Block API requests for 5 mins if API rate limit exceeds using WebApiThrottle - C# Web API

Question

There's a real nice library WebApiThrottle for API rate limiting in Web API.
As mentioned on the Wiki page, I can rate limit the API based on the authorization token header of API call.
But, how can I block the api call for the next 5 minutes if this api rate limit exceeds? Also, not that any request within next 5 minutes will reset the rate limiting exceeded time.

I checked the code but couldn't find this feature. Any other way if someone can suggest?

Larkins

Answer 1

For the time being, I'm using this fork of WebApiThrottle and adding the dll manually to the solution. @adamriyadi has implemented this feature in the fork. Waiting for it to come to NuGet package.

---

Update: Later, I went with my own implementation for API rate limiting with blocking period using HttpRuntime.Cache. So there is no need to add any additional library.

public class ThrottleAttribute : ActionFilterAttribute
    {
        private int _API_RATEQUOTA = 60;

        // per x minute value
        private int _API_TIMELIMIT = 1;

        private int _API_BLOCKDURATION = 5;

        private readonly object syncLock = new object();

        public override void OnActionExecuting(HttpActionContext actionContext)
        {
            // Extract access_token or id or ip address to uniquely identify an API call
            var access_token = AuthHelper.GetAuthToken(actionContext.Request);

            if (access_token != null)
            {

                string throttleBaseKey = GetThrottleBaseKey(access_token);
                string throttleCounterKey = GetThrottleCounterKey(access_token);

                lock (syncLock)
                {
                    //add a listner for new api request count
                    if (HttpRuntime.Cache[throttleBaseKey] == null)
                    {
                        // add api unique key.. this cache will get expire after _API_TIMELIMIT
                        HttpRuntime.Cache.Add(throttleBaseKey,
                            DateTime.UtcNow,
                            null,
                            DateTime.Now.AddMinutes(_API_TIMELIMIT),
                            Cache.NoSlidingExpiration,
                            CacheItemPriority.High,
                            null);

                        // add count as value for that api.. this cache will get expire after _API_TIMELIMIT
                        HttpRuntime.Cache.Add(throttleCounterKey,
                           1,
                           null,
                           DateTime.Now.AddMinutes(_API_TIMELIMIT),
                           Cache.NoSlidingExpiration,
                           CacheItemPriority.High,
                           null);
                    }
                    else
                    {
                        //listener exists for api request count
                        var current_requests = (int)HttpRuntime.Cache[throttleCounterKey];

                        if (current_requests < _API_RATEQUOTA)
                        {
                            // increase api count
                           HttpRuntime.Cache.Insert(throttleCounterKey,
                           current_requests + 1,
                           null,
                           DateTime.Now.AddMinutes(_API_TIMELIMIT),
                           Cache.NoSlidingExpiration,
                           CacheItemPriority.High,
                           null);
                        }

                        //hit rate limit, wait for another 5 minutes (_API_BLOCKDURATION)
                        else
                        {
                            HttpRuntime.Cache.Insert(throttleBaseKey,
                           DateTime.UtcNow,
                           null,
                           DateTime.Now.AddMinutes(_API_BLOCKDURATION),
                           Cache.NoSlidingExpiration,
                           CacheItemPriority.High,
                           null);

                            HttpRuntime.Cache.Insert(throttleCounterKey,
                          current_requests + 1,
                          null,
                          DateTime.Now.AddMinutes(_API_BLOCKDURATION),
                          Cache.NoSlidingExpiration,
                          CacheItemPriority.High,
                          null);

                            Forbidden(actionContext);
                        }
                    }
                }
            }
            else
            {
                BadRequest(actionContext);
            }

            base.OnActionExecuting(actionContext);
        }

        private string GetThrottleBaseKey(string app_id)
        {
            return Identifier.THROTTLE_BASE_IDENTIFIER + app_id;
        }

        private string GetThrottleCounterKey(string app_id)
        {
            return Identifier.THROTTLE_COUNTER_IDENTIFIER + app_id;
        }

        private void BadRequest(HttpActionContext actionContext)
        {
            actionContext.Response = actionContext.Request.CreateResponse(HttpStatusCode.BadRequest);
        }

        private void Forbidden(HttpActionContext actionContext)
        {
            actionContext.Response = actionContext.Request.CreateResponse(HttpStatusCode.Forbidden, "Application Rate Limit Exceeded");
        }

    }

    public static class Identifier
    {
        public static readonly string THROTTLE_BASE_IDENTIFIER = "LA_THROTTLE_BASE_";
        public static readonly string THROTTLE_COUNTER_IDENTIFIER = "LA_THROTTLE_COUNT_";
    }

Now decorate the required API with [ThrottleAttribute]

Larkins

Perhaps this logic should be implemented higher up the pipeline with a DelegatingHandler learn.microsoft.com/en-us/aspnet/web-api/overview/advanced/… – Conte