Pull request 2006: 6182-fix-fallback-dns

Updates #6182.

Squashed commit of the following:

commit 7467bf851932a878af0eda01c140056a4261b597
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Fri Sep 8 17:29:44 2023 +0300

    dnsforward: imp test

commit b807123d6030012bf9e9a4a0e454983a2e012a96
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Fri Sep 8 17:22:49 2023 +0300

    dnsforward: add test

commit 698fc69e441e9f1e0e4c2878c81309967c058cab
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Fri Sep 8 16:50:39 2023 +0300

    dnsforward: fix more

commit 444ae2870cd78ef736df744d80438b4dae5133ce
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Fri Sep 8 16:32:49 2023 +0300

    all: upd chlog

commit 114ff58c7010528249f27bdc0b2f9bcc537f74c1
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Fri Sep 8 15:59:13 2023 +0300

    dnsforward: fix fallback dns

CHANGELOG.md

@@ -25,10 +25,12 @@ NOTE: Add new changes BELOW THIS COMMENT.
 
 ### Fixed
 
+- Comments in the *Fallback DNS servers* field in the UI ([#6182]).
 - Empty or default Safe Browsing and Parental Control settings ([#6181]).
 - Various UI issues.
 
 [#6181]: https://github.com/AdguardTeam/AdGuardHome/issues/6181
+[#6182]: https://github.com/AdguardTeam/AdGuardHome/issues/6182
 
 <!--
 NOTE: Add new changes ABOVE THIS COMMENT.

internal/dnsforward/dnsforward.go

@@ -614,6 +614,7 @@ func (s *Server) Prepare(conf *ServerConfig) (err error) {
 // setupFallbackDNS initializes the fallback DNS servers.
 func (s *Server) setupFallbackDNS() (err error) {
 	fallbacks := s.conf.FallbackDNS
+	fallbacks = stringutil.FilterOut(fallbacks, IsCommentOrEmpty)
 	if len(fallbacks) == 0 {
 		return nil
 	}

internal/dnsforward/dnsforward_test.go

@@ -372,6 +372,27 @@ func TestServer_timeout(t *testing.T) {
 	})
 }
 
+func TestServer_Prepare_fallbacks(t *testing.T) {
+	srvConf := &ServerConfig{
+		Config: Config{
+			FallbackDNS: []string{
+				"#tls://1.1.1.1",
+				"8.8.8.8",
+			},
+			EDNSClientSubnet: &EDNSClientSubnet{Enabled: false},
+		},
+	}
+
+	s, err := NewServer(DNSCreateParams{})
+	require.NoError(t, err)
+
+	err = s.Prepare(srvConf)
+	require.NoError(t, err)
+	require.NotNil(t, s.dnsProxy.Fallbacks)
+
+	assert.Len(t, s.dnsProxy.Fallbacks.Upstreams, 1)
+}
+
 func TestServerWithProtectionDisabled(t *testing.T) {
 	s := createTestServer(t, &filtering.Config{
 		BlockingMode: filtering.BlockingModeDefault,

internal/dnsforward/http.go

@@ -749,6 +749,7 @@ func (s *Server) handleTestUpstreamDNS(w http.ResponseWriter, r *http.Request) {
 	}
 
 	req.Upstreams = stringutil.FilterOut(req.Upstreams, IsCommentOrEmpty)
+	req.FallbackDNS = stringutil.FilterOut(req.FallbackDNS, IsCommentOrEmpty)
 	req.PrivateUpstreams = stringutil.FilterOut(req.PrivateUpstreams, IsCommentOrEmpty)
 
 	upsNum := len(req.Upstreams) + len(req.FallbackDNS) + len(req.PrivateUpstreams)

internal/dnsforward/http_test.go

@@ -577,6 +577,14 @@ func TestServer_HandleTestUpstreamDNS(t *testing.T) {
 				badUps + ` over tcp: dns: id mismatch`,
 		},
 		name: "fallback_broken",
+	}, {
+		body: map[string]any{
+			"fallback_dns": []string{goodUps, "#this.is.comment"},
+		},
+		wantResp: map[string]any{
+			goodUps: "OK",
+		},
+		name: "fallback_comment_mix",
 	}}
 
 	for _, tc := range testCases {