Mock class for demonstrate apply cache policy for controlling duplicated request.

RequestMonitorEx.cs

 // supposed we have class to monitor request
 public class RequestMonitor {

     private readonly Context _context;
     private readonly IMemoryCache _cache;
     
     public RequestMonitor (Context context, IMemoryCache cache) {
         _context = context; // DI the context of Http request
         _cache = cache;
     }

     public void OnRequested () {
         // retrieved http request information
         var hostName = _context.GetHttpContext ().Request.Host.Value;
         var hostAddress = _context.GetHttpContext ().Request.HttpContext.Connection.RemoteIpAddress;
         var keys = _context.GetHttpContext ().Request.Headers.Keys;
         var host = _context.GetHttpContext ().Request.Headers["Host"];
         var userAgent = _context.GetHttpContext ().Request.Headers["User-Agent"];
         var realIP = _context.GetHttpContext ().Request.Headers["X-Real-IP"];
         var forwardeds = _context.GetHttpContext ().Request.Headers["X-Forwarded-For"];

         var connectedInfo = new Dictionary<string, string> () { { "HostAddress", hostAddress.ToString () }, { "Host", host }, { "UserAgent", userAgent }, { "Real-IP", realIP }, { "Forward-For", forwardeds },
             };
             
          var key = string.Concat(hostAddress, "|", realIP.ToString());
          var isExisted = _cache.TryGetValue(key, out var entry);
          
         // place further action logic for the request
         // check if belongs to black list..
         // ...
          
          if (isExisted) return;

          Console.WriteLine("----------------------------------------------->");
          Console.WriteLine($"{DateTime.UtcNow:yyyy/MM/dd HH:mm:ss}, [Info]: {JsonConvert.SerializeObject(connectedInfo)}");
          Console.WriteLine("<-----------------------------------------------");

          // add to cache with expired time (20 secs)
          var cacheEntryOptions = new MemoryCacheEntryOptions().SetAbsoluteExpiration(TimeSpan.FromSeconds(20));
          _cache.Set(key, connectedInfo, cacheEntryOptions);
         

     }
 }