dns server code refactoring done.

DnsServerCore/Dns/ResolverPrefetchDnsCache.cs

@@ -0,0 +1,54 @@
+/*
+Technitium DNS Server
+Copyright (C) 2019  Shreyas Zare (shreyas@technitium.com)
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) 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 General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+using TechnitiumLibrary.Net.Dns;
+
+namespace DnsServerCore.Dns
+{
+    class ResolverPrefetchDnsCache : ResolverDnsCache
+    {
+        #region variables
+
+        readonly DnsQuestionRecord _prefetchQuery;
+
+        #endregion
+
+        #region constructor
+
+        public ResolverPrefetchDnsCache(Zone cacheZoneRoot, DnsQuestionRecord prefetchQuery)
+            : base(cacheZoneRoot)
+        {
+            _prefetchQuery = prefetchQuery;
+        }
+
+        #endregion
+
+        #region public
+
+        public override DnsDatagram Query(DnsDatagram request)
+        {
+            if (_prefetchQuery.Equals(request.Question[0]))
+                return _cacheZoneRoot.QueryCacheGetClosestNameServers(request); //return closest name servers so that the recursive resolver queries them to refreshes cache instead of returning response from cache
+
+            return _cacheZoneRoot.Query(request);
+        }
+
+        #endregion
+    }
+}