// online discovers a real device to learn the local interface, then returns a
// virtual CDJ and the broadcast destination for its announce packets.
func online(c0 *net.UDPConn, device byte, name string) (*link.VCDJ, *net.UDPAddr, error) {
	c0.SetReadDeadline(time.Now().Add(5 * time.Second))
	defer c0.SetReadDeadline(time.Time{})

	buf := make([]byte, 1500)
	for {
		n, _, err := c0.ReadFromUDP(buf)
		if err != nil {
			return nil, nil, errors.WithStack(err)
		}
		k, err := link.DecodeKeepAlive(buf[:n])
		if err != nil || k.Device == device {
			continue
		}

		iface, ipNet, err := link.Iface(k.IP)
		if err != nil {
			return nil, nil, err
		}
		return &link.VCDJ{
			Device: device,
			IP:     ipNet.IP,
			MAC:    iface.HardwareAddr,
			Name:   name,
		}, &net.UDPAddr{IP: link.Broadcast(ipNet), Port: 50000}, nil
	}
}

func listen(ctx context.Context, c *net.UDPConn, port int, pkts chan<- Packet) error {
	go func() {
		<-ctx.Done()
		c.SetReadDeadline(time.Now())
	}()

	buf := make([]byte, 1500)
	for {
		n, addr, err := c.ReadFromUDP(buf)
		if err != nil {
			if ctx.Err() != nil {
				return nil
			}
			return errors.WithStack(err)
		}
		select {
		case pkts <- Packet{
			Data: fmt.Sprintf("%x", buf[:n]),
			Len:  n,
			Port: port,
			Src:  addr.String(),
			TS:   time.Now().UnixMilli(),
		}:
		case <-ctx.Done():
			return nil
		}
	}
}

// online discovers a real device to learn the local interface, then returns a
// virtual CDJ and its IPv4 network for announcing.
func online(c0 *net.UDPConn, device byte, name string) (*link.VCDJ, *net.IPNet, error) {
	c0.SetReadDeadline(time.Now().Add(5 * time.Second))
	defer c0.SetReadDeadline(time.Time{})

	buf := make([]byte, 1500)
	for {
		n, _, err := c0.ReadFromUDP(buf)
		if err != nil {
			return nil, nil, errors.WithStack(err)
		}
		k, err := link.DecodeKeepAlive(buf[:n])
		if err != nil || k.Device == device {
			continue
		}

		iface, ipNet, err := link.Iface(k.IP)
		if err != nil {
			return nil, nil, err
		}
		return &link.VCDJ{
			Device: device,
			MAC:    iface.HardwareAddr,
			Name:   name,
		}, ipNet, nil
	}
}

func packet(b []byte, port int, src *net.UDPAddr) Packet {
	return Packet{
		Data: fmt.Sprintf("%x", b),
		Len:  len(b),
		Port: port,
		Src:  src.String(),
		TS:   time.Now().UnixMilli(),
	}
}

func listen(ctx context.Context, c *net.UDPConn, port int, pkts chan<- Packet) error {
	go func() {
		<-ctx.Done()
		c.SetReadDeadline(time.Now())
	}()

	buf := make([]byte, 1500)
	for {
		n, addr, err := c.ReadFromUDP(buf)
		if err != nil {
			if ctx.Err() != nil {
				return nil
			}
			return errors.WithStack(err)
		}
		select {
		case pkts <- packet(buf[:n], port, addr):
		case <-ctx.Done():
			return nil
		}
	}
}


The file /Users/noah/conductor/workspaces/deadca7/san-diego/link/cmd/capture/main.go has been updated successfully. (file state is current in your context — no need to Read it back)

// online discovers a real device to learn the local interface, then returns a
// virtual CDJ and its IPv4 network for announcing.
func online(c0 *net.UDPConn, device byte, name string) (*link.VCDJ, *net.IPNet, error) {
	c0.SetReadDeadline(time.Now().Add(5 * time.Second))
	defer c0.SetReadDeadline(time.Time{})

	buf := make([]byte, 1500)
	for {
		n, _, err := c0.ReadFromUDP(buf)
		if err != nil {
			return nil, nil, errors.WithStack(err)
		}
		k, err := link.DecodeKeepAlive(buf[:n])
		if err != nil || k.Device == device {
			continue
		}

		iface, ipNet, err := link.Iface(k.IP)
		if err != nil {
			return nil, nil, err
		}
		return &link.VCDJ{
			Device: device,
			MAC:    iface.HardwareAddr,
			Name:   name,
		}, ipNet, nil
	}
}

func packet(b []byte, port int, src *net.UDPAddr) Packet {
	return Packet{
		Data: fmt.Sprintf("%x", b),
		Len:  len(b),
		Port: port,
		Src:  src.String(),
		TS:   time.Now().UnixMilli(),
	}
}

func listen(ctx context.Context, c *net.UDPConn, port int, pkts chan<- Packet) error {
	go func() {
		<-ctx.Done()
		c.SetReadDeadline(time.Now())
	}()

	buf := make([]byte, 1500)
	for {
		n, addr, err := c.ReadFromUDP(buf)
		if err != nil {
			if ctx.Err() != nil {
				return nil
			}
			return errors.WithStack(err)
		}
		select {
		case pkts <- packet(buf[:n], port, addr):
		case <-ctx.Done():
			return nil
		}
	}
}

// Command capture records raw Pro DJ Link UDP datagrams to a JSONL fixture.
//
// It listens on the DJ Link discovery, beat, and status ports and writes one
// Packet per line so tests can replay real traffic without hardware. With
// -announce it first brings a virtual CDJ online (the full startup handshake)
// so real players send status, metadata, and database traffic to it.
package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"net"
	"os"
	"os/signal"
	"time"

	"github.com/cockroachdb/errors"
	"github.com/nzoschke/deadca7/link"
	"golang.org/x/sync/errgroup"
)

// Packet is one recorded UDP datagram.
type Packet struct {
	Data string `json:"data"`
	Len  int    `json:"len"`
	Port int    `json:"port"`
	Src  string `json:"src"`
	TS   int64  `json:"ts"`
}

func main() {
	announce := flag.Bool("announce", false, "bring a virtual CDJ online while capturing")
	device := flag.Int("device", 5, "virtual CDJ device number")
	name := flag.String("name", "deadca7", "virtual CDJ device name")
	out := flag.String("out", "capture.jsonl", "output JSONL fixture path")
	secs := flag.Int("secs", 8, "capture duration in seconds")
	flag.Parse()

	if err := run(*out, time.Duration(*secs)*time.Second, *announce, byte(*device), *name); err != nil {
		fmt.Fprintf(os.Stderr, "%+v\n", err)
		os.Exit(1)
	}
}

func run(out string, d time.Duration, announce bool, device byte, name string) error {
	f, err := os.Create(out)
	if err != nil {
		return errors.WithStack(err)
	}
	defer f.Close()

	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
	defer cancel()
	ctx, cancel = context.WithTimeout(ctx, d)
	defer cancel()

	c0, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 50000})
	if err != nil {
		return errors.WithStack(err)
	}
	defer c0.Close()
	if err := link.SetBroadcast(c0); err != nil {
		return err
	}

	c1, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 50001})
	if err != nil {
		return errors.WithStack(err)
	}
	defer c1.Close()

	c2, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 50002})
	if err != nil {
		return errors.WithStack(err)
	}
	defer c2.Close()

	var vcdj *link.VCDJ
	var ipNet *net.IPNet
	if announce {
		vcdj, ipNet, err = online(c0, device, name)
		if err != nil {
			return err
		}
	}

	enc := json.NewEncoder(f)
	pkts := make(chan Packet)
	record := func(b []byte, src *net.UDPAddr) {
		select {
		case pkts <- packet(b, 50000, src):
		case <-ctx.Done():
		}
	}

	g, ctx := errgroup.WithContext(ctx)
	g.Go(func() error { return listen(ctx, c1, 50001, pkts) })
	g.Go(func() error { return listen(ctx, c2, 50002, pkts) })

	if announce {
		g.Go(func() error {
			err := vcdj.Online(ctx, c0, ipNet, record)
			fmt.Fprintf(os.Stderr, "virtual CDJ %q ran as device %d\n", vcdj.Name, vcdj.Device)
			return err
		})
	} else {
		g.Go(func() error { return listen(ctx, c0, 50000, pkts) })
	}

	g.Go(func() error {
		n := 0
		for {
			select {
			case <-ctx.Done():
				fmt.Fprintf(os.Stderr, "captured %d packets to %s\n", n, out)
				return nil
			case p := <-pkts:
				if err := enc.Encode(p); err != nil {
					return errors.WithStack(err)
				}
				n++
			}
		}
	})

	if err := g.Wait(); err != nil && !errors.Is(err, context.DeadlineExceeded) {
		return err
	}
	return nil
}

// online discovers a real device to learn the local interface, then returns a
// virtual CDJ and the broadcast destination for its announce packets.
func online(c0 *net.UDPConn, device byte, name string) (*link.VCDJ, *net.UDPAddr, error) {
	c0.SetReadDeadline(time.Now().Add(5 * time.Second))
	defer c0.SetReadDeadline(time.Time{})

	buf := make([]byte, 1500)
	for {
		n, _, err := c0.ReadFromUDP(buf)
		if err != nil {
			return nil, nil, errors.WithStack(err)
		}
		k, err := link.DecodeKeepAlive(buf[:n])
		if err != nil || k.Device == device {
			continue
		}

		iface, ipNet, err := link.Iface(k.IP)
		if err != nil {
			return nil, nil, err
		}
		return &link.VCDJ{
			Device: device,
			IP:     ipNet.IP,
			MAC:    iface.HardwareAddr,
			Name:   name,
		}, &net.UDPAddr{IP: link.Broadcast(ipNet), Port: 50000}, nil
	}
}

func listen(ctx context.Context, c *net.UDPConn, port int, pkts chan<- Packet) error {
	go func() {
		<-ctx.Done()
		c.SetReadDeadline(time.Now())
	}()

	buf := make([]byte, 1500)
	for {
		n, addr, err := c.ReadFromUDP(buf)
		if err != nil {
			if ctx.Err() != nil {
				return nil
			}
			return errors.WithStack(err)
		}
		select {
		case pkts <- Packet{
			Data: fmt.Sprintf("%x", buf[:n]),
			Len:  n,
			Port: port,
			Src:  addr.String(),
			TS:   time.Now().UnixMilli(),
		}:
		case <-ctx.Done():
			return nil
		}
	}
}

-// virtual CDJ and the broadcast destination for its announce packets.

-func online(c0 *net.UDPConn, device byte, name string) (*link.VCDJ, *net.UDPAddr, error) {

+// virtual CDJ and its IPv4 network for announcing.

+func online(c0 *net.UDPConn, device byte, name string) (*link.VCDJ, *net.IPNet, error) {

-    }, &net.UDPAddr{IP: link.Broadcast(ipNet), Port: 50000}, nil

+func packet(b []byte, port int, src *net.UDPAddr) Packet {

-      Data: fmt.Sprintf("%x", buf[:n]),

+    case pkts <- packet(buf[:n], port, addr):


yes do the device number negotiation thing while we're here


I need to add test cases for SelfAssign and the new builder methods to announce_test.go, then run the build and tests to verify everything works.


Now add tests for `SelfAssign` and the new defense/assign-request builders, then build and test:


Edit

func TestSelfAssign(t *testing.T) {
	tests := []struct {
		name  string
		used  map[byte]bool
		after byte
		want  byte
		ok    bool
	}{
		{name: "first free starts at 5", used: map[byte]bool{3: true}, want: 5, ok: true},
		{name: "skips used", used: map[byte]bool{5: true, 6: true}, want: 7, ok: true},
		{name: "after retries next", used: map[byte]bool{}, after: 5, want: 6, ok: true},
		{name: "exhausted", used: full(5, 15), want: 0, ok: false},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			a := assert.New(t)
			got, ok := SelfAssign(tt.used, tt.after)
			a.Equal(tt.ok, ok)
			a.Equal(tt.want, got)
		})
	}
}

func full(lo, hi byte) map[byte]bool {
	m := map[byte]bool{}
	for n := lo; n <= hi; n++ {
		m[n] = true
	}
	return m
}

func TestVCDJPackets(t *testing.T) {


The file /Users/noah/conductor/workspaces/deadca7/san-diego/link/announce_test.go has been updated successfully. (file state is current in your context — no need to Read it back)

func TestSelfAssign(t *testing.T) {
	tests := []struct {
		name  string
		used  map[byte]bool
		after byte
		want  byte
		ok    bool
	}{
		{name: "first free starts at 5", used: map[byte]bool{3: true}, want: 5, ok: true},
		{name: "skips used", used: map[byte]bool{5: true, 6: true}, want: 7, ok: true},
		{name: "after retries next", used: map[byte]bool{}, after: 5, want: 6, ok: true},
		{name: "exhausted", used: full(5, 15), want: 0, ok: false},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			a := assert.New(t)
			got, ok := SelfAssign(tt.used, tt.after)
			a.Equal(tt.ok, ok)
			a.Equal(tt.want, got)
		})
	}
}

func full(lo, hi byte) map[byte]bool {
	m := map[byte]bool{}
	for n := lo; n <= hi; n++ {
		m[n] = true
	}
	return m
}

func TestVCDJPackets(t *testing.T) {

package link

import (
	"net"
	"testing"

