Refactor the multicast code a bit

src/multicast/multicast.go

@@ -15,6 +15,11 @@ import (
 	"golang.org/x/net/ipv6"
 )
 
+const (
+	// GroupAddr contains the multicast group and port used for multicast packets.
+	GroupAddr = "[ff02::114]:9001"
+)
+
 // Multicast represents the multicast advertisement and discovery mechanism used
 // by Yggdrasil to find peers on the same subnet. When a beacon is received on a
 // configured multicast interface, Yggdrasil will attempt to peer with that node
@@ -25,30 +30,42 @@ type Multicast struct {
 	config           *config.NodeState
 	log              *log.Logger
 	sock             *ipv6.PacketConn
-	groupAddr       string
-	listeners       map[string]*listenerInfo
+	groupAddr        *net.UDPAddr
+	listeners        map[string]*multicastInterface
 	listenPort       uint16
 	isOpen           bool
+	interfaceMonitor *time.Timer
 	announcer        *time.Timer
 	platformhandler  *time.Timer
 }
 
-type listenerInfo struct {
+type multicastInterface struct {
+	phony.Inbox
+	sock     *ipv6.PacketConn
+	destAddr net.UDPAddr
 	listener *yggdrasil.TcpListener
-	time     time.Time
+	zone     string
+	timer    *time.Timer
 	interval time.Duration
+	send     chan<- beacon
+	stop     chan interface{}
+}
+
+type beacon struct {
+	llAddr string
+	zone   string
 }
 
 // Init prepares the multicast interface for use.
-func (m *Multicast) Init(core *yggdrasil.Core, state *config.NodeState, log *log.Logger, options interface{}) error {
+func (m *Multicast) Init(core *yggdrasil.Core, state *config.NodeState, log *log.Logger, options interface{}) (err error) {
 	m.core = core
 	m.config = state
 	m.log = log
-	m.listeners = make(map[string]*listenerInfo)
+	m.listeners = make(map[string]*multicastInterface)
 	current := m.config.GetCurrent()
 	m.listenPort = current.LinkLocalTCPPort
-	m.groupAddr = "[ff02::114]:9001"
-	return nil
+	m.groupAddr, err = net.ResolveUDPAddr("udp6", GroupAddr)
+	return
 }
 
 // Start starts the multicast interface. This launches goroutines which will
@@ -71,7 +88,7 @@ func (m *Multicast) _start() error {
 		return nil
 	}
 	m.log.Infoln("Starting multicast module")
-	addr, err := net.ResolveUDPAddr("udp", m.groupAddr)
+	addr, err := net.ResolveUDPAddr("udp", GroupAddr)
 	if err != nil {
 		return err
 	}
@@ -91,7 +108,7 @@ func (m *Multicast) _start() error {
 	m.isOpen = true
 	go m.listen()
 	m.Act(m, m.multicastStarted)
-	m.Act(m, m.announce)
+	m.Act(m, m.monitorInterfaceChanges)
 
 	return nil
 }
@@ -118,9 +135,14 @@ func (m *Multicast) Stop() error {
 func (m *Multicast) _stop() error {
 	m.log.Infoln("Stopping multicast module")
 	m.isOpen = false
-	if m.announcer != nil {
-		m.announcer.Stop()
+	/*
+		if m.monitorInterfaceChanges != nil {
+			m.monitorInterfaceChanges.Stop()
 		}
+		if m.sendBeacons != nil {
+			m.sendBeacons.Stop()
+		}
+	*/
 	if m.platformhandler != nil {
 		m.platformhandler.Stop()
 	}
@@ -156,6 +178,83 @@ func (m *Multicast) _updateConfig(config *config.NodeConfig) {
 	m.log.Debugln("Reloaded multicast configuration successfully")
 }
 
+func (m *Multicast) monitorInterfaceChanges() {
+	interfaces := m.Interfaces()
+
+	// Look for interfaces we don't know about yet.
+	for name, intf := range interfaces {
+		if _, ok := m.listeners[name]; !ok {
+			// Look up interface addresses.
+			addrs, err := intf.Addrs()
+			if err != nil {
+				continue
+			}
+			// Find the first link-local address.
+			for _, addr := range addrs {
+				addrIP, _, _ := net.ParseCIDR(addr.String())
+				// Join the multicast group.
+				m.sock.JoinGroup(&intf, m.groupAddr)
+				// Construct a listener on this address.
+				listenaddr := fmt.Sprintf("[%s%%%s]:%d", addrIP, intf.Name, m.listenPort)
+				listener, err := m.core.ListenTCP(listenaddr)
+				if err != nil {
+					m.log.Warnln("Not multicasting on", name, "due to error:", err)
+					continue
+				}
+				// This is a new interface. Start an announcer for it.
+				multicastInterface := &multicastInterface{
+					sock:     m.sock,
+					destAddr: *m.groupAddr,
+					listener: listener,
+					stop:     make(chan interface{}),
+					zone:     name,
+				}
+				multicastInterface.Act(multicastInterface, multicastInterface.announce)
+				m.listeners[name] = multicastInterface
+				m.log.Infoln("Started multicasting on", name)
+				break
+			}
+		}
+	}
+	// Look for interfaces we knew about but are no longer there.
+	for name, intf := range m.listeners {
+		if _, ok := interfaces[name]; !ok {
+			// This is a disappeared interface. Stop the announcer.
+			close(intf.stop)
+			delete(m.listeners, name)
+			m.log.Infoln("Stopped multicasting on", name)
+		}
+	}
+	// Queue the next check.
+	m.interfaceMonitor = time.AfterFunc(time.Second, func() {
+		m.Act(m, m.monitorInterfaceChanges)
+	})
+}
+
+func (m *multicastInterface) announce() {
+	// Check if the multicast interface has been stopped. This will happen
+	// if it disappears from the system or goes down.
+	select {
+	case <-m.stop:
+		return
+	default:
+	}
+	// Send the beacon.
+	lladdr := m.listener.Listener.Addr().String()
+	if a, err := net.ResolveTCPAddr("tcp6", lladdr); err == nil {
+		a.Zone = ""
+		msg := []byte(a.String())
+		m.sock.WriteTo(msg, nil, &m.destAddr)
+	}
+	// Queue the next beacon.
+	if m.interval.Seconds() < 15 {
+		m.interval += time.Second
+	}
+	m.timer = time.AfterFunc(m.interval, func() {
+		m.Act(m, m.announce)
+	})
+}
+
 // GetInterfaces returns the currently known/enabled multicast interfaces. It is
 // expected that UpdateInterfaces has been called at least once before calling
 // this method.
@@ -183,6 +282,19 @@ func (m *Multicast) Interfaces() map[string]net.Interface {
 			// Ignore point-to-point interfaces
 			continue
 		}
+		addrs, _ := iface.Addrs()
+		hasLLAddr := false
+		for _, addr := range addrs {
+			addrIP, _, _ := net.ParseCIDR(addr.String())
+			if addrIP.To4() == nil && addrIP.IsLinkLocalUnicast() {
+				hasLLAddr = true
+				break
+			}
+		}
+		if !hasLLAddr {
+			// Ignore interfaces without link-local addresses
+			continue
+		}
 		for _, expr := range exprs {
 			// Compile each regular expression
 			e, err := regexp.Compile(expr)
@@ -198,127 +310,8 @@ func (m *Multicast) Interfaces() map[string]net.Interface {
 	return interfaces
 }
 
