Added null checks

Author: zbalkan

DnsServerCore/Dns/Security/DnsCookieSecretManager.cs

@@ -183,7 +183,7 @@ public void Rotate()
             {
                 Snapshot currentSnapshot = Volatile.Read(ref _snapshot);
 
-                byte[] previous = currentSnapshot is null ? null : currentSnapshot.CurrentSecret;
+                byte[] previous = currentSnapshot?.CurrentSecret;
                 Snapshot nextSnapshot = GenerateNewSnapshot(previous);
 
                 SaveLocked(nextSnapshot);
@@ -195,13 +195,13 @@ public void Rotate()
         public byte[] GetCurrentSecret()
         {
             Snapshot snapshot = Volatile.Read(ref _snapshot);
-            return snapshot is null ? null : snapshot.CurrentSecret;
+            return snapshot?.CurrentSecret;
         }
 
         public byte[] GetPreviousSecret()
         {
             Snapshot snapshot = Volatile.Read(ref _snapshot);
-            return snapshot is null ? null : snapshot.PreviousSecret;
+            return snapshot?.PreviousSecret;
         }
 
         #endregion

DnsServerCore/Dns/Security/DnsCookieValidator.cs

@@ -253,13 +253,14 @@ public bool Validate(IPAddress clientAddress, EDnsCookieOptionData cookie)
             if (cookie.ClientCookie.Length != ClientCookieLen)
                 return false;
 
-            ReadOnlySpan<byte> currentSecret = _secretManager.GetCurrentSecret();
-            if (!currentSecret.IsEmpty &&
+            byte[] currentSecret = _secretManager.GetCurrentSecret();
+
+            if (currentSecret != null && currentSecret.Length > 0 &&
                 ValidateServerCookieWithSecret(clientAddress, cookie.ClientCookie, cookie.ServerCookie, currentSecret))
                 return true;
 
-            ReadOnlySpan<byte> previousSecret = _secretManager.GetPreviousSecret();
-            if (!previousSecret.IsEmpty &&
+            byte[] previousSecret = _secretManager.GetPreviousSecret();
+            if (previousSecret != null && previousSecret.Length > 0 &&
                 ValidateServerCookieWithSecret(clientAddress, cookie.ClientCookie, cookie.ServerCookie, previousSecret))
                 return true;
 
@@ -277,7 +278,7 @@ public EDnsCookieOptionData CreateResponseCookie(IPAddress clientAddress, EDnsCo
             if (requestCookie.ClientCookie.Length != ClientCookieLen)
                 throw new ArgumentException($"Client cookie must be {ClientCookieLen} bytes.", nameof(requestCookie));
 
-            ReadOnlySpan<byte> currentSecret = _secretManager.GetCurrentSecret();
+            byte[] currentSecret = _secretManager.GetCurrentSecret();
             ValidateSecret(currentSecret);
 
             byte[] serverCookie = ComputeServerCookie(clientAddress, requestCookie.ClientCookie, currentSecret);