Pull request: all: custom autohost tlds

Updates #2393. Squashed commit of the following: commit 87034134e240480938cdeec14d6b44294bf6442c Author: Ainar Garipov <A.Garipov@AdGuard.COM> Date: Thu Mar 25 15:48:46 2021 +0300 dnsforward: fix commit abf3a1ce8ed7a148d1cc631007fb0422f6da4ae6 Author: Ainar Garipov <A.Garipov@AdGuard.COM> Date: Thu Mar 25 15:21:11 2021 +0300 dnsforward: imp code, validation commit fac389bdafc093ce17a7e0831166b89293b550be Author: Ainar Garipov <A.Garipov@AdGuard.COM> Date: Thu Mar 25 14:54:45 2021 +0300 all: add validation, imp docs, tests commit 21b4532afe59f3b89383cb330c9a7d49ec124b6e Author: Ainar Garipov <A.Garipov@AdGuard.COM> Date: Wed Mar 24 19:09:43 2021 +0300 all: custom autohost tlds
2024-08-16 22:20:30 +03:00 · 2021-03-25 16:00:27 +03:00 · 2021-03-25 16:00:27 +03:00 · a7f9e0122b
commit a7f9e0122b
parent ba3fc242ab
12 changed files with 389 additions and 121 deletions
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@ -15,6 +15,7 @@ and this project adheres to

 ### Added

+- The ability to set a custom TLD for known local-network hosts ([#2393]).
 - The ability to serve DNS queries on multiple hosts and interfaces ([#1401]).
 - `ips` and `text` DHCP server options ([#2385]).
 - `SRV` records support in `$dnsrewrite` filters ([#2533]).
@ -41,6 +42,7 @@ and this project adheres to

 [#1401]: https://github.com/AdguardTeam/AdGuardHome/issues/1401
 [#2385]: https://github.com/AdguardTeam/AdGuardHome/issues/2385
+[#2393]: https://github.com/AdguardTeam/AdGuardHome/issues/2393
 [#2412]: https://github.com/AdguardTeam/AdGuardHome/issues/2412
 [#2498]: https://github.com/AdguardTeam/AdGuardHome/issues/2498
 [#2533]: https://github.com/AdguardTeam/AdGuardHome/issues/2533
--- a/internal/dnsforward/clientid.go
+++ b/internal/dnsforward/clientid.go
@ -10,20 +10,31 @@ import (
 	"github.com/lucas-clemente/quic-go"
 )

-const maxDomainPartLen = 64
+// maxDomainLabelLen is the maximum allowed length of a domain name label
+// according to RFC 1035.
+const maxDomainLabelLen = 63
+
+// validateDomainNameLabel returns an error if label is not a valid label of
+// a domain name.
+func validateDomainNameLabel(label string) (err error) {
+	if len(label) > maxDomainLabelLen {
+		return fmt.Errorf("%q is too long, max: %d", label, maxDomainLabelLen)
+	}
+
+	for i, r := range label {
+		if (r < 'a' || r > 'z') && (r < '0' || r > '9') && r != '-' {
+			return fmt.Errorf("invalid char %q at index %d in %q", r, i, label)
+		}
+	}
+
+	return nil
+}

 // ValidateClientID returns an error if clientID is not a valid client ID.
 func ValidateClientID(clientID string) (err error) {
-	if len(clientID) > maxDomainPartLen {
-		return fmt.Errorf("client id %q is too long, max: %d", clientID, maxDomainPartLen)
-	}
-
-	for i, r := range clientID {
-		if (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') || r == '-' {
-			continue
-		}
-
-		return fmt.Errorf("invalid char %q at index %d in client id %q", r, i, clientID)
+	err = validateDomainNameLabel(clientID)
+	if err != nil {
+		return fmt.Errorf("invalid client id: %w", err)
 	}

 	return nil
@ -49,7 +60,8 @@ func clientIDFromClientServerName(hostSrvName, cliSrvName string, strict bool) (
 	clientID = cliSrvName[:len(cliSrvName)-len(hostSrvName)-1]
 	err = ValidateClientID(clientID)
 	if err != nil {
-		return "", fmt.Errorf("invalid client id: %w", err)
+		// Don't wrap the error, because it's informative enough as is.
+		return "", err
 	}

 	return clientID, nil
@ -93,7 +105,7 @@ func processClientIDHTTPS(ctx *dnsContext) (rc resultCode) {

 	err := ValidateClientID(clientID)
 	if err != nil {
-		ctx.err = fmt.Errorf("client id check: invalid client id: %w", err)
+		ctx.err = fmt.Errorf("client id check: %w", err)

 		return resultCodeError
 	}
--- a/internal/dnsforward/clientid_test.go
+++ b/internal/dnsforward/clientid_test.go
@ -118,7 +118,7 @@ func TestProcessClientID(t *testing.T) {
 		cliSrvName:   "!!!.example.com",
 		wantClientID: "",
 		wantErrMsg: `client id check: invalid client id: invalid char '!' ` +
-			`at index 0 in client id "!!!"`,
+			`at index 0 in "!!!"`,
 		wantRes:   resultCodeError,
 		strictSNI: true,
 	}, {
@ -128,9 +128,9 @@ func TestProcessClientID(t *testing.T) {
 		cliSrvName: `abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmno` +
 			`pqrstuvwxyz0123456789.example.com`,
 		wantClientID: "",
-		wantErrMsg: `client id check: invalid client id: client id "abcdefghijklmno` +
+		wantErrMsg: `client id check: invalid client id: "abcdefghijklmno` +
 			`pqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz0123456789" ` +
-			`is too long, max: 64`,
+			`is too long, max: 63`,
 		wantRes:   resultCodeError,
 		strictSNI: true,
 	}, {
@ -182,9 +182,9 @@ func TestProcessClientID(t *testing.T) {
 			assert.Equal(t, tc.wantClientID, dctx.clientID)

 			if tc.wantErrMsg == "" {
-				assert.Nil(t, dctx.err)
+				assert.NoError(t, dctx.err)
 			} else {
-				require.NotNil(t, dctx.err)
+				require.Error(t, dctx.err)
 				assert.Equal(t, tc.wantErrMsg, dctx.err.Error())
 			}
 		})
@ -239,7 +239,7 @@ func TestProcessClientID_https(t *testing.T) {
 		path:         "/dns-query/!!!",
 		wantClientID: "",
 		wantErrMsg: `client id check: invalid client id: invalid char '!'` +
-			` at index 0 in client id "!!!"`,
+			` at index 0 in "!!!"`,
 		wantRes: resultCodeError,
 	}}

