3djuggler

A daemon that turns a 3D printer into a shared, network-managed resource.

3djuggler runs on a small device next to a printer. It polls a web endpoint for queued print jobs, waits for someone to physically confirm at the machine, then streams the G-code to the printer over serial, reporting progress as it goes.

It was written for a hackathon in 2018 to replace a paper queue taped to the wall next to two office printers. It is still in production today, driving printers across dozens of offices.

Why a daemon and not a web UI on the printer

The design constraint was that a printer sits on an office network, and the people using it do not. Rather than exposing anything per printer, the daemon only ever dials out:

  person → web UI → job queue ← 3djuggler → printer
                                (polls)     (serial/USB)

Nothing reaches into the office. There is no inbound port, no firewall exception and no per-printer DNS record to maintain, and the poll doubles as the liveness heartbeat. That narrow contract, poll HTTP out and write serial in, is why the same binary has outlived three generations of the hardware it runs on.

What you need to run it

• A 3D printer that accepts G-code over a serial connection. Tested against Prusa MK3/MK3S (including MMU2) and MK4.
• A machine to run the daemon on, connected to the printer by USB. Anything that runs Go will do; in production this is a small ARM panel.
• A backend implementing the job API below.

Job API

The daemon is the client, so you supply the server. Every call is a POST and must include app and token credentials.

POST /job/

action	Purpose
get	Return the next queued job, or the job named by id
update	Record a new status for job id
delete	Remove job id from the queue

A get responds with:

{
  "Success": true,
  "Content": {
    "id": 42,
    "file_name": "bracket.gcode",
    "file_content": "G28\nG1 X10\n...",
    "owner": "someone",
    "status": "New",
    "color": "Galaxy Black"
  }
}

Return "Content": null or an id of 0 when the queue is empty.

POST /printer/

action	Purpose
heartbeat	Mark the printer online; sent on every poll
reschedule	Reset the confirmation timer for the current job

Local control API

The daemon also serves a small HTTP API on localhost:8888, which is what a touchscreen next to the printer talks to. /start, /pause and /cancel wait for the daemon to apply the state transition before responding.

Endpoint	Purpose
GET /info	Current job as JSON: owner, file name, status, progress
GET /start	Confirm and start the job, or resume a paused one
GET /pause	Pause the running job
GET /cancel	Cancel the running job
GET /reschedule	Give the owner more time to confirm
GET /version	Build commit, as plain text

Job lifecycle

Waiting for job → Waiting for a button → Sending to printer → Printing → Finished
                          ↓                                       ↓
                   Button timeout                               Paused

A job does not start until a person presses the button at the machine, which they have ten minutes to do. Miss it and the job moves to the back of the queue rather than being discarded, so nobody loses their place by being late, and nobody can hold a printer they are not standing next to.

Build

go build ./...

/version reports the commit the binary was built from. The Go toolchain records it automatically, so there is nothing to pass at build time. Building from a tree with uncommitted changes appends -dirty.

Cross-compiling for the device is a normal Go cross-compile:

GOOS=linux GOARCH=arm64 go build .

Run

3djuggler -config 3djuggler.json

Flag	Default	Purpose
-config	3djuggler.json	Config file path
-log	/var/log/3djuggler.log	Log file path
-verbose	false	Debug-level logging
-insecure	false	Skip TLS verification. Development only

See 3djuggler.json for a complete example config.

Note that the config key is spelled InternEnpoint. The typo is from the original 2018 commit and is kept deliberately, because every deployed config in the fleet still uses it.

Development

fakejuggler/ is an interactive stub that serves the local control API without any hardware, for developing a client against.

gcodefeeder/ is the serial-facing half and is usable on its own, for any device that takes G-code over a serial line.

go test -race ./...

License

Apache 2.0, see LICENSE.

I am providing code in the repository to you under an open source license. Because this is my personal repository, the license you receive to my code is from me and not my employer (Meta).