Resolve conflicts

dns/client.go

@@ -2,12 +2,14 @@ package dns
 
 import (
 	"context"
+	"errors"
 	"net"
 	"net/netip"
 	"strings"
 	"time"
 
 	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing-box/common/compatible"
 	C "github.com/sagernet/sing-box/constant"
 	"github.com/sagernet/sing/common"
 	E "github.com/sagernet/sing/common/exceptions"
@@ -17,7 +19,7 @@ import (
 	"github.com/sagernet/sing/contrab/freelru"
 	"github.com/sagernet/sing/contrab/maphash"
 
-	dns "github.com/miekg/dns"
+	"github.com/miekg/dns"
 )
 
 var (
@@ -30,16 +32,18 @@ var (
 var _ adapter.DNSClient = (*Client)(nil)
 
 type Client struct {
-	timeout          time.Duration
-	disableCache     bool
-	disableExpire    bool
-	independentCache bool
-	clientSubnet     netip.Prefix
-	rdrc             adapter.RDRCStore
-	initRDRCFunc     func() adapter.RDRCStore
-	logger           logger.ContextLogger
-	cache            freelru.Cache[dns.Question, *dns.Msg]
-	transportCache   freelru.Cache[transportCacheKey, *dns.Msg]
+	timeout            time.Duration
+	disableCache       bool
+	disableExpire      bool
+	independentCache   bool
+	clientSubnet       netip.Prefix
+	rdrc               adapter.RDRCStore
+	initRDRCFunc       func() adapter.RDRCStore
+	logger             logger.ContextLogger
+	cache              freelru.Cache[dns.Question, *dns.Msg]
+	cacheLock          compatible.Map[dns.Question, chan struct{}]
+	transportCache     freelru.Cache[transportCacheKey, *dns.Msg]
+	transportCacheLock compatible.Map[dns.Question, chan struct{}]
 }
 
 type ClientOptions struct {
@@ -96,17 +100,15 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
 		if c.logger != nil {
 			c.logger.WarnContext(ctx, "bad question size: ", len(message.Question))
 		}
-		responseMessage := dns.Msg{
-			MsgHdr: dns.MsgHdr{
-				Id:       message.Id,
-				Response: true,
-				Rcode:    dns.RcodeFormatError,
-			},
-			Question: message.Question,
-		}
-		return &responseMessage, nil
+		return FixedResponseStatus(message, dns.RcodeFormatError), nil
 	}
 	question := message.Question[0]
+	if question.Qtype == dns.TypeA && options.Strategy == C.DomainStrategyIPv6Only || question.Qtype == dns.TypeAAAA && options.Strategy == C.DomainStrategyIPv4Only {
+		if c.logger != nil {
+			c.logger.DebugContext(ctx, "strategy rejected")
+		}
+		return FixedResponseStatus(message, dns.RcodeSuccess), nil
+	}
 	clientSubnet := options.ClientSubnet
 	if !clientSubnet.IsValid() {
 		clientSubnet = c.clientSubnet
@@ -114,12 +116,38 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
 	if clientSubnet.IsValid() {
 		message = SetClientSubnet(message, clientSubnet)
 	}
+
 	isSimpleRequest := len(message.Question) == 1 &&
 		len(message.Ns) == 0 &&
-		len(message.Extra) == 0 &&
+		(len(message.Extra) == 0 || len(message.Extra) == 1 &&
+			message.Extra[0].Header().Rrtype == dns.TypeOPT &&
+			message.Extra[0].Header().Class > 0 &&
+			message.Extra[0].Header().Ttl == 0 &&
+			len(message.Extra[0].(*dns.OPT).Option) == 0) &&
 		!options.ClientSubnet.IsValid()
 	disableCache := !isSimpleRequest || c.disableCache || options.DisableCache
 	if !disableCache {
+		if c.cache != nil {
+			cond, loaded := c.cacheLock.LoadOrStore(question, make(chan struct{}))
+			if loaded {
+				<-cond
+			} else {
+				defer func() {
+					c.cacheLock.Delete(question)
+					close(cond)
+				}()
+			}
+		} else if c.transportCache != nil {
+			cond, loaded := c.transportCacheLock.LoadOrStore(question, make(chan struct{}))
+			if loaded {
+				<-cond
+			} else {
+				defer func() {
+					c.transportCacheLock.Delete(question)
+					close(cond)
+				}()
+			}
+		}
 		response, ttl := c.loadResponse(question, transport)
 		if response != nil {
 			logCachedResponse(c.logger, ctx, response, ttl)
@@ -127,27 +155,14 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
 			return response, nil
 		}
 	}
-	if question.Qtype == dns.TypeA && options.Strategy == C.DomainStrategyIPv6Only || question.Qtype == dns.TypeAAAA && options.Strategy == C.DomainStrategyIPv4Only {
-		responseMessage := dns.Msg{
-			MsgHdr: dns.MsgHdr{
-				Id:       message.Id,
-				Response: true,
-				Rcode:    dns.RcodeSuccess,
-			},
-			Question: []dns.Question{question},
-		}
-		if c.logger != nil {
-			c.logger.DebugContext(ctx, "strategy rejected")
-		}
-		return &responseMessage, nil
-	}
+
 	messageId := message.Id
 	contextTransport, clientSubnetLoaded := transportTagFromContext(ctx)
 	if clientSubnetLoaded && transport.Tag() == contextTransport {
 		return nil, E.New("DNS query loopback in transport[", contextTransport, "]")
 	}
 	ctx = contextWithTransportTag(ctx, transport.Tag())
-	if responseChecker != nil && c.rdrc != nil {
+	if !disableCache && responseChecker != nil && c.rdrc != nil {
 		rejected := c.rdrc.LoadRDRC(transport.Tag(), question.Name, question.Qtype)
 		if rejected {
 			return nil, ErrResponseRejectedCached
@@ -157,7 +172,12 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
 	response, err := transport.Exchange(ctx, message)
 	cancel()
 	if err != nil {
-		return nil, err
+		var rcodeError RcodeError
+		if errors.As(err, &rcodeError) {
+			response = FixedResponseStatus(message, int(rcodeError))
+		} else {
+			return nil, err
+		}
 	}
 	/*if question.Qtype == dns.TypeA || question.Qtype == dns.TypeAAAA {
 		validResponse := response
@@ -194,15 +214,17 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
 			response.Answer = append(response.Answer, validResponse.Answer...)
 		}
 	}*/
+	disableCache = disableCache || response.Rcode != dns.RcodeSuccess || len(response.Answer) == 0
 	if responseChecker != nil {
 		var rejected bool
-		if !(response.Rcode == dns.RcodeSuccess || response.Rcode == dns.RcodeNameError) {
+		// TODO: add accept_any rule and support to check response instead of addresses
+		if response.Rcode != dns.RcodeSuccess || len(response.Answer) == 0 {
 			rejected = true
 		} else {
 			rejected = !responseChecker(MessageToAddresses(response))
 		}
 		if rejected {
-			if c.rdrc != nil {
+			if !disableCache && c.rdrc != nil {
 				c.rdrc.SaveRDRCAsync(transport.Tag(), question.Name, question.Qtype, c.logger)
 			}
 			logRejectedResponse(c.logger, ctx, response)
@@ -259,7 +281,7 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
 		}
 	}
 	logExchangedResponse(c.logger, ctx, response, timeToLive)
-	return response, err
+	return response, nil
 }
 
