cherry-pick: 4216 simpl hosts

Merge in DNS/adguard-home from 4216-hosts-explode to master

Updates #4216.

Squashed commit of the following:

commit a6ed131923496d9bbd1d80c652d4584951528c4a
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jan 27 19:11:23 2022 +0300

    aghnet: imp docs

commit 25cca065c3c6dc227288cdd0803dc3ff8f9c3ca4
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jan 27 18:53:16 2022 +0300

    aghnet: simpl hosts container

CHANGELOG.md

@@ -27,6 +27,11 @@ and this project adheres to
 -->
 - Go 1.17 support.  v0.109.0 will require at least Go 1.18 to build.
 
+## Fixed
+
+- Unnecessarily complex hosts-related logic leading to infinite recursion in
+  some cases ([#4216]).
+
 ### Removed
 
 - Go 1.16 support.

internal/aghnet/hostscontainer.go

@@ -46,13 +46,8 @@ type requestMatcher struct {
 }
 
 // MatchRequest processes the request rewriting hostnames and addresses read
-// from the operating system's hosts files.
+// from the operating system's hosts files.  res is nil for any request having
-//
+// not an A/AAAA or PTR type, see man 5 hosts.
-// res is nil for any request having not an A/AAAA or PTR type.  Results
-// containing CNAME information may be queried again with the same question type
-// and the returned CNAME for Host field of request.  Results are guaranteed to
-// be direct, i.e. any returned CNAME resolves into actual address like an alias
-// in hosts does, see man hosts (5).
 //
 // It's safe for concurrent use.
 func (rm *requestMatcher) MatchRequest(
@@ -203,7 +198,7 @@ func (hc *HostsContainer) Close() (err error) {
 }
 
 // Upd returns the channel into which the updates are sent.  The receivable
-// map's values are guaranteed to be of type of *aghnet.Hosts.
+// map's values are guaranteed to be of type of *stringutil.Set.
 func (hc *HostsContainer) Upd() (updates <-chan *netutil.IPMap) {
 	return hc.updates
 }
@@ -259,28 +254,14 @@ func (hc *HostsContainer) handleEvents() {
 	}
 }
 
-// ipRules is the pair of generated A/AAAA and PTR rules with related IP.
-type ipRules struct {
-	// rule is the A/AAAA $dnsrewrite rule.
-	rule string
-	// rulePtr is the PTR $dnsrewrite rule.
-	rulePtr string
-	// ip is the IP address related to the rules.
-	ip net.IP
-}
-
 // hostsParser is a helper type to parse rules from the operating system's hosts
 // file.  It exists for only a single refreshing session.
 type hostsParser struct {
 	// rulesBuilder builds the resulting rules list content.
 	rulesBuilder *strings.Builder
 
-	// rules stores the rules for main hosts to generate translations.
+	// translations maps generated rules into actual hosts file lines.
-	rules []ipRules
+	translations map[string]string
-
-	// cnameSet prevents duplicating cname rules, e.g. same hostname for
-	// different IP versions.
-	cnameSet *stringutil.Set
 
 	// table stores only the unique IP-hostname pairs.  It's also sent to the
 	// updates channel afterwards.
@@ -290,13 +271,10 @@ type hostsParser struct {
 // newHostsParser creates a new *hostsParser with buffers of size taken from the
 // previous parse.
 func (hc *HostsContainer) newHostsParser() (hp *hostsParser) {
-	lastLen := hc.last.Len()
-
 	return &hostsParser{
 		rulesBuilder: &strings.Builder{},
-		rules:        make([]ipRules, 0, lastLen),
+		translations: map[string]string{},
-		cnameSet:     stringutil.NewSet(),
+		table:        netutil.NewIPMap(hc.last.Len()),
-		table:        netutil.NewIPMap(lastLen),
 	}
 }
 
@@ -342,6 +320,8 @@ func (hp *hostsParser) parseLine(line string) (ip net.IP, hosts []string) {
 		// Make sure that invalid hosts aren't turned into rules.
 		//
 		// See https://github.com/AdguardTeam/AdGuardHome/issues/3946.
+		//
+		// TODO(e.burkov):  Investigate if hosts may contain DNS-SD domains.
 		err := netutil.ValidateDomainName(f)
 		if err != nil {
 			log.Error("%s: host %q is invalid, ignoring", hostsContainerPref, f)
@@ -355,107 +335,45 @@ func (hp *hostsParser) parseLine(line string) (ip net.IP, hosts []string) {
 	return ip, hosts
 }
 
