From 849df07c731660eddfba40fd899678905d094ddc Mon Sep 17 00:00:00 2001
From: Shreyas Zare <shreyas@technitium.com>
Date: Sat, 12 Dec 2020 16:40:06 +0530
Subject: [PATCH] DnsServer: returning format error response when domain name
 is invalid. Setting recursion available flag in response for auth zone when
 recursion is desired since dns clients like nslookup and dig complain about
 it otherwise.

---
 DnsServerCore/Dns/DnsServer.cs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/DnsServerCore/Dns/DnsServer.cs b/DnsServerCore/Dns/DnsServer.cs
index baf8b0f4..0c10f1f4 100644
--- a/DnsServerCore/Dns/DnsServer.cs
+++ b/DnsServerCore/Dns/DnsServer.cs
@@ -926,6 +926,11 @@ namespace DnsServerCore.Dns
                                 return await ProcessRecursiveQueryAsync(request, null, null, !inAllowedZone, false);
                         }
                     }
+                    catch (InvalidDomainNameException)
+                    {
+                        //format error response
+                        return new DnsDatagram(request.Identifier, true, request.OPCODE, false, false, request.RecursionDesired, IsRecursionAllowed(remoteEP), false, false, DnsResponseCode.FormatError, request.Question);
+                    }
                     catch (Exception ex)
                     {
                         LogManager log = _log;
@@ -1087,6 +1092,9 @@ namespace DnsServerCore.Dns
                 }
             }
 
+            if (response.RecursionAvailable != isRecursionAllowed)
+                response = new DnsDatagram(response.Identifier, response.IsResponse, response.OPCODE, response.AuthoritativeAnswer, response.Truncation, response.RecursionDesired, isRecursionAllowed, response.AuthenticData, response.CheckingDisabled, response.RCODE, response.Question, response.Answer, response.Authority, response.Additional);
+
             return Task.FromResult(response);
         }