 func (c *Client) Lookup(ctx context.Context, transport adapter.DNSTransport, domain string, options adapter.DNSQueryOptions, responseChecker func(responseAddrs []netip.Addr) bool) ([]netip.Addr, error) {
@@ -305,8 +327,7 @@ func (c *Client) Lookup(ctx context.Context, transport adapter.DNSTransport, dom
 func (c *Client) ClearCache() {
 	if c.cache != nil {
 		c.cache.Purge()
-	}
-	if c.transportCache != nil {
+	} else if c.transportCache != nil {
 		c.transportCache.Purge()
 	}
 }
@@ -320,36 +341,36 @@ func (c *Client) LookupCache(domain string, strategy C.DomainStrategy) ([]netip.
 	}
 	dnsName := dns.Fqdn(domain)
 	if strategy == C.DomainStrategyIPv4Only {
-		response, err := c.questionCache(dns.Question{
+		addresses, err := c.questionCache(dns.Question{
 			Name:   dnsName,
 			Qtype:  dns.TypeA,
 			Qclass: dns.ClassINET,
 		}, nil)
 		if err != ErrNotCached {
-			return response, true
+			return addresses, true
 		}
 	} else if strategy == C.DomainStrategyIPv6Only {
-		response, err := c.questionCache(dns.Question{
+		addresses, err := c.questionCache(dns.Question{
 			Name:   dnsName,
 			Qtype:  dns.TypeAAAA,
 			Qclass: dns.ClassINET,
 		}, nil)
 		if err != ErrNotCached {
-			return response, true
+			return addresses, true
 		}
 	} else {
-		response4, _ := c.questionCache(dns.Question{
+		response4, _ := c.loadResponse(dns.Question{
 			Name:   dnsName,
 			Qtype:  dns.TypeA,
 			Qclass: dns.ClassINET,
 		}, nil)
-		response6, _ := c.questionCache(dns.Question{
+		response6, _ := c.loadResponse(dns.Question{
 			Name:   dnsName,
 			Qtype:  dns.TypeAAAA,
 			Qclass: dns.ClassINET,
 		}, nil)
-		if len(response4) > 0 || len(response6) > 0 {
-			return sortAddresses(response4, response6, strategy), true
+		if response4 != nil || response6 != nil {
+			return sortAddresses(MessageToAddresses(response4), MessageToAddresses(response6), strategy), true
 		}
 	}
 	return nil, false
@@ -390,15 +411,15 @@ func (c *Client) storeCache(transport adapter.DNSTransport, question dns.Questio
 				transportTag: transport.Tag(),
 			}, message)
 		}
-		return
-	}
-	if !c.independentCache {
-		c.cache.AddWithLifetime(question, message, time.Second*time.Duration(timeToLive))
 	} else {
-		c.transportCache.AddWithLifetime(transportCacheKey{
-			Question:     question,
-			transportTag: transport.Tag(),
-		}, message, time.Second*time.Duration(timeToLive))
+		if !c.independentCache {
+			c.cache.AddWithLifetime(question, message, time.Second*time.Duration(timeToLive))
+		} else {
+			c.transportCache.AddWithLifetime(transportCacheKey{
+				Question:     question,
+				transportTag: transport.Tag(),
+			}, message, time.Second*time.Duration(timeToLive))
+		}
 	}
 }
 
