fix CI and rework package structure (#111)

dns/mdns/definitions.go

@@ -0,0 +1,152 @@
+package mdns
+
+import (
+	"github.com/soypat/lneto/dns"
+)
+
+// IPv4MulticastAddr is the IPv4 multicast address used by mDNS (224.0.0.251).
+// Defined by RFC 6762. Packets sent to this address use UDP port 5353 and are
+// link-local (not routed beyond the local network segment).
+func IPv4MulticastAddr() [4]byte {
+	return [4]byte{224, 0, 0, 251}
+}
+
+// IPv4MulticastMAC is the Ethernet multicast MAC address corresponding to
+// 224.0.0.251 (01:00:5e:00:00:fb). Used for L2 delivery of mDNS over Ethernet.
+func IPv4MulticastMAC() [6]byte {
+	return [6]byte{0x01, 0x00, 0x5e, 0x00, 0x00, 0xfb}
+}
+
+// Service describes a service to advertise via mDNS.
+// A single Service produces PTR, SRV, TXT, and A resource records.
+//
+// i.e: To generate a hostname styled A record like the one
+// linux machines provide to reach them at hostname.local:
+//
+//	s := Service{
+//		Host: dns.NewName("yourhostname.local"),
+//		Addr: ipAddressSlice,
+//	}
+type Service struct {
+	// Name is the fully-qualified service instance name in wire format,
+	//  e.g. "My Web Server._http._tcp.local".
+	Name dns.Name
+	// Host is the hostname in wire format, e.g. "mydevice.local".
+	Host dns.Name
+	// TXTData is raw TXT record data (length-prefixed strings).
+	TXTData []byte
+	// Addr is the IP address for the A record.
+	Addr []byte
+	// TTL is the record TTL in seconds. Zero uses DefaultTTL.
+	TTL uint32
+	// Port is the TCP/UDP port for the SRV record.
+	Port uint16
+}
+
+func (s *Service) ttl() uint32 {
+	if s.TTL == 0 {
+		return DefaultTTL
+	}
+	return s.TTL
+}
+
+// serviceType extracts the service type portion of the instance name.
+// For "_http._tcp.local" it returns the same; for "My Web._http._tcp.local"
+// it returns "_http._tcp.local" by trimming the first label.
+// Returns a view into the original Name data — zero allocation.
+func (s *Service) serviceType() dns.Name {
+	var totalLabels int
+	s.Name.VisitLabels(func(label []byte) {
+		totalLabels++
+	})
+	if totalLabels <= 3 {
+		return s.Name
+	}
+	return s.Name.TrimLabels(1)
+}
+
+// matchQuestion reports whether the question matches the given service.
+func matchQuestion(q *dns.Question, svc *Service) bool {
+	switch q.Type {
+	case dns.TypePTR:
+		svcType := svc.serviceType()
+		return dns.NamesEqual(q.Name, svcType)
+	case dns.TypeSRV, dns.TypeTXT:
+		return dns.NamesEqual(q.Name, svc.Name)
+	case dns.TypeA:
+		return dns.NamesEqual(q.Name, svc.Host)
+	case dns.TypeALL:
+		svcType := svc.serviceType()
+		return dns.NamesEqual(q.Name, svc.Name) || dns.NamesEqual(q.Name, svc.Host) || dns.NamesEqual(q.Name, svcType)
+	}
+	return false
+}
+func MulticastMAC(ip [4]byte) (mac [6]byte, ok bool) {
+	// Check IPv4 multicast range: 224.0.0.0/4
+	if ip[0]&0xf0 != 0xe0 {
+		return mac, false
+	}
+
+	mac[0] = 0x01
+	mac[1] = 0x00
+	mac[2] = 0x5e
+
+	// Lower 23 bits of IP
+	mac[3] = ip[1] & 0x7f // drop top bit
+	mac[4] = ip[2]
+	mac[5] = ip[3]
+
+	return mac, true
+}
+
+// addServiceAnswers adds the appropriate answer records for a matched question.
+// It grows ans in-place, reusing existing Resource buffers when available.
+func addServiceAnswers(dst *[]dns.Resource, q *dns.Question, svc *Service) {
+	cacheFlush := dns.Class(uint16(dns.ClassINET) | classCacheFlush)
+	ttl := svc.ttl()
+	txtData := svc.TXTData
+	avail := cap(*dst) - len(*dst)
+	switch q.Type {
+	case dns.TypePTR:
+		if avail < 1 {
+			return
+		}
+		setPTR(growSlice(dst), svc)
+	case dns.TypeSRV:
+		if avail < 2 {
+			return
+		}
+		growSlice(dst).SetSRV(svc.Name, cacheFlush, ttl, 0, 0, svc.Port, svc.Host)
+		growSlice(dst).SetA(svc.Host, cacheFlush, ttl, svc.Addr)
+	case dns.TypeTXT:
+		if avail < 1 {
+			return
+		}
+		growSlice(dst).SetTXT(svc.Name, cacheFlush, ttl, txtData)
+	case dns.TypeA:
+		if avail < 1 {
+			return
+		}
+		growSlice(dst).SetA(svc.Host, cacheFlush, ttl, svc.Addr)
+	case dns.TypeALL:
+		if avail < 4 {
+			return
+		}
+		setPTR(growSlice(dst), svc)
+		growSlice(dst).SetSRV(svc.Name, cacheFlush, ttl, 0, 0, svc.Port, svc.Host)
+		growSlice(dst).SetTXT(svc.Name, cacheFlush, ttl, txtData)
+		growSlice(dst).SetA(svc.Host, cacheFlush, ttl, svc.Addr)
+	}
+}
+
+// growSlice grows the slice by one element and returns a pointer to the new last element.
+// Panics if at capacity — callers must check available space before calling.
+func growSlice[T any](s *[]T) *T {
+	*s = (*s)[:len(*s)+1]
+	return &(*s)[len(*s)-1]
+}
+
+func setPTR(ans *dns.Resource, svc *Service) {
+	svcType := svc.serviceType()
+	ans.SetPTR(svcType, dns.ClassINET, svc.ttl(), svc.Name)
+}