Building REST APIs with PHP

# CHAPTER 20

Building REST APIs with PHP #

1. Introduction #

2. Learning Objectives #

• Structure a basic PHP directory for an API project.

• Implement a front-controller routing system using index.php.

• Parse URL paths and HTTP methods dynamically.

• Read JSON payloads from php://input.

• Create a helper function to output standardized JSON responses.

3. Beginner-Friendly Explanation #

4. Real-World Examples #

• Frameworks: This exact routing pattern is what powers massive frameworks like Laravel, CodeIgniter, and Express.js. All requests funnel through one entry point to ensure security, validation, and database connections are initialized once.

5. Detailed Code Examples #

1. .htaccess (Apache configuration to force all traffic to index.php):

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?request=$1 [QSA,NC,L]

2. index.php (The Router / Front Controller):

<?php
header("Access-Control-Allow-Origin: *");
header("Content-Type: application/json; charset=UTF-8");
header("Access-Control-Allow-Methods: OPTIONS,GET,POST,PUT,DELETE");

// Helper function to send JSON responses
function sendResponse($status, $data) {
    http_response_code($status);
    echo json_encode($data);
    exit;
}

// Get the requested URL path
$uri = parse_url($_SERVER[&#039;REQUEST_URI'], PHP_URL_PATH);
$uri = explode(&#039;/', $uri);
$method = $_SERVER["REQUEST_METHOD"];

// Handle CORS Preflight
if ($method == "OPTIONS") {
    sendResponse(200, ["message" => "OK"]);
}

// Basic Routing Logic
if (isset($uri[2]) && $uri[2] == &#039;users') {
    $userId = $uri[3] ?? null;

    if ($method == &#039;GET') {
        if ($userId) {
            sendResponse(200, ["message" => "Get user $userId"]);
        } else {
            sendResponse(200, ["message" => "Get all users"]);
        }
    } 
    
    elseif ($method == &#039;POST') {
        // Reading incoming JSON payload
        $input = json_decode(file_get_contents(&#039;php://input'), true);
        sendResponse(201, ["message" => "User created", "data" => $input]);
    }
    
    else {
        sendResponse(405, ["error" => "Method not allowed"]);
    }
} else {
    sendResponse(404, ["error" => "Endpoint not found"]);
}
?>

6. Request/Response Examples #

Request:

POST /api/users HTTP/1.1
Host: localhost
Content-Type: application/json

{
  "name": "Alice"
}

Response:

{
  "message": "User created",
  "data": {
    "name": "Alice"
  }
}

7. HTTP Examples #

• Access-Control-Allow-Origin: * allows frontend apps (like React running on a different port) to access the API without CORS blocking.

• Content-Type: application/json ensures the browser interprets the output as JSON data, not HTML text.

8. JSON Examples #

// Calling this:
sendResponse(404, ["error" => "File not found"]);

// Will always output valid JSON:
// {"error": "File not found"}

9. Best Practices #

• Separate Logic from Routing: In the example above, we put the logic directly inside index.php. For a real app, index.php should merely *call* a separate class (like UserController.php) to keep files clean.

• Always handle OPTIONS: Browsers send OPTIONS preflight requests before making POST/PUT requests from a frontend app. If your PHP script doesn't handle OPTIONS and return a 200 OK, the browser will block the real request.

• Centralize Output: Never echo or printr randomly in your code. Always use a centralized function like sendResponse() so you have one place to format your JSON structure.

1. 1. Look at the parseurl logic. If a client requests http://localhost/api/users/5, what value will be stored in $uri[2] and $uri[3]?

12. Coding Challenges #

13. MCQs with Answers #

14. Interview Questions #

• Q: Explain the "Front Controller" design pattern and why it is superior to creating separate PHP files for every endpoint.

• Q: How do you handle CORS (Cross-Origin Resource Sharing) in a raw PHP API?

• Q: Walk me through how you extract the resource name and ID from a URL string in PHP without using a framework.

15. FAQs #

16. Summary #

17. Next Chapter Recommendation #