@@ -517,6 +538,9 @@ func (c *Client) loadResponse(question dns.Question, transport adapter.DNSTransp
 }
 
 func MessageToAddresses(response *dns.Msg) []netip.Addr {
+	if response == nil || response.Rcode != dns.RcodeSuccess {
+		return nil
+	}
 	addresses := make([]netip.Addr, 0, len(response.Answer))
 	for _, rawAnswer := range response.Answer {
 		switch answer := rawAnswer.(type) {
@@ -561,9 +585,12 @@ func transportTagFromContext(ctx context.Context) (string, bool) {
 func FixedResponseStatus(message *dns.Msg, rcode int) *dns.Msg {
 	return &dns.Msg{
 		MsgHdr: dns.MsgHdr{
-			Id:       message.Id,
-			Rcode:    rcode,
-			Response: true,
+			Id:                 message.Id,
+			Response:           true,
+			Authoritative:      true,
+			RecursionDesired:   true,
+			RecursionAvailable: true,
+			Rcode:              rcode,
 		},
 		Question: message.Question,
 	}

dns/rcode.go

@@ -5,6 +5,7 @@ import (
 )
 
 const (
+	RcodeSuccess     RcodeError = mDNS.RcodeSuccess
 	RcodeFormatError RcodeError = mDNS.RcodeFormatError
 	RcodeNameError   RcodeError = mDNS.RcodeNameError
 	RcodeRefused     RcodeError = mDNS.RcodeRefused

dns/router.go

@@ -293,12 +293,7 @@ func (r *Router) Exchange(ctx context.Context, message *mDNS.Msg, options adapte
 					} else if errors.Is(err, ErrResponseRejected) {
 						rejected = true
 						r.logger.DebugContext(ctx, E.Cause(err, "response rejected for ", FormatQuestion(message.Question[0].String())))
-						/*} else if responseCheck!= nil && errors.Is(err, RcodeError(mDNS.RcodeNameError)) {
-						rejected = true
-						r.logger.DebugContext(ctx, E.Cause(err, "response rejected for ", FormatQuestion(message.Question[0].String())))
-						*/
 					} else if len(message.Question) > 0 {
-						rejected = true
 						r.logger.ErrorContext(ctx, E.Cause(err, "exchange failed for ", FormatQuestion(message.Question[0].String())))
 					} else {
 						r.logger.ErrorContext(ctx, E.Cause(err, "exchange failed for <empty query>"))

dns/transport/dhcp/dhcp.go

@@ -2,17 +2,18 @@ package dhcp
 
 import (
 	"context"
+	"errors"
+	"io"
 	"net"
 	"runtime"
 	"strings"
 	"sync"
+	"syscall"
 	"time"
 
 	"github.com/sagernet/sing-box/adapter"
-	"github.com/sagernet/sing-box/common/dialer"
 	C "github.com/sagernet/sing-box/constant"
 	"github.com/sagernet/sing-box/dns"
-	"github.com/sagernet/sing-box/dns/transport"
 	"github.com/sagernet/sing-box/log"
 	"github.com/sagernet/sing-box/option"
 	"github.com/sagernet/sing-tun"
@@ -29,6 +30,7 @@ import (
 