-// Hosts is used to contain the main host and all it's aliases.
-type Hosts struct {
-	// Aliases contains all the aliases for Main.
-	Aliases *stringutil.Set
-	// Main is the host itself.
-	Main string
-}
-
-// Equal returns true if h equals hh.
-func (h *Hosts) Equal(hh *Hosts) (ok bool) {
-	if h == nil || hh == nil {
-		return h == hh
-	}
-
-	return h.Main == hh.Main && h.Aliases.Equal(hh.Aliases)
-}
-
-// add tries to add the ip-host pair.  It returns:
-//
-//   main host    if the host is not the first one added for the ip.
-//   host itself  if the host is the first one added for the ip.
-//   ""           if the ip-host pair has already been added.
-//
-func (hp *hostsParser) add(ip net.IP, host string) (mainHost string) {
-	v, ok := hp.table.Get(ip)
-	switch h, _ := v.(*Hosts); {
-	case !ok:
-		// This is the first host for the ip.
-		hp.table.Set(ip, &Hosts{Main: host})
-
-		return host
-	case h.Main == host:
-		// This is a duplicate.  Go on.
-	case h.Aliases == nil:
-		// This is the first alias.
-		h.Aliases = stringutil.NewSet(host)
-
-		return h.Main
-	case !h.Aliases.Has(host):
-		// This is a new alias.
-		h.Aliases.Add(host)
-
-		return h.Main
-	default:
-		// This is a duplicate.  Go on.
-	}
-
-	return ""
-}
-
 // addPair puts the pair of ip and host to the rules builder if needed.  For
 // each ip the first member of hosts will become the main one.
 func (hp *hostsParser) addPairs(ip net.IP, hosts []string) {
-	for _, host := range hosts {
+	v, ok := hp.table.Get(ip)
-		switch mainHost := hp.add(ip, host); mainHost {
+	if !ok {
-		case "":
+		// This ip is added at the first time.
-			// This host is a duplicate.
+		v = stringutil.NewSet()
-			continue
+		hp.table.Set(ip, v)
-		case host:
+	}
-			// This host is main.
+
-			added, addedPtr := hp.writeMainRule(host, ip)
+	var set *stringutil.Set
-			hp.rules = append(hp.rules, ipRules{
+	set, ok = v.(*stringutil.Set)
-				rule:    added,
+	if !ok {
-				rulePtr: addedPtr,
+		log.Debug("%s: adding pairs: unexpected value type %T", hostsContainerPref, v)
-				ip:      ip,
+
-			})
+		return
-		default:
+	}
-			// This host is an alias.
+
-			pair := fmt.Sprint(host, " ", mainHost)
+	processed := strings.Join(append([]string{ip.String()}, hosts...), " ")
-			if hp.cnameSet.Has(pair) {
+	for _, h := range hosts {
+		if set.Has(h) {
 			continue
 		}
-			hp.writeAliasRule(host, mainHost)
-			hp.cnameSet.Add(pair)
-		}
 
-		log.Debug("%s: added ip-host pair %q-%q", hostsContainerPref, ip, host)
+		set.Add(h)
+
+		rule, rulePtr := hp.writeRules(h, ip)
+		hp.translations[rule], hp.translations[rulePtr] = processed, processed
+
+		log.Debug("%s: added ip-host pair %q-%q", hostsContainerPref, ip, h)
 	}
 }
 
-// writeAliasRule writes the CNAME rule for the alias-host pair into internal
+// writeRules writes the actual rule for the qtype and the PTR for the
-// builders.
-func (hp *hostsParser) writeAliasRule(alias, host string) {
-	const (
-		nl = "\n"
-		sc = ";"
-
-		rwSuccess = rules.MaskSeparator + "$dnsrewrite=NOERROR" + sc + "CNAME" + sc
-		constLen  = len(rules.MaskPipe) + len(rwSuccess) + len(nl)
-	)
-
-	hp.rulesBuilder.Grow(constLen + len(host) + len(alias))
-	stringutil.WriteToBuilder(hp.rulesBuilder, rules.MaskPipe, alias, rwSuccess, host, nl)
-}
-
-// writeMainRule writes the actual rule for the qtype and the PTR for the
 // host-ip pair into internal builders.
-func (hp *hostsParser) writeMainRule(host string, ip net.IP) (added, addedPtr string) {
+func (hp *hostsParser) writeRules(host string, ip net.IP) (rule, rulePtr string) {
 	arpa, err := netutil.IPToReversedAddr(ip)
 	if err != nil {
-		return
+		return "", ""
 	}
 
