client: use a single goroutine during play / record

client.go

@@ -38,9 +38,10 @@ const (
 	clientUDPKeepalivePeriod = 30 * time.Second
 )
 
-func isErrNOUDPPacketsReceivedRecently(err error) bool {
-	_, ok := err.(liberrors.ErrClientNoUDPPacketsRecently)
-	return ok
+func emptyTimer() *time.Timer {
+	t := time.NewTimer(0)
+	<-t.C
+	return t
 }
 
 func isAnyPort(p int) bool {
@@ -214,12 +215,17 @@ type Client struct {
 	tracks             map[int]clientTrack
 	tracksByChannel    map[int]int
 	lastRange          *headers.Range
-	backgroundRunning bool
-	backgroundErr     error
 	tcpFrameBuffer     *multibuffer.MultiBuffer // tcp
 	tcpWriteMutex      sync.Mutex               // tcp
 	writeMutex         sync.RWMutex             // write
 	writeFrameAllowed  bool                     // write
+	reportTimer        *time.Timer
+	checkStreamTimer   *time.Timer
+	checkStreamInitial bool
+	tcpLastFrameTime   int64
+	keepaliveTimer     *time.Timer
+	readerRunning      bool
+	finalErr           error
 
 	// in
 	options  chan optionsReq
@@ -229,11 +235,9 @@ type Client struct {
 	play     chan playReq
 	record   chan recordReq
 	pause    chan pauseReq
-	backgroundTerminate chan struct{}
 
 	// out
-	backgroundInnerDone chan error
-	backgroundDone      chan struct{}
+	readerErr chan error
 	done      chan struct{}
 }
 
@@ -291,6 +295,9 @@ func (c *Client) Dial(scheme string, host string) error {
 	c.host = host
 	c.ctx = ctx
 	c.ctxCancel = ctxCancel
+	c.reportTimer = emptyTimer()
+	c.checkStreamTimer = emptyTimer()
+	c.keepaliveTimer = emptyTimer()
 	c.options = make(chan optionsReq)
 	c.describe = make(chan describeReq)
 	c.announce = make(chan announceReq)
@@ -416,7 +423,7 @@ func (c *Client) Tracks() Tracks {
 func (c *Client) run() {
 	defer close(c.done)
 
-outer:
+	c.finalErr = func() error {
 		for {
 			select {
 			case req := <-c.options:
@@ -447,34 +454,128 @@ outer:
 				res, err := c.doPause()
 				req.res <- clientRes{res: res, err: err}
 
-		case err := <-c.backgroundInnerDone:
-			c.backgroundRunning = false
-			err = c.switchProtocolIfTimeout(err)
-			if err != nil {
-				c.backgroundErr = err
-				close(c.backgroundDone)
-
-				c.writeMutex.Lock()
-				c.writeFrameAllowed = false
-				c.writeMutex.Unlock()
+			case <-c.reportTimer.C:
+				if c.state == clientStatePlay {
+					now := time.Now()
+					for trackID, cct := range c.tracks {
+						rr := cct.rtcpReceiver.Report(now)
+						c.WritePacketRTCP(trackID, rr)
 					}
 
