### Discovery / keep-alive — 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
- [ ] mixer/gateway packet seen on 50002 (type 0x40, "NXS-GW") — identify & decode
- [ ] full announce/channel-negotiation handshake (claim device # 1-4)
- [ ] virtual CDJ Announce + KeepAlive sender (prereq for all active flows)

### Beat sync — port 50001
- [ ] beat packet (type 0x28): BPM, beat-within-bar, pitch, next/prev beat timing
- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

# 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 / keep-alive — port 50000
- [x] keep-alive (type 0x06): name, device #, IP, MAC — `testdata/keepalive.jsonl`
- [ ] mixer/gateway packet seen on 50002 (type 0x40, "NXS-GW") — identify & decode
- [ ] full announce/channel-negotiation handshake (claim device # 1-4)
- [ ] virtual CDJ Announce + KeepAlive sender (prereq for all active flows)

### Beat sync — port 50001
- [ ] beat packet (type 0x28): BPM, beat-within-bar, pitch, next/prev beat timing
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002
- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] mixer status (DJM) if present
- [ ] 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)

- [ ] replace `time.Sleep(5s)` FIXME in `Start()` with discovery/mount readiness
- [ ] make the media query deterministic (vizlab's was "unreliable")
- [ ] swap `github.com/pkg/errors` → `github.com/cockroachdb/errors`
- [ ] live integration suite gated behind `testing.Short()` / env, separate from
      the hermetic fixture-replay tests

-- [x] keep-alive (type 0x06): name, device #, IP, MAC — `testdata/keepalive.jsonl`

+- [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

+- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode


Captured the mixer. Both devices now in one fixture and under test.

## Results

`testdata/devices.jsonl` (37 packets, 8s) now has both devices, and `TestDecodeKeepAlive` is table-driven over them — both pass:

| Device | # | IP | MAC | Ports seen |
|---|---|---|---|---|
| CDJ-3000 | 3 | 192.168.0.192 | c8:3d:fc:11:26:c2 | 50000 (`0x06`), 50002 (`0x40` "NXS-GW") |
| DJM-V10 | 33 | 192.168.0.193 | c8:3d:fc:12:9e:d5 | 50000 (`0x06`), 50001 (`0x03`, ~3/s) |

Key takeaways:
- **Mixer keep-alive decodes with the existing `DecodeKeepAlive`** — no new code needed. Note mixers claim a high channel number (33), unlike CDJs (1–4).
- **New unknowns to decode** (recorded in `TODO.md`): the CDJ's `0x40`/50002 "NXS-GW" gateway packet, and the DJM-V10's steady `0x03`/50001 stream — which uses a *different framing* (device name at offset `0x0b`, not `0x0c`). Good to have caught that framing difference from a real capture rather than guessing.

I consolidated the two single-device fixtures into one `devices.jsonl` and deleted the redundant `keepalive.jsonl`.

Since the mixer is providing a steady beat-port stream, a natural next step is the **virtual-CDJ announce sender** (unlocks active status/metadata/NFS), or decoding the two unknown packet types now that we have real samples of both. Which would you like next?


lets do more passive packets... let me know and I can start playing a track


 I'm thinking through what happens when a track starts playing—the CDJ sends beat packets on port 50001, and there are status packets on port 50002, but I need to clarify whether those status packets are broadcast passively or only sent to specific devices that have announced themselves.

The empirical approach makes sense: I'll start a longer capture in the background while the user plays a track, then analyze what actually appears on the network. I'll run the capture for about 45 seconds and tell them to start playing now—that gives them time to load a track, hit play, and do various actions while I'm capturing. Once the background task finishes, I can analyze the results and see exactly what traffic we're getting passively. I'll extend the capture window to 60 seconds and guide the user through specific actions to generate different packet types—loading tracks, pressing play, adjusting jog/pitch, changing tempo and faders, and cueing—so we can capture the full range of behavior.


Let me start a longer passive capture in the background so you have time to play. I'll have it record for 60s on all three ports.


Bash

cd /Users/noah/conductor/workspaces/deadca7/san-diego/link && go run ./cmd/capture -out testdata/playing.jsonl -secs 60 2>&1; echo "DONE exit=$?"; wc -l testdata/playing.jsonl

60s passive capture while track plays


Command running in background with ID: bc9oek0nc. Output is being written to: /private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/bc9oek0nc.output. You will be notified when it completes. To check interim output, use Read on that file path.


🎬 **Capturing now for 60 seconds → `testdata/playing.jsonl`.** Go ahead and play a track. To exercise as many distinct packet types as possible, if you can, run through these during the window:

1. **Load a track** onto the CDJ-3000
2. **Press play** (this kicks off beat packets on 50001)
3. **Nudge the jog wheel** / pitch-bend
4. **Move the tempo/pitch fader** (a tempo change shows up in the beat stream)
5. **Raise/lower the channel fader** on the DJM-V10 (on-air state) and the **crossfader**
6. **Hit cue / pause**

No need to rush or hit all of them — anything you do will show up. I'll analyze what arrived as soon as the 60s capture finishes and report which packet types we got (and what's still missing because it needs an announced virtual CDJ).


<task-notification>
<task-id>bc9oek0nc</task-id>
<tool-use-id>toolu_01Pf3uyYVSuspsPTh7zsuXEJ</tool-use-id>
<output-file>/private/tmp/claude-501/-Users-noah-conductor-workspaces-deadca7-san-diego/5e143c63-1d6b-4233-91af-bb63e39e8beb/tasks/bc9oek0nc.output</output-file>
<status>completed</status>
<summary>Background command "60s passive capture while track plays" completed (exit code 0)</summary>
</task-notification>


cd /Users/noah/conductor/workspaces/deadca7/san-diego/link && python3 -c '
import json,collections
seen=collections.OrderedDict()
for line in open("testdata/playing.jsonl"):
    p=json.loads(line); d=bytes.fromhex(p["data"])
    magic=d[:10]==bytes.fromhex("5173707431576d4a4f4c")
    typ=d[0x0a] if magic and len(d)>0x0a else None
    key=(p["src"].split(":")[0],p["port"],typ)
    e=seen.setdefault(key,[0,set()]); e[0]+=1; e[1].add(p["len"])
print("total lines:",sum(1 for _ in open("testdata/playing.jsonl")))
for (src,port,typ),(cnt,lens) in sorted(seen.items()):
    t=f"0x{typ:02x}" if typ is not None else "??"
    print(f"{src:15} port={port} type={t} count={cnt:4} lens={sorted(lens)}")
'

Summarize playing capture by device/port/type


total lines: 314
192.168.0.192   port=50000 type=0x06 count=  28 lens=[54]
192.168.0.192   port=50001 type=0x28 count=  28 lens=[96]
192.168.0.192   port=50002 type=0x40 count=  30 lens=[38]
192.168.0.193   port=50000 type=0x06 count=  30 lens=[54]
192.168.0.193   port=50001 type=0x03 count= 198 lens=[53]


 So the beat packets (0x28) are coming through on port 50001 — that's the key discovery here. The gateway keepalive (0x40) is still there on 50002, and the mixer continues streaming, but notably we're not seeing the full CDJ status packets (0x0a) without announcing ourselves as a virtual CDJ. The beat packets alone are valuable though, since they broadcast whenever something's playing.

Now I'm noticing the count seems low — 28 packets in 60 seconds is only about 0.5 per second, but at typical BPM (around 120) we'd expect roughly 2 per second. This suggests the track wasn't playing continuously throughout the capture window, or the tempo was much slower. Either way, we're getting beat packets now, which is progress.

I need to decode one of these 0x28 packets to extract the actual BPM, beat position within the bar, and player number. The structure has the device name starting at offset 0x0b, BPM at 0x5a (2 bytes, big-endian, divided by 100), beat-in-bar at 0x5c, and the player/device number at 0x5f. Let me pull a sample packet and parse those fields.

Printing the decoded packets to verify the beat-in-bar cycles through 1-2-3-4 as expected...


Beat packets arrived. Big new data: **CDJ-3000 type `0x28` on 50001 (beat packets, len 96)** — that's the playing track's beat stream. Let me decode a few to confirm the BPM / beat-in-bar / pitch fields line up.


python3 -c '
import json
beats=[bytes.fromhex(json.loads(l)["data"]) for l in open("testdata/playing.jsonl")
       if json.loads(l)["port"]==50001 and bytes.fromhex(json.loads(l)["data"])[0x0a]==0x28]
print("beat packets:",len(beats))
b=beats[0]
print("sample hex:",b.hex())
print("name@0x0b:",b[0x0b:0x1f].rstrip(b"\x00").decode("latin1"))
import struct
for i,b in enumerate(beats[:8]):
    bpm=struct.unpack(">H",b[0x5a:0x5c])[0]/100
    beat=b[0x5c]
    pitch=struct.unpack(">I",b[0x54:0x58])[0]
    dev=b[0x5f]
    print(f"  #{i} dev={dev} bpm={bpm:.2f} beat-in-bar={beat} pitch_raw={pitch}")
print("beat-in-bar sequence:",[b[0x5c] for b in beats[:16]])
'

Decode beat packet fields


beat packets: 28
sample hex: 5173707431576d4a4f4c2843444a2d33303030000000000000000000000000010003003c00000258000004b00000096000000960000012c0000012c0ffffffffffffffffffffffffffffffffffffffffffffffff000ffbe70000271001000003
name@0x0b: CDJ-3000
  #0 dev=3 bpm=100.00 beat-in-bar=1 pitch_raw=1047527
  #1 dev=3 bpm=100.00 beat-in-bar=2 pitch_raw=1047527
  #2 dev=3 bpm=100.00 beat-in-bar=3 pitch_raw=1049100
  #3 dev=3 bpm=100.00 beat-in-bar=4 pitch_raw=1109917
  #4 dev=3 bpm=100.00 beat-in-bar=1 pitch_raw=1067450
  #5 dev=3 bpm=100.00 beat-in-bar=2 pitch_raw=1053294
  #6 dev=3 bpm=100.00 beat-in-bar=3 pitch_raw=1053294
  #7 dev=3 bpm=100.00 beat-in-bar=4 pitch_raw=1053294
beat-in-bar sequence: [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4]


 The beat packet is decoding well — I'm seeing the CDJ-3000 device with a steady 100 BPM and the beat counter cycling through 1-2-3-4 as expected. The field at 0x54 is varying with values like 1047527 and 1049, which could be pitch data or possibly the distance to the next beat rather than pitch bend information.

