Request and response handling in Wordpress - Mini Project: Build & Apply

Request and Response Handling in WordPress

📖 Scenario: You are building a simple WordPress plugin that handles a custom HTTP request and sends a JSON response. This is useful when you want to create an API endpoint or handle AJAX requests in WordPress.

🎯 Goal: Create a WordPress plugin that registers a custom REST API endpoint at /wp-json/custom/v1/message which returns a JSON response with a greeting message.

📋 What You'll Learn

Create a function to register a REST API route

Add a callback function that returns a JSON response

Use WordPress REST API functions to handle the request and response

Register the route on the rest_api_init action hook

💡 Why This Matters

🌍 Real World

Custom REST API endpoints are used to extend WordPress functionality, allowing integration with other apps, mobile clients, or custom frontends.

💼 Career

Understanding how to handle requests and responses in WordPress REST API is essential for WordPress plugin developers and backend developers working with WordPress.

1

Create the plugin header and initial function

Create a PHP file with the plugin header comment and define a function called custom_register_route that will later register the REST API route.

Wordpress

<?php
// Your code here

Hint

Start by creating a PHP file with the plugin header comment and define an empty function named custom_register_route.

2

Add the REST API route registration

Inside the custom_register_route function, use register_rest_route to register a route with namespace custom/v1 and route /message. Set the methods to GET and the callback to custom_message_callback.

Wordpress

<?php
/**
 * Plugin Name: Custom REST API Message
 * Description: A plugin to create a custom REST API endpoint that returns a greeting message.
 * Version: 1.0
 * Author: Your Name
 */

function custom_register_route() {
    // Register the REST API route here
}

Hint

Use register_rest_route inside the function to define the route, HTTP method, and callback function.

3

Create the callback function to return JSON response

Create a function called custom_message_callback that returns an array with a key message and value 'Hello from custom REST API!'. This array will be automatically converted to JSON by WordPress.

Wordpress

 'GET',
        'callback' => 'custom_message_callback',
    ));
}

// Create the callback function here
# Your code here

Hint

Define the callback function that returns an array with the greeting message.

4

Hook the route registration to rest_api_init

Add an action hook to call custom_register_route on the rest_api_init action so WordPress registers the route when the REST API initializes.

Wordpress

 'GET',
        'callback' => 'custom_message_callback',
    ));
}

function custom_message_callback() {
    return array('message' => 'Hello from custom REST API!');
}

// Hook the route registration here
# Your code here

Hint

Use add_action to connect your route registration function to the rest_api_init hook.

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