Add support HomeKit server

pkg/mdns/server.go

@@ -0,0 +1,157 @@
+package mdns
+
+import (
+	"net"
+
+	"github.com/miekg/dns"
+)
+
+// ClassCacheFlush https://datatracker.ietf.org/doc/html/rfc6762#section-10.2
+const ClassCacheFlush = 0x8001
+
+func Serve(service string, entries []*ServiceEntry) error {
+	b := Browser{Service: service}
+
+	if err := b.ListenMulticastUDP(); err != nil {
+		return err
+	}
+
+	return b.Serve(entries)
+}
+
+func (b *Browser) Serve(entries []*ServiceEntry) error {
+	var msg dns.Msg
+
+	buf := make([]byte, 1500)
+	for {
+		n, addr, err := b.Recv.ReadFrom(buf)
+		if err != nil {
+			break
+		}
+
+		if err = msg.Unpack(buf[:n]); err != nil {
+			continue
+		}
+
+		if !HasQuestionPTP(&msg, b.Service) {
+			continue
+		}
+
+		remoteIP := addr.(*net.UDPAddr).IP
+		localIP := MatchLocalIP(remoteIP)
+		if localIP == nil {
+			continue
+		}
+
+		answer, err := NewDNSAnswer(entries, b.Service, localIP).Pack()
+		if err != nil {
+			continue
+		}
+
+		for _, send := range b.Sends {
+			_, _ = send.WriteTo(answer, MulticastAddr)
+		}
+	}
+
+	return nil
+}
+
+func HasQuestionPTP(msg *dns.Msg, name string) bool {
+	for _, q := range msg.Question {
+		if q.Qtype == dns.TypePTR && q.Name == name {
+			return true
+		}
+	}
+	return false
+}
+
+func NewDNSAnswer(entries []*ServiceEntry, service string, ip net.IP) *dns.Msg {
+	msg := dns.Msg{
+		MsgHdr: dns.MsgHdr{
+			Response:      true,
+			Authoritative: true,
+		},
+	}
+
+	for _, entry := range entries {
+		ptrName := entry.name() + "." + service
+		srvName := entry.name() + ".local."
+
+		msg.Answer = append(
+			msg.Answer,
+			&dns.PTR{
+				Hdr: dns.RR_Header{
+					Name:   service,
+					Rrtype: dns.TypePTR,
+					Class:  dns.ClassINET,
+					Ttl:    4500,
+				},
+				Ptr: ptrName,
+			},
+		)
+		msg.Extra = append(
+			msg.Extra,
+			&dns.TXT{
+				Hdr: dns.RR_Header{
+					Name:   ptrName,
+					Rrtype: dns.TypeTXT,
+					Class:  ClassCacheFlush,
+					Ttl:    4500,
+				},
+				Txt: entry.TXT(),
+			},
+			&dns.SRV{
+				Hdr: dns.RR_Header{
+					Name:     ptrName,
+					Rrtype:   dns.TypeSRV,
+					Class:    ClassCacheFlush,
+					Ttl:      120,
+					Rdlength: 0,
+				},
+				Port:   entry.Port,
+				Target: srvName,
+			},
+			&dns.A{
+				Hdr: dns.RR_Header{
+					Name:     srvName,
+					Rrtype:   dns.TypeA,
+					Class:    ClassCacheFlush,
+					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
+}