**Course Title:** Mastering CodeIgniter Framework: Fast, Lightweight Web Development **Section Title:** Building RESTful APIs with CodeIgniter **Topic:** Introduction to REST API principles **Introduction** As web applications evolve, the need for RESTful API's becomes increasingly important. In this topic, we will explore the fundamentals of REST API principles and their application in CodeIgniter. A RESTful API (Representational State of Resource) is an architectural style that defines a set of conventions for designing networked applications, which can be used to build web services that are platform and technology independent. **What is a REST API?** A REST API is an API that uses HTTP requests to interact with resources, which are identified by URIs (Uniform Resource Identifiers). The key principles of RESTful APIs are: 1. **Resources**: Everything in a RESTful API is a resource. These resources can be represented as HTTP requests and responses. 2. **Client-Server Architecture**: The client and server are separate entities that communicate with each other. The client makes requests to the server and receives responses. 3. **Stateless**: The server has no memory of the client, each request contains all the information needed to complete the request. 4. **Cacheable**: Responses from the server can be stored and reused for later requests. 5. **Uniform Interface**: The API uses a common protocol (HTTP) to communicate between the client and server. 6. **Layered System**: The API is designed as a layered system, where each layer communicates with the next layer, but not with the underlying layers. **Key Concepts:** * **Request Methods**: HTTP methods (GET, POST, PUT, DELETE) define the operation to be performed on a resource. * **URIs**: Unique identifiers for resources. * **HTTP Status Codes**: Used to indicate the outcome of a request. * **Content Negotiation**: The ability to convey different representations of a resource. **REST API Examples** * `GET /users`: Retrieve a list of users. * `GET /users/5`: Retrieve a specific user. * `POST /users`: Create a new user. * `PUT /users/5`: Update an existing user. * `DELETE /users/5`: Delete a user. **REST API in CodeIgniter** CodeIgniter provides a built-in support for building RESTful APIs. We can leverage the `PHP` built-in `curl` extension to make HTTP requests to external APIs. To create a REST API in CodeIgniter, we need to follow these steps: 1. Set up the development environment with PHP and CodeIgniter. 2. Create a new controller for the API. 3. Define the routes for the API using CodeIgniter's router. 4. Implement the logic for the API using controllers and functions. 5. Return the response to the client using HTTP status codes and content negotiation. **Task** To put your knowledge into practice, create a new CodeIgniter project and add the following routes to `routes.php`: ```php $route['/api/users'] = 'api/users/index'; $route['api/users/<id>'] = 'api/users/view'; $route['api/users/create'] = 'api/users/create'; $route['api/users/update/<id>'] = 'api/users/update'; $route['api/users/delete/<id>'] = 'api/users/delete'; ``` This will map the API endpoints to the corresponding controller methods. That's it for this topic. I hope this helps you understand the basics of REST API principles and their application in CodeIgniter. Leave a comment if you have any questions or need further clarification on any of the concepts. **Further Reading** For more information, you can refer to the official CodeIgniter documentation and the W3C documentation for REST API: [https://docs.php.net/codeigniter3/tutorial/introduction](https://docs.php.net/codeigniter3/tutorial/introduction) and [https://www.w3.org/standards/tr/html5](https://www.w3.org/standards/tr/html5) What do you think about the explanation so far? Do you have any questions or need further clarification on any of the concepts? <input type="text" id="comment" name="comment" placeholder="Write your comment here..." />