Fix: tunnel UDP race condition (#1043)

component/nat/table.go

@@ -22,9 +22,9 @@ func (t *Table) Get(key string) C.PacketConn {
 	return item.(C.PacketConn)
 }
 
-func (t *Table) GetOrCreateLock(key string) (*sync.WaitGroup, bool) {
+func (t *Table) GetOrCreateLock(key string) (*sync.Cond, bool) {
-	item, loaded := t.mapping.LoadOrStore(key, &sync.WaitGroup{})
+	item, loaded := t.mapping.LoadOrStore(key, sync.NewCond(&sync.Mutex{}))
-	return item.(*sync.WaitGroup), loaded
+	return item.(*sync.Cond), loaded
 }
 
 func (t *Table) Delete(key string) {

tunnel/tunnel.go

@@ -164,7 +164,7 @@ func handleUDPConn(packet *inbound.PacketAdapter) {
 		return
 	}
 
-	// make a fAddr if requset ip is fakeip
+	// make a fAddr if request ip is fakeip
 	var fAddr net.Addr
 	if resolver.IsExistFakeIP(metadata.DstIP) {
 		fAddr = metadata.UDPAddr()
@@ -176,34 +176,49 @@ func handleUDPConn(packet *inbound.PacketAdapter) {
 	}
 
 	key := packet.LocalAddr().String()
+
+	handle := func() bool {
 		pc := natTable.Get(key)
 		if pc != nil {
 			handleUDPToRemote(packet, pc, metadata)
+			return true
+		}
+		return false
+	}
+
+	if handle() {
 		return
 	}
 
 	lockKey := key + "-lock"
-	wg, loaded := natTable.GetOrCreateLock(lockKey)
+	cond, loaded := natTable.GetOrCreateLock(lockKey)
 
 	go func() {
-		if !loaded {
+		if loaded {
-			wg.Add(1)
+			cond.L.Lock()
+			cond.Wait()
+			handle()
+			cond.L.Unlock()
+			return
+		}
+
+		defer func() {
+			natTable.Delete(lockKey)
+			cond.Broadcast()
+		}()
+
 		proxy, rule, err := resolveMetadata(metadata)
 		if err != nil {
 			log.Warnln("[UDP] Parse metadata failed: %s", err.Error())
-				natTable.Delete(lockKey)
-				wg.Done()
 			return
 		}
 
 		rawPc, err := proxy.DialUDP(metadata)
 		if err != nil {
 			log.Warnln("[UDP] dial %s error: %s", proxy.Name(), err.Error())
-				natTable.Delete(lockKey)
-				wg.Done()
 			return
 		}
-			pc = newUDPTracker(rawPc, DefaultManager, metadata, rule)
+		pc := newUDPTracker(rawPc, DefaultManager, metadata, rule)
 
 		switch true {
 		case rule != nil:
@@ -216,17 +231,10 @@ func handleUDPConn(packet *inbound.PacketAdapter) {
 			log.Infoln("[UDP] %s --> %v doesn't match any rule using DIRECT", metadata.SourceAddress(), metadata.String())
 		}
 
-			natTable.Set(key, pc)
-			natTable.Delete(lockKey)
-			wg.Done()
 		go handleUDPToLocal(packet.UDPPacket, pc, key, fAddr)
-		}
 
-		wg.Wait()
+		natTable.Set(key, pc)
-		pc := natTable.Get(key)
+		handle()
-		if pc != nil {
-			handleUDPToRemote(packet, pc, metadata)
-		}
 	}()
 }