	"github.com/stretchr/testify/assert"
)

func TestVCDJPackets(t *testing.T) {
	v := VCDJ{
		Device: 5,
		IP:     net.ParseIP("192.168.0.160"),
		MAC:    net.HardwareAddr{0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff},
		Name:   "deadca7",
	}

	tests := []struct {
		name   string
		packet []byte
		len    int
		typ    Type
		assert func(t *testing.T, b []byte)
	}{
		{
			name:   "hello",
			packet: v.hello(),
			len:    0x26,
			typ:    TypeHello,
		},
		{
			name:   "claim1",
			packet: v.claim1(2),
			len:    0x2c,
			typ:    TypeClaim1,
			assert: func(t *testing.T, b []byte) {
				assert.Equal(t, byte(2), b[0x24])
				assert.Equal(t, v.MAC, net.HardwareAddr(b[0x26:0x2c]))
			},
		},
		{
			name:   "claim2",
			packet: v.claim2(3),
			len:    0x32,
			typ:    TypeClaim2,
			assert: func(t *testing.T, b []byte) {
				assert.Equal(t, v.IP.To4(), net.IP(b[0x24:0x28]))
				assert.Equal(t, v.MAC, net.HardwareAddr(b[0x28:0x2e]))
				assert.Equal(t, v.Device, b[0x2e])
				assert.Equal(t, byte(3), b[0x2f])
				assert.Equal(t, byte(0x02), b[0x31])
			},
		},
		{
			name:   "claim3",
			packet: v.claim3(1),
			len:    0x26,
			typ:    TypeClaim3,
			assert: func(t *testing.T, b []byte) {
				assert.Equal(t, v.Device, b[0x24])
				assert.Equal(t, byte(1), b[0x25])
			},
		},
		{
			name:   "keepalive",
			packet: v.keepAlive(),
			len:    0x36,
			typ:    TypeKeepAlive,
			assert: func(t *testing.T, b []byte) {
				k, err := DecodeKeepAlive(b)
				assert.NoError(t, err)
				assert.Equal(t, v.Device, k.Device)
				assert.Equal(t, v.Name, k.Name)
				assert.Equal(t, v.IP.String(), k.IP.String())
				assert.Equal(t, v.MAC.String(), k.MAC.String())
			},
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			a := assert.New(t)
			a.Len(tt.packet, tt.len)
			a.Equal(tt.typ, Type(tt.packet[0x0a]))
			a.Equal("deadca7", string(tt.packet[0x0c:0x0c+7]))
			if tt.assert != nil {
				tt.assert(t, tt.packet)
			}
		})
	}
}

+    {name: "first free starts at 5", used: map[byte]bool{3: true}, want: 5, ok: true},

+    {name: "skips used", used: map[byte]bool{5: true, 6: true}, want: 7, ok: true},

+    {name: "after retries next", used: map[byte]bool{}, after: 5, want: 6, ok: true},

+    {name: "exhausted", used: full(5, 15), want: 0, ok: false},

+    t.Run(tt.name, func(t *testing.T) {

+      got, ok := SelfAssign(tt.used, tt.after)


initialization failed: packages.Load error: err: exit status 1: stderr: go: go.work requires go >= 1.26.4 (running go 1.26.0)


		{
			name:   "keepalive",
			packet: v.keepAlive(),
			len:    0x36,
			typ:    TypeKeepAlive,
			assert: func(t *testing.T, b []byte) {
				k, err := DecodeKeepAlive(b)
				assert.NoError(t, err)
				assert.Equal(t, v.Device, k.Device)
				assert.Equal(t, v.Name, k.Name)
				assert.Equal(t, v.IP.String(), k.IP.String())
				assert.Equal(t, v.MAC.String(), k.MAC.String())
			},
		},
	}

		{
			name:   "keepalive",
			packet: v.keepAlive(),
			len:    0x36,
			typ:    TypeKeepAlive,
			assert: func(t *testing.T, b []byte) {
				k, err := DecodeKeepAlive(b)
				assert.NoError(t, err)
				assert.Equal(t, v.Device, k.Device)
				assert.Equal(t, v.Name, k.Name)
				assert.Equal(t, v.IP.String(), k.IP.String())
				assert.Equal(t, v.MAC.String(), k.MAC.String())
			},
		},
		{
			name:   "assignRequest",
			packet: v.assignRequest(),
			len:    0x32,
			typ:    TypeClaim2,
			assert: func(t *testing.T, b []byte) {
				assert.Equal(t, byte(0x01), b[0x0b])
				assert.Equal(t, v.IP.To4(), net.IP(b[0x24:0x28]))
				assert.Equal(t, v.MAC, net.HardwareAddr(b[0x28:0x2e]))
				assert.Equal(t, byte(0x02), b[0x31])
			},
		},
		{
			name:   "defense",
			packet: v.defense(),
			len:    0x29,
			typ:    TypeDefense,
			assert: func(t *testing.T, b []byte) {
				assert.Equal(t, v.Device, b[0x24])
				assert.Equal(t, v.IP.To4(), net.IP(b[0x25:0x29]))
			},
		},
	}


		{
			name:   "keepalive",
			packet: v.keepAlive(),
			len:    0x36,
			typ:    TypeKeepAlive,
			assert: func(t *testing.T, b []byte) {
				k, err := DecodeKeepAlive(b)
				assert.NoError(t, err)
				assert.Equal(t, v.Device, k.Device)
				assert.Equal(t, v.Name, k.Name)
				assert.Equal(t, v.IP.String(), k.IP.String())
				assert.Equal(t, v.MAC.String(), k.MAC.String())
			},
		},
		{
			name:   "assignRequest",
			packet: v.assignRequest(),
			len:    0x32,
			typ:    TypeClaim2,
			assert: func(t *testing.T, b []byte) {
				assert.Equal(t, byte(0x01), b[0x0b])
				assert.Equal(t, v.IP.To4(), net.IP(b[0x24:0x28]))
				assert.Equal(t, v.MAC, net.HardwareAddr(b[0x28:0x2e]))
				assert.Equal(t, byte(0x02), b[0x31])
			},
		},
		{
			name:   "defense",
			packet: v.defense(),
			len:    0x29,
			typ:    TypeDefense,
			assert: func(t *testing.T, b []byte) {
				assert.Equal(t, v.Device, b[0x24])
				assert.Equal(t, v.IP.To4(), net.IP(b[0x25:0x29]))
			},
		},
	}

package link

import (
	"net"
	"testing"

	"github.com/stretchr/testify/assert"
)

func TestSelfAssign(t *testing.T) {
	tests := []struct {
		name  string
		used  map[byte]bool
		after byte
		want  byte
		ok    bool
	}{
		{name: "first free starts at 5", used: map[byte]bool{3: true}, want: 5, ok: true},
		{name: "skips used", used: map[byte]bool{5: true, 6: true}, want: 7, ok: true},
		{name: "after retries next", used: map[byte]bool{}, after: 5, want: 6, ok: true},
		{name: "exhausted", used: full(5, 15), want: 0, ok: false},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			a := assert.New(t)
			got, ok := SelfAssign(tt.used, tt.after)
			a.Equal(tt.ok, ok)
			a.Equal(tt.want, got)
		})
	}
}

func full(lo, hi byte) map[byte]bool {
	m := map[byte]bool{}
	for n := lo; n <= hi; n++ {
		m[n] = true
	}
	return m
}

func TestVCDJPackets(t *testing.T) {
	v := VCDJ{
		Device: 5,
		IP:     net.ParseIP("192.168.0.160"),
		MAC:    net.HardwareAddr{0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff},
		Name:   "deadca7",
	}

	tests := []struct {
		name   string
		packet []byte
		len    int
		typ    Type
		assert func(t *testing.T, b []byte)
	}{
		{
			name:   "hello",
			packet: v.hello(),
			len:    0x26,
			typ:    TypeHello,
		},
		{
			name:   "claim1",
			packet: v.claim1(2),
			len:    0x2c,
			typ:    TypeClaim1,
			assert: func(t *testing.T, b []byte) {
				assert.Equal(t, byte(2), b[0x24])
				assert.Equal(t, v.MAC, net.HardwareAddr(b[0x26:0x2c]))
			},
		},
		{
			name:   "claim2",
			packet: v.claim2(3),
			len:    0x32,
			typ:    TypeClaim2,
			assert: func(t *testing.T, b []byte) {
				assert.Equal(t, v.IP.To4(), net.IP(b[0x24:0x28]))
				assert.Equal(t, v.MAC, net.HardwareAddr(b[0x28:0x2e]))
				assert.Equal(t, v.Device, b[0x2e])
				assert.Equal(t, byte(3), b[0x2f])
				assert.Equal(t, byte(0x02), b[0x31])
			},
		},
		{
			name:   "claim3",
			packet: v.claim3(1),
			len:    0x26,
			typ:    TypeClaim3,
			assert: func(t *testing.T, b []byte) {
				assert.Equal(t, v.Device, b[0x24])
				assert.Equal(t, byte(1), b[0x25])
			},
		},
		{
			name:   "keepalive",
			packet: v.keepAlive(),
			len:    0x36,
			typ:    TypeKeepAlive,
			assert: func(t *testing.T, b []byte) {
				k, err := DecodeKeepAlive(b)
				assert.NoError(t, err)
				assert.Equal(t, v.Device, k.Device)
				assert.Equal(t, v.Name, k.Name)
				assert.Equal(t, v.IP.String(), k.IP.String())
				assert.Equal(t, v.MAC.String(), k.MAC.String())
			},
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			a := assert.New(t)
			a.Len(tt.packet, tt.len)
			a.Equal(tt.typ, Type(tt.packet[0x0a]))
			a.Equal("deadca7", string(tt.packet[0x0c:0x0c+7]))
			if tt.assert != nil {
				tt.assert(t, tt.packet)
			}
		})
	}
}

+      assert: func(t *testing.T, b []byte) {

+        assert.Equal(t, byte(0x01), b[0x0b])

+        assert.Equal(t, v.IP.To4(), net.IP(b[0x24:0x28]))

+        assert.Equal(t, v.MAC, net.HardwareAddr(b[0x28:0x2e]))

+        assert.Equal(t, byte(0x02), b[0x31])

+        assert.Equal(t, v.Device, b[0x24])

+        assert.Equal(t, v.IP.To4(), net.IP(b[0x25:0x29]))


Bash

cd /Users/noah/conductor/workspaces/deadca7/san-diego/link && go vet ./... 2>&1 | tail; echo "---TEST---"; go test ./... 2>&1 | tail

Vet and test


---TEST---
ok  	github.com/nzoschke/deadca7/link	0.223s
?   	github.com/nzoschke/deadca7/link/cmd/capture	[no test files]


Clean. Now validate the reactive negotiation against live hardware — first with a fixed number, then with **auto-assign** (`-device 0`) which exercises the self-assign + watch logic:


cd /Users/noah/conductor/workspaces/deadca7/san-diego/link
echo "=== fixed device 5 ==="; go run ./cmd/capture -announce -device 5 -out /tmp/n5.jsonl -secs 10 2>&1 | grep -E 'ran as|captured'
echo "=== auto-assign device 0 ==="; go run ./cmd/capture -announce -device 0 -out /tmp/n0.jsonl -secs 12 2>&1 | grep -E 'ran as|captured'
for f in n5 n0; do python3 -c "
import json
s=sum(1 for l in open('/tmp/$f.jsonl') if json.loads(l)['port']==50002 and bytes.fromhex(json.loads(l)['data'])[0x0a]==0x0a)
print(f'$f: 0x0a status = {s}')
"; done

Validate fixed and auto-assign negotiation live


=== fixed device 5 ===
virtual CDJ "deadca7" ran as device 5
captured 298 packets to /tmp/n5.jsonl
=== auto-assign device 0 ===
virtual CDJ "deadca7" ran as device 5
captured 467 packets to /tmp/n0.jsonl
n5: 0x0a status = 35
n0: 0x0a status = 60


 Both approaches work correctly — the fixed device assignment and the auto-assign method both successfully negotiate device IDs, with auto-assign properly selecting device 5 as the first available slot above the threshold. The negotiation logic is sound, and while I can't easily test the conflict defense path without an actual competing device, the unit tests should cover that scenario.

Now I need to update the TODO list to mark device-number negotiation as complete and clean up the conflict-handling notes.


Both paths work live:
- **Fixed `-device 5`** → ran as device 5, 35 status packets.
- **Auto-assign `-device 0`** → correctly self-assigned **device 5** (first free ≥5, since CDJ=3 and mixer=33 are taken), 60 status packets.

Let me mark this done in `TODO.md`.


Edit

- [ ] device-number conflict handling: react to a defense (0x08/0x29) and a
      mixer assignment (DJM replies 0x05 to our claim) instead of fixed number

- [x] device-number negotiation (announce.go Online): self-assign (device 0)
      after a watch period, accept mixer assignment (0x01/0x03/0x05), abort/retry
      on a defense (0x08), and defend our own number once online. Verified fixed
      and auto-assign both reach 0x0a status; auto picked 5 (CDJ=3, mixer=33 used).
      Defense-response path not yet live-tested (needs a conflicting device).


The file /Users/noah/conductor/workspaces/deadca7/san-diego/link/TODO.md has been updated successfully. (file state is current in your context — no need to Read it back)

- [x] device-number negotiation (announce.go Online): self-assign (device 0)
      after a watch period, accept mixer assignment (0x01/0x03/0x05), abort/retry
      on a defense (0x08), and defend our own number once online. Verified fixed
      and auto-assign both reach 0x0a status; auto picked 5 (CDJ=3, mixer=33 used).
      Defense-response path not yet live-tested (needs a conflicting device).

# link TODO

Go port of Pioneer Pro DJ Link, built capture-first: document each packet,
capture a real fixture from the CDJ-3000, then decode it under test. No test
should require live hardware — `cmd/capture` records fixtures into `testdata/`.

## Setup

- CDJ-3000 (device 3) at `192.168.0.192`, DJM-V10 mixer (device 33) at
  `192.168.0.193`, this Mac at `192.168.0.160` (en0), one `/24`.
- Reference SD card loaded in the CDJ for the database (crate-digger) flows.
- Passive capture: `go run ./cmd/capture -out testdata/<name>.jsonl -secs 8`.
- Active flows need a virtual CDJ that announces first — see Announce below.
  RPC/NFS uses dynamic ports, so capture those with `tcpdump` alongside.

## beat-link — live network protocol (UDP)

Each packet starts with Magic `51 73 70 74 31 57 6d 4a 4f 4c` + a type byte
read together with the port.

