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.

Practice

1. In WordPress, which superglobal variable is commonly used to access data sent via an HTTP POST request?

easy

A. $_REQUEST

B. $_POST

C. $_GET

D. $GLOBALS

Solution

1. Step 1: Understand HTTP POST data handling

   Data sent by users through a POST request is stored in the $_POST superglobal in PHP.

2. Step 2: Differentiate from other superglobals

   $_GET holds URL query parameters, $_REQUEST combines GET, POST, and COOKIE but is less specific, and $GLOBALS holds all global variables.

3. Final Answer:

   $_POST -> Option B

4. Quick Check:

   POST data = $_POST [OK]

Hint: POST data is always in $_POST superglobal [OK]

Common Mistakes:

• Confusing $_GET with $_POST
• Using $_REQUEST without knowing its mixed content
• Assuming $GLOBALS holds request data

2. Which of the following is the correct way to send a JSON response in a WordPress REST API callback function?

easy

A. wp_send_json($data);

B. header('Content-Type: text/plain'); echo $data;

C. echo json_encode($data);

D. return new WP_REST_Response($data, 200);

Solution

1. Step 1: Understand WordPress REST API callback requirements

   REST API callbacks should return a WP_REST_Response, array, or WP_Error. The framework handles headers, JSON encoding, and status.

2. Step 2: Compare other options

   wp_send_json($data); sends JSON and exits with wp_die(), suitable for AJAX but bypasses REST processing/filters. echo json_encode($data); outputs JSON without headers or exit. header('Content-Type: text/plain'); echo $data; wrong type.

3. Final Answer:

   return new WP_REST_Response($data, 200); -> Option D

4. Quick Check:

   Return WP_REST_Response [OK]

Hint: Return WP_REST_Response for REST API JSON response [OK]

Common Mistakes:

• Using wp_send_json() (intended for AJAX handlers)
• Using echo without proper headers and exit
• Sending wrong content type header

3. Consider this WordPress REST API callback function:

function get_custom_data(\WP_REST_Request $request) {
  $param = $request->get_param('id');
  if ($param === '42') {
    return ['message' => 'Found'];
  }
  return new WP_Error('not_found', 'ID not found', ['status' => 404]);
}

What will be the HTTP status code if the request URL includes ?id=42?

medium

A. 200

B. 404

C. 500

D. 302

Solution

1. Step 1: Analyze the parameter check

   The function checks if id equals '42'. If yes, it returns an array with message 'Found'.

2. Step 2: Understand default REST API response codes

   Returning an array results in a 200 OK status. Returning WP_Error sets the error status (404 here).

3. Final Answer:

   200 -> Option A

4. Quick Check:

   Valid data returns 200 OK [OK]

Hint: Array return = 200 OK; WP_Error return = error code [OK]

Common Mistakes:

• Assuming WP_Error always returns 200
• Confusing string '42' with integer 42
• Ignoring default REST API status codes

4. You wrote this WordPress REST API endpoint callback:

function my_callback(\WP_REST_Request $request) {
  $data = $request->get_param('data');
  wp_send_json_success($data);
  echo 'Done';
}

What is the problem with this code?

medium

A. The echo statement after wp_send_json_success() will never run

B. wp_send_json_success() does not send JSON

C. get_param() cannot retrieve 'data' parameter

D. Missing return statement causes error

Solution

1. Step 1: Understand wp_send_json_success behavior

   This function sends JSON response and calls exit(), stopping further code execution.

2. Step 2: Analyze code after wp_send_json_success

   The echo 'Done'; line is unreachable because the script exits before it.

3. Final Answer:

   The echo statement after wp_send_json_success() will never run -> Option A

4. Quick Check:

   wp_send_json_success() exits script [OK]

Hint: Code after wp_send_json_success() is unreachable [OK]

Common Mistakes:

• Expecting code after wp_send_json_success() to run
• Confusing get_param() usage
• Thinking wp_send_json_success() returns data instead of exiting

5. You want to create a WordPress REST API endpoint that accepts a POST request with a JSON body containing a 'name' field. Which sequence correctly handles the request and sends a JSON response with a greeting message?

hard

A. Use $request->get_body_params()['name'] to get 'name', then return ['greeting' => 'Hello ' . $name].

B. Use $_POST['name'] directly, then echo JSON encoded greeting and exit.

C. Use $request->get_json_params()['name'] to get 'name', then return new WP_REST_Response(['greeting' => 'Hello ' . $name], 200).

D. Use file_get_contents('php://input') to read JSON body, then use wp_send_json() to send response.

Solution

1. Step 1: Retrieve JSON body parameters properly

   In WordPress REST API, $request->get_json_params() safely parses JSON body data.

2. Step 2: Return a proper REST response object

   Returning WP_REST_Response with data and status code is the recommended way to send structured responses.

3. Step 3: Evaluate other options

   A uses get_body_params() which checks form data ($_POST), empty for JSON body POSTs. C uses $_POST['name'] directly, same issue. D manually reads input bypassing framework helpers and uses wp_send_json() which exits.

4. Final Answer:

   Use $request->get_json_params()['name'] and return WP_REST_Response -> Option C

5. Quick Check:

   Use get_json_params() + WP_REST_Response for JSON POST [OK]

Hint: Use get_json_params() for JSON body in REST API [OK]

Common Mistakes:

• Using $_POST or get_body_params for JSON body data
• Not decoding JSON body properly
• Returning raw arrays instead of WP_REST_Response