From e9ea621b93fbb58d9edfca8375918791637bbd52 Mon Sep 17 00:00:00 2001
From: chai <chaifix@163.com>
Date: Wed, 30 Dec 2020 20:59:04 +0800
Subject: +init

---
 .../Impostor.Hazel/Udp/UdpConnectionRateLimit.cs   | 75 ++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 Impostor-dev/src/Impostor.Hazel/Udp/UdpConnectionRateLimit.cs

(limited to 'Impostor-dev/src/Impostor.Hazel/Udp/UdpConnectionRateLimit.cs')

diff --git a/Impostor-dev/src/Impostor.Hazel/Udp/UdpConnectionRateLimit.cs b/Impostor-dev/src/Impostor.Hazel/Udp/UdpConnectionRateLimit.cs
new file mode 100644
index 0000000..64881d3
--- /dev/null
+++ b/Impostor-dev/src/Impostor.Hazel/Udp/UdpConnectionRateLimit.cs
@@ -0,0 +1,75 @@
+using System;
+using System.Collections.Concurrent;
+using System.Net;
+using System.Threading;
+using Serilog;
+
+namespace Impostor.Hazel.Udp
+{
+    public class UdpConnectionRateLimit : IDisposable
+    {
+        private static readonly ILogger Logger = Log.ForContext<UdpConnectionRateLimit>();
+
+        // Allow burst to 5 connections.
+        // Decrease by 1 every second.
+        private const int MaxConnections = 5;
+        private const int FalloffMs = 1000;
+
+        private readonly ConcurrentDictionary<IPAddress, int> _connectionCount;
+        private readonly Timer _timer;
+        private bool _isDisposed;
+
+        public UdpConnectionRateLimit()
+        {
+            _connectionCount = new ConcurrentDictionary<IPAddress, int>();
+            _timer = new Timer(UpdateRateLimit, null, FalloffMs, Timeout.Infinite);
+        }
+
+        private void UpdateRateLimit(object state)
+        {
+            try
+            {
+                foreach (var pair in _connectionCount)
+                {
+                    var count = pair.Value - 1;
+                    if (count > 0)
+                    {
+                        _connectionCount.TryUpdate(pair.Key, count, pair.Value);
+                    }
+                    else
+                    {
+                        _connectionCount.TryRemove(pair);
+                    }
+                }
+            }
+            catch (Exception e)
+            {
+                Logger.Error(e, "Exception caught in UpdateRateLimit.");
+            }
+            finally
+            {
+                if (!_isDisposed)
+                {
+                    _timer.Change(FalloffMs, Timeout.Infinite);
+                }
+            }
+        }
+
+        public bool IsAllowed(IPAddress key)
+        {
+            if (_connectionCount.TryGetValue(key, out var value) && value >= MaxConnections)
+            {
+                return false;
+            }
+
+            _connectionCount.AddOrUpdate(key, _ => 1, (_, i) => i + 1);
+            return true;
+        }
+
+        public void Dispose()
+        {
+            _isDisposed = true;
+            _timer.Dispose();
+        }
+    }
+}
\ No newline at end of file
-- 
cgit v1.1-26-g67d0