chore: ensures packets can be sent without blocking the tunnel

component/nat/table.go

@@ -10,47 +10,30 @@ import (
 )
 
 type Table struct {
-	mapping *xsync.MapOf[string, *Entry]
+	mapping *xsync.MapOf[string, *entry]
-	lockMap *xsync.MapOf[string, *sync.Cond]
 }
 
-type Entry struct {
+type entry struct {
-	PacketConn      C.PacketConn
+	PacketSender    C.PacketSender
-	WriteBackProxy  C.WriteBackProxy
 	LocalUDPConnMap *xsync.MapOf[string, *net.UDPConn]
 	LocalLockMap    *xsync.MapOf[string, *sync.Cond]
 }
 
-func (t *Table) Set(key string, e C.PacketConn, w C.WriteBackProxy) {
+func (t *Table) GetOrCreate(key string, maker func() C.PacketSender) (C.PacketSender, bool) {
-	t.mapping.Store(key, &Entry{
+	item, loaded := t.mapping.LoadOrCompute(key, func() *entry {
-		PacketConn:      e,
+		return &entry{
-		WriteBackProxy:  w,
+			PacketSender:    maker(),
 			LocalUDPConnMap: xsync.NewMapOf[string, *net.UDPConn](),
 			LocalLockMap:    xsync.NewMapOf[string, *sync.Cond](),
+		}
 	})
-}
+	return item.PacketSender, loaded
-
-func (t *Table) Get(key string) (C.PacketConn, C.WriteBackProxy) {
-	entry, exist := t.getEntry(key)
-	if !exist {
-		return nil, nil
-	}
-	return entry.PacketConn, entry.WriteBackProxy
-}
-
-func (t *Table) GetOrCreateLock(key string) (*sync.Cond, bool) {
-	item, loaded := t.lockMap.LoadOrCompute(key, makeLock)
-	return item, loaded
 }
 
 func (t *Table) Delete(key string) {
 	t.mapping.Delete(key)
 }
 
-func (t *Table) DeleteLock(lockKey string) {
-	t.lockMap.Delete(lockKey)
-}
-
 func (t *Table) GetForLocalConn(lAddr, rAddr string) *net.UDPConn {
 	entry, exist := t.getEntry(lAddr)
 	if !exist {
@@ -105,7 +88,7 @@ func (t *Table) DeleteLockForLocalConn(lAddr, key string) {
 	entry.LocalLockMap.Delete(key)
 }
 
-func (t *Table) getEntry(key string) (*Entry, bool) {
+func (t *Table) getEntry(key string) (*entry, bool) {
 	return t.mapping.Load(key)
 }
 
@@ -116,7 +99,6 @@ func makeLock() *sync.Cond {
 // New return *Cache
 func New() *Table {
 	return &Table{
-		mapping: xsync.NewMapOf[string, *Entry](),
+		mapping: xsync.NewMapOf[string, *entry](),
-		lockMap: xsync.NewMapOf[string, *sync.Cond](),
 	}
 }

constant/adapters.go

@@ -255,12 +255,16 @@ type UDPPacketInAddr interface {
 // PacketAdapter is a UDP Packet adapter for socks/redir/tun
 type PacketAdapter interface {
 	UDPPacket
+	// Metadata returns destination metadata
 	Metadata() *Metadata
+	// Key is a SNAT key
+	Key() string
 }
 
 type packetAdapter struct {
 	UDPPacket
 	metadata *Metadata
+	key      string
 }
 
 // Metadata returns destination metadata
@@ -268,10 +272,16 @@ func (s *packetAdapter) Metadata() *Metadata {
 	return s.metadata
 }
 
+// Key is a SNAT key
+func (s *packetAdapter) Key() string {
+	return s.key
+}
+
 func NewPacketAdapter(packet UDPPacket, metadata *Metadata) PacketAdapter {
 	return &packetAdapter{
 		packet,
 		metadata,
+		packet.LocalAddr().String(),
 	}
 }
 
@@ -284,17 +294,19 @@ type WriteBackProxy interface {
 	UpdateWriteBack(wb WriteBack)
 }
 