@ -263,9 +263,10 @@ func TestProcessClientID_https(t *testing.T) {
 			assert.Equal(t, tc.wantClientID, dctx.clientID)

 			if tc.wantErrMsg == "" {
-				assert.Nil(t, dctx.err)
+				assert.NoError(t, dctx.err)
 			} else {
-				require.NotNil(t, dctx.err)
+				require.Error(t, dctx.err)
+
 				assert.Equal(t, tc.wantErrMsg, dctx.err.Error())
 			}
 		})
--- a/internal/dnsforward/config.go
+++ b/internal/dnsforward/config.go
@ -277,7 +277,7 @@ func (s *Server) prepareUpstreamSettings() error {
 			s := util.SplitNext(&d, '\n')
 			upstreams = append(upstreams, s)
 		}
-		log.Debug("DNS: using %d upstream servers from file %s", len(upstreams), s.conf.UpstreamDNSFileName)
+		log.Debug("dns: using %d upstream servers from file %s", len(upstreams), s.conf.UpstreamDNSFileName)
 	} else {
 		upstreams = s.conf.UpstreamDNS
 	}
@ -357,11 +357,11 @@ func (s *Server) prepareTLS(proxyConfig *proxy.Config) error {
 		}
 		if len(x.DNSNames) != 0 {
 			s.conf.dnsNames = x.DNSNames
-			log.Debug("DNS: using DNS names from certificate's SAN: %v", x.DNSNames)
+			log.Debug("dns: using DNS names from certificate's SAN: %v", x.DNSNames)
 			sort.Strings(s.conf.dnsNames)
 		} else {
 			s.conf.dnsNames = append(s.conf.dnsNames, x.Subject.CommonName)
-			log.Debug("DNS: using DNS name from certificate's CN: %s", x.Subject.CommonName)
+			log.Debug("dns: using DNS name from certificate's CN: %s", x.Subject.CommonName)
 		}
 	}

@ -377,7 +377,7 @@ func (s *Server) prepareTLS(proxyConfig *proxy.Config) error {
 // If the server name (from SNI) supplied by client is incorrect - we terminate the ongoing TLS handshake.
 func (s *Server) onGetCertificate(ch *tls.ClientHelloInfo) (*tls.Certificate, error) {
 	if s.conf.StrictSNICheck && !matchDNSName(s.conf.dnsNames, ch.ServerName) {
-		log.Info("DNS: TLS: unknown SNI in Client Hello: %s", ch.ServerName)
+		log.Info("dns: tls: unknown SNI in Client Hello: %s", ch.ServerName)
 		return nil, fmt.Errorf("invalid SNI")
 	}
 	return &s.conf.cert, nil
--- a/internal/dnsforward/dns.go
+++ b/internal/dnsforward/dns.go
@ -15,6 +15,8 @@ import (

 // To transfer information between modules
 type dnsContext struct {
+	// TODO(a.garipov): Remove this and rewrite processors to be methods of
+	// *Server instead.
 	srv      *Server
 	proxyCtx *proxy.DNSContext
 	// setts are the filtering settings for the client.
@ -75,7 +77,7 @@ func (s *Server) handleDNSRequest(_ *proxy.Proxy, d *proxy.DNSContext) error {
 	// appropriate handler.
 	mods := []modProcessFunc{
 		processInitial,
-		processInternalHosts,
+		s.processInternalHosts,
 		processInternalIPAddrs,
 		processClientID,
 		processFilteringBeforeRequest,
@ -136,7 +138,7 @@ func isHostnameOK(hostname string) bool {
 			(c >= 'A' && c <= 'Z') ||
 			(c >= '0' && c <= '9') ||
 			c == '.' || c == '-') {
-			log.Debug("DNS: skipping invalid hostname %s from DHCP", hostname)
+			log.Debug("dns: skipping invalid hostname %s from DHCP", hostname)
 			return false
 		}
 	}
@ -172,7 +174,7 @@ func (s *Server) onDHCPLeaseChanged(flags int) {
 		hostToIP[lowhost] = ip
 	}

-	log.Debug("DNS: added %d A/PTR entries from DHCP", len(m))
+	log.Debug("dns: added %d A/PTR entries from DHCP", len(m))

 	s.tableHostToIPLock.Lock()
 	s.tableHostToIP = hostToIP
@ -183,20 +185,22 @@ func (s *Server) onDHCPLeaseChanged(flags int) {
 	s.tablePTRLock.Unlock()
 }

-// Respond to A requests if the target host name is associated with a lease from our DHCP server
-func processInternalHosts(ctx *dnsContext) (rc resultCode) {
-	s := ctx.srv
-	req := ctx.proxyCtx.Req
-	if !(req.Question[0].Qtype == dns.TypeA || req.Question[0].Qtype == dns.TypeAAAA) {
+// processInternalHosts respond to A requests if the target hostname is known to
+// the server.
+//
+// TODO(a.garipov): Adapt to AAAA as well.
+func (s *Server) processInternalHosts(dctx *dnsContext) (rc resultCode) {
+	req := dctx.proxyCtx.Req
+	q := req.Question[0]
+	if q.Qtype != dns.TypeA {
 		return resultCodeSuccess
 	}

