What is an API: A deep dive into Application Programming Interface

API: Application Programming Interface

Imagine you’re at a restaurant. You have a menu with a list of dishes you can order, along with a description of each dish. When you specify what you’d like to eat, the kitchen (i.e., the system) does its work and serves you the dish you ordered. In this analogy, you are the user, the menu is the API, the order is the request, and the dish that is served to you is the response.

So, What Does an API Do?

1. Communication Bridge: It acts as a bridge between different software systems, enabling them to communicate with each other.
2. Requests and Responses: You send a request to the API to ask for certain information or perform an action, and it sends back a response.
3. Defined Methods: APIs define the methods for requesting information, the required format of those requests, and the structure of the responses.

Types of APIs

1. Web APIs: Used for web applications to communicate with servers. Examples include Google Maps API, Twitter API.
2. Operating System APIs: Allow applications to interact with an operating system. Example: Windows API.
3. Library APIs: Provide reusable functions and procedures for software development. Example: jQuery in JavaScript.

Why Use APIs?

1. Efficiency: They save time, allowing developers to use pre-built functions rather than writing code from scratch.
2. Integration: They enable integration between different systems and software.
3. Abstraction: They hide the complex underlying logic of systems, providing a simpler interface for developers.

Example in Tech

Think of Facebook. When you log in to another app using your Facebook credentials, that app is using Facebook’s API to authenticate you.

API (Application Programming Interface) Design Patterns:

These are standard solutions to common problems encountered while designing APIs. They help create consistent, scalable, and efficient APIs that are a joy for developers to work with.

1. REST (Representational State Transfer):

• What is it?: A stateless architecture where you use standard HTTP methods (GET, POST, etc.) and paths to manipulate resources.
• Example: A Twitter API where you can retrieve a tweet using GET /tweets/{id} or post a new tweet using POST /tweets.

2. GraphQL:

• What is it?: A query language for APIs where clients can request exactly the data they need.
• Example: A movie database API where clients can retrieve a movie’s title, director, and release year, ignoring other details.

3. RPC (Remote Procedure Call):

• What is it?: Exposing functions or procedures in the API, allowing clients to execute them as if they were local.
• Example: A calculator API where clients can call a function add(5, 3) to get the result 8.

4. SOAP (Simple Object Access Protocol):

• What is it?: A protocol for exchanging structured information, relying on XML as its message format.
• Example: A weather service API that sends and receives XML messages to provide weather data.

5. Webhooks:

• What is it?: A way for APIs to provide real-time data to clients as soon as an event occurs.
• Example: A payment gateway API that sends a webhook to your server when a user completes a payment.

6. Versioning:

• What is it?: Managing different versions of your API to maintain compatibility with existing clients while introducing new features.
• Example: Having URLs like /v1/users and /v2/users to support two different versions of the user’s endpoint.

7. Rate Limiting:

• What is it?: Limiting the number of API requests a client can make in a given time period to prevent abuse.
• Example: Allowing a client to make 1000 requests per hour and returning a 429 Too Many Requests status code if they exceed this limit.

8. Caching:

• What is it?: Storing responses from the API to serve future identical requests faster.
• Example: Caching the result of a popular search query so subsequent searches return faster.

9. HATEOAS (Hypermedia as the Engine of Application State):

• What is it?: Embedding links in API responses to help clients navigate to related resources or actions.
• Example: A product API that includes links to related products in its responses.

LAN: Awesome! I love the enthusiasm. Let’s dive deeper into more API design patterns, ensuring everything is clear and easy to grasp.

10. Pagination:

• What is it?: Breaking down a large list of items into smaller chunks and serving them page by page.
• Example: A social media API showing 10 posts at a time and providing a “next” link to load the next 10.

11. Filtering, Sorting, and Searching:

• What is it?: Allowing clients to refine their API requests to get exactly what they need.
• Example: An e-commerce API letting users filter products by price, sort by popularity, and search by name.

12. Error Handling:

• What is it?: Providing clear and helpful error messages and status codes when things go wrong.
• Example: Returning a 404 Not Found with a message "User not found" when a client requests a non-existent user profile.

13. Authentication and Authorization:

• What is it?: Ensuring that only valid users can access your API and only access what they are allowed to.
• Example: Using OAuth to ensure that only authenticated users can access their own order history.

14. Field Selection:

• What is it?: Allowing clients to specify which fields they want in the response.
• Example: A movie API letting clients retrieve just the title and release date of a movie, ignoring other details.

15. Bulk Operations:

• What is it?: Supporting actions on multiple resources in a single request.
• Example: An email API allowing clients to send a message to multiple recipients with one request.

16. Statelessness:

• What is it?: Ensuring that each API request is independent and does not rely on previous requests.
• Example: A shopping cart API that does not rely on server-stored session data but carries all needed info in each request.

17. Idempotency:

• What is it?: Ensuring that performing the same operation multiple times has the same result as doing it once.
• Example: A payment API where clicking the “pay” button multiple times doesn’t charge the user multiple times.

18. Asynchronous Operations:

• What is it?: Handling long-running tasks by providing a way for clients to check back later for results.
• Example: A video processing API that returns a job ID, allowing clients to check the status of their video encoding job later.

19. Consistency:

• What is it?: Ensuring a consistent look and feel across all parts of the API, making it predictable for developers.
• Example: Using the same date format, error structure, and naming conventions throughout your entire API.

20. Deprecation Policy:

• What is it?: Providing a clear strategy for phasing out old versions or features of the API.
• Example: Including headers in your API responses indicating when a feature is deprecated and when it will be removed.

Want to learn more about API and system design interviews:

1. 18 System Design Concepts Every Engineer Must Know Before the Interview.
2. Ace Your System Design Interview with 7 Must-Read Papers in 2023
3. System Design Interview Survival Guide (2023): Preparation Strategies and Practical Tips
4. Mastering the API Interview: Common Questions and Expert Answers
5. System Design Interview Survival Guide (2023)