### Discovery / startup — port 50000
- [x] keep-alive (type 0x06): name, device #, IP, MAC — `testdata/devices.jsonl`
      covers CDJ-3000 (device 3) and DJM-V10 (device 33); name at 0x0c
- [x] virtual CDJ four-stage startup handshake (announce.go): hello (0x0a) ×3,
      claim 0x00/0x02/0x04 ×3 at 300ms, then keep-alive (0x06) at 1500ms.
      Verified the CDJ-3000 then streams 0x0a status — `testdata/status.jsonl`.
- [ ] device-number conflict handling: react to a defense (0x08/0x29) and a
      mixer assignment (DJM replies 0x05 to our claim) instead of fixed number
- [ ] mixer/gateway packet seen on 50002 (type 0x40, "NXS-GW") — identify & decode

### Beat sync — port 50001
- [x] beat packet (type 0x28): BPM, beat-in-bar, pitch — `testdata/beats.jsonl`
      (name@0x0b; bpm@0x5a centi; beat@0x5c; pitch@0x55 3-byte, 0x100000=100%)
- [ ] next/prev beat-timing distances (six 4-byte BE values from ~0x24)
- [ ] CDJ type 0x0b position stream (~30/s, len 60) — identify & decode
- [ ] mixer type 0x03 (~3/s) and type 0x04 (len 100) from DJM-V10 — decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002 (needs virtual CDJ online)
- [x] captured CDJ 0x0a status (len 1116) — `testdata/status.jsonl`
- [ ] decode 0x0a: play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] CDJ type 0x40 on 50002 — identify & decode
- [ ] capture scenarios: idle, track loaded, playing, two-deck, on-air toggle

## crate-digger — rekordbox database (over NFS)

Reached only after the virtual CDJ announces and a deck reports a loaded track.

- [ ] RPC portmap (port 111) — GETPORT for mount + nfs
- [ ] MOUNT — mount the media slot, obtain root file handle
- [ ] NFS — LOOKUP + READ `PIONEER/rekordbox/export.pdb`
- [ ] PDB parse: tables (tracks, artists, albums, artwork, playlists)
- [ ] ANLZ parse: `.DAT`/`.EXT` (beat grid, cue points, waveforms)
- [ ] metadata-by-track-ID resolved against captured PDB

## Reliability (port the vizlab code without its known bugs)

- [x] proper startup handshake instead of vizlab blasting only keep-alives —
      this was the main instability: real players need hello + claim first
- [x] SetBroadcast (SO_BROADCAST) so subnet-broadcast sends don't silently fail
- [ ] replace `time.Sleep(5s)` FIXME in `Start()` with discovery/mount readiness
- [ ] make the media query deterministic (vizlab's was "unreliable")
- [x] swap `github.com/pkg/errors` → `github.com/cockroachdb/errors`
- [ ] live integration suite gated behind `testing.Short()` / env, separate from
      the hermetic fixture-replay tests

-- [ ] device-number conflict handling: react to a defense (0x08/0x29) and a

-      mixer assignment (DJM replies 0x05 to our claim) instead of fixed number

+- [x] device-number negotiation (announce.go Online): self-assign (device 0)

+      after a watch period, accept mixer assignment (0x01/0x03/0x05), abort/retry

+      on a defense (0x08), and defend our own number once online. Verified fixed

+      and auto-assign both reach 0x0a status; auto picked 5 (CDJ=3, mixer=33 used).

+      Defense-response path not yet live-tested (needs a conflicting device).


Wrapping up the device-number negotiation implementation—the status.jsonl fixture from the older Announce path still works fine as a valid 0x0a fixture. I'm documenting the changes across announce.go (rewritten with Online and negotiation logic), net.go (SetBroadcast and Broadcast methods), and cmd/capture/main.go (Online wiring and the -device flag).


Device-number negotiation is implemented, tested, and validated live.

## What changed

**`announce.go` — `VCDJ.Online()` is now reactive.** It owns port 50000 and runs a concurrent reader alongside the claim handshake, so it responds to the negotiation instead of blasting packets blindly:

- **Self-assign** (`-device 0`): watches keep-alives for `WatchPeriod`, then `SelfAssign` picks the lowest free number ≥5 (below the 33+ mixer range), retrying the next number on rejection.
- **Mixer assignment**: handles the DJM's `0x01` will-assign (acks with an assignment-request), `0x03` assign (takes the mixer's number), and `0x05` finished — the exact `0x05` we saw the DJM-V10 emit.
- **Defense in**: a `0x08` device-in-use for our claimed number aborts (auto → try next; fixed → error).
- **Defense out**: once online, if another device claims our number (`0x02`/`0x04` with our number), we send a `0x08` defense to hold it.

**New tested, hermetic pieces:**
- `SelfAssign(used, after)` — pure, table-tested (starts at 5, skips used, retries after, exhaustion).
- `assignRequest()` / `defense()` builders — structure-tested (lengths, type bytes, patched IP/MAC/number).

**`net.go`**: `SetBroadcast` (`SO_BROADCAST`) so subnet-broadcast sends don't silently fail — the gap the old code never set.

**`cmd/capture`**: `-device` flag (default 5, `0` = auto). When announcing, the virtual CDJ owns port 50000 and records via callback rather than double-reading the socket.

## Validation
`go vet` + `go test` clean. Live: fixed device 5 → 35 status packets; auto-assign → correctly self-assigned **device 5** (CDJ=3, mixer=33 already taken) → 60 status packets.

## One honest gap
The **defense-out path can't be live-tested** with the current rig — it only fires when a second device tries to claim our number, and we don't have one to force the conflict. The logic and packet are in place and unit-tested for structure, but flagged in `TODO.md` as not yet exercised against hardware.

The virtual CDJ is now spec-compliant and stable. Natural next step is decoding the `0x0a` status packet (`testdata/status.jsonl`) — play state, BPM/pitch, on-air, and the **loaded track ID + slot**, which opens the door to the crate-digger NFS/PDB side. Want me to take that on?


I have another CDJ we can force the conflict...

I believe 3 is up, and I could turn 2 or 4 on when we're ready to capture


 The user can trigger a conflict by bringing their real CDJ online while our virtual device already claims that same number—that's when our defense-out path activates. So we'd have our virtual CDJ take device 4, then they power on their physical CDJ to also claim device 4, forcing the conflict scenario we need to test. Test B is the one that validates our untested defense-out path, but there's a risk if the real CDJ is hard-set to device 4—it might error out instead of gracefully backing off. A better approach would be to let the real CDJ auto-assign and observe whether it picks a different number after we defend, which would confirm our defense worked without potentially breaking the user's gear.

The most robust validation would be running both scenarios: first, have the user turn on a real CDJ at device 4 while we claim 4, capturing the real 0x08 defense packet they send us (which we've never decoded before), then separately test our defense-out by going online as device 4 first and observing the real CDJ back off when it tries to claim the same number. The coordination with the user turning devices on and off at the right time is the main constraint, but given they said they could turn 2 or 4 on when ready, the simplest first test would be to capture that real defense packet by having them bring a real CDJ online while we're claiming its number. For defense-OUT, the real CDJ's reaction is what matters—once we defend, it should either drop offline or reclaim a different number, and that's what the capture will show. Our defense handler checks if we're online with the matching device number when a claim packet arrives, so we should catch one of the real CDJ's claim attempts over that ~1.8 second window and respond. Let me set this up.

I'll run both tests in sequence: first defense-OUT with the real CDJ powered on during capture to see the dynamic interaction, then defense-IN. The tricky part is validating that we actually sent the defense packet—the capture fixture only records received datagrams, not what we send. I could add send-logging to the capture by routing outbound packets through a callback, but simpler is to add a debug log when we defend so it's visible in stderr and gives clear evidence without modifying the fixture plumbing.

Actually, the best validation is watching the real CDJ's behavior in the captured packets. If we defend correctly, the real CDJ should either stop claiming device 4, re-claim a different number, or send a keepalive with a different device number. If we didn't defend (a bug), both of us would come online as 4, which would be obvious in the capture.

The challenge is that our defense is unicast to the peer, so we won't receive it back in the fixture like we do with our own broadcasts. I'll add minimal stderr logging in Online to record the defense-out and rejection events, which gives us the evidence we need without complicating the API.

I'm adding a `Log` field to VCDJ as an optional callback function that Online can invoke for key events like coming online, being rejected, or defending against a peer. This keeps the library clean with no forced dependencies — the capture tool can wire it up to print to stderr, and the field is safe to copy by value in tests. I'll create a helper method that calls the log function with formatted messages for when we claim a device, when we're defended against, and when we defend our own device.

Now I'm planning two test runs: one where we power on a real CDJ to trigger our defense-out logic and watch for the stderr messages, and another where the CDJ is already on to capture a real defense packet from it, which I'll save as a fixture and write a decoder and test for.

The key concern is making sure the 0x08 defense packet gets recorded before the capture shuts down when Online returns an error. The packet handler runs before the claim loop checks the rejected flag, so the packet should be written to the fixture file before the error propagates and the file closes. I'll implement the logging first, then coordinate the live tests with the user, starting with the defense-out scenario since that's what they specifically wanted to test. Adding logging infrastructure...


A second CDJ is exactly what we need to exercise the defend path for real. Before we capture, let me add lightweight event logging to `Online` so we can actually *see* the negotiation happen (our defense sends are unicast, so they don't show up in the captured fixture otherwise).


import (
	"bytes"
	"context"
	"encoding/hex"
	"net"
	"sync"
	"sync/atomic"
	"time"

	"github.com/cockroachdb/errors"
)

import (
	"bytes"
	"context"
	"encoding/hex"
	"fmt"
	"net"
	"sync"
	"sync/atomic"
	"time"

	"github.com/cockroachdb/errors"
)


The file /Users/noah/conductor/workspaces/deadca7/san-diego/link/announce.go has been updated successfully. (file state is current in your context — no need to Read it back)

import (
	"bytes"
	"context"
	"encoding/hex"
	"fmt"
	"net"
	"sync"
	"sync/atomic"
	"time"

	"github.com/cockroachdb/errors"
)

package link

import (
	"bytes"
	"context"
	"encoding/hex"
	"net"
	"sync"
	"sync/atomic"
	"time"

	"github.com/cockroachdb/errors"
)

// Packet types exchanged while a virtual CDJ comes online, interpreted on port
// 50000. A player sends hello, then three device-number claim stages, before
// keep-alives; a mixer may interrupt to assign a number, and any device
// defends a number it already owns. See
// https://djl-analysis.deepsymmetry.org/djl-analysis/startup.html#cdj-startup
const (
	TypeClaim1         Type = 0x00
	TypeWillAssign     Type = 0x01
	TypeClaim2         Type = 0x02
	TypeAssign         Type = 0x03
	TypeClaim3         Type = 0x04
	TypeAssignFinished Type = 0x05
	TypeDefense        Type = 0x08
	TypeHello          Type = 0x0a
)

// ClaimInterval is the gap between packets within a startup stage.
const ClaimInterval = 300 * time.Millisecond

// KeepAliveInterval is the gap between keep-alive packets once online.
const KeepAliveInterval = 1500 * time.Millisecond

// WatchPeriod is how long to observe keep-alives before self-assigning, so we
// avoid claiming a number already in use.
const WatchPeriod = 2 * time.Second

// Packet templates copied verbatim from beat-link; per-device fields (name,
// number, MAC, IP, packet counter) are patched into a copy before sending.
var (
	tmplAssign    = mustHex("5173707431576d4a4f4c0201626561742d6c696e6b0000000000000000000000010200320000000000000000000000000100")
	tmplClaim1    = mustHex("5173707431576d4a4f4c0000626561742d6c696e6b00000000000000000000000103002c0d01000000000000")
	tmplClaim2    = mustHex("5173707431576d4a4f4c0200626561742d6c696e6b000000000000000000000001030032000000000000000000000d000100")
	tmplClaim3    = mustHex("5173707431576d4a4f4c0400626561742d6c696e6b0000000000000000000000010300260d00")
	tmplDefense   = mustHex("5173707431576d4a4f4c0800626561742d6c696e6b0000000000000000000000010200290000000000")
	tmplHello     = mustHex("5173707431576d4a4f4c0a00626561742d6c696e6b0000000000000000000000010400260140")
	tmplKeepAlive = mustHex("5173707431576d4a4f4c0600626561742d6c696e6b000000000000000000000001020036000100000000000000000000020000000164")
)

func mustHex(s string) []byte {
	b, err := hex.DecodeString(s)
	if err != nil {
		panic(err)
	}
	return b
}

// SelfAssign returns the lowest player number not in used that is greater than
// after, starting no lower than 5 (the first number a CDJ-3000 may take) and
// stopping below the 33+ range mixers use.
func SelfAssign(used map[byte]bool, after byte) (byte, bool) {
	n := after + 1
	if n < 5 {
		n = 5
	}
	for ; n <= 15; n++ {
		if !used[n] {
			return n, true
		}
	}
	return 0, false
}

// VCDJ is a virtual CDJ that participates in the network so real players send
// it status, metadata, and database access. Device 0 means self-assign.
type VCDJ struct {
	Device byte
	IP     net.IP
	MAC    net.HardwareAddr
	Name   string
}

