APIs, REST APIs, and RESTful APIs: Functions and Differences

Date: 30-01-2024

The Application Programming Interface (API) acts as a mediator between the applications to streamline their interaction with each other. API provides readily available codes and information to assist developers in integrating various applications. This article explains APIs, REST APIs, and RESTful APIs and their differences. 

What is an API?

API is a software interface offering services to other applications or software to enhance their functionalities. APIs set rules that must be followed to communicate with other software systems. Developers create APIs so that applications can communicate programmatically. Over the past few years, API has revolutionized the IT industry. Almost every web application uses APIs to improve the functionalities of applications like data transfer, automation, security, and integration. 

Consider a web API to be a bridge between clients and web resources. 

Clients

Clients are users, or they can be software that wants to access information from the web using an API. For instance, developers can write programs that access location data from a map system. Or you can access the same data from your browser by directly visiting the map website. 

Resources

Resources are the information stored on the server. This information could be images, videos, texts, numbers, or any type of data. Organizations use APIs to share resources and provide services while controlling security and authentication. Additionally, API helps organizations determine which clients have access to specific internal resources. 

What is REST?

Representational State Transfer (REST) is a software architecture that determines how an API should work. REST was initially developed as a guideline for managing communications between applications on a complex network like the internet. The REST-based architecture supports reliable communication at scale. They are easy to implement and modify, bringing visibility and cross-platform portability to any API.  

REST APIs are the APIs that follow the REST architectural style. RESTful APIs generally refer to RESTful web services that implement REST architecture. The terms REST API and RESTful API are used interchangeably.

Below are some of the principles of the REST architectural style:

Uniform interface

RESTful web services are designed with a fundamental principle called the uniform interface. This principle necessitates that the server must transfer data in a standard format known as a representation. The representation of a resource can vary from its internal representation on the server application. For instance, the server can store data as text but send it in an HTML representation format. 

The uniform interface imposes four constraints on the architecture of RESTful web services. 

• Requests must identify resources using a uniform resource identifier. 
• Clients must possess enough information in the resource representation to modify or delete the resource if they want to. The server fulfills this condition by sending metadata that describes the resource further. 
• Clients must receive information about how to process the representation further. The server achieves this by sending self-descriptive messages that contain metadata about how the client can best use them. 
• Clients must be aware of all other related resources they need to complete a task. The server accomplishes this by sending hyperlinks in the representation so that clients can dynamically discover more resources.

Statelessness 

In the realm of REST architecture, statelessness is a communication method that entails the server’s completion of each client request independently of previous requests made. This method allows clients to request resources in any order, and each request is completely isolated from other requests, ensuring that the server can understand and fulfill the request every time. 

Layered system 

In layered system architecture, clients have the freedom to connect with other authorized intermediaries between the client and server while still receiving responses from the server. Similarly, servers can pass on requests to other servers. RESTful web service can be designed to run on multiple servers with multiple layers, such as security, application, and business logic, working together to fulfill client requests. These layers remain invisible to the client. 

Cacheabilty

RESTful web services support caching, which is the process of storing some responses on the client or an intermediary to improve server response time. Caching allows the client to store common header and footer images after the first response and then use them directly from the cache, preventing the server from repeatedly sending the same images. RESTful web services control caching by defining API responses as cacheable or non-cacheable. 

Code on demand

In the REST architectural style, servers can temporarily extend or customize client functionality by transferring software programming code to the client. For instance, when filling a registration form on any website, the browser immediately highlights any mistakes made, such as incorrect phone numbers. This functionality is enabled through the code sent by the server.

What is RESTful API? 

A RESTful API interface is used by two or more computer systems to exchange information securely over the Internet. The majority of business applications are integrated with other internal and third-party applications to perform various tasks. RESTful APIs follow secure, reliable, and efficient software communication standards, allowing secure communication between applications. 

For instance, for a social media application, developers can streamline the registration process of users using the application’s identification system. The API also enables the display of posts to users based on their interests. 