Let me trace through the packet structure more carefully. Looking at the hex layout and cross-referencing with the beat-link protocol, I can see the beat distance fields starting around 0x24, then the BPM at 0x5a (0x2710 = 10000 centi-BPM = 100.00), beat-in-bar at 0x5c, and device at 0x5f. The field at 0x55-0x57 appears to be the pitch value where 0x100000 represents normal playback speed — those varying values like 1047527 and 1109917 are actually the pitch nudges from the jog wheel, representing slight speed variations around the 100% baseline.

Now I should add a Beat decoder struct to capture these fields cleanly: BeatInBar, BPM, Device, Name, and Pitch as raw integers for testability, then write a test against the playing.jsonl fixture to verify the decode works correctly.


The beat packet decodes perfectly — and it captured your jog nudges:

- **`name`** "CDJ-3000", **`device`** 3
- **BPM** 100.00 (raw `0x2710` at offset `0x5a`, centi-BPM)
- **beat-in-bar** cycling cleanly `1,2,3,4,1,2,3,4` (offset `0x5c`) — the downbeat counter
- **pitch** at `0x55` (3 bytes, `0x100000` = 100%): values wobble `0x0ffbe7`→`0x10ef5d` ≈ 99.9%→105.8% — that's your jog/pitch-bend nudges showing up live

Let me lock this in with a `DecodeBeat` + test against the fixture, the same way as keep-alive.


Edit

const (
	TypeBeat      Type = 0x28
	TypeKeepAlive Type = 0x06
)

// PitchNormal is the raw pitch value representing 100% (normal) playback speed.
const PitchNormal = 0x100000


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

const (
	TypeBeat      Type = 0x28
	TypeKeepAlive Type = 0x06
)

// PitchNormal is the raw pitch value representing 100% (normal) playback speed.
const PitchNormal = 0x100000

package link

import (
	"bytes"
	"net"

	"github.com/cockroachdb/errors"
)

// Magic is the ten-byte preamble that begins every Pro DJ Link packet.
var Magic = []byte{0x51, 0x73, 0x70, 0x74, 0x31, 0x57, 0x6d, 0x4a, 0x4f, 0x4c}

// Type is the packet kind, found at the byte following Magic and interpreted
// together with the UDP port the packet arrived on.
type Type byte

const (
	TypeKeepAlive Type = 0x06
)

// ErrNotDJLink is returned when a payload does not begin with Magic.
var ErrNotDJLink = errors.New("not a DJ Link packet")

// KeepAlive is a device announcement broadcast on port 50000.
type KeepAlive struct {
	Device byte
	IP     net.IP
	MAC    net.HardwareAddr
	Name   string
}

// DecodeKeepAlive parses a keep-alive (type 0x06) packet.
func DecodeKeepAlive(b []byte) (KeepAlive, error) {
	if len(b) < 0x30 || !bytes.Equal(b[:len(Magic)], Magic) {
		return KeepAlive{}, ErrNotDJLink
	}
	if t := Type(b[0x0a]); t != TypeKeepAlive {
		return KeepAlive{}, errors.Errorf("want keep-alive 0x06, got 0x%02x", byte(t))
	}

	return KeepAlive{
		Device: b[0x24],
		IP:     net.IP(append([]byte(nil), b[0x2c:0x30]...)),
		MAC:    net.HardwareAddr(append([]byte(nil), b[0x26:0x2c]...)),
		Name:   string(bytes.TrimRight(b[0x0c:0x20], "\x00")),
	}, nil
}

+// PitchNormal is the raw pitch value representing 100% (normal) playback speed.


	return KeepAlive{
		Device: b[0x24],
		IP:     net.IP(append([]byte(nil), b[0x2c:0x30]...)),
		MAC:    net.HardwareAddr(append([]byte(nil), b[0x26:0x2c]...)),
		Name:   string(bytes.TrimRight(b[0x0c:0x20], "\x00")),
	}, nil
}

	return KeepAlive{
		Device: b[0x24],
		IP:     net.IP(append([]byte(nil), b[0x2c:0x30]...)),
		MAC:    net.HardwareAddr(append([]byte(nil), b[0x26:0x2c]...)),
		Name:   string(bytes.TrimRight(b[0x0c:0x20], "\x00")),
	}, nil
}

// Beat is a beat packet broadcast on port 50001 by a playing player.
type Beat struct {
	BeatInBar byte
	BPM       float64
	Device    byte
	Name      string
	Pitch     int
}

// DecodeBeat parses a beat (type 0x28) packet. BPM is the track tempo; multiply
// by Pitch/PitchNormal for the effective tempo.
func DecodeBeat(b []byte) (Beat, error) {
	if len(b) < 0x60 || !bytes.Equal(b[:len(Magic)], Magic) {
		return Beat{}, ErrNotDJLink
	}
	if t := Type(b[0x0a]); t != TypeBeat {
		return Beat{}, errors.Errorf("want beat 0x28, got 0x%02x", byte(t))
	}

	return Beat{
		BeatInBar: b[0x5c],
		BPM:       float64(binary.BigEndian.Uint16(b[0x5a:0x5c])) / 100,
		Device:    b[0x5f],
		Name:      string(bytes.TrimRight(b[0x0b:0x1f], "\x00")),
		Pitch:     int(b[0x55])<<16 | int(b[0x56])<<8 | int(b[0x57]),
	}, nil
}


	return KeepAlive{
		Device: b[0x24],
		IP:     net.IP(append([]byte(nil), b[0x2c:0x30]...)),
		MAC:    net.HardwareAddr(append([]byte(nil), b[0x26:0x2c]...)),
		Name:   string(bytes.TrimRight(b[0x0c:0x20], "\x00")),
	}, nil
}

// Beat is a beat packet broadcast on port 50001 by a playing player.
type Beat struct {
	BeatInBar byte
	BPM       float64
	Device    byte
	Name      string
	Pitch     int
}

// DecodeBeat parses a beat (type 0x28) packet. BPM is the track tempo; multiply
// by Pitch/PitchNormal for the effective tempo.
func DecodeBeat(b []byte) (Beat, error) {
	if len(b) < 0x60 || !bytes.Equal(b[:len(Magic)], Magic) {
		return Beat{}, ErrNotDJLink
	}
	if t := Type(b[0x0a]); t != TypeBeat {
		return Beat{}, errors.Errorf("want beat 0x28, got 0x%02x", byte(t))
	}

	return Beat{
		BeatInBar: b[0x5c],
		BPM:       float64(binary.BigEndian.Uint16(b[0x5a:0x5c])) / 100,
		Device:    b[0x5f],
		Name:      string(bytes.TrimRight(b[0x0b:0x1f], "\x00")),
		Pitch:     int(b[0x55])<<16 | int(b[0x56])<<8 | int(b[0x57]),
	}, nil
}

package link

import (
	"bytes"
	"net"

	"github.com/cockroachdb/errors"
)

// Magic is the ten-byte preamble that begins every Pro DJ Link packet.
var Magic = []byte{0x51, 0x73, 0x70, 0x74, 0x31, 0x57, 0x6d, 0x4a, 0x4f, 0x4c}

// Type is the packet kind, found at the byte following Magic and interpreted
// together with the UDP port the packet arrived on.
type Type byte

const (
	TypeBeat      Type = 0x28
	TypeKeepAlive Type = 0x06
)

// PitchNormal is the raw pitch value representing 100% (normal) playback speed.
const PitchNormal = 0x100000

// ErrNotDJLink is returned when a payload does not begin with Magic.
var ErrNotDJLink = errors.New("not a DJ Link packet")

// KeepAlive is a device announcement broadcast on port 50000.
type KeepAlive struct {
	Device byte
	IP     net.IP
	MAC    net.HardwareAddr
	Name   string
}

// DecodeKeepAlive parses a keep-alive (type 0x06) packet.
func DecodeKeepAlive(b []byte) (KeepAlive, error) {
	if len(b) < 0x30 || !bytes.Equal(b[:len(Magic)], Magic) {
		return KeepAlive{}, ErrNotDJLink
	}
	if t := Type(b[0x0a]); t != TypeKeepAlive {
		return KeepAlive{}, errors.Errorf("want keep-alive 0x06, got 0x%02x", byte(t))
	}

	return KeepAlive{
		Device: b[0x24],
		IP:     net.IP(append([]byte(nil), b[0x2c:0x30]...)),
		MAC:    net.HardwareAddr(append([]byte(nil), b[0x26:0x2c]...)),
		Name:   string(bytes.TrimRight(b[0x0c:0x20], "\x00")),
	}, nil
}

+// Beat is a beat packet broadcast on port 50001 by a playing player.

+// DecodeBeat parses a beat (type 0x28) packet. BPM is the track tempo; multiply

+// by Pitch/PitchNormal for the effective tempo.

+func DecodeBeat(b []byte) (Beat, error) {

+  if len(b) < 0x60 || !bytes.Equal(b[:len(Magic)], Magic) {

+  if t := Type(b[0x0a]); t != TypeBeat {

+    return Beat{}, errors.Errorf("want beat 0x28, got 0x%02x", byte(t))

+    BPM:       float64(binary.BigEndian.Uint16(b[0x5a:0x5c])) / 100,

+    Name:      string(bytes.TrimRight(b[0x0b:0x1f], "\x00")),


import (
	"bytes"
	"net"

	"github.com/cockroachdb/errors"
)

import (
	"bytes"
	"encoding/binary"
	"net"

	"github.com/cockroachdb/errors"
)


import (
	"bytes"
	"encoding/binary"
	"net"

	"github.com/cockroachdb/errors"
)

package link

import (
	"bytes"
	"net"

	"github.com/cockroachdb/errors"
)

// Magic is the ten-byte preamble that begins every Pro DJ Link packet.
var Magic = []byte{0x51, 0x73, 0x70, 0x74, 0x31, 0x57, 0x6d, 0x4a, 0x4f, 0x4c}

// Type is the packet kind, found at the byte following Magic and interpreted
// together with the UDP port the packet arrived on.
type Type byte

const (
	TypeBeat      Type = 0x28
	TypeKeepAlive Type = 0x06
)

// PitchNormal is the raw pitch value representing 100% (normal) playback speed.
const PitchNormal = 0x100000

// ErrNotDJLink is returned when a payload does not begin with Magic.
var ErrNotDJLink = errors.New("not a DJ Link packet")

// KeepAlive is a device announcement broadcast on port 50000.
type KeepAlive struct {
	Device byte
	IP     net.IP
	MAC    net.HardwareAddr
	Name   string
}

