client: use server interface as multicast interface (#762) (#847)

this fixes most errors "found no interface that is multicast-capable
and can communicate with IP".

client.go

@@ -252,6 +252,48 @@ func supportsGetParameter(header base.Header) bool {
 	return false
 }
 
+func interfaceOfConn(c net.Conn) (*net.Interface, error) {
+	var localIP net.IP
+
+	switch addr := c.LocalAddr().(type) {
+	case *net.TCPAddr:
+		localIP = addr.IP
+	case *net.UDPAddr:
+		localIP = addr.IP
+	default:
+		return nil, fmt.Errorf("unknown connection type: %T", c.LocalAddr())
+	}
+
+	interfaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, iface := range interfaces {
+		var addrs []net.Addr
+		addrs, err = iface.Addrs()
+		if err != nil {
+			continue
+		}
+
+		for _, addr := range addrs {
+			var ip net.IP
+			switch v := addr.(type) {
+			case *net.IPNet:
+				ip = v.IP
+			case *net.IPAddr:
+				ip = v.IP
+			}
+
+			if ip != nil && ip.Equal(localIP) {
+				return &iface, nil
+			}
+		}
+	}
+
+	return nil, fmt.Errorf("no interface found for IP %s", localIP)
+}
+
 type clientState int
 
 const (
@@ -1796,9 +1838,16 @@ func (c *Client) doSetup(
 			remoteIP = c.nconn.RemoteAddr().(*net.TCPAddr).IP
 		}
 
+		var intf *net.Interface
+		intf, err = interfaceOfConn(c.nconn)
+		if err != nil {
+			cm.close()
+			return nil, err
+		}
+
 		err = cm.createUDPListeners(
 			true,
-			remoteIP,
+			intf,
 			net.JoinHostPort(thRes.Destination.String(), strconv.FormatInt(int64(thRes.Ports[0]), 10)),
 			net.JoinHostPort(thRes.Destination.String(), strconv.FormatInt(int64(thRes.Ports[1]), 10)),
 		)

client_media.go

@@ -101,17 +101,17 @@ func (cm *clientMedia) close() {
 }
 
 func (cm *clientMedia) createUDPListeners(
-	multicastEnable bool,
-	multicastSourceIP net.IP,
+	multicast bool,
+	multicastInterface *net.Interface,
 	rtpAddress string,
 	rtcpAddress string,
 ) error {
 	if rtpAddress != ":0" {
 		l1 := &clientUDPListener{
-			c:                 cm.c,
-			multicastEnable:   multicastEnable,
-			multicastSourceIP: multicastSourceIP,
-			address:           rtpAddress,
+			c:                  cm.c,
+			multicast:          multicast,
+			multicastInterface: multicastInterface,
+			address:            rtpAddress,
 		}
 		err := l1.initialize()
 		if err != nil {
@@ -119,10 +119,10 @@ func (cm *clientMedia) createUDPListeners(
 		}
 
 		l2 := &clientUDPListener{
-			c:                 cm.c,
-			multicastEnable:   multicastEnable,
-			multicastSourceIP: multicastSourceIP,
-			address:           rtcpAddress,
+			c:                  cm.c,
+			multicast:          multicast,
+			multicastInterface: multicastInterface,
+			address:            rtcpAddress,
 		}
 		err = l2.initialize()
 		if err != nil {
@@ -146,10 +146,8 @@ func (cm *clientMedia) createUDPListeners(
 		rtcpPort := rtpPort + 1
 
 		cm.udpRTPListener = &clientUDPListener{
-			c:                 cm.c,
-			multicastEnable:   false,
-			multicastSourceIP: nil,
-			address:           net.JoinHostPort("", strconv.FormatInt(int64(rtpPort), 10)),
+			c:       cm.c,
+			address: net.JoinHostPort("", strconv.FormatInt(int64(rtpPort), 10)),
 		}
 		err = cm.udpRTPListener.initialize()
 		if err != nil {
@@ -158,10 +156,8 @@ func (cm *clientMedia) createUDPListeners(
 		}
 
 		cm.udpRTCPListener = &clientUDPListener{
-			c:                 cm.c,
-			multicastEnable:   false,
-			multicastSourceIP: nil,
-			address:           net.JoinHostPort("", strconv.FormatInt(int64(rtcpPort), 10)),
+			c:       cm.c,
+			address: net.JoinHostPort("", strconv.FormatInt(int64(rtcpPort), 10)),
 		}
 		err = cm.udpRTCPListener.initialize()
 		if err != nil {

client_udp_listener.go

@@ -29,10 +29,10 @@ type packetConn interface {
 }
 
 type clientUDPListener struct {
-	c                 *Client
-	multicastEnable   bool
-	multicastSourceIP net.IP
-	address           string
+	c                  *Client
+	multicast          bool
+	multicastInterface *net.Interface
+	address            string
 
 	pc        packetConn
 	readFunc  readFunc
@@ -47,13 +47,9 @@ type clientUDPListener struct {
 }
 
 func (u *clientUDPListener) initialize() error {
-	if u.multicastEnable {
-		intf, err := multicast.InterfaceForSource(u.multicastSourceIP)
-		if err != nil {
-			return err
-		}
-
-		u.pc, err = multicast.NewSingleConn(intf, u.address, u.c.ListenPacket)
+	if u.multicast {
+		var err error
+		u.pc, err = multicast.NewSingleConn(u.multicastInterface, u.address, u.c.ListenPacket)
 		if err != nil {
 			return err
 		}

pkg/multicast/multicast.go

@@ -13,6 +13,8 @@ type Conn interface {
 }
 
 // InterfaceForSource returns a multicast-capable interface that can communicate with given IP.
+//
+// Deprecated: not used anymore.
 func InterfaceForSource(ip net.IP) (*net.Interface, error) {
 	if ip.Equal(net.ParseIP("127.0.0.1")) {
 		return nil, fmt.Errorf("IP 127.0.0.1 can't be used as source of a multicast stream. Use the LAN IP of your PC")