3D Printer Power Control API

REST API in Go for controlling a 3D printer power relay through MQTT, with a safe power-off flow coordinated with Moonraker and SSH.

Current behavior (from code)

• HTTP server listens on :8000
• Endpoints:
  • GET /api/3d-printer
  • POST /api/3d-printer
• MQTT topics are currently hardcoded:
  • read state from zigbee2mqtt/R
  • publish commands to zigbee2mqtt/R/set
• POST OFF is a blocking flow (waits until print is done and hotend cools down)

Prerequisites

• Go 1.25+ (module is set to go 1.25.0)
• Reachable MQTT broker on port 1883
• SSH access to printer host (password auth)
• Moonraker API reachable by this service

Environment variables

The app loads variables from:

1. .env in project root
2. /root/power-api/.env (useful for deployments)
3. process environment

Use lowercase keys exactly as below:

mqtt_host=
mqtt_user=
mqtt_pass=
ssh_host=
ssh_user=
ssh_pass=
ssh_host_public_key=
moonraker_url=
threshold_temp=

Notes:

• threshold_temp defaults to 49 when missing/invalid
• ssh_host_public_key should contain the full OpenSSH public key line for the printer host (for example ecdsa-sha2-nistp256 AAAA...)
• no strict startup validation is done for empty values, so wrong/missing config will usually fail at runtime (MQTT/HTTP/SSH operations)

Local run

1. Prepare env file:

cp template.env .env

2. Fill .env with your values.

3. Run:

go run .

The service starts on http://localhost:8000.

Build

go build -o power-api .

Tests

Tests are organized in the dedicated tests/ folder and split by source responsibility:

• tests/config_test.go
• tests/moonraker_test.go
• tests/mqtt_test.go
• tests/handlers_test.go
• tests/shutdown_test.go
• tests/helpers_test.go

Run all tests:

go test ./...

Code coverage

Generate and print coverage summary:

make coverage

This runs tests from ./tests and measures coverage for ./src/....

Generate HTML coverage report:

make coverage-html

This creates:

• coverage.out (profile)
• coverage.html (visual report)

API

GET /api/3d-printer

Returns current relay state from MQTT.

Example response:

{
    "state": "ON"
}

POST /api/3d-printer

Request body:

{
    "state": "ON"
}

Allowed values:

• ON – immediately publishes MQTT ON
• OFF – starts safe shutdown flow:
  1. poll Moonraker print state (standby or complete required)
  2. poll Moonraker temperature store and compute average of recent extruder readings
  3. wait until average temp is below threshold_temp
  4. execute SSH command /sbin/shutdown 0
  5. wait until host no longer responds to ping
  6. publish MQTT OFF

Moonraker endpoints used

• {moonraker_url}/printer/objects/query?print_stats
• {moonraker_url}/server/temperature_store

Docker image (current Dockerfile)

• multi-stage build
• final image is scratch
• binary entrypoint is /power-api

If you run in a container, pass env vars explicitly (or mount a file at /root/power-api/.env if your runtime allows it).

Operational notes

• MQTT client uses auto-reconnect
• API request for POST OFF can be long-running due to cooldown and host shutdown waiting
• app runs Gin in release mode