install go2rtc on bob

installs_on_host/go2rtc/pkg/mdns/server.go

@@ -0,0 +1,162 @@
+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 {
+	names := make(map[string]*ServiceEntry, len(entries))
+	for _, entry := range entries {
+		name := entry.name() + "." + b.Service
+		names[name] = entry
+	}
+
+	buf := make([]byte, 1500)
+	for {
+		n, addr, err := b.Recv.ReadFrom(buf)
+		if err != nil {
+			break
+		}
+
+		var req dns.Msg // request
+		if err = req.Unpack(buf[:n]); err != nil {
+			continue
+		}
+
+		// skip messages without Questions
+		if req.Question == nil {
+			continue
+		}
+
+		remoteIP := addr.(*net.UDPAddr).IP
+		localIP := b.MatchLocalIP(remoteIP)
+
+		// skip messages from unknown networks (can be docker network)
+		if localIP == nil {
+			continue
+		}
+
+		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(data, MulticastAddr)
+		}
+	}
+
+	return nil
+}
+
+func (b *Browser) MatchLocalIP(remote net.IP) net.IP {
+	for _, ipn := range b.Nets {
+		if ipn.Contains(remote) {
+			return ipn.IP
+		}
+	}
+	return nil
+}
+
+func AppendDNSSD(msg *dns.Msg, service string) {
+	msg.Answer = append(
+		msg.Answer,
+		&dns.PTR{
+			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.
+		},
+	)
+}
+
+func AppendEntry(msg *dns.Msg, entry *ServiceEntry, service string, ip net.IP) {
+	ptrName := entry.name() + "." + service
+	srvName := entry.name() + ".local."
+
+	msg.Answer = append(
+		msg.Answer,
+		&dns.PTR{
+			Hdr: dns.RR_Header{
+				Name:   service,       // _home-assistant._tcp.local.
+				Rrtype: dns.TypePTR,   // 12
+				Class:  dns.ClassINET, // 1
+				Ttl:    4500,
+			},
+			Ptr: ptrName, // Home\ Assistant._home-assistant._tcp.local.
+		},
+	)
+	msg.Extra = append(
+		msg.Extra,
+		&dns.TXT{
+			Hdr: dns.RR_Header{
+				Name:   ptrName,         // Home\ Assistant._home-assistant._tcp.local.
+				Rrtype: dns.TypeTXT,     // 16
+				Class:  ClassCacheFlush, // 32769
+				Ttl:    4500,
+			},
+			Txt: entry.TXT(),
+		},
+		&dns.SRV{
+			Hdr: dns.RR_Header{
+				Name:   ptrName,         // Home\ Assistant._home-assistant._tcp.local.
+				Rrtype: dns.TypeSRV,     // 33
+				Class:  ClassCacheFlush, // 32769
+				Ttl:    120,
+			},
+			Port:   entry.Port, // 8123
+			Target: srvName,    // 963f1fa82b7142809711cebe7c826322.local.
+		},
+		&dns.A{
+			Hdr: dns.RR_Header{
+				Name:   srvName,         // 963f1fa82b7142809711cebe7c826322.local.
+				Rrtype: dns.TypeA,       // 1
+				Class:  ClassCacheFlush, // 32769
+				Ttl:    120,
+			},
+			A: ip,
+		},
+	)
+}