Rewrite mDNS processing

pkg/mdns/mdns.go

@@ -0,0 +1,139 @@
+package mdns
+
+import (
+	"fmt"
+	"github.com/miekg/dns"
+	"net"
+	"strings"
+	"time"
+)
+
+const ServiceHAP = "_hap._tcp.local." // HomeKit Accessory Protocol
+
+const requestTimeout = time.Millisecond * 505
+const responseTimeout = time.Second * 2
+
+type ServiceEntry struct {
+	Name string
+	IP   net.IP
+	Port uint16
+	Info map[string]string
+}
+
+func (e *ServiceEntry) Complete() bool {
+	return e.IP != nil && e.Port > 0 && e.Info != nil
+}
+
+func (e *ServiceEntry) Addr() string {
+	return fmt.Sprintf("%s:%d", e.IP, e.Port)
+}
+
+func Discovery(service string, onentry func(*ServiceEntry) bool) error {
+	addr := &net.UDPAddr{
+		IP:   net.IP{224, 0, 0, 251},
+		Port: 5353,
+	}
+
+	conn, err := net.ListenMulticastUDP("udp4", nil, addr)
+	if err != nil {
+		return err
+	}
+
+	defer conn.Close()
+
+	if err = conn.SetDeadline(time.Now().Add(responseTimeout)); err != nil {
+		return err
+	}
+
+	msg := &dns.Msg{
+		Question: []dns.Question{
+			{service, dns.TypePTR, dns.ClassINET},
+		},
+	}
+
+	b1, err := msg.Pack()
+	if err != nil {
+		return err
+	}
+
+	go func() {
+		for {
+			if _, err := conn.WriteToUDP(b1, addr); err != nil {
+				return
+			}
+			time.Sleep(requestTimeout)
+		}
+	}()
+
+	var skipIPs []net.IP
+
+	b2 := make([]byte, 1500)
+loop:
+	for {
+		n, addr, err := conn.ReadFromUDP(b2)
+		if err != nil {
+			break
+		}
+
+		for _, ip := range skipIPs {
+			if ip.Equal(addr.IP) {
+				continue loop
+			}
+		}
+
+		if err = msg.Unpack(b2[:n]); err != nil {
+			continue
+		}
+
+		if !EqualService(msg, service) {
+			continue
+		}
+
+		if entry := NewServiceEntry(msg); onentry(entry) {
+			break
+		}
+
+		skipIPs = append(skipIPs, addr.IP)
+	}
+
+	return nil
+}
+
+func EqualService(msg *dns.Msg, service string) bool {
+	for _, rr := range msg.Answer {
+		if rr, ok := rr.(*dns.PTR); ok {
+			return strings.HasSuffix(rr.Ptr, service)
+		}
+	}
+
+	return false
+}
+
+func NewServiceEntry(msg *dns.Msg) *ServiceEntry {
+	entry := &ServiceEntry{}
+
+	records := make([]dns.RR, 0, len(msg.Answer)+len(msg.Ns)+len(msg.Extra))
+	records = append(records, msg.Answer...)
+	records = append(records, msg.Ns...)
+	records = append(records, msg.Extra...)
+	for _, record := range records {
+		switch record := record.(type) {
+		case *dns.PTR:
+			if i := strings.IndexByte(record.Ptr, '.'); i > 0 {
+				entry.Name = record.Ptr[:i]
+			}
+		case *dns.A:
+			entry.IP = record.A
+		case *dns.SRV:
+			entry.Port = record.Port
+		case *dns.TXT:
+			entry.Info = make(map[string]string, len(record.Txt))
+			for _, txt := range record.Txt {
+				k, v, _ := strings.Cut(txt, "=")
+				entry.Info[k] = v
+			}
+		}
+	}
+
+	return entry
+}

pkg/mdns/mdns_test.go

@@ -0,0 +1,16 @@
+package mdns
+
+import (
+	"github.com/stretchr/testify/require"
+	"testing"
+)
+
+func TestDiscovery(t *testing.T) {
+	onentry := func(entry *ServiceEntry) bool {
+		return true
+	}
+	err := Discovery(ServiceHAP, onentry)
+	//err := Discovery("_ewelink._tcp.local.", time.Second, onentry)
+	// err := Discovery("_googlecast._tcp.local.", time.Second, onentry)
+	require.Nil(t, err)
+}