Top 10 .NET REST API Interview Questions And Answers

RESTful APIs (Representational State Transfer) are essential for enabling communication between client applications and services over HTTP. `

.NET, specifically ASP.NET Core, is a popular framework for building robust and scalable REST APIs.

Here are some frequently asked interview questions about .NET REST and Web APIs along with detailed answers to help you get started or enhance your existing knowledge.

Page Contents

1. What is a REST API ?

2. What is the difference between REST and SOAP?

3. What are the differences between ASP.NET MVC and ASP.NET Web API?

4. What are the common HTTP methods ?

5. What are the best practices to develop RESTful services ?

6. What are the different status Codes in APIs ?

7. What are HTTP headers, and which ones are most commonly used?

8. What is CORS in Web API ?

9. Explain authentication and authorization for APIs.

10. What is the difference between ApiController and Controller ?

1. What is a REST API ?

A REST API is an application programming interface that conforms to the principles of REST, an architectural style for distributed systems.

It uses HTTP methods (GET, POST, PUT, DELETE, etc.) to perform CRUD (Create, Read, Update, Delete) operations on resources, typically represented in JSON or XML format.

2. What is the difference between REST and SOAP?

REST and SOAP are two different architectural styles for building APIs.

REST is a highly flexible approach that uses standard HTTP methods to interact with resources that are represented primarily in JSON or otherwise in XML.

In contrast, SOAP is an XML-based messaging protocol that is used to transfer data between distributed applications and systems. It follows a very strict structure.

REST is more popular than SOAP, but SOAP is still used in many enterprise-scale systems that require advanced security and error handling features.

3. What are the differences between ASP.NET MVC and ASP.NET Web API?

MVC is used to create web applications that can return views as well as data.

ASP.NET Web API is used to create RESTful HTTP services which return only data and no view.

In MVC, the request is mapped to the actions name, while the request is mapped to the actions based on HTTP verbs in Web API.

4. What are the common HTTP methods ?

HTTP methods (also known as verbs) define the type of operation performed on a resource.

GET: Used to retrieve information or data from the server. It is a safe and idempotent method, meaning it should not have any side effects on the server and can be repeated multiple times without changing the server's state.
POST: Data is sent to the server for processing. It is frequently used to create new server resources. POST, unlike GET, is not idempotent, as multiple requests may result in the generation of many resources.
PUT: Used to update or replace a resource on the server. It is idempotent in the sense that several identical PUT requests should produce the same results as a single request..
PATCH: Similar to PUT, PATCH is used to update a resource. However, while PUT typically replaces the entire resource, PATCH applies partial modifications. It is also idempotent.
DELETE: Used to request that a resource be removed from the server. Like GET, DELETE is also idempotent.
OPTIONS : Used to determine the HTTP methods supported by the resource or server.
HEAD : Same as GET, but it transfers the status line and header section only. It is used to check if a resource is available without fetching the resource body.

5. What are the best practices to develop RESTful services ?

API Design:

Define clear and consistent API endpoints and resource naming conventions.
Use HTTP verbs (GET, POST, PUT, DELETE) correctly to represent CRUD operations.
Design resource representations (JSON, XML) that are easy to understand and work with.
Version your API to maintain backward compatibility.

Security:

Implement authentication and authorization mechanisms to protect your API endpoints.
Use HTTPS to encrypt data transmitted between clients and the server.
Implement rate limiting to prevent abuse and protect against denial-of-service attacks.
Sanitize input and validate data to prevent injection attacks (e.g., SQL injection, XSS).

Performance:

Optimize response times by minimizing network latency and payload size.
Use caching strategies (e.g., HTTP caching, in-memory caching) to reduce database load and improve response times.
Implement pagination and filtering to handle large datasets efficiently.
Use asynchronous programming techniques to handle concurrent requests and improve scalability.

Documentation:

Provide comprehensive API documentation with clear explanations of endpoints, request/response formats, error codes, and usage examples.
Use tools like Swagger/OpenAPI to generate interactive API documentation and client SDKs.

Error Handling:

Define consistent error handling mechanisms and error response formats.
Use appropriate HTTP status codes to indicate the success or failure of API requests.
Provide meaningful error messages and error details to help developers troubleshoot issues.

Testing:

Write automated tests to verify the functionality and behavior of your API endpoints.
Test different scenarios, including edge cases, invalid input, and error conditions.
Use tools like Postman for manual and automated API testing.
Write Unit Tests using XUnit or NUnit.

