }

        if (!$this->sessionId) {
            $this->sessionId = substr($this->session->getId(), 0, 8) ?: '????????';
        }

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

        return $record;
    }
}

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

YAML

# 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 }

XML

<!-- 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
        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="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>

PHP

// 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', ['method' => 'processRecord']);

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

YAML

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

XML

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

PHP

// config/packages/prod/monolog.php
$container->loadFromExtension('monolog', [
    'handlers' => [
        '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).

Registering Processors per Handler¶

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

YAML

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

XML

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

PHP

// 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:

YAML

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

XML

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

PHP

// 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.