Introduce a special Session closing frame

internal/multiplex/session.go

@@ -1,6 +1,7 @@
 package multiplex
 
 import (
+	"crypto/rand"
 	"errors"
 	"fmt"
 	"net"
@@ -134,14 +135,46 @@ func (sesh *Session) Accept() (net.Conn, error) {
 	return stream, nil
 }
 
-func (sesh *Session) delStream(id uint32) {
+func (sesh *Session) closeStream(s *Stream, active bool) error {
+	atomic.StoreUint32(&s.closed, 1)
+	_ = s.recvBuf.Close() // both datagramBuffer and streamBuffer won't return err on Close()
+
+	if active {
+		s.writingM.Lock()
+		defer s.writingM.Unlock()
+		if s.isClosed() {
+			return errors.New("Already Closed")
+		}
+
+		// Notify remote that this stream is closed
+		pad := genRandomPadding()
+		f := &Frame{
+			StreamID: s.id,
+			Seq:      atomic.AddUint64(&s.nextSendSeq, 1) - 1,
+			Closing:  1,
+			Payload:  pad,
+		}
+		i, err := s.session.Obfs(f, s.obfsBuf)
+		if err != nil {
+			return err
+		}
+		_, err = s.session.sb.send(s.obfsBuf[:i], &s.assignedConnId)
+		if err != nil {
+			return err
+		}
+		log.Tracef("stream %v actively closed", s.id)
+	} else {
+		log.Tracef("stream %v passively closed", s.id)
+	}
+
 	sesh.streamsM.Lock()
-	delete(sesh.streams, id)
+	delete(sesh.streams, s.id)
 	if len(sesh.streams) == 0 {
 		log.Tracef("session %v has no active stream left", sesh.id)
 		go sesh.timeoutAfter(30 * time.Second)
 	}
 	sesh.streamsM.Unlock()
+	return nil
 }
 
 func (sesh *Session) recvDataFromRemote(data []byte) error {
@@ -159,6 +192,9 @@ func (sesh *Session) recvDataFromRemote(data []byte) error {
 		if frame.Closing == 1 {
 			// If the stream has been closed and the current frame is a closing frame, we do noop
 			return nil
+		} else if frame.Closing == 2 {
+			// Closing session
+			return sesh.passiveClose()
 		} else {
 			// it may be tempting to use the connId from which the frame was received. However it doesn't make
 			// any difference because we only care to send the data from the same stream through the same
@@ -171,7 +207,6 @@ func (sesh *Session) recvDataFromRemote(data []byte) error {
 			return stream.writeFrame(*frame)
 		}
 	}
-
 }
 
 func (sesh *Session) SetTerminalMsg(msg string) {
@@ -187,20 +222,18 @@ func (sesh *Session) TerminalMsg() string {
 	}
 }
 
-func (sesh *Session) Close() error {
-	log.Debugf("attempting to close session %v", sesh.id)
+func (sesh *Session) passiveClose() error {
+	log.Debugf("attempting to passively close session %v", sesh.id)
 	if atomic.SwapUint32(&sesh.closed, 1) == 1 {
 		log.Debugf("session %v has already been closed", sesh.id)
 		return errRepeatSessionClosing
 	}
-	sesh.streamsM.Lock()
 	sesh.acceptCh <- nil
+
+	sesh.streamsM.Lock()
 	for id, stream := range sesh.streams {
-		// If we call stream.Close() here, streamsM will result in a deadlock
-		// because stream.Close calls sesh.delStream, which locks the mutex.
-		// so we need to implement a method of stream that closes the stream without calling
-		// sesh.delStream
-		go stream.closeNoDelMap()
+		atomic.StoreUint32(&stream.closed, 1)
+		_ = stream.recvBuf.Close() // both datagramBuffer and streamBuffer won't return err on Close()
 		delete(sesh.streams, id)
 	}
 	sesh.streamsM.Unlock()
@@ -208,7 +241,52 @@ func (sesh *Session) Close() error {
 	sesh.sb.closeAll()
 	log.Debugf("session %v closed gracefully", sesh.id)
 	return nil
+}
 