-	host := req.Question[0].Name
-	host = strings.ToLower(host)
-	if !strings.HasSuffix(host, ".lan.") {
+	reqHost := strings.ToLower(q.Name)
+	host := strings.TrimSuffix(reqHost, s.autohostSuffix)
+	if host == reqHost {
 		return resultCodeSuccess
 	}
-	host = strings.TrimSuffix(host, ".lan.")

 	s.tableHostToIPLock.Lock()
 	if s.tableHostToIP == nil {
@ -209,24 +213,22 @@ func processInternalHosts(ctx *dnsContext) (rc resultCode) {
 		return resultCodeSuccess
 	}

-	log.Debug("DNS: internal record: %s -> %s", req.Question[0].Name, ip)
+	log.Debug("dns: internal record: %s -> %s", q.Name, ip)

 	resp := s.makeResponse(req)

-	if req.Question[0].Qtype == dns.TypeA {
-		a := &dns.A{}
-		a.Hdr = dns.RR_Header{
-			Name:   req.Question[0].Name,
-			Rrtype: dns.TypeA,
-			Ttl:    s.conf.BlockedResponseTTL,
-			Class:  dns.ClassINET,
+	if q.Qtype == dns.TypeA {
+		a := &dns.A{
+			Hdr: s.hdr(req, dns.TypeA),
+			A:   make([]byte, len(ip)),
 		}
-		a.A = make([]byte, 4)
+
 		copy(a.A, ip)
 		resp.Answer = append(resp.Answer, a)
 	}

-	ctx.proxyCtx.Res = resp
+	dctx.proxyCtx.Res = resp
+
 	return resultCodeSuccess
 }

@ -257,7 +259,7 @@ func processInternalIPAddrs(ctx *dnsContext) (rc resultCode) {
 		return resultCodeSuccess
 	}

-	log.Debug("DNS: reverse-lookup: %s -> %s", arpa, host)
+	log.Debug("dns: reverse-lookup: %s -> %s", arpa, host)

 	resp := s.makeResponse(req)
 	ptr := &dns.PTR{}
@ -325,7 +327,7 @@ func processUpstream(ctx *dnsContext) (rc resultCode) {
 	if s.conf.EnableDNSSEC {
 		opt := d.Req.IsEdns0()
 		if opt == nil {
-			log.Debug("DNS: Adding OPT record with DNSSEC flag")
+			log.Debug("dns: Adding OPT record with DNSSEC flag")
 			d.Req.SetEdns0(4096, true)
 		} else if !opt.Do() {
 			opt.SetDo(true)
--- a/internal/dnsforward/dns_test.go
+++ b/internal/dnsforward/dns_test.go
@ -0,0 +1,107 @@
+package dnsforward
+
+import (
+	"net"
+	"testing"
+
+	"github.com/AdguardTeam/dnsproxy/proxy"
+	"github.com/miekg/dns"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestServer_ProcessInternalHosts(t *testing.T) {
+	knownIP := net.IP{1, 2, 3, 4}
+	testCases := []struct {
+		name       string
+		host       string
+		suffix     string
+		wantErrMsg string
+		wantIP     net.IP
+		qtyp       uint16
+		wantRes    resultCode
+	}{{
+		name:       "success_external",
+		host:       "example.com",
+		suffix:     defaultAutohostSuffix,
+		wantErrMsg: "",
+		wantIP:     nil,
+		qtyp:       dns.TypeA,
+		wantRes:    resultCodeSuccess,
+	}, {
+		name:       "success_external_non_a",
+		host:       "example.com",
+		suffix:     defaultAutohostSuffix,
+		wantErrMsg: "",
+		wantIP:     nil,
+		qtyp:       dns.TypeCNAME,
+		wantRes:    resultCodeSuccess,
+	}, {
+		name:       "success_internal",
+		host:       "example.lan",
+		suffix:     defaultAutohostSuffix,
+		wantErrMsg: "",
+		wantIP:     knownIP,
+		qtyp:       dns.TypeA,
+		wantRes:    resultCodeSuccess,
+	}, {
+		name:       "success_internal_unknown",
+		host:       "example-new.lan",
+		suffix:     defaultAutohostSuffix,
+		wantErrMsg: "",
+		wantIP:     nil,
+		qtyp:       dns.TypeA,
+		wantRes:    resultCodeSuccess,
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			s := &Server{
+				autohostSuffix: tc.suffix,
+				tableHostToIP: map[string]net.IP{
+					"example": knownIP,
+				},
+			}
+
+			req := &dns.Msg{
+				MsgHdr: dns.MsgHdr{
+					Id: 1234,
+				},
+				Question: []dns.Question{{
+					Name:   dns.Fqdn(tc.host),
+					Qtype:  tc.qtyp,
+					Qclass: dns.ClassINET,
+				}},
+			}
+
+			dctx := &dnsContext{
+				proxyCtx: &proxy.DNSContext{
+					Req: req,
+				},
+			}
+
+			res := s.processInternalHosts(dctx)
+			assert.Equal(t, tc.wantRes, res)
+
+			if tc.wantErrMsg == "" {
+				assert.NoError(t, dctx.err)
+			} else {
+				require.Error(t, dctx.err)
+
+				assert.Equal(t, tc.wantErrMsg, dctx.err.Error())
+			}
+
+			pctx := dctx.proxyCtx
+			if tc.wantIP == nil {
+				assert.Nil(t, pctx.Res)
+			} else {
+				require.NotNil(t, pctx.Res)
+
+				ans := pctx.Res.Answer
+				require.Len(t, ans, 1)
+
+				assert.Equal(t, tc.wantIP, ans[0].(*dns.A).A)
+			}
+		})
+	}
+}
--- a/internal/dnsforward/dnsforward.go
+++ b/internal/dnsforward/dnsforward.go
@ -56,6 +56,10 @@ type Server struct {
 	stats      stats.Stats
 	access     *accessCtx

