Initial implementation of ArtNet remapping proxy

Channel-level DMX remapping between ArtNet universes with:
- TOML configuration with multiple address formats (net.subnet.universe, plain number)
- ArtPoll discovery for output nodes
- Configurable channel ranges for fixture spillover handling

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

artnet/receiver.go

@@ -0,0 +1,103 @@
+package artnet
+
+import (
+	"log"
+	"net"
+)
+
+// PacketHandler is called when a packet is received
+type PacketHandler interface {
+	HandleDMX(src *net.UDPAddr, pkt *DMXPacket)
+	HandlePoll(src *net.UDPAddr, pkt *PollPacket)
+	HandlePollReply(src *net.UDPAddr, pkt *PollReplyPacket)
+}
+
+// Receiver listens for ArtNet packets
+type Receiver struct {
+	conn    *net.UDPConn
+	handler PacketHandler
+	done    chan struct{}
+}
+
+// NewReceiver creates a new ArtNet receiver
+func NewReceiver(port int, handler PacketHandler) (*Receiver, error) {
+	addr := &net.UDPAddr{
+		Port: port,
+		IP:   net.IPv4zero,
+	}
+
+	conn, err := net.ListenUDP("udp4", addr)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Receiver{
+		conn:    conn,
+		handler: handler,
+		done:    make(chan struct{}),
+	}, nil
+}
+
+// Start begins receiving packets
+func (r *Receiver) Start() {
+	go r.receiveLoop()
+}
+
+// Stop stops the receiver
+func (r *Receiver) Stop() {
+	close(r.done)
+	r.conn.Close()
+}
+
+func (r *Receiver) receiveLoop() {
+	buf := make([]byte, 1024)
+
+	for {
+		select {
+		case <-r.done:
+			return
+		default:
+		}
+
+		n, src, err := r.conn.ReadFromUDP(buf)
+		if err != nil {
+			select {
+			case <-r.done:
+				return
+			default:
+				log.Printf("read error: %v", err)
+				continue
+			}
+		}
+
+		r.handlePacket(src, buf[:n])
+	}
+}
+
+func (r *Receiver) handlePacket(src *net.UDPAddr, data []byte) {
+	opCode, pkt, err := ParsePacket(data)
+	if err != nil {
+		// Silently ignore invalid packets
+		return
+	}
+
+	switch opCode {
+	case OpDmx:
+		if dmx, ok := pkt.(*DMXPacket); ok {
+			r.handler.HandleDMX(src, dmx)
+		}
+	case OpPoll:
+		if poll, ok := pkt.(*PollPacket); ok {
+			r.handler.HandlePoll(src, poll)
+		}
+	case OpPollReply:
+		if reply, ok := pkt.(*PollReplyPacket); ok {
+			r.handler.HandlePollReply(src, reply)
+		}
+	}
+}
+
+// LocalAddr returns the local address the receiver is bound to
+func (r *Receiver) LocalAddr() net.Addr {
+	return r.conn.LocalAddr()
+}