In the previous chapter, we discussed Web APIs and their role in linking various applications across the internet. Moving forward, we'll explore a distinct category of Web API known as REST API. REST, short for Representational State Transfer, functions as a protocol that APIs utilize for communication. Picture yourself at MacDrive, selecting a menu item. You make a specific request and receive exactly what you ordered. Similarly, REST APIs facilitate a standardized and effective way for different computer systems to communicate over the internet.

REST APIs adhere to several key principles:

1. Uniform Interface: this principle standardizes the interaction between client and server, enhancing compatibility across different systems;
2. Client-Server Architecture: in this model, the client (such as your web browser) and the server (where data is stored) function independently. Clients are only required to know resource URIs;
3. Statelessness: every request from a client must contain all the information necessary for the server to fulfill that request. The server does not retain memory of past requests, treating each one as new;
4. Cacheability: similar to how you might store snacks in your backpack for later, responses can be cached for faster retrieval;
5. Layered System: REST supports a tiered system architecture, allowing APIs to be hosted on one server, data to be stored on another, and requests to be authenticated on yet another. Typically, a client cannot distinguish if it is connected directly to the end server or an intermediary;
6. Code on Demand: this optional feature allows servers to send executable code to clients as part of the response, like JavaScript, enabling clients to temporarily enhance their functionality. This is akin to a web page that provides not only data (HTML, CSS) but also interactive features (JavaScript).

The uniform interface of REST is defined by specific HTTP request types, each serving a unique function:

• GET: utilized for retrieving information. For example, when you access a webpage, your browser issues a GET request to fetch the content. Similarly, you can request a single item or multiple items from a list, like ordering a burger, cola, or chips separately;
• POST: used to create a new resource, like posting a new blog entry on a server;
• PUT: updates existing resources;
• DELETE: removes resources.

These HTTP requests encompass CRUD (Create, Read, Update, Delete) functionalities, enabling developers to build efficient, robust applications that communicate effectively within the vast digital landscape.