+	// autohostSuffix is the suffix used to detect internal hosts.  It must
+	// be a valid top-level domain plus dots on each side.
+	autohostSuffix string
+
 	ipset ipsetCtx

 	tableHostToIP     map[string]net.IP // "hostname -> IP" table for internal addresses (DHCP)
@ -74,21 +78,50 @@ type Server struct {
 	conf ServerConfig
 }

-// DNSCreateParams - parameters for NewServer()
+// defaultAutohostSuffix is the default suffix used to detect internal hosts
+// when no suffix is provided.  See the documentation for Server.autohostSuffix.
+const defaultAutohostSuffix = ".lan."
+
+// DNSCreateParams are parameters to create a new server.
 type DNSCreateParams struct {
-	DNSFilter  *dnsfilter.DNSFilter
-	Stats      stats.Stats
-	QueryLog   querylog.QueryLog
-	DHCPServer dhcpd.ServerInterface
+	DNSFilter   *dnsfilter.DNSFilter
+	Stats       stats.Stats
+	QueryLog    querylog.QueryLog
+	DHCPServer  dhcpd.ServerInterface
+	AutohostTLD string
+}
+
+// tldToSuffix converts a top-level domain into an autohost suffix.
+func tldToSuffix(tld string) (suffix string) {
+	l := len(tld) + 2
+	b := make([]byte, l)
+	b[0] = '.'
+	copy(b[1:], tld)
+	b[l-1] = '.'
+
+	return string(b)
 }

 // NewServer creates a new instance of the dnsforward.Server
 // Note: this function must be called only once
-func NewServer(p DNSCreateParams) *Server {
-	s := &Server{
-		dnsFilter: p.DNSFilter,
-		stats:     p.Stats,
-		queryLog:  p.QueryLog,
+func NewServer(p DNSCreateParams) (s *Server, err error) {
+	var autohostSuffix string
+	if p.AutohostTLD == "" {
+		autohostSuffix = defaultAutohostSuffix
+	} else {
+		err = validateDomainNameLabel(p.AutohostTLD)
+		if err != nil {
+			return nil, fmt.Errorf("autohost tld: %w", err)
+		}
+
+		autohostSuffix = tldToSuffix(p.AutohostTLD)
+	}
+
+	s = &Server{
+		dnsFilter:      p.DNSFilter,
+		stats:          p.Stats,
+		queryLog:       p.QueryLog,
+		autohostSuffix: autohostSuffix,
 	}

 	if p.DHCPServer != nil {
@ -101,7 +134,8 @@ func NewServer(p DNSCreateParams) *Server {
 		// Use plain DNS on MIPS, encryption is too slow
 		defaultDNS = defaultBootstrap
 	}
-	return s
+
+	return s, nil
 }

 // NewCustomServer creates a new instance of *Server with custom internal proxy.
--- a/internal/dnsforward/dnsforward_test.go
+++ b/internal/dnsforward/dnsforward_test.go
@ -19,10 +19,9 @@ import (
 	"time"

 	"github.com/AdguardTeam/AdGuardHome/internal/aghtest"
-	"github.com/AdguardTeam/AdGuardHome/internal/util"
-
 	"github.com/AdguardTeam/AdGuardHome/internal/dhcpd"
 	"github.com/AdguardTeam/AdGuardHome/internal/dnsfilter"
+	"github.com/AdguardTeam/AdGuardHome/internal/util"
 	"github.com/AdguardTeam/dnsproxy/proxy"
 	"github.com/AdguardTeam/dnsproxy/upstream"
 	"github.com/miekg/dns"
@ -43,11 +42,11 @@ func startDeferStop(t *testing.T, s *Server) {
 	t.Helper()

 	err := s.Start()
-	require.Nilf(t, err, "failed to start server: %s", err)
+	require.NoErrorf(t, err, "failed to start server: %s", err)

 	t.Cleanup(func() {
 		serr := s.Stop()
-		require.Nilf(t, serr, "dns server failed to stop: %s", serr)
+		require.NoErrorf(t, serr, "dns server failed to stop: %s", serr)
 	})
 }

@ -65,9 +64,13 @@ func createTestServer(t *testing.T, filterConf *dnsfilter.Config, forwardConf Se

 	f := dnsfilter.New(filterConf, filters)

-	s := NewServer(DNSCreateParams{DNSFilter: f})
+	s, err := NewServer(DNSCreateParams{DNSFilter: f})
+	require.NoError(t, err)
+
 	s.conf = forwardConf
-	require.Nil(t, s.Prepare(nil))
+
+	err = s.Prepare(nil)
+	require.NoError(t, err)

 	return s
 }
@ -76,11 +79,11 @@ func createServerTLSConfig(t *testing.T) (*tls.Config, []byte, []byte) {
 	t.Helper()

 	privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
-	require.Nilf(t, err, "cannot generate RSA key: %s", err)
+	require.NoErrorf(t, err, "cannot generate RSA key: %s", err)

 	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
 	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
-	require.Nilf(t, err, "failed to generate serial number: %s", err)
+	require.NoErrorf(t, err, "failed to generate serial number: %s", err)

 	notBefore := time.Now()
 	notAfter := notBefore.Add(5 * 365 * time.Hour * 24)
@ -101,13 +104,13 @@ func createServerTLSConfig(t *testing.T) (*tls.Config, []byte, []byte) {
 	template.DNSNames = append(template.DNSNames, tlsServerName)

