Pull request: 3136 show default resolvers

Merge in DNS/adguard-home from 3136-show-default to master

Closes #3136.

Squashed commit of the following:

commit add09a772dddcccd404056e7649c2d3350a79fec
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Jun 1 11:11:24 2021 +0300

    openapi: fix typo

commit 69e402c49318d53a0d03b81207644d9fb04a139a
Merge: 76e8492c e17e1f20
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Jun 1 11:09:51 2021 +0300

    Merge branch 'master' into 3136-show-default

commit 76e8492c8da679e204ceb7a77f1c6f73a2488040
Author: Ildar Kamalov <ik@adguard.com>
Date:   Tue Jun 1 10:55:09 2021 +0300

    client: check upstreams

commit 05fe6ea196a1ed9386eec25dbfbe22779fe7bcfd
Author: Vlad <v.abdulmyanov@adguard.com>
Date:   Mon May 31 19:23:35 2021 +0300

    add defaul resolvers line

commit 8d63c7df9947c9588478d1173834b42569fd8951
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon May 31 11:56:08 2021 +0300

    all: imp changelog

commit e3912e3b20eca9dcf90ddddaa5edb54d1e0cfe6e
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri May 28 20:23:05 2021 +0300

    all: add local ptr resolvers addresses output

internal/dnsforward/dnsforward.go

@@ -76,6 +76,7 @@ type Server struct {
 	ipset          ipsetCtx
 	subnetDetector *aghnet.SubnetDetector
 	localResolvers *proxy.Proxy
+	sysResolvers   aghnet.SystemResolvers
 	recDetector    *recursionDetector
 
 	tableHostToIP     hostToIPTable
@@ -154,6 +155,13 @@ func NewServer(p DNSCreateParams) (s *Server, err error) {
 		recDetector:       newRecursionDetector(recursionTTL, cachedRecurrentReqNum),
 	}
 
+	// TODO(e.burkov): Enable the refresher after the actual implementation
+	// passes the public testing.
+	s.sysResolvers, err = aghnet.NewSystemResolvers(0, nil)
+	if err != nil {
+		return nil, fmt.Errorf("initializing system resolvers: %w", err)
+	}
+
 	if p.DHCPServer != nil {
 		s.dhcpServer = p.DHCPServer
 		s.dhcpServer.SetOnLeaseChanged(s.onDHCPLeaseChanged)
@@ -375,28 +383,11 @@ func (s *Server) collectDNSIPAddrs() (addrs []string, err error) {
 	return addrs[:i], nil
 }
 
-// setupResolvers initializes the resolvers for local addresses.  For internal
-// use only.
-func (s *Server) setupResolvers(localAddrs []string) (err error) {
-	bootstraps := s.conf.BootstrapDNS
-	if len(localAddrs) == 0 {
-		var sysRes aghnet.SystemResolvers
-		// TODO(e.burkov): Enable the refresher after the actual
-		// implementation passes the public testing.
-		sysRes, err = aghnet.NewSystemResolvers(0, nil)
-		if err != nil {
-			return err
-		}
-
-		localAddrs = sysRes.Get()
-		bootstraps = nil
-	}
-	log.Debug("upstreams to resolve PTR for local addresses: %v", localAddrs)
-
+func (s *Server) filterOurDNSAddrs(addrs []string) (filtered []string, err error) {
 	var ourAddrs []string
 	ourAddrs, err = s.collectDNSIPAddrs()
 	if err != nil {
-		return err
+		return nil, err
 	}
 
 	ourAddrsSet := aghstrings.NewSet(ourAddrs...)
@@ -405,7 +396,24 @@ func (s *Server) setupResolvers(localAddrs []string) (err error) {
 	// really applicable here since in case of listening on all network
 	// interfaces we should check the whole interface's network to cut off
 	// all the loopback addresses as well.
-	localAddrs = aghstrings.FilterOut(localAddrs, ourAddrsSet.Has)
+	return aghstrings.FilterOut(addrs, ourAddrsSet.Has), nil
+}
+
+// setupResolvers initializes the resolvers for local addresses.  For internal
+// use only.
+func (s *Server) setupResolvers(localAddrs []string) (err error) {
+	bootstraps := s.conf.BootstrapDNS
+	if len(localAddrs) == 0 {
+		localAddrs = s.sysResolvers.Get()
+		bootstraps = nil
+	}
+
+	localAddrs, err = s.filterOurDNSAddrs(localAddrs)
+	if err != nil {
+		return err
+	}
+
+	log.Debug("upstreams to resolve PTR for local addresses: %v", localAddrs)
 
 	var upsConfig proxy.UpstreamConfig
 	upsConfig, err = proxy.ParseUpstreamsConfig(localAddrs, upstream.Options{

internal/dnsforward/http.go

@@ -96,12 +96,25 @@ func (s *Server) getDNSConfig() dnsConfig {
 }
 
 func (s *Server) handleGetConfig(w http.ResponseWriter, r *http.Request) {
-	resp := s.getDNSConfig()
+	defLocalPTRUps, err := s.filterOurDNSAddrs(s.sysResolvers.Get())
+	if err != nil {
+		log.Debug("getting dns configuration: %s", err)
+	}
+
+	resp := struct {
+		dnsConfig
+		// DefautLocalPTRUpstreams is used to pass the addresses from
+		// systemResolvers to the front-end.  It's not a pointer to the slice
+		// since there is no need to omit it while decoding from JSON.
+		DefautLocalPTRUpstreams []string `json:"default_local_ptr_upstreams,omitempty"`
+	}{
+		dnsConfig:               s.getDNSConfig(),
+		DefautLocalPTRUpstreams: defLocalPTRUps,
+	}
 
 	w.Header().Set("Content-Type", "application/json")
 
-	enc := json.NewEncoder(w)
-	if err := enc.Encode(resp); err != nil {
+	if err = json.NewEncoder(w).Encode(resp); err != nil {
 		httpError(r, w, http.StatusInternalServerError, "json.Encoder: %s", err)
 		return
 	}

internal/dnsforward/http_test.go

@@ -12,11 +12,25 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/AdguardTeam/AdGuardHome/internal/aghnet"
 	"github.com/AdguardTeam/AdGuardHome/internal/filtering"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
+// fakeSystemResolvers is a mock aghnet.SystemResolvers implementation for tests.
+type fakeSystemResolvers struct {
+	// SystemResolvers is embedded here simply to make *fakeSystemResolvers
+	// an aghnet.SystemResolvers without actually implementing all methods.
+	aghnet.SystemResolvers
+}
+
+// Get implements the aghnet.SystemResolvers interface for *fakeSystemResolvers.
+// It always returns nil.
+func (fsr *fakeSystemResolvers) Get() (rs []string) {
+	return nil
+}
+
 func loadTestData(t *testing.T, casesFileName string, cases interface{}) {
 	t.Helper()
 
@@ -52,6 +66,8 @@ func TestDNSForwardHTTTP_handleGetConfig(t *testing.T) {
 		ConfigModified: func() {},
 	}
 	s := createTestServer(t, filterConf, forwardConf, nil)
+	s.sysResolvers = &fakeSystemResolvers{}
+
 	require.Nil(t, s.Start())
 	t.Cleanup(func() {
 		require.Nil(t, s.Stop())
@@ -125,6 +141,7 @@ func TestDNSForwardHTTTP_handleSetConfig(t *testing.T) {
 		ConfigModified: func() {},
 	}
 	s := createTestServer(t, filterConf, forwardConf, nil)
+	s.sysResolvers = &fakeSystemResolvers{}
 
 	defaultConf := s.conf