Learn to build strict, schema-driven input sanitization pipelines in WordPress to secure your plugin against injection and data corruption.
Previously in this course, we explored the Data Access Objects Pattern to handle our database interactions. While that layer ensures we use prepared statements, it assumes the data reaching it is already "clean." This lesson introduces the Sanitization Pipeline, a mandatory architectural boundary that sits between your request handlers and your data access layer to ensure only validated, sanitized data enters your system.
Most developers treat sanitization as an afterthought—calling sanitize_text_field() somewhere deep inside a model or repository. This is an anti-pattern. If you wait until the data reaches the database layer, you've already allowed "dirty" data to propagate through your service providers and business logic.
A proper Sanitization Pipeline follows the principle of "Validate at the edge, sanitize at the sink." By defining an input schema at the controller level, you guarantee that your internal services only ever process predictable, well-formed data.
In our Knowledge Base plugin, we want to ensure that every POST request to our custom endpoints undergoes a strict check. We will define an interface for our validators, allowing us to enforce schemas consistently across the application.
PHPinterface InputValidatorInterface { public function validate(array $data): array; }
By using this interface, we can inject specific validators into our controllers, keeping our request handling clean and testable.
Let's implement a KnowledgeBaseEntryValidator that handles the creation of a new knowledge base article. We'll use WordPress core functions to enforce types and lengths before the data ever hits our EntryRepository.
PHPnamespace KnowledgeBase\Validation; class EntryValidator implements InputValidatorInterface { public function validate(array $data): array { $validated = []; #6A9955">// 1. Strict Type Validation if (empty($data['title']) || !is_string($data['title'])) { throw new \InvalidArgumentException('Title is required and must be a string.'); } #6A9955">// 2. Sanitization $validated['title'] = sanitize_text_field($data['title']); #6A9955">// 3. Schema Enforcement $validated['category_id'] = isset($data['category_id']) ? absint($data['category_id']) : 0; #6A9955">// 4. Content Sanitization(using wp_kses_post for HTML content) $validated['content'] = isset($data['content']) ? wp_kses_post($data['content']) : ''; return $validated; } }
In your controller, you now have a single, predictable point of entry:
PHPpublic function store(WP_REST_Request $request) { try { $data = $this->validator->validate($request->get_params()); return $this->repository->create($data); } catch (\InvalidArgumentException $e) { return new WP_Error('invalid_input', $e->getMessage(), ['status' => 400]); } }
InputValidatorInterface for a new "Settings" update feature in your plugin.user_email field is passed through sanitize_email() and is_email().InvalidArgumentException.sanitize_text_field is magic: It strips tags and removes newlines, but it doesn't validate business logic. It won't tell you if a user provided a valid ID or a properly formatted date.sanitize_text_field on data that requires specific formatting (like serialized JSON or complex HTML). Use contextual functions like wp_kses_post or absint instead.wp_unslash: Remember that $_POST data in WordPress is slashed by default. When building APIs, use the WP_REST_Request object, which handles unslashing for you automatically.By implementing a dedicated validation layer, you shift security from a reactive "patch" to a proactive architectural requirement. Your services become more robust because they can trust the data they receive, and your controllers become readable, focused handlers of the HTTP lifecycle.
Up next: Output Escaping Patterns, where we ensure that the data we just sanitized is safely rendered back to the user.
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