+					c.reportTimer = time.NewTimer(c.receiverReportPeriod)
+				} else { // Record
+					now := time.Now()
+					for trackID, cct := range c.tracks {
+						sr := cct.rtcpSender.Report(now)
+						if sr != nil {
+							c.WritePacketRTCP(trackID, sr)
+						}
+					}
+
+					c.reportTimer = time.NewTimer(c.senderReportPeriod)
+				}
+
+			case <-c.checkStreamTimer.C:
+				if *c.protocol == TransportUDP ||
+					*c.protocol == TransportUDPMulticast {
+					if c.checkStreamInitial {
+						c.checkStreamInitial = false
+
+						// check that at least one packet has been received
+						inTimeout := func() bool {
+							for _, cct := range c.tracks {
+								lft := atomic.LoadInt64(cct.udpRTPListener.lastFrameTime)
+								if lft != 0 {
+									return false
+								}
+
+								lft = atomic.LoadInt64(cct.udpRTCPListener.lastFrameTime)
+								if lft != 0 {
+									return false
+								}
+							}
+							return true
+						}()
+						if inTimeout {
+							err := c.trySwitchingProtocol()
+							if err != nil {
+								return err
+							}
+						}
+
+						c.checkStreamTimer = time.NewTimer(clientCheckStreamPeriod)
+					} else {
+						inTimeout := func() bool {
+							now := time.Now()
+							for _, cct := range c.tracks {
+								lft := time.Unix(atomic.LoadInt64(cct.udpRTPListener.lastFrameTime), 0)
+								if now.Sub(lft) < c.ReadTimeout {
+									return false
+								}
+
+								lft = time.Unix(atomic.LoadInt64(cct.udpRTCPListener.lastFrameTime), 0)
+								if now.Sub(lft) < c.ReadTimeout {
+									return false
+								}
+							}
+							return true
+						}()
+						if inTimeout {
+							return liberrors.ErrClientUDPTimeout{}
+						}
+
+						c.checkStreamTimer = time.NewTimer(clientCheckStreamPeriod)
+					}
+				} else { // TCP
+					inTimeout := func() bool {
+						now := time.Now()
+						lft := time.Unix(atomic.LoadInt64(&c.tcpLastFrameTime), 0)
+						return now.Sub(lft) >= c.ReadTimeout
+					}()
+					if inTimeout {
+						return liberrors.ErrClientTCPTimeout{}
+					}
+
+					c.checkStreamTimer = time.NewTimer(clientCheckStreamPeriod)
+				}
+
+			case <-c.keepaliveTimer.C:
+				_, err := c.do(&base.Request{
+					Method: func() base.Method {
+						// the vlc integrated rtsp server requires GET_PARAMETER
+						if c.useGetParameter {
+							return base.GetParameter
+						}
+						return base.Options
+					}(),
+					// use the stream base URL, otherwise some cameras do not reply
+					URL: c.streamBaseURL,
+				}, true)
+				if err != nil {
+					return err
+				}
+
+				c.keepaliveTimer = time.NewTimer(clientUDPKeepalivePeriod)
+
+			case err := <-c.readerErr:
+				c.readerRunning = false
+				return err
+
 			case <-c.ctx.Done():
-			break outer
+				return liberrors.ErrClientTerminated{}
 			}
 		}
+	}()
 
 	c.ctxCancel()
 
-	c.doClose(false)
+	c.doClose()
 }
 
-func (c *Client) doClose(isSwitchingProtocol bool) {
-	if c.backgroundRunning {
-		c.backgroundClose(isSwitchingProtocol)
-	}
-
+func (c *Client) doClose() {
 	if c.state == clientStatePlay || c.state == clientStateRecord {
+		c.playRecordClose()
+
 		c.do(&base.Request{
 			Method: base.Teardown,
 			URL:    c.streamBaseURL,
@@ -494,8 +595,8 @@ func (c *Client) doClose(isSwitchingProtocol bool) {
 	}
 }
 
-func (c *Client) reset(isSwitchingProtocol bool) {
-	c.doClose(isSwitchingProtocol)
+func (c *Client) reset() {
+	c.doClose()
 
 	c.state = clientStateInitial
 	c.session = ""
@@ -524,19 +625,12 @@ func (c *Client) checkState(allowed map[clientState]struct{}) error {
 	return liberrors.ErrClientInvalidState{AllowedList: allowedList, State: c.state}
 }
 
-func (c *Client) switchProtocolIfTimeout(err error) error {
-	if *c.protocol != TransportUDP ||
-		c.state != clientStatePlay ||
-		!isErrNOUDPPacketsReceivedRecently(err) ||
-		c.Transport != nil {
-		return err
-	}
-
+func (c *Client) trySwitchingProtocol() error {
 	prevBaseURL := c.streamBaseURL
 	oldUseGetParameter := c.useGetParameter
 	prevTracks := c.tracks
 
-	c.reset(true)
+	c.reset()
 
 	v := TransportTCP
 	c.protocol = &v
@@ -551,7 +645,7 @@ func (c *Client) switchProtocolIfTimeout(err error) error {
 		}
 	}
 
-	_, err = c.doPlay(c.lastRange, true)
+	_, err := c.doPlay(c.lastRange, true)
 	if err != nil {
 		return err
 	}
@@ -559,198 +653,74 @@ func (c *Client) switchProtocolIfTimeout(err error) error {
 	return nil
 }
 
