Refactor multicast so that it creates a new TCP listener for each interface with LL addresses (so that it will not break if Listen is not set with a wildcard address)

src/yggdrasil/multicast.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"net"
 	"regexp"
-	"sync"
 	"time"
 
 	"golang.org/x/net/ipv6"
@@ -16,19 +15,16 @@ type multicast struct {
 	reconfigure chan chan error
 	sock        *ipv6.PacketConn
 	groupAddr   string
-	myAddr      *net.TCPAddr
-	myAddrMutex sync.RWMutex
+	listeners   map[string]*tcpListener
 }
 
 func (m *multicast) init(core *Core) {
 	m.core = core
 	m.reconfigure = make(chan chan error, 1)
+	m.listeners = make(map[string]*tcpListener)
 	go func() {
 		for {
 			e := <-m.reconfigure
-			m.myAddrMutex.Lock()
-			m.myAddr = m.core.link.tcp.getAddr()
-			m.myAddrMutex.Unlock()
 			e <- nil
 		}
 	}()
@@ -94,10 +90,12 @@ func (m *multicast) interfaces() []net.Interface {
 			continue
 		}
 		for _, expr := range exprs {
+			// Compile each regular expression
 			e, err := regexp.Compile(expr)
 			if err != nil {
 				panic(err)
 			}
+			// Does the interface match the regular expression? Store it if so
 			if e.MatchString(iface.Name) {
 				interfaces = append(interfaces, iface)
 			}
@@ -107,10 +105,6 @@ func (m *multicast) interfaces() []net.Interface {
 }
 
 func (m *multicast) announce() {
-	var anAddr net.TCPAddr
-	m.myAddrMutex.Lock()
-	m.myAddr = m.core.link.tcp.getAddr()
-	m.myAddrMutex.Unlock()
 	groupAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr)
 	if err != nil {
 		panic(err)
@@ -121,27 +115,47 @@ func (m *multicast) announce() {
 	}
 	for {
 		for _, iface := range m.interfaces() {
-			m.sock.JoinGroup(&iface, groupAddr)
+			// Find interface addresses
 			addrs, err := iface.Addrs()
 			if err != nil {
 				panic(err)
 			}
-			m.myAddrMutex.RLock()
-			anAddr.Port = m.myAddr.Port
-			m.myAddrMutex.RUnlock()
 			for _, addr := range addrs {
 				addrIP, _, _ := net.ParseCIDR(addr.String())
+				// Ignore IPv4 addresses
 				if addrIP.To4() != nil {
 					continue
-				} // IPv6 only
+				}
+				// Ignore non-link-local addresses
 				if !addrIP.IsLinkLocalUnicast() {
 					continue
 				}
-				anAddr.IP = addrIP
-				anAddr.Zone = iface.Name
-				destAddr.Zone = iface.Name
-				msg := []byte(anAddr.String())
-				m.sock.WriteTo(msg, nil, destAddr)
+				// Join the multicast group
+				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 {
+					// 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 {
+						// 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
+					}
+				} else {
+					// An existing listener was found
+					listener = m.listeners[iface.Name]
+				}
+				// Get the listener details and construct the multicast beacon
+				lladdr := (*listener.listener).Addr().String()
+				if a, err := net.ResolveTCPAddr("tcp6", lladdr); err == nil {
+					destAddr.Zone = iface.Name
+					msg := []byte(a.String())
+					m.sock.WriteTo(msg, nil, destAddr)
+				}
 				break
 			}
 			time.Sleep(time.Second)