Written by Sümeyye Sever (notes I took while creating web development projects)

REST (Representational State Transfer) is an architectural style for designing networked applications. It provides a set of principles and constraints to create efficient, scalable, and interoperable web services. REST is not a protocol or standard but a guideline that developers follow to build APIs.

A RESTful API is an implementation of REST principles in the form of a web service. It allows clients (such as web browsers, mobile apps, or other servers) to interact with resources on a server via HTTP methods. RESTful APIs are a practical application of the REST architectural style.

Key Concepts of REST

1. Resource-Based:
   • Everything in REST revolves around resources.
   • A resource can be any object or data, such as a user, a product, or a document.
   • Each resource is identified by a URI (Uniform Resource Identifier).
   • Example: https://api.example.com/users refers to a list of users.
2. Representation of Resources:
   • Resources are represented in different formats like JSON, XML, HTML or plain text.
   • JSON is the most commonly used format because it is lightweight and easily readable.
3. Stateless Communication:
   • Each RESTful interaction between the client and server is stateless.
   • The server does not remember the client’s state between requests. Each request must include all the information the server needs to fulfill it.
   • This makes REST highly scalable, as the server doesn't need to maintain session data.
4. Uniform Interface:
   • RESTful systems use a consistent, predictable, and uniform approach to interacting with resources.
   • Operations are performed using standard HTTP methods:
     • GET: Retrieve a resource.
     • POST: Create a new resource.
     • PUT: Update a resource entirely.
     • PATCH: Update part of a resource.
     • DELETE: Remove a resource.
5. Client-Server Separation:
   • REST separates the client (e.g., frontend) and server (e.g., backend) responsibilities.
   • The client handles the user interface and interacts with the REST API.
   • The server manages the data and business logic.
6. Layered System:
   • REST allows for a layered architecture where components (e.g., caching systems, load balancers) can exist between the client and server without affecting the interaction.

How REST Works

1. Client Request:

• The client (e.g., a web app or mobile app) sends an HTTP request to the server.
• The request includes:
  • URL: Identifies the resource (e.g., /users).
  • HTTP Method: Specifies the action (e.g., GET or POST).
  • Headers: Include additional information (e.g., content type, authentication).
  • Body: Optional, contains data for the request (e.g., new user details in a POST request).

2. Server Response:

• The server processes the request and sends an HTTP response.
• The response includes:
  • Status Code: Indicates success or error (e.g., 200 OK, 404 Not Found).
  • Headers: Provide metadata about the response.
  • Body: Contains the resource data or a confirmation of the operation.

REST Example

Let’s take an example of a RESTful API for managing books.