-func (c *Client) backgroundStart(isSwitchingProtocol bool) {
+func (c *Client) playRecordStart() {
+	// start timers
+	if c.state == clientStatePlay {
+		c.reportTimer = time.NewTimer(c.receiverReportPeriod)
+
+		switch *c.protocol {
+		case TransportUDP:
+			c.checkStreamTimer = time.NewTimer(c.InitialUDPReadTimeout)
+			c.checkStreamInitial = true
+			c.keepaliveTimer = time.NewTimer(clientUDPKeepalivePeriod)
+
+		case TransportUDPMulticast:
+			c.checkStreamTimer = time.NewTimer(clientCheckStreamPeriod)
+			c.keepaliveTimer = time.NewTimer(clientUDPKeepalivePeriod)
+
+		default: // TCP
+			c.checkStreamTimer = time.NewTimer(clientCheckStreamPeriod)
+			c.tcpLastFrameTime = time.Now().Unix()
+		}
+
+	} else {
+		c.reportTimer = time.NewTimer(c.senderReportPeriod)
+	}
+
+	// allow writing
 	c.writeMutex.Lock()
 	c.writeFrameAllowed = true
 	c.writeMutex.Unlock()
 
-	c.backgroundRunning = true
-	c.backgroundTerminate = make(chan struct{})
-	c.backgroundInnerDone = make(chan error)
-
-	if !isSwitchingProtocol {
-		c.backgroundDone = make(chan struct{})
-	}
-
-	go c.runBackground()
-}
-
-func (c *Client) backgroundClose(isSwitchingProtocol bool) {
-	close(c.backgroundTerminate)
-	err := <-c.backgroundInnerDone
-	c.backgroundRunning = false
-
-	if !isSwitchingProtocol {
-		c.backgroundErr = err
-		close(c.backgroundDone)
-	}
-
-	c.writeMutex.Lock()
-	c.writeFrameAllowed = false
-	c.writeMutex.Unlock()
-}
-
-func (c *Client) runBackground() {
-	c.backgroundInnerDone <- func() error {
-		if c.state == clientStatePlay {
+	// start UDP listeners
 	if *c.protocol == TransportUDP || *c.protocol == TransportUDPMulticast {
-				return c.runBackgroundPlayUDP()
-			}
-			return c.runBackgroundPlayTCP()
-		}
-
-		if *c.protocol == TransportUDP {
-			return c.runBackgroundRecordUDP()
-		}
-		return c.runBackgroundRecordTCP()
-	}()
-}
-
-func (c *Client) runBackgroundPlayUDP() error {
 		for _, cct := range c.tracks {
 			cct.udpRTPListener.start()
 			cct.udpRTCPListener.start()
 		}
-
-	defer func() {
-		for _, cct := range c.tracks {
-			cct.udpRTPListener.stop()
-			cct.udpRTCPListener.stop()
 	}
-	}()
 
-	// disable deadline
+	// for some reason, SetReadDeadline() must always be called in the same
+	// goroutine, otherwise Read() freezes.
+	// therefore, we disable the deadline and perform a check with a ticker.
 	c.nconn.SetReadDeadline(time.Time{})
 
