Initial sACN library with protocol, sender, receiver, and discovery

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

receiver.go

@@ -0,0 +1,100 @@
+package sacn
+
+import (
+	"net"
+	"time"
+
+	"golang.org/x/net/ipv4"
+)
+
+type Receiver struct {
+	conn    *ipv4.PacketConn
+	rawConn net.PacketConn
+	handler func(src *net.UDPAddr, pkt interface{})
+	done    chan struct{}
+}
+
+func NewReceiver(ifaceName string) (*Receiver, error) {
+	c, err := net.ListenPacket("udp4", ":5568")
+	if err != nil {
+		return nil, err
+	}
+
+	p := ipv4.NewPacketConn(c)
+
+	if ifaceName != "" {
+		iface, err := net.InterfaceByName(ifaceName)
+		if err != nil {
+			c.Close()
+			return nil, err
+		}
+		p.SetMulticastInterface(iface)
+	}
+
+	return &Receiver{
+		conn:    p,
+		rawConn: c,
+		done:    make(chan struct{}),
+	}, nil
+}
+
+func (r *Receiver) JoinUniverse(iface *net.Interface, universe uint16) error {
+	group := net.IPv4(239, 255, byte(universe>>8), byte(universe&0xff))
+	return r.conn.JoinGroup(iface, &net.UDPAddr{IP: group})
+}
+
+func (r *Receiver) JoinDiscovery(iface *net.Interface) error {
+	return r.conn.JoinGroup(iface, DiscoveryAddr)
+}
+
+func (r *Receiver) SetHandler(fn func(src *net.UDPAddr, pkt interface{})) {
+	r.handler = fn
+}
+
+func (r *Receiver) Start() {
+	go r.receiveLoop()
+}
+
+func (r *Receiver) Stop() {
+	select {
+	case <-r.done:
+	default:
+		close(r.done)
+	}
+	r.rawConn.Close()
+}
+
+func (r *Receiver) receiveLoop() {
+	buf := make([]byte, 638)
+
+	for {
+		select {
+		case <-r.done:
+			return
+		default:
+		}
+
+		r.rawConn.SetReadDeadline(time.Now().Add(1 * time.Second))
+		n, _, src, err := r.conn.ReadFrom(buf)
+		if err != nil {
+			if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
+				continue
+			}
+			select {
+			case <-r.done:
+				return
+			default:
+				continue
+			}
+		}
+
+		pkt, err := ParsePacket(buf[:n])
+		if err != nil {
+			continue
+		}
+
+		if r.handler != nil {
+			r.handler(src.(*net.UDPAddr), pkt)
+		}
+	}
+}