return NS record for localhost.loki to squash errors in host lookups

llarp/dns/message.cpp

@@ -193,6 +193,31 @@ namespace llarp
       }
     }
 
+    void
+    Message::AddNSReply(std::string name, RR_TTL_t ttl)
+    {
+      if(not questions.empty())
+      {
+        hdr_fields = reply_flags(hdr_fields);
+
+        const auto& question = questions[0];
+        answers.emplace_back();
+        auto& rec                     = answers.back();
+        rec.rr_name                   = question.qname;
+        rec.rr_type                   = qTypeNS;
+        rec.rr_class                  = qClassIN;
+        rec.ttl                       = ttl;
+        std::array< byte_t, 512 > tmp = {{0}};
+        llarp_buffer_t buf(tmp);
+        if(EncodeName(&buf, name))
+        {
+          buf.sz = buf.cur - buf.base;
+          rec.rData.resize(buf.sz);
+          memcpy(rec.rData.data(), buf.base, buf.sz);
+        }
+      }
+    }
+
     void
     Message::AddCNAMEReply(std::string name, RR_TTL_t ttl)
     {

llarp/dns/message.hpp

@@ -69,6 +69,9 @@ namespace llarp
       void
       AddAReply(std::string name, RR_TTL_t ttl = 1);
 
+      void
+      AddNSReply(std::string name, RR_TTL_t ttl = 1);
+
       bool
       Encode(llarp_buffer_t* buf) const override;
 

llarp/handlers/tun.cpp

@@ -513,7 +513,8 @@ namespace llarp
         const bool isV4 = msg.questions[0].qtype == dns::qTypeA;
         llarp::service::Address addr;
         if(isV6 && !SupportsV6())
-        { // empty reply but not a NXDOMAIN so that client can retry IPv4
+        {  // empty reply but not a NXDOMAIN so that client can retry IPv4
+          msg.AddNSReply("localhost.loki.");
         }
         // on MacOS this is a typeA query
         else if(is_random_snode(msg))