-	readerDone := make(chan error)
+	// start reader
+	c.readerRunning = true
+	c.readerErr = make(chan error)
 	go func() {
+		c.readerErr <- c.runReader()
+	}()
+}
+
+func (c *Client) runReader() error {
+	if *c.protocol == TransportUDP || *c.protocol == TransportUDPMulticast {
 		for {
 			var res base.Response
 			err := res.Read(c.br)
 			if err != nil {
-				readerDone <- err
-				return
-			}
-		}
-	}()
-
-	reportTicker := time.NewTicker(c.receiverReportPeriod)
-	defer reportTicker.Stop()
-
-	keepaliveTicker := time.NewTicker(clientUDPKeepalivePeriod)
-	defer keepaliveTicker.Stop()
-
-	checkStreamInitial := true
-	checkStreamTicker := time.NewTicker(c.InitialUDPReadTimeout)
-	defer func() {
-		checkStreamTicker.Stop()
-	}()
-
-	for {
-		select {
-		case <-c.backgroundTerminate:
-			c.nconn.SetReadDeadline(time.Now())
-			<-readerDone
-			return fmt.Errorf("terminated")
-
-		case <-reportTicker.C:
-			now := time.Now()
-			for trackID, cct := range c.tracks {
-				rr := cct.rtcpReceiver.Report(now)
-				c.WritePacketRTCP(trackID, rr)
-			}
-
-		case <-keepaliveTicker.C:
-			_, err := c.do(&base.Request{
-				Method: func() base.Method {
-					// the vlc integrated rtsp server requires GET_PARAMETER
-					if c.useGetParameter {
-						return base.GetParameter
-					}
-					return base.Options
-				}(),
-				// use the stream base URL, otherwise some cameras do not reply
-				URL: c.streamBaseURL,
-			}, true)
-			if err != nil {
-				c.nconn.SetReadDeadline(time.Now())
-				<-readerDone
 				return err
 			}
-
-		case <-checkStreamTicker.C:
-			if checkStreamInitial {
-				// check that at least one packet has been received
-				inTimeout := func() bool {
-					for _, cct := range c.tracks {
-						lft := atomic.LoadInt64(cct.udpRTPListener.lastFrameTime)
-						if lft != 0 {
-							return false
 		}
-
-						lft = atomic.LoadInt64(cct.udpRTCPListener.lastFrameTime)
-						if lft != 0 {
-							return false
-						}
-					}
-					return true
-				}()
-				if inTimeout {
-					c.nconn.SetReadDeadline(time.Now())
-					<-readerDone
-					return liberrors.ErrClientNoUDPPacketsRecently{}
-				}
-
-				checkStreamInitial = false
-				checkStreamTicker.Stop()
-				checkStreamTicker = time.NewTicker(clientCheckStreamPeriod)
 	} else {
-				inTimeout := func() bool {
-					now := time.Now()
-					for _, cct := range c.tracks {
-						lft := time.Unix(atomic.LoadInt64(cct.udpRTPListener.lastFrameTime), 0)
-						if now.Sub(lft) < c.ReadTimeout {
-							return false
-						}
-
-						lft = time.Unix(atomic.LoadInt64(cct.udpRTCPListener.lastFrameTime), 0)
-						if now.Sub(lft) < c.ReadTimeout {
-							return false
-						}
-					}
-					return true
-				}()
-				if inTimeout {
-					c.nconn.SetReadDeadline(time.Now())
-					<-readerDone
-					return liberrors.ErrClientUDPTimeout{}
-				}
-			}
-
-		case err := <-readerDone:
-			return err
-		}
-	}
-}
-
-func (c *Client) runBackgroundPlayTCP() error {
-	// for some reason, SetReadDeadline() must always be called in the same
-	// goroutine, otherwise Read() freezes.
-	// therefore, we disable the deadline and perform check with a ticker.
-	c.nconn.SetReadDeadline(time.Time{})
-
-	lastFrameTime := time.Now().Unix()
-
-	readerDone := make(chan error)
-	go func() {
+		if c.state == clientStatePlay {
 			for {
 				frame := base.InterleavedFrame{
 					Payload: c.tcpFrameBuffer.Next(),
 				}
 				err := frame.Read(c.br)
 				if err != nil {
-				readerDone <- err
-				return
+					return err
 				}
 
 				channel := frame.Channel
@@ -766,7 +736,7 @@ func (c *Client) runBackgroundPlayTCP() error {
 				}
 
 				now := time.Now()
-			atomic.StoreInt64(&lastFrameTime, now.Unix())
+				atomic.StoreInt64(&c.tcpLastFrameTime, now.Unix())
 