// DecodeKeepAlive parses a keep-alive (type 0x06) packet.
func DecodeKeepAlive(b []byte) (KeepAlive, error) {
	if len(b) < 0x30 || !bytes.Equal(b[:len(Magic)], Magic) {
		return KeepAlive{}, ErrNotDJLink
	}
	if t := Type(b[0x0a]); t != TypeKeepAlive {
		return KeepAlive{}, errors.Errorf("want keep-alive 0x06, got 0x%02x", byte(t))
	}

	return KeepAlive{
		Device: b[0x24],
		IP:     net.IP(append([]byte(nil), b[0x2c:0x30]...)),
		MAC:    net.HardwareAddr(append([]byte(nil), b[0x26:0x2c]...)),
		Name:   string(bytes.TrimRight(b[0x0c:0x20], "\x00")),
	}, nil
}

// Beat is a beat packet broadcast on port 50001 by a playing player.
type Beat struct {
	BeatInBar byte
	BPM       float64
	Device    byte
	Name      string
	Pitch     int
}

// DecodeBeat parses a beat (type 0x28) packet. BPM is the track tempo; multiply
// by Pitch/PitchNormal for the effective tempo.
func DecodeBeat(b []byte) (Beat, error) {
	if len(b) < 0x60 || !bytes.Equal(b[:len(Magic)], Magic) {
		return Beat{}, ErrNotDJLink
	}
	if t := Type(b[0x0a]); t != TypeBeat {
		return Beat{}, errors.Errorf("want beat 0x28, got 0x%02x", byte(t))
	}

	return Beat{
		BeatInBar: b[0x5c],
		BPM:       float64(binary.BigEndian.Uint16(b[0x5a:0x5c])) / 100,
		Device:    b[0x5f],
		Name:      string(bytes.TrimRight(b[0x0b:0x1f], "\x00")),
		Pitch:     int(b[0x55])<<16 | int(b[0x56])<<8 | int(b[0x57]),
	}, nil
}

import (
"bytes"
+  "encoding/binary"
"net"
"github.com/cockroachdb/errors"


Now the beat test and rename the fixture to something descriptive:


Bash

mv testdata/playing.jsonl testdata/beats.jsonl && ls testdata

Rename playing fixture to beats


beats.jsonl
devices.jsonl


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


Edit

func mac(t *testing.T, s string) net.HardwareAddr {

func TestDecodeBeat(t *testing.T) {
	a := assert.New(t)
	r := require.New(t)

	var got []Beat
	for _, p := range fixture(t, "testdata/beats.jsonl") {
		if p.Port != 50001 {
			continue
		}
		b, err := hex.DecodeString(p.Data)
		r.NoError(err)
		if Type(b[0x0a]) != TypeBeat {
			continue
		}
		k, err := DecodeBeat(b)
		r.NoError(err)
		got = append(got, k)
	}

	r.NotEmpty(got)
	bars := map[byte]bool{}
	for _, k := range got {
		a.Equal("CDJ-3000", k.Name)
		a.Equal(byte(3), k.Device)
		a.Equal(100.0, k.BPM)
		a.Contains([]byte{1, 2, 3, 4}, k.BeatInBar)
		a.InEpsilon(PitchNormal, k.Pitch, 0.1)
		bars[k.BeatInBar] = true
	}
	a.Len(bars, 4)
}

func mac(t *testing.T, s string) net.HardwareAddr {


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

func TestDecodeBeat(t *testing.T) {
	a := assert.New(t)
	r := require.New(t)

	var got []Beat
	for _, p := range fixture(t, "testdata/beats.jsonl") {
		if p.Port != 50001 {
			continue
		}
		b, err := hex.DecodeString(p.Data)
		r.NoError(err)
		if Type(b[0x0a]) != TypeBeat {
			continue
		}
		k, err := DecodeBeat(b)
		r.NoError(err)
		got = append(got, k)
	}

	r.NotEmpty(got)
	bars := map[byte]bool{}
	for _, k := range got {
		a.Equal("CDJ-3000", k.Name)
		a.Equal(byte(3), k.Device)
		a.Equal(100.0, k.BPM)
		a.Contains([]byte{1, 2, 3, 4}, k.BeatInBar)
		a.InEpsilon(PitchNormal, k.Pitch, 0.1)
		bars[k.BeatInBar] = true
	}
	a.Len(bars, 4)
}

func mac(t *testing.T, s string) net.HardwareAddr {

package link

import (
	"bufio"
	"encoding/hex"
	"encoding/json"
	"net"
	"os"
	"testing"

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

// packet mirrors a record written by cmd/capture.
type packet struct {
	Data string `json:"data"`
	Port int    `json:"port"`
}

// fixture reads captured packets from a JSONL file.
func fixture(t *testing.T, name string) []packet {
	t.Helper()
	f, err := os.Open(name)
	require.NoError(t, err)
	defer f.Close()

	var ps []packet
	s := bufio.NewScanner(f)
	for s.Scan() {
		var p packet
		require.NoError(t, json.Unmarshal(s.Bytes(), &p))
		ps = append(ps, p)
	}
	require.NoError(t, s.Err())
	return ps
}

func TestDecodeKeepAlive(t *testing.T) {
	r := require.New(t)

	got := map[string]KeepAlive{}
	for _, p := range fixture(t, "testdata/devices.jsonl") {
		if p.Port != 50000 {
			continue
		}
		b, err := hex.DecodeString(p.Data)
		r.NoError(err)
		k, err := DecodeKeepAlive(b)
		r.NoError(err)
		got[k.Name] = k
	}

	want := []KeepAlive{
		{Device: 3, IP: net.ParseIP("192.168.0.192"), MAC: mac(t, "c8:3d:fc:11:26:c2"), Name: "CDJ-3000"},
		{Device: 33, IP: net.ParseIP("192.168.0.193"), MAC: mac(t, "c8:3d:fc:12:9e:d5"), Name: "DJM-V10"},
	}
	for _, w := range want {
		t.Run(w.Name, func(t *testing.T) {
			a := assert.New(t)
			k, ok := got[w.Name]
			a.True(ok)
			a.Equal(w.Device, k.Device)
			a.Equal(w.IP.String(), k.IP.String())
			a.Equal(w.MAC.String(), k.MAC.String())
		})
	}
}

func mac(t *testing.T, s string) net.HardwareAddr {
	t.Helper()
	m, err := net.ParseMAC(s)
	require.NoError(t, err)
	return m
}

+  for _, p := range fixture(t, "testdata/beats.jsonl") {

+    a.Contains([]byte{1, 2, 3, 4}, k.BeatInBar)

+    a.InEpsilon(PitchNormal, k.Pitch, 0.1)


Bash

Run tests with beat decoder


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


Now update `TODO.md` to mark the beat packet done and record the key finding (no `0x0a` status passively → confirms a virtual CDJ is required).


Edit

### Beat sync — port 50001
- [ ] beat packet (type 0x28): BPM, beat-in-bar, pitch, next/prev beat timing
- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002
- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] mixer status (DJM) if present
- [ ] capture scenarios: idle, track loaded, playing, two-deck, on-air toggle

### 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)
- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002
- NOTE: passively only the CDJ's low-rate type 0x40 ("NXS-GW", ~0.5/s) appears.
  Full 0x0a status is NOT broadcast — it requires announcing a virtual CDJ first.
- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] mixer status (DJM) if present
- [ ] CDJ type 0x40 on 50002 — identify & decode
- [ ] capture scenarios: idle, track loaded, playing, two-deck, on-air toggle


<tool_use_error>String to replace not found in file.
String: ### Beat sync — port 50001
- [ ] beat packet (type 0x28): BPM, beat-in-bar, pitch, next/prev beat timing
- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002
- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] mixer status (DJM) if present
- [ ] capture scenarios: idle, track loaded, playing, two-deck, on-air toggle
(note: Edit also tried swapping \uXXXX escapes and their characters; neither form matched, so the mismatch is likely elsewhere in old_string. Re-read the file and copy the exact surrounding text.)</tool_use_error>

Error: String to replace not found in file.
String: ### Beat sync — port 50001
- [ ] beat packet (type 0x28): BPM, beat-in-bar, pitch, next/prev beat timing
- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002
- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] mixer status (DJM) if present
- [ ] capture scenarios: idle, track loaded, playing, two-deck, on-air toggle
(note: Edit also tried swapping \uXXXX escapes and their characters; neither form matched, so the mismatch is likely elsewhere in old_string. Re-read the file and copy the exact surrounding text.)


I'm reviewing the beat sync section that I modified earlier by adding the mixer type line, and checking what still needs to be addressed in that area.


28	### Beat sync — port 50001
29	- [ ] beat packet (type 0x28): BPM, beat-within-bar, pitch, next/prev beat timing
30	- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
31	- [ ] capture across a tempo change and a loaded vs. stopped deck
32
33	### Status — port 50002
34	- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
35	- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
36	- [ ] mixer status (DJM) if present
37	- [ ] capture scenarios: idle, track loaded, playing, two-deck, on-air toggle
38
39	## crate-digger — rekordbox database (over NFS)
40
41	Reached only after the virtual CDJ announces and a deck reports a loaded track.
42
43	- [ ] RPC portmap (port 111) — GETPORT for mount + nfs
44	- [ ] MOUNT — mount the media slot, obtain root file handle
45	- [ ] NFS — LOOKUP + READ `PIONEER/rekordbox/export.pdb`
46	- [ ] PDB parse: tables (tracks, artists, albums, artwork, playlists)
47	- [ ] ANLZ parse: `.DAT`/`.EXT` (beat grid, cue points, waveforms)
48	- [ ] metadata-by-track-ID resolved against captured PDB
49

### Beat sync — port 50001
- [ ] beat packet (type 0x28): BPM, beat-within-bar, pitch, next/prev beat timing
- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002
- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] mixer status (DJM) if present
- [ ] 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


### Beat sync — port 50001
- [ ] beat packet (type 0x28): BPM, beat-within-bar, pitch, next/prev beat timing
- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002
- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] mixer status (DJM) if present
- [ ] capture scenarios: idle, track loaded, playing, two-deck, on-air toggle

### 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)
- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002
- NOTE: passively only the CDJ's low-rate type 0x40 ("NXS-GW", ~0.5/s) appears.
  Full 0x0a status is NOT broadcast — it requires announcing a virtual CDJ first.
- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] mixer status (DJM) if present
- [ ] CDJ type 0x40 on 50002 — identify & decode
- [ ] capture scenarios: idle, track loaded, playing, two-deck, on-air toggle


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)

### 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)
- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002
- NOTE: passively only the CDJ's low-rate type 0x40 ("NXS-GW", ~0.5/s) appears.
  Full 0x0a status is NOT broadcast — it requires announcing a virtual CDJ first.
- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] mixer status (DJM) if present
- [ ] CDJ type 0x40 on 50002 — identify & decode
- [ ] capture scenarios: idle, track loaded, playing, two-deck, on-air toggle

