From 1f5abecefc0c50e5f6e12ab054407e7d3365d59f Mon Sep 17 00:00:00 2001
From: Stanislav Chzhen <s.chzhen@adguard.com>
Date: Wed, 30 Aug 2023 13:21:31 +0300
Subject: [PATCH] Pull request 1975: 3701-fallback-dns-api

Squashed commit of the following:

commit 0f96137c629d7df99d40e479f66dd78248185ca3
Merge: 0d640fe37 aac36a2d2
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Wed Aug 30 12:53:03 2023 +0300

    Merge branch 'master' into 3701-fallback-dns-api

commit 0d640fe37a563d9fcea1ff4b6c86f37629af0ebd
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Wed Aug 30 12:49:05 2023 +0300

    dnsforward: imp tests

commit 6b7f7aad76566b70852146bc6629ae7fb71eec09
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Aug 25 18:51:34 2023 +0300

    client: add fallback dns field

commit c2ac7e3656431f7d44645786296e58ac7d012fed
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Thu Aug 24 13:22:07 2023 +0300

    all: add fallback dns api
---
 client/src/__locales/en.json                  |  5 +-
 client/src/actions/dnsConfig.js               |  4 ++
 .../components/Settings/Dns/Upstream/Form.js  | 25 ++++++++
 .../components/Settings/Dns/Upstream/index.js |  4 ++
 client/src/reducers/dnsConfig.js              |  2 +
 internal/dnsforward/config.go                 |  3 +-
 internal/dnsforward/http.go                   | 27 ++++++++
 internal/dnsforward/http_test.go              |  4 ++
 .../TestDNSForwardHTTP_handleGetConfig.json   |  9 +++
 .../TestDNSForwardHTTP_handleSetConfig.json   | 61 +++++++++++++++++++
 openapi/CHANGELOG.md                          |  6 ++
 openapi/openapi.yaml                          | 10 +++
 12 files changed, 158 insertions(+), 2 deletions(-)