+type PacketSender interface {
+	// Send will send PacketAdapter nonblocking
+	// the implement must call UDPPacket.Drop() inside Send
+	Send(PacketAdapter)
+	Process(PacketConn, WriteBackProxy)
+	Close()
+}
+
 type NatTable interface {
-	Set(key string, e PacketConn, w WriteBackProxy)
+	GetOrCreate(key string, maker func() PacketSender) (PacketSender, bool)
-
-	Get(key string) (PacketConn, WriteBackProxy)
-
-	GetOrCreateLock(key string) (*sync.Cond, bool)
 
 	Delete(key string)
 
-	DeleteLock(key string)
-
 	GetForLocalConn(lAddr, rAddr string) *net.UDPConn
 
 	AddForLocalConn(lAddr, rAddr string, conn *net.UDPConn) bool

tunnel/connection.go

@@ -1,6 +1,7 @@
 package tunnel
 
 import (
+	"context"
 	"errors"
 	"net"
 	"net/netip"
@@ -11,7 +12,78 @@ import (
 	"github.com/metacubex/mihomo/log"
 )
 
+type packetSender struct {
+	ctx    context.Context
+	cancel context.CancelFunc
+	ch     chan C.PacketAdapter
+}
+
+// newPacketSender return a chan based C.PacketSender
+// It ensures that packets can be sent sequentially and without blocking
+func newPacketSender() C.PacketSender {
+	ctx, cancel := context.WithCancel(context.Background())
+	ch := make(chan C.PacketAdapter, senderCapacity)
+	return &packetSender{
+		ctx:    ctx,
+		cancel: cancel,
+		ch:     ch,
+	}
+}
+
+func (s *packetSender) Process(pc C.PacketConn, proxy C.WriteBackProxy) {
+	for {
+		select {
+		case <-s.ctx.Done():
+			return // sender closed
+		case packet := <-s.ch:
+			if proxy != nil {
+				proxy.UpdateWriteBack(packet)
+			}
+			_ = handleUDPToRemote(packet, pc, packet.Metadata())
+			packet.Drop()
+		}
+	}
+}
+
+func (s *packetSender) dropAll() {
+	for {
+		select {
+		case data := <-s.ch:
+			data.Drop() // drop all data still in chan
+		default:
+			return // no data, exit goroutine
+		}
+	}
+}
+
+func (s *packetSender) Send(packet C.PacketAdapter) {
+	select {
+	case <-s.ctx.Done():
+		packet.Drop() // sender closed before Send()
+		return
+	default:
+	}
+
+	select {
+	case s.ch <- packet:
+		// put ok, so don't drop packet, will process by other side of chan
+	case <-s.ctx.Done():
+		packet.Drop() // sender closed when putting data to chan
+	default:
+		packet.Drop() // chan is full
+	}
+}
+
+func (s *packetSender) Close() {
+	s.cancel()
+	s.dropAll()
+}
+
 func handleUDPToRemote(packet C.UDPPacket, pc C.PacketConn, metadata *C.Metadata) error {
+	if err := resolveUDP(metadata); err != nil {
+		return err
+	}
+
 	addr := metadata.UDPAddr()
 	if addr == nil {
 		return errors.New("udp addr invalid")
@@ -26,8 +98,9 @@ func handleUDPToRemote(packet C.UDPPacket, pc C.PacketConn, metadata *C.Metadata
 	return nil
 }
 
-func handleUDPToLocal(writeBack C.WriteBack, pc N.EnhancePacketConn, key string, oAddrPort netip.AddrPort, fAddr netip.Addr) {
+func handleUDPToLocal(writeBack C.WriteBack, pc N.EnhancePacketConn, sender C.PacketSender, key string, oAddrPort netip.AddrPort, fAddr netip.Addr) {
 	defer func() {
+		sender.Close()
 		_ = pc.Close()
 		closeAllLocalCoon(key)
 		natTable.Delete(key)

tunnel/tunnel.go

@@ -28,11 +28,14 @@ import (
 	"github.com/metacubex/mihomo/tunnel/statistic"
 )
 
-const queueSize = 200
+const (
+	queueCapacity  = 64  // chan capacity tcpQueue and udpQueue
+	senderCapacity = 128 // chan capacity of PacketSender
+)
 
 var (
 	status        = newAtomicStatus(Suspend)
-	tcpQueue      = make(chan C.ConnContext, queueSize)
+	udpInit       sync.Once
 	udpQueues     []chan C.PacketAdapter
 	natTable      = nat.New()
 	rules         []C.Rule
@@ -43,6 +46,12 @@ var (
 	ruleProviders map[string]provider.RuleProvider
 	configMux     sync.RWMutex
 