+func genRandomPadding() []byte {
+	lenB := make([]byte, 1)
+	rand.Read(lenB)
+	pad := make([]byte, lenB[0])
+	rand.Read(pad)
+	return pad
+}
+
+func (sesh *Session) Close() error {
+	log.Debugf("attempting to actively close session %v", sesh.id)
+	if atomic.SwapUint32(&sesh.closed, 1) == 1 {
+		log.Debugf("session %v has already been closed", sesh.id)
+		return errRepeatSessionClosing
+	}
+	sesh.acceptCh <- nil
+
+	sesh.streamsM.Lock()
+	for id, stream := range sesh.streams {
+		atomic.StoreUint32(&stream.closed, 1)
+		_ = stream.recvBuf.Close() // both datagramBuffer and streamBuffer won't return err on Close()
+		delete(sesh.streams, id)
+	}
+	sesh.streamsM.Unlock()
+
+	pad := genRandomPadding()
+	f := &Frame{
+		StreamID: 0xffffffff,
+		Seq:      0,
+		Closing:  2,
+		Payload:  pad,
+	}
+	obfsBuf := make([]byte, len(pad)+64)
+	i, err := sesh.Obfs(f, obfsBuf)
+	if err != nil {
+		return err
+	}
+	_, err = sesh.sb.send(obfsBuf[:i], new(uint32))
+	if err != nil {
+		return err
+	}
+
+	sesh.sb.closeAll()
+	log.Debugf("session %v closed gracefully", sesh.id)
+	return nil
 }
 
 func (sesh *Session) IsClosed() bool {

internal/multiplex/stream.go

@@ -7,8 +7,6 @@ import (
 	"time"
 
 	log "github.com/sirupsen/logrus"
-	"math"
-	prand "math/rand"
 	"sync"
 	"sync/atomic"
 )
@@ -113,7 +111,8 @@ func (s *Stream) Write(in []byte) (n int, err error) {
 	log.Tracef("%v sent to remote through stream %v with err %v", len(in), s.id, err)
 	if err != nil {
 		if err == errBrokenSwitchboard {
-			s.session.Close()
+			s.session.SetTerminalMsg(err.Error())
+			s.session.passiveClose()
 		}
 		return
 	}
@@ -121,61 +120,13 @@ func (s *Stream) Write(in []byte) (n int, err error) {
 
 }
 
-// the necessary steps to mark the stream as closed and to release resources
-func (s *Stream) _close() {
-	atomic.StoreUint32(&s.closed, 1)
-	_ = s.recvBuf.Close() // both datagramBuffer and streamBuffer won't return err on Close()
-}
-
-// only close locally. Used when the stream close is notified by the remote
-func (s *Stream) passiveClose() {
-	s._close()
-	s.session.delStream(s.id)
-	log.Tracef("stream %v passively closed", s.id)
+func (s *Stream) passiveClose() error {
+	return s.session.closeStream(s, false)
 }
 
 // active close. Close locally and tell the remote that this stream is being closed
 func (s *Stream) Close() error {
-
-	s.writingM.Lock()
-	defer s.writingM.Unlock()
-	if s.isClosed() {
-		return errors.New("Already Closed")
-	}
-
-	// Notify remote that this stream is closed
-	prand.Seed(int64(s.id))
-	padLen := int(math.Floor(prand.Float64()*200 + 300))
-	pad := make([]byte, padLen)
-	prand.Read(pad)
-	f := &Frame{
-		StreamID: s.id,
-		Seq:      atomic.AddUint64(&s.nextSendSeq, 1) - 1,
-		Closing:  1,
-		Payload:  pad,
-	}
-	i, err := s.session.Obfs(f, s.obfsBuf)
-	if err != nil {
-		return err
-	}
-	_, err = s.session.sb.send(s.obfsBuf[:i], &s.assignedConnId)
-	if err != nil {
-		return err
-	}
-
-	s._close()
-	s.session.delStream(s.id)
-	log.Tracef("stream %v actively closed", s.id)
-	return nil
-}
-
-// Same as passiveClose() but no call to session.delStream.
-// This is called in session.Close() to avoid mutex deadlock
-// We don't notify the remote because session.Close() is always
-// called when the session is passively closed
-func (s *Stream) closeNoDelMap() {
-	log.Tracef("stream %v closed by session", s.id)
-	s._close()
+	return s.session.closeStream(s, true)
 }
 
 // the following functions are purely for implementing net.Conn interface.

internal/multiplex/switchboard.go

@@ -62,7 +62,7 @@ func (sb *switchboard) removeConn(connId uint32) {
 	if remaining == 0 {
 		atomic.StoreUint32(&sb.broken, 1)
 		sb.session.SetTerminalMsg("no underlying connection left")
-		sb.session.Close()
+		sb.session.passiveClose()
 	}
 }
 
@@ -149,12 +149,12 @@ func (sb *switchboard) closeAll() {
 	if atomic.SwapUint32(&sb.broken, 1) == 1 {
 		return
 	}
-	sb.connsM.RLock()
+	sb.connsM.Lock()
 	for key, conn := range sb.conns {
 		conn.Close()
 		delete(sb.conns, key)
 	}
-	sb.connsM.RUnlock()
+	sb.connsM.Unlock()
 }
 
 // deplex function costantly reads from a TCP connection