diff --git a/client/src/__locales/en.json b/client/src/__locales/en.json
index b8e72b3f..d4673e5e 100644
--- a/client/src/__locales/en.json
+++ b/client/src/__locales/en.json
@@ -8,11 +8,14 @@
     "load_balancing_desc": "Query one upstream server at a time. AdGuard Home uses its weighted random algorithm to pick the server so that the fastest server is used more often.",
     "bootstrap_dns": "Bootstrap DNS servers",
     "bootstrap_dns_desc": "IP addresses of DNS servers used to resolve IP addresses of the DoH/DoT resolvers you specify as upstreams. Comments are not permitted.",
+    "fallback_dns_title": "Fallback DNS servers",
+    "fallback_dns_desc": "List of fallback DNS servers used when upstream DNS servers are not responding. The syntax is the same as in the main upstreams field above.",
+    "fallback_dns_placeholder": "Enter one fallback DNS server per line",
     "local_ptr_title": "Private reverse DNS servers",
     "local_ptr_desc": "The DNS servers that AdGuard Home uses for local PTR queries. These servers are used to resolve PTR requests for addresses in private IP ranges, for example \"192.168.12.34\", using reverse DNS. If not set, AdGuard Home uses the addresses of the default DNS resolvers of your OS except for the addresses of AdGuard Home itself.",
     "local_ptr_default_resolver": "By default, AdGuard Home uses the following reverse DNS resolvers: {{ip}}.",
     "local_ptr_no_default_resolver": "AdGuard Home could not determine suitable private reverse DNS resolvers for this system.",
-    "local_ptr_placeholder": "Enter one server address per line",
+    "local_ptr_placeholder": "Enter one IP address per line",
     "resolve_clients_title": "Enable reverse resolving of clients' IP addresses",
     "resolve_clients_desc": "Reversely resolve clients' IP addresses into their hostnames by sending PTR queries to corresponding resolvers (private DNS servers for local clients, upstream servers for clients with public IP addresses).",
     "use_private_ptr_resolvers_title": "Use private reverse DNS resolvers",
diff --git a/client/src/actions/dnsConfig.js b/client/src/actions/dnsConfig.js
index f8141fd5..47823f66 100644
--- a/client/src/actions/dnsConfig.js
+++ b/client/src/actions/dnsConfig.js
@@ -50,6 +50,10 @@ export const setDnsConfig = (config) => async (dispatch) => {
             data.bootstrap_dns = splitByNewLine(config.bootstrap_dns);
             hasDnsSettings = true;
         }
+        if (Object.prototype.hasOwnProperty.call(data, 'fallback_dns')) {
+            data.fallback_dns = splitByNewLine(config.fallback_dns);
+            hasDnsSettings = true;
+        }
         if (Object.prototype.hasOwnProperty.call(data, 'local_ptr_upstreams')) {
             data.local_ptr_upstreams = splitByNewLine(config.local_ptr_upstreams);
             hasDnsSettings = true;
diff --git a/client/src/components/Settings/Dns/Upstream/Form.js b/client/src/components/Settings/Dns/Upstream/Form.js
index be01b2b7..3c534f0c 100644
--- a/client/src/components/Settings/Dns/Upstream/Form.js
+++ b/client/src/components/Settings/Dns/Upstream/Form.js
@@ -179,6 +179,30 @@ const Form = ({
                 <Examples />
                 <hr />
             </div>
+            <div className="col-12">
+                <label
+                    className="form__label form__label--with-desc"
+                    htmlFor="fallback_dns"
+                >
+                    <Trans>fallback_dns_title</Trans>
+                </label>
+                <div className="form__desc form__desc--top">
+                    <Trans>fallback_dns_desc</Trans>
+                </div>
+                <Field
+                    id="fallback_dns"
+                    name="fallback_dns"
+                    component={renderTextareaField}
+                    type="text"
+                    className="form-control form-control--textarea form-control--textarea-small font-monospace"
+                    placeholder={t('fallback_dns_placeholder')}
+                    disabled={processingSetConfig}
+                    normalizeOnBlur={removeEmptyLines}
+                />
+            </div>
+            <div className="col-12">
+                <hr />
+            </div>
             <div className="col-12 mb-2">
                 <label
                     className="form__label form__label--with-desc"
@@ -286,6 +310,7 @@ Form.propTypes = {
     invalid: PropTypes.bool,
     initialValues: PropTypes.object,
     upstream_dns: PropTypes.string,
+    fallback_dns: PropTypes.string,
     bootstrap_dns: PropTypes.string,
 };
 
diff --git a/client/src/components/Settings/Dns/Upstream/index.js b/client/src/components/Settings/Dns/Upstream/index.js
index 05dc929e..f085a55d 100644
--- a/client/src/components/Settings/Dns/Upstream/index.js
+++ b/client/src/components/Settings/Dns/Upstream/index.js
@@ -10,6 +10,7 @@ const Upstream = () => {
     const dispatch = useDispatch();
     const {
         upstream_dns,
+        fallback_dns,
         bootstrap_dns,
         upstream_mode,
         resolve_clients,
@@ -21,6 +22,7 @@ const Upstream = () => {
 
     const handleSubmit = (values) => {
         const {
+            fallback_dns,
             bootstrap_dns,
             upstream_dns,
             upstream_mode,
@@ -30,6 +32,7 @@ const Upstream = () => {
         } = values;
 
