Pull request: all: add srv handling to dnsrewrite filters

Closes #2498.
Updates #2533.

Squashed commit of the following:

commit 452e0e7d281c1f10bef069bf7a73205266b8f1e0
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Mar 12 19:33:18 2021 +0300

    all: add srv handling to dnsrewrite filters

internal/dnsforward/dnsrewrite.go

@@ -20,7 +20,8 @@ func (s *Server) filterDNSRewriteResponse(req *dns.Msg, rr rules.RRType, v rules
 	// the answer generation logic from the Server.
 
 	switch rr {
-	case dns.TypeA, dns.TypeAAAA:
+	case dns.TypeA,
+		dns.TypeAAAA:
 		ip, ok := v.(net.IP)
 		if !ok {
 			return nil, fmt.Errorf("value for rr type %d has type %T, not net.IP", rr, v)
@@ -62,6 +63,13 @@ func (s *Server) filterDNSRewriteResponse(req *dns.Msg, rr rules.RRType, v rules
 		}
 
 		return s.genAnswerSVCB(req, svcb), nil
+	case dns.TypeSRV:
+		srv, ok := v.(*rules.DNSSRV)
+		if !ok {
+			return nil, fmt.Errorf("value for rr type %d has type %T, not *rules.DNSSRV", rr, v)
+		}
+
+		return s.genAnswerSRV(req, srv), nil
 	default:
 		log.Debug("don't know how to handle dns rr type %d, skipping", rr)
 

internal/dnsforward/dnsrewrite_test.go

@@ -14,18 +14,24 @@ import (
 
 func TestServer_FilterDNSRewrite(t *testing.T) {
 	// Helper data.
+	const domain = "example.com"
 	ip4 := net.IP{127, 0, 0, 1}
 	ip6 := net.IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}
-	mx := &rules.DNSMX{
+	mxVal := &rules.DNSMX{
 		Exchange:   "mail.example.com",
 		Preference: 32,
 	}
-	svcb := &rules.DNSSVCB{
+	svcbVal := &rules.DNSSVCB{
 		Params:   map[string]string{"alpn": "h3"},
-		Target:   "example.com",
+		Target:   domain,
 		Priority: 32,
 	}
-	const domain = "example.com"
+	srvVal := &rules.DNSSRV{
+		Priority: 32,
+		Weight:   60,
+		Port:     8080,
+		Target:   domain,
+	}
 
 	// Helper functions and entities.
 	srv := &Server{}
@@ -125,7 +131,7 @@ func TestServer_FilterDNSRewrite(t *testing.T) {
 
 	t.Run("noerror_mx", func(t *testing.T) {
 		req := makeQ(dns.TypeMX)
-		res := makeRes(dns.RcodeSuccess, dns.TypeMX, mx)
+		res := makeRes(dns.RcodeSuccess, dns.TypeMX, mxVal)
 		d := &proxy.DNSContext{}
 
 		err := srv.filterDNSRewrite(req, res, d)
@@ -136,13 +142,13 @@ func TestServer_FilterDNSRewrite(t *testing.T) {
 		ans, ok := d.Res.Answer[0].(*dns.MX)
 
 		require.True(t, ok)
-		assert.Equal(t, mx.Exchange, ans.Mx)
-		assert.Equal(t, mx.Preference, ans.Preference)
+		assert.Equal(t, mxVal.Exchange, ans.Mx)
+		assert.Equal(t, mxVal.Preference, ans.Preference)
 	})
 
 	t.Run("noerror_svcb", func(t *testing.T) {
 		req := makeQ(dns.TypeSVCB)
-		res := makeRes(dns.RcodeSuccess, dns.TypeSVCB, svcb)
+		res := makeRes(dns.RcodeSuccess, dns.TypeSVCB, svcbVal)
 		d := &proxy.DNSContext{}
 
 		err := srv.filterDNSRewrite(req, res, d)
@@ -154,14 +160,14 @@ func TestServer_FilterDNSRewrite(t *testing.T) {
 		require.True(t, ok)
 
