/* Technitium DNS Server Copyright (C) 2021 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 . */ using DnsApplicationCommon; using Newtonsoft.Json; using System; using System.Collections.Generic; using System.Net; using System.Threading.Tasks; using TechnitiumLibrary.Net; using TechnitiumLibrary.Net.Dns; using TechnitiumLibrary.Net.Dns.ResourceRecords; namespace SplitHorizon { public class SimpleCNAME : IDnsApplicationRequestHandler { #region IDisposable public void Dispose() { //do nothing } #endregion #region public public Task InitializeAsync(IDnsServer dnsServer, string config) { //no config needed return Task.CompletedTask; } public Task ProcessRequestAsync(DnsDatagram request, IPEndPoint remoteEP, string zoneName, uint appRecordTtl, string appRecordData, bool isRecursionAllowed, IDnsServer dnsServer) { dynamic jsonAppRecordData = JsonConvert.DeserializeObject(appRecordData); dynamic jsonCname; if (NetUtilities.IsPrivateIP(remoteEP.Address)) jsonCname = jsonAppRecordData.@private; else jsonCname = jsonAppRecordData.@public; if (jsonCname == null) return Task.FromResult(null); string cname = jsonCname.Value; if (string.IsNullOrEmpty(cname)) return Task.FromResult(null); IReadOnlyList answers; if (request.Question[0].Name.Equals(zoneName, StringComparison.OrdinalIgnoreCase)) //check for zone apex answers = new DnsResourceRecord[] { new DnsResourceRecord(request.Question[0].Name, DnsResourceRecordType.ANAME, DnsClass.IN, appRecordTtl, new DnsANAMERecord(cname)) }; //use ANAME else answers = new DnsResourceRecord[] { new DnsResourceRecord(request.Question[0].Name, DnsResourceRecordType.CNAME, DnsClass.IN, appRecordTtl, new DnsCNAMERecord(cname)) }; return Task.FromResult(new DnsDatagram(request.Identifier, true, request.OPCODE, true, false, request.RecursionDesired, isRecursionAllowed, false, false, DnsResponseCode.NoError, request.Question, answers)); } #endregion #region properties public string Description { get { return "Returns different CNAME record for clients querying over public and private networks. Note that the app will return ANAME record for an APP record at zone apex."; } } public string ApplicationRecordDataTemplate { get { return @"{ ""public"": ""api.example.com"", ""private"": ""api.example.corp"" }"; } } #endregion } }