         const dnsConfig = {
+            fallback_dns,
             bootstrap_dns,
             upstream_mode,
             resolve_clients,
@@ -52,6 +55,7 @@ const Upstream = () => {
                 <Form
                     initialValues={{
                         upstream_dns: upstreamDns,
+                        fallback_dns,
                         bootstrap_dns,
                         upstream_mode,
                         resolve_clients,
diff --git a/client/src/reducers/dnsConfig.js b/client/src/reducers/dnsConfig.js
index fbc3afdb..47dd4d67 100644
--- a/client/src/reducers/dnsConfig.js
+++ b/client/src/reducers/dnsConfig.js
@@ -15,6 +15,7 @@ const dnsConfig = handleActions(
                 blocking_ipv4,
                 blocking_ipv6,
                 upstream_dns,
+                fallback_dns,
                 bootstrap_dns,
                 local_ptr_upstreams,
                 ...values
@@ -26,6 +27,7 @@ const dnsConfig = handleActions(
                 blocking_ipv4: blocking_ipv4 || DEFAULT_BLOCKING_IPV4,
                 blocking_ipv6: blocking_ipv6 || DEFAULT_BLOCKING_IPV6,
                 upstream_dns: (upstream_dns && upstream_dns.join('\n')) || '',
+                fallback_dns: (fallback_dns && fallback_dns.join('\n')) || '',
                 bootstrap_dns: (bootstrap_dns && bootstrap_dns.join('\n')) || '',
                 local_ptr_upstreams: (local_ptr_upstreams && local_ptr_upstreams.join('\n')) || '',
                 processingGetConfig: false,
diff --git a/internal/dnsforward/config.go b/internal/dnsforward/config.go
index a59b8a8e..331310dc 100644
--- a/internal/dnsforward/config.go
+++ b/internal/dnsforward/config.go
@@ -118,7 +118,8 @@ type FilteringConfig struct {
 	// resolvers (plain DNS only).
 	BootstrapDNS []string `yaml:"bootstrap_dns"`
 
-	// FallbackDNS is the list of fallback DNS servers.
+	// FallbackDNS is the list of fallback DNS servers used when upstream DNS
+	// servers are not responding.
 	FallbackDNS []string `yaml:"fallback_dns"`
 
 	// AllServers, if true, parallel queries to all configured upstream servers
diff --git a/internal/dnsforward/http.go b/internal/dnsforward/http.go
index 3be25372..431e979a 100644
--- a/internal/dnsforward/http.go
+++ b/internal/dnsforward/http.go
@@ -36,6 +36,10 @@ type jsonDNSConfig struct {
 	// upstream DoH/DoT resolvers.
 	Bootstraps *[]string `json:"bootstrap_dns"`
 
+	// Fallbacks is the list of fallback DNS servers used when upstream DNS
+	// servers are not responding.
+	Fallbacks *[]string `json:"fallback_dns"`
+
 	// ProtectionEnabled defines if protection is enabled.
 	ProtectionEnabled *bool `json:"protection_enabled"`
 
@@ -108,6 +112,7 @@ func (s *Server) getDNSConfig() (c *jsonDNSConfig) {
 	upstreams := stringutil.CloneSliceOrEmpty(s.conf.UpstreamDNS)
 	upstreamFile := s.conf.UpstreamDNSFileName
 	bootstraps := stringutil.CloneSliceOrEmpty(s.conf.BootstrapDNS)
+	fallbacks := stringutil.CloneSliceOrEmpty(s.conf.FallbackDNS)
 	blockingMode := s.conf.BlockingMode
 	blockingIPv4 := s.conf.BlockingIPv4
 	blockingIPv6 := s.conf.BlockingIPv6
@@ -143,6 +148,7 @@ func (s *Server) getDNSConfig() (c *jsonDNSConfig) {
 		Upstreams:                &upstreams,
 		UpstreamsFile:            &upstreamFile,
 		Bootstraps:               &bootstraps,
+		Fallbacks:                &fallbacks,
 		ProtectionEnabled:        &protectionEnabled,
 		BlockingMode:             &blockingMode,
 		BlockingIPv4:             blockingIPv4,
@@ -207,6 +213,20 @@ func (req *jsonDNSConfig) checkBootstrap() (err error) {
 	return nil
 }
 
+// checkFallbacks returns an error if any fallback address is invalid.
+func (req *jsonDNSConfig) checkFallbacks() (err error) {
+	if req.Fallbacks == nil {
+		return nil
+	}
+
+	err = ValidateUpstreams(*req.Fallbacks)
+	if err != nil {
+		return fmt.Errorf("validating fallback servers: %w", err)
+	}
+
+	return nil
+}
+
 // validate returns an error if any field of req is invalid.
 func (req *jsonDNSConfig) validate(privateNets netutil.SubnetSet) (err error) {
 	if req.Upstreams != nil {
@@ -228,6 +248,11 @@ func (req *jsonDNSConfig) validate(privateNets netutil.SubnetSet) (err error) {
 		return err
 	}
 
