“RESTful APIs: Principles and Challenges”

Imagine any E-commerce or Travel agency etc. websites without any integrations. your site would need to build tools for processing payment, shipping, email automation, user accounts, finding flights from different providers, findings hotels, and other functions all by itself. This isn’t a scalable solution — it’s more efficient to outsource these tasks to other services.

In order to work together, software applications use Application Programming Interfaces. APIs provide a standardized way for two applications to send data back and forth(Using Client Server architecture). Your e-commerce site can interact with payment software, shipping software, and any other necessary integrations through their respective APIs.

What are REST APIs?

There are many approaches to building an API. One popular approach is REST APIs. In this article, we will talk about REST APIs in detail. But first, let’s understand some important key terms.

1. Client: A client is any software or application that will use the API, and sends HTTP requests to a server to access or modify resources. The client is responsible for initiating communication with the server, sending requests, and interpreting the responses returned by the server. For eg: Web browsers like Google Chrome, Mozilla Firefox, and Safari can act as clients to consume resources from a RESTful API. These browsers can use HTTP methods like GET and POST to interact with the other website’s API to get the data from there and display it on your screen.
2. Server: A server is an application that receives the client request, processes the request, and then returns the resource/appropriate resource to the client. The server implements security measures to authenticate and authorize clients, restrict access to resources, and protect against malicious attacks.
3. Resource: A resource can be anything that can be represented as a state or object on the server, such as data, images, videos, or services. The server is responsible for managing the state of the resources and ensuring that the client can access or modify them according to the API’s rules and protocols. A resource is typically identified by a unique URI (Uniform Resource Identifier)
4. HTTP (Hypertext Transfer Protocol): The protocol used to transfer data between the client and server in a RESTful API.
5. HTTP methods: The standard methods used in HTTP to perform operations on resources, including GET, POST, PUT, PATCH, and DELETE. We will talk about them in more detail.
6. Status code: A three-digit number returned by the server to indicate the status of a request, such as success (2xx), client error (4xx), or server error (5xx). Later, we will discuss status codes also.
7. URI (Uniform Resource Identifier): A unique string of characters that identifies a resource’s location on the server or we can say its address.

Principles of REST API design

Although REST APIs can be developed using virtually any programming language and support a variety of data formats. but the only requirement is that they align with the following REST design principles.

1. Client-server decoupling: In REST API design, client and server applications must be completely independent of each other. The only information the client application should know is the URI of the requested resource; it can’t interact with the server application in any other way. Similarly, a server application shouldn’t modify the client application other than passing it to the requested data via HTTP.
2. Statelessness: REST APIs are stateless, meaning that each request needs to include all the information necessary for processing it.
3. Uniform interface: All API requests for the same resource should look the same, no matter where the request comes from. The REST API should ensure that the same piece of data, such as the name or email address of a user, belongs to only one uniform resource identifier (URI).
4. Layered system architecture: In REST APIs, the calls and responses go through different layers. As a rule of thumb, don’t assume that the client and server applications connect directly to each other. There may be a number of different intermediaries in the communication loop. REST APIs need to be designed so that neither the client nor the server can tell whether it communicates with the end application or an intermediary.
5. Cacheability: When possible, resources should be cacheable on the client or server side. Server responses also need to contain information about whether caching is allowed for the delivered resource. The goal is to improve performance on the client side while increasing scalability on the server side.

Challenges in the REST API Testing

1. Testing Edge Cases: During Testing many parameters must be covered as Input. A specific combination of parameters may uncover any issue, making the API vulnerable to security threats or not functioning at all. Hence while doing REST API testing, testing edge cases can be challenging.
2. Versioning: APIs are often updated with new features or changes, which can affect how they behave. Testing across different versions can be challenging and requires careful management of test data and environments.
3. Data Management: In REST API testing, data management can be challenging since data is typically sent and received in JSON or XML formats, which can be difficult to read and manage.
4. Authentication and Authorization: REST APIs often require authentication and authorization, which can add an extra layer of complexity to testing. As a QA you must ensure that the API correctly handles access and permissions for various types of users.

Reasons why do we need API Tests?

1. Early detection of issues: API testing is done before an application is coupled with any user interface (UI) components. This enables developers to detect errors and misconfigurations in the early testing phase. It can also help reduce costs.
2. Consistent business Logic: An application uses the same set of APIs across multiple platforms. Testing API collections can help ensure that the same business logic offers the same functionality across all platforms.
3. Security Test: By testing your APIs, you can discover business logic issues and security vulnerabilities that can expose your API to attacks.

HTTP methods used for API Testing

HTTP methods, also known as HTTP verbs, are the standard request methods used by RESTful web services. The below (POST, GET, PUT, DELETE) methods are also called CRUD(Create, Retrieve, Update, and Delete) operations.

The most commonly used HTTP methods in REST API are:

1. GET: Used to retrieve a resource or a collection of resources from the server.
2. POST: Used to create a new resource.
3. PUT: Used to update an existing resource, or to create a new resource if it does not exist.
4. DELETE: Used to delete a resource.
5. PATCH: Used to update a resource partially.
6. OPTIONS: Used to retrieve information about the communication options available for a resource.
7. HEAD: Used to retrieve the headers of a resource without fetching the entire resource.

Each of these HTTP methods has a specific purpose and can be used to perform different operations on the resources exposed by the REST API. When designing a REST API, it’s important to use the appropriate HTTP methods for each operation to ensure that the API follows the REST architectural principles.

HTTP Status codes

Status codes indicate the outcome of a client’s request to the server. As per my experience, here are some of the most common HTTP status codes used in REST APIs:

1. 200 OK: The client’s request has been successful, and the server has returned the requested data.
2. 201 Created: The client’s request has been successful, and the server has created a new resource.
3. 400 Bad Request: The client’s request is invalid or malformed, and the server cannot process it.
4. 401 Unauthorized: The client’s request requires authentication, and the client has not provided valid credentials.
5. 403 Forbidden: The client’s request is valid, but the server refuses to fulfill it.
6. 404 Not Found: The requested resource is not available on the server.
7. 405 Method Not Allowed: The client has used an HTTP method that is not supported by the server.
8. 408 Request Timeout: The server timed out waiting for the request. According to HTTP specifications: “The client did not produce a request within the time that the server was prepared to wait.
9. 500 Internal Server Error: An error has occurred on the server, and the client’s request cannot be completed.
10. 502 Bad Gateway: The server was acting as a gateway or proxy and received an invalid response from the upstream server.
11. 503 Service Unavailable: The server is currently unavailable or overloaded and cannot fulfill the client’s request.
12. 504 Gateway Timeout: The server was acting as a gateway or proxy and did not receive a timely response from the upstream server.

Conclusion

In conclusion, RESTful APIs have become a popular way of exposing data and functionality to other systems, mobile apps, and web applications. The REST architectural style is based on principles such as resource identification, and statelessness as the engine of the application state. These principles enable API designers to create scalable, self-descriptive, and easy-to-use APIs that can be accessed by any client using standard HTTP operations such as GET, POST, PUT, and DELETE. By following the principles of REST, API developers can create robust and flexible APIs that are widely adopted by developers, businesses, and industries.

I hope you liked this article. Happy Learning !! DG