 	const (
@@ -482,28 +400,20 @@ func (hp *hostsParser) writeMainRule(host string, ip net.IP) (added, addedPtr st
 
 	ruleBuilder := &strings.Builder{}
 	ruleBuilder.Grow(modLen + len(host) + len(qtype) + len(ipStr))
-	stringutil.WriteToBuilder(
+	stringutil.WriteToBuilder(ruleBuilder, rules.MaskPipe, host, rwSuccess, qtype, ";", ipStr)
-		ruleBuilder,
+	rule = ruleBuilder.String()
-		rules.MaskPipe,
-		host,
-		rwSuccess,
-		qtype,
-		";",
-		ipStr,
-	)
-	added = ruleBuilder.String()
 
 	ruleBuilder.Reset()
 
 	ruleBuilder.Grow(modLenPTR + len(arpa) + len(fqdn))
 	stringutil.WriteToBuilder(ruleBuilder, rules.MaskPipe, arpa, rwSuccessPTR, fqdn)
 
-	addedPtr = ruleBuilder.String()
+	rulePtr = ruleBuilder.String()
 
-	hp.rulesBuilder.Grow(len(added) + len(addedPtr) + 2*len(nl))
+	hp.rulesBuilder.Grow(len(rule) + len(rulePtr) + 2*len(nl))
-	stringutil.WriteToBuilder(hp.rulesBuilder, added, nl, addedPtr, nl)
+	stringutil.WriteToBuilder(hp.rulesBuilder, rule, nl, rulePtr, nl)
 
-	return added, addedPtr
+	return rule, rulePtr
 }
 
 // equalSet returns true if the internal hosts table just parsed equals target.
@@ -519,12 +429,11 @@ func (hp *hostsParser) equalSet(target *netutil.IPMap) (ok bool) {
 
 	hp.table.Range(func(ip net.IP, b interface{}) (cont bool) {
 		// ok is set to true if the target doesn't contain ip or if the
-		// appropriate hosts set isn't equal to the checked one, i.e. the main
+		// appropriate hosts set isn't equal to the checked one.
-		// hosts differ or the maps have at least one discrepancy.
 		if a, hasIP := target.Get(ip); !hasIP {
 			ok = true
-		} else if hosts, aok := a.(*Hosts); aok {
+		} else if hosts, aok := a.(*stringutil.Set); aok {
-			ok = !hosts.Equal(b.(*Hosts))
+			ok = !hosts.Equal(b.(*stringutil.Set))
 		}
 
 		// Continue only if maps has no discrepancies.
@@ -563,35 +472,6 @@ func (hp *hostsParser) newStrg(id int) (s *filterlist.RuleStorage, err error) {
 	}})
 }
 
-// translations generates the map to translate $dnsrewrite rules to
-// hosts-syntax ones.
-func (hp *hostsParser) translations() (trans map[string]string) {
-	l := len(hp.rules)
-	if l == 0 {
-		return nil
-	}
-
-	trans = make(map[string]string, l*2)
-	for _, r := range hp.rules {
-		v, ok := hp.table.Get(r.ip)
-		if !ok {
-			continue
-		}
-
-		var hosts *Hosts
-		hosts, ok = v.(*Hosts)
-		if !ok {
-			continue
-		}
-
-		strs := append([]string{r.ip.String(), hosts.Main}, hosts.Aliases.Values()...)
-		hostsLine := strings.Join(strs, " ")
-		trans[r.rule], trans[r.rulePtr] = hostsLine, hostsLine
-	}
-
-	return trans
-}
-
 // refresh gets the data from specified files and propagates the updates if
 // needed.
 //
@@ -618,7 +498,7 @@ func (hc *HostsContainer) refresh() (err error) {
 		return fmt.Errorf("initializing rules storage: %w", err)
 	}
 