# 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 / keep-alive — 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
- [ ] mixer/gateway packet seen on 50002 (type 0x40, "NXS-GW") — identify & decode
- [ ] full announce/channel-negotiation handshake (claim device # 1-4)
- [ ] virtual CDJ Announce + KeepAlive sender (prereq for all active flows)

### Beat sync — port 50001
- [ ] beat packet (type 0x28): BPM, beat-within-bar, pitch, next/prev beat timing
- [ ] mixer type 0x03 (~3/s from DJM-V10, name at 0x0b not 0x0c) — identify & decode
- [ ] capture across a tempo change and a loaded vs. stopped deck

### Status — port 50002
- [ ] CDJ status (type 0x0a): play state, BPM, pitch, on-air, master, sync
- [ ] loaded-track fields: track ID, source player, source slot (SD/USB)
- [ ] mixer status (DJM) if present
- [ ] 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)

- [ ] replace `time.Sleep(5s)` FIXME in `Start()` with discovery/mount readiness
- [ ] make the media query deterministic (vizlab's was "unreliable")
- [ ] swap `github.com/pkg/errors` → `github.com/cockroachdb/errors`
- [ ] live integration suite gated behind `testing.Short()` / env, separate from
      the hermetic fixture-replay tests

-- [ ] beat packet (type 0x28): BPM, beat-within-bar, pitch, next/prev beat timing

+- [x] beat packet (type 0x28): BPM, beat-in-bar, pitch — `testdata/beats.jsonl`

+- [ ] next/prev beat-timing distances (six 4-byte BE values from ~0x24)

+- NOTE: passively only the CDJ's low-rate type 0x40 ("NXS-GW", ~0.5/s) appears.

+  Full 0x0a status is NOT broadcast — it requires announcing a virtual CDJ first.

+- [ ] CDJ type 0x40 on 50002 — identify & decode


The tests are passing, so I'm ready to summarize what the passive capture revealed and what's been decoded and tested, though I still need to address the 0x0a status that requires announcing.


Done — beat packets decoded, tested, and documented.

## What the 60s passive capture (314 packets) showed

| Source | Port | Type | Count | Meaning |
|---|---|---|---|---|
| CDJ-3000 | 50000 | `0x06` | 28 | keep-alive |
| CDJ-3000 | **50001** | **`0x28`** | **28** | **beat packets (playing)** ✅ now decoded |
| CDJ-3000 | 50002 | `0x40` | 30 | low-rate "NXS-GW" gateway packet (~0.5/s) |
| DJM-V10 | 50000 | `0x06` | 30 | keep-alive |
| DJM-V10 | 50001 | `0x03` | 198 | mixer stream (~3/s, still undecoded) |

## Now decoded + under test
- **`DecodeBeat`** (`TestDecodeBeat` passes against `testdata/beats.jsonl`): BPM 100.00, beat-in-bar cycling 1→4 (asserts all 4 bars seen), pitch ≈ normal, device 3. Added `PitchNormal = 0x100000` and a note that effective tempo = `BPM × Pitch/PitchNormal`.

## The important finding
**Full CDJ status (`0x0a`) is never broadcast.** Even with a track playing, the only thing the CDJ puts on 50002 passively is the low-rate `0x40` packet. So play state, on-air, master/sync, and the **loaded-track ID + slot** (the gateway into the crate-digger/NFS database flow) all require us to **announce a virtual CDJ first**. Passive capture has now given us everything it can on the discovery + beat layers.

## Still capturable passively (if you want more)
- **Tempo change**: move the pitch fader to a new resting value during a capture — confirms BPM/pitch tracking in the beat stream and gives a non-100% fixture.
- **The two mystery packets**: the DJM-V10 `0x03` and the CDJ `0x40` — we have samples but haven't decoded their fields.

But the highest-value next step is the **virtual-CDJ announce sender** — it's the gate for `0x0a` status and the whole NFS/PDB side. Want me to do another passive round (e.g. a tempo-change fixture), start decoding the two unknown packets, or move on to the announce sender?


yes lets do the virtual CDJ now


I'm building the virtual CDJ announce sender to gate active flows, so I need to understand the handshake protocol from vizlab's announce logic and port it over. I'll need to examine the announce, device, and network modules to get the full picture of how status messages are received and processed.


Let me pull the vizlab announce + net code to port the handshake correctly, rather than guess at the channel-negotiation packets.


Bash

cd /tmp && for f in announce.go net.go device.go; do echo "═══════════ $f ═══════════"; gh api repos/nzoschke/vizlab/contents/pkg/link/$f --jq '.content' 2>/dev/null | base64 -d; done 2>/dev/null

Fetch vizlab announce.go, net.go, device.go


═══════════ announce.go ═══════════
package link

import (
	"bytes"
	"context"
	"log/slog"
	"net"
	"time"

	"github.com/pkg/errors"
)

// Announce configures and announces a Virtual CDJ.
// To assert network functionality it blocks until one status from a real CDJ is received, or times out with an error.
func (l *Link) Announce(ctx context.Context, name string, id DeviceID, timeout time.Duration) (net.IP, *net.IPNet, net.HardwareAddr, Status, error) {
	dctx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()

	// discover first device
	d, err := l.discover(dctx)
	if err != nil {
		return nil, nil, nil, Status{}, errors.WithStack(err)
	}

	slog.Info("Announce.discover", "name", d.Name, "id", d.ID, "ip", d.IP.String())

	// find interface and broadcast that matches discovered device
	iface, err := iface(d.IP)
	if err != nil {
		return nil, nil, nil, Status{}, errors.WithStack(err)
	}

	ipNet, err := ipNet(iface)
	if err != nil {
		return nil, nil, nil, Status{}, errors.WithStack(err)
	}

	addr := bcast(ipNet)

	// announce virtual CDJ
	slog.Info("Announce.keepalive", "name", name, "id", id, "ip", ipNet.IP.String(), "addr", iface.HardwareAddr.String(), "broadcast", addr.IP.String())
	_, err = l.c0.WriteToUDP(keepalive(name, id, iface.HardwareAddr, ipNet.IP), addr)
	if err != nil {
		return nil, nil, nil, Status{}, errors.WithStack(err)
	}

	// get first status
	sctx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()
	s, err := l.status(sctx)
	if err != nil {
		return nil, nil, nil, Status{}, errors.WithStack(err)
	}

	slog.Info("Announce.status", "name", s.PlayerName, "id", s.Device, "track", s.TrackID, "onAir", s.IsOnAir, "master", s.IsMaster, "sync", s.IsSync, "usb", s.USBState, "sd", s.SDState)

	return d.IP, ipNet, iface.HardwareAddr, s, nil
}

// KeepAlive periodically sends Virtual CDJ keep-alive packets to all devices
// https://djl-analysis.deepsymmetry.org/djl-analysis/packets.html#_port_50000_packets
// https://djl-analysis.deepsymmetry.org/djl-analysis/startup.html#cdj-keep-alive
func (l *Link) KeepAlive(ctx context.Context, name string, id DeviceID, ipNet *net.IPNet, addr net.HardwareAddr) error {
	slog.Info("KeepAlive", "name", name, "id", id, "ip", ipNet.IP.String(), "addr", addr.String(), "broadcast", bcast(ipNet))

	t := time.NewTicker(1500 * time.Millisecond)
	defer t.Stop()

	for range t.C {
		_, err := l.c0.WriteToUDP(keepalive(name, id, addr, ipNet.IP), bcast(ipNet))
		if err != nil {
			return errors.WithStack(err)
		}
	}

	return nil
}

// https://djl-analysis.deepsymmetry.org/djl-analysis/startup.html#cdj-keep-alive
func keepalive(name string, id DeviceID, addr net.HardwareAddr, ip net.IP) []byte {
	n := make([]byte, 20)
	copy(n[:], []byte(name))

	return bytes.Join([][]byte{
		header,                // 0x00: 10 byte header
		{0x06, 0x00},          // 0x0A: 02 byte announce packet type
		n,                     // 0x0c: 20 byte device name
		{0x01, 0x02},          // 0x20: 02 byte subtype
		{0x00, 0x36},          // 0x22: 02 byte len_p
		{byte(id)},            // 0x24: 01 byte for the player ID
		{byte(DeviceTypeCDJ)}, // 0x25: 01 byte for the player type
		addr[:6],              // 0x26: 06 byte mac address
		ip.To4(),              // 0x2C: 04 byte IP address
		{0x01},                // 0x30: 01 byte number peer devices
		{0x00, 0x00, 0x00},    // 0x31: 03 byte padding
		{byte(DeviceTypeCDJ)}, // 0x34: 01 byte for the player type
		{0x00},                // 0x35: 01 byte final padding
	}, nil)
}
═══════════ net.go ═══════════
package link

import (
	"fmt"
	"net"

	"github.com/pkg/errors"
)

func bcast(ipNet *net.IPNet) *net.UDPAddr {
	ip := make(net.IP, net.IPv4len)
	for i, b := range ipNet.IP.To4() {
		ip[i] = b | ^ipNet.Mask[i]
	}

	return &net.UDPAddr{
		IP:   ip,
		Port: 50000,
	}
}

func iface(ip net.IP) (*net.Interface, error) {
	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, errors.WithStack(err)
	}

	for _, iface := range ifaces {
		if iface.Flags&net.FlagUp == 0 {
			continue
		}

		addrs, err := iface.Addrs()
		if err != nil {
			return nil, errors.WithStack(err)
		}

		var matched *net.Interface
		subnet := 0x00

		for _, addr := range addrs {
			net, ok := addr.(*net.IPNet)
			if !ok {
				continue
			}

			size, _ := net.Mask.Size()
			if net.Contains(ip) && size > subnet {
				matched = &iface
				subnet = size
			}
		}

		if matched != nil {
			return matched, nil
		}
	}

	return nil, fmt.Errorf("no matching interface for %s", ip)
}

func ipNet(iface *net.Interface) (*net.IPNet, error) {
	addrs, err := iface.Addrs()
	if err != nil {
		return nil, errors.WithStack(err)
	}

	for _, addr := range addrs {
		ipNet, ok := addr.(*net.IPNet)
		if ok && ipNet.IP.To4() != nil && !ipNet.IP.IsLoopback() {
			return ipNet, nil
		}
	}

	return nil, fmt.Errorf("no IPv4 broadcast interface for %s", iface.Name)
}
═══════════ device.go ═══════════
package link

import (
	"bytes"
	"fmt"
	"net"
	"time"