 	"github.com/insomniacslk/dhcp/dhcpv4"
 	mDNS "github.com/miekg/dns"
+	"golang.org/x/exp/slices"
 )
 
 func RegisterTransport(registry *dns.TransportRegistry) {
@@ -45,9 +47,12 @@ type Transport struct {
 	networkManager    adapter.NetworkManager
 	interfaceName     string
 	interfaceCallback *list.Element[tun.DefaultInterfaceUpdateCallback]
-	transports        []adapter.DNSTransport
-	updateAccess      sync.Mutex
+	transportLock     sync.RWMutex
 	updatedAt         time.Time
+	servers           []M.Socksaddr
+	search            []string
+	ndots             int
+	attempts          int
 }
 
 func NewTransport(ctx context.Context, logger log.ContextLogger, tag string, options option.DHCPDNSServerOptions) (adapter.DNSTransport, error) {
@@ -62,27 +67,40 @@ func NewTransport(ctx context.Context, logger log.ContextLogger, tag string, opt
 		logger:           logger,
 		networkManager:   service.FromContext[adapter.NetworkManager](ctx),
 		interfaceName:    options.Interface,
+		ndots:            1,
+		attempts:         2,
 	}, nil
 }
 
+func NewRawTransport(transportAdapter dns.TransportAdapter, ctx context.Context, dialer N.Dialer, logger log.ContextLogger) *Transport {
+	return &Transport{
+		TransportAdapter: transportAdapter,
+		ctx:              ctx,
+		dialer:           dialer,
+		logger:           logger,
+		networkManager:   service.FromContext[adapter.NetworkManager](ctx),
+		ndots:            1,
+		attempts:         2,
+	}
+}
+
 func (t *Transport) Start(stage adapter.StartStage) error {
 	if stage != adapter.StartStateStart {
 		return nil
 	}
-	err := t.fetchServers()
-	if err != nil {
-		return err
-	}
 	if t.interfaceName == "" {
 		t.interfaceCallback = t.networkManager.InterfaceMonitor().RegisterCallback(t.interfaceUpdated)
 	}
+	go func() {
+		_, err := t.Fetch()
+		if err != nil {
+			t.logger.Error(E.Cause(err, "fetch DNS servers"))
+		}
+	}()
 	return nil
 }
 
 func (t *Transport) Close() error {
-	for _, transport := range t.transports {
-		transport.Close()
-	}
 	if t.interfaceCallback != nil {
 		t.networkManager.InterfaceMonitor().UnregisterCallback(t.interfaceCallback)
 	}
@@ -90,23 +108,44 @@ func (t *Transport) Close() error {
 }
 
 func (t *Transport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {
-	err := t.fetchServers()
+	servers, err := t.Fetch()
 	if err != nil {
 		return nil, err
 	}
-
-	if len(t.transports) == 0 {
+	if len(servers) == 0 {
 		return nil, E.New("dhcp: empty DNS servers from response")
 	}
+	return t.Exchange0(ctx, message, servers)
+}
 
-	var response *mDNS.Msg
-	for _, transport := range t.transports {
-		response, err = transport.Exchange(ctx, message)
-		if err == nil {
-			return response, nil
-		}
+func (t *Transport) Exchange0(ctx context.Context, message *mDNS.Msg, servers []M.Socksaddr) (*mDNS.Msg, error) {
+	question := message.Question[0]
+	domain := dns.FqdnToDomain(question.Name)
+	if len(servers) == 1 || !(message.Question[0].Qtype == mDNS.TypeA || message.Question[0].Qtype == mDNS.TypeAAAA) {
+		return t.exchangeSingleRequest(ctx, servers, message, domain)
+	} else {
+		return t.exchangeParallel(ctx, servers, message, domain)
 	}
-	return nil, err
+}
+
+func (t *Transport) Fetch() ([]M.Socksaddr, error) {
+	t.transportLock.RLock()
+	updatedAt := t.updatedAt
+	servers := t.servers
+	t.transportLock.RUnlock()
+	if time.Since(updatedAt) < C.DHCPTTL {
+		return servers, nil
+	}
+	t.transportLock.Lock()
+	defer t.transportLock.Unlock()
+	if time.Since(t.updatedAt) < C.DHCPTTL {
+		return t.servers, nil
+	}
+	err := t.updateServers()
+	if err != nil {
+		return nil, err
+	}
+	return t.servers, nil
 }
 
 func (t *Transport) fetchInterface() (*control.Interface, error) {
@@ -124,18 +163,6 @@ func (t *Transport) fetchInterface() (*control.Interface, error) {
 	}
 }
 
