How is the repeatability of POST requests ensured without changing their result?.

To ensure repeatability of POST requests without changing their result, idempotency is usually applied at the application level. One common method is to use a unique identifier (for example, UUID) for each request, which the client generates and sends along with the request.

When the server receives a request with such an identifier, it checks whether a request with this ID has already been processed. If yes, it returns the same result without re-executing the operation. If no, it processes the request and saves the result along with the ID.

This allows safe repetition of POST requests (for example, in case of network errors) without the risk of duplicating actions.

Example in Python (simplified):

processed_requests = {}

def handle_post(request_id, data):
    if request_id in processed_requests:
        return processed_requests[request_id]  # Return the saved result
    # Process the request
    result = do_expensive_operation(data)
    processed_requests[request_id] = result
    return result

Thus, a repeated POST with the same request_id will not change the server state.