 	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, publicKey(privateKey), privateKey)
-	require.Nilf(t, err, "failed to create certificate: %s", err)
+	require.NoErrorf(t, err, "failed to create certificate: %s", err)

 	certPem := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
 	keyPem := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(privateKey)})

 	cert, err := tls.X509KeyPair(certPem, keyPem)
-	require.Nilf(t, err, "failed to create certificate: %s", err)
+	require.NoErrorf(t, err, "failed to create certificate: %s", err)

 	return &tls.Config{
 		Certificates: []tls.Certificate{cert},
@ -131,7 +134,7 @@ func createTestTLS(t *testing.T, tlsConf TLSConfig) (s *Server, certPem []byte)
 	s.conf.TLSConfig = tlsConf

 	err := s.Prepare(nil)
-	require.Nilf(t, err, "failed to prepare server: %s", err)
+	require.NoErrorf(t, err, "failed to prepare server: %s", err)

 	return s, certPem
 }
@ -191,10 +194,10 @@ func sendTestMessagesAsync(t *testing.T, conn *dns.Conn) {
 			defer wg.Done()

 			err := conn.WriteMsg(msg)
-			require.Nilf(t, err, "cannot write message: %s", err)
+			require.NoErrorf(t, err, "cannot write message: %s", err)

 			res, err := conn.ReadMsg()
-			require.Nilf(t, err, "cannot read response to message: %s", err)
+			require.NoErrorf(t, err, "cannot read response to message: %s", err)

 			assertGoogleAResponse(t, res)
 		}()
@ -248,7 +251,7 @@ func TestServer(t *testing.T) {
 			client := dns.Client{Net: tc.proto}

 			reply, _, err := client.Exchange(createGoogleATestMessage(), addr.String())
-			require.Nilf(t, err, "сouldn't talk to server %s: %s", addr, err)
+			require.NoErrorf(t, err, "сouldn't talk to server %s: %s", addr, err)

 			assertGoogleAResponse(t, reply)
 		})
@ -275,7 +278,7 @@ func TestServerWithProtectionDisabled(t *testing.T) {
 	client := dns.Client{Net: proxy.ProtoUDP}

 	reply, _, err := client.Exchange(req, addr.String())
-	require.Nilf(t, err, "сouldn't talk to server %s: %s", addr, err)
+	require.NoErrorf(t, err, "сouldn't talk to server %s: %s", addr, err)
 	assertGoogleAResponse(t, reply)
 }

@ -304,7 +307,7 @@ func TestDoTServer(t *testing.T) {
 	// Create a DNS-over-TLS client connection.
 	addr := s.dnsProxy.Addr(proxy.ProtoTLS)
 	conn, err := dns.DialWithTLS("tcp-tls", addr.String(), tlsConfig)
-	require.Nilf(t, err, "cannot connect to the proxy: %s", err)
+	require.NoErrorf(t, err, "cannot connect to the proxy: %s", err)

 	sendTestMessages(t, conn)
 }
@ -326,12 +329,12 @@ func TestDoQServer(t *testing.T) {
 	addr := s.dnsProxy.Addr(proxy.ProtoQUIC)
 	opts := upstream.Options{InsecureSkipVerify: true}
 	u, err := upstream.AddressToUpstream(fmt.Sprintf("%s://%s", proxy.ProtoQUIC, addr), opts)
-	require.Nil(t, err)
+	require.NoError(t, err)

 	// Send the test message.
 	req := createGoogleATestMessage()
 	res, err := u.Exchange(req)
-	require.Nil(t, err)
+	require.NoError(t, err)

 	assertGoogleAResponse(t, res)
 }
@ -369,7 +372,7 @@ func TestServerRace(t *testing.T) {
 	// Message over UDP.
 	addr := s.dnsProxy.Addr(proxy.ProtoUDP)
 	conn, err := dns.Dial(proxy.ProtoUDP, addr.String())
-	require.Nilf(t, err, "cannot connect to the proxy: %s", err)
+	require.NoErrorf(t, err, "cannot connect to the proxy: %s", err)

 	sendTestMessagesAsync(t, conn)
 }
@ -432,7 +435,7 @@ func TestSafeSearch(t *testing.T) {
 			req := createTestMessage(tc.host)

 			reply, _, err := client.Exchange(req, addr)
-			require.Nilf(t, err, "couldn't talk to server %s: %s", addr, err)
+			require.NoErrorf(t, err, "couldn't talk to server %s: %s", addr, err)
 			assertResponse(t, reply, tc.want)
 		})
 	}
@ -459,7 +462,7 @@ func TestInvalidRequest(t *testing.T) {
 		Timeout: 500 * time.Millisecond,
 	}).Exchange(&req, addr)

-	assert.Nil(t, err, "got a response to an invalid query")
+	assert.NoErrorf(t, err, "got a response to an invalid query")
 }

 func TestBlockedRequest(t *testing.T) {
@ -479,7 +482,8 @@ func TestBlockedRequest(t *testing.T) {
 	req := createTestMessage("nxdomain.example.org.")

 	reply, err := dns.Exchange(req, addr.String())
-	require.Nilf(t, err, "couldn't talk to server %s: %s", addr, err)
+	require.NoErrorf(t, err, "couldn't talk to server %s: %s", addr, err)
+
 	assert.Equal(t, dns.RcodeSuccess, reply.Rcode)

 	require.Len(t, reply.Answer, 1)
@ -514,8 +518,8 @@ func TestServerCustomClientUpstream(t *testing.T) {
 	req := createTestMessage("host.")

 	reply, err := dns.Exchange(req, addr.String())
+	require.NoError(t, err)

-	require.Nil(t, err)
 	assert.Equal(t, dns.RcodeSuccess, reply.Rcode)
 	require.NotEmpty(t, reply.Answer)

@ -558,7 +562,8 @@ func TestBlockCNAMEProtectionEnabled(t *testing.T) {
 	req := createTestMessage("badhost.")

