mdns: change NewMDNS to
1) allow no hostname to be truly anonymous.
2) make sure a hostname isn't already in use and return an error if it is
3) allow the caller to specify the host name as "hostname()". The "()"
will be turned into "(lexically highest mac address)".
TBR:
Change-Id: If0e6c7faf54fc0acb74e29cdb06e8e723dba220d
diff --git a/go/src/github.com/presotto/go-mdns-sd/mdns.go b/go/src/github.com/presotto/go-mdns-sd/mdns.go
index 0c8d17c..a3a32db 100644
--- a/go/src/github.com/presotto/go-mdns-sd/mdns.go
+++ b/go/src/github.com/presotto/go-mdns-sd/mdns.go
@@ -224,6 +224,7 @@
// The host name.
hostName string
+ hostFQDN string
// Services we are announcing and their ports
services map[string]announceRequest
@@ -250,6 +251,48 @@
return y
}
+func ipsAreAllMine(ips []net.IP) bool {
+ if len(ips) == 0 {
+ return true
+ }
+ addrs, _ := net.InterfaceAddrs()
+ for _, ip := range ips {
+ found := false
+ for _, addr := range addrs {
+ switch x := addr.(type) {
+ case *net.IPNet:
+ if x.IP.Equal(ip) {
+ found = true
+ break
+ }
+ }
+ }
+ if !found {
+ return false
+ }
+ }
+ return true
+}
+
+func (s *MDNS) isDoppelGanger(rr []dns.RR) bool {
+ var ips []net.IP
+ for _, rr := range rr {
+ if rr.Header().Name != s.hostFQDN {
+ continue
+ }
+ switch x := rr.(type) {
+ case *dns.RR_A:
+ ips = append(ips, AtoIP(x))
+ case *dns.RR_AAAA:
+ ips = append(ips, AAAAtoIP(x))
+ }
+ }
+ if len(ips) == 0 {
+ return false
+ }
+ return !ipsAreAllMine(ips)
+}
+
// Create a new MDNS service.
func NewMDNS(host, v4addr, v6addr string, loopback, debug bool) (s *MDNS, err error) {
s = new(MDNS)
@@ -267,7 +310,6 @@
}
s.debug = debug
s.loopback = loopback
- s.hostName = host
s.ttl = 120
// Allocate channels for communications internal to MDNS
@@ -287,14 +329,26 @@
log.Fatalf("scanning interfaces: %s", err)
}
- // If we weren't passed in a host name, use the highest lexicographic hardware address.
- if len(s.hostName) == 0 {
- s.hostName = losecolons(highesthwaddr)
- }
-
go s.mainLoop()
go s.alarmClock()
+ // If the name ends in a '()', tack on our hwaddr.
+ if len(host) != 0 {
+ if strings.HasSuffix(host, "()") {
+ host = fmt.Sprintf("%s(%s)", strings.TrimSuffix(host, "()"), losecolons(highesthwaddr))
+ }
+
+ // Make sure someone else isn't using our name already.
+ ips, _ := s.ResolveAddress(host)
+ if !ipsAreAllMine(ips) {
+ // Close down our multicasts ifcs.
+ s.Stop()
+ return nil, errors.New("host name in use")
+ }
+ s.hostName = host
+ s.hostFQDN = hostFQDN(host)
+ }
+
// Announce ourselves if the host name is set.
if len(s.hostName) > 0 {
s.refreshAlarm <- struct{}{}
@@ -597,6 +651,10 @@
if s.debug {
log.Printf("%s: response %v\n", s.hostName, m.msg)
}
+ if s.isDoppelGanger(m.msg.Answer) {
+ log.Printf("%s: name collision, %s also claims to be %s\n", s.hostName, m.sender, s.hostFQDN)
+ continue
+ }
for _, rr := range m.msg.Answer {
if m.mifc.cache.Add(rr) {
s.changedRR(rr)
@@ -677,6 +735,9 @@
return errors.New("service name cannot be null")
}
if len(host) == 0 {
+ if s.hostName == "" {
+ return errors.New("AddService requires a host name")
+ }
host = s.hostName
} else {
host = hostUnqualify(host)
