PSR-Logger Interface in PHP

Ahnii!

Recently, I assisted a team migrating from Monolog to a custom logging solution. Their logging wasn't standardized, requiring code changes across numerous files. This highlights the value of PSR-3, a solution I'll demonstrate here.

Understanding PSR-3 (5 minutes)

PSR-3 acts as a logging contract in PHP. Similar to how a standardized car design ensures ease of operation across different models, PSR-3 provides consistent logging library behavior.

1. The Logger Interface

This contract defines the interface:

<?php namespace Psr\Log;

interface LoggerInterface
{
    public function emergency($message, array $context = array());
    public function alert($message, array $context = array());
    public function critical($message, array $context = array());
    public function error($message, array $context = array());
    public function warning($message, array $context = array());
    public function notice($message, array $context = array());
    public function info($message, array $context = array());
    public function debug($message, array $context = array());
    public function log($level, $message, array $context = array());
}

?>

2. Log Levels (3 minutes)

These levels represent a severity scale:

1. Emergency: ? Catastrophic failure (system unusable).
2. Alert: ? Requires immediate action.
3. Critical: ⚠️ Major component failure.
4. Error: ❌ Failure, but system operational.
5. Warning: ⚡ Potential problem.
6. Notice: ? Normal but significant event.
7. Info: ℹ️ Informational message.
8. Debug: ? Debugging information.

Real-World Implementation (10 minutes)

Let's create a logger writing to files and sending critical errors to Slack:

<?php namespace App\Logging;

use Psr\Log\AbstractLogger;
use Psr\Log\LogLevel;

class SmartLogger extends AbstractLogger
{
    private $logFile;
    private $slackWebhook;

    public function __construct(string $logFile, string $slackWebhook)
    {
        $this->logFile = $logFile;
        $this->slackWebhook = $slackWebhook;
    }

    public function log($level, $message, array $context = array())
    {
        $timestamp = date('Y-m-d H:i:s');
        $message = $this->interpolate($message, $context);
        $logLine = "[$timestamp] [$level] $message" . PHP_EOL;

        file_put_contents($this->logFile, $logLine, FILE_APPEND);

        if (in_array($level, [LogLevel::CRITICAL, LogLevel::EMERGENCY])) {
            $this->notifySlack($level, $message);
        }
    }

    private function notifySlack($level, $message)
    {
        $emoji = $level === LogLevel::EMERGENCY ? '?' : '⚠️';
        $payload = json_encode([
            'text' => "$emoji *$level*: $message"
        ]);

        $ch = curl_init($this->slackWebhook);
        curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'POST');
        curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_exec($ch);
        curl_close($ch);
    }

    private function interpolate($message, array $context = array())
    {
        $replace = array();
        foreach ($context as $key => $val) {
            $replace['{' . $key . '}'] = $val;
        }
        return strtr($message, $replace);
    }
}

Using It In Your Project (5 minutes)

Example usage:

$logger = new SmartLogger(
    '/var/log/app.log',
    'https://hooks.slack.com/services/YOUR/WEBHOOK/HERE'
);

$logger->info('User {user} logged in from {ip}', [
    'user' => 'jonesrussell',
    'ip' => '192.168.1.1'
]);

$logger->critical('Payment gateway {gateway} is down!', [
    'gateway' => 'Stripe',
    'error_code' => 500
]);

Framework Integration (5 minutes)

Laravel and Symfony provide built-in PSR-3 support.

Laravel:

public function processOrder($orderId)
{
    try {
        Log::info('Order processed', ['order_id' => $orderId]);
    } catch (\Exception $e) {
        Log::error('Order failed', [
            'order_id' => $orderId,
            'error' => $e->getMessage()
        ]);
        throw $e;
    }
}

Symfony:

class OrderController extends AbstractController
{
    public function process(LoggerInterface $logger, string $orderId)
    {
        $logger->info('Starting order process', ['order_id' => $orderId]);
        // Your code here
    }
}

Quick Tips (2 minutes)

1. ? Be Specific: Include detailed context in logs.
2. ? Use the Right Level: Avoid overuse of high-severity levels.

Next Steps & Resources

This post is part of a series on PSR standards in PHP. Future topics include PSR-4.

Resources:

• Official PSR-3 Specification
• Monolog Documentation
• Series Example Repository (v0.2.0 - PSR-3 Implementation)

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