+	// for compatibility, lazy init
+	tcpQueue  chan C.ConnContext
+	tcpInOnce sync.Once
+	udpQueue  chan C.PacketAdapter
+	udpInOnce sync.Once
+
 	// Outbound Rule
 	mode = Rule
 
@@ -70,15 +79,33 @@ func (t tunnel) HandleTCPConn(conn net.Conn, metadata *C.Metadata) {
 	handleTCPConn(connCtx)
 }
 
-func (t tunnel) HandleUDPPacket(packet C.UDPPacket, metadata *C.Metadata) {
+func initUDP() {
-	packetAdapter := C.NewPacketAdapter(packet, metadata)
+	numUDPWorkers := 4
+	if num := runtime.GOMAXPROCS(0); num > numUDPWorkers {
+		numUDPWorkers = num
+	}
 
-	hash := utils.MapHash(metadata.SourceAddress() + "-" + metadata.RemoteAddress())
+	udpQueues = make([]chan C.PacketAdapter, numUDPWorkers)
+	for i := 0; i < numUDPWorkers; i++ {
+		queue := make(chan C.PacketAdapter, queueCapacity)
+		udpQueues[i] = queue
+		go processUDP(queue)
+	}
+}
+
+func (t tunnel) HandleUDPPacket(packet C.UDPPacket, metadata *C.Metadata) {
+	udpInit.Do(initUDP)
+
+	packetAdapter := C.NewPacketAdapter(packet, metadata)
+	key := packetAdapter.Key()
+
+	hash := utils.MapHash(key)
 	queueNo := uint(hash) % uint(len(udpQueues))
 
 	select {
 	case udpQueues[queueNo] <- packetAdapter:
 	default:
+		packet.Drop()
 	}
 }
 
@@ -134,21 +161,32 @@ func IsSniffing() bool {
 	return sniffingEnable
 }
 
-func init() {
-	go process()
-}
-
 // TCPIn return fan-in queue
 // Deprecated: using Tunnel instead
 func TCPIn() chan<- C.ConnContext {
+	tcpInOnce.Do(func() {
+		tcpQueue = make(chan C.ConnContext, queueCapacity)
+		go func() {
+			for connCtx := range tcpQueue {
+				go handleTCPConn(connCtx)
+			}
+		}()
+	})
 	return tcpQueue
 }
 
 // UDPIn return fan-in udp queue
 // Deprecated: using Tunnel instead
 func UDPIn() chan<- C.PacketAdapter {
-	// compatibility: first queue is always available for external callers
+	udpInOnce.Do(func() {
-	return udpQueues[0]
+		udpQueue = make(chan C.PacketAdapter, queueCapacity)
+		go func() {
+			for packet := range udpQueue {
+				Tunnel.HandleUDPPacket(packet, packet.Metadata())
+			}
+		}()
+	})
+	return udpQueue
 }
 
 // NatTable return nat table
@@ -249,32 +287,6 @@ func isHandle(t C.Type) bool {
 	return status == Running || (status == Inner && t == C.INNER)
 }
 
-// processUDP starts a loop to handle udp packet
-func processUDP(queue chan C.PacketAdapter) {
-	for conn := range queue {
-		handleUDPConn(conn)
-	}
-}
-
-func process() {
-	numUDPWorkers := 4
-	if num := runtime.GOMAXPROCS(0); num > numUDPWorkers {
-		numUDPWorkers = num
-	}
-
-	udpQueues = make([]chan C.PacketAdapter, numUDPWorkers)
-	for i := 0; i < numUDPWorkers; i++ {
-		queue := make(chan C.PacketAdapter, queueSize)
-		udpQueues[i] = queue
-		go processUDP(queue)
-	}
-
-	queue := tcpQueue
-	for conn := range queue {
-		go handleTCPConn(conn)
-	}
-}
-
 func needLookupIP(metadata *C.Metadata) bool {
 	return resolver.MappingEnabled() && metadata.Host == "" && metadata.DstIP.IsValid()
 }
@@ -334,6 +346,25 @@ func resolveMetadata(metadata *C.Metadata) (proxy C.Proxy, rule C.Rule, err erro
 	return
 }
 
