chore: add logic + tests for cache invalidation

src/CommonLib/Cache.cs

@@ -1,4 +1,6 @@
-using System.Collections.Concurrent;
+using System;
+using System.Collections.Concurrent;
+using System.ComponentModel;
 using System.Runtime.Serialization;
 using SharpHoundCommonLib.Enums;
 
@@ -18,6 +20,8 @@ public class Cache
         //
         // [DataMember]private ConcurrentDictionary<string, string> _valueToIDCache;
 
+        private static Version defaultVersion = new(1, 0, 0);
+
         private Cache()
         {
             ValueToIdCache = new ConcurrentDictionary<string, string>();
@@ -36,6 +40,8 @@ private Cache()
         [DataMember] public ConcurrentDictionary<string, string> SIDToDomainCache { get; private set; }
 
         [DataMember] public ConcurrentDictionary<string, string> ValueToIdCache { get; private set; }
+        [DataMember] public DateTime CacheCreationDate { get; set; }
+        [DataMember] public Version CacheCreationVersion { get; set; }
 
         [IgnoreDataMember] private static Cache CacheInstance { get; set; }
 
@@ -137,9 +143,17 @@ private static string GetPrefixKey(string key, string domain)
         ///     Creates a new empty cache instance
         /// </summary>
         /// <returns></returns>
-        public static Cache CreateNewCache()
+        public static Cache CreateNewCache(Version version = null)
         {
-            return new Cache();
+            if (version == null)
+            {
+                version = defaultVersion;
+            }
+            return new Cache
+            {
+                CacheCreationVersion = version,
+                CacheCreationDate = DateTime.Now.Date
+            };
         }
 
         /// <summary>
@@ -152,6 +166,22 @@ public static void SetCacheInstance(Cache cache)
             CreateMissingDictionaries();
         }
 
+        public static bool CacheNeedsInvalidation(Cache cache, Version version)
+        {
+            var threshold = DateTime.Now.Subtract(TimeSpan.FromDays(30));
+            if (cache.CacheCreationDate < threshold)
+            {
+                return true;
+            }
+
+            if (cache.CacheCreationVersion == null || version > cache.CacheCreationVersion)
+            {
+                return true;
+            }
+
+            return false;
+        }
+
         /// <summary>
         ///     Gets stats from the currently loaded cache
         /// </summary>

test/unit/CacheTest.cs

@@ -0,0 +1,55 @@
+using System;
+using Newtonsoft.Json;
+using SharpHoundCommonLib;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CommonLibTest
+{
+    public class CacheTest
+    {
+        private ITestOutputHelper _testOutputHelper;
+        public CacheTest(ITestOutputHelper testOutputHelper)
+        {
+            _testOutputHelper = testOutputHelper;
+        }
+
+        [Fact]
+        public void Cache_TestCacheInvalidation()
+        {
+            var cache = Cache.CreateNewCache();
+            var version = new Version(1, 0, 0);
+            cache.CacheCreationVersion = version;
+
+            Assert.True(Cache.CacheNeedsInvalidation(cache, new Version(1,0,1)));
+            Assert.False(Cache.CacheNeedsInvalidation(cache, new Version(1,0,0)));
+
+            var time = DateTime.Now.Subtract(TimeSpan.FromDays(29));
+            cache.CacheCreationDate = time;
+            Assert.False(Cache.CacheNeedsInvalidation(cache, version));
+            cache.CacheCreationDate = DateTime.Now.Subtract(TimeSpan.FromDays(31));
+            Assert.True(Cache.CacheNeedsInvalidation(cache, version));
+        }
+
+        [Fact]
+        public void Cache_TestNewCache()
+        {
+            var cache = Cache.CreateNewCache();
+            Assert.Equal(cache.CacheCreationVersion, new Version(1,0,0));
+            var version = new Version(1, 0, 1);
+            cache = Cache.CreateNewCache(version);
+            var time = DateTime.Now.Date;
+            Assert.Equal(cache.CacheCreationVersion, version);
+            Assert.Equal(cache.CacheCreationDate, time);
+        }
+
+        [Fact]
+        public void Cache_OldCacheWillInvalidate()
+        {
+            const string json = "{\"GlobalCatalogCache\": {}, \"IdToTypeCache\": {}, \"MachineSidCache\": {}, \"SIDToDomainCache\": {}, \"ValueToIdCache\": {}}";
+            var cache = JsonConvert.DeserializeObject<Cache>(json);
+            Assert.Null(cache.CacheCreationVersion);
+            Assert.True(Cache.CacheNeedsInvalidation(cache, new Version(1,0,0)));
+        }
+    }
+}