-func (t *Transport) fetchServers() error {
-	if time.Since(t.updatedAt) < C.DHCPTTL {
-		return nil
-	}
-	t.updateAccess.Lock()
-	defer t.updateAccess.Unlock()
-	if time.Since(t.updatedAt) < C.DHCPTTL {
-		return nil
-	}
-	return t.updateServers()
-}
-
 func (t *Transport) updateServers() error {
 	iface, err := t.fetchInterface()
 	if err != nil {
@@ -148,7 +175,7 @@ func (t *Transport) updateServers() error {
 	cancel()
 	if err != nil {
 		return err
-	} else if len(t.transports) == 0 {
+	} else if len(t.servers) == 0 {
 		return E.New("dhcp: empty DNS servers response")
 	} else {
 		t.updatedAt = time.Now()
@@ -171,13 +198,27 @@ func (t *Transport) fetchServers0(ctx context.Context, iface *control.Interface)
 	if runtime.GOOS == "linux" || runtime.GOOS == "android" {
 		listenAddr = "255.255.255.255:68"
 	}
-	packetConn, err := listener.ListenPacket(t.ctx, "udp4", listenAddr)
+	var (
+		packetConn net.PacketConn
+		err        error
+	)
+	for i := 0; i < 5; i++ {
+		packetConn, err = listener.ListenPacket(t.ctx, "udp4", listenAddr)
+		if err == nil || !errors.Is(err, syscall.EADDRINUSE) {
+			break
+		}
+		time.Sleep(time.Second)
+	}
 	if err != nil {
 		return err
 	}
 	defer packetConn.Close()
 
-	discovery, err := dhcpv4.NewDiscovery(iface.HardwareAddr, dhcpv4.WithBroadcast(true), dhcpv4.WithRequestedOptions(dhcpv4.OptionDomainNameServer))
+	discovery, err := dhcpv4.NewDiscovery(iface.HardwareAddr, dhcpv4.WithBroadcast(true), dhcpv4.WithRequestedOptions(
+		dhcpv4.OptionDomainName,
+		dhcpv4.OptionDomainNameServer,
+		dhcpv4.OptionDNSDomainSearchList,
+	))
 	if err != nil {
 		return err
 	}
@@ -204,6 +245,9 @@ func (t *Transport) fetchServersResponse(iface *control.Interface, packetConn ne
 	for {
 		_, _, err := buffer.ReadPacketFrom(packetConn)
 		if err != nil {
+			if errors.Is(err, io.ErrShortBuffer) {
+				continue
+			}
 			return err
 		}
 
@@ -223,31 +267,23 @@ func (t *Transport) fetchServersResponse(iface *control.Interface, packetConn ne
 			continue
 		}
 
-		dns := dhcpPacket.DNS()
-		if len(dns) == 0 {
-			return nil
-		}
-		return t.recreateServers(iface, common.Map(dns, func(it net.IP) M.Socksaddr {
-			return M.SocksaddrFrom(M.AddrFromIP(it), 53)
-		}))
+		return t.recreateServers(iface, dhcpPacket)
 	}
 }
 
-func (t *Transport) recreateServers(iface *control.Interface, serverAddrs []M.Socksaddr) error {
-	if len(serverAddrs) > 0 {
-		t.logger.Info("dhcp: updated DNS servers from ", iface.Name, ": [", strings.Join(common.Map(serverAddrs, M.Socksaddr.String), ","), "]")
+func (t *Transport) recreateServers(iface *control.Interface, dhcpPacket *dhcpv4.DHCPv4) error {
+	searchList := dhcpPacket.DomainSearch()
+	if searchList != nil && len(searchList.Labels) > 0 {
+		t.search = searchList.Labels
+	} else if dhcpPacket.DomainName() != "" {
+		t.search = []string{dhcpPacket.DomainName()}
 	}
-	serverDialer := common.Must1(dialer.NewDefault(t.ctx, option.DialerOptions{
-		BindInterface:      iface.Name,
-		UDPFragmentDefault: true,
-	}))
-	var transports []adapter.DNSTransport
-	for _, serverAddr := range serverAddrs {
-		transports = append(transports, transport.NewUDPRaw(t.logger, t.TransportAdapter, serverDialer, serverAddr))
+	serverAddrs := common.Map(dhcpPacket.DNS(), func(it net.IP) M.Socksaddr {
+		return M.SocksaddrFrom(M.AddrFromIP(it), 53)
+	})
+	if len(serverAddrs) > 0 && !slices.Equal(t.servers, serverAddrs) {
+		t.logger.Info("dhcp: updated DNS servers from ", iface.Name, ": [", strings.Join(common.Map(serverAddrs, M.Socksaddr.String), ","), "], search: [", strings.Join(t.search, ","), "]")
 	}
-	for _, transport := range t.transports {
-		transport.Close()
-	}
-	t.transports = transports
+	t.servers = serverAddrs
 	return nil
 }