 				if isRTP {
 					c.tracks[trackID].rtcpReceiver.ProcessPacketRTP(now, frame.Payload)
@@ -776,113 +746,14 @@ func (c *Client) runBackgroundPlayTCP() error {
 					c.OnPacketRTCP(c, trackID, frame.Payload)
 				}
 			}
-	}()
-
-	reportTicker := time.NewTicker(c.receiverReportPeriod)
-	defer reportTicker.Stop()
-
-	checkStreamTicker := time.NewTicker(clientCheckStreamPeriod)
-	defer checkStreamTicker.Stop()
-
-	for {
-		select {
-		case <-c.backgroundTerminate:
-			c.nconn.SetReadDeadline(time.Now())
-			<-readerDone
-			return fmt.Errorf("terminated")
-
-		case <-reportTicker.C:
-			now := time.Now()
-			for trackID, cct := range c.tracks {
-				rr := cct.rtcpReceiver.Report(now)
-				c.WritePacketRTCP(trackID, rr)
-			}
-
-		case <-checkStreamTicker.C:
-			inTimeout := func() bool {
-				now := time.Now()
-				lft := time.Unix(atomic.LoadInt64(&lastFrameTime), 0)
-				return now.Sub(lft) >= c.ReadTimeout
-			}()
-			if inTimeout {
-				c.nconn.SetReadDeadline(time.Now())
-				<-readerDone
-				return liberrors.ErrClientTCPTimeout{}
-			}
-
-		case err := <-readerDone:
-			return err
-		}
-	}
-}
-
-func (c *Client) runBackgroundRecordUDP() error {
-	for _, cct := range c.tracks {
-		cct.udpRTPListener.start()
-		cct.udpRTCPListener.start()
-	}
-
-	defer func() {
-		for _, cct := range c.tracks {
-			cct.udpRTPListener.stop()
-			cct.udpRTCPListener.stop()
-		}
-	}()
-
-	// disable deadline
-	c.nconn.SetReadDeadline(time.Time{})
-
-	readerDone := make(chan error)
-	go func() {
-		for {
-			var res base.Response
-			err := res.Read(c.br)
-			if err != nil {
-				readerDone <- err
-				return
-			}
-		}
-	}()
-
-	reportTicker := time.NewTicker(c.senderReportPeriod)
-	defer reportTicker.Stop()
-
-	for {
-		select {
-		case <-c.backgroundTerminate:
-			c.nconn.SetReadDeadline(time.Now())
-			<-readerDone
-			return fmt.Errorf("terminated")
-
-		case <-reportTicker.C:
-			now := time.Now()
-			for trackID, cct := range c.tracks {
-				sr := cct.rtcpSender.Report(now)
-				if sr != nil {
-					c.WritePacketRTCP(trackID, sr)
-				}
-			}
-
-		case err := <-readerDone:
-			return err
-		}
-	}
-}
-
-func (c *Client) runBackgroundRecordTCP() error {
-	// disable deadline
-	c.nconn.SetReadDeadline(time.Time{})
-
-	readerDone := make(chan error)
-	go func() {
+		} else { // Record
 			for {
 				frame := base.InterleavedFrame{
 					Payload: c.tcpFrameBuffer.Next(),
 				}
 				err := frame.Read(c.br)
 				if err != nil {
-				readerDone <- err
-				return
+					return err
 				}
 
 				channel := frame.Channel
@@ -901,31 +772,34 @@ func (c *Client) runBackgroundRecordTCP() error {
 					c.OnPacketRTCP(c, trackID, frame.Payload)
 				}
 			}
-	}()
+		}
+	}
+}
 
-	reportTicker := time.NewTicker(c.senderReportPeriod)
-	defer reportTicker.Stop()
-
-	for {
-		select {
-		case <-c.backgroundTerminate:
+func (c *Client) playRecordClose() {
+	// stop reader
+	if c.readerRunning {
 		c.nconn.SetReadDeadline(time.Now())
-			<-readerDone
-			return fmt.Errorf("terminated")
+		<-c.readerErr
+	}
 
-		case <-reportTicker.C:
-			now := time.Now()
-			for trackID, cct := range c.tracks {
-				sr := cct.rtcpSender.Report(now)
-				if sr != nil {
-					c.WritePacketRTCP(trackID, sr)
+	// stop UDP listeners
+	if *c.protocol == TransportUDP || *c.protocol == TransportUDPMulticast {
+		for _, cct := range c.tracks {
+			cct.udpRTPListener.stop()
+			cct.udpRTCPListener.stop()
 		}
 	}
 
-		case err := <-readerDone:
-			return err
-		}
-	}
+	// forbid writing
+	c.writeMutex.Lock()
+	c.writeFrameAllowed = false
+	c.writeMutex.Unlock()
+
+	// stop timers
+	c.reportTimer = emptyTimer()
+	c.checkStreamTimer = emptyTimer()
+	c.keepaliveTimer = emptyTimer()
 }
 
 func (c *Client) connOpen() error {
@@ -1164,7 +1038,7 @@ func (c *Client) doDescribe(u *base.URL) (Tracks, *base.URL, *base.Response, err
 			res.StatusCode >= base.StatusMovedPermanently &&
 			res.StatusCode <= base.StatusUseProxy &&
 			len(res.Header["Location"]) == 1 {
-			c.reset(false)
+			c.reset()
 
 			u, err := base.ParseURL(res.Header["Location"][0])
 			if err != nil {
@@ -1336,7 +1210,7 @@ func (c *Client) doSetup(
 	}
 
 	proto := func() Transport {
-		// protocol set by previous Setup() or switchProtocolIfTimeout()
+		// protocol set by previous Setup() or trySwitchingProtocol()
 		if c.protocol != nil {
 			return *c.protocol
 		}
@@ -1676,7 +1550,7 @@ func (c *Client) doPlay(ra *headers.Range, isSwitchingProtocol bool) (*base.Resp
 	c.state = clientStatePlay
 	c.lastRange = ra
 