	"github.com/pkg/errors"
)

const (
	DeviceTypeCDJ   DeviceType = 0x01
	DeviceTypeMixer DeviceType = 0x03
	DeviceTypeRB    DeviceType = 0x04
)

type Device struct {
	Name       string
	ID         DeviceID
	Type       DeviceType
	MacAddr    net.HardwareAddr
	IP         net.IP
	LastActive time.Time
}

type DeviceID byte
type DeviceType byte

type DeviceSlot struct {
	Device DeviceID
	Slot   Slot
}

var SlotNames = map[Slot]string{
	SlotEmpty: "empty",
	SlotCD:    "cd",
	SlotSD:    "sd",
	SlotUSB:   "usb",
	SlotRB:    "rb",
}

func (ds DeviceSlot) String() string {
	return fmt.Sprintf("%d/%s", ds.Device, SlotNames[ds.Slot])
}

var Slots = []Slot{SlotSD, SlotUSB}

type TrackID struct {
	ID         int
	DeviceSlot DeviceSlot
}

func device(p []byte) (*Device, error) {
	if !bytes.HasPrefix(p, header) {
		return nil, errors.New("invalid header")
	}

	if p[0x0A] != 0x06 {
		return nil, nil
	}

	return &Device{
		Name:       string(bytes.TrimRight(p[0x0C:0x0C+20], "\x00")),
		ID:         DeviceID(p[0x24]),
		MacAddr:    net.HardwareAddr(p[0x26 : 0x26+6]),
		IP:         net.IP(p[0x2C : 0x2C+4]),
		Type:       DeviceType(p[0x34]),
		LastActive: time.Now(),
	}, nil
}
Shell cwd was reset to /Users/noah/conductor/workspaces/deadca7/san-diego


review that against the spec, and the general implementation, weve had some instability


 I see how vizlab simplifies the Pro DJ Link announce process—it sends a single keep-alive packet and waits for status responses, whereas the full handshake involves multiple channel-claim packets. Based on what beat-link and dysentery demonstrate, a virtual CDJ can get by with just periodic keep-alive packets to receive status updates without implementing the complete negotiation sequence.

The key insight is that CDJs unicast their status packets to devices that have announced themselves on the network. So my approach is to extend the capture tool with an announce flag: it'll discover the local interface by listening for the first keep-alive from a real device, then send periodic keep-alive broadcasts on port 50000 while simultaneously recording all three ports to see what status packets arrive on 50002.

I'll restructure the capture tool to reuse the port 50000 connection for both reading and writing, then add network helpers to the link package (interface discovery, broadcast address calculation) and a keep-alive packet encoder, keeping everything consistent with our error handling and style. Writing the capture tool...


The vizlab approach is clear and pragmatic: skip the formal channel-claim handshake, just broadcast keep-alive (`0x06`) packets every 1.5s claiming a device number, and real CDJs start sending status to us. I'll port the packet builder + net helpers cleanly into our package (reusing our `KeepAlive` struct so encode/decode round-trips), then teach the capture tool to announce while recording — so we capture the active `0x0a` flow.

First, the net helpers and the keep-alive encoder:


Write

package link

import (
	"net"

	"github.com/cockroachdb/errors"
)

// broadcast returns the IPv4 broadcast address for n.
func broadcast(n *net.IPNet) net.IP {
	v4 := n.IP.To4()
	ip := make(net.IP, net.IPv4len)
	for i := range v4 {
		ip[i] = v4[i] | ^n.Mask[i]
	}
	return ip
}

// Iface returns the up interface and IPv4 network whose subnet contains ip,
// used to match the local address to a discovered DJ Link device.
func Iface(ip net.IP) (*net.Interface, *net.IPNet, error) {
	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, nil, errors.WithStack(err)
	}

	for i := range ifaces {
		f := ifaces[i]
		if f.Flags&net.FlagUp == 0 {
			continue
		}

		addrs, err := f.Addrs()
		if err != nil {
			return nil, nil, errors.WithStack(err)
		}

		for _, a := range addrs {
			n, ok := a.(*net.IPNet)
			if ok && n.IP.To4() != nil && n.Contains(ip) {
				return &f, n, nil
			}
		}
	}

	return nil, nil, errors.Errorf("no interface for %s", ip)
}


File created successfully at: /Users/noah/conductor/workspaces/deadca7/san-diego/link/net.go (file state is current in your context — no need to Read it back)

package link

import (
	"net"

	"github.com/cockroachdb/errors"
)

// broadcast returns the IPv4 broadcast address for n.
func broadcast(n *net.IPNet) net.IP {
	v4 := n.IP.To4()
	ip := make(net.IP, net.IPv4len)
	for i := range v4 {
		ip[i] = v4[i] | ^n.Mask[i]
	}
	return ip
}

// Iface returns the up interface and IPv4 network whose subnet contains ip,
// used to match the local address to a discovered DJ Link device.
func Iface(ip net.IP) (*net.Interface, *net.IPNet, error) {
	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, nil, errors.WithStack(err)
	}

	for i := range ifaces {
		f := ifaces[i]
		if f.Flags&net.FlagUp == 0 {
			continue
		}

		addrs, err := f.Addrs()
		if err != nil {
			return nil, nil, errors.WithStack(err)
		}

		for _, a := range addrs {
			n, ok := a.(*net.IPNet)
			if ok && n.IP.To4() != nil && n.Contains(ip) {
				return &f, n, nil
			}
		}
	}

	return nil, nil, errors.Errorf("no interface for %s", ip)
}


Prompt: review that against the spec, and the general implementation, weve had some instability


 The user wants me to validate the virtual CDJ announcement approach against the actual Pro DJ Link spec and the vizlab implementation, since they've experienced instability issues. Rather than just copying vizlab's simplified announce method, I need to carefully review the spec to understand what's actually required for reliability.

I'm going to look up the Deep Symmetry startup spec documentation to understand the full device-number-claim handshake procedure. The instability is likely because vizlab skips critical parts of the proper startup sequence, which could cause the mixer and CDJs to not consistently recognize the virtual device or lead to device-number conflicts.


Good call — they flagged this exact code path as unstable, so let me check the vizlab shortcut against the actual spec before porting it. Let me read the Deep-Symmetry startup/device-number-claim documentation.


WebFetch

Prompt: Describe the full Pro DJ Link startup / device-number self-assignment handshake in detail. What is the exact sequence and timing of packets a virtual CDJ must send on port 50000 before it can send keep-alive (type 0x06) packets? List the packet types involved (e.g. 0x0a announcement, 0x00/0x02/0x04 device-number claim stages, mixer-assigned numbers), how many of each and at what interval, how the device number is chosen/defended, and what happens if you skip the claim phase and just send keep-alives. Include exact timing values in milliseconds.


# Pro DJ Link CDJ Startup Handshake Sequence

## Full Device-Number Self-Assignment Process

A virtual CDJ must complete this exact sequence before sending keep-alive packets:

### Stage 1: Initial Announcement (Type 0x0a)
**3 packets at ~300ms intervals**
- 25-byte packets broadcast to UDP port 50000
- Final byte: `0x01` (CDJ identifier, vs `0x02` for mixer)
- Announces device existence without claiming a channel

### Stage 2: First-Stage Device Number Claim (Type 0x00)
**3 packets at ~300ms intervals**
- 44-byte (`0x2c`) packets to port 50000 broadcast
- Byte `0x24` cycles through values `01`, `02`, `03`
- Includes MAC address
- Purpose unclear; possibly mixer uses this to assign channels

### Stage 3: Second-Stage Device Number Claim (Type 0x02)
**3 packets at ~300ms intervals**
- 50-byte (`0x32`) packets broadcast
- Claims specific device number `D` (player 1, 2, 3, etc.)
- Includes IP address and MAC address
- Byte `0x1f` = `01` for auto-assign mode, `02` for fixed channel
- Player observes network to select unused `D` value

### Stage 4: Final-Stage Device Number Claim (Type 0x04)
**3 packets at ~300ms intervals**
- 42-byte (`0x2a`) packets broadcast
- Confirms claimed device number `D`
- Bytes `0x24`-`0x25` contain device number and sequence counter

### Stage 5: Keep-Alive Packets (Type 0x06)
**Begins after final stage**
- 54-byte packets broadcast every ~1.5 seconds
- Maintains network presence and device number ownership
- Includes peer device count (`p`)

## Critical Timing Details

- Each three-packet series: **~900ms total** (3 packets × 300ms)
- Complete startup sequence: **~3.6 seconds minimum** (four stages)
- Keep-alive interval: **~1500ms**

## Channel Conflicts & Defense

If claiming a number already in use, the existing device sends a 41-byte (`0x29`) packet directly to the new player, forcing it to "give up on trying to claim channel."

## What Happens If You Skip the Claim Phase

The documentation doesn't explicitly state consequences, but the handshake structure suggests a virtual CDJ cannot reliably "retain presence on the network" without completing the full claiming sequence first.


 Looking at the vizlab implementation, it's skipping the entire handshake sequence and jumping straight to keep-alive messages. This is a critical flaw—it never sends the initial announcements, never performs the device-number claim handshake, and just starts blasting keep-alives with a fixed device ID. This approach creates device number conflicts and leaves the protocol in an unstable state from the start.

The implementation also has a race condition: it sends a single keep-alive in Announce(), then immediately starts the keep-alive goroutine, the discovery goroutine, and sleeps for 5 seconds before sending status. That sleep is a band-aid masking the real problem—the device was never properly registered on the network.

To fix this properly, I need to implement the full four-stage handshake: send initial announcements, claim a device number with conflict detection, handle the 0x29 "give up" response if there's a collision, and only then start the keep-alive cycle. I'll need the exact byte layouts for each packet type to build them correctly, so let me fetch those from a reference implementation like beat-link or prolink-connect to ensure I get the protocol details right.


This is the smoking gun for the instability. The vizlab code **skips Stages 1–4 of the startup handshake entirely** and jumps straight to keep-alives. Let me get the exact byte layouts for the claim packets from a reference implementation so the corrected version is right, then I'll write up the review.