How do RESTful APIs work?

The fundamental role of a RESTful API is analogous to browsing the internet. When a client requires a resource, it contacts the server by utilizing the API. Developers of the API provide instructions to the client on how to use the REST API in the server application API documentation. The following are the general steps for any REST API call: 

• The client sends a request to the server. The client formats the request according to the API documentation to ensure that the server understands it. 
• The server authenticates the client and verifies that the client has the necessary authorization to make the request. 
• The server internally processes the request. 
• The server sends a response to the client, which contains information that informs the client whether the request was successful. Additionally, the response includes any information that the client requested. 

The details of the REST API request and response vary slightly based on the design of the API developed by the API developers.

Components of RESTful API client request 

The RESTful API request contains the following main components:

Unique Resource Identifiers

RESTful APIs use unique resource identifiers to identify each resource. The server typically uses a Uniform Resource Locator (URL) to perform resource identification. The URL specifies the path to the resource and is similar to a website address that you enter into your browser to visit any webpage. It’s also called the request endpoint and clearly specifies to the server what the client requires.

Methods

HTTP methods are used to implement RESTful APIs, with the Hypertext Transfer Protocol (HTTP) being the most common. An HTTP method tells the server what to do with the resource. There are four common HTTP methods: 

GET: Clients use GET to access resources at the specified URL on the server, 

POST: POST is used to send data to the server. 

PUT: Clients use PUT to update existing resources on the server, 

DELETE: DELETE to remove the resource. A DELETE request can change the server state, but it fails if the user does not have the proper authentication.

HTTP Headers

Request headers are metadata exchanged between the client and server. They indicate the format of the request and response, provide information about request status, and more.

Data

REST API requests may include data for the POST, PUT, and other HTTP methods to work successfully. 

Parameters

They may also include parameters that give the server more details about what needs to be done. The three types of parameters include:

• Path parameters that specify URL details
• Query parameters that request more information about the resource
• Cookie parameters that authenticate clients quickly

What does the RESTful API server response contain?

When you send a request to the server, it sends a response back to you. This response has three main components, as follows: 

Status line 

The status line has a three-digit code that tells you if your request was successful or not. For example, 2XX means your request was successful, 4XX or 5XX means there was an error, and 3XX means the URL was redirected.

Here are some common status codes:

• 200: Generic success response
• 201: POST method success response
• 400: Incorrect request that the server cannot process
• 404: Resource not found

Message body

The second part is called the message body, which contains the information that you requested. The server will send this information in a format that your computer can understand, like XML or JSON. For example, if you asked for the name and age of a person named John, the server might send you something like this: 

‘{“name”:”John”, “age”:30}’.

Headers 

The third part is called the headers, which give you more information about the response. This includes things like the date and time when the response was sent, as well as details about the server that sent it.

What are the benefits of RESTful APIs?

RESTful APIs include the following benefits:

Scalability

RESTful APIs offer a range of benefits, including enhanced scalability, flexibility, and independence. In particular, these APIs optimize client-server interactions, facilitating efficient scaling without causing communication bottlenecks. By maintaining statelessness and well-managed caching, RESTful web services reduce server load and eliminate the need to retain past client request information. 

Flexibility 

RESTful APIs enable total separation between the client and server components, decoupling them to evolve independently. As a result, platform or technology changes at the server application do not impact the client application. The ability to layer application functions also enhances flexibility, allowing developers to make changes to the database layer without rewriting the application logic.

Independence 

REST APIs are independent of the technology used, allowing client and server applications to be written in various programming languages without affecting the API design. The underlying technology on either side can also be changed without affecting communication, providing greater independence.

Conclusion 

APIs have become an essential tool for developers to improve the functionality and efficiency of their applications. RESTful APIs, known for their stateless and scalable nature, offer specific advantages in web services. However, other APIs play critical roles where these attributes are not a primary concern. A thorough understanding of the unique features of APIs can guide developers in making informed decisions tailored to the specific needs of their projects.