 		assert.Equal(t, dns.SVCB_ALPN, ans.Value[0].Key())
-		assert.Equal(t, svcb.Params["alpn"], ans.Value[0].String())
-		assert.Equal(t, svcb.Target, ans.Target)
-		assert.Equal(t, svcb.Priority, ans.Priority)
+		assert.Equal(t, svcbVal.Params["alpn"], ans.Value[0].String())
+		assert.Equal(t, svcbVal.Target, ans.Target)
+		assert.Equal(t, svcbVal.Priority, ans.Priority)
 	})
 
 	t.Run("noerror_https", func(t *testing.T) {
 		req := makeQ(dns.TypeHTTPS)
-		res := makeRes(dns.RcodeSuccess, dns.TypeHTTPS, svcb)
+		res := makeRes(dns.RcodeSuccess, dns.TypeHTTPS, svcbVal)
 		d := &proxy.DNSContext{}
 
 		err := srv.filterDNSRewrite(req, res, d)
@@ -173,8 +179,27 @@ func TestServer_FilterDNSRewrite(t *testing.T) {
 
 		require.True(t, ok)
 		assert.Equal(t, dns.SVCB_ALPN, ans.Value[0].Key())
-		assert.Equal(t, svcb.Params["alpn"], ans.Value[0].String())
-		assert.Equal(t, svcb.Target, ans.Target)
-		assert.Equal(t, svcb.Priority, ans.Priority)
+		assert.Equal(t, svcbVal.Params["alpn"], ans.Value[0].String())
+		assert.Equal(t, svcbVal.Target, ans.Target)
+		assert.Equal(t, svcbVal.Priority, ans.Priority)
+	})
+
+	t.Run("noerror_srv", func(t *testing.T) {
+		req := makeQ(dns.TypeSRV)
+		res := makeRes(dns.RcodeSuccess, dns.TypeSRV, srvVal)
+		d := &proxy.DNSContext{}
+
+		err := srv.filterDNSRewrite(req, res, d)
+		require.Nil(t, err)
+		assert.Equal(t, dns.RcodeSuccess, d.Res.Rcode)
+
+		require.Len(t, d.Res.Answer, 1)
+		ans, ok := d.Res.Answer[0].(*dns.SRV)
+
+		require.True(t, ok)
+		assert.Equal(t, srvVal.Priority, ans.Priority)
+		assert.Equal(t, srvVal.Weight, ans.Weight)
+		assert.Equal(t, srvVal.Port, ans.Port)
+		assert.Equal(t, srvVal.Target, ans.Target)
 	})
 }

internal/dnsforward/msg.go

@@ -136,7 +136,7 @@ func (s *Server) genAnswerCNAME(req *dns.Msg, cname string) (ans *dns.CNAME) {
 
 func (s *Server) genAnswerMX(req *dns.Msg, mx *rules.DNSMX) (ans *dns.MX) {
 	return &dns.MX{
-		Hdr:        s.hdr(req, dns.TypePTR),
+		Hdr:        s.hdr(req, dns.TypeMX),
 		Preference: mx.Preference,
 		Mx:         mx.Exchange,
 	}
@@ -149,6 +149,16 @@ func (s *Server) genAnswerPTR(req *dns.Msg, ptr string) (ans *dns.PTR) {
 	}
 }
 
+func (s *Server) genAnswerSRV(req *dns.Msg, srv *rules.DNSSRV) (ans *dns.SRV) {
+	return &dns.SRV{
+		Hdr:      s.hdr(req, dns.TypeSRV),
+		Priority: srv.Priority,
+		Weight:   srv.Weight,
+		Port:     srv.Port,
+		Target:   srv.Target,
+	}
+}
+
 func (s *Server) genAnswerTXT(req *dns.Msg, strs []string) (ans *dns.TXT) {
 	return &dns.TXT{
 		Hdr: s.hdr(req, dns.TypeTXT),