Bash

cd /tmp && echo "=== search prolink-connect for announce/claim packet builders ===" && gh api repos/evanpurkhiser/prolink-connect/git/trees/main?recursive=1 --jq '.tree[].path' 2>/dev/null | grep -iE 'announc|network|device' | head; echo "=== beat-link VirtualCdj claim methods ===" && gh api repos/Deep-Symmetry/beat-link/contents/src/main/java/org/deepsymmetry/beatlink/VirtualCdj.java --jq '.content' 2>/dev/null | base64 -d | grep -nE 'claimStage|0x0a|0x00, 0x00|assembleAndSendAnnounce|defendAnnounce|0x2c|0x32|0x2a|new byte\[\]|deviceNumberAssign' | head -40

Find reference announce/claim packet code


=== search prolink-connect for announce/claim packet builders ===
(eval):1: no matches found: repos/evanpurkhiser/prolink-connect/git/trees/main?recursive=1
=== beat-link VirtualCdj claim methods ===
250:            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
251:            0x01, 0x02, 0x00, 0x36,  0x00, 0x01, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
252:            0x02, 0x00, 0x00, 0x00,  0x01, 0x64
312:            0x51, 0x73, 0x70, 0x74,  0x31, 0x57, 0x6d, 0x4a,   0x4f, 0x4c, 0x0a, 0x00,  0x62, 0x65, 0x61, 0x74,
313:            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
320:    private static final byte[] claimStage1bytes = {
321:            0x51, 0x73, 0x70, 0x74,  0x31, 0x57, 0x6d, 0x4a,   0x4f, 0x4c, 0x00, 0x00,  0x62, 0x65, 0x61, 0x74,
322:            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
323:            0x01, 0x03, 0x00, 0x2c,  0x0d, 0x01, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00
329:    private static final byte[] claimStage2bytes = {
331:            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
332:            0x01, 0x03, 0x00, 0x32,  0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x0d, 0x00,
339:    private static final byte[] claimStage3bytes = {
341:            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
350:            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
351:            0x01, 0x02, 0x00, 0x32,  0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
360:            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
361:            0x01, 0x02, 0x00, 0x29,  0x00, 0x00, 0x00, 0x00,   0x00
814:            Arrays.fill(claimStage1bytes, DEVICE_NAME_OFFSET, DEVICE_NAME_LENGTH, (byte)0);
815:            System.arraycopy(getDeviceName().getBytes(), 0, claimStage1bytes, DEVICE_NAME_OFFSET, getDeviceName().getBytes().length);
816:            System.arraycopy(keepAliveBytes, MAC_ADDRESS_OFFSET, claimStage1bytes, 0x26, 6);
818:                claimStage1bytes[0x24] = (byte)i;  // The packet counter.
821:                    DatagramPacket announcement = new DatagramPacket(claimStage1bytes, claimStage1bytes.length,
843:            Arrays.fill(claimStage2bytes, DEVICE_NAME_OFFSET, DEVICE_NAME_LENGTH, (byte)0);
844:            System.arraycopy(getDeviceName().getBytes(), 0, claimStage2bytes, DEVICE_NAME_OFFSET, getDeviceName().getBytes().length);
845:            System.arraycopy(matchedAddress.getAddress().getAddress(), 0, claimStage2bytes, 0x24, 4);
846:            System.arraycopy(keepAliveBytes, MAC_ADDRESS_OFFSET, claimStage2bytes, 0x28, 6);
847:            claimStage2bytes[0x2e] = (byte)claimingNumber.get();  // The number we are claiming.
848:            claimStage2bytes[0x31] = (getDeviceNumber() == 0)? (byte)1 : (byte)2;  // The auto-assign flag.
850:                claimStage2bytes[0x2f] = (byte)i;  // The packet counter.
852:                    logger.debug("Sending claim stage 2 packet {} for device {}", i, claimStage2bytes[0x2e]);
853:                    DatagramPacket announcement = new DatagramPacket(claimStage2bytes, claimStage2bytes.length,
881:            Arrays.fill(claimStage3bytes, DEVICE_NAME_OFFSET, DEVICE_NAME_LENGTH, (byte)0);
882:            System.arraycopy(getDeviceName().getBytes(), 0, claimStage3bytes, DEVICE_NAME_OFFSET, getDeviceName().getBytes().length);
883:            claimStage3bytes[0x24] = (byte)claimingNumber.get();  // The number we are claiming.
885:                claimStage3bytes[0x25] = (byte)i;  // The packet counter.
887:                    logger.debug("Sending claim stage 3 packet {} for device {}", i, claimStage3bytes[0x24]);
888:                    DatagramPacket announcement = new DatagramPacket(claimStage3bytes, claimStage3bytes.length,
1704:    0x00, 0x0d, 0x00, 0x0c, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
1734:            0x00, 0x0d, 0x00, 0x08, 0x00, 0x00, 0x00, 0x0d, 0x00, 0x00, 0x00, 0x0f };
Shell cwd was reset to /Users/noah/conductor/workspaces/deadca7/san-diego


I need to examine the VirtualCdj.java source code to understand the exact byte templates for beat-link announcements and claims, along with the device number assignment logic and defense handling mechanisms.


Excellent — beat-link has the authoritative templates. Let me pull the full byte arrays and the claim/defense logic.


cd /tmp && gh api repos/Deep-Symmetry/beat-link/contents/src/main/java/org/deepsymmetry/beatlink/VirtualCdj.java --jq '.content' 2>/dev/null | base64 -d > vcdj.java; sed -n '300,375p' vcdj.java

Read announce/claim packet templates


     */
    private final DeviceUpdateListener updateListener = this::processUpdate;

    @API(status = API.Status.STABLE)
    public DeviceUpdateListener getUpdateListener() {
        return updateListener;
    }

    /**
     * The initial packet sent three times when coming online.
     */
    private static final byte[] helloBytes = {
            0x51, 0x73, 0x70, 0x74,  0x31, 0x57, 0x6d, 0x4a,   0x4f, 0x4c, 0x0a, 0x00,  0x62, 0x65, 0x61, 0x74,
            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
            0x01, 0x04, 0x00, 0x26,  0x01, 0x40
    };

    /**
     * The first-stage device number claim packet series.
     */
    private static final byte[] claimStage1bytes = {
            0x51, 0x73, 0x70, 0x74,  0x31, 0x57, 0x6d, 0x4a,   0x4f, 0x4c, 0x00, 0x00,  0x62, 0x65, 0x61, 0x74,
            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
            0x01, 0x03, 0x00, 0x2c,  0x0d, 0x01, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00
    };

    /**
     * The second-stage device number claim packet series.
     */
    private static final byte[] claimStage2bytes = {
            0x51, 0x73, 0x70, 0x74,  0x31, 0x57, 0x6d, 0x4a,   0x4f, 0x4c, 0x02, 0x00,  0x62, 0x65, 0x61, 0x74,
            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
            0x01, 0x03, 0x00, 0x32,  0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x0d, 0x00,
            0x01, 0x00
    };

    /**
     * The third-stage (final) device number claim packet series.
     */
    private static final byte[] claimStage3bytes = {
            0x51, 0x73, 0x70, 0x74,  0x31, 0x57, 0x6d, 0x4a,   0x4f, 0x4c, 0x04, 0x00,  0x62, 0x65, 0x61, 0x74,
            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
            0x01, 0x03, 0x00, 0x26,  0x0d, 0x00
    };

    /**
     * Packet used to acknowledge a mixer's intention to assign us a device number.
     */
    private static final byte[] assignmentRequestBytes = {
            0x51, 0x73, 0x70, 0x74,  0x31, 0x57, 0x6d, 0x4a,   0x4f, 0x4c, 0x02, 0x01,  0x62, 0x65, 0x61, 0x74,
            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
            0x01, 0x02, 0x00, 0x32,  0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
            0x01, 0x00
    };

    /**
     * Packet used to tell another device we are already using a device number.
     */
    private static final byte[] deviceNumberDefenseBytes = {
            0x51, 0x73, 0x70, 0x74,  0x31, 0x57, 0x6d, 0x4a,   0x4f, 0x4c, 0x08, 0x00,  0x62, 0x65, 0x61, 0x74,
            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
            0x01, 0x02, 0x00, 0x29,  0x00, 0x00, 0x00, 0x00,   0x00
    };

    /**
     * Keep track of which device has reported itself as the current tempo master.
     */
    private final AtomicReference<DeviceUpdate> tempoMaster = new AtomicReference<>();

    /**
     * Check which device is the current tempo master, returning the {@link DeviceUpdate} packet in which it
     * reported itself to be master. If there is no current tempo master returns {@code null}. Note that when
     * we are acting as tempo master ourselves in order to control player tempo and beat alignment, this will
     * also have a {@code null} value, as there is no real player that is acting as master; we will instead
     * send tempo and beat updates ourselves.
     *
Shell cwd was reset to /Users/noah/conductor/workspaces/deadca7/san-diego


I need to look at the claim loop section to understand the timing intervals and how devices get assigned.


Now the claim-loop timing and device-number selection logic:


Read claim loop timing and selection logic


deviceNumberDefenseBytes[0x24] = keepAliveBytes[DEVICE_NUMBER_OFFSET];
        System.arraycopy(matchedAddress.getAddress().getAddress(), 0, deviceNumberDefenseBytes, 0x25, 4);
        try {
            DatagramPacket defense = new DatagramPacket(deviceNumberDefenseBytes, deviceNumberDefenseBytes.length,
                    invaderAddress, DeviceFinder.ANNOUNCEMENT_PORT);
            logger.info("Sending device number defense packet to invader at address {}, port {}", defense.getAddress().getHostAddress(), defense.getPort());
            currentSocket.send(defense);
        } catch (Exception e) {
            logger.error("Unable to send device defense packet.", e);
        }
    }

    /**
     * Implement the device-number claim protocol described in the
     * protocol analysis.
     *
     * @return true iff a device number was successfully established and startup can proceed
     */
    private boolean claimDeviceNumber() {
        // Set up our state trackers for device assignment negotiation.
        claimRejected.set(false);
        mixerAssigned.set(0);

        // Send the initial series of three "coming online" packets.
        Arrays.fill(helloBytes, DEVICE_NAME_OFFSET, DEVICE_NAME_LENGTH, (byte)0);
        System.arraycopy(getDeviceName().getBytes(), 0, helloBytes, DEVICE_NAME_OFFSET, getDeviceName().getBytes().length);
        for (int i = 1; i <= 3; i++) {
            try {
                logger.debug("Sending hello packet {}", i);
                DatagramPacket announcement = new DatagramPacket(helloBytes, helloBytes.length,
                        broadcastAddress.get(), DeviceFinder.ANNOUNCEMENT_PORT);
                socket.get().send(announcement);
                Thread.sleep(300);
            } catch (Exception e) {
                logger.warn("Unable to send hello packet to network, failing to go online.", e);
                return false;
            }
        }

        // Establish the device number we want to claim; if zero that means we will try to self-assign.
        claimingNumber.set(getDeviceNumber());
        boolean claimed = false;  // Indicates we have successfully claimed a number and can be done.