+	err = req.checkFallbacks()
+	if err != nil {
+		return err
+	}
+
 	err = req.checkBlockingMode()
 	if err != nil {
 		return err
@@ -341,6 +366,7 @@ func (s *Server) setConfigRestartable(dc *jsonDNSConfig) (shouldRestart bool) {
 		setIfNotNil(&s.conf.LocalPTRResolvers, dc.LocalPTRUpstreams),
 		setIfNotNil(&s.conf.UpstreamDNSFileName, dc.UpstreamsFile),
 		setIfNotNil(&s.conf.BootstrapDNS, dc.Bootstraps),
+		setIfNotNil(&s.conf.FallbackDNS, dc.Fallbacks),
 		setIfNotNil(&s.conf.EDNSClientSubnet.Enabled, dc.EDNSCSEnabled),
 		setIfNotNil(&s.conf.EDNSClientSubnet.UseCustom, dc.EDNSCSUseCustom),
 		setIfNotNil(&s.conf.CacheSize, dc.CacheSize),
@@ -730,6 +756,7 @@ func (s *Server) handleTestUpstreamDNS(w http.ResponseWriter, r *http.Request) {
 	result := make(map[string]string, upsNum)
 	resCh := make(chan upsCheckResult, upsNum)
 
+	// TODO(s.chzhen):  Check fallback DNS servers.
 	for _, ups := range req.Upstreams {
 		go func(ups string) {
 			resCh <- upsCheckResult{
diff --git a/internal/dnsforward/http_test.go b/internal/dnsforward/http_test.go
index 9746e4ed..11a1a53f 100644
--- a/internal/dnsforward/http_test.go
+++ b/internal/dnsforward/http_test.go
@@ -72,6 +72,7 @@ func TestDNSForwardHTTP_handleGetConfig(t *testing.T) {
 			ProtectionEnabled: true,
 			BlockingMode:      BlockingModeDefault,
 			UpstreamDNS:       []string{"8.8.8.8:53", "8.8.4.4:53"},
+			FallbackDNS:       []string{"9.9.9.10"},
 			EDNSClientSubnet:  &EDNSClientSubnet{Enabled: false},
 		},
 		ConfigModified: func() {},
@@ -225,6 +226,9 @@ func TestDNSForwardHTTP_handleSetConfig(t *testing.T) {
 	}, {
 		name:    "local_ptr_upstreams_null",
 		wantSet: "",
+	}, {
+		name:    "fallbacks",
+		wantSet: "",
 	}}
 