-	c.backgroundStart(isSwitchingProtocol)
+	c.playRecordStart()
 
 	return res, nil
 }
@@ -1719,7 +1593,7 @@ func (c *Client) doRecord() (*base.Response, error) {
 
 	c.state = clientStateRecord
 
-	c.backgroundStart(false)
+	c.playRecordStart()
 
 	return nil, nil
 }
@@ -1747,7 +1621,7 @@ func (c *Client) doPause() (*base.Response, error) {
 		return nil, err
 	}
 
-	c.backgroundClose(false)
+	c.playRecordClose()
 
 	res, err := c.do(&base.Request{
 		Method: base.Pause,
@@ -1799,21 +1673,27 @@ func (c *Client) Seek(ra *headers.Range) (*base.Response, error) {
 
 // ReadFrames starts reading frames.
 func (c *Client) ReadFrames() error {
-	<-c.backgroundDone
-	return c.backgroundErr
+	<-c.done
+	return c.finalErr
 }
 
 // WritePacketRTP writes a RTP packet.
 func (c *Client) WritePacketRTP(trackID int, payload []byte) error {
-	now := time.Now()
+	select {
+	case <-c.done:
+		return c.finalErr
+	default:
+	}
 
 	c.writeMutex.RLock()
 	defer c.writeMutex.RUnlock()
 
 	if !c.writeFrameAllowed {
-		return c.backgroundErr
+		return liberrors.ErrClientWriteNotAllowed{}
 	}
 
+	now := time.Now()
+
 	if c.tracks[trackID].rtcpSender != nil {
 		c.tracks[trackID].rtcpSender.ProcessPacketRTP(now, payload)
 	}
@@ -1838,15 +1718,21 @@ func (c *Client) WritePacketRTP(trackID int, payload []byte) error {
 
 // WritePacketRTCP writes a RTCP packet.
 func (c *Client) WritePacketRTCP(trackID int, payload []byte) error {
-	now := time.Now()
+	select {
+	case <-c.done:
+		return c.finalErr
+	default:
+	}
 
 	c.writeMutex.RLock()
 	defer c.writeMutex.RUnlock()
 
 	if !c.writeFrameAllowed {
-		return c.backgroundErr
+		return liberrors.ErrClientWriteNotAllowed{}
 	}
 
+	now := time.Now()
+
 	if c.tracks[trackID].rtcpSender != nil {
 		c.tracks[trackID].rtcpSender.ProcessPacketRTCP(now, payload)
 	}

client_read_test.go

@@ -1768,9 +1768,6 @@ func TestClientReadPause(t *testing.T) {
 			<-frameRecv
 			_, err = c.Pause()
 			require.NoError(t, err)
-			<-done
-
-			c.ReadFrames()
 
 			firstFrame = int32(0)
 			frameRecv = make(chan struct{})
@@ -1778,12 +1775,6 @@ func TestClientReadPause(t *testing.T) {
 			_, err = c.Play(nil)
 			require.NoError(t, err)
 
-			done = make(chan struct{})
-			go func() {
-				defer close(done)
-				c.ReadFrames()
-			}()
-
 			<-frameRecv
 			c.Close()
 			<-done

pkg/liberrors/client.go

@@ -163,14 +163,6 @@ func (e ErrClientTransportHeaderInterleavedIDsAlreadyUsed) Error() string {
 	return "interleaved IDs already used"
 }
 
-// ErrClientNoUDPPacketsRecently is an error that can be returned by a client.
-type ErrClientNoUDPPacketsRecently struct{}
-
-// Error implements the error interface.
-func (e ErrClientNoUDPPacketsRecently) Error() string {
-	return "no UDP packets received (maybe there's a firewall/NAT in between)"
-}
-
 // ErrClientUDPTimeout is an error that can be returned by a client.
 type ErrClientUDPTimeout struct{}
 
@@ -196,3 +188,11 @@ type ErrClientRTPInfoInvalid struct {
 func (e ErrClientRTPInfoInvalid) Error() string {
 	return fmt.Sprintf("invalid RTP-Info: %v", e.Err)
 }
+
+// ErrClientWriteNotAllowed is an error that can be returned by a client.
+type ErrClientWriteNotAllowed struct{}
+
+// Error implements the error interface.
+func (e ErrClientWriteNotAllowed) Error() string {
+	return "writing is not allowed at the moment"
+}