dns/transport/dhcp/dhcp_shared.go

@@ -0,0 +1,213 @@
+package dhcp
+
+import (
+	"context"
+	"errors"
+	"math/rand"
+	"strings"
+	"syscall"
+
+	"github.com/sagernet/sing-box/dns"
+	"github.com/sagernet/sing-box/dns/transport"
+	"github.com/sagernet/sing/common/buf"
+	E "github.com/sagernet/sing/common/exceptions"
+	M "github.com/sagernet/sing/common/metadata"
+	N "github.com/sagernet/sing/common/network"
+
+	mDNS "github.com/miekg/dns"
+)
+
+func (t *Transport) exchangeSingleRequest(ctx context.Context, servers []M.Socksaddr, message *mDNS.Msg, domain string) (*mDNS.Msg, error) {
+	var lastErr error
+	for _, fqdn := range t.nameList(domain) {
+		response, err := t.tryOneName(ctx, servers, fqdn, message)
+		if err != nil {
+			lastErr = err
+			continue
+		}
+		return response, nil
+	}
+	return nil, lastErr
+}
+
+func (t *Transport) exchangeParallel(ctx context.Context, servers []M.Socksaddr, message *mDNS.Msg, domain string) (*mDNS.Msg, error) {
+	returned := make(chan struct{})
+	defer close(returned)
+	type queryResult struct {
+		response *mDNS.Msg
+		err      error
+	}
+	results := make(chan queryResult)
+	startRacer := func(ctx context.Context, fqdn string) {
+		response, err := t.tryOneName(ctx, servers, fqdn, message)
+		if err == nil {
+			if response.Rcode != mDNS.RcodeSuccess {
+				err = dns.RcodeError(response.Rcode)
+			} else if len(dns.MessageToAddresses(response)) == 0 {
+				err = dns.RcodeSuccess
+			}
+		}
+		select {
+		case results <- queryResult{response, err}:
+		case <-returned:
+		}
+	}
+	queryCtx, queryCancel := context.WithCancel(ctx)
+	defer queryCancel()
+	var nameCount int
+	for _, fqdn := range t.nameList(domain) {
+		nameCount++
+		go startRacer(queryCtx, fqdn)
+	}
+	var errors []error
+	for {
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case result := <-results:
+			if result.err == nil {
+				return result.response, nil
+			}
+			errors = append(errors, result.err)
+			if len(errors) == nameCount {
+				return nil, E.Errors(errors...)
+			}
+		}
+	}
+}
+
+func (t *Transport) tryOneName(ctx context.Context, servers []M.Socksaddr, fqdn string, message *mDNS.Msg) (*mDNS.Msg, error) {
+	sLen := len(servers)
+	var lastErr error
+	for i := 0; i < t.attempts; i++ {
+		for j := 0; j < sLen; j++ {
+			server := servers[j]
+			question := message.Question[0]
+			question.Name = fqdn
+			response, err := t.exchangeOne(ctx, server, question)
+			if err != nil {
+				lastErr = err
+				continue
+			}
+			return response, nil
+		}
+	}
+	return nil, E.Cause(lastErr, fqdn)
+}
+
+func (t *Transport) exchangeOne(ctx context.Context, server M.Socksaddr, question mDNS.Question) (*mDNS.Msg, error) {
+	if server.Port == 0 {
+		server.Port = 53
+	}
+	request := &mDNS.Msg{
+		MsgHdr: mDNS.MsgHdr{
+			Id:                uint16(rand.Uint32()),
+			RecursionDesired:  true,
+			AuthenticatedData: true,
+		},
+		Question: []mDNS.Question{question},
+		Compress: true,
+	}
+	request.SetEdns0(buf.UDPBufferSize, false)
+	return t.exchangeUDP(ctx, server, request)
+}
+
+func (t *Transport) exchangeUDP(ctx context.Context, server M.Socksaddr, request *mDNS.Msg) (*mDNS.Msg, error) {
+	conn, err := t.dialer.DialContext(ctx, N.NetworkUDP, server)
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+	if deadline, loaded := ctx.Deadline(); loaded && !deadline.IsZero() {
+		conn.SetDeadline(deadline)
+	}
+	buffer := buf.Get(buf.UDPBufferSize)
+	defer buf.Put(buffer)
+	rawMessage, err := request.PackBuffer(buffer)
+	if err != nil {
+		return nil, E.Cause(err, "pack request")
+	}
+	_, err = conn.Write(rawMessage)
+	if err != nil {
+		if errors.Is(err, syscall.EMSGSIZE) {
+			return t.exchangeTCP(ctx, server, request)
+		}
+		return nil, E.Cause(err, "write request")
+	}
+	n, err := conn.Read(buffer)
+	if err != nil {
+		if errors.Is(err, syscall.EMSGSIZE) {
+			return t.exchangeTCP(ctx, server, request)
+		}
+		return nil, E.Cause(err, "read response")
+	}
+	var response mDNS.Msg
+	err = response.Unpack(buffer[:n])
+	if err != nil {
+		return nil, E.Cause(err, "unpack response")
+	}
+	if response.Truncated {
+		return t.exchangeTCP(ctx, server, request)
+	}
+	return &response, nil
+}
+
+func (t *Transport) exchangeTCP(ctx context.Context, server M.Socksaddr, request *mDNS.Msg) (*mDNS.Msg, error) {
+	conn, err := t.dialer.DialContext(ctx, N.NetworkTCP, server)
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+	if deadline, loaded := ctx.Deadline(); loaded && !deadline.IsZero() {
+		conn.SetDeadline(deadline)
+	}
+	err = transport.WriteMessage(conn, 0, request)
+	if err != nil {
+		return nil, err
+	}
+	return transport.ReadMessage(conn)
+}
+
+func (t *Transport) nameList(name string) []string {
+	l := len(name)
+	rooted := l > 0 && name[l-1] == '.'
+	if l > 254 || l == 254 && !rooted {
+		return nil
+	}
+
+	if rooted {
+		if avoidDNS(name) {
+			return nil
+		}
+		return []string{name}
+	}
+
+	hasNdots := strings.Count(name, ".") >= t.ndots
+	name += "."
+	// l++
+
+	names := make([]string, 0, 1+len(t.search))
+	if hasNdots && !avoidDNS(name) {
+		names = append(names, name)
+	}
+	for _, suffix := range t.search {
+		fqdn := name + suffix
+		if !avoidDNS(fqdn) && len(fqdn) <= 254 {
+			names = append(names, fqdn)
+		}
+	}
+	if !hasNdots && !avoidDNS(name) {
+		names = append(names, name)
+	}
+	return names
+}
+
+func avoidDNS(name string) bool {
+	if name == "" {
+		return true
+	}
+	if name[len(name)-1] == '.' {
+		name = name[:len(name)-1]
+	}
+	return strings.HasSuffix(name, ".onion")
+}

