Standardize hosts path

dns/transport/hosts/hosts.go

@@ -33,7 +33,11 @@ func NewTransport(ctx context.Context, logger log.ContextLogger, tag string, opt
 		predefined = make(map[string][]netip.Addr)
 	)
 	if len(options.Path) == 0 {
-		files = append(files, NewFile(DefaultPath))
+		defaultFile, err := NewDefault()
+		if err != nil {
+			return nil, err
+		}
+		files = append(files, defaultFile)
 	} else {
 		for _, path := range options.Path {
 			files = append(files, NewFile(filemanager.BasePath(ctx, os.ExpandEnv(path))))

dns/transport/hosts/hosts_file.go

@@ -10,6 +10,8 @@ import (
 	"sync"
 	"time"
 
+	E "github.com/sagernet/sing/common/exceptions"
+
 	"github.com/miekg/dns"
 )
 
@@ -30,6 +32,14 @@ func NewFile(path string) *File {
 	}
 }
 
+func NewDefault() (*File, error) {
+	defaultPathResolved, err := defaultPath()
+	if err != nil {
+		return nil, E.Cause(err, "resolve default hosts path")
+	}
+	return NewFile(defaultPathResolved), nil
+}
+
 func (f *File) Lookup(name string) []netip.Addr {
 	f.access.Lock()
 	defer f.access.Unlock()

dns/transport/hosts/hosts_test.go

@@ -1,16 +1,29 @@
-package hosts_test
+package hosts
 
 import (
 	"net/netip"
+	"os"
+	"runtime"
 	"testing"
 
-	"github.com/sagernet/sing-box/dns/transport/hosts"
+	E "github.com/sagernet/sing/common/exceptions"
 
 	"github.com/stretchr/testify/require"
 )
 
 func TestHosts(t *testing.T) {
 	t.Parallel()
-	require.Equal(t, []netip.Addr{netip.AddrFrom4([4]byte{127, 0, 0, 1}), netip.IPv6Loopback()}, hosts.NewFile("testdata/hosts").Lookup("localhost"))
-	require.NotEmpty(t, hosts.NewFile(hosts.DefaultPath).Lookup("localhost"))
+	require.Equal(t, []netip.Addr{netip.AddrFrom4([4]byte{127, 0, 0, 1}), netip.IPv6Loopback()}, NewFile("testdata/hosts").Lookup("localhost"))
+	if runtime.GOOS != "windows" {
+		defaultPathResolved, err := defaultPath()
+		if err != nil {
+			t.Fatal(E.Cause(err, "resolve default hosts path"))
+		}
+		content, readErr := os.ReadFile(defaultPathResolved)
+		require.NoError(t, readErr)
+		hFile := NewFile(defaultPathResolved)
+		if len(hFile.Lookup("localhost")) == 0 {
+			t.Fatal("failed to resolve localhost: ", defaultPathResolved, ": \n", string(content))
+		}
+	}
 }

dns/transport/hosts/hosts_unix.go

@@ -2,4 +2,6 @@
 
 package hosts
 
-var DefaultPath = "/etc/hosts"
+func defaultPath() (string, error) {
+	return "/etc/hosts", nil
+}

dns/transport/hosts/hosts_windows.go

@@ -2,16 +2,15 @@ package hosts
 
 import (
 	"path/filepath"
+	"sync"
 
 	"golang.org/x/sys/windows"
 )
 
-var DefaultPath string
-
-func init() {
+var defaultPath = sync.OnceValues(func() (string, error) {
 	systemDirectory, err := windows.GetSystemDirectory()
 	if err != nil {
-		systemDirectory = "C:\\Windows\\System32"
+		return "", err
 	}
-	DefaultPath = filepath.Join(systemDirectory, "Drivers/etc/hosts")
-}
+	return filepath.Join(systemDirectory, "Drivers", "etc", "hosts"), nil
+})

dns/transport/local/local.go

@@ -39,11 +39,11 @@ func NewTransport(ctx context.Context, logger log.ContextLogger, tag string, opt
 	if err != nil {
 		return nil, err
 	}
+
 	return &Transport{
 		TransportAdapter: dns.NewTransportAdapterWithLocalOptions(C.DNSTypeLocal, tag, options),
 		ctx:              ctx,
 		logger:           logger,
-		hosts:            hosts.NewFile(hosts.DefaultPath),
 		dialer:           transportDialer,
 		preferGo:         options.PreferGo,
 	}, nil
@@ -52,6 +52,12 @@ func NewTransport(ctx context.Context, logger log.ContextLogger, tag string, opt
 func (t *Transport) Start(stage adapter.StartStage) error {
 	switch stage {
 	case adapter.StartStateInitialize:
+		defaultHosts, err := hosts.NewDefault()
+		if err != nil {
+			t.logger.Warn(err)
+		} else {
+			t.hosts = defaultHosts
+		}
 		if !t.preferGo {
 			if isSystemdResolvedManaged() {
 				resolvedResolver, err := NewResolvedResolver(t.ctx, t.logger)
@@ -84,7 +90,7 @@ func (t *Transport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg,
 		return t.resolved.Exchange(ctx, message)
 	}
 	question := message.Question[0]
-	if question.Qtype == mDNS.TypeA || question.Qtype == mDNS.TypeAAAA {
+	if t.hosts != nil && (question.Qtype == mDNS.TypeA || question.Qtype == mDNS.TypeAAAA) {
 		addresses := t.hosts.Lookup(dns.FqdnToDomain(question.Name))
 		if len(addresses) > 0 {
 			return dns.FixedResponse(message.Id, question, addresses, C.DefaultDNSTTL), nil

dns/transport/local/local_darwin.go

@@ -51,7 +51,6 @@ func NewTransport(ctx context.Context, logger log.ContextLogger, tag string, opt
 		TransportAdapter: dns.NewTransportAdapterWithLocalOptions(C.DNSTypeLocal, tag, options),
 		ctx:              ctx,
 		logger:           logger,
-		hosts:            hosts.NewFile(hosts.DefaultPath),
 		dialer:           transportDialer,
 	}, nil
 }
@@ -60,6 +59,12 @@ func (t *Transport) Start(stage adapter.StartStage) error {
 	if stage != adapter.StartStateStart {
 		return nil
 	}
+	defaultHosts, err := hosts.NewDefault()
+	if err != nil {
+		t.logger.Warn(err)
+	} else {
+		t.hosts = defaultHosts
+	}
 	inboundManager := service.FromContext[adapter.InboundManager](t.ctx)
 	for _, inbound := range inboundManager.Inbounds() {
 		if inbound.Type() == C.TypeTun {

dns/transport/local/local_darwin_cgo.go

@@ -197,7 +197,7 @@ func darwinResolverHErrno(name string, hErrno int) error {
 
 func (t *Transport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {
 	question := message.Question[0]
-	if question.Qtype == mDNS.TypeA || question.Qtype == mDNS.TypeAAAA {
+	if t.hosts != nil && (question.Qtype == mDNS.TypeA || question.Qtype == mDNS.TypeAAAA) {
 		addresses := t.hosts.Lookup(dns.FqdnToDomain(question.Name))
 		if len(addresses) > 0 {
 			return dns.FixedResponse(message.Id, question, addresses, boxC.DefaultDNSTTL), nil