Transceiver Lab

Test tool for UDP multicast messaging. Single binary — drop it anywhere, open a browser.

It handles CoT 2.0 XML, JSON, VMF binary, and raw payloads. You can send one-shot messages or loop them on a timer, join multicast groups and watch live traffic, save templates, and browse TX/RX history. Multiple sessions run independently, so you can be sending to 239.2.3.1:6969 and listening on 239.0.0.5:4000 at the same time.

Built to replace the usual socat/Wireshark combo when you just need to poke at a multicast pipeline.

Build

Go 1.22+ and Node.js 18+.

cd impl/multicast-tester
make build
# output: bin/mmt

Cross-compile flags work as expected:

GOOS=linux   GOARCH=amd64 make build
GOOS=windows GOARCH=amd64 make build
GOOS=darwin  GOARCH=arm64 make build

The binary embeds the web UI — no separate web server, no static files to manage.

Run

./bin/mmt
# Open http://localhost:8080

--port        HTTP server port          (default: 8080)
--bind        Bind address              (default: 127.0.0.1)
--db          SQLite path               (default: ./mmt.db)
--log-level   debug | info | warn | error (default: info)
--dev         Proxy UI to Vite dev server at :5173
--version     Print version and exit

By default it binds to loopback only. Pass --bind 0.0.0.0 if you need it reachable from other machines, but there is no auth.

Dev mode

Go handles the API; Vite handles the frontend with hot reload.

# terminal 1
cd impl/multicast-tester/web && npm install && npm run dev

# terminal 2
cd impl/multicast-tester && go run ./cmd/mmt --dev --port 8080

Formats

CoT 2.0 — Cursor on Target XML. The send page has a default template. Dynamic tokens work anywhere in the payload: {{timestamp}}, {{seq}}, {{uuid}}.

JSON — any JSON. No schema required, but schema validation is available via the API if you want it.

VMF — Variable Message Format binary. Input as a hex string (spaces allowed). Wire format: 4-byte magic 0x4d4d5400, 2-byte message type, 2-byte body length, body bytes.

Raw — sent verbatim, no processing. Useful for custom protocols or seeing how a receiver handles garbage.

On receive, format is auto-detected: XML prefix → CoT, { or [ → JSON, less than 70% printable bytes → VMF, otherwise unknown.

Multicast

Default group: 239.2.3.1:6969. ASM and SSM both work.

Send uses net.UDPConn with ipv4.PacketConn socket options for TTL and loopback control. Receive uses net.ListenMulticastUDP. Both are configurable per session.

On Windows, the TTL and loopback socket options fail silently. The connection still works.

Data

SQLite at ./mmt.db. Sessions are in memory only — they do not survive a restart. History records are trimmed automatically once you hit the configured limit (default 10,000).

Templates and history persist across restarts. Settings too.

Stack

Go backend: Chi router, gorilla/websocket, modernc/sqlite (pure Go, no CGo required).

Frontend: React 18, Vite 6, TypeScript, Tailwind 3, Zustand.

Format codecs: beevik/etree for CoT XML, xeipuuv/gojsonschema for JSON schema validation, custom VMF codec.