How is the processing of duplicate incoming requests in the system prevented?

To prevent processing duplicate incoming requests (for example, duplicate HTTP requests) in a system, the following approaches are often used:

• Idempotency of operations: designing the API so that a repeated request does not change the system state or has the same effect as the first.
• Using unique request identifiers (idempotent keys): the client generates a unique ID for each request, the server stores processed IDs and ignores repeats with the same ID.
• Caching responses: if a request with the same ID has already been processed, the server returns the stored result.
• Locking or synchronization: upon receiving a request with a certain ID, the server blocks further processing until the current one is completed.

An example using a unique ID in Go (simplified):

var processedRequests = make(map[string]bool)

func handleRequest(id string) string {
    if processedRequests[id] {
        return "Request already processed"
    }
    // Process the request
    processedRequests[id] = true
    return "Request processed successfully"
}

In real systems, processed IDs are stored in databases or distributed caches to ensure robustness and scalability.