Pull request: 1868 fix rdns

Merge in DNS/adguard-home from 1868-rdns-ipv6 to master

Updates #2943.
Updates #2704.

Squashed commit of the following:

commit 53d67ecf17ed4f9c544344288b58f3596c7246e2
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Apr 13 16:18:33 2021 +0300

    all: imp code, docs

commit 2bc15941b87f92b6fa0a7568538e02700a4385a3
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Apr 13 16:09:08 2021 +0300

    all: imp code

internal/dnsforward/clientid_test.go

@@ -16,7 +16,7 @@ import (
 // testTLSConn is a tlsConn for tests.
 type testTLSConn struct {
 	// Conn is embedded here simply to make testTLSConn a net.Conn without
-	// acctually implementing all methods.
+	// actually implementing all methods.
 	net.Conn
 
 	serverName string

internal/dnsforward/stats_test.go

@@ -18,7 +18,7 @@ import (
 // testQueryLog is a simple querylog.QueryLog implementation for tests.
 type testQueryLog struct {
 	// QueryLog is embedded here simply to make testQueryLog
-	// a querylog.QueryLog without acctually implementing all methods.
+	// a querylog.QueryLog without actually implementing all methods.
 	querylog.QueryLog
 
 	lastParams querylog.AddParams
@@ -32,7 +32,7 @@ func (l *testQueryLog) Add(p querylog.AddParams) {
 // testStats is a simple stats.Stats implementation for tests.
 type testStats struct {
 	// Stats is embedded here simply to make testStats a stats.Stats without
-	// acctually implementing all methods.
+	// actually implementing all methods.
 	stats.Stats
 
 	lastEntry stats.Entry

internal/dnsforward/util_test.go

@@ -0,0 +1,60 @@
+package dnsforward
+
+import (
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// fakeAddr is a mock implementation of net.Addr interface to simplify testing.
+type fakeAddr struct {
+	// Addr is embedded here simply to make fakeAddr a net.Addr without
+	// actually implementing all methods.
+	net.Addr
+}
+
+func TestIPFromAddr(t *testing.T) {
+	supIPv4 := net.IP{1, 2, 3, 4}
+	supIPv6 := net.ParseIP("2a00:1450:400c:c06::93")
+
+	testCases := []struct {
+		name string
+		addr net.Addr
+		want net.IP
+	}{{
+		name: "ipv4_tcp",
+		addr: &net.TCPAddr{
+			IP: supIPv4,
+		},
+		want: supIPv4,
+	}, {
+		name: "ipv6_tcp",
+		addr: &net.TCPAddr{
+			IP: supIPv6,
+		},
+		want: supIPv6,
+	}, {
+		name: "ipv4_udp",
+		addr: &net.UDPAddr{
+			IP: supIPv4,
+		},
+		want: supIPv4,
+	}, {
+		name: "ipv6_udp",
+		addr: &net.UDPAddr{
+			IP: supIPv6,
+		},
+		want: supIPv6,
+	}, {
+		name: "non-ip_addr",
+		addr: &fakeAddr{},
+		want: nil,
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			assert.Equal(t, tc.want, IPFromAddr(tc.addr))
+		})
+	}
+}