 	reply, err := dns.Exchange(req, addr.String())
-	require.Nil(t, err)
+	require.NoError(t, err)
+
 	assert.Equal(t, dns.RcodeSuccess, reply.Rcode)
 }

@ -608,7 +613,8 @@ func TestBlockCNAME(t *testing.T) {
 			req := createTestMessage(tc.host)

 			reply, err := dns.Exchange(req, addr)
-			require.Nil(t, err)
+			require.NoError(t, err)
+
 			assert.Equal(t, dns.RcodeSuccess, reply.Rcode)
 			if tc.want {
 				require.Len(t, reply.Answer, 1)
@ -658,7 +664,8 @@ func TestClientRulesForCNAMEMatching(t *testing.T) {
 	// However, in our case it should not be blocked as filtering is
 	// disabled on the client level.
 	reply, err := dns.Exchange(&req, addr.String())
-	require.Nil(t, err)
+	require.NoError(t, err)
+
 	assert.Equal(t, dns.RcodeSuccess, reply.Rcode)
 }

@ -689,7 +696,7 @@ func TestNullBlockedRequest(t *testing.T) {
 	}

 	reply, err := dns.Exchange(&req, addr.String())
-	require.Nilf(t, err, "couldn't talk to server %s: %s", addr, err)
+	require.NoErrorf(t, err, "couldn't talk to server %s: %s", addr, err)
 	require.Lenf(t, reply.Answer, 1, "dns server %s returned reply with wrong number of answers - %d", addr, len(reply.Answer))
 	a, ok := reply.Answer[0].(*dns.A)
 	require.Truef(t, ok, "dns server %s returned wrong answer type instead of A: %v", addr, reply.Answer[0])
@ -703,9 +710,11 @@ func TestBlockedCustomIP(t *testing.T) {
 		Data: []byte(rules),
 	}}

-	s := NewServer(DNSCreateParams{
+	s, err := NewServer(DNSCreateParams{
 		DNSFilter: dnsfilter.New(&dnsfilter.Config{}, filters),
 	})
+	require.NoError(t, err)
+
 	conf := &ServerConfig{
 		UDPListenAddrs: []*net.UDPAddr{{}},
 		TCPListenAddrs: []*net.TCPAddr{{}},
@ -716,12 +725,16 @@ func TestBlockedCustomIP(t *testing.T) {
 			UpstreamDNS:       []string{"8.8.8.8:53", "8.8.4.4:53"},
 		},
 	}
+
 	// Invalid BlockingIPv4.
-	assert.NotNil(t, s.Prepare(conf))
+	err = s.Prepare(conf)
+	assert.Error(t, err)

 	conf.BlockingIPv4 = net.IP{0, 0, 0, 1}
 	conf.BlockingIPv6 = net.ParseIP("::1")
-	require.Nil(t, s.Prepare(conf))
+
+	err = s.Prepare(conf)
+	require.NoError(t, err)

 	startDeferStop(t, s)

@ -729,18 +742,24 @@ func TestBlockedCustomIP(t *testing.T) {

 	req := createTestMessageWithType("null.example.org.", dns.TypeA)
 	reply, err := dns.Exchange(req, addr.String())
-	require.Nil(t, err)
+	require.NoError(t, err)
+
 	require.Len(t, reply.Answer, 1)
+
 	a, ok := reply.Answer[0].(*dns.A)
 	require.True(t, ok)
+
 	assert.True(t, net.IP{0, 0, 0, 1}.Equal(a.A))

 	req = createTestMessageWithType("null.example.org.", dns.TypeAAAA)
 	reply, err = dns.Exchange(req, addr.String())
-	require.Nil(t, err)
+	require.NoError(t, err)
+
 	require.Len(t, reply.Answer, 1)
+
 	a6, ok := reply.Answer[0].(*dns.AAAA)
 	require.True(t, ok)
+
 	assert.Equal(t, "::1", a6.AAAA.String())
 }

@ -760,7 +779,7 @@ func TestBlockedByHosts(t *testing.T) {
 	req := createTestMessage("host.example.org.")

 	reply, err := dns.Exchange(req, addr.String())
-	require.Nilf(t, err, "couldn't talk to server %s: %s", addr, err)
+	require.NoErrorf(t, err, "couldn't talk to server %s: %s", addr, err)
 	require.Lenf(t, reply.Answer, 1, "dns server %s returned reply with wrong number of answers - %d", addr, len(reply.Answer))
 	a, ok := reply.Answer[0].(*dns.A)
 	require.Truef(t, ok, "dns server %s returned wrong answer type instead of A: %v", addr, reply.Answer[0])
@ -796,7 +815,7 @@ func TestBlockedBySafeBrowsing(t *testing.T) {
 	req := createTestMessage(hostname + ".")

 	reply, err := dns.Exchange(req, addr.String())
-	require.Nilf(t, err, "couldn't talk to server %s: %s", addr, err)
+	require.NoErrorf(t, err, "couldn't talk to server %s: %s", addr, err)
 	require.Lenf(t, reply.Answer, 1, "dns server %s returned reply with wrong number of answers - %d", addr, len(reply.Answer))

 	a, ok := reply.Answer[0].(*dns.A)
@ -822,15 +841,19 @@ func TestRewrite(t *testing.T) {
 	}
 	f := dnsfilter.New(c, nil)

