add mdns hostname discovery and artnet universe tracking

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

mdns.go

@@ -0,0 +1,149 @@
+package tendrils
+
+import (
+	"context"
+	"log"
+	"net"
+	"strings"
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+const (
+	mdnsAddr = "224.0.0.251:5353"
+)
+
+func (t *Tendrils) listenMDNS(ctx context.Context, iface net.Interface) {
+	addr, err := net.ResolveUDPAddr("udp4", mdnsAddr)
+	if err != nil {
+		log.Printf("[ERROR] failed to resolve mdns address: %v", err)
+		return
+	}
+
+	conn, err := net.ListenMulticastUDP("udp4", &iface, addr)
+	if err != nil {
+		log.Printf("[ERROR] failed to listen mdns on %s: %v", iface.Name, err)
+		return
+	}
+	defer conn.Close()
+
+	go t.runMDNSQuerier(ctx, iface)
+
+	buf := make([]byte, 65536)
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		default:
+		}
+
+		conn.SetReadDeadline(time.Now().Add(1 * time.Second))
+		n, src, err := conn.ReadFromUDP(buf)
+		if err != nil {
+			if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
+				continue
+			}
+			continue
+		}
+
+		t.handleMDNSPacket(iface.Name, src.IP, buf[:n])
+	}
+}
+
+func (t *Tendrils) handleMDNSPacket(ifaceName string, srcIP net.IP, data []byte) {
+	msg := new(dns.Msg)
+	if err := msg.Unpack(data); err != nil {
+		return
+	}
+
+	if msg.Response {
+		t.processMDNSResponse(ifaceName, srcIP, msg)
+	}
+}
+
+func (t *Tendrils) processMDNSResponse(ifaceName string, srcIP net.IP, msg *dns.Msg) {
+	var hostname string
+
+	allRecords := append(msg.Answer, msg.Extra...)
+	for _, rr := range allRecords {
+		switch r := rr.(type) {
+		case *dns.A:
+			name := strings.TrimSuffix(r.Hdr.Name, ".local.")
+			name = strings.TrimSuffix(name, ".")
+			if name != "" && r.A.Equal(srcIP) {
+				hostname = name
+			}
+		case *dns.AAAA:
+			continue
+		case *dns.PTR:
+			name := strings.TrimSuffix(r.Ptr, ".local.")
+			name = strings.TrimSuffix(name, ".")
+			if hostname == "" && name != "" && !strings.HasPrefix(name, "_") {
+				hostname = name
+			}
+		}
+	}
+
+	if hostname != "" {
+		if t.DebugMDNS {
+			log.Printf("[mdns] %s: %s -> %s", ifaceName, srcIP, hostname)
+		}
+		t.nodes.Update(nil, nil, []net.IP{srcIP}, "", hostname, "mdns")
+	}
+}
+
+func (t *Tendrils) runMDNSQuerier(ctx context.Context, iface net.Interface) {
+	addrs, err := iface.Addrs()
+	if err != nil {
+		return
+	}
+
+	var srcIP net.IP
+	for _, addr := range addrs {
+		if ipnet, ok := addr.(*net.IPNet); ok && ipnet.IP.To4() != nil {
+			srcIP = ipnet.IP.To4()
+			break
+		}
+	}
+	if srcIP == nil {
+		return
+	}
+
+	ticker := time.NewTicker(60 * time.Second)
+	defer ticker.Stop()
+
+	t.sendMDNSQuery(iface.Name, srcIP)
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			t.sendMDNSQuery(iface.Name, srcIP)
+		}
+	}
+}
+
+func (t *Tendrils) sendMDNSQuery(ifaceName string, srcIP net.IP) {
+	conn, err := net.DialUDP("udp4", &net.UDPAddr{IP: srcIP}, &net.UDPAddr{IP: net.IPv4(224, 0, 0, 251), Port: 5353})
+	if err != nil {
+		return
+	}
+	defer conn.Close()
+
+	msg := new(dns.Msg)
+	msg.SetQuestion("_services._dns-sd._udp.local.", dns.TypePTR)
+	msg.RecursionDesired = false
+
+	data, err := msg.Pack()
+	if err != nil {
+		return
+	}
+
+	conn.Write(data)
+
+	if t.DebugMDNS {
+		log.Printf("[mdns] %s: sent query", ifaceName)
+	}
+}