REST APIs Overview

What is a REST API?

A REST API is a type of web service that follows the architectural principles of REST (Representational State Transfer). It allows different applications to communicate with each other over the internet using standard HTTP methods, making it lightweight, scalable, and flexible.

Advantages of REST APIs :

1. Simplicity:

Easy to understand and use with standard HTTP methods.

2. Scalability:

Statelessness makes it easier to scale REST APIs horizontally.

3. Platform Independence:

REST APIs can be consumed by any client (web, mobile, IoT) that can make HTTP requests.

4. Caching Support:

REST APIs can leverage caching mechanisms to reduce load on servers.

Core Principles of REST :

1. Statelessness :

Each request from the client contains all the information needed to process the request.
The server does not store any client-specific session data.
Example: A user's login token is sent with every request instead of being stored on the server.

2. Client-Server Separation :

The client (frontend) and server (backend) are independent.
Example: A React app as the client and a Flask/Django app as the server.

3. Uniform Interface :

Resources are accessed using a consistent structure like /users, /products, etc.
HTTP methods (GET, POST, PUT, DELETE) define actions.

4. Cacheable :

Responses should include metadata to indicate whether they can be cached.
Example: Public APIs for weather data often include cache headers.

5. Layered System :

REST APIs can be designed with multiple layers, such as load balancers or authentication layers, without impacting the client.

Key Concepts in REST APIs :

1. Resources :

Anything that can be identified with a URI (Uniform Resource Identifier).
Example:
- /users for all users
- /users/1 for a specific user

2. HTTP Methods :

REST APIs use standard HTTP methods to interact with resources:

GET: Retrieve data.
POST: Create new data.
PUT: Update existing data completely.
PATCH: Partially update existing data.
DELETE: Remove data.

3. Request and Response Format :

REST APIs typically use JSON for data exchange because it is lightweight and widely supported.
Example of a request and response :

Request :

GET /users/1
Host: api.example.com

Response :

{
    "id": 1,
    "name": "John Doe",
    "email": "john@example.com"
}

REST API Example with Python Flask :

Let’s build a REST API to manage a list of users.

Code Example :

from flask import Flask, jsonify, request

app = Flask(__name__)

# Sample data
users = [
    {"id": 1, "name": "Alice"},
    {"id": 2, "name": "Bob"}
]

# GET all users
@app.route('/users', methods=['GET'])
def get_users():
    return jsonify(users)

# GET a single user
@app.route('/users/<int:user_id>', methods=['GET'])
def get_user(user_id):
    user = next((u for u in users if u["id"] == user_id), None)
    if user:
        return jsonify(user)
    return jsonify({"error": "User not found"}), 404

# POST a new user
@app.route('/users', methods=['POST'])
def create_user():
    new_user = request.get_json()
    users.append(new_user)
    return jsonify(new_user), 201

# DELETE a user
@app.route('/users/<int:user_id>', methods=['DELETE'])
def delete_user(user_id):
    global users
    users = [u for u in users if u["id"] != user_id]
    return jsonify({"message": "User deleted"}), 200

if __name__ == '__main__':
    app.run(debug=True)

Testing :

Start the server with python app.py.
Access endpoints:

GET /users: Get all users.
POST /users: Add a user (use tools like Postman).
GET /users/1: Get a specific user.
DELETE /users/1: Remove a user.

RESTful API Real-Life Use Cases :

1. E-Commerce Platforms :

Fetching products (GET /products), adding items to cart (POST /cart), and placing orders (POST /orders).

Facebook or Instagram APIs let you retrieve posts, upload images, and interact with likes and comments.

3. Weather Apps :

OpenWeatherMap API lets you fetch weather updates (GET /weather?q=city).

4. Healthcare Systems :

A REST API might manage patient records (GET /patients) and book appointments (POST /appointments).

Tools for Testing and Using REST APIs :

Postman :

A powerful tool to send API requests, inspect responses, and debug APIs.

Curl (Command-Line) :

Example:

curl -X GET https://api.example.com/users

Browser Extensions :

Use tools like Restlet Client or Talend API Tester for quick API tests.