fix unexpected close of backchannel streams

pkg/doorbird/backchannel.go

@@ -15,7 +15,10 @@ import (
 	"github.com/pion/rtp"
 )
 
-var clt Client
+var (
+	cltMu  sync.Mutex
+	cltMap = make(map[string]*Client)
+)
 
 type AudioMixer struct {
 	mu      sync.Mutex
@@ -68,6 +71,11 @@ func (m *AudioMixer) mixLoop() {
 
 	for range ticker.C {
 		m.mu.Lock()
+		if m.closed {
+			m.mu.Unlock()
+			return
+		}
+
 		if len(m.streams) == 0 {
 			m.mu.Unlock()
 			continue
@@ -153,8 +161,12 @@ type Client struct {
 }
 
 func Dial(rawURL string) (*Client, error) {
-	if clt.conn != nil {
-		return &clt, nil
+	cltMu.Lock()
+	defer cltMu.Unlock()
+
+	// Check if we already have a client for this URL
+	if existingClient, exists := cltMap[rawURL]; exists && existingClient.conn != nil {
+		return existingClient, nil
 	}
 
 	u, err := url.Parse(rawURL)
@@ -183,6 +195,7 @@ func Dial(rawURL string) (*Client, error) {
 
 	_ = conn.SetWriteDeadline(time.Now().Add(core.ConnDeadline))
 	if _, err = conn.Write([]byte(s)); err != nil {
+		conn.Close()
 		return nil, err
 	}
 
@@ -208,7 +221,7 @@ func Dial(rawURL string) (*Client, error) {
 		},
 	}
 
-	clt = Client{
+	client := &Client{
 		Connection: core.Connection{
 			ID:         core.NewID(),
 			FormatName: "doorbird",
@@ -222,7 +235,10 @@ func Dial(rawURL string) (*Client, error) {
 		senderStats: make(map[*core.Sender]time.Time),
 	}
 
-	return &clt, nil
+	// Store the client in the map
+	cltMap[rawURL] = client
+
+	return client, nil
 }
 
 func (c *Client) GetTrack(media *core.Media, codec *core.Codec) (*core.Receiver, error) {
@@ -238,17 +254,22 @@ func (c *Client) AddTrack(media *core.Media, codec *core.Codec, track *core.Rece
 	streamChan := c.mixer.AddStream(trackID)
 
 	sender.Handler = func(pkt *rtp.Packet) {
+		if len(pkt.Payload) == 0 {
+			return
+		}
+
 		c.mu.RLock()
 		conn := c.conn
 		c.mu.RUnlock()
 
-		if conn != nil && len(pkt.Payload) > 0 {
+		if conn != nil {
 			select {
 			case streamChan <- pkt.Payload:
 				c.mu.Lock()
 				c.senderStats[sender] = time.Now()
 				c.mu.Unlock()
 			default:
+				// Channel is full, skip this packet
 			}
 		}
 	}
@@ -258,11 +279,24 @@ func (c *Client) AddTrack(media *core.Media, codec *core.Codec, track *core.Rece
 
 	if len(c.Senders) == 0 {
 		go func() {
+			defer func() {
+				if r := recover(); r != nil {
+					// Recover from any panics when mixer is closed
+				}
+			}()
+
 			for mixedData := range c.mixer.output {
-				if c.conn != nil {
-					_ = c.conn.SetWriteDeadline(time.Now().Add(core.ConnDeadline))
-					if n, err := c.conn.Write(mixedData); err == nil {
+				c.mu.RLock()
+				conn := c.conn
+				c.mu.RUnlock()
+
+				if conn != nil && len(mixedData) > 0 {
+					_ = conn.SetWriteDeadline(time.Now().Add(core.ConnDeadline))
+					if n, err := conn.Write(mixedData); err == nil {
 						c.Send += n
+					} else {
+						// Connection failed, break out of loop
+						break
 					}
 				}
 			}
@@ -289,9 +323,15 @@ func (c *Client) Start() error {
 
 	buf := make([]byte, 1)
 	for {
+		// Set read deadline to detect connection issues
+		_ = c.conn.SetReadDeadline(time.Now().Add(30 * time.Second))
 		_, err := c.conn.Read(buf)
 		if err != nil {
 			c.cleanup()
+			// Remove this client from the global map
+			cltMu.Lock()
+			delete(cltMap, c.URL)
+			cltMu.Unlock()
 			return err
 		}
 	}
@@ -320,8 +360,19 @@ func (c *Client) cleanup() {
 		c.mixer.mu.Unlock()
 	}
 
+	// Close all senders
+	for _, sender := range c.Senders {
+		sender.Close()
+	}
+	c.Senders = nil
+
 	c.trackMap = make(map[*core.Sender]string)
 	c.senderStats = make(map[*core.Sender]time.Time)
+
+	// Remove from global map
+	cltMu.Lock()
+	delete(cltMap, c.URL)
+	cltMu.Unlock()
 }
 
 func (c *Client) cleanupOrphanedSenders() {