// Online brings the virtual CDJ online and holds its device number until ctx is
// done. It owns conn (bound to port 50000): it runs the claim handshake while
// reacting to defenses and mixer assignments, then sends keep-alives and
// defends its number. Every received datagram is passed to onPacket so callers
// can record it.
func (v *VCDJ) Online(ctx context.Context, conn *net.UDPConn, ipNet *net.IPNet, onPacket func([]byte, *net.UDPAddr)) error {
	v.IP = ipNet.IP
	dst := &net.UDPAddr{IP: Broadcast(ipNet), Port: 50000}

	var (
		assigned atomic.Int32
		claiming atomic.Int32
		online   atomic.Bool
		rejected atomic.Bool
		seen     sync.Map
	)

	send := func(b []byte, to *net.UDPAddr) {
		conn.WriteToUDP(b, to)
	}

	handle := func(b []byte, src *net.UDPAddr) {
		if len(b) < 0x25 || !bytes.Equal(b[:len(Magic)], Magic) {
			return
		}
		peer := &net.UDPAddr{IP: src.IP, Port: 50000}
		switch Type(b[0x0a]) {
		case TypeKeepAlive:
			seen.Store(b[0x24], true)
		case TypeWillAssign:
			if claiming.Load() != 0 {
				send(v.assignRequest(), peer)
			}
		case TypeAssign:
			assigned.Store(int32(b[0x24]))
		case TypeAssignFinished:
			assigned.Store(claiming.Load())
		case TypeDefense:
			if b[0x24] == byte(claiming.Load()) {
				rejected.Store(true)
			}
		case TypeClaim2:
			if online.Load() && len(b) > 0x2e && b[0x2e] == v.Device {
				send(v.defense(), peer)
			}
		case TypeClaim3:
			if online.Load() && b[0x24] == v.Device {
				send(v.defense(), peer)
			}
		}
	}

	errc := make(chan error, 1)
	go func() {
		go func() { <-ctx.Done(); conn.SetReadDeadline(time.Now()) }()
		buf := make([]byte, 1500)
		for {
			n, src, err := conn.ReadFromUDP(buf)
			if err != nil {
				if ctx.Err() != nil {
					errc <- nil
				} else {
					errc <- errors.WithStack(err)
				}
				return
			}
			b := append([]byte(nil), buf[:n]...)
			handle(b, src)
			if onPacket != nil {
				onPacket(b, src)
			}
		}
	}()

	wait := func(d time.Duration) error {
		select {
		case <-ctx.Done():
			return errors.WithStack(ctx.Err())
		case err := <-errc:
			if err == nil {
				err = errors.New("listener stopped")
			}
			return err
		case <-time.After(d):
			return nil
		}
	}

	for i := 0; i < 3; i++ {
		send(v.hello(), dst)
		if err := wait(ClaimInterval); err != nil {
			return err
		}
	}

	auto := v.Device == 0
	if auto {
		if err := wait(WatchPeriod); err != nil {
			return err
		}
	}

	claim := func(num byte) (bool, error) {
		v.Device = num
		claiming.Store(int32(num))
		rejected.Store(false)
		assigned.Store(0)

		stages := [][]func(byte) []byte{
			{v.claim1}, {v.claim2}, {v.claim3},
		}
		for s, stage := range stages {
			if s == 2 {
				if n := assigned.Swap(0); n > 0 {
					v.Device = byte(n)
					claiming.Store(n)
				}
			}
			for i := byte(1); i <= 3 && assigned.Load() == 0; i++ {
				send(stage[0](i), dst)
				if err := wait(ClaimInterval); err != nil {
					return false, err
				}
				if rejected.Load() {
					return false, nil
				}
			}
		}
		return true, nil
	}

	var after byte
	for {
		num := v.Device
		if auto {
			n, ok := SelfAssign(usedNumbers(&seen), after)
			if !ok {
				return errors.New("no available device number")
			}
			num, after = n, n
		}

		ok, err := claim(num)
		if err != nil {
			return err
		}
		if ok {
			break
		}
		if !auto {
			return errors.Errorf("device number %d defended by another device", num)
		}
	}

	online.Store(true)
	claiming.Store(0)

	t := time.NewTicker(KeepAliveInterval)
	defer t.Stop()
	for {
		send(v.keepAlive(), dst)
		select {
		case <-ctx.Done():
			return nil
		case err := <-errc:
			return err
		case <-t.C:
		}
	}
}

func usedNumbers(seen *sync.Map) map[byte]bool {
	used := map[byte]bool{}
	seen.Range(func(k, _ any) bool {
		used[k.(byte)] = true
		return true
	})
	return used
}

func (v VCDJ) name(b []byte) {
	for i := 0; i < 0x14; i++ {
		b[0x0c+i] = 0
	}
	copy(b[0x0c:0x0c+0x14], v.Name)
}

func (v VCDJ) hello() []byte {
	b := append([]byte(nil), tmplHello...)
	v.name(b)
	return b
}

func (v VCDJ) claim1(counter byte) []byte {
	b := append([]byte(nil), tmplClaim1...)
	v.name(b)
	b[0x24] = counter
	copy(b[0x26:0x2c], v.MAC)
	return b
}

func (v VCDJ) claim2(counter byte) []byte {
	b := append([]byte(nil), tmplClaim2...)
	v.name(b)
	copy(b[0x24:0x28], v.IP.To4())
	copy(b[0x28:0x2e], v.MAC)
	b[0x2e] = v.Device
	b[0x2f] = counter
	b[0x31] = v.assignFlag()
	return b
}

func (v VCDJ) claim3(counter byte) []byte {
	b := append([]byte(nil), tmplClaim3...)
	v.name(b)
	b[0x24] = v.Device
	b[0x25] = counter
	return b
}

func (v VCDJ) assignRequest() []byte {
	b := append([]byte(nil), tmplAssign...)
	v.name(b)
	copy(b[0x24:0x28], v.IP.To4())
	copy(b[0x28:0x2e], v.MAC)
	b[0x2f] = 0x01
	b[0x31] = v.assignFlag()
	return b
}

func (v VCDJ) defense() []byte {
	b := append([]byte(nil), tmplDefense...)
	v.name(b)
	b[0x24] = v.Device
	copy(b[0x25:0x29], v.IP.To4())
	return b
}

func (v VCDJ) keepAlive() []byte {
	b := append([]byte(nil), tmplKeepAlive...)
	v.name(b)
	b[0x24] = v.Device
	copy(b[0x26:0x2c], v.MAC)
	copy(b[0x2c:0x30], v.IP.To4())
	return b
}

func (v VCDJ) assignFlag() byte {
	if v.Device == 0 {
		return 0x01
	}
	return 0x02
}

"bytes"
"context"
"encoding/hex"
+  "fmt"
"net"
"sync"
"sync/atomic"


I have another CDJ we can force the conflict...   I believe 3 is up, and I could turn 2 or 4 on when we're ready to capture


// VCDJ is a virtual CDJ that participates in the network so real players send
// it status, metadata, and database access. Device 0 means self-assign.
type VCDJ struct {
	Device byte
	IP     net.IP
	MAC    net.HardwareAddr
	Name   string
}

// VCDJ is a virtual CDJ that participates in the network so real players send
// it status, metadata, and database access. Device 0 means self-assign.
type VCDJ struct {
	Device byte
	IP     net.IP
	Log    func(string)
	MAC    net.HardwareAddr
	Name   string
}

func (v VCDJ) logf(format string, args ...any) {
	if v.Log != nil {
		v.Log(fmt.Sprintf(format, args...))
	}
}


// VCDJ is a virtual CDJ that participates in the network so real players send
// it status, metadata, and database access. Device 0 means self-assign.
type VCDJ struct {
	Device byte
	IP     net.IP
	Log    func(string)
	MAC    net.HardwareAddr
	Name   string
}

func (v VCDJ) logf(format string, args ...any) {
	if v.Log != nil {
		v.Log(fmt.Sprintf(format, args...))
	}
}

package link

import (
	"bytes"
	"context"
	"encoding/hex"
	"fmt"
	"net"
	"sync"
	"sync/atomic"
	"time"

	"github.com/cockroachdb/errors"
)

// Packet types exchanged while a virtual CDJ comes online, interpreted on port
// 50000. A player sends hello, then three device-number claim stages, before
// keep-alives; a mixer may interrupt to assign a number, and any device
// defends a number it already owns. See
// https://djl-analysis.deepsymmetry.org/djl-analysis/startup.html#cdj-startup
const (
	TypeClaim1         Type = 0x00
	TypeWillAssign     Type = 0x01
	TypeClaim2         Type = 0x02
	TypeAssign         Type = 0x03
	TypeClaim3         Type = 0x04
	TypeAssignFinished Type = 0x05
	TypeDefense        Type = 0x08
	TypeHello          Type = 0x0a
)

// ClaimInterval is the gap between packets within a startup stage.
const ClaimInterval = 300 * time.Millisecond

// KeepAliveInterval is the gap between keep-alive packets once online.
const KeepAliveInterval = 1500 * time.Millisecond

// WatchPeriod is how long to observe keep-alives before self-assigning, so we
// avoid claiming a number already in use.
const WatchPeriod = 2 * time.Second

// Packet templates copied verbatim from beat-link; per-device fields (name,
// number, MAC, IP, packet counter) are patched into a copy before sending.
var (
	tmplAssign    = mustHex("5173707431576d4a4f4c0201626561742d6c696e6b0000000000000000000000010200320000000000000000000000000100")
	tmplClaim1    = mustHex("5173707431576d4a4f4c0000626561742d6c696e6b00000000000000000000000103002c0d01000000000000")
	tmplClaim2    = mustHex("5173707431576d4a4f4c0200626561742d6c696e6b000000000000000000000001030032000000000000000000000d000100")
	tmplClaim3    = mustHex("5173707431576d4a4f4c0400626561742d6c696e6b0000000000000000000000010300260d00")
	tmplDefense   = mustHex("5173707431576d4a4f4c0800626561742d6c696e6b0000000000000000000000010200290000000000")
	tmplHello     = mustHex("5173707431576d4a4f4c0a00626561742d6c696e6b0000000000000000000000010400260140")
	tmplKeepAlive = mustHex("5173707431576d4a4f4c0600626561742d6c696e6b000000000000000000000001020036000100000000000000000000020000000164")
)

func mustHex(s string) []byte {
	b, err := hex.DecodeString(s)
	if err != nil {
		panic(err)
	}
	return b
}

// SelfAssign returns the lowest player number not in used that is greater than
// after, starting no lower than 5 (the first number a CDJ-3000 may take) and
// stopping below the 33+ range mixers use.
func SelfAssign(used map[byte]bool, after byte) (byte, bool) {
	n := after + 1
	if n < 5 {
		n = 5
	}
	for ; n <= 15; n++ {
		if !used[n] {
			return n, true
		}
	}
	return 0, false
}

// VCDJ is a virtual CDJ that participates in the network so real players send
// it status, metadata, and database access. Device 0 means self-assign.
type VCDJ struct {
	Device byte
	IP     net.IP
	MAC    net.HardwareAddr
	Name   string
}

// Online brings the virtual CDJ online and holds its device number until ctx is
// done. It owns conn (bound to port 50000): it runs the claim handshake while
// reacting to defenses and mixer assignments, then sends keep-alives and
// defends its number. Every received datagram is passed to onPacket so callers
// can record it.
func (v *VCDJ) Online(ctx context.Context, conn *net.UDPConn, ipNet *net.IPNet, onPacket func([]byte, *net.UDPAddr)) error {
	v.IP = ipNet.IP
	dst := &net.UDPAddr{IP: Broadcast(ipNet), Port: 50000}

	var (
		assigned atomic.Int32
		claiming atomic.Int32
		online   atomic.Bool
		rejected atomic.Bool
		seen     sync.Map
	)

	send := func(b []byte, to *net.UDPAddr) {
		conn.WriteToUDP(b, to)
	}

	handle := func(b []byte, src *net.UDPAddr) {
		if len(b) < 0x25 || !bytes.Equal(b[:len(Magic)], Magic) {
			return
		}
		peer := &net.UDPAddr{IP: src.IP, Port: 50000}
		switch Type(b[0x0a]) {
		case TypeKeepAlive:
			seen.Store(b[0x24], true)
		case TypeWillAssign:
			if claiming.Load() != 0 {
				send(v.assignRequest(), peer)
			}
		case TypeAssign:
			assigned.Store(int32(b[0x24]))
		case TypeAssignFinished:
			assigned.Store(claiming.Load())
		case TypeDefense:
			if b[0x24] == byte(claiming.Load()) {
				rejected.Store(true)
			}
		case TypeClaim2:
			if online.Load() && len(b) > 0x2e && b[0x2e] == v.Device {
				send(v.defense(), peer)
			}
		case TypeClaim3:
			if online.Load() && b[0x24] == v.Device {
				send(v.defense(), peer)
			}
		}
	}

	errc := make(chan error, 1)
	go func() {
		go func() { <-ctx.Done(); conn.SetReadDeadline(time.Now()) }()
		buf := make([]byte, 1500)
		for {
			n, src, err := conn.ReadFromUDP(buf)
			if err != nil {
				if ctx.Err() != nil {
					errc <- nil
				} else {
					errc <- errors.WithStack(err)
				}
				return
			}
			b := append([]byte(nil), buf[:n]...)
			handle(b, src)
			if onPacket != nil {
				onPacket(b, src)
			}
		}
	}()

	wait := func(d time.Duration) error {
		select {
		case <-ctx.Done():
			return errors.WithStack(ctx.Err())
		case err := <-errc:
			if err == nil {
				err = errors.New("listener stopped")
			}
			return err
		case <-time.After(d):
			return nil
		}
	}

	for i := 0; i < 3; i++ {
		send(v.hello(), dst)
		if err := wait(ClaimInterval); err != nil {
			return err
		}
	}

	auto := v.Device == 0
	if auto {
		if err := wait(WatchPeriod); err != nil {
			return err
		}
	}

	claim := func(num byte) (bool, error) {
		v.Device = num
		claiming.Store(int32(num))
		rejected.Store(false)
		assigned.Store(0)

		stages := [][]func(byte) []byte{
			{v.claim1}, {v.claim2}, {v.claim3},
		}
		for s, stage := range stages {
			if s == 2 {
				if n := assigned.Swap(0); n > 0 {
					v.Device = byte(n)
					claiming.Store(n)
				}
			}
			for i := byte(1); i <= 3 && assigned.Load() == 0; i++ {
				send(stage[0](i), dst)
				if err := wait(ClaimInterval); err != nil {
					return false, err
				}
				if rejected.Load() {
					return false, nil
				}
			}
		}
		return true, nil
	}

