Lesson 14 • Expert

APIs & JSON 🌐

Build REST APIs, encode and decode JSON, consume external services with cURL, and structure professional API responses in PHP.

What You'll Learn in This Lesson

• Encode PHP arrays to JSON and decode JSON back to arrays
• Build a REST API that handles GET, POST, PUT, DELETE requests
• Consume external APIs using cURL with authentication
• Use proper HTTP status codes and response formats
• Handle JSON errors and build reusable API clients

Note: PHP runs on a server. Our examples simulate PHP logic using JavaScript. To run real PHP, install PHP.

🎯 Real-World Analogy: An API is like a restaurant waiter. You (the client) give your order (request) to the waiter (API), who takes it to the kitchen (server), and brings back your food (response). JSON is the language on the menu — a structured format both the waiter and kitchen understand. REST is the set of rules the restaurant follows: different actions (GET = read menu, POST = place order, PUT = change order, DELETE = cancel order).

JSON: The Language of APIs

JSON (JavaScript Object Notation) is the most common data format for APIs. PHP has built-in functions json_encode() and json_decode() to convert between PHP arrays and JSON strings. Always pass true as the second argument to json_decode() to get an associative array instead of an object.

Try It: JSON Encoding & Decoding

Convert PHP arrays to JSON and back — learn the flags and error handling

Try it Yourself »

JavaScript

// PHP APIs & JSON: Encoding and Decoding
console.log("=== JSON in PHP ===");
console.log();

console.log("1️⃣ ENCODING — PHP Array → JSON String");
console.log("─────────────────────────────────────");
console.log();

// Simulate PHP's json_encode
let user = { name: "Alice", age: 28, skills: ["PHP", "MySQL", "JavaScript"] };
let jsonString = JSON.stringify(user, null, 2);
console.log("PHP:  $json = json_encode($user);");
console.log("Output:");
console.log(jsonString);
console.log();

console.l
...

Building a REST API

REST (Representational State Transfer) is an architectural pattern for building APIs. Each URL represents a resource, and HTTP methods define what action to take. A well-structured API uses proper status codes, consistent response formats, and input validation.

Try It: REST API Endpoints

Build GET, POST, PUT, DELETE endpoints with proper status codes

Try it Yourself »

JavaScript

// PHP REST API: Building Endpoints
console.log("=== Building a REST API in PHP ===");
console.log();

console.log("📁 File: api/users.php");
console.log("───────────────────────");
console.log();

// Simulate HTTP methods
let methods = ["GET", "POST", "PUT", "DELETE"];

for (let method of methods) {
  console.log("📌 " + method + " /api/users");
  
  if (method === "GET") {
    console.log("   Code: header('Content-Type: application/json');");
    console.log("         $users = $pdo->query('SEL
...

Consuming APIs with cURL

cURL is PHP's built-in library for making HTTP requests to external services. It supports all HTTP methods, custom headers, authentication tokens, and file uploads. For production apps, consider using Guzzle HTTP client for a cleaner API.

Try It: cURL API Client

Make GET and POST requests, add auth headers, build a reusable client

Try it Yourself »

JavaScript

// PHP cURL: Consuming External APIs
console.log("=== Consuming APIs with cURL ===");
console.log();

console.log("1️⃣ BASIC GET REQUEST");
console.log("─────────────────────");
console.log();
console.log("  $ch = curl_init('https://api.example.com/users');");
console.log("  curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);");
console.log("  $response = curl_exec($ch);");
console.log("  $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);");
console.log("  curl_close($ch);");
console.log("  $data = 
...

⚠️ Common Mistakes

⚠️

Forgetting Content-Type header — always set header('Content-Type: application/json') before echoing JSON. Without it, clients may misinterpret the response.

⚠️

Using $_POST for JSON input — $_POST only works with form data. For JSON request bodies, use json_decode(file_get_contents('php://input'), true).

⚠️

Not checking curl_errno() — cURL can fail silently. Always check for errors after curl_exec() and handle timeouts gracefully.

💡

Pro Tip: Version your API URLs (/api/v1/users) from day one. This lets you make breaking changes in v2 without affecting existing clients.

📋 Quick Reference — APIs & JSON

Function / Concept	Purpose
json_encode($data)	PHP array → JSON string
json_decode($str, true)	JSON string → PHP array
$_SERVER['REQUEST_METHOD']	Get HTTP method (GET, POST, etc.)
file_get_contents('php://input')	Read raw JSON request body
http_response_code(201)	Set HTTP status code
curl_init() / curl_exec()	Make HTTP requests to external APIs

🎉 Lesson Complete!

You can now build and consume REST APIs in PHP! Next, explore advanced OOP design patterns for production-quality code.

APIs & JSON 🌐

What You'll Learn in This Lesson

JSON: The Language of APIs

Try It: JSON Encoding & Decoding

Building a REST API

Try It: REST API Endpoints

Consuming APIs with cURL

Try It: cURL API Client

⚠️ Common Mistakes

📋 Quick Reference — APIs & JSON

🎉 Lesson Complete!

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