Versioning:

Plan for API versioning to support backward compatibility and allow for future changes without breaking existing clients.
Use versioning in the URI (e.g., /api/v1/resource) or headers (e.g., Accept-Version) to specify API versions.

Logging and Monitoring:

Implement logging to capture information about API requests, responses, and errors.
Use monitoring tools to track API performance, usage patterns, and system health.
Set up alerts and notifications to quickly identify and respond to issues.

Compliance:

Ensure compliance with industry standards and regulations (e.g., GDPR, HIPAA) when handling sensitive data.
Follow best practices for data privacy, security, and compliance with relevant laws and regulations.

Scalability:

Design your API with scalability in mind to handle increasing loads and growing user bases.
Use distributed architectures, caching, and load balancing to distribute traffic and handle high volumes of requests.
Monitor performance metrics and scale resources dynamically as needed.

6. What are the different status Codes in APIs ?

Understanding the status codes helps in debugging issues, enhancing API design, and providing clear communication between clients and servers.

1xx: Informational – Communicates transfer protocol-level information.

2xx: Success – Indicates that the client’s request was accepted successfully.

3xx: Redirection – Indicates that the client must take some additional action in order to complete their request.

4xx: Client Error – This category of error status codes points the finger at clients.

5xx: Server Error – The server takes responsibility for these error status codes.

Most commonly used codes are as below

200 - OK

201 - Created

202 - Accepted

204 - No Content

301 - Moved Permanently

302 - Found

303 - See Other

304 - Not Modified

307 - Temporary Redirect

400 - Bad Request

401 - Unauthorized

403 - Forbidden

404 - Not Found

405 - Method Not Allowed

406 - Not Acceptable

412 - Precondition Failed

415 - Unsupported Media Type

500 - Internal Server Error

501 - Not Implemented

502 - Bad Gateway

7. What are HTTP headers, and which ones are most commonly used?

HTTP headers are key-value pairs sent in HTTP requests and responses, providing essential information about the request or response. They play a crucial role in controlling how data is transmitted, formatted, and processed. Here's an overview of HTTP headers and some of the most commonly used ones.

Categories of HTTP Headers

1. General Headers: Apply to both requests and responses but do not relate to the data in the body.

Cache-Control: no-cache
Connection: keep-alive

2. Request Headers: Provide additional information about the request.

Accept: application/json
Accept-Encoding: gzip, deflate
Authorization: Bearer <token>
Content-Type: application/json
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64)
Host: www.dotnetinterviews.com
Referer: https://www.dotnetinterviews.com
Cookie: sessionId=abc123

3. Response Headers: Provide additional information about the response.

Content-Type: application/json
Content-Length: 348
Set-Cookie: sessionId=abc123; Path=/; HttpOnly
Location: https://www.dotnetinterviews.com/new-resource
Server: Apache/2.4.1 (Unix)
WWW-Authenticate: Basic realm="Access to the site"

4. Entity Headers: Provide information about the body of the resource, such as its content length or MIME type.

Content-Encoding: gzip
Content-Language: en-US
Content-Location: /index.htm
Last-Modified: Wed, 21 Oct 2015 07:28:00 GMT
ETag: "686897696a7c876b7e"

8. What is CORS in Web API ?

Cross-Origin Resource Sharing (CORS) is a security feature implemented by web browsers to prevent web pages from making requests to a different domain than the one that served the web page.

It is a mechanism that allows or restricts resources on a web page to be requested from another domain outside the domain from which the resource originated.

9. Explain authentication and authorization for APIs.

Authentication verifies the identity of a user or system. Common methods include Basic Authentication, Token-Based Authentication (JWT), OAuth 2.0, and API Keys.

Authorization determines what an authenticated user is allowed to do. Strategies include Role-Based Access Control (RBAC), Attribute-Based Access Control (ABAC), and Access Control Lists (ACLs).

Implementing robust authentication and authorization mechanisms is essential for securing APIs and ensuring that only authorized users can access or modify resources.

10. What is the difference between ApiController and Controller ?

The ApiController class is used for building HTTP APIs. It provides several features and conventions that are specifically designed to simplify the creation and maintenance of APIs.

The Controller class is used for building web applications with views, following the Model-View-Controller (MVC) pattern. It provides features suitable for rendering HTML views and handling web forms. Conclusion

Conclusion

By following these best practices and leveraging the powerful features of ASP.NET Core, you can build secure, reliable, and scalable REST APIs.

Whether you are just starting out or looking to enhance your existing .NET REST APIs knowledge, these questions and answers should help you navigate common challenges and crack the interviews.

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