-	s := NewServer(DNSCreateParams{DNSFilter: f})
-	assert.Nil(t, s.Prepare(&ServerConfig{
+	s, err := NewServer(DNSCreateParams{DNSFilter: f})
+	require.NoError(t, err)
+
+	err = s.Prepare(&ServerConfig{
 		UDPListenAddrs: []*net.UDPAddr{{}},
 		TCPListenAddrs: []*net.TCPAddr{{}},
 		FilteringConfig: FilteringConfig{
 			ProtectionEnabled: true,
 			UpstreamDNS:       []string{"8.8.8.8:53"},
 		},
-	}))
+	})
+	assert.NoError(t, err)
+
 	s.conf.UpstreamConfig.Upstreams = []upstream.Upstream{
 		&aghtest.TestUpstream{
 			CName: map[string]string{
@ -847,34 +870,41 @@ func TestRewrite(t *testing.T) {

 	req := createTestMessageWithType("test.com.", dns.TypeA)
 	reply, err := dns.Exchange(req, addr.String())
-	require.Nil(t, err)
+	require.NoError(t, err)
+
 	require.Len(t, reply.Answer, 1)
+
 	a, ok := reply.Answer[0].(*dns.A)
 	require.True(t, ok)
+
 	assert.True(t, net.IP{1, 2, 3, 4}.Equal(a.A))

 	req = createTestMessageWithType("test.com.", dns.TypeAAAA)
 	reply, err = dns.Exchange(req, addr.String())
-	require.Nil(t, err)
+	require.NoError(t, err)
+
 	assert.Empty(t, reply.Answer)

 	req = createTestMessageWithType("alias.test.com.", dns.TypeA)
 	reply, err = dns.Exchange(req, addr.String())
-	require.Nil(t, err)
+	require.NoError(t, err)

 	require.Len(t, reply.Answer, 2)
+
 	assert.Equal(t, "test.com.", reply.Answer[0].(*dns.CNAME).Target)
 	assert.True(t, net.IP{1, 2, 3, 4}.Equal(reply.Answer[1].(*dns.A).A))

 	req = createTestMessageWithType("my.alias.example.org.", dns.TypeA)
 	reply, err = dns.Exchange(req, addr.String())
-	require.Nil(t, err)
+	require.NoError(t, err)

 	// The original question is restored.
 	require.Len(t, reply.Question, 1)
+
 	assert.Equal(t, "my.alias.example.org.", reply.Question[0].Name)

 	require.Len(t, reply.Answer, 2)
+
 	assert.Equal(t, "example.org.", reply.Answer[0].(*dns.CNAME).Target)
 	assert.Equal(t, dns.TypeA, reply.Answer[1].Header().Rrtype)
 }
@ -1104,17 +1134,23 @@ func (d *testDHCP) Leases(flags int) []dhcpd.Lease {
 func (d *testDHCP) SetOnLeaseChanged(onLeaseChanged dhcpd.OnLeaseChangedT) {}

 func TestPTRResponseFromDHCPLeases(t *testing.T) {
-	s := NewServer(DNSCreateParams{
+	s, err := NewServer(DNSCreateParams{
 		DNSFilter:  dnsfilter.New(&dnsfilter.Config{}, nil),
 		DHCPServer: &testDHCP{},
 	})
+	require.NoError(t, err)

 	s.conf.UDPListenAddrs = []*net.UDPAddr{{}}
 	s.conf.TCPListenAddrs = []*net.TCPAddr{{}}
 	s.conf.UpstreamDNS = []string{"127.0.0.1:53"}
 	s.conf.FilteringConfig.ProtectionEnabled = true
-	require.Nil(t, s.Prepare(nil))
-	require.Nil(t, s.Start())
+
+	err = s.Prepare(nil)
+	require.NoError(t, err)
+
+	err = s.Start()
+	require.NoError(t, err)
+
 	t.Cleanup(func() {
 		s.Close()
 	})
@ -1123,8 +1159,10 @@ func TestPTRResponseFromDHCPLeases(t *testing.T) {
 	req := createTestMessageWithType("1.0.0.127.in-addr.arpa.", dns.TypePTR)

 	resp, err := dns.Exchange(req, addr.String())
-	require.Nil(t, err)
+	require.NoError(t, err)
+
 	require.Len(t, resp.Answer, 1)
+
 	assert.Equal(t, dns.TypePTR, resp.Answer[0].Header().Rrtype)
 	assert.Equal(t, "1.0.0.127.in-addr.arpa.", resp.Answer[0].Header().Name)

@ -1140,10 +1178,11 @@ func TestPTRResponseFromHosts(t *testing.T) {

 	// Prepare test hosts file.
 	hf, err := ioutil.TempFile("", "")
-	require.Nil(t, err)
+	require.NoError(t, err)
+
 	t.Cleanup(func() {
-		assert.Nil(t, hf.Close())
-		assert.Nil(t, os.Remove(hf.Name()))
+		assert.NoError(t, hf.Close())
+		assert.NoError(t, os.Remove(hf.Name()))
 	})

 	_, _ = hf.WriteString("  127.0.0.1   host # comment \n")
@ -1153,14 +1192,20 @@ func TestPTRResponseFromHosts(t *testing.T) {
 	c.AutoHosts.Init(hf.Name())
 	t.Cleanup(c.AutoHosts.Close)

-	s := NewServer(DNSCreateParams{DNSFilter: dnsfilter.New(&c, nil)})
+	s, err := NewServer(DNSCreateParams{DNSFilter: dnsfilter.New(&c, nil)})
+	require.NoError(t, err)
+
 	s.conf.UDPListenAddrs = []*net.UDPAddr{{}}
 	s.conf.TCPListenAddrs = []*net.TCPAddr{{}}
 	s.conf.UpstreamDNS = []string{"127.0.0.1:53"}
 	s.conf.FilteringConfig.ProtectionEnabled = true
-	require.Nil(t, s.Prepare(nil))

-	require.Nil(t, s.Start())
+	err = s.Prepare(nil)
+	require.NoError(t, err)
+
+	err = s.Start()
+	require.NoError(t, err)
+
 	t.Cleanup(func() {
 		s.Close()
 	})
@ -1169,8 +1214,10 @@ func TestPTRResponseFromHosts(t *testing.T) {
 	req := createTestMessageWithType("1.0.0.127.in-addr.arpa.", dns.TypePTR)

 	resp, err := dns.Exchange(req, addr.String())
-	require.Nil(t, err)
+	require.NoError(t, err)
+
 	require.Len(t, resp.Answer, 1)
+
 	assert.Equal(t, dns.TypePTR, resp.Answer[0].Header().Rrtype)
 	assert.Equal(t, "1.0.0.127.in-addr.arpa.", resp.Answer[0].Header().Name)