        selfAssignLoop:
        while (!claimed) {
            // If we are supposed to self-assign a number, find the next one we can try.
            if (getDeviceNumber() == 0 && !selfAssignDeviceNumber()) {
                // There are no addresses left for us to try, give up and report failure.
                claimingNumber.set(0);
                return false;
            }

            // Send the series of three initial device number claim packets, unless we are interrupted by a defense
            // or a mixer assigning us a specific number.
            Arrays.fill(claimStage1bytes, DEVICE_NAME_OFFSET, DEVICE_NAME_LENGTH, (byte)0);
            System.arraycopy(getDeviceName().getBytes(), 0, claimStage1bytes, DEVICE_NAME_OFFSET, getDeviceName().getBytes().length);
            System.arraycopy(keepAliveBytes, MAC_ADDRESS_OFFSET, claimStage1bytes, 0x26, 6);
            for (int i = 1; i <= 3 && mixerAssigned.get() == 0; i++) {
                claimStage1bytes[0x24] = (byte)i;  // The packet counter.
                try {
                    logger.debug("Sending claim stage 1 packet {}", i);
                    DatagramPacket announcement = new DatagramPacket(claimStage1bytes, claimStage1bytes.length,
                            broadcastAddress.get(), DeviceFinder.ANNOUNCEMENT_PORT);
                    socket.get().send(announcement);
                    //noinspection BusyWait
                    Thread.sleep(300);
                } catch (Exception e) {
                    logger.warn("Unable to send device number claim stage 1 packet to network, failing to go online.", e);
                    claimingNumber.set(0);
                    return false;
                }
                if (claimRejected.get()) {  // Some other player is defending the number we tried to claim.
                    if (getDeviceNumber() == 0) {  // We are trying to pick a number.
                        continue selfAssignLoop;  // Try the next available number, if any.
                    }
                    logger.warn("Unable to use device number {}, another device has it. Failing to go online.", getDeviceNumber());
                    claimingNumber.set(0);
                    return false;
                }
            }

            // Send the middle series of device claim packets, unless we are interrupted by a defense
            // or a mixer assigning us a specific number.
            Arrays.fill(claimStage2bytes, DEVICE_NAME_OFFSET, DEVICE_NAME_LENGTH, (byte)0);
            System.arraycopy(getDeviceName().getBytes(), 0, claimStage2bytes, DEVICE_NAME_OFFSET, getDeviceName().getBytes().length);
            System.arraycopy(matchedAddress.getAddress().getAddress(), 0, claimStage2bytes, 0x24, 4);
            System.arraycopy(keepAliveBytes, MAC_ADDRESS_OFFSET, claimStage2bytes, 0x28, 6);
            claimStage2bytes[0x2e] = (byte)claimingNumber.get();  // The number we are claiming.
            claimStage2bytes[0x31] = (getDeviceNumber() == 0)? (byte)1 : (byte)2;  // The auto-assign flag.
            for (int i = 1; i <= 3 && mixerAssigned.get() == 0; i++) {
                claimStage2bytes[0x2f] = (byte)i;  // The packet counter.
                try {
                    logger.debug("Sending claim stage 2 packet {} for device {}", i, claimStage2bytes[0x2e]);
                    DatagramPacket announcement = new DatagramPacket(claimStage2bytes, claimStage2bytes.length,
                            broadcastAddress.get(), DeviceFinder.ANNOUNCEMENT_PORT);
                    socket.get().send(announcement);
                    //noinspection BusyWait
                    Thread.sleep(300);
                } catch (Exception e) {
                    logger.warn("Unable to send device number claim stage 2 packet to network, failing to go online.", e);
                    claimingNumber.set(0);
                    return false;
                }
                if (claimRejected.get()) {  // Some other player is defending the number we tried to claim.
                    if (getDeviceNumber() == 0) {  // We are trying to pick a number.
                        continue selfAssignLoop;  // Try the next available number, if any.
                    }
                    logger.warn("Unable to use device number {}, another device has it. Failing to go online.", getDeviceNumber());
                    claimingNumber.set(0);
                    return false;
                }
            }

            // If the mixer assigned us a number, use it.
            final int assigned = mixerAssigned.getAndSet(0);
            if (assigned > 0) {
                claimingNumber.set(assigned);
            }

            // Send the final series of device claim packets, unless we are interrupted by a defense, or the mixer
            // acknowledges our acceptance of its assignment.
            Arrays.fill(claimStage3bytes, DEVICE_NAME_OFFSET, DEVICE_NAME_LENGTH, (byte)0);
            System.arraycopy(getDeviceName().getBytes(), 0, claimStage3bytes, DEVICE_NAME_OFFSET, getDeviceName().getBytes().length);
            claimStage3bytes[0x24] = (byte)claimingNumber.get();  // The number we are claiming.
            for (int i = 1; i <= 3 && mixerAssigned.get() == 0; i++) {
                claimStage3bytes[0x25] = (byte)i;  // The packet counter.
                try {
                    logger.debug("Sending claim stage 3 packet {} for device {}", i, claimStage3bytes[0x24]);
                    DatagramPacket announcement = new DatagramPacket(claimStage3bytes, claimStage3bytes.length,
                            broadcastAddress.get(), DeviceFinder.ANNOUNCEMENT_PORT);
                    socket.get().send(announcement);
                    //noinspection BusyWait
                    Thread.sleep(300);
                } catch (Exception e) {
                    logger.warn("Unable to send device number claim stage 3 packet to network, failing to go online.", e);
                    claimingNumber.set(0);
                    return false;
                }
                if (claimRejected.get()) {  // Some other player is defending the number we tried to claim.
                    if (getDeviceNumber() == 0) {  // We are trying to pick a number.
                        continue selfAssignLoop;  // Try the next available number, if any.
                    }
                    logger.warn("Unable to use device number {}, another device has it. Failing to go online.", getDeviceNumber());
                    claimingNumber.set(0);
                    return false;
                }
            }

            claimed = true;  // If we finished all our loops, the number we wanted is ours.
        }
        // Set the device number we claimed.
        keepAliveBytes[DEVICE_NUMBER_OFFSET] = (byte)claimingNumber.getAndSet(0);
        mixerAssigned.set(0);
        return true;  // Huzzah, we found the right device number to use!
    }

    /**
     * Once we have seen some DJ Link devices on the network, we can proceed to create a virtual player on that
     * same network.
     *
     * @return true if we found DJ Link devices and were able to create the {@code VirtualCdj}.
Shell cwd was reset to /Users/noah/conductor/workspaces/deadca7/san-diego


 I've got the full startup sequence and message templates now, so I can write a solid review and build a stable virtual CDJ implementation. The device numbering works by selecting an unused number, and the keep-alive pings need to continue every 1.5 seconds after claiming the device. The initialization starts with three hello messages spaced 300ms apart, each 25 bytes.

Looking at the vizlab implementation, I can see why it's unstable: it skips the entire claim handshake (stages 1-3) and only sends a single keep-alive before starting a ticker, which means devices—especially mixers—won't properly recognize the virtual CDJ since they expect the full claim dialog. It also hardcodes the device number without any conflict detection or defense handling, so if another device claims that number or defends it, vizlab just ignores the rejection and keeps going. There are also some socket configuration gaps: no SO_BROADCAST flag set, which could prevent broadcast packets from being sent reliably on some systems, and binding to 0.0.0.0 means the OS picks the source interface, which could send packets out the wrong network interface if multiple are present.

The user wants a review of the instability plus an implementation of the corrected version. I should deliver a clear analysis of the root causes first, then build a proper virtual CDJ that performs the full claim handshake with self-assignment and defense listening so we can reliably capture status packets. I'll structure this as a new announce module in the link package that handles the complete initialization sequence and keeps the device alive with proper error handling.

For the implementation, I'll define packet types and builders for hello, claim stages 1-3, and keep-alive, then create an Announce routine that sends the full sequence with a chosen device number and listens for defense rejections. I'll wire this into the capture tool so it can run the handshake before recording, ensuring the virtual CDJ is properly registered on the network. I'll also note that handling mixer-assignment (when a DJM wants to assign us a number) is a follow-up, but the core self-assign path with defense detection will fix the main instability.

Defining the packet templates and offset constants...


I now have the complete authoritative handshake. Let me grab the keep-alive template and the offset constants to mirror beat-link exactly.


cd /tmp && sed -n '240,256p' vcdj.java; echo "=== offsets & self-assign ==="; grep -nE 'DEVICE_NAME_OFFSET =|DEVICE_NAME_LENGTH =|DEVICE_NUMBER_OFFSET =|MAC_ADDRESS_OFFSET =|_OFFSET =' vcdj.java | head; echo "---"; grep -n 'selfAssignDeviceNumber' vcdj.java | head -1

Read keepalive template and offset constants


}

    /**
     * Used to construct the keep-alive packet we broadcast in order to participate in the DJ Link network.
     * Some of these bytes are fixed, some get replaced by things like our device name and number, MAC address,
     * and IP address, as described in the
     * Packet Analysis document.
     */
    private static final byte[] keepAliveBytes = {
            0x51, 0x73, 0x70, 0x74,  0x31, 0x57, 0x6d, 0x4a,   0x4f, 0x4c, 0x06, 0x00,  0x62, 0x65, 0x61, 0x74,
            0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
            0x01, 0x02, 0x00, 0x36,  0x00, 0x01, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
            0x02, 0x00, 0x00, 0x00,  0x01, 0x64
    };

    /**
     * The location of the device name in the announcement packet.
=== offsets & self-assign ===
48:    public static final int MAC_ADDRESS_OFFSET = 38;
259:    public static final int DEVICE_NAME_OFFSET = 0x0c;
265:    public static final int DEVICE_NAME_LENGTH = 0x14;
271:    public static final int DEVICE_NUMBER_OFFSET = 0x24;
---
619:    private boolean selfAssignDeviceNumber() {
Shell cwd was reset to /Users/noah/conductor/workspaces/deadca7/san-diego


 I've mapped out all the offsets for the keepAlive packet template: the device name goes at 0x0c, the MAC address at 0x26, the device number at 0x24, and the IP address at 0x2c.

Looking at the actual byte layout from beat-link's template, I can see the structure clearly—the device type is fixed at 0x25 (value 0x01 for CDJ), and there are some other fields like the peer device count at 0x30 that I'll leave as-is from the template. Rather than trying to match every detail of a real CDJ-3000, I'll use beat-link's exact template verbatim and only patch the four fields that need to change per instance: name, device number, MAC, and IP.

