How to Monitor Your 3D Printers with Node.js

type PrinterApiType = "octoprint" | "moonraker" | "bambu" | "mqtt" | "custom";
type PrinterStatus = "online" | "offline" | "idle" | "printing" | "paused" | "error";

export interface Printer {
  id: string;
  name: string;
  model: string;
  location: string;
  apiType: PrinterApiType;
  apiUrl: string;
  status: PrinterStatus;
  lastSeenAt: Date | null;
}

export interface PrinterSnapshot {
  printerId: string;
  status: PrinterStatus;
  jobName: string | null;
  progress: number | null;
  nozzleTemp: number | null;
  bedTemp: number | null;
  errorCode: string | null;
  capturedAt: Date;
}

import express from "express";

type PrinterStatus = "online" | "offline" | "idle" | "printing" | "paused" | "error";

type Printer = {
  id: string;
  name: string;
  apiUrl: string;
  apiType: "octoprint" | "moonraker" | "custom";
  tokenRef?: string;
};

type PrinterSnapshot = {
  printerId: string;
  status: PrinterStatus;
  jobName: string | null;
  progress: number | null;
  nozzleTemp: number | null;
  bedTemp: number | null;
  errorCode: string | null;
  capturedAt: Date;
};

const app = express();
const latestSnapshots = new Map<string, PrinterSnapshot>();

const printers: Printer[] = [
  {
    id: "printer-1",
    name: "Printer 1",
    apiUrl: "http://printer-one.local",
    apiType: "custom"
  }
];

function buildAuthHeaders(printer: Printer) {
  // Load tokens from an environment variable, secret store, or database.
  // Do not hardcode real API keys in source code.
  if (!printer.tokenRef) {
    return {};
  }

  const token = process.env[printer.tokenRef];
  return token ? { Authorization: "Bearer " + token } : {};
}

function normalizeSnapshot(printer: Printer, raw: any): PrinterSnapshot {
  return {
    printerId: printer.id,
    status: raw.status ?? "online",
    jobName: raw.jobName ?? null,
    progress: typeof raw.progress === "number" ? raw.progress : null,
    nozzleTemp: typeof raw.nozzleTemp === "number" ? raw.nozzleTemp : null,
    bedTemp: typeof raw.bedTemp === "number" ? raw.bedTemp : null,
    errorCode: raw.errorCode ?? null,
    capturedAt: new Date()
  };
}

async function pollPrinter(printer: Printer) {
  try {
    const url = new URL("/api/printer/status", printer.apiUrl);
    const response = await fetch(url, { headers: buildAuthHeaders(printer) });

    if (!response.ok) {
      throw new Error("Printer returned HTTP " + response.status);
    }

    const raw = await response.json();
    latestSnapshots.set(printer.id, normalizeSnapshot(printer, raw));
  } catch (error) {
    latestSnapshots.set(