Pull request: 5972-ip-dupl-ans

Updates #5972.

Squashed commit of the following:

commit 0e089f9ff8fd7e6d7cb53aa7c3b92435d1d41a81
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Tue Jul 11 15:33:16 2023 +0300

    dnsforward: imp code

commit 39527c078fd9ad6ea4906659e185d54e74ef6465
Merge: 03641b0b5 61ed74374
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Tue Jul 11 11:29:19 2023 +0300

    Merge remote-tracking branch 'origin/master' into 5972-ip-dupl-ans

    # Conflicts:
    #	CHANGELOG.md

commit 03641b0b511f8e48d386be76d0a4776296cf047d
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Mon Jul 10 14:03:28 2023 +0300

    all: dupl ips in answer

CHANGELOG.md

@@ -66,6 +66,7 @@ In this release, the schema version has changed from 23 to 24.
 
 ### Fixed
 
+- Two unspecified IPs when a host is blocked in two filter lists ([#5972]).
 - Incorrect setting of Parental Control cache size.
 - Excessive RAM and CPU consumption by Safe Browsing and Parental Control
   filters ([#5896]).
@@ -81,6 +82,7 @@ In this release, the schema version has changed from 23 to 24.
   image, and reload it from scratch.
 
 [#5896]: https://github.com/AdguardTeam/AdGuardHome/issues/5896
+[#5972]: https://github.com/AdguardTeam/AdGuardHome/issues/5972
 
 <!--
 NOTE: Add new changes ABOVE THIS COMMENT.

internal/dnsforward/filter_test.go

@@ -21,6 +21,8 @@ func TestHandleDNSRequest_filterDNSResponse(t *testing.T) {
 ||cname.specific^$dnstype=~CNAME
 ||0.0.0.1^$dnstype=~A
 ||::1^$dnstype=~AAAA
+0.0.0.0 duplicate.domain
+0.0.0.0 duplicate.domain
 `
 
 	forwardConf := ServerConfig{
@@ -137,6 +139,17 @@ func TestHandleDNSRequest_filterDNSResponse(t *testing.T) {
 			},
 			A: netutil.IPv4Zero(),
 		}},
+	}, {
+		req:  createTestMessage("duplicate.domain."),
+		name: "duplicate_domain",
+		wantAns: []dns.RR{&dns.A{
+			Hdr: dns.RR_Header{
+				Name:   "duplicate.domain.",
+				Rrtype: dns.TypeA,
+				Class:  dns.ClassINET,
+			},
+			A: netutil.IPv4Zero(),
+		}},
 	}}
 
 	for _, tc := range testCases {

internal/dnsforward/msg.go

@@ -26,11 +26,25 @@ func (s *Server) makeResponse(req *dns.Msg) (resp *dns.Msg) {
 	return resp
 }
 
-// ipsFromRules extracts non-IP addresses from the filtering result rules.
+// containsIP returns true if the IP is already in the list.
+func containsIP(ips []net.IP, ip net.IP) bool {
+	for _, a := range ips {
+		if a.Equal(ip) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// ipsFromRules extracts unique non-IP addresses from the filtering result
+// rules.
 func ipsFromRules(resRules []*filtering.ResultRule) (ips []net.IP) {
 	for _, r := range resRules {
-		if r.IP != nil {
+		// len(resRules) and len(ips) are actually small enough for O(n^2) to do
-			ips = append(ips, r.IP)
+		// not raise performance questions.
+		if ip := r.IP; ip != nil && !containsIP(ips, ip) {
+			ips = append(ips, ip)
 		}
 	}