	var after byte
	for {
		num := v.Device
		if auto {
			n, ok := SelfAssign(usedNumbers(&seen), after)
			if !ok {
				return errors.New("no available device number")
			}
			num, after = n, n
		}

		ok, err := claim(num)
		if err != nil {
			return err
		}
		if ok {
			break
		}
		if !auto {
			return errors.Errorf("device number %d defended by another device", num)
		}
	}

	online.Store(true)
	claiming.Store(0)

	t := time.NewTicker(KeepAliveInterval)
	defer t.Stop()
	for {
		send(v.keepAlive(), dst)
		select {
		case <-ctx.Done():
			return nil
		case err := <-errc:
			return err
		case <-t.C:
		}
	}
}

func usedNumbers(seen *sync.Map) map[byte]bool {
	used := map[byte]bool{}
	seen.Range(func(k, _ any) bool {
		used[k.(byte)] = true
		return true
	})
	return used
}

func (v VCDJ) name(b []byte) {
	for i := 0; i < 0x14; i++ {
		b[0x0c+i] = 0
	}
	copy(b[0x0c:0x0c+0x14], v.Name)
}

func (v VCDJ) hello() []byte {
	b := append([]byte(nil), tmplHello...)
	v.name(b)
	return b
}

func (v VCDJ) claim1(counter byte) []byte {
	b := append([]byte(nil), tmplClaim1...)
	v.name(b)
	b[0x24] = counter
	copy(b[0x26:0x2c], v.MAC)
	return b
}

func (v VCDJ) claim2(counter byte) []byte {
	b := append([]byte(nil), tmplClaim2...)
	v.name(b)
	copy(b[0x24:0x28], v.IP.To4())
	copy(b[0x28:0x2e], v.MAC)
	b[0x2e] = v.Device
	b[0x2f] = counter
	b[0x31] = v.assignFlag()
	return b
}

func (v VCDJ) claim3(counter byte) []byte {
	b := append([]byte(nil), tmplClaim3...)
	v.name(b)
	b[0x24] = v.Device
	b[0x25] = counter
	return b
}

func (v VCDJ) assignRequest() []byte {
	b := append([]byte(nil), tmplAssign...)
	v.name(b)
	copy(b[0x24:0x28], v.IP.To4())
	copy(b[0x28:0x2e], v.MAC)
	b[0x2f] = 0x01
	b[0x31] = v.assignFlag()
	return b
}

func (v VCDJ) defense() []byte {
	b := append([]byte(nil), tmplDefense...)
	v.name(b)
	b[0x24] = v.Device
	copy(b[0x25:0x29], v.IP.To4())
	return b
}

func (v VCDJ) keepAlive() []byte {
	b := append([]byte(nil), tmplKeepAlive...)
	v.name(b)
	b[0x24] = v.Device
	copy(b[0x26:0x2c], v.MAC)
	copy(b[0x2c:0x30], v.IP.To4())
	return b
}

func (v VCDJ) assignFlag() byte {
	if v.Device == 0 {
		return 0x01
	}
	return 0x02
}

+func (v VCDJ) logf(format string, args ...any) {

+    v.Log(fmt.Sprintf(format, args...))


Now wire the events into the negotiation:


		case TypeClaim2:
			if online.Load() && len(b) > 0x2e && b[0x2e] == v.Device {
				send(v.defense(), peer)
			}
		case TypeClaim3:
			if online.Load() && b[0x24] == v.Device {
				send(v.defense(), peer)
			}
		}

		case TypeClaim2:
			if online.Load() && len(b) > 0x2e && b[0x2e] == v.Device {
				v.logf("defending device %d against %s", v.Device, src.IP)
				send(v.defense(), peer)
			}
		case TypeClaim3:
			if online.Load() && b[0x24] == v.Device {
				v.logf("defending device %d against %s", v.Device, src.IP)
				send(v.defense(), peer)
			}
		}


		case TypeClaim2:
			if online.Load() && len(b) > 0x2e && b[0x2e] == v.Device {
				v.logf("defending device %d against %s", v.Device, src.IP)
				send(v.defense(), peer)
			}
		case TypeClaim3:
			if online.Load() && b[0x24] == v.Device {
				v.logf("defending device %d against %s", v.Device, src.IP)
				send(v.defense(), peer)
			}
		}

package link

import (
	"bytes"
	"context"
	"encoding/hex"
	"fmt"
	"net"
	"sync"
	"sync/atomic"
	"time"

	"github.com/cockroachdb/errors"
)

// Packet types exchanged while a virtual CDJ comes online, interpreted on port
// 50000. A player sends hello, then three device-number claim stages, before
// keep-alives; a mixer may interrupt to assign a number, and any device
// defends a number it already owns. See
// https://djl-analysis.deepsymmetry.org/djl-analysis/startup.html#cdj-startup
const (
	TypeClaim1         Type = 0x00
	TypeWillAssign     Type = 0x01
	TypeClaim2         Type = 0x02
	TypeAssign         Type = 0x03
	TypeClaim3         Type = 0x04
	TypeAssignFinished Type = 0x05
	TypeDefense        Type = 0x08
	TypeHello          Type = 0x0a
)

// ClaimInterval is the gap between packets within a startup stage.
const ClaimInterval = 300 * time.Millisecond

// KeepAliveInterval is the gap between keep-alive packets once online.
const KeepAliveInterval = 1500 * time.Millisecond

// WatchPeriod is how long to observe keep-alives before self-assigning, so we
// avoid claiming a number already in use.
const WatchPeriod = 2 * time.Second

// Packet templates copied verbatim from beat-link; per-device fields (name,
// number, MAC, IP, packet counter) are patched into a copy before sending.
var (
	tmplAssign    = mustHex("5173707431576d4a4f4c0201626561742d6c696e6b0000000000000000000000010200320000000000000000000000000100")
	tmplClaim1    = mustHex("5173707431576d4a4f4c0000626561742d6c696e6b00000000000000000000000103002c0d01000000000000")
	tmplClaim2    = mustHex("5173707431576d4a4f4c0200626561742d6c696e6b000000000000000000000001030032000000000000000000000d000100")
	tmplClaim3    = mustHex("5173707431576d4a4f4c0400626561742d6c696e6b0000000000000000000000010300260d00")
	tmplDefense   = mustHex("5173707431576d4a4f4c0800626561742d6c696e6b0000000000000000000000010200290000000000")
	tmplHello     = mustHex("5173707431576d4a4f4c0a00626561742d6c696e6b0000000000000000000000010400260140")
	tmplKeepAlive = mustHex("5173707431576d4a4f4c0600626561742d6c696e6b000000000000000000000001020036000100000000000000000000020000000164")
)

func mustHex(s string) []byte {
	b, err := hex.DecodeString(s)
	if err != nil {
		panic(err)
	}
	return b
}

// SelfAssign returns the lowest player number not in used that is greater than
// after, starting no lower than 5 (the first number a CDJ-3000 may take) and
// stopping below the 33+ range mixers use.
func SelfAssign(used map[byte]bool, after byte) (byte, bool) {
	n := after + 1
	if n < 5 {
		n = 5
	}
	for ; n <= 15; n++ {
		if !used[n] {
			return n, true
		}
	}
	return 0, false
}

// VCDJ is a virtual CDJ that participates in the network so real players send
// it status, metadata, and database access. Device 0 means self-assign.
type VCDJ struct {
	Device byte
	IP     net.IP
	Log    func(string)
	MAC    net.HardwareAddr
	Name   string
}

func (v VCDJ) logf(format string, args ...any) {
	if v.Log != nil {
		v.Log(fmt.Sprintf(format, args...))
	}
}

// Online brings the virtual CDJ online and holds its device number until ctx is
// done. It owns conn (bound to port 50000): it runs the claim handshake while
// reacting to defenses and mixer assignments, then sends keep-alives and
// defends its number. Every received datagram is passed to onPacket so callers
// can record it.
func (v *VCDJ) Online(ctx context.Context, conn *net.UDPConn, ipNet *net.IPNet, onPacket func([]byte, *net.UDPAddr)) error {
	v.IP = ipNet.IP
	dst := &net.UDPAddr{IP: Broadcast(ipNet), Port: 50000}

	var (
		assigned atomic.Int32
		claiming atomic.Int32
		online   atomic.Bool
		rejected atomic.Bool
		seen     sync.Map
	)

	send := func(b []byte, to *net.UDPAddr) {
		conn.WriteToUDP(b, to)
	}

	handle := func(b []byte, src *net.UDPAddr) {
		if len(b) < 0x25 || !bytes.Equal(b[:len(Magic)], Magic) {
			return
		}
		peer := &net.UDPAddr{IP: src.IP, Port: 50000}
		switch Type(b[0x0a]) {
		case TypeKeepAlive:
			seen.Store(b[0x24], true)
		case TypeWillAssign:
			if claiming.Load() != 0 {
				send(v.assignRequest(), peer)
			}
		case TypeAssign:
			assigned.Store(int32(b[0x24]))
		case TypeAssignFinished:
			assigned.Store(claiming.Load())
		case TypeDefense:
			if b[0x24] == byte(claiming.Load()) {
				rejected.Store(true)
			}
		case TypeClaim2:
			if online.Load() && len(b) > 0x2e && b[0x2e] == v.Device {
				send(v.defense(), peer)
			}
		case TypeClaim3:
			if online.Load() && b[0x24] == v.Device {
				send(v.defense(), peer)
			}
		}
	}

	errc := make(chan error, 1)
	go func() {
		go func() { <-ctx.Done(); conn.SetReadDeadline(time.Now()) }()
		buf := make([]byte, 1500)
		for {
			n, src, err := conn.ReadFromUDP(buf)
			if err != nil {
				if ctx.Err() != nil {
					errc <- nil
				} else {
					errc <- errors.WithStack(err)
				}
				return
			}
			b := append([]byte(nil), buf[:n]...)
			handle(b, src)
			if onPacket != nil {
				onPacket(b, src)
			}
		}
	}()

	wait := func(d time.Duration) error {
		select {
		case <-ctx.Done():
			return errors.WithStack(ctx.Err())
		case err := <-errc:
			if err == nil {
				err = errors.New("listener stopped")
			}
			return err
		case <-time.After(d):
			return nil
		}
	}

	for i := 0; i < 3; i++ {
		send(v.hello(), dst)
		if err := wait(ClaimInterval); err != nil {
			return err
		}
	}

	auto := v.Device == 0
	if auto {
		if err := wait(WatchPeriod); err != nil {
			return err
		}
	}

	claim := func(num byte) (bool, error) {
		v.Device = num
		claiming.Store(int32(num))
		rejected.Store(false)
		assigned.Store(0)

		stages := [][]func(byte) []byte{
			{v.claim1}, {v.claim2}, {v.claim3},
		}
		for s, stage := range stages {
			if s == 2 {
				if n := assigned.Swap(0); n > 0 {
					v.Device = byte(n)
					claiming.Store(n)
				}
			}
			for i := byte(1); i <= 3 && assigned.Load() == 0; i++ {
				send(stage[0](i), dst)
				if err := wait(ClaimInterval); err != nil {
					return false, err
				}
				if rejected.Load() {
					return false, nil
				}
			}
		}
		return true, nil
	}

	var after byte
	for {
		num := v.Device
		if auto {
			n, ok := SelfAssign(usedNumbers(&seen), after)
			if !ok {
				return errors.New("no available device number")
			}
			num, after = n, n
		}

		ok, err := claim(num)
		if err != nil {
			return err
		}
		if ok {
			break
		}
		if !auto {
			return errors.Errorf("device number %d defended by another device", num)
		}
	}

	online.Store(true)
	claiming.Store(0)

	t := time.NewTicker(KeepAliveInterval)
	defer t.Stop()
	for {
		send(v.keepAlive(), dst)
		select {
		case <-ctx.Done():
			return nil
		case err := <-errc:
			return err
		case <-t.C:
		}
	}
}

func usedNumbers(seen *sync.Map) map[byte]bool {
	used := map[byte]bool{}
	seen.Range(func(k, _ any) bool {
		used[k.(byte)] = true
		return true
	})
	return used
}

func (v VCDJ) name(b []byte) {
	for i := 0; i < 0x14; i++ {
		b[0x0c+i] = 0
	}
	copy(b[0x0c:0x0c+0x14], v.Name)
}

func (v VCDJ) hello() []byte {
	b := append([]byte(nil), tmplHello...)
	v.name(b)
	return b
}

func (v VCDJ) claim1(counter byte) []byte {
	b := append([]byte(nil), tmplClaim1...)
	v.name(b)
	b[0x24] = counter
	copy(b[0x26:0x2c], v.MAC)
	return b
}

func (v VCDJ) claim2(counter byte) []byte {
	b := append([]byte(nil), tmplClaim2...)
	v.name(b)
	copy(b[0x24:0x28], v.IP.To4())
	copy(b[0x28:0x2e], v.MAC)
	b[0x2e] = v.Device
	b[0x2f] = counter
	b[0x31] = v.assignFlag()
	return b
}

func (v VCDJ) claim3(counter byte) []byte {
	b := append([]byte(nil), tmplClaim3...)
	v.name(b)
	b[0x24] = v.Device
	b[0x25] = counter
	return b
}

func (v VCDJ) assignRequest() []byte {
	b := append([]byte(nil), tmplAssign...)
	v.name(b)
	copy(b[0x24:0x28], v.IP.To4())
	copy(b[0x28:0x2e], v.MAC)
	b[0x2f] = 0x01
	b[0x31] = v.assignFlag()
	return b
}

func (v VCDJ) defense() []byte {
	b := append([]byte(nil), tmplDefense...)
	v.name(b)
	b[0x24] = v.Device
	copy(b[0x25:0x29], v.IP.To4())
	return b
}

func (v VCDJ) keepAlive() []byte {
	b := append([]byte(nil), tmplKeepAlive...)
	v.name(b)
	b[0x24] = v.Device
	copy(b[0x26:0x2c], v.MAC)
	copy(b[0x2c:0x30], v.IP.To4())
	return b
}

func (v VCDJ) assignFlag() byte {
	if v.Device == 0 {
		return 0x01
	}
	return 0x02
}

