Request and response handling in Wordpress - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this WordPress REST API callback?

Consider this REST API endpoint callback in WordPress. What will the response contain when accessed?

Wordpress

<?php
add_action('rest_api_init', function () {
  register_rest_route('myplugin/v1', '/data', array(
    'methods' => 'GET',
    'callback' => function () {
      return new WP_REST_Response(array('message' => 'Hello World'), 200);
    },
  ));
});

A A PHP error because WP_REST_Response is undefined

B An empty JSON object {} with HTTP status 404

C A plain text response 'Hello World' with HTTP status 200

D {"message":"Hello World"} with HTTP status 200

💡 Hint

WP_REST_Response formats the array as JSON with the given status code.

The callback returns a WP_REST_Response object with data and status 200. WordPress converts this to JSON with the message key.

📝 Syntax

intermediate

Which option correctly registers a POST REST API route in WordPress?

You want to create a REST API route that accepts POST requests at 'myplugin/v1/submit'. Which code snippet is correct?

A register_rest_route('myplugin/v1', '/submit', array('methods' => 'post', 'callback' => 'handle_submit'));

B register_rest_route('myplugin/v1', '/submit', array('methods' => 'POST', 'callback' => 'handle_submit'));

C register_rest_route('myplugin/v1', '/submit', array('methods' => ['GET', 'POST'], 'callback' => 'handle_submit'));

D register_rest_route('myplugin/v1', '/submit', array('method' => 'POST', 'callback' => 'handle_submit'));

💡 Hint

The key for HTTP verbs is 'methods' and it is case sensitive.

The correct key is 'methods' (plural) and the value must be uppercase 'POST'. Option B uses the correct syntax.

🔧 Debug

advanced

Why does this REST API callback cause a 500 Internal Server Error?

Examine this callback code for a WordPress REST API route. Why does it cause a server error?

Wordpress

<?php
function my_callback(WP_REST_Request $request) {
  $param = $request->get_param('id');
  if (!$param) {
    return new WP_Error('no_id', 'ID parameter missing', array('status' => 400));
  }
  return array('id' => $param);
}

add_action('rest_api_init', function () {
  register_rest_route('myplugin/v1', '/item', array(
    'methods' => 'GET',
    'callback' => 'my_callback',
  ));
});

A The callback returns an array instead of WP_REST_Response or WP_Error, causing the error.

B The callback uses get_param() which is not a valid method of WP_REST_Request.

C The callback returns WP_Error correctly, but the route is missing permission_callback causing 500 error.

D The callback returns WP_Error and array correctly; the 500 error is caused by missing permission_callback.

💡 Hint

WordPress REST API requires permission_callback for routes unless explicitly allowed.

Without a permission_callback, WordPress denies access causing a 500 error. Returning WP_Error is correct but permission_callback is mandatory.

❓ state_output

advanced

What is the HTTP status code returned by this REST API callback?

This callback returns a WP_Error with a custom status. What status code will the client receive?

Wordpress

<?php
function error_callback() {
  return new WP_Error('forbidden', 'You do not have access', array('status' => 403));
}

add_action('rest_api_init', function () {
  register_rest_route('myplugin/v1', '/secret', array(
    'methods' => 'GET',
    'callback' => 'error_callback',
    'permission_callback' => '__return_true',
  ));
});

A 403 Forbidden

B 200 OK

C 500 Internal Server Error

D 401 Unauthorized

💡 Hint

WP_Error with 'status' in data sets the HTTP status code.

WP_Error with 'status' => 403 causes WordPress to send HTTP 403 Forbidden status code.

🧠 Conceptual

expert

Which statement about WordPress REST API request and response handling is TRUE?

Select the correct statement about how WordPress handles REST API requests and responses.

A Returning a plain array from a callback automatically converts it to JSON with status 200.

B All REST API routes must have a permission_callback; otherwise, WordPress returns 403 Forbidden automatically.

C WP_REST_Response objects cannot set custom HTTP headers in the response.

D WP_Error objects returned from callbacks always cause a 500 Internal Server Error.

💡 Hint

Think about default behaviors for arrays and errors in WordPress REST API.

Returning a plain array is converted to JSON with HTTP 200 by default. Permission_callback is required but missing it causes 500 error, not 403. WP_REST_Response can set headers. WP_Error status depends on 'status' field, not always 500.