Implement MDNS cache expiration

Author: jdomnitz

TinyDNS/RecordCache.cs TinyDNS/Cache/RecordCache.csTinyDNS/RecordCache.cs renamed to TinyDNS/Cache/RecordCache.cs

@@ -13,30 +13,19 @@
 using System.Collections.Concurrent;
 using System.Net;
 
-namespace TinyDNS
+namespace TinyDNS.Cache
 {
     internal sealed class RecordCache
     {
-        private struct RecordEntry : IEquatable<RecordEntry>
-        {
-            public Message message;
-            public IPAddress Address;
-
-            public bool Equals(RecordEntry other)
-            {
-                if (Address.Equals(other.Address))
-                    return message.Equals(other.message);
-
-                return false;
-            }
-        }
-
         readonly int sizeLimit;
+        readonly TimeSpan ttl;
         private readonly ConcurrentStack<RecordEntry> stack = new ConcurrentStack<RecordEntry>();
 
-        public RecordCache(int sizeLimit)
+        public RecordCache(int sizeLimit, TimeSpan ttl)
         {
             this.sizeLimit = sizeLimit;
+            this.ttl = ttl;
+
         }
 
         public void Clear()
@@ -46,15 +35,27 @@ public void Clear()
 
         public bool Cached(Message message, IPAddress endPoint)
         {
+            Expire();
             RecordEntry entry = new RecordEntry();
             entry.message = message;
             entry.Address = endPoint;
+            entry.Time = DateTime.Now;
             if (stack.Contains(entry))
                 return true;
             stack.Push(entry);
             if (stack.Count > sizeLimit)
                 stack.TryPop(out _);
             return false;
         }
+
+        private void Expire()
+        {
+            while (stack.TryPeek(out RecordEntry entry))
+            {
+                if (entry.Time + ttl > DateTime.Now)
+                    return;
+                stack.TryPop(out _);
+            }
+        }
     }
 }

TinyDNS/Cache/RecordEntry.cs

@@ -0,0 +1,31 @@
+// TinyDNS Copyright (C) 2024 
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or any later version.
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY, without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU Affero General Public License for more details.
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using System.Net;
+
+namespace TinyDNS.Cache
+{
+    internal struct RecordEntry : IEquatable<RecordEntry>
+    {
+        public DateTime Time;
+        public Message message;
+        public IPAddress Address;
+
+        public bool Equals(RecordEntry other)
+        {
+            if (Address.Equals(other.Address))
+                return message.Equals(other.message);
+
+            return false;
+        }
+    }
+}

TinyDNS/MDNS.cs

@@ -14,6 +14,7 @@
 using System.Net.NetworkInformation;
 using System.Net.Sockets;
 using System.Runtime.InteropServices;
+using TinyDNS.Cache;
 using TinyDNS.Enums;
 using TinyDNS.Events;
 using TinyDNS.Records;
@@ -33,7 +34,7 @@ public class MDNS : IDisposable
 
         public delegate Task MessageEventHandler(DNSMsgEvent e);
         public event MessageEventHandler? AnswerReceived;
-        private readonly RecordCache messageCache = new RecordCache(25);
+        private readonly RecordCache messageCache = new RecordCache(100, TimeSpan.FromSeconds(5));
         private readonly bool UNICAST_SUPPORTED;
 
         public MDNS()
@@ -60,8 +61,7 @@ public async Task Start()
             NetworkInterface[] nics = NetworkInterface.GetAllNetworkInterfaces();
             foreach (NetworkInterface nic in nics)
             {
-                if (nic.OperationalStatus != OperationalStatus.Up ||
-                    !nic.SupportsMulticast ||
+                if (nic.OperationalStatus != OperationalStatus.Up || !nic.SupportsMulticast ||
                     nic.NetworkInterfaceType == NetworkInterfaceType.Tunnel ||
                     nic.NetworkInterfaceType == NetworkInterfaceType.Loopback ||
                     nic.IsReceiveOnly)