For the device number assignment, I'll use a fixed configurable value (defaulting to 5) with the auto-assign flag set, which avoids needing to implement the network scan logic and is spec-compliant for fixed-channel mode.

Now I'm structuring the announce module with template byte arrays as package variables, a VCDJ struct to hold the device configuration, and methods to generate each packet type (hello, claim phases, keepAlive). The main Announce function will send the handshake sequence at 300ms intervals, then return control so the caller can run the keepAlive ticker at 1500ms intervals. I also need to set SO_BROADCAST on the socket to ensure broadcast packets are sent reliably, which I'll do via syscall control on the UDP connection.

For the capture tool integration, I'll restructure the main flow to open the socket first, optionally discover a peer device to learn the local IP and interface, then start all three recorders concurrently before running the announce handshake—this way the recorders capture packets while announce is sending.

Defining the packet methods...

Writing announce.go... Writing hex strings... I'm verifying the byte count and structure of the hex string by breaking it down piece by piece, then I'll generate the exact hex values using Python to avoid manual transcription errors.


I have the complete authoritative startup sequence and exact byte templates. Let me generate precise hex strings for each template from beat-link's arrays so I don't transcribe them by hand.


Generate exact hex template strings


hello     len=38 (0x26)  "5173707431576d4a4f4c0a00626561742d6c696e6b0000000000000000000000010400260140"
claim1    len=44 (0x2c)  "5173707431576d4a4f4c0000626561742d6c696e6b00000000000000000000000103002c0d01000000000000"
claim2    len=50 (0x32)  "5173707431576d4a4f4c0200626561742d6c696e6b000000000000000000000001030032000000000000000000000d000100"
claim3    len=38 (0x26)  "5173707431576d4a4f4c0400626561742d6c696e6b0000000000000000000000010300260d00"
keepalive len=54 (0x36)  "5173707431576d4a4f4c0600626561742d6c696e6b000000000000000000000001020036000100000000000000000000020000000164"


I've got the templates ready, so I'm starting with announce.go, then I'll add SetBroadcast to net.go, rewrite the capture tool, run a stability test on 0x0a status, and wrap up with a review summary.


Now I'll write the spec-compliant virtual CDJ with the full 4-stage handshake. First `announce.go`:


Write

package link

import (
	"context"
	"encoding/hex"
	"net"
	"time"

	"github.com/cockroachdb/errors"
)

// Packet types sent while a virtual CDJ comes online, in order. A real player
// sends hello, then three device-number claim stages, before keep-alives; see
// https://djl-analysis.deepsymmetry.org/djl-analysis/startup.html#cdj-startup
const (
	TypeClaim1  Type = 0x00
	TypeClaim2  Type = 0x02
	TypeClaim3  Type = 0x04
	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

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

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

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

// Announce performs the four-stage startup handshake on conn (bound to port
// 50000), broadcasting each packet to dst. It blocks for the full sequence
// (~3.6s) so a caller can treat its return as "online".
func (v VCDJ) Announce(ctx context.Context, conn *net.UDPConn, dst *net.UDPAddr) error {
	var pkts [][]byte
	pkts = append(pkts, v.hello(), v.hello(), v.hello())
	for i := byte(1); i <= 3; i++ {
		pkts = append(pkts, v.claim1(i))
	}
	for i := byte(1); i <= 3; i++ {
		pkts = append(pkts, v.claim2(i))
	}
	for i := byte(1); i <= 3; i++ {
		pkts = append(pkts, v.claim3(i))
	}

	for _, p := range pkts {
		if _, err := conn.WriteToUDP(p, dst); err != nil {
			return errors.WithStack(err)
		}
		select {
		case <-ctx.Done():
			return errors.WithStack(ctx.Err())
		case <-time.After(ClaimInterval):
		}
	}
	return nil
}

// KeepAlive broadcasts a keep-alive immediately and then every
// KeepAliveInterval until ctx is done, holding the claimed device number.
func (v VCDJ) KeepAlive(ctx context.Context, conn *net.UDPConn, dst *net.UDPAddr) error {
	t := time.NewTicker(KeepAliveInterval)
	defer t.Stop()
	for {
		if _, err := conn.WriteToUDP(v.keepAlive(), dst); err != nil {
			return errors.WithStack(err)
		}
		select {
		case <-ctx.Done():
			return nil
		case <-t.C:
		}
	}
}

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] = 0x02
	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) 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
}


File created successfully at: /Users/noah/conductor/workspaces/deadca7/san-diego/link/announce.go (file state is current in your context — no need to Read it back)

package link

import (
	"context"
	"encoding/hex"
	"net"
	"time"

	"github.com/cockroachdb/errors"
)

// Packet types sent while a virtual CDJ comes online, in order. A real player
// sends hello, then three device-number claim stages, before keep-alives; see
// https://djl-analysis.deepsymmetry.org/djl-analysis/startup.html#cdj-startup
const (
	TypeClaim1  Type = 0x00
	TypeClaim2  Type = 0x02
	TypeClaim3  Type = 0x04
	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

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

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

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

// Announce performs the four-stage startup handshake on conn (bound to port
// 50000), broadcasting each packet to dst. It blocks for the full sequence
// (~3.6s) so a caller can treat its return as "online".
func (v VCDJ) Announce(ctx context.Context, conn *net.UDPConn, dst *net.UDPAddr) error {
	var pkts [][]byte
	pkts = append(pkts, v.hello(), v.hello(), v.hello())
	for i := byte(1); i <= 3; i++ {
		pkts = append(pkts, v.claim1(i))
	}
	for i := byte(1); i <= 3; i++ {
		pkts = append(pkts, v.claim2(i))
	}
	for i := byte(1); i <= 3; i++ {
		pkts = append(pkts, v.claim3(i))
	}

	for _, p := range pkts {
		if _, err := conn.WriteToUDP(p, dst); err != nil {
			return errors.WithStack(err)
		}
		select {
		case <-ctx.Done():
			return errors.WithStack(ctx.Err())
		case <-time.After(ClaimInterval):
		}
	}
	return nil
}

// KeepAlive broadcasts a keep-alive immediately and then every
// KeepAliveInterval until ctx is done, holding the claimed device number.
func (v VCDJ) KeepAlive(ctx context.Context, conn *net.UDPConn, dst *net.UDPAddr) error {
	t := time.NewTicker(KeepAliveInterval)
	defer t.Stop()
	for {
		if _, err := conn.WriteToUDP(v.keepAlive(), dst); err != nil {
			return errors.WithStack(err)
		}
		select {
		case <-ctx.Done():
			return nil
		case <-t.C:
		}
	}
}

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] = 0x02
	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) 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
}


I need to add the SetBroadcast function to net.go using the unix package from x/sys, then write a round-trip test to verify it works correctly.


Now add `SetBroadcast` (sending to a subnet broadcast on macOS requires `SO_BROADCAST` — a likely silent-failure source the vizlab code never set):


Edit

import (
	"net"

	"github.com/cockroachdb/errors"
)

// broadcast returns the IPv4 broadcast address for n.
func broadcast(n *net.IPNet) net.IP {

import (
	"net"

	"github.com/cockroachdb/errors"
	"golang.org/x/sys/unix"
)

// SetBroadcast enables SO_BROADCAST on conn so it may send to a subnet
// broadcast address, which the OS otherwise rejects.
func SetBroadcast(conn *net.UDPConn) error {
	rc, err := conn.SyscallConn()
	if err != nil {
		return errors.WithStack(err)
	}
	var serr error
	if err := rc.Control(func(fd uintptr) {
		serr = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_BROADCAST, 1)
	}); err != nil {
		return errors.WithStack(err)
	}
	return errors.WithStack(serr)
}

// Broadcast returns the IPv4 broadcast address for n.
func Broadcast(n *net.IPNet) net.IP {


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

import (
	"net"

	"github.com/cockroachdb/errors"
	"golang.org/x/sys/unix"
)

// SetBroadcast enables SO_BROADCAST on conn so it may send to a subnet
// broadcast address, which the OS otherwise rejects.
func SetBroadcast(conn *net.UDPConn) error {
	rc, err := conn.SyscallConn()
	if err != nil {
		return errors.WithStack(err)
	}
	var serr error
	if err := rc.Control(func(fd uintptr) {
		serr = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_BROADCAST, 1)
	}); err != nil {
		return errors.WithStack(err)
	}
	return errors.WithStack(serr)
}

// Broadcast returns the IPv4 broadcast address for n.
func Broadcast(n *net.IPNet) net.IP {

package link

import (
	"net"

	"github.com/cockroachdb/errors"
)

// broadcast returns the IPv4 broadcast address for n.
func broadcast(n *net.IPNet) net.IP {
	v4 := n.IP.To4()
	ip := make(net.IP, net.IPv4len)
	for i := range v4 {
		ip[i] = v4[i] | ^n.Mask[i]
	}
	return ip
}

// Iface returns the up interface and IPv4 network whose subnet contains ip,
// used to match the local address to a discovered DJ Link device.
func Iface(ip net.IP) (*net.Interface, *net.IPNet, error) {
	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, nil, errors.WithStack(err)
	}

	for i := range ifaces {
		f := ifaces[i]
		if f.Flags&net.FlagUp == 0 {
			continue
		}

		addrs, err := f.Addrs()
		if err != nil {
			return nil, nil, errors.WithStack(err)
		}

		for _, a := range addrs {
			n, ok := a.(*net.IPNet)
			if ok && n.IP.To4() != nil && n.Contains(ip) {
				return &f, n, nil
			}
		}
	}

	return nil, nil, errors.Errorf("no interface for %s", ip)
}

-// broadcast returns the IPv4 broadcast address for n.

+// SetBroadcast enables SO_BROADCAST on conn so it may send to a subnet

+// broadcast address, which the OS otherwise rejects.

+func SetBroadcast(conn *net.UDPConn) error {

+  if err := rc.Control(func(fd uintptr) {

+    serr = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_BROADCAST, 1)

+// Broadcast returns the IPv4 broadcast address for n.


 I renamed broadcast to Broadcast since the capture tool needs to import it. Now I'm writing table-driven unit tests for the announce packet encoder to validate packet structure—checking lengths, types, and patched fields like names, counters, MACs, and IPs across different packet variants.

Adding more test cases...


Now a round-trip/structure test for the virtual-CDJ packets (hermetic, no hardware) — this is exactly the kind of thing that was never tested before:


Write

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)
			}
		})
	}
}


File created successfully at: /Users/noah/conductor/workspaces/deadca7/san-diego/link/announce_test.go (file state is current in your context — no need to Read it back)

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)
			}
		})
	}
}


Now wire the handshake into the capture tool with an `-announce` flag: