symfony/web-profiler-bundle

The `symfony/web-profiler-bundle` is an essential Symfony bundle designed to provide powerful debugging and performance monitoring tools for Symfony applications during development. It injects a "Web Debug Toolbar" at the bottom of web pages and offers a comprehensive "Profiler" interface.\n\nPurpose and Core Functionality:\nIts primary goal is to help developers understand, debug, and optimize their applications by offering deep insights into every HTTP request. The bundle collects vast amounts of data about the application's state, performance, and behavior during a request, then presents this information in an easily digestible format.\n\nKey Features and Information Panels:\nThe profiler offers a multitude of panels, each dedicated to a specific aspect of the application:\n* Request & Response: Detailed information about HTTP headers, request parameters, session attributes, routing, and response content.\n* Performance: Crucial metrics like execution time, memory usage, CPU time, and a visual timeline of events.\n* Database: For applications using Doctrine, this panel displays all executed database queries (SQL, DQL), their parameters, and execution times, helping identify N+1 problems or slow queries.\n* Logs: Aggregates all log messages (e.g., from Monolog) generated during the request, categorizing them by level (info, debug, warning, error).\n* Security: Provides insights into the authenticated user, assigned roles, security voters, and firewall configuration.\n* Container: Allows inspection of the Dependency Injection container, listing services, parameters, and their definitions.\n* Twig: Details about rendered Twig templates, variables passed to them, and template rendering times.\n* Mailer/Messenger/Cache: Dedicated panels for debugging these specific components, showing dispatched emails, handled messages, or cache hits/misses.\n* Events: Lists all Symfony events dispatched during the request lifecycle.\n\nHow it Works:\n1. Data Collection: During an HTTP request, various "data collectors" (provided by the bundle itself and other Symfony components) gather information about different parts of the application.\n2. Data Storage: This collected data is serialized and stored in a profiler storage (by default, the file system in `var/cache/dev/profiler/` for development environments). Each request's data is uniquely identified by a profiler token.\n3. Web Debug Toolbar: A small, unobtrusive toolbar is injected into the HTML response of non-XHR requests. It provides quick access to key metrics (status code, time, memory, database queries) and a link to the full profiler page for the current request.\n4. Profiler Interface: Clicking on the toolbar's token or navigating to `/_profiler/{token}` opens the full profiler interface, which presents all collected data across various panels.\n\nActivation and Best Practices:\nThe `WebProfilerBundle` is typically installed via Composer and enabled conditionally in `config/bundles.php`, usually only for the `dev` and `test` environments. It is crucial to disable it in production environments due to the potential performance overhead of data collection and storage. Its presence is invaluable for identifying bottlenecks, understanding application flow, debugging errors, and ensuring correct configuration throughout the development process.

// config/bundles.php\n// This is where you enable the bundle. It's crucial for the profiler to work.\n// Note: It's typically enabled only for 'dev' and 'test' environments.\nreturn [\n    // ... other bundles ...\n    Symfony\Bundle\WebProfilerBundle\WebProfilerBundle::class => ['dev' => true, 'test' => true],\n];\n\n// src/Controller/DemoProfilerController.php\n<?php\n\nnamespace App\Controller;\n\nuse Psr\Log\LoggerInterface;\nuse Symfony\Bundle\FrameworkBundle\Controller\AbstractController;\nuse Symfony\Component\HttpFoundation\Response;\nuse Symfony\Component\Routing\Annotation\Route;\nuse App\Repository\ProductRepository; // Assume this exists for demonstration\n\nclass DemoProfilerController extends AbstractController\n{\n    private LoggerInterface $logger;\n    private ProductRepository $productRepository;\n\n    public function __construct(LoggerInterface $logger, ProductRepository $productRepository)\n    {\n        $this->logger = $logger;\n        $this->productRepository = $productRepository;\n    }\n\n    #[Route('/profiler-demo', name: 'app_profiler_demo')]\n    public function index(): Response\n    {\n        $this->logger->info('Accessed profiler demo route.');\n\n        // Simulate a database call that the profiler would show\n        $products = $this->productRepository->findAll();\n\n        $this->logger->debug('Fetched products.', ['count' => count($products)]);\n\n        return $this->render('profiler_demo/index.html.twig', [\n            'controller_name' => 'DemoProfilerController',\n            'product_count' => count($products),\n        ]);\n    }\n}\n\n// src/Repository/ProductRepository.php\n<?php\n\nnamespace App\Repository;\n\n// In a real application, this would interact with a database (e.g., Doctrine).\n// For demonstration, we'll return dummy data.\n\nclass ProductRepository\n{\n    public function findAll(): array\n    {\n        // Simulate a delay and return some dummy data\n        usleep(10000); // Simulate 10ms database query\n        return [\n            ['id' => 1, 'name' => 'Product A', 'price' => 10.00],\n            ['id' => 2, 'name' => 'Product B', 'price' => 20.00],\n            ['id' => 3, 'name' => 'Product C', 'price' => 30.00],\n        ];\n    }\n}\n\n// templates/profiler_demo/index.html.twig\n{# This is a simple Twig template. The Web Debug Toolbar will automatically appear at the bottom. #}\n<!DOCTYPE html>\n<html>\n    <head>\n        <meta charset="UTF-8">\n        <title>Profiler Demo</title>\n        <style>body { font-family: sans-serif; margin: 2em; }</style>\n    </head>\n    <body>\n        <h1>Welcome to the {{ controller_name }}!</h1>\n        <p>This page demonstrates features that the Symfony Web Profiler will capture.</p>\n        <p>We "fetched" {{ product_count }} products.</p>\n        <p>Check the Web Debug Toolbar at the bottom of this page for details on request, logs, and "database" queries.</p>\n    </body>\n</html>