Properly handle multicast interfaces going up and down

src/yggdrasil/link.go

@@ -261,11 +261,11 @@ func (intf *linkInterface) handler() error {
 			// Now block until something is ready or the timer triggers keepalive traffic
 			select {
 			case <-tcpTimer.C:
-				intf.link.core.log.Debugf("Sending (legacy) keep-alive to %s: %s, source %s",
+				intf.link.core.log.Tracef("Sending (legacy) keep-alive to %s: %s, source %s",
 					strings.ToUpper(intf.info.linkType), themString, intf.info.local)
 				send(nil)
 			case <-sendAck:
-				intf.link.core.log.Debugf("Sending ack to %s: %s, source %s",
+				intf.link.core.log.Tracef("Sending ack to %s: %s, source %s",
 					strings.ToUpper(intf.info.linkType), themString, intf.info.local)
 				send(nil)
 			case msg := <-intf.peer.linkOut:
@@ -280,7 +280,7 @@ func (intf *linkInterface) handler() error {
 				case signalReady <- struct{}{}:
 				default:
 				}
-				//intf.link.core.log.Debugf("Sending packet to %s: %s, source %s",
+				//intf.link.core.log.Tracef("Sending packet to %s: %s, source %s",
 				//	strings.ToUpper(intf.info.linkType), themString, intf.info.local)
 			}
 		}
@@ -331,7 +331,7 @@ func (intf *linkInterface) handler() error {
 					sendTimerRunning = true
 				}
 				if !gotMsg {
-					intf.link.core.log.Debugf("Received ack from %s: %s, source %s",
+					intf.link.core.log.Tracef("Received ack from %s: %s, source %s",
 						strings.ToUpper(intf.info.linkType), themString, intf.info.local)
 				}
 			case sentMsg, ok := <-signalSent:

src/yggdrasil/multicast.go

@@ -64,13 +64,13 @@ func (m *multicast) start() error {
 	return nil
 }
 
-func (m *multicast) interfaces() []net.Interface {
+func (m *multicast) interfaces() map[string]net.Interface {
 	// Get interface expressions from config
 	m.core.configMutex.RLock()
 	exprs := m.core.config.MulticastInterfaces
 	m.core.configMutex.RUnlock()
 	// Ask the system for network interfaces
-	var interfaces []net.Interface
+	interfaces := make(map[string]net.Interface)
 	allifaces, err := net.Interfaces()
 	if err != nil {
 		panic(err)
@@ -97,7 +97,7 @@ func (m *multicast) interfaces() []net.Interface {
 			}
 			// Does the interface match the regular expression? Store it if so
 			if e.MatchString(iface.Name) {
-				interfaces = append(interfaces, iface)
+				interfaces[iface.Name] = iface
 			}
 		}
 	}
@@ -114,7 +114,10 @@ func (m *multicast) announce() {
 		panic(err)
 	}
 	for {
-		for _, iface := range m.interfaces() {
+		interfaces := m.interfaces()
+		// Now that we have a list of valid interfaces from the operating system,
+		// we can start checking if we can send multicasts on them
+		for _, iface := range interfaces {
 			// Find interface addresses
 			addrs, err := iface.Addrs()
 			if err != nil {
@@ -134,23 +137,24 @@ func (m *multicast) announce() {
 				m.sock.JoinGroup(&iface, groupAddr)
 				// Try and see if we already have a TCP listener for this interface
 				var listener *tcpListener
-				if _, ok := m.listeners[iface.Name]; !ok {
+				if l, ok := m.listeners[iface.Name]; !ok || l.listener == nil {
 					// No listener was found - let's create one
 					listenaddr := fmt.Sprintf("[%s%%%s]:0", addrIP, iface.Name)
 					if l, err := m.core.link.tcp.listen(listenaddr); err == nil {
+						m.core.log.Debugln("Started multicasting on", iface.Name)
 						// Store the listener so that we can stop it later if needed
-						listener = &tcpListener{
-							listener: l,
-							stop:     make(chan bool),
-						}
-						m.listeners[iface.Name] = listener
+						m.listeners[iface.Name] = l
 					}
 				} else {
 					// An existing listener was found
 					listener = m.listeners[iface.Name]
 				}
+				// Make sure nothing above failed for some reason
+				if listener == nil {
+					continue
+				}
 				// Get the listener details and construct the multicast beacon
-				lladdr := (*listener.listener).Addr().String()
+				lladdr := listener.listener.Addr().String()
 				if a, err := net.ResolveTCPAddr("tcp6", lladdr); err == nil {
 					destAddr.Zone = iface.Name
 					msg := []byte(a.String())
@@ -160,7 +164,16 @@ func (m *multicast) announce() {
 			}
 			time.Sleep(time.Second)
 		}
-		time.Sleep(time.Second)
+		// There might be interfaces that we configured listeners for but are no
+		// longer up - if that's the case then we should stop the listeners
+		for name, listener := range m.listeners {
+			if _, ok := interfaces[name]; !ok {
+				listener.stop <- true
+				delete(m.listeners, name)
+				m.core.log.Debugln("No longer multicasting on", name)
+			}
+		}
+		time.Sleep(time.Second * 5)
 	}
 }
 