@ -1178,3 +1225,39 @@ func TestPTRResponseFromHosts(t *testing.T) {
 	require.True(t, ok)
 	assert.Equal(t, "host.", ptr.Ptr)
 }
+
+func TestNewServer(t *testing.T) {
+	testCases := []struct {
+		name       string
+		in         DNSCreateParams
+		wantErrMsg string
+	}{{
+		name:       "success",
+		in:         DNSCreateParams{},
+		wantErrMsg: "",
+	}, {
+		name: "success_autohost_tld",
+		in: DNSCreateParams{
+			AutohostTLD: "mynet",
+		},
+		wantErrMsg: "",
+	}, {
+		name: "bad_autohost_tld",
+		in: DNSCreateParams{
+			AutohostTLD: "!!!",
+		},
+		wantErrMsg: `autohost tld: invalid char '!' at index 0 in "!!!"`,
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := NewServer(tc.in)
+			if tc.wantErrMsg == "" {
+				assert.NoError(t, err)
+			} else {
+				require.Error(t, err)
+				assert.Equal(t, tc.wantErrMsg, err.Error())
+			}
+		})
+	}
+}
--- a/internal/home/config.go
+++ b/internal/home/config.go
@ -93,6 +93,11 @@ type dnsConfig struct {
 	FilteringEnabled           bool             `yaml:"filtering_enabled"`       // whether or not use filter lists
 	FiltersUpdateIntervalHours uint32           `yaml:"filters_update_interval"` // time period to update filters (in hours)
 	DnsfilterConf              dnsfilter.Config `yaml:",inline"`
+
+	// AutohostTLD is the top-level domain used for known internal hosts.
+	// For example, a machine called "myhost" can be addressed as
+	// "myhost.lan" when AutohostTLD is "lan".
+	AutohostTLD string `yaml:"autohost_tld"`
 }

 type tlsConfigSettings struct {
@ -144,6 +149,7 @@ var config = configuration{
 		},
 		FilteringEnabled:           true, // whether or not use filter lists
 		FiltersUpdateIntervalHours: 24,
+		AutohostTLD:                "lan",
 	},
 	TLS: tlsConfigSettings{
 		PortHTTPS:       443,
--- a/internal/home/dns.go
+++ b/internal/home/dns.go
@ -61,18 +61,27 @@ func initDNSServer() error {
 	Context.dnsFilter = dnsfilter.New(&filterConf, nil)

 	p := dnsforward.DNSCreateParams{
-		DNSFilter: Context.dnsFilter,
-		Stats:     Context.stats,
-		QueryLog:  Context.queryLog,
+		DNSFilter:   Context.dnsFilter,
+		Stats:       Context.stats,
+		QueryLog:    Context.queryLog,
+		AutohostTLD: config.DNS.AutohostTLD,
 	}
 	if Context.dhcpServer != nil {
 		p.DHCPServer = Context.dhcpServer
 	}
-	Context.dnsServer = dnsforward.NewServer(p)
+
+	Context.dnsServer, err = dnsforward.NewServer(p)
+	if err != nil {
+		closeDNSServer()
+
+		return fmt.Errorf("dnsforward.NewServer: %w", err)
+	}
+
 	Context.clients.dnsServer = Context.dnsServer
 	dnsConfig, err := generateServerConfig()
 	if err != nil {
 		closeDNSServer()
+
 		return fmt.Errorf("generateServerConfig: %w", err)
 	}

--- a/internal/home/whois_test.go
+++ b/internal/home/whois_test.go
@ -6,15 +6,23 @@ import (

 	"github.com/AdguardTeam/AdGuardHome/internal/dnsforward"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )

-func prepareTestDNSServer() error {
+func prepareTestDNSServer(t *testing.T) {
+	t.Helper()
+
 	config.DNS.Port = 1234
-	Context.dnsServer = dnsforward.NewServer(dnsforward.DNSCreateParams{})
+
+	var err error
+	Context.dnsServer, err = dnsforward.NewServer(dnsforward.DNSCreateParams{})
+	require.NoError(t, err)
+
 	conf := &dnsforward.ServerConfig{}
 	conf.UpstreamDNS = []string{"8.8.8.8"}

-	return Context.dnsServer.Prepare(conf)
+	err = Context.dnsServer.Prepare(conf)
+	require.NoError(t, err)
 }

 // TODO(e.burkov): It's kind of complicated to get rid of network access in this
@ -22,12 +30,15 @@ func prepareTestDNSServer() error {
 // the server, so it becomes hard to simulate handling of request from test even
 // with substituted upstream.  However, it must be done.
 func TestWhois(t *testing.T) {
-	assert.Nil(t, prepareTestDNSServer())
+	prepareTestDNSServer(t)

 	w := Whois{timeoutMsec: 5000}
 	resp, err := w.queryAll(context.Background(), "8.8.8.8")
-	assert.Nil(t, err)
+	assert.NoError(t, err)
+
 	m := whoisParse(resp)
+	require.NotEmpty(t, m)
+
 	assert.Equal(t, "Google LLC", m["orgname"])
 	assert.Equal(t, "US", m["country"])
 	assert.Equal(t, "Mountain View", m["city"])
--- a/staticcheck.conf
+++ b/staticcheck.conf
@ -15,6 +15,7 @@ initialisms = [
 , "SDNS"
 , "SLAAC"
 , "SVCB"
+, "TLD"
 ]
 dot_import_whitelist = []
 http_status_code_whitelist = []