Pull request 1943: 6046 Local PTR

Merge in DNS/adguard-home from 6046-local-ptr to master

Updates #6046.

Squashed commit of the following:

commit 3e90815f29173d2f68970278bd7b1b29cc0a4465
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jul 27 18:17:41 2023 +0300

    all: log changes

commit 7639f6f785670c15911fb3ca20abeb4e2b8f8582
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jul 27 17:40:49 2023 +0300

    all: fix 0 ttl ptr

internal/dnsforward/dnsforward_test.go

@@ -1374,6 +1374,24 @@ func TestServer_Exchange(t *testing.T) {
 	refusingUpstream := aghtest.NewUpstreamMock(func(req *dns.Msg) (resp *dns.Msg, err error) {
 		return new(dns.Msg).SetRcode(req, dns.RcodeRefused), nil
 	})
+	zeroTTLUps := &aghtest.UpstreamMock{
+		OnAddress: func() (addr string) { return "zero.ttl.example" },
+		OnExchange: func(req *dns.Msg) (resp *dns.Msg, err error) {
+			resp = new(dns.Msg).SetReply(req)
+			hdr := dns.RR_Header{
+				Name:   req.Question[0].Name,
+				Rrtype: dns.TypePTR,
+				Class:  dns.ClassINET,
+				Ttl:    0,
+			}
+			resp.Answer = []dns.RR{&dns.PTR{
+				Hdr: hdr,
+				Ptr: localDomainHost,
+			}}
+
+			return resp, nil
+		},
+	}
 
 	srv := &Server{
 		recDetector: newRecursionDetector(0, 1),
@@ -1445,6 +1463,13 @@ func TestServer_Exchange(t *testing.T) {
 		locUpstream: nil,
 		req:         twosIP,
 		wantTTL:     defaultTTL * 2,
+	}, {
+		name:        "zero_ttl",
+		want:        localDomainHost,
+		wantErr:     nil,
+		locUpstream: zeroTTLUps,
+		req:         localIP,
+		wantTTL:     0,
 	}}
 
 	for _, tc := range testCases {
@@ -1468,6 +1493,7 @@ func TestServer_Exchange(t *testing.T) {
 
 	t.Run("resolving_disabled", func(t *testing.T) {
 		srv.conf.UsePrivateRDNS = false
+		t.Cleanup(func() { srv.conf.UsePrivateRDNS = true })
 
 		host, _, eerr := srv.Exchange(localIP)