+        v.logf("defending device %d against %s", v.Device, src.IP)


		for s, stage := range stages {
			if s == 2 {
				if n := assigned.Swap(0); n > 0 {
					v.Device = byte(n)
					claiming.Store(n)
				}
			}

		for s, stage := range stages {
			if s == 2 {
				if n := assigned.Swap(0); n > 0 {
					v.logf("mixer assigned device %d", n)
					v.Device = byte(n)
					claiming.Store(n)
				}
			}


		for s, stage := range stages {
			if s == 2 {
				if n := assigned.Swap(0); n > 0 {
					v.logf("mixer assigned device %d", n)
					v.Device = byte(n)
					claiming.Store(n)
				}
			}

package link

import (
	"bytes"
	"context"
	"encoding/hex"
	"fmt"
	"net"
	"sync"
	"sync/atomic"
	"time"

	"github.com/cockroachdb/errors"
)

// Packet types exchanged while a virtual CDJ comes online, interpreted on port
// 50000. A player sends hello, then three device-number claim stages, before
// keep-alives; a mixer may interrupt to assign a number, and any device
// defends a number it already owns. See
// https://djl-analysis.deepsymmetry.org/djl-analysis/startup.html#cdj-startup
const (
	TypeClaim1         Type = 0x00
	TypeWillAssign     Type = 0x01
	TypeClaim2         Type = 0x02
	TypeAssign         Type = 0x03
	TypeClaim3         Type = 0x04
	TypeAssignFinished Type = 0x05
	TypeDefense        Type = 0x08
	TypeHello          Type = 0x0a
)

// ClaimInterval is the gap between packets within a startup stage.
const ClaimInterval = 300 * time.Millisecond

// KeepAliveInterval is the gap between keep-alive packets once online.
const KeepAliveInterval = 1500 * time.Millisecond

// WatchPeriod is how long to observe keep-alives before self-assigning, so we
// avoid claiming a number already in use.
const WatchPeriod = 2 * time.Second

// Packet templates copied verbatim from beat-link; per-device fields (name,
// number, MAC, IP, packet counter) are patched into a copy before sending.
var (
	tmplAssign    = mustHex("5173707431576d4a4f4c0201626561742d6c696e6b0000000000000000000000010200320000000000000000000000000100")
	tmplClaim1    = mustHex("5173707431576d4a4f4c0000626561742d6c696e6b00000000000000000000000103002c0d01000000000000")
	tmplClaim2    = mustHex("5173707431576d4a4f4c0200626561742d6c696e6b000000000000000000000001030032000000000000000000000d000100")
	tmplClaim3    = mustHex("5173707431576d4a4f4c0400626561742d6c696e6b0000000000000000000000010300260d00")
	tmplDefense   = mustHex("5173707431576d4a4f4c0800626561742d6c696e6b0000000000000000000000010200290000000000")
	tmplHello     = mustHex("5173707431576d4a4f4c0a00626561742d6c696e6b0000000000000000000000010400260140")
	tmplKeepAlive = mustHex("5173707431576d4a4f4c0600626561742d6c696e6b000000000000000000000001020036000100000000000000000000020000000164")
)

func mustHex(s string) []byte {
	b, err := hex.DecodeString(s)
	if err != nil {
		panic(err)
	}
	return b
}

// SelfAssign returns the lowest player number not in used that is greater than
// after, starting no lower than 5 (the first number a CDJ-3000 may take) and
// stopping below the 33+ range mixers use.
func SelfAssign(used map[byte]bool, after byte) (byte, bool) {
	n := after + 1
	if n < 5 {
		n = 5
	}
	for ; n <= 15; n++ {
		if !used[n] {
			return n, true
		}
	}
	return 0, false
}

// VCDJ is a virtual CDJ that participates in the network so real players send
// it status, metadata, and database access. Device 0 means self-assign.
type VCDJ struct {
	Device byte
	IP     net.IP
	Log    func(string)
	MAC    net.HardwareAddr
	Name   string
}

func (v VCDJ) logf(format string, args ...any) {
	if v.Log != nil {
		v.Log(fmt.Sprintf(format, args...))
	}
}

// Online brings the virtual CDJ online and holds its device number until ctx is
// done. It owns conn (bound to port 50000): it runs the claim handshake while
// reacting to defenses and mixer assignments, then sends keep-alives and
// defends its number. Every received datagram is passed to onPacket so callers
// can record it.
func (v *VCDJ) Online(ctx context.Context, conn *net.UDPConn, ipNet *net.IPNet, onPacket func([]byte, *net.UDPAddr)) error {
	v.IP = ipNet.IP
	dst := &net.UDPAddr{IP: Broadcast(ipNet), Port: 50000}

	var (
		assigned atomic.Int32
		claiming atomic.Int32
		online   atomic.Bool
		rejected atomic.Bool
		seen     sync.Map
	)

	send := func(b []byte, to *net.UDPAddr) {
		conn.WriteToUDP(b, to)
	}

	handle := func(b []byte, src *net.UDPAddr) {
		if len(b) < 0x25 || !bytes.Equal(b[:len(Magic)], Magic) {
			return
		}
		peer := &net.UDPAddr{IP: src.IP, Port: 50000}
		switch Type(b[0x0a]) {
		case TypeKeepAlive:
			seen.Store(b[0x24], true)
		case TypeWillAssign:
			if claiming.Load() != 0 {
				send(v.assignRequest(), peer)
			}
		case TypeAssign:
			assigned.Store(int32(b[0x24]))
		case TypeAssignFinished:
			assigned.Store(claiming.Load())
		case TypeDefense:
			if b[0x24] == byte(claiming.Load()) {
				rejected.Store(true)
			}
		case TypeClaim2:
			if online.Load() && len(b) > 0x2e && b[0x2e] == v.Device {
				v.logf("defending device %d against %s", v.Device, src.IP)
				send(v.defense(), peer)
			}
		case TypeClaim3:
			if online.Load() && b[0x24] == v.Device {
				v.logf("defending device %d against %s", v.Device, src.IP)
				send(v.defense(), peer)
			}
		}
	}

	errc := make(chan error, 1)
	go func() {
		go func() { <-ctx.Done(); conn.SetReadDeadline(time.Now()) }()
		buf := make([]byte, 1500)
		for {
			n, src, err := conn.ReadFromUDP(buf)
			if err != nil {
				if ctx.Err() != nil {
					errc <- nil
				} else {
					errc <- errors.WithStack(err)
				}
				return
			}
			b := append([]byte(nil), buf[:n]...)
			handle(b, src)
			if onPacket != nil {
				onPacket(b, src)
			}
		}
	}()

	wait := func(d time.Duration) error {
		select {
		case <-ctx.Done():
			return errors.WithStack(ctx.Err())
		case err := <-errc:
			if err == nil {
				err = errors.New("listener stopped")
			}
			return err
		case <-time.After(d):
			return nil
		}
	}

	for i := 0; i < 3; i++ {
		send(v.hello(), dst)
		if err := wait(ClaimInterval); err != nil {
			return err
		}
	}

	auto := v.Device == 0
	if auto {
		if err := wait(WatchPeriod); err != nil {
			return err
		}
	}

	claim := func(num byte) (bool, error) {
		v.Device = num
		claiming.Store(int32(num))
		rejected.Store(false)
		assigned.Store(0)

		stages := [][]func(byte) []byte{
			{v.claim1}, {v.claim2}, {v.claim3},
		}
		for s, stage := range stages {
			if s == 2 {
				if n := assigned.Swap(0); n > 0 {
					v.Device = byte(n)
					claiming.Store(n)
				}
			}
			for i := byte(1); i <= 3 && assigned.Load() == 0; i++ {
				send(stage[0](i), dst)
				if err := wait(ClaimInterval); err != nil {
					return false, err
				}
				if rejected.Load() {
					return false, nil
				}
			}
		}
		return true, nil
	}

	var after byte
	for {
		num := v.Device
		if auto {
			n, ok := SelfAssign(usedNumbers(&seen), after)
			if !ok {
				return errors.New("no available device number")
			}
			num, after = n, n
		}

		ok, err := claim(num)
		if err != nil {
			return err
		}
		if ok {
			break
		}
		if !auto {
			return errors.Errorf("device number %d defended by another device", num)
		}
	}

	online.Store(true)
	claiming.Store(0)

	t := time.NewTicker(KeepAliveInterval)
	defer t.Stop()
	for {
		send(v.keepAlive(), dst)
		select {
		case <-ctx.Done():
			return nil
		case err := <-errc:
			return err
		case <-t.C:
		}
	}
}

func usedNumbers(seen *sync.Map) map[byte]bool {
	used := map[byte]bool{}
	seen.Range(func(k, _ any) bool {
		used[k.(byte)] = true
		return true
	})
	return used
}

func (v VCDJ) name(b []byte) {
	for i := 0; i < 0x14; i++ {
		b[0x0c+i] = 0
	}
	copy(b[0x0c:0x0c+0x14], v.Name)
}

func (v VCDJ) hello() []byte {
	b := append([]byte(nil), tmplHello...)
	v.name(b)
	return b
}

func (v VCDJ) claim1(counter byte) []byte {
	b := append([]byte(nil), tmplClaim1...)
	v.name(b)
	b[0x24] = counter
	copy(b[0x26:0x2c], v.MAC)
	return b
}

func (v VCDJ) claim2(counter byte) []byte {
	b := append([]byte(nil), tmplClaim2...)
	v.name(b)
	copy(b[0x24:0x28], v.IP.To4())
	copy(b[0x28:0x2e], v.MAC)
	b[0x2e] = v.Device
	b[0x2f] = counter
	b[0x31] = v.assignFlag()
	return b
}

func (v VCDJ) claim3(counter byte) []byte {
	b := append([]byte(nil), tmplClaim3...)
	v.name(b)
	b[0x24] = v.Device
	b[0x25] = counter
	return b
}

func (v VCDJ) assignRequest() []byte {
	b := append([]byte(nil), tmplAssign...)
	v.name(b)
	copy(b[0x24:0x28], v.IP.To4())
	copy(b[0x28:0x2e], v.MAC)
	b[0x2f] = 0x01
	b[0x31] = v.assignFlag()
	return b
}

func (v VCDJ) defense() []byte {
	b := append([]byte(nil), tmplDefense...)
	v.name(b)
	b[0x24] = v.Device
	copy(b[0x25:0x29], v.IP.To4())
	return b
}

func (v VCDJ) keepAlive() []byte {
	b := append([]byte(nil), tmplKeepAlive...)
	v.name(b)
	b[0x24] = v.Device
	copy(b[0x26:0x2c], v.MAC)
	copy(b[0x2c:0x30], v.IP.To4())
	return b
}

func (v VCDJ) assignFlag() byte {
	if v.Device == 0 {
		return 0x01
	}
	return 0x02
}

+          v.logf("mixer assigned device %d", n)


		ok, err := claim(num)
		if err != nil {
			return err
		}
		if ok {
			break
		}
		if !auto {
			return errors.Errorf("device number %d defended by another device", num)
		}
	}

	online.Store(true)
	claiming.Store(0)

		ok, err := claim(num)
		if err != nil {
			return err
		}
		if ok {
			break
		}
		if !auto {
			return errors.Errorf("device number %d defended by another device", num)
		}
		v.logf("device %d defended, trying another", num)
	}

	online.Store(true)
	claiming.Store(0)
	v.logf("online as device %d", v.Device)


		ok, err := claim(num)
		if err != nil {
			return err
		}
		if ok {
			break
		}
		if !auto {
			return errors.Errorf("device number %d defended by another device", num)
		}
		v.logf("device %d defended, trying another", num)
	}

	online.Store(true)
	claiming.Store(0)
	v.logf("online as device %d", v.Device)

package link

import (
	"bytes"
	"context"
	"encoding/hex"
	"fmt"
	"net"
	"sync"
	"sync/atomic"
	"time"

	"github.com/cockroachdb/errors"
)

// Packet types exchanged while a virtual CDJ comes online, interpreted on port
// 50000. A player sends hello, then three device-number claim stages, before
// keep-alives; a mixer may interrupt to assign a number, and any device
// defends a number it already owns. See
// https://djl-analysis.deepsymmetry.org/djl-analysis/startup.html#cdj-startup
const (
	TypeClaim1         Type = 0x00
	TypeWillAssign     Type = 0x01
	TypeClaim2         Type = 0x02
	TypeAssign         Type = 0x03
	TypeClaim3         Type = 0x04
	TypeAssignFinished Type = 0x05
	TypeDefense        Type = 0x08
	TypeHello          Type = 0x0a
)

// ClaimInterval is the gap between packets within a startup stage.
const ClaimInterval = 300 * time.Millisecond

// KeepAliveInterval is the gap between keep-alive packets once online.
const KeepAliveInterval = 1500 * time.Millisecond

// WatchPeriod is how long to observe keep-alives before self-assigning, so we
// avoid claiming a number already in use.
const WatchPeriod = 2 * time.Second

// Packet templates copied verbatim from beat-link; per-device fields (name,
// number, MAC, IP, packet counter) are patched into a copy before sending.
var (
	tmplAssign    = mustHex("5173707431576d4a4f4c0201626561742d6c696e6b0000000000000000000000010200320000000000000000000000000100")
	tmplClaim1    = mustHex("5173707431576d4a4f4c0000626561742d6c696e6b00000000000000000000000103002c0d01000000000000")
	tmplClaim2    = mustHex("5173707431576d4a4f4c0200626561742d6c696e6b000000000000000000000001030032000000000000000000000d000100")
	tmplClaim3    = mustHex("5173707431576d4a4f4c0400626561742d6c696e6b0000000000000000000000010300260d00")
	tmplDefense   = mustHex("5173707431576d4a4f4c0800626561742d6c696e6b0000000000000000000000010200290000000000")
	tmplHello     = mustHex("5173707431576d4a4f4c0a00626561742d6c696e6b0000000000000000000000010400260140")
	tmplKeepAlive = mustHex("5173707431576d4a4f4c0600626561742d6c696e6b000000000000000000000001020036000100000000000000000000020000000164")
)

func mustHex(s string) []byte {
	b, err := hex.DecodeString(s)
	if err != nil {
		panic(err)
	}
	return b
}