dns/transport/https.go

@@ -8,7 +8,6 @@ import (
 	"net"
 	"net/http"
 	"net/url"
-	"os"
 	"strconv"
 	"sync"
 	"time"
@@ -178,7 +177,7 @@ func (t *HTTPSTransport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS
 	startAt := time.Now()
 	response, err := t.exchange(ctx, message)
 	if err != nil {
-		if errors.Is(err, os.ErrDeadlineExceeded) {
+		if errors.Is(err, context.DeadlineExceeded) {
 			t.transportAccess.Lock()
 			defer t.transportAccess.Unlock()
 			if t.transportResetAt.After(startAt) {

dns/transport/local/local.go

@@ -2,12 +2,15 @@ package local
 
 import (
 	"context"
+	"errors"
 	"math/rand"
+	"syscall"
 	"time"
 
 	"github.com/sagernet/sing-box/adapter"
 	C "github.com/sagernet/sing-box/constant"
 	"github.com/sagernet/sing-box/dns"
+	"github.com/sagernet/sing-box/dns/transport"
 	"github.com/sagernet/sing-box/dns/transport/hosts"
 	"github.com/sagernet/sing-box/log"
 	"github.com/sagernet/sing-box/option"
@@ -93,7 +96,7 @@ func (t *Transport) exchangeParallel(ctx context.Context, systemConfig *dnsConfi
 			if response.Rcode != mDNS.RcodeSuccess {
 				err = dns.RcodeError(response.Rcode)
 			} else if len(dns.MessageToAddresses(response)) == 0 {
-				err = E.New(fqdn, ": empty result")
+				err = dns.RcodeSuccess
 			}
 		}
 		select {
@@ -149,12 +152,6 @@ func (t *Transport) exchangeOne(ctx context.Context, server M.Socksaddr, questio
 	if server.Port == 0 {
 		server.Port = 53
 	}
-	var networks []string
-	if useTCP {
-		networks = []string{N.NetworkTCP}
-	} else {
-		networks = []string{N.NetworkUDP, N.NetworkTCP}
-	}
 	request := &mDNS.Msg{
 		MsgHdr: mDNS.MsgHdr{
 			Id:                uint16(rand.Uint32()),
@@ -164,41 +161,74 @@ func (t *Transport) exchangeOne(ctx context.Context, server M.Socksaddr, questio
 		Question: []mDNS.Question{question},
 		Compress: true,
 	}
-	request.SetEdns0(maxDNSPacketSize, false)
+	request.SetEdns0(buf.UDPBufferSize, false)
+	if !useTCP {
+		return t.exchangeUDP(ctx, server, request, timeout)
+	} else {
+		return t.exchangeTCP(ctx, server, request, timeout)
+	}
+}
+
+func (t *Transport) exchangeUDP(ctx context.Context, server M.Socksaddr, request *mDNS.Msg, timeout time.Duration) (*mDNS.Msg, error) {
+	conn, err := t.dialer.DialContext(ctx, N.NetworkUDP, server)
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+	if deadline, loaded := ctx.Deadline(); loaded && !deadline.IsZero() {
+		newDeadline := time.Now().Add(timeout)
+		if deadline.After(newDeadline) {
+			deadline = newDeadline
+		}
+		conn.SetDeadline(deadline)
+	}
 	buffer := buf.Get(buf.UDPBufferSize)
 	defer buf.Put(buffer)
-	for _, network := range networks {
-		ctx, cancel := context.WithDeadline(ctx, time.Now().Add(timeout))
-		defer cancel()
-		conn, err := t.dialer.DialContext(ctx, network, server)
-		if err != nil {
-			return nil, err
-		}
-		defer conn.Close()
-		if deadline, loaded := ctx.Deadline(); loaded && !deadline.IsZero() {
-			conn.SetDeadline(deadline)
-		}
-		rawMessage, err := request.PackBuffer(buffer)
