Hey buddy, let's talk about how to protect your API from repeated requests! Alright, we all know that networks aren't always stable, and people often accidentally press the "Submit" button twice. This can lead to a big problem; for example, if a customer presses "Pay" twice, the money might be deducted twice! 🤯 So, what concept can help us solve this issue? It's something called Idempotency. Simply put, it means that if you request something once or ten times with the same data, the final result remains the same, without updating the data more than once. For instance, if you delete an order once and try to delete it again, nothing new will happen. It's guaranteed! 🙌 What actually happens? Very often, the frontend freezes, the network lags, the user presses the button twice, or the client retries due to a timeout. For example, if a customer mistakenly presses "Pay" twice, it's not logical for the request to be registered twice, and it's unacceptable for the money to be deducted twice. The idea here is that the server returns the same response it gave for the first request, without re-executing the operation. So, if the requests are sent again, the server would say: "Are you sure you want to do this again? I already did it for you the first time!" 😄 Do all requests need to be idempotent? The answer is no ❌. Here, we need to distinguish between two important concepts: 1. **Safe Requests** like GET, which don't modify any data and can be executed a thousand times without side effects. For example, when you go to buy a cup of coffee, you can ask about the types available from the vendor, and you're not worried about changing anything. 2. **Idempotent Requests** like PUT and DELETE, which do modify data, but repeating them shouldn't change the result after the first time. So, if you delete an order and try to delete it again, nothing new will happen. It's like going to a kiosk and ordering a cup of coffee, then ordering it again, and the vendor says: "I already got you the first one, sir!" 😂 Why is this important? This is very important, and it's not a luxury 🚨. Since networks are not always stable, timeouts occur, and retries happen involuntarily. If your API isn't designed to handle these issues, it can lead to serious problems. **Idempotent** You might encounter issues such as: - Duplicate Orders - Duplicate Payments - Data Inconsistency - Bugs with no end Therefore, follow the golden rule: Design for Retries. Assume that any request can be sent more than once. **How to Make an API Idempotent?** There are multiple levels of solutions: 1. **Frontend Level** A simple but insufficient solution on its own: Disable the Submit button after the first click, use a loading state, and prevent double clicks. This reduces the problem but never eliminates it 100%. 2. **Backend Level (The Real Solution) 🗝** Use an Idempotency Key, which is a unique token, transaction ID, or UUID. The flow would be: - The client sends the Idempotency-Key with the request. - The server checks if the key exists in the database or cache. - If the key exists: Return the same old response. - If the key does not exist: Store it, execute the operation, and save the result. This way, the same request will always return the same response, and the operation will only be executed once ✅. 3. **With Payment Systems (Best Scenario 💳)** If you are dealing with Stripe, Paymob, PayPal, or any other payment provider, you usually have a `transactionId` or `paymentIntentId`. The smart solution is: - Store this ID in the database with a unique constraint. - If the request is sent again, the second insertion will fail due to the unique constraint. - Handle the error gracefully and return the same result. A simple, practical, and highly effective solution 🔥. **Important Note (Senior Tip ⚠️)** One drawback of the unique constraint solution is that sometimes you send a request to the database knowing it will fail. However, this is an expected and controlled failure, which is much cheaper than dealing with duplicate payments later 😄. **Summary 🧠** Idempotency is not just a theoretical term; it's a way of thinking and designing that protects your APIs and saves you from bugs and production disasters. If your API deals with money, orders, or sensitive operations, always ask yourself: If the request is repeated, will my system remain consistent? If the answer is yes, then you are on the right track 👌.