// SelfAssign returns the lowest player number not in used that is greater than
// after, starting no lower than 5 (the first number a CDJ-3000 may take) and
// stopping below the 33+ range mixers use.
func SelfAssign(used map[byte]bool, after byte) (byte, bool) {
	n := after + 1
	if n < 5 {
		n = 5
	}
	for ; n <= 15; n++ {
		if !used[n] {
			return n, true
		}
	}
	return 0, false
}

// VCDJ is a virtual CDJ that participates in the network so real players send
// it status, metadata, and database access. Device 0 means self-assign.
type VCDJ struct {
	Device byte
	IP     net.IP
	Log    func(string)
	MAC    net.HardwareAddr
	Name   string
}

func (v VCDJ) logf(format string, args ...any) {
	if v.Log != nil {
		v.Log(fmt.Sprintf(format, args...))
	}
}

// Online brings the virtual CDJ online and holds its device number until ctx is
// done. It owns conn (bound to port 50000): it runs the claim handshake while
// reacting to defenses and mixer assignments, then sends keep-alives and
// defends its number. Every received datagram is passed to onPacket so callers
// can record it.
func (v *VCDJ) Online(ctx context.Context, conn *net.UDPConn, ipNet *net.IPNet, onPacket func([]byte, *net.UDPAddr)) error {
	v.IP = ipNet.IP
	dst := &net.UDPAddr{IP: Broadcast(ipNet), Port: 50000}

	var (
		assigned atomic.Int32
		claiming atomic.Int32
		online   atomic.Bool
		rejected atomic.Bool
		seen     sync.Map
	)

	send := func(b []byte, to *net.UDPAddr) {
		conn.WriteToUDP(b, to)
	}

	handle := func(b []byte, src *net.UDPAddr) {
		if len(b) < 0x25 || !bytes.Equal(b[:len(Magic)], Magic) {
			return
		}
		peer := &net.UDPAddr{IP: src.IP, Port: 50000}
		switch Type(b[0x0a]) {
		case TypeKeepAlive:
			seen.Store(b[0x24], true)
		case TypeWillAssign:
			if claiming.Load() != 0 {
				send(v.assignRequest(), peer)
			}
		case TypeAssign:
			assigned.Store(int32(b[0x24]))
		case TypeAssignFinished:
			assigned.Store(claiming.Load())
		case TypeDefense:
			if b[0x24] == byte(claiming.Load()) {
				rejected.Store(true)
			}
		case TypeClaim2:
			if online.Load() && len(b) > 0x2e && b[0x2e] == v.Device {
				v.logf("defending device %d against %s", v.Device, src.IP)
				send(v.defense(), peer)
			}
		case TypeClaim3:
			if online.Load() && b[0x24] == v.Device {
				v.logf("defending device %d against %s", v.Device, src.IP)
				send(v.defense(), peer)
			}
		}
	}

	errc := make(chan error, 1)
	go func() {
		go func() { <-ctx.Done(); conn.SetReadDeadline(time.Now()) }()
		buf := make([]byte, 1500)
		for {
			n, src, err := conn.ReadFromUDP(buf)
			if err != nil {
				if ctx.Err() != nil {
					errc <- nil
				} else {
					errc <- errors.WithStack(err)
				}
				return
			}
			b := append([]byte(nil), buf[:n]...)
			handle(b, src)
			if onPacket != nil {
				onPacket(b, src)
			}
		}
	}()

	wait := func(d time.Duration) error {
		select {
		case <-ctx.Done():
			return errors.WithStack(ctx.Err())
		case err := <-errc:
			if err == nil {
				err = errors.New("listener stopped")
			}
			return err
		case <-time.After(d):
			return nil
		}
	}

	for i := 0; i < 3; i++ {
		send(v.hello(), dst)
		if err := wait(ClaimInterval); err != nil {
			return err
		}
	}

	auto := v.Device == 0
	if auto {
		if err := wait(WatchPeriod); err != nil {
			return err
		}
	}

	claim := func(num byte) (bool, error) {
		v.Device = num
		claiming.Store(int32(num))
		rejected.Store(false)
		assigned.Store(0)

		stages := [][]func(byte) []byte{
			{v.claim1}, {v.claim2}, {v.claim3},
		}
		for s, stage := range stages {
			if s == 2 {
				if n := assigned.Swap(0); n > 0 {
					v.logf("mixer assigned device %d", n)
					v.Device = byte(n)
					claiming.Store(n)
				}
			}
			for i := byte(1); i <= 3 && assigned.Load() == 0; i++ {
				send(stage[0](i), dst)
				if err := wait(ClaimInterval); err != nil {
					return false, err
				}
				if rejected.Load() {
					return false, nil
				}
			}
		}
		return true, nil
	}

	var after byte
	for {
		num := v.Device
		if auto {
			n, ok := SelfAssign(usedNumbers(&seen), after)
			if !ok {
				return errors.New("no available device number")
			}
			num, after = n, n
		}

		ok, err := claim(num)
		if err != nil {
			return err
		}
		if ok {
			break
		}
		if !auto {
			return errors.Errorf("device number %d defended by another device", num)
		}
	}

	online.Store(true)
	claiming.Store(0)

	t := time.NewTicker(KeepAliveInterval)
	defer t.Stop()
	for {
		send(v.keepAlive(), dst)
		select {
		case <-ctx.Done():
			return nil
		case err := <-errc:
			return err
		case <-t.C:
		}
	}
}

func usedNumbers(seen *sync.Map) map[byte]bool {
	used := map[byte]bool{}
	seen.Range(func(k, _ any) bool {
		used[k.(byte)] = true
		return true
	})
	return used
}

func (v VCDJ) name(b []byte) {
	for i := 0; i < 0x14; i++ {
		b[0x0c+i] = 0
	}
	copy(b[0x0c:0x0c+0x14], v.Name)
}

func (v VCDJ) hello() []byte {
	b := append([]byte(nil), tmplHello...)
	v.name(b)
	return b
}

func (v VCDJ) claim1(counter byte) []byte {
	b := append([]byte(nil), tmplClaim1...)
	v.name(b)
	b[0x24] = counter
	copy(b[0x26:0x2c], v.MAC)
	return b
}

func (v VCDJ) claim2(counter byte) []byte {
	b := append([]byte(nil), tmplClaim2...)
	v.name(b)
	copy(b[0x24:0x28], v.IP.To4())
	copy(b[0x28:0x2e], v.MAC)
	b[0x2e] = v.Device
	b[0x2f] = counter
	b[0x31] = v.assignFlag()
	return b
}

func (v VCDJ) claim3(counter byte) []byte {
	b := append([]byte(nil), tmplClaim3...)
	v.name(b)
	b[0x24] = v.Device
	b[0x25] = counter
	return b
}

func (v VCDJ) assignRequest() []byte {
	b := append([]byte(nil), tmplAssign...)
	v.name(b)
	copy(b[0x24:0x28], v.IP.To4())
	copy(b[0x28:0x2e], v.MAC)
	b[0x2f] = 0x01
	b[0x31] = v.assignFlag()
	return b
}

func (v VCDJ) defense() []byte {
	b := append([]byte(nil), tmplDefense...)
	v.name(b)
	b[0x24] = v.Device
	copy(b[0x25:0x29], v.IP.To4())
	return b
}

func (v VCDJ) keepAlive() []byte {
	b := append([]byte(nil), tmplKeepAlive...)
	v.name(b)
	b[0x24] = v.Device
	copy(b[0x26:0x2c], v.MAC)
	copy(b[0x2c:0x30], v.IP.To4())
	return b
}

func (v VCDJ) assignFlag() byte {
	if v.Device == 0 {
		return 0x01
	}
	return 0x02
}

+    v.logf("device %d defended, trying another", num)

+  v.logf("online as device %d", v.Device)


Now wire the logger in the capture tool:


		return &link.VCDJ{
			Device: device,
			MAC:    iface.HardwareAddr,
			Name:   name,
		}, ipNet, nil

		return &link.VCDJ{
			Device: device,
			Log:    func(s string) { fmt.Fprintln(os.Stderr, s) },
			MAC:    iface.HardwareAddr,
			Name:   name,
		}, ipNet, nil


		return &link.VCDJ{
			Device: device,
			Log:    func(s string) { fmt.Fprintln(os.Stderr, s) },
			MAC:    iface.HardwareAddr,
			Name:   name,
		}, ipNet, nil

// Command capture records raw Pro DJ Link UDP datagrams to a JSONL fixture.
//
// It listens on the DJ Link discovery, beat, and status ports and writes one
// Packet per line so tests can replay real traffic without hardware. With
// -announce it first brings a virtual CDJ online (the full startup handshake)
// so real players send status, metadata, and database traffic to it.
package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"net"
	"os"
	"os/signal"
	"time"

	"github.com/cockroachdb/errors"
	"github.com/nzoschke/deadca7/link"
	"golang.org/x/sync/errgroup"
)

// Packet is one recorded UDP datagram.
type Packet struct {
	Data string `json:"data"`
	Len  int    `json:"len"`
	Port int    `json:"port"`
	Src  string `json:"src"`
	TS   int64  `json:"ts"`
}

func main() {
	announce := flag.Bool("announce", false, "bring a virtual CDJ online while capturing")
	device := flag.Int("device", 5, "virtual CDJ device number")
	name := flag.String("name", "deadca7", "virtual CDJ device name")
	out := flag.String("out", "capture.jsonl", "output JSONL fixture path")
	secs := flag.Int("secs", 8, "capture duration in seconds")
	flag.Parse()

	if err := run(*out, time.Duration(*secs)*time.Second, *announce, byte(*device), *name); err != nil {
		fmt.Fprintf(os.Stderr, "%+v\n", err)
		os.Exit(1)
	}
}

func run(out string, d time.Duration, announce bool, device byte, name string) error {
	f, err := os.Create(out)
	if err != nil {
		return errors.WithStack(err)
	}
	defer f.Close()

	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
	defer cancel()
	ctx, cancel = context.WithTimeout(ctx, d)
	defer cancel()

	c0, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 50000})
	if err != nil {
		return errors.WithStack(err)
	}
	defer c0.Close()
	if err := link.SetBroadcast(c0); err != nil {
		return err
	}

	c1, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 50001})
	if err != nil {
		return errors.WithStack(err)
	}
	defer c1.Close()

	c2, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 50002})
	if err != nil {
		return errors.WithStack(err)
	}
	defer c2.Close()

	var vcdj *link.VCDJ
	var ipNet *net.IPNet
	if announce {
		vcdj, ipNet, err = online(c0, device, name)
		if err != nil {
			return err
		}
	}

	enc := json.NewEncoder(f)
	pkts := make(chan Packet)
	record := func(b []byte, src *net.UDPAddr) {
		select {
		case pkts <- packet(b, 50000, src):
		case <-ctx.Done():
		}
	}

	g, ctx := errgroup.WithContext(ctx)
	g.Go(func() error { return listen(ctx, c1, 50001, pkts) })
	g.Go(func() error { return listen(ctx, c2, 50002, pkts) })

	if announce {
		g.Go(func() error {
			err := vcdj.Online(ctx, c0, ipNet, record)
			fmt.Fprintf(os.Stderr, "virtual CDJ %q ran as device %d\n", vcdj.Name, vcdj.Device)
			return err
		})
	} else {
		g.Go(func() error { return listen(ctx, c0, 50000, pkts) })
	}

	g.Go(func() error {
		n := 0
		for {
			select {
			case <-ctx.Done():
				fmt.Fprintf(os.Stderr, "captured %d packets to %s\n", n, out)
				return nil
			case p := <-pkts:
				if err := enc.Encode(p); err != nil {
					return errors.WithStack(err)
				}
				n++
			}
		}
	})

	if err := g.Wait(); err != nil && !errors.Is(err, context.DeadlineExceeded) {
		return err
	}
	return nil
}

// online discovers a real device to learn the local interface, then returns a
// virtual CDJ and its IPv4 network for announcing.
func online(c0 *net.UDPConn, device byte, name string) (*link.VCDJ, *net.IPNet, error) {
	c0.SetReadDeadline(time.Now().Add(5 * time.Second))
	defer c0.SetReadDeadline(time.Time{})

	buf := make([]byte, 1500)
	for {
		n, _, err := c0.ReadFromUDP(buf)
		if err != nil {
			return nil, nil, errors.WithStack(err)
		}
		k, err := link.DecodeKeepAlive(buf[:n])
		if err != nil || k.Device == device {
			continue
		}

		iface, ipNet, err := link.Iface(k.IP)
		if err != nil {
			return nil, nil, err
		}
		return &link.VCDJ{
			Device: device,
			MAC:    iface.HardwareAddr,
			Name:   name,
		}, ipNet, nil
	}
}

func packet(b []byte, port int, src *net.UDPAddr) Packet {
	return Packet{
		Data: fmt.Sprintf("%x", b),
		Len:  len(b),
		Port: port,
		Src:  src.String(),
		TS:   time.Now().UnixMilli(),
	}
}

func listen(ctx context.Context, c *net.UDPConn, port int, pkts chan<- Packet) error {
	go func() {
		<-ctx.Done()
		c.SetReadDeadline(time.Now())
	}()

	buf := make([]byte, 1500)
	for {
		n, addr, err := c.ReadFromUDP(buf)
		if err != nil {
			if ctx.Err() != nil {
				return nil
			}
			return errors.WithStack(err)
		}
		select {
		case pkts <- packet(buf[:n], port, addr):
		case <-ctx.Done():
			return nil
		}
	}
}

+      Log:    func(s string) { fmt.Fprintln(os.Stderr, s) },


Bash

cd /Users/noah/conductor/workspaces/deadca7/san-diego/link && go vet ./... 2>&1 | tail -5 && go test ./... 2>&1 | tail -3

Vet and test with logging


ok  	github.com/nzoschke/deadca7/link	0.224s
?   	github.com/nzoschke/deadca7/link/cmd/capture	[no test files]


I'll run a quick 6-second baseline with device 5 to verify the logging is wired correctly, then walk through both experiments with the user and get them set up.


