Fix critical bugs in session opening for TCP and UDP in case of Singleplex mode.

- In case of TCP, don't open the session in the listener accept thread. This
  causes resource exhaustion of the tcp listener backlog queue in case of internet
  connection disruption or timeout.

- In case of UDP, don't create a new session for every UDP packet.

cmd/ck-client/ck-client.go

@@ -184,12 +184,12 @@ func main() {
 			return net.ListenUDP("udp", udpAddr)
 		}
 
-		client.RouteUDP(acceptor, localConfig.Timeout, seshMaker)
+		client.RouteUDP(acceptor, localConfig.Timeout, remoteConfig.Singleplex, seshMaker)
 	} else {
 		listener, err := net.Listen("tcp", localConfig.LocalAddr)
 		if err != nil {
 			log.Fatal(err)
 		}
-		client.RouteTCP(listener, localConfig.Timeout, seshMaker)
+		client.RouteTCP(listener, localConfig.Timeout, remoteConfig.Singleplex, seshMaker)
 	}
 }

internal/client/piper.go

@@ -10,8 +10,8 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-func RouteUDP(bindFunc func() (*net.UDPConn, error), streamTimeout time.Duration, newSeshFunc func() *mux.Session) {
+func RouteUDP(bindFunc func() (*net.UDPConn, error), streamTimeout time.Duration, singleplex bool, newSeshFunc func() *mux.Session) {
-	var sesh *mux.Session
+	var multiplexSession *mux.Session
 	localConn, err := bindFunc()
 	if err != nil {
 		log.Fatal(err)
@@ -27,17 +27,24 @@ func RouteUDP(bindFunc func() (*net.UDPConn, error), streamTimeout time.Duration
 			continue
 		}
 
-		if sesh == nil || sesh.IsClosed() || sesh.Singleplex {
+		if !singleplex && (multiplexSession == nil || multiplexSession.IsClosed()) {
-			sesh = newSeshFunc()
+			multiplexSession = newSeshFunc()
 		}
 
 		stream, ok := streams[addr.String()]
 		if !ok {
-			stream, err = sesh.OpenStream()
+			var session *mux.Session
+			if multiplexSession != nil {
+				session = multiplexSession
+			} else {
+				session = newSeshFunc()
+			}
+
+			stream, err = session.OpenStream()
 			if err != nil {
 				log.Errorf("Failed to open stream: %v", err)
-				if sesh.Singleplex {
+				if session.Singleplex {
-					sesh.Close()
+					session.Close()
 				}
 				continue
 			}
@@ -74,18 +81,25 @@ func RouteUDP(bindFunc func() (*net.UDPConn, error), streamTimeout time.Duration
 	}
 }
 
-func RouteTCP(listener net.Listener, streamTimeout time.Duration, newSeshFunc func() *mux.Session) {
+func RouteTCP(listener net.Listener, streamTimeout time.Duration, singleplex bool, newSeshFunc func() *mux.Session) {
-	var sesh *mux.Session
+	var multiplexSession *mux.Session
 	for {
 		localConn, err := listener.Accept()
 		if err != nil {
 			log.Fatal(err)
 			continue
 		}
-		if sesh == nil || sesh.IsClosed() || sesh.Singleplex {
+		if !singleplex && (multiplexSession == nil || multiplexSession.IsClosed()) {
-			sesh = newSeshFunc()
+			multiplexSession = newSeshFunc()
 		}
-		go func(sesh *mux.Session, localConn net.Conn, timeout time.Duration) {
+		go func(multiplexSession *mux.Session, newSingleplexSeshFunc func() *mux.Session, localConn net.Conn, timeout time.Duration) {
+			var session *mux.Session
+			if multiplexSession != nil {
+				session = multiplexSession
+			} else {
+				session = newSingleplexSeshFunc()
+			}
+
 			data := make([]byte, 10240)
 			_ = localConn.SetReadDeadline(time.Now().Add(streamTimeout))
 			i, err := io.ReadAtLeast(localConn, data, 1)
@@ -97,12 +111,12 @@ func RouteTCP(listener net.Listener, streamTimeout time.Duration, newSeshFunc fu
 			var zeroTime time.Time
 			_ = localConn.SetReadDeadline(zeroTime)
 
-			stream, err := sesh.OpenStream()
+			stream, err := session.OpenStream()
 			if err != nil {
 				log.Errorf("Failed to open stream: %v", err)
 				localConn.Close()
-				if sesh.Singleplex {
+				if session.Singleplex {
-					sesh.Close()
+					session.Close()
 				}
 				return
 			}
@@ -123,7 +137,6 @@ func RouteTCP(listener net.Listener, streamTimeout time.Duration, newSeshFunc fu
 			if _, err = common.Copy(stream, localConn); err != nil {
 				log.Tracef("copying proxy client to stream: %v", err)
 			}
-		}(sesh, localConn, streamTimeout)
+		}(multiplexSession, newSeshFunc, localConn, streamTimeout)
 	}
-
 }

internal/test/integration_test.go

@@ -206,12 +206,12 @@ func establishSession(lcc client.LocalConnConfig, rcc client.RemoteConnConfig, a
 			addrCh <- conn.LocalAddr().(*net.UDPAddr)
 			return conn, err
 		}
-		go client.RouteUDP(acceptor, lcc.Timeout, clientSeshMaker)
+		go client.RouteUDP(acceptor, lcc.Timeout, rcc.Singleplex, clientSeshMaker)
 		proxyToCkClientD = mDialer
 	} else {
 		var proxyToCkClientL *connutil.PipeListener
 		proxyToCkClientD, proxyToCkClientL = connutil.DialerListener(10 * 1024)
-		go client.RouteTCP(proxyToCkClientL, lcc.Timeout, clientSeshMaker)
+		go client.RouteTCP(proxyToCkClientL, lcc.Timeout, rcc.Singleplex, clientSeshMaker)
 	}
 
 	// set up server