-		if err != nil {
-			return nil, E.Cause(err, "pack request")
-		}
-		_, err = conn.Write(rawMessage)
-		if err != nil {
-			return nil, E.Cause(err, "write request")
-		}
-		n, err := conn.Read(buffer)
-		if err != nil {
-			return nil, E.Cause(err, "read response")
-		}
-		var response mDNS.Msg
-		err = response.Unpack(buffer[:n])
-		if err != nil {
-			return nil, E.Cause(err, "unpack response")
-		}
-		if response.Truncated && network == N.NetworkUDP {
-			continue
-		}
-		return &response, nil
+	rawMessage, err := request.PackBuffer(buffer)
+	if err != nil {
+		return nil, E.Cause(err, "pack request")
 	}
-	panic("unexpected")
+	_, err = conn.Write(rawMessage)
+	if err != nil {
+		if errors.Is(err, syscall.EMSGSIZE) {
+			return t.exchangeTCP(ctx, server, request, timeout)
+		}
+		return nil, E.Cause(err, "write request")
+	}
+	n, err := conn.Read(buffer)
+	if err != nil {
+		if errors.Is(err, syscall.EMSGSIZE) {
+			return t.exchangeTCP(ctx, server, request, timeout)
+		}
+		return nil, E.Cause(err, "read response")
+	}
+	var response mDNS.Msg
+	err = response.Unpack(buffer[:n])
+	if err != nil {
+		return nil, E.Cause(err, "unpack response")
+	}
+	if response.Truncated {
+		return t.exchangeTCP(ctx, server, request, timeout)
+	}
+	return &response, nil
+}
+
+func (t *Transport) exchangeTCP(ctx context.Context, server M.Socksaddr, request *mDNS.Msg, timeout time.Duration) (*mDNS.Msg, error) {
+	conn, err := t.dialer.DialContext(ctx, N.NetworkTCP, server)
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+	if deadline, loaded := ctx.Deadline(); loaded && !deadline.IsZero() {
+		newDeadline := time.Now().Add(timeout)
+		if deadline.After(newDeadline) {
+			deadline = newDeadline
+		}
+		conn.SetDeadline(deadline)
+	}
+	err = transport.WriteMessage(conn, 0, request)
+	if err != nil {
+		return nil, err
+	}
+	return transport.ReadMessage(conn)
 }

dns/transport/local/resolv.go

@@ -10,11 +10,6 @@ import (
 	"time"
 )
 
-const (
-	// net.maxDNSPacketSize
-	maxDNSPacketSize = 1232
-)
-
 type resolverConfig struct {
 	initOnce    sync.Once
 	ch          chan struct{}
@@ -104,7 +99,7 @@ func (c *dnsConfig) serverOffset() uint32 {
 	return 0
 }
 
-func (conf *dnsConfig) nameList(name string) []string {
+func (c *dnsConfig) nameList(name string) []string {
 	l := len(name)
 	rooted := l > 0 && name[l-1] == '.'
 	if l > 254 || l == 254 && !rooted {
@@ -118,15 +113,15 @@ func (conf *dnsConfig) nameList(name string) []string {
 		return []string{name}
 	}
 
-	hasNdots := strings.Count(name, ".") >= conf.ndots
+	hasNdots := strings.Count(name, ".") >= c.ndots
 	name += "."
 	// l++
 
-	names := make([]string, 0, 1+len(conf.search))
+	names := make([]string, 0, 1+len(c.search))
 	if hasNdots && !avoidDNS(name) {
 		names = append(names, name)
 	}
-	for _, suffix := range conf.search {
+	for _, suffix := range c.search {
 		fqdn := name + suffix
 		if !avoidDNS(fqdn) && len(fqdn) <= 254 {
 			names = append(names, fqdn)