package yggdrasil import ( "context" "fmt" "net" "time" "golang.org/x/net/ipv6" ) type multicast struct { core *Core sock *ipv6.PacketConn groupAddr string } func (m *multicast) init(core *Core) { m.core = core m.groupAddr = "[ff02::114]:9001" // Check if we've been given any expressions if len(m.core.ifceExpr) == 0 { return } // Ask the system for network interfaces m.core.log.Println("Found", len(m.interfaces()), "multicast interface(s)") } func (m *multicast) start() error { if len(m.core.ifceExpr) == 0 { m.core.log.Println("Multicast discovery is disabled") } else { m.core.log.Println("Multicast discovery is enabled") addr, err := net.ResolveUDPAddr("udp", m.groupAddr) if err != nil { return err } listenString := fmt.Sprintf("[::]:%v", addr.Port) lc := net.ListenConfig{ Control: multicastReuse, } conn, err := lc.ListenPacket(context.Background(), "udp6", listenString) if err != nil { return err } m.sock = ipv6.NewPacketConn(conn) if err = m.sock.SetControlMessage(ipv6.FlagDst, true); err != nil { // Windows can't set this flag, so we need to handle it in other ways } go m.listen() go m.announce() } return nil } func (m *multicast) interfaces() []net.Interface { // Ask the system for network interfaces var interfaces []net.Interface allifaces, err := net.Interfaces() if err != nil { panic(err) } // Work out which interfaces to announce on for _, iface := range allifaces { if iface.Flags&net.FlagUp == 0 { // Ignore interfaces that are down continue } if iface.Flags&net.FlagMulticast == 0 { // Ignore non-multicast interfaces continue } if iface.Flags&net.FlagPointToPoint != 0 { // Ignore point-to-point interfaces continue } for _, expr := range m.core.ifceExpr { if expr.MatchString(iface.Name) { interfaces = append(interfaces, iface) } } } return interfaces } func (m *multicast) announce() { groupAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr) if err != nil { panic(err) } var anAddr net.TCPAddr myAddr := m.core.tcp.getAddr() anAddr.Port = myAddr.Port destAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr) if err != nil { panic(err) } for { for _, iface := range m.interfaces() { m.sock.JoinGroup(&iface, groupAddr) addrs, err := iface.Addrs() if err != nil { panic(err) } for _, addr := range addrs { addrIP, _, _ := net.ParseCIDR(addr.String()) if addrIP.To4() != nil { continue } // IPv6 only 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) break } time.Sleep(time.Second) } time.Sleep(time.Second) } } func (m *multicast) listen() { groupAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr) if err != nil { panic(err) } bs := make([]byte, 2048) for { nBytes, rcm, fromAddr, err := m.sock.ReadFrom(bs) if err != nil { panic(err) } if rcm != nil { // Windows can't set the flag needed to return a non-nil value here // So only make these checks if we get something useful back // TODO? Skip them always, I'm not sure if they're really needed... if !rcm.Dst.IsLinkLocalMulticast() { continue } if !rcm.Dst.Equal(groupAddr.IP) { continue } } anAddr := string(bs[:nBytes]) addr, err := net.ResolveTCPAddr("tcp6", anAddr) if err != nil { continue } from := fromAddr.(*net.UDPAddr) if addr.IP.String() != from.IP.String() { continue } addr.Zone = from.Zone saddr := addr.String() m.core.tcp.connect(saddr, "") } }