refactor: DNS

dns/transport/hosts/hosts.go

@@ -0,0 +1,63 @@
+package hosts
+
+import (
+	"context"
+
+	"github.com/sagernet/sing-box/adapter"
+	C "github.com/sagernet/sing-box/constant"
+	"github.com/sagernet/sing-box/dns"
+	"github.com/sagernet/sing-box/log"
+	"github.com/sagernet/sing-box/option"
+
+	mDNS "github.com/miekg/dns"
+)
+
+func RegisterTransport(registry *dns.TransportRegistry) {
+	dns.RegisterTransport[option.HostsDNSServerOptions](registry, C.DNSTypeHosts, NewTransport)
+}
+
+var _ adapter.DNSTransport = (*Transport)(nil)
+
+type Transport struct {
+	dns.TransportAdapter
+	files []*File
+}
+
+func NewTransport(ctx context.Context, logger log.ContextLogger, tag string, options option.HostsDNSServerOptions) (adapter.DNSTransport, error) {
+	var files []*File
+	if len(options.Path) == 0 {
+		files = append(files, NewFile(DefaultPath))
+	} else {
+		for _, path := range options.Path {
+			files = append(files, NewFile(path))
+		}
+	}
+	return &Transport{
+		TransportAdapter: dns.NewTransportAdapter(C.DNSTypeHosts, tag, nil),
+		files:            files,
+	}, nil
+}
+
+func (t *Transport) Reset() {
+}
+
+func (t *Transport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {
+	question := message.Question[0]
+	domain := dns.FqdnToDomain(question.Name)
+	if question.Qtype == mDNS.TypeA || question.Qtype == mDNS.TypeAAAA {
+		for _, file := range t.files {
+			addresses := file.Lookup(domain)
+			if len(addresses) > 0 {
+				return dns.FixedResponse(message.Id, question, addresses, C.DefaultDNSTTL), nil
+			}
+		}
+	}
+	return &mDNS.Msg{
+		MsgHdr: mDNS.MsgHdr{
+			Id:       message.Id,
+			Rcode:    mDNS.RcodeNameError,
+			Response: true,
+		},
+		Question: []mDNS.Question{question},
+	}, nil
+}

dns/transport/hosts/hosts_file.go

@@ -0,0 +1,102 @@
+package hosts
+
+import (
+	"bufio"
+	"errors"
+	"io"
+	"net/netip"
+	"os"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+const cacheMaxAge = 5 * time.Second
+
+type File struct {
+	path    string
+	access  sync.Mutex
+	byName  map[string][]netip.Addr
+	expire  time.Time
+	modTime time.Time
+	size    int64
+}
+
+func NewFile(path string) *File {
+	return &File{
+		path: path,
+	}
+}
+
+func (f *File) Lookup(name string) []netip.Addr {
+	f.access.Lock()
+	defer f.access.Unlock()
+	f.update()
+	return f.byName[name]
+}
+
+func (f *File) update() {
+	now := time.Now()
+	if now.Before(f.expire) && len(f.byName) > 0 {
+		return
+	}
+	stat, err := os.Stat(f.path)
+	if err != nil {
+		return
+	}
+	if f.modTime.Equal(stat.ModTime()) && f.size == stat.Size() {
+		f.expire = now.Add(cacheMaxAge)
+		return
+	}
+	byName := make(map[string][]netip.Addr)
+	file, err := os.Open(f.path)
+	if err != nil {
+		return
+	}
+	defer file.Close()
+	reader := bufio.NewReader(file)
+	var (
+		prefix   []byte
+		line     []byte
+		isPrefix bool
+	)
+	for {
+		line, isPrefix, err = reader.ReadLine()
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			return
+		}
+		if isPrefix {
+			prefix = append(prefix, line...)
+			continue
+		} else if len(prefix) > 0 {
+			line = append(prefix, line...)
+			prefix = nil
+		}
+		commentIndex := strings.IndexRune(string(line), '#')
+		if commentIndex != -1 {
+			line = line[:commentIndex]
+		}
+		fields := strings.Fields(string(line))
+		if len(fields) < 2 {
+			continue
+		}
+		var addr netip.Addr
+		addr, err = netip.ParseAddr(fields[0])
+		if err != nil {
+			continue
+		}
+		for index := 1; index < len(fields); index++ {
+			canonicalName := dns.CanonicalName(fields[index])
+			byName[canonicalName] = append(byName[canonicalName], addr)
+		}
+	}
+	f.expire = now.Add(cacheMaxAge)
+	f.modTime = stat.ModTime()
+	f.size = stat.Size()
+	f.byName = byName
+}

dns/transport/hosts/hosts_test.go

@@ -0,0 +1,16 @@
+package hosts_test
+
+import (
+	"net/netip"
+	"testing"
+
+	"github.com/sagernet/sing-box/dns/transport/hosts"
+
+	"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."))
+}

dns/transport/hosts/hosts_unix.go

@@ -0,0 +1,5 @@
+//go:build !windows
+
+package hosts
+
+var DefaultPath = "/etc/hosts"

dns/transport/hosts/hosts_windows.go

@@ -0,0 +1,17 @@
+package hosts
+
+import (
+	"path/filepath"
+
+	"golang.org/x/sys/windows"
+)
+
+var DefaultPath string
+
+func init() {
+	systemDirectory, err := windows.GetSystemDirectory()
+	if err != nil {
+		systemDirectory = "C:\\Windows\\System32"
+	}
+	DefaultPath = filepath.Join(systemDirectory, "Drivers/etc/hosts")
+}

dns/transport/hosts/testdata/hosts

@@ -0,0 +1,2 @@
+127.0.0.1       localhost
+::1             localhost