add blackmagic atem discovery via udp 9910

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

bmd.go

@@ -0,0 +1,111 @@
+package tendrils
+
+import (
+	"context"
+	"log"
+	"net"
+	"time"
+)
+
+func (t *Tendrils) listenBMD(ctx context.Context, iface net.Interface) {
+	addrs, err := iface.Addrs()
+	if err != nil {
+		return
+	}
+
+	var srcIP net.IP
+	var broadcast net.IP
+	for _, addr := range addrs {
+		if ipnet, ok := addr.(*net.IPNet); ok && ipnet.IP.To4() != nil {
+			srcIP = ipnet.IP.To4()
+			mask := ipnet.Mask
+			broadcast = make(net.IP, 4)
+			for i := 0; i < 4; i++ {
+				broadcast[i] = srcIP[i] | ^mask[i]
+			}
+			break
+		}
+	}
+	if srcIP == nil {
+		return
+	}
+
+	conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: srcIP, Port: 0})
+	if err != nil {
+		return
+	}
+	defer conn.Close()
+
+	ticker := time.NewTicker(30 * time.Second)
+	defer ticker.Stop()
+
+	t.sendATEMDiscovery(conn, broadcast, iface.Name)
+
+	go t.receiveATEMResponses(ctx, conn, iface.Name)
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			t.sendATEMDiscovery(conn, broadcast, iface.Name)
+		}
+	}
+}
+
+func (t *Tendrils) sendATEMDiscovery(conn *net.UDPConn, broadcast net.IP, ifaceName string) {
+	// ATEM protocol hello packet
+	// Flag 0x10 (hello), length 20 bytes
+	packet := []byte{
+		0x10, 0x14, // Flags (0x10 = hello) + length (20 = 0x14)
+		0x00, 0x00, // Session ID
+		0x00, 0x00, // Ack number
+		0x00, 0x00, // Local sequence
+		0x00, 0x00, // Remote sequence
+		0x00, 0x00, // Unknown
+		0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // Client hello data
+	}
+
+	conn.WriteToUDP(packet, &net.UDPAddr{IP: broadcast, Port: 9910})
+
+	if t.DebugBMD {
+		log.Printf("[bmd] %s: sent atem discovery to %s", ifaceName, broadcast)
+	}
+}
+
+func (t *Tendrils) receiveATEMResponses(ctx context.Context, conn *net.UDPConn, ifaceName string) {
+	seen := map[string]bool{}
+	buf := make([]byte, 2048)
+	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
+		}
+
+		if n < 12 {
+			continue
+		}
+
+		ipKey := src.IP.String()
+		if seen[ipKey] {
+			continue
+		}
+		seen[ipKey] = true
+
+		if t.DebugBMD {
+			log.Printf("[bmd] %s: atem at %s", ifaceName, src.IP)
+		}
+
+		t.nodes.Update(nil, nil, []net.IP{src.IP}, "", "atem", "bmd")
+	}
+}