-	hc.resetEng(rulesStrg, hp.translations())
+	hc.resetEng(rulesStrg, hp.translations)
 
 	return nil
 }

internal/aghnet/hostscontainer_test.go

@@ -14,6 +14,7 @@ import (
 	"github.com/AdguardTeam/AdGuardHome/internal/aghtest"
 	"github.com/AdguardTeam/golibs/errors"
 	"github.com/AdguardTeam/golibs/stringutil"
+	"github.com/AdguardTeam/golibs/testutil"
 	"github.com/AdguardTeam/urlfilter"
 	"github.com/AdguardTeam/urlfilter/rules"
 	"github.com/miekg/dns"
@@ -86,6 +87,7 @@ func TestNewHostsContainer(t *testing.T) {
 
 				return
 			}
+			testutil.CleanupAndRequireSuccess(t, hc.Close)
 
 			require.NoError(t, err)
 			require.NotNil(t, hc)
@@ -156,8 +158,9 @@ func TestHostsContainer_refresh(t *testing.T) {
 
 	hc, err := NewHostsContainer(0, testFS, w, "dir")
 	require.NoError(t, err)
+	testutil.CleanupAndRequireSuccess(t, hc.Close)
 
-	checkRefresh := func(t *testing.T, wantHosts Hosts) {
+	checkRefresh := func(t *testing.T, wantHosts *stringutil.Set) {
 		upd, ok := <-hc.Upd()
 		require.True(t, ok)
 		require.NotNil(t, upd)
@@ -167,22 +170,21 @@ func TestHostsContainer_refresh(t *testing.T) {
 		v, ok := upd.Get(ip)
 		require.True(t, ok)
 
-		var hosts *Hosts
+		var set *stringutil.Set
-		hosts, ok = v.(*Hosts)
+		set, ok = v.(*stringutil.Set)
 		require.True(t, ok)
 
-		assert.Equal(t, wantHosts.Main, hosts.Main)
+		assert.True(t, set.Equal(wantHosts))
-		assert.True(t, hosts.Aliases.Equal(wantHosts.Aliases))
 	}
 
 	t.Run("initial_refresh", func(t *testing.T) {
-		checkRefresh(t, Hosts{Main: "hostname"})
+		checkRefresh(t, stringutil.NewSet("hostname"))
 	})
 
 	t.Run("second_refresh", func(t *testing.T) {
 		testFS["dir/file2"] = &fstest.MapFile{Data: []byte(ipStr + ` alias` + nl)}
 		eventsCh <- event{}
-		checkRefresh(t, Hosts{Main: "hostname", Aliases: stringutil.NewSet("alias")})
+		checkRefresh(t, stringutil.NewSet("hostname", "alias"))
 	})
 
 	t.Run("double_refresh", func(t *testing.T) {
@@ -288,6 +290,7 @@ func TestHostsContainer_Translate(t *testing.T) {
 
 	hc, err := NewHostsContainer(0, testdata, &stubWatcher, "etc_hosts")
 	require.NoError(t, err)
+	testutil.CleanupAndRequireSuccess(t, hc.Close)
 
 	testCases := []struct {
 		name      string
@@ -300,7 +303,11 @@ func TestHostsContainer_Translate(t *testing.T) {
 	}, {
 		name:      "hello",
 		rule:      "|hello^$dnsrewrite=NOERROR;A;1.0.0.0",
-		wantTrans: []string{"1.0.0.0", "hello", "hello.world", "hello.world.again"},
+		wantTrans: []string{"1.0.0.0", "hello", "hello.world"},
+	}, {
+		name:      "hello-alias",
+		rule:      "|hello.world.again^$dnsrewrite=NOERROR;A;1.0.0.0",
+		wantTrans: []string{"1.0.0.0", "hello.world.again"},
 	}, {
 		name:      "simplehost_v6",
 		rule:      "|simplehost^$dnsrewrite=NOERROR;AAAA;::1",
@@ -308,7 +315,11 @@ func TestHostsContainer_Translate(t *testing.T) {
 	}, {
 		name:      "hello_v6",
 		rule:      "|hello^$dnsrewrite=NOERROR;AAAA;::",
-		wantTrans: []string{"::", "hello", "hello.world", "hello.world.again"},
+		wantTrans: []string{"::", "hello", "hello.world"},
+	}, {
+		name:      "hello_v6-alias",
+		rule:      "|hello.world.again^$dnsrewrite=NOERROR;AAAA;::",
+		wantTrans: []string{"::", "hello.world.again"},
 	}, {
 		name:      "simplehost_ptr",
 		rule:      "|1.0.0.1.in-addr.arpa^$dnsrewrite=NOERROR;PTR;simplehost.",
@@ -316,7 +327,11 @@ func TestHostsContainer_Translate(t *testing.T) {
 	}, {
 		name:      "hello_ptr",
 		rule:      "|0.0.0.1.in-addr.arpa^$dnsrewrite=NOERROR;PTR;hello.",
-		wantTrans: []string{"1.0.0.0", "hello", "hello.world", "hello.world.again"},
+		wantTrans: []string{"1.0.0.0", "hello", "hello.world"},
+	}, {
+		name:      "hello_ptr-alias",
+		rule:      "|0.0.0.1.in-addr.arpa^$dnsrewrite=NOERROR;PTR;hello.world.again.",
+		wantTrans: []string{"1.0.0.0", "hello.world.again"},
 	}, {
 		name: "simplehost_ptr_v6",
 		rule: "|1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa" +
@@ -326,14 +341,18 @@ func TestHostsContainer_Translate(t *testing.T) {
 		name: "hello_ptr_v6",
 		rule: "|0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa" +
 			"^$dnsrewrite=NOERROR;PTR;hello.",
-		wantTrans: []string{"::", "hello", "hello.world", "hello.world.again"},
+		wantTrans: []string{"::", "hello", "hello.world"},
+	}, {
+		name: "hello_ptr_v6-alias",
+		rule: "|0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa" +
+			"^$dnsrewrite=NOERROR;PTR;hello.world.again.",
+		wantTrans: []string{"::", "hello.world.again"},
 	}}
 
