RateLimitComparison.cs

using System;
using System.Threading.Tasks;
using System.Xml;
using Waher.Content;
using Waher.Content.Xml.Attributes;
using Waher.Networking.HTTP.Interfaces;
using Waher.Runtime.IO;
using Waher.Runtime.Threading;
 
namespace Waher.Security.WAF.Model.Comparisons
{
    public abstract class RateLimitComparison : LimitComparison
    {
        private readonly DurationAttribute duration;
 
        public RateLimitComparison()
            : base()
        {
        }
 
        public RateLimitComparison(XmlElement Xml, WafAction Parent, WebApplicationFirewall Document)
            : base(Xml, Parent, Document)
        {
            this.duration = new DurationAttribute(Xml, "duration");
        }
 
        protected Task<Duration> EvaluateDurationAsync(ProcessingState State)
        {
            return this.duration.EvaluateAsync(State.Variables, Duration.Zero);
        }
 
        public async Task<WafResult?> ReviewIncrement(ProcessingState State, long Delta)
        {
            string Key = State.Request.RemoteEndPoint.RemovePortNumber() + "|Count";
            long Count;
 
            using (Semaphore Semaphore = await Semaphores.BeginWrite(Key))
            {
                if (State.TryGetCachedObject(Key, out RateCounter Counter))
                    Counter.Count += Delta;
                else
                {
                    Duration Duration = await this.EvaluateDurationAsync(State);
 
                    Counter = new RateCounter()
                    {
                        Count = Delta
                    };
 
                    State.AddToCache(Key, Counter, DateTime.UtcNow + Duration);
                }
 
                Count = Counter.Count;
            }
 
            return await this.Review(State, Count);
        }
 
        private class RateCounter
        {
            public long Count = 0;
        }
    }
}