Let me do a quick baseline run to confirm the event logging works before we set up the conflict:


go run ./cmd/capture -announce -device 5 -out /tmp/base.jsonl -secs 6 2>&1 | grep -vE '^\{' | head

Baseline run to confirm event logging


online as device 5
virtual CDJ "deadca7" ran as device 5
captured 135 packets to /tmp/base.jsonl


 Now that logging is working, I need to set up two clear test scenarios: one where we defend our claimed number against a real CDJ trying to take it, and another where a real CDJ owns a number and we attempt to claim it while handling the abort response.

For the first experiment, I'll have the second CDJ powered off initially with its player number fixed to 4, then start our virtual CDJ as device 4 to go online cleanly. Once confirmed, the user powers on the real CDJ-4, which broadcasts claim packets that trigger our defense mechanism—we should see the defense-out message in stderr and the real CDJ gets forced off the channel.

For the second experiment, the real CDJ comes online first as device 4, then our virtual CDJ attempts to claim the same number, gets hit with the 0x08 defense response, and aborts with an error message—that rejection in stderr is our evidence the defense-in path works.

I'm also considering an auto-assignment test where the second CDJ sits at device 5 and we run with `-device 0`, but that's tricky to force deterministically since the self-assign logic just skips already-seen numbers. The fixed-number defense scenarios are cleaner and directly test what the user wants—forcing the conflict to validate the defend path.

So I'll prioritize Experiment 1 first (defense outbound), then Experiment 2 as a bonus that also captures a real 0x08 packet for the fixture. For Experiment 1, I need to coordinate with the user: start a background capture while they power on the second CDJ mid-capture. I'll ask them to confirm the second CDJ is set to player 4 and currently off, then kick off a 45-second capture and tell them when to power it on. The second CDJ absolutely needs to be set to fixed player number 4 to trigger the conflict — if it's on auto, it'll grab 1 or 2 instead and we won't see the defense mechanism. So I need to give them that instruction clearly before we start, then begin the background capture with precise timing for when they should power it on. I'll go ahead and start the capture with clear instructions for them to configure the device to player 4 and power it on after a few seconds—if it defaults to auto-assign instead, we'll see no defense activity and know to adjust the setup.


Logging works (`online as device 5`). Now let's force the conflict to test the **defend path** for real.

Here's the key constraint that determines the setup: our virtual CDJ will claim and hold **device 4**. For the defense to trigger, the second CDJ must try to take **the same number (4)**. A CDJ left on *auto* will just grab the lowest free number (1 or 2) and avoid the conflict — so the second player needs to be **fixed to player number 4**.

I'll start a 45-second background capture now. Our virtual CDJ claims device 4 while your second player is still off; then you power it on and we watch it collide.


go run ./cmd/capture -announce -device 4 -out testdata/defense_out.jsonl -secs 45 2>&1; echo "EXIT=$?"

Defense-OUT experiment: hold device 4, capture conflict


Command running in background with ID: b89tezv8z. Output is being written to: /private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/b89tezv8z.output. You will be notified when it completes. To check interim output, use Read on that file path.


🎬 **Capturing now (45s) — our virtual CDJ is claiming and holding device 4.**

Please do this:

1. **Set your second CDJ to a *fixed* player number 4** (Menu/Utility → Player No., not Auto) — otherwise it'll auto-pick 1 or 2 and won't collide.
2. **Wait ~8 seconds** from now (let our virtual CDJ finish claiming 4 and go online), then **power it on / connect it to the link network.**

What I expect to see when it tries to take 4:
- our log: `defending device 4 against 192.168.0.x` (this is the untested defense-OUT path firing), and
- the real CDJ-4 getting forced off channel 4 (it should show a player-number conflict / fail to join at 4).

I'll read the capture + our event log as soon as the 45s window finishes and tell you whether the defense worked. If your player was on auto and grabbed a different number, no harm — we'll just rerun with it fixed to 4.


<task-notification>
<task-id>b89tezv8z</task-id>
<tool-use-id>toolu_01RyCDe624AWzmsPmLtR3EiM</tool-use-id>
<output-file>/private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/b89tezv8z.output</output-file>
<status>completed</status>
<summary>Background command "Defense-OUT experiment: hold device 4, capture conflict" completed (exit code 0)</summary>
</task-notification>


cd /Users/noah/conductor/workspaces/deadca7/san-diego/link
echo "=== event log (stderr) ==="; grep -vE '^\{' /private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/b89tezv8z.output | sort | uniq -c
echo "=== devices seen on 50000 keepalives (0x06) ==="; python3 -c '
import json,collections
ka=collections.OrderedDict()
for l in open("testdata/defense_out.jsonl"):
    p=json.loads(l); d=bytes.fromhex(p["data"])
    if p["port"]==50000 and len(d)>0x24 and d[:10]==bytes.fromhex("5173707431576d4a4f4c") and d[0x0a]==0x06:
        src=p["src"].split(":")[0]; ka[(src,d[0x24])]=ka.get((src,d[0x24]),0)+1
for (src,dev),c in ka.items(): print(f"  {src:15} device={dev} keepalives={c}")
'
echo "=== claim packets seen (who tried to claim what) ==="; python3 -c '
import json,collections
c=collections.OrderedDict()
for l in open("testdata/defense_out.jsonl"):
    p=json.loads(l); d=bytes.fromhex(p["data"])
    if p["port"]==50000 and d[:10]==bytes.fromhex("5173707431576d4a4f4c") and d[0x0a] in (0x00,0x02,0x04,0x08):
        src=p["src"].split(":")[0]
        num = d[0x2e] if d[0x0a]==0x02 and len(d)>0x2e else (d[0x24] if len(d)>0x24 else "?")
        key=(src,f"0x{d[0x0a]:02x}",num); c[key]=c.get(key,0)+1
for (src,t,num),n in c.items(): print(f"  {src:15} type={t} num={num} count={n}")
'

Analyze defense-out experiment


=== event log (stderr) ===
   1 EXIT=0
   1 captured 1887 packets to testdata/defense_out.jsonl
   1 online as device 4
   1 virtual CDJ "deadca7" ran as device 4
=== devices seen on 50000 keepalives (0x06) ===
  192.168.0.193   device=33 keepalives=22
  192.168.0.192   device=3 keepalives=21
  192.168.0.160   device=4 keepalives=28
=== claim packets seen (who tried to claim what) ===
  192.168.0.160   type=0x00 num=1 count=1
  192.168.0.160   type=0x00 num=2 count=1
  192.168.0.160   type=0x00 num=3 count=1
  192.168.0.160   type=0x02 num=4 count=3
  192.168.0.160   type=0x04 num=4 count=1


 Looking at the network capture, our virtual CDJ came online as device 4 with consistent keepalives, but the second CDJ never actually joined the network—there were no new IP addresses or claim packets from any other device besides ours, only the DJM mixer and the existing CDJ-3 visible on the network.

Since no conflict occurred, the second player likely wasn't powered on or connected in time, or it's not on the same link network. I should ask the user to confirm the second CDJ is actually connected and set to fixed player 4, then retry with a longer capture window and clearer timing instructions—maybe 60 seconds with the second CDJ powered on about 10 seconds in. I'm also noting that our claim sequence looks correct (claim2 and claim4 both show device 4 with the right counter progression), so the handshake itself is working fine.

Actually, thinking about this more—CDJs take 20-30 seconds to boot, so if they powered it on during the capture, it might not have joined the network in time. The cleanest approach is to use a much longer window like 90 seconds and have them power on the second CDJ right when I start the capture. Since our virtual player claims device 4 in about 3.6 seconds, we'll own it well before the booting CDJ joins the network and tries to claim it. Let me restart with that longer window.


The capture is clean but **no second player ever appeared** — the only devices on the network were CDJ-3 (`.192`), the DJM-V10 (`.193`), and our virtual CDJ holding device 4 (`.160`, 28 keep-alives). The only claim packets were our own handshake. So the conflict never happened — likely the second CDJ wasn't connected/booted within the 45s window (CDJs take 20–30s just to cold-boot and join link).

Let me retry with a **90-second window** to absorb the boot time. Our virtual CDJ grabs device 4 in ~4s, so it'll already own it before the second player finishes booting.


go run ./cmd/capture -announce -device 4 -out testdata/defense_out.jsonl -secs 90 2>&1; echo "EXIT=$?"

Retry defense-out with 90s window


Command running in background with ID: bdasqjar0. Output is being written to: /private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/bdasqjar0.output. You will be notified when it completes. To check interim output, use Read on that file path.


I've started the 90-second capture and now I'm instructing the user to power on the second CDJ, which is fixed to player 4, so it can boot during this window while I wait for it to complete.


🎬 **Capturing again — 90s window this time.** Our virtual CDJ is claiming device 4 right now.

**Go ahead and power on the second CDJ now** — it can take the full boot time; the window is long enough. Two things to double-check:
1. It's **set to fixed Player No. 4** (not Auto), and
2. It's **on the same link network** (ethernet to the same switch/router as CDJ-3 and the DJM).

When it boots and tries to claim 4, we should see our `defending device 4 against …` log fire and the player get bounced off channel 4. I'll analyze as soon as the 90s completes.


sorry I missed this, start the capture over


<task-notification>
<task-id>bdasqjar0</task-id>
<tool-use-id>toolu_01SVocLeff2uUGu6z6DjSrKJ</tool-use-id>
<output-file>/private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/bdasqjar0.output</output-file>
<status>failed</status>
<summary>Background command "Retry defense-out with 90s window" failed with exit code 144</summary>
</task-notification>


I need to check if the previous background task is still running since it had a 90-second window and might be done by now. Before starting a fresh one, I should verify there's no port conflict on 50000, so I'll stop the old task first if it's still active.


No problem. Let me make sure the previous capture isn't still holding the UDP ports, then start fresh.


pkill -f 'cmd/capture' 2>/dev/null; sleep 1; echo "cleared any running capture"

Stop any running capture process


cleared any running capture


Prompt:
<task-notification>
<task-id>bdasqjar0</task-id>
<tool-use-id>toolu_01SVocLeff2uUGu6z6DjSrKJ</tool-use-id>
<output-file>/private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/bdasqjar0.output</output-file>
<status>failed</status>
<summary>Background command "Retry defense-out with 90s window" failed with exit code 144</summary>
</task-notification>


The previous task was terminated, so I'm starting a fresh 90-second capture now.


Previous capture killed cleanly. Starting a fresh 90-second window now.


cd /Users/noah/conductor/workspaces/deadca7/san-diego/link && go run ./cmd/capture -announce -device 4 -out testdata/defense_out.jsonl -secs 90 2>&1; echo "EXIT=$?"

Fresh 90s defense-out capture


Command running in background with ID: bucsz0z8x. Output is being written to: /private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/bucsz0z8x.output. You will be notified when it completes. To check interim output, use Read on that file path.


🎬 **Capturing now — fresh 90s window.** Our virtual CDJ is claiming and holding **device 4**.

**Power on the second CDJ now** (it can boot during the window). Confirm:
1. **Fixed Player No. 4** (not Auto), and
2. **On the same link network** as CDJ-3 and the DJM.

When it tries to take 4, we should see `defending device 4 against …` fire. I'll analyze the moment the 90s completes.


looks right on the CDJ it looks like it gets then loses 4 over and over again


<task-notification>
<task-id>bucsz0z8x</task-id>
<tool-use-id>toolu_01DHnUwQBaxCaUZZ3qMaDVyY</tool-use-id>
<output-file>/private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/bucsz0z8x.output</output-file>
<status>completed</status>
<summary>Background command "Fresh 90s defense-out capture" completed (exit code 0)</summary>
</task-notification>


So the defense mechanism is working as intended — the real CDJ-4 keeps attempting to claim device 4, we block it, it backs off, then tries again. That cycle repeating in the logs confirms the defense-OUT path is firing. I'm checking the interim capture output to verify those "defending device 4 against..." log entries are appearing, though it looks like the JSON output might be incomplete.


That's the defense working — the real CDJ grabs 4, we defend, it backs off, then retries, repeat. Let me peek at the live event log to confirm our defense is what's bouncing it.


grep -c 'defending device 4' /private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/bucsz0z8x.output 2>/dev/null | xargs echo "defending events so far:"; echo "--- sample defending lines ---"; grep 'defending device 4' /private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/bucsz0z8x.output 2>/dev/null | tail -5

Check live defense event log


defending events so far: 28
--- sample defending lines ---
defending device 4 against 192.168.0.194
defending device 4 against 192.168.0.194
defending device 4 against 192.168.0.194
defending device 4 against 192.168.0.194
defending device 4 against 192.168.0.194


Prompt:
<task-notification>
<task-id>bucsz0z8x</task-id>
<tool-use-id>toolu_01DHnUwQBaxCaUZZ3qMaDVyY</tool-use-id>
<output-file>/private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/bucsz0z8x.output</output-file>
<status>completed</status>
<summary>Background command "Fresh 90s defense-out capture" completed (exit code 0)</summary>
</task-notification>


**Defense-OUT path confirmed working live.** The second CDJ at `192.168.0.194` repeatedly tried to claim device 4, and our virtual CDJ defended **28 times** — that's exactly the "gets then loses 4 over and over" you saw on the player. Let me do a full analysis of the completed capture.