+func resolveUDP(metadata *C.Metadata) error {
+	// local resolve UDP dns
+	if !metadata.Resolved() {
+		ip, err := resolver.ResolveIP(context.Background(), metadata.Host)
+		if err != nil {
+			return err
+		}
+		metadata.DstIP = ip
+	}
+	return nil
+}
+
+// processUDP starts a loop to handle udp packet
+func processUDP(queue chan C.PacketAdapter) {
+	for conn := range queue {
+		handleUDPConn(conn)
+	}
+}
+
 func handleUDPConn(packet C.PacketAdapter) {
 	if !isHandle(packet.Metadata().Type) {
 		packet.Drop()
@@ -363,56 +394,19 @@ func handleUDPConn(packet C.PacketAdapter) {
 		snifferDispatcher.UDPSniff(packet)
 	}
 
-	// local resolve UDP dns
+	key := packet.Key()
-	if !metadata.Resolved() {
+	sender, loaded := natTable.GetOrCreate(key, newPacketSender)
-		ip, err := resolver.ResolveIP(context.Background(), metadata.Host)
+	if !loaded {
-		if err != nil {
+		dial := func() (C.PacketConn, C.WriteBackProxy, error) {
-			return
+			if err := resolveUDP(metadata); err != nil {
+				log.Warnln("[UDP] Resolve Ip error: %s", err)
+				return nil, nil, err
 			}
-		metadata.DstIP = ip
-	}
-
-	key := packet.LocalAddr().String()
-
-	handle := func() bool {
-		pc, proxy := natTable.Get(key)
-		if pc != nil {
-			if proxy != nil {
-				proxy.UpdateWriteBack(packet)
-			}
-			_ = handleUDPToRemote(packet, pc, metadata)
-			return true
-		}
-		return false
-	}
-
-	if handle() {
-		packet.Drop()
-		return
-	}
-
-	cond, loaded := natTable.GetOrCreateLock(key)
-
-	go func() {
-		defer packet.Drop()
-
-		if loaded {
-			cond.L.Lock()
-			cond.Wait()
-			handle()
-			cond.L.Unlock()
-			return
-		}
-
-		defer func() {
-			natTable.DeleteLock(key)
-			cond.Broadcast()
-		}()
 
 			proxy, rule, err := resolveMetadata(metadata)
 			if err != nil {
 				log.Warnln("[UDP] Parse metadata failed: %s", err.Error())
-			return
+				return nil, nil, err
 			}
 
 			ctx, cancel := context.WithTimeout(context.Background(), C.DefaultUDPTimeout)
@@ -423,26 +417,36 @@ func handleUDPConn(packet C.PacketAdapter) {
 				logMetadataErr(metadata, rule, proxy, err)
 			})
 			if err != nil {
-			return
+				return nil, nil, err
 			}
 			logMetadata(metadata, rule, rawPc)
 
 			pc := statistic.NewUDPTracker(rawPc, statistic.DefaultManager, metadata, rule, 0, 0, true)
 
 			if rawPc.Chains().Last() == "REJECT-DROP" {
-			pc.Close()
+				_ = pc.Close()
-			return
+				return nil, nil, errors.New("rejected drop packet")
 			}
 
 			oAddrPort := metadata.AddrPort()
 			writeBackProxy := nat.NewWriteBackProxy(packet)
-		natTable.Set(key, pc, writeBackProxy)
 
-		go handleUDPToLocal(writeBackProxy, pc, key, oAddrPort, fAddr)
+			go handleUDPToLocal(writeBackProxy, pc, sender, key, oAddrPort, fAddr)
+			return pc, writeBackProxy, nil
+		}
 
-		handle()
+		go func() {
+			pc, proxy, err := dial()
+			if err != nil {
+				sender.Close()
+				natTable.Delete(key)
+				return
+			}
+			sender.Process(pc, proxy)
 		}()
 	}
+	sender.Send(packet) // nonblocking
+}
 
 func handleTCPConn(connCtx C.ConnContext) {
 	if !isHandle(connCtx.Metadata().Type) {