From 4540a4e94ad204fc1cba9e15b95ce9b684ed2335 Mon Sep 17 00:00:00 2001
From: Simon Zolin <s.zolin@adguard.com>
Date: Thu, 19 Dec 2019 11:52:21 +0300
Subject: [PATCH] - DNS: set RecursionAvailable flag in response message

---
 dnsforward/dnsforward.go | 35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/dnsforward/dnsforward.go b/dnsforward/dnsforward.go
index c3c05ad7..ccfa410b 100644
--- a/dnsforward/dnsforward.go
+++ b/dnsforward/dnsforward.go
@@ -635,8 +635,7 @@ func (s *Server) filterDNSRequest(d *proxy.DNSContext) (*dnsfilter.Result, error
 		d.Res = s.genDNSFilterMessage(d, &res)
 
 	} else if res.Reason == dnsfilter.ReasonRewrite && len(res.IPList) != 0 {
-		resp := dns.Msg{}
-		resp.SetReply(req)
+		resp := s.makeResponse(req)
 
 		name := host
 		if len(res.CanonName) != 0 {
@@ -657,7 +656,7 @@ func (s *Server) filterDNSRequest(d *proxy.DNSContext) (*dnsfilter.Result, error
 			}
 		}
 
-		d.Res = &resp
+		d.Res = resp
 	}
 
 	return &res, err
@@ -711,6 +710,15 @@ func (s *Server) filterResponse(d *proxy.DNSContext) (*dnsfilter.Result, error)
 	return nil, nil
 }
 
+// Create a DNS response by DNS request and set necessary flags
+func (s *Server) makeResponse(req *dns.Msg) *dns.Msg {
+	resp := dns.Msg{}
+	resp.SetReply(req)
+	resp.RecursionAvailable = true
+	resp.Compress = true
+	return &resp
+}
+
 // genDNSFilterMessage generates a DNS message corresponding to the filtering result
 func (s *Server) genDNSFilterMessage(d *proxy.DNSContext, result *dnsfilter.Result) *dns.Msg {
 	m := d.Req
@@ -758,17 +766,15 @@ func (s *Server) genServerFailure(request *dns.Msg) *dns.Msg {
 }
 
 func (s *Server) genARecord(request *dns.Msg, ip net.IP) *dns.Msg {
-	resp := dns.Msg{}
-	resp.SetReply(request)
+	resp := s.makeResponse(request)
 	resp.Answer = append(resp.Answer, s.genAAnswer(request, ip))
-	return &resp
+	return resp
 }
 
 func (s *Server) genAAAARecord(request *dns.Msg, ip net.IP) *dns.Msg {
-	resp := dns.Msg{}
-	resp.SetReply(request)
+	resp := s.makeResponse(request)
 	resp.Answer = append(resp.Answer, s.genAAAAAnswer(request, ip))
-	return &resp
+	return resp
 }
 
 func (s *Server) genAAnswer(req *dns.Msg, ip net.IP) *dns.A {
@@ -804,9 +810,8 @@ func (s *Server) genResponseWithIP(req *dns.Msg, ip net.IP) *dns.Msg {
 	}
 
 	// empty response
-	resp := dns.Msg{}
-	resp.SetReply(req)
-	return &resp
+	resp := s.makeResponse(req)
+	return resp
 }
 
 func (s *Server) genBlockedHost(request *dns.Msg, newAddr string, d *proxy.DNSContext) *dns.Msg {
@@ -834,9 +839,7 @@ func (s *Server) genBlockedHost(request *dns.Msg, newAddr string, d *proxy.DNSCo
 		return s.genServerFailure(request)
 	}
 
-	resp := dns.Msg{}
-	resp.SetReply(request)
-	resp.Authoritative, resp.RecursionAvailable = true, true
+	resp := s.makeResponse(request)
 	if newContext.Res != nil {
 		for _, answer := range newContext.Res.Answer {
 			answer.Header().Name = request.Question[0].Name
@@ -844,7 +847,7 @@ func (s *Server) genBlockedHost(request *dns.Msg, newAddr string, d *proxy.DNSCo
 		}
 	}
 
-	return &resp
+	return resp
 }
 
 // Make a CNAME response