-func (m *Multicast) announce() {
-	groupAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr)
-	if err != nil {
-		panic(err)
-	}
-	destAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr)
-	if err != nil {
-		panic(err)
-	}
-	interfaces := m.Interfaces()
-	// 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, info := range m.listeners {
-		// Prepare our stop function!
-		stop := func() {
-			info.listener.Stop()
-			delete(m.listeners, name)
-			m.log.Debugln("No longer multicasting on", name)
-		}
-		// If the interface is no longer visible on the system then stop the
-		// listener, as another one will be started further down
-		if _, ok := interfaces[name]; !ok {
-			stop()
-			continue
-		}
-		// It's possible that the link-local listener address has changed so if
-		// that is the case then we should clean up the interface listener
-		found := false
-		listenaddr, err := net.ResolveTCPAddr("tcp6", info.listener.Listener.Addr().String())
-		if err != nil {
-			stop()
-			continue
-		}
-		// Find the interface that matches the listener
-		if intf, err := net.InterfaceByName(name); err == nil {
-			if addrs, err := intf.Addrs(); err == nil {
-				// Loop through the addresses attached to that listener and see if any
-				// of them match the current address of the listener
-				for _, addr := range addrs {
-					if ip, _, err := net.ParseCIDR(addr.String()); err == nil {
-						// Does the interface address match our listener address?
-						if ip.Equal(listenaddr.IP) {
-							found = true
-							break
-						}
-					}
-				}
-			}
-		}
-		// If the address has not been found on the adapter then we should stop
-		// and clean up the TCP listener. A new one will be created below if a
-		// suitable link-local address is found
-		if !found {
-			stop()
-		}
-	}
-	// 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 {
-			panic(err)
-		}
-		for _, addr := range addrs {
-			addrIP, _, _ := net.ParseCIDR(addr.String())
-			// Ignore IPv4 addresses
-			if addrIP.To4() != nil {
-				continue
-			}
-			// Ignore non-link-local addresses
-			if !addrIP.IsLinkLocalUnicast() {
-				continue
-			}
-			// Join the multicast group
-			m.sock.JoinGroup(&iface, groupAddr)
-			// Try and see if we already have a TCP listener for this interface
-			var info *listenerInfo
-			if nfo, ok := m.listeners[iface.Name]; !ok || nfo.listener.Listener == nil {
-				// No listener was found - let's create one
-				listenaddr := fmt.Sprintf("[%s%%%s]:%d", addrIP, iface.Name, m.listenPort)
-				if li, err := m.core.ListenTCP(listenaddr); err == nil {
-					m.log.Debugln("Started multicasting on", iface.Name)
-					// Store the listener so that we can stop it later if needed
-					info = &listenerInfo{listener: li, time: time.Now()}
-					m.listeners[iface.Name] = info
-				} else {
-					m.log.Warnln("Not multicasting on", iface.Name, "due to error:", err)
-				}
-			} else {
-				// An existing listener was found
-				info = m.listeners[iface.Name]
-			}
-			// Make sure nothing above failed for some reason
-			if info == nil {
-				continue
-			}
-			if time.Since(info.time) < info.interval {
-				continue
-			}
-			// Get the listener details and construct the multicast beacon
-			lladdr := info.listener.Listener.Addr().String()
-			if a, err := net.ResolveTCPAddr("tcp6", lladdr); err == nil {
-				a.Zone = ""
-				destAddr.Zone = iface.Name
-				msg := []byte(a.String())
-				m.sock.WriteTo(msg, nil, destAddr)
-			}
-			if info.interval.Seconds() < 15 {
-				info.interval += time.Second
-			}
-			break
-		}
-	}
-	m.announcer = time.AfterFunc(time.Second, func() {
-		m.Act(m, m.announce)
-	})
-}
-
 func (m *Multicast) listen() {
-	groupAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr)
+	groupAddr, err := net.ResolveUDPAddr("udp6", GroupAddr)
 	if err != nil {
 		panic(err)
 	}