Getting Started

Minimal Steps

Installation:

composer require cethyworks/content-injector-bundle

new Cethyworks\ContentInjectorBundle\CethyworksContentInjectorBundle(),

First Injection: Inject a simple string into all responses:

$subscriber = $container->get('cethyworks_content_injector.subscriber');
$subscriber->registerCommand(function() { return '<script>console.log("Hello!");</script>'; });

Verify: Check the rendered page source to confirm the injected content appears.

First Use Case

Inject a footer script dynamically:

$subscriber->registerCommand(function() {
    return '<script src="/dynamic-footer.js?v=' . time() . '"></script>';
});

Trigger: Visit any route—script appears in the response.

Implementation Patterns

Core Workflow

Register Commands:

Simple Strings: Use registerCommand(callable) for static content.

Dynamic Logic: Pass a closure with access to the Request or Response via dependency injection.

$subscriber->registerCommand(function($request) {
    return $request->get('debug') ? '<!-- DEBUG MODE -->' : '';
});

Twig Templates: Use TwigCommandHandler for dynamic templates.

$handler = $container->get('cethyworks_content_injector.twig_command_handler');
$handler->registerCommand('@App/Resources/views/inject/footer.html.twig', ['user' => $user]);

Form Integration: Extend FormType to inject form-specific content:

$builder->add('field', TextType::class, [
    'injector' => [
        'command' => function($formView) {
            return '<div class="form-hint">' . $formView->children['field']->vars['label'] . '</div>';
        }
    ]
]);

Conditional Injection: Filter commands by route, HTTP method, or user role:

$subscriber->registerCommand(function($request) {
    return $request->get('_route') === 'dashboard' ? '<div class="dashboard-only">...</div>' : '';
});

Integration Tips

Symfony Events: Hook into kernel.response to inspect/modify injected content:

$dispatcher->addListener('kernel.response', function($event) {
    $response = $event->getResponse();
    if ($response->headers->contains('X-Injected')) {
        // Custom logic for injected responses
    }
});

Asset Management: Combine with AssetMapper for versioned injected assets:

$subscriber->registerCommand(function() {
    return $this->get('asset_mapper')->getUrl('js/injector.js');
});

Performance: Cache compiled Twig templates if commands are static:

$handler->registerCommand('@App/Resources/views/cacheable.html.twig', [], ['cache_key' => 'footer_v1']);

Gotchas and Tips

Pitfalls

Event Timing:
- Commands run after the response is generated but before it’s sent. Avoid injecting into responses that are already modified (e.g., by HttpCache).
- Debugging: Check if kernel.response fires too early by logging $event->getResponse()->getContent().
Twig Autoloading:
- Ensure Twig templates are in a bundle’s Resources/views directory or configure custom paths in twig.form.templates (Symfony 3) or twig.path (Symfony 4+).
- Error: TemplateNotFoundException → Verify template paths and bundle compilation.

FormType Extension:

The injector option only works with FormType (not CollectionType or FormInterface directly). Use FormEvents::PRE_SET_DATA to attach to nested forms:

$builder->addEventListener(FormEvents::PRE_SET_DATA, function($event) {
    $event->getForm()->add('sub_form', SubFormType::class, ['injector' => [...]]);
});

Command Order:

Commands are executed in registration order. Use priorities (if supported) or wrap commands in closures to enforce order:

$subscriber->registerCommand(function() { return '<head>'; });
$subscriber->registerCommand(function() { return '<body>'; }, 10); // Lower priority = later execution

Debugging

Inspect Injected Content: Override the subscriber to log commands:

$subscriber = $container->get('cethyworks_content_injector.subscriber');
$subscriber->registerCommand(function() {
    return '<!-- INJECTED: ' . microtime(true) . ' -->';
});

Disable Injection: Temporarily remove the bundle from AppKernel.php to isolate issues.

Extension Points

Custom Command Handlers: Extend CommandHandlerInterface to support new injection types (e.g., JSON APIs):

class JsonCommandHandler implements CommandHandlerInterface {
    public function handle($command, $request, $response) {
        if ($response->headers->contains('Content-Type', 'application/json')) {
            $response->setContent(json_encode(['injected' => $command]));
        }
    }
}

Response Modifiers: Hook into kernel.response to transform injected content:

$dispatcher->addListener('kernel.response', function($event) {
    $response = $event->getResponse();
    $content = $response->getContent();
    $content = preg_replace('/<!-- INJECTED_START -->(.*)<!-- INJECTED_END -->/s', '$1', $content);
    $response->setContent($content);
});

Configuration: Override default behavior via config/packages/cethyworks_content_injector.yaml:

cethyworks_content_injector:
    enabled: true # Disable globally
    twig:
        debug: false # Disable Twig debug for injected templates

Pro Tips

A/B Testing: Use commands to inject dynamic CSS/JS based on user segments:

$subscriber->registerCommand(function($request) {
    return $request->get('variant') === 'A' ? '<link rel="stylesheet" href="/a.css">' : '<link rel="stylesheet" href="/b.css">';
});

Analytics: Track injections via data-* attributes:

$subscriber->registerCommand(function() {
    return '<div data-injected="footer" data-timestamp="' . time() . '">...</div>';
});

Security: Sanitize injected content to prevent XSS:

$subscriber->registerCommand(function($command) {
    return $this->get('twig')->escapeFilter($command);
});

Content Injector Bundle Laravel Package