src/yggdrasil/tcp.go

@@ -42,7 +42,7 @@ type tcp struct {
 }
 
 type tcpListener struct {
-	listener *net.Listener
+	listener net.Listener
 	stop     chan bool
 }
 
@@ -63,8 +63,8 @@ func (t *tcp) getAddr() *net.TCPAddr {
 	// doesn't have the ability to send more than one address in a packet either
 	t.mutex.Lock()
 	defer t.mutex.Unlock()
-	for _, listener := range t.listeners {
-		return (*listener.listener).Addr().(*net.TCPAddr)
+	for _, l := range t.listeners {
+		return l.listener.Addr().(*net.TCPAddr)
 	}
 	return nil
 }
@@ -121,7 +121,7 @@ func (t *tcp) init(l *link) error {
 	return nil
 }
 
-func (t *tcp) listen(listenaddr string) (*net.Listener, error) {
+func (t *tcp) listen(listenaddr string) (*tcpListener, error) {
 	var err error
 
 	ctx := context.Background()
@@ -131,37 +131,40 @@ func (t *tcp) listen(listenaddr string) (*net.Listener, error) {
 	listener, err := lc.Listen(ctx, "tcp", listenaddr)
 	if err == nil {
 		l := tcpListener{
-			listener: &listener,
-			stop:     make(chan bool, 1),
+			listener: listener,
+			stop:     make(chan bool),
 		}
-		t.mutex.Lock()
-		t.listeners[listenaddr[6:]] = &l
-		t.mutex.Unlock()
-		go t.listener(&l)
-		return &listener, nil
+		go t.listener(&l, listenaddr[6:])
+		return &l, nil
 	}
 
 	return nil, err
 }
 
 // Runs the listener, which spawns off goroutines for incoming connections.
-func (t *tcp) listener(listener *tcpListener) {
-	if listener == nil {
+func (t *tcp) listener(l *tcpListener, listenaddr string) {
+	if l == nil {
 		return
 	}
-	reallistener := *listener.listener
-	reallistenaddr := reallistener.Addr().String()
-	stop := listener.stop
-	defer reallistener.Close()
-	t.link.core.log.Infoln("Listening for TCP on:", reallistenaddr)
+	// Track the listener so that we can find it again in future
+	t.mutex.Lock()
+	t.listeners[listenaddr] = l
+	t.mutex.Unlock()
+	// And here we go!
 	accepted := make(chan bool)
+	defer l.listener.Close()
+	t.link.core.log.Infoln("Listening for TCP on:", l.listener.Addr().String())
 	for {
 		var sock net.Conn
 		var err error
+		// Listen in a separate goroutine, as that way it does not block us from
+		// receiving "stop" events
 		go func() {
-			sock, err = reallistener.Accept()
+			sock, err = l.listener.Accept()
 			accepted <- true
 		}()
+		// Wait for either an accepted connection, or a message telling us to stop
+		// the TCP listener
 		select {
 		case <-accepted:
 			if err != nil {
@@ -169,8 +172,12 @@ func (t *tcp) listener(listener *tcpListener) {
 				return
 			}
 			go t.handler(sock, true)
-		case <-stop:
-			t.link.core.log.Errorln("Stopping TCP listener on:", reallistenaddr)
+		case <-l.stop:
+			t.link.core.log.Infoln("Stopping TCP listener on:", l.listener.Addr().String())
+			l.listener.Close()
+			t.mutex.Lock()
+			delete(t.listeners, listenaddr)
+			t.mutex.Unlock()
 			return
 		}
 	}