Update mDNS server handler

pkg/mdns/client.go

@@ -13,7 +13,10 @@ import (
 	"github.com/miekg/dns" // awesome library for parsing mDNS records
 )
 
-const ServiceHAP = "_hap._tcp.local." // HomeKit Accessory Protocol
+const (
+	ServiceDNSSD = "_services._dns-sd._udp.local."
+	ServiceHAP   = "_hap._tcp.local." // HomeKit Accessory Protocol
+)
 
 type ServiceEntry struct {
 	Name string            `json:"name,omitempty"`
@@ -153,6 +156,7 @@ type Browser struct {
 	Service string
 
 	Addr  net.Addr
+	Nets  []*net.IPNet
 	Recv  net.PacketConn
 	Sends []net.PacketConn
 
@@ -165,7 +169,7 @@ type Browser struct {
 // Receiver will get multicast responses on senders requests.
 func (b *Browser) ListenMulticastUDP() error {
 	// 1. Collect IPv4 interfaces
-	ip4s, err := InterfacesIP4()
+	nets, err := IPNets()
 	if err != nil {
 		return err
 	}
@@ -182,11 +186,12 @@ func (b *Browser) ListenMulticastUDP() error {
 
 	ctx := context.Background()
 
-	for _, ip4 := range ip4s {
+	for _, ipn := range nets {
-		conn, err := lc1.ListenPacket(ctx, "udp4", ip4.String()+":5353") // same port important
+		conn, err := lc1.ListenPacket(ctx, "udp4", ipn.IP.String()+":5353") // same port important
 		if err != nil {
 			continue
 		}
+		b.Nets = append(b.Nets, ipn)
 		b.Sends = append(b.Sends, conn)
 	}
 
@@ -365,35 +370,39 @@ func NewServiceEntries(msg *dns.Msg, ip net.IP) (entries []*ServiceEntry) {
 	return
 }
 
-func InterfacesIP4() ([]net.IP, error) {
+// Common docker addresses (class B):
+// https://en.wikipedia.org/wiki/Private_network
+// - docker0 172.17.0.1/16
+// - br-xxxx 172.18.0.1/16
+// - hassio  172.30.32.1/23
+var docker = net.IPNet{
+	IP:   []byte{172, 16, 0, 0},
+	Mask: []byte{255, 240, 0, 0},
+}
+
+func IPNets() ([]*net.IPNet, error) {
 	intfs, err := net.Interfaces()
 	if err != nil {
 		return nil, err
 	}
 
-	var ips []net.IP
+	var nets []*net.IPNet
 
-loop:
 	for _, intf := range intfs {
 		if intf.Flags&net.FlagUp == 0 || intf.Flags&net.FlagLoopback != 0 {
 			continue
 		}
 
-		addrs, err := intf.Addrs()
+		addrs, _ := intf.Addrs()
-		if err != nil {
-			continue
-		}
-
 		for _, addr := range addrs {
 			switch v := addr.(type) {
 			case *net.IPNet:
-				if ip := v.IP.To4(); ip != nil {
+				if ip := v.IP.To4(); ip != nil && !docker.Contains(ip) {
-					ips = append(ips, ip)
+					nets = append(nets, v)
-					continue loop
 				}
 			}
 		}
 	}
 
-	return ips, nil
+	return nets, nil
 }

pkg/mdns/server.go

@@ -20,7 +20,11 @@ func Serve(service string, entries []*ServiceEntry) error {
 }
 
 func (b *Browser) Serve(entries []*ServiceEntry) error {
-	var msg dns.Msg
+	names := make(map[string]*ServiceEntry, len(entries))
+	for _, entry := range entries {
+		name := entry.name() + "." + b.Service
+		names[name] = entry
+	}
 
 	buf := make([]byte, 1500)
 	for {
@@ -29,51 +33,86 @@ func (b *Browser) Serve(entries []*ServiceEntry) error {
 			break
 		}
 
-		if err = msg.Unpack(buf[:n]); err != nil {
+		var req dns.Msg // request
+		if err = req.Unpack(buf[:n]); err != nil {
 			continue
 		}
 
-		if !HasQuestionPTP(&msg, b.Service) {
+		// skip messages without Questions
+		if req.Question == nil {
 			continue
 		}
 
 		remoteIP := addr.(*net.UDPAddr).IP
-		localIP := MatchLocalIP(remoteIP)
+		localIP := b.MatchLocalIP(remoteIP)
+
+		// skip messages from unknown networks (can be docker network)
 		if localIP == nil {
 			continue
 		}
 
