* (dnsforward): fix reverse lookups from /etc/hosts

There was a bug with empty PTR responses for IPs that are in the hosts
file

Closes: #2085

dnsforward/dnsforward_test.go

@@ -9,13 +9,17 @@ import (
 	"crypto/x509/pkix"
 	"encoding/pem"
 	"fmt"
+	"io/ioutil"
 	"math/big"
 	"net"
+	"os"
 	"sort"
 	"sync"
 	"testing"
 	"time"
 
+	"github.com/AdguardTeam/AdGuardHome/util"
+
 	"github.com/AdguardTeam/AdGuardHome/dhcpd"
 	"github.com/AdguardTeam/AdGuardHome/dnsfilter"
 	"github.com/AdguardTeam/dnsproxy/proxy"
@@ -664,17 +668,17 @@ func TestBlockedBySafeBrowsing(t *testing.T) {
 func TestRewrite(t *testing.T) {
 	c := dnsfilter.Config{}
 	c.Rewrites = []dnsfilter.RewriteEntry{
-		dnsfilter.RewriteEntry{
+		{
 			Domain: "test.com",
 			Answer: "1.2.3.4",
 			Type:   dns.TypeA,
 		},
-		dnsfilter.RewriteEntry{
+		{
 			Domain: "alias.test.com",
 			Answer: "test.com",
 			Type:   dns.TypeCNAME,
 		},
-		dnsfilter.RewriteEntry{
+		{
 			Domain: "my.alias.example.org",
 			Answer: "example.org",
 			Type:   dns.TypeCNAME,
@@ -1066,7 +1070,7 @@ func (d *testDHCP) SetOnLeaseChanged(onLeaseChanged dhcpd.OnLeaseChangedT) {
 	return
 }
 
-func TestPTRResponse(t *testing.T) {
+func TestPTRResponseFromDHCPLeases(t *testing.T) {
 	dhcp := &testDHCP{}
 
 	c := dnsfilter.Config{}
@@ -1094,3 +1098,45 @@ func TestPTRResponse(t *testing.T) {
 
 	s.Close()
 }
+
+func TestPTRResponseFromHosts(t *testing.T) {
+	c := dnsfilter.Config{
+		AutoHosts: &util.AutoHosts{},
+	}
+
+	// Prepare test hosts file
+	hf, _ := ioutil.TempFile("", "")
+	defer func() { _ = os.Remove(hf.Name()) }()
+	defer hf.Close()
+
+	_, _ = hf.WriteString("  127.0.0.1   host # comment \n")
+	_, _ = hf.WriteString("  ::1   localhost#comment  \n")
+
+	// Init auto hosts
+	c.AutoHosts.Init(hf.Name())
+	defer c.AutoHosts.Close()
+
+	f := dnsfilter.New(&c, nil)
+	s := NewServer(DNSCreateParams{DNSFilter: f})
+	s.conf.UDPListenAddr = &net.UDPAddr{Port: 0}
+	s.conf.TCPListenAddr = &net.TCPAddr{Port: 0}
+	s.conf.UpstreamDNS = []string{"127.0.0.1:53"}
+	s.conf.FilteringConfig.ProtectionEnabled = true
+	err := s.Prepare(nil)
+	assert.True(t, err == nil)
+	assert.Nil(t, s.Start())
+
+	addr := s.dnsProxy.Addr(proxy.ProtoUDP)
+	req := createTestMessage("1.0.0.127.in-addr.arpa.")
+	req.Question[0].Qtype = dns.TypePTR
+
+	resp, err := dns.Exchange(req, addr.String())
+	assert.Nil(t, err)
+	assert.Equal(t, 1, len(resp.Answer))
+	assert.Equal(t, dns.TypePTR, resp.Answer[0].Header().Rrtype)
+	assert.Equal(t, "1.0.0.127.in-addr.arpa.", resp.Answer[0].Header().Name)
+	ptr := resp.Answer[0].(*dns.PTR)
+	assert.Equal(t, "host.", ptr.Ptr)
+
+	s.Close()
+}