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
-			want := stringutil.NewSet(tc.wantTrans...)
 			got := stringutil.NewSet(strings.Fields(hc.Translate(tc.rule))...)
-			assert.True(t, want.Equal(got))
+			assert.True(t, stringutil.NewSet(tc.wantTrans...).Equal(got))
 		})
 	}
 }
@@ -354,7 +373,7 @@ func TestHostsContainer(t *testing.T) {
 			RRType: dns.TypeA,
 		}, {
 			RCode:  dns.RcodeSuccess,
-			Value:  net.IP(append((&[15]byte{})[:], byte(1))),
+			Value:  net.ParseIP("::1"),
 			RRType: dns.TypeAAAA,
 		}},
 		name: "simple",
@@ -365,7 +384,12 @@ func TestHostsContainer(t *testing.T) {
 	}, {
 		want: []*rules.DNSRewrite{{
 			RCode:  dns.RcodeSuccess,
-			NewCNAME: "hello",
+			Value:  net.IPv4(1, 0, 0, 0),
+			RRType: dns.TypeA,
+		}, {
+			RCode:  dns.RcodeSuccess,
+			Value:  net.ParseIP("::"),
+			RRType: dns.TypeAAAA,
 		}},
 		name: "hello_alias",
 		req: urlfilter.DNSRequest{
@@ -375,7 +399,12 @@ func TestHostsContainer(t *testing.T) {
 	}, {
 		want: []*rules.DNSRewrite{{
 			RCode:  dns.RcodeSuccess,
-			NewCNAME: "hello",
+			Value:  net.IPv4(1, 0, 0, 0),
+			RRType: dns.TypeA,
+		}, {
+			RCode:  dns.RcodeSuccess,
+			Value:  net.ParseIP("::"),
+			RRType: dns.TypeAAAA,
 		}},
 		name: "other_line_alias",
 		req: urlfilter.DNSRequest{
@@ -399,7 +428,12 @@ func TestHostsContainer(t *testing.T) {
 	}, {
 		want: []*rules.DNSRewrite{{
 			RCode:  dns.RcodeSuccess,
-			NewCNAME: "a.whole",
+			RRType: dns.TypeA,
+			Value:  net.IPv4(1, 0, 0, 2),
+		}, {
+			RCode:  dns.RcodeSuccess,
+			RRType: dns.TypeAAAA,
+			Value:  net.ParseIP("::2"),
 		}},
 		name: "lots_of_aliases",
 		req: urlfilter.DNSRequest{
@@ -431,6 +465,51 @@ func TestHostsContainer(t *testing.T) {
 			Hostname: "1.0.0.1.in-addr.arpa",
 			DNSType:  dns.TypeSRV,
 		},
+	}, {
+		want: []*rules.DNSRewrite{{
+			RCode:  dns.RcodeSuccess,
+			RRType: dns.TypeA,
+			Value:  net.IPv4(4, 2, 1, 6),
+		}, {
+			RCode:  dns.RcodeSuccess,
+			RRType: dns.TypeAAAA,
+			Value:  net.ParseIP("::42"),
+		}},
+		name: "issue_4216_4_6",
+		req: urlfilter.DNSRequest{
+			Hostname: "domain",
+			DNSType:  dns.TypeA,
+		},
+	}, {
+		want: []*rules.DNSRewrite{{
+			RCode:  dns.RcodeSuccess,
+			RRType: dns.TypeA,
+			Value:  net.IPv4(7, 5, 3, 1),
+		}, {
+			RCode:  dns.RcodeSuccess,
+			RRType: dns.TypeA,
+			Value:  net.IPv4(1, 3, 5, 7),
+		}},
+		name: "issue_4216_4",
+		req: urlfilter.DNSRequest{
+			Hostname: "domain4",
+			DNSType:  dns.TypeA,
+		},
+	}, {
+		want: []*rules.DNSRewrite{{
+			RCode:  dns.RcodeSuccess,
+			RRType: dns.TypeAAAA,
+			Value:  net.ParseIP("::13"),
+		}, {
+			RCode:  dns.RcodeSuccess,
+			RRType: dns.TypeAAAA,
+			Value:  net.ParseIP("::31"),
+		}},
+		name: "issue_4216_6",
+		req: urlfilter.DNSRequest{
+			Hostname: "domain6",
+			DNSType:  dns.TypeAAAA,
+		},
 	}}
 