-		answer, err := NewDNSAnswer(entries, b.Service, localIP).Pack()
+		var res dns.Msg // response
+		for _, q := range req.Question {
+			if q.Qtype != dns.TypePTR || q.Qclass != dns.ClassINET {
+				continue
+			}
+
+			if q.Name == ServiceDNSSD {
+				AppendDNSSD(&res, b.Service)
+			} else if q.Name == b.Service {
+				for _, entry := range entries {
+					AppendEntry(&res, entry, b.Service, localIP)
+				}
+			} else if entry, ok := names[q.Name]; ok {
+				AppendEntry(&res, entry, b.Service, localIP)
+			}
+		}
+
+		if res.Answer == nil {
+			continue
+		}
+
+		res.MsgHdr.Response = true
+		res.MsgHdr.Authoritative = true
+
+		data, err := res.Pack()
 		if err != nil {
 			continue
 		}
 
 		for _, send := range b.Sends {
-			_, _ = send.WriteTo(answer, MulticastAddr)
+			_, _ = send.WriteTo(data, MulticastAddr)
 		}
 	}
 
 	return nil
 }
 
-func HasQuestionPTP(msg *dns.Msg, name string) bool {
+func (b *Browser) MatchLocalIP(remote net.IP) net.IP {
-	for _, q := range msg.Question {
+	for _, ipn := range b.Nets {
-		if q.Qtype == dns.TypePTR && q.Name == name {
+		if ipn.Contains(remote) {
-			return true
+			return ipn.IP
 		}
 	}
-	return false
+	return nil
 }
 
-func NewDNSAnswer(entries []*ServiceEntry, service string, ip net.IP) *dns.Msg {
+func AppendDNSSD(msg *dns.Msg, service string) {
-	msg := dns.Msg{
+	msg.Answer = append(
-		MsgHdr: dns.MsgHdr{
+		msg.Answer,
-			Response:      true,
+		&dns.PTR{
-			Authoritative: true,
+			Hdr: dns.RR_Header{
+				Name:   ServiceDNSSD,  // _services._dns-sd._udp.local.
+				Rrtype: dns.TypePTR,   // 12
+				Class:  dns.ClassINET, // 1
+				Ttl:    4500,
 			},
-	}
+			Ptr: service, // _home-assistant._tcp.local.
+		},
+	)
+}
 
-	for _, entry := range entries {
+func AppendEntry(msg *dns.Msg, entry *ServiceEntry, service string, ip net.IP) {
 	ptrName := entry.name() + "." + service
 	srvName := entry.name() + ".local."
 
@@ -81,77 +120,43 @@ func NewDNSAnswer(entries []*ServiceEntry, service string, ip net.IP) *dns.Msg {
 		msg.Answer,
 		&dns.PTR{
 			Hdr: dns.RR_Header{
-					Name:   service,
+				Name:   service,       // _home-assistant._tcp.local.
-					Rrtype: dns.TypePTR,
+				Rrtype: dns.TypePTR,   // 12
-					Class:  dns.ClassINET,
+				Class:  dns.ClassINET, // 1
 				Ttl:    4500,
 			},
-				Ptr: ptrName,
+			Ptr: ptrName, // Home\ Assistant._home-assistant._tcp.local.
 		},
 	)
 	msg.Extra = append(
 		msg.Extra,
 		&dns.TXT{
 			Hdr: dns.RR_Header{
-					Name:   ptrName,
+				Name:   ptrName,         // Home\ Assistant._home-assistant._tcp.local.
-					Rrtype: dns.TypeTXT,
+				Rrtype: dns.TypeTXT,     // 16
-					Class:  ClassCacheFlush,
+				Class:  ClassCacheFlush, // 32769
 				Ttl:    4500,
 			},
 			Txt: entry.TXT(),
 		},
 		&dns.SRV{
 			Hdr: dns.RR_Header{
-					Name:     ptrName,
+				Name:   ptrName,         // Home\ Assistant._home-assistant._tcp.local.
-					Rrtype:   dns.TypeSRV,
+				Rrtype: dns.TypeSRV,     // 33
-					Class:    ClassCacheFlush,
+				Class:  ClassCacheFlush, // 32769
 				Ttl:    120,
-					Rdlength: 0,
 			},
-				Port:   entry.Port,
+			Port:   entry.Port, // 8123
-				Target: srvName,
+			Target: srvName,    // 963f1fa82b7142809711cebe7c826322.local.
 		},
 		&dns.A{
 			Hdr: dns.RR_Header{
-					Name:     srvName,
+				Name:   srvName,         // 963f1fa82b7142809711cebe7c826322.local.
-					Rrtype:   dns.TypeA,
+				Rrtype: dns.TypeA,       // 1
-					Class:    ClassCacheFlush,
+				Class:  ClassCacheFlush, // 32769
 				Ttl:    120,
-					Rdlength: 0,
 			},
 			A: ip,
 		},
 	)
-	}
-
-	return &msg
-}
-
-func MatchLocalIP(remote net.IP) net.IP {
-	intfs, err := net.Interfaces()
-	if err != nil {
-		return nil
-	}
-
-	for _, intf := range intfs {
-		if intf.Flags&net.FlagUp == 0 || intf.Flags&net.FlagLoopback != 0 {
-			continue
-		}
-
-		addrs, err := intf.Addrs()
-		if err != nil {
-			continue
-		}
-
-		for _, addr := range addrs {
-			switch v := addr.(type) {
-			case *net.IPNet:
-				if local := v.IP.To4(); local != nil && v.Contains(remote) {
-					return local
-				}
-			}
-		}
-	}
-
-	return nil
 }