 	var data map[string]struct {
diff --git a/internal/dnsforward/testdata/TestDNSForwardHTTP_handleGetConfig.json b/internal/dnsforward/testdata/TestDNSForwardHTTP_handleGetConfig.json
index 11c8766d..d2f4680d 100644
--- a/internal/dnsforward/testdata/TestDNSForwardHTTP_handleGetConfig.json
+++ b/internal/dnsforward/testdata/TestDNSForwardHTTP_handleGetConfig.json
@@ -11,6 +11,9 @@
       "2620:fe::10",
       "2620:fe::fe:10"
     ],
+    "fallback_dns": [
+      "9.9.9.10"
+    ],
     "protection_enabled": true,
     "protection_disabled_until": null,
     "ratelimit": 0,
@@ -43,6 +46,9 @@
       "2620:fe::10",
       "2620:fe::fe:10"
     ],
+    "fallback_dns": [
+      "9.9.9.10"
+    ],
     "protection_enabled": true,
     "protection_disabled_until": null,
     "ratelimit": 0,
@@ -75,6 +81,9 @@
       "2620:fe::10",
       "2620:fe::fe:10"
     ],
+    "fallback_dns": [
+      "9.9.9.10"
+    ],
     "protection_enabled": true,
     "protection_disabled_until": null,
     "ratelimit": 0,
diff --git a/internal/dnsforward/testdata/TestDNSForwardHTTP_handleSetConfig.json b/internal/dnsforward/testdata/TestDNSForwardHTTP_handleSetConfig.json
index 3404471f..232acba3 100644
--- a/internal/dnsforward/testdata/TestDNSForwardHTTP_handleSetConfig.json
+++ b/internal/dnsforward/testdata/TestDNSForwardHTTP_handleSetConfig.json
@@ -18,6 +18,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -54,6 +55,7 @@
       "bootstrap_dns": [
         "9.9.9.10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -91,6 +93,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -128,6 +131,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -165,6 +169,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 6,
@@ -202,6 +207,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -241,6 +247,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -280,6 +287,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -317,6 +325,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -354,6 +363,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -391,6 +401,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -428,6 +439,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -467,6 +479,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -506,6 +519,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -544,6 +558,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -581,6 +596,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -620,6 +636,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -662,6 +679,7 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
@@ -699,6 +717,49 @@
         "2620:fe::10",
         "2620:fe::fe:10"
       ],
+      "fallback_dns": [],
+      "protection_enabled": true,
+      "protection_disabled_until": null,
+      "ratelimit": 0,
+      "blocking_mode": "default",
+      "blocking_ipv4": "",
+      "blocking_ipv6": "",
+      "edns_cs_enabled": false,
+      "dnssec_enabled": false,
+      "disable_ipv6": false,
+      "upstream_mode": "",
+      "cache_size": 0,
+      "cache_ttl_min": 0,
+      "cache_ttl_max": 0,
+      "cache_optimistic": false,
+      "resolve_clients": false,
+      "use_private_ptr_resolvers": false,
+      "local_ptr_upstreams": [],
+      "edns_cs_use_custom": false,
+      "edns_cs_custom_ip": ""
+    }
+  },
+  "fallbacks": {
+    "req": {
+      "fallback_dns": [
+        "9.9.9.10"
+      ]
+    },
+    "want": {
+      "upstream_dns": [
+        "8.8.8.8:53",
+        "8.8.4.4:53"
+      ],
+      "upstream_dns_file": "",
+      "bootstrap_dns": [
+        "9.9.9.10",
+        "149.112.112.10",
+        "2620:fe::10",
+        "2620:fe::fe:10"
+      ],
+      "fallback_dns": [
+        "9.9.9.10"
+      ],
       "protection_enabled": true,
       "protection_disabled_until": null,
       "ratelimit": 0,
diff --git a/openapi/CHANGELOG.md b/openapi/CHANGELOG.md
index 667dff8c..9ae20255 100644
--- a/openapi/CHANGELOG.md
+++ b/openapi/CHANGELOG.md
@@ -6,6 +6,12 @@
 
 ## v0.107.37: API changes
 
+### The new field `"fallback_dns"` in `DNSConfig` object
+
+* The new field `"fallback_dns"` in `GET /control/dns_info` and `POST
+  /control/dns_config` is the list of fallback DNS servers used when upstream
+  DNS servers are not responding.
+
 ### Deprecated blocked services APIs
 
 * The `GET /control/blocked_services/list` HTTP API; use the new `GET
diff --git a/openapi/openapi.yaml b/openapi/openapi.yaml
index 89a1a1c1..497cb210 100644
--- a/openapi/openapi.yaml
+++ b/openapi/openapi.yaml
@@ -1432,6 +1432,16 @@
           'example':
           - 'tls://1.1.1.1'
           - 'tls://1.0.0.1'
+        'fallback_dns':
+          'type': 'array'
+          'description': >
+            List of fallback DNS servers used when upstream DNS servers are not
+            responding.  Empty value will clear the list.
+          'items':
+            'type': 'string'
+          'example':
+          - '8.8.8.8'
+          - '1.1.1.1:53'
         'upstream_dns_file':
           'type': 'string'
         'protection_enabled':