 	stubWatcher := aghtest.FSWatcher{
@@ -441,6 +520,7 @@ func TestHostsContainer(t *testing.T) {
 
 	hc, err := NewHostsContainer(listID, testdata, &stubWatcher, "etc_hosts")
 	require.NoError(t, err)
+	testutil.CleanupAndRequireSuccess(t, hc.Close)
 
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {

internal/aghnet/testdata/etc_hosts

@@ -28,3 +28,11 @@
 ::  hello.world.again
 ::1 simplehost
 ::  hello.world
+
+# See https://github.com/AdguardTeam/AdGuardHome/issues/4216.
+4.2.1.6 domain domain.alias
+::42    domain.alias domain
+1.3.5.7 domain4 domain4.alias
+7.5.3.1 domain4.alias domain4
+::13    domain6 domain6.alias
+::31    domain6.alias domain6

internal/filtering/filtering.go

@@ -477,7 +477,7 @@ func (d *DNSFilter) matchSysHosts(
 		return res, nil
 	}
 
-	return d.matchSysHostsIntl(&urlfilter.DNSRequest{
+	dnsres, _ := d.EtcHosts.MatchRequest(urlfilter.DNSRequest{
 		Hostname:         host,
 		SortedClientTags: setts.ClientTags,
 		// TODO(e.burkov):  Wait for urlfilter update to pass net.IP.
@@ -485,12 +485,6 @@ func (d *DNSFilter) matchSysHosts(
 		ClientName: setts.ClientName,
 		DNSType:    qtype,
 	})
-}
-
-// matchSysHostsIntl actually matches the request.  It's separated to avoid
-// performing checks twice.
-func (d *DNSFilter) matchSysHostsIntl(req *urlfilter.DNSRequest) (res Result, err error) {
-	dnsres, _ := d.EtcHosts.MatchRequest(*req)
 	if dnsres == nil {
 		return res, nil
 	}
@@ -501,13 +495,6 @@ func (d *DNSFilter) matchSysHostsIntl(req *urlfilter.DNSRequest) (res Result, er
 	}
 
 	res = d.processDNSRewrites(dnsr)
-	if cn := res.CanonName; cn != "" {
-		// Probably an alias.
-		req.Hostname = cn
-
-		return d.matchSysHostsIntl(req)
-	}
-
 	res.Reason = RewrittenAutoHosts
 	for _, r := range res.Rules {
 		r.Text = stringutil.Coalesce(d.EtcHosts.Translate(r.Text), r.Text)

internal/home/clients.go

@@ -783,17 +783,14 @@ func (clients *clientsContainer) addFromHostsFile(hosts *netutil.IPMap) {
 
 	n := 0
 	hosts.Range(func(ip net.IP, v interface{}) (cont bool) {
-		hosts, ok := v.(*aghnet.Hosts)
+		hosts, ok := v.(*stringutil.Set)
 		if !ok {
 			log.Error("dns: bad type %T in ipToRC for %s", v, ip)
 
 			return true
 		}
 
-		if clients.addHostLocked(ip, hosts.Main, ClientSourceHostsFile) {
+		hosts.Range(func(name string) (cont bool) {
-			n++
-		}
-		hosts.Aliases.Range(func(name string) (cont bool) {
 			if clients.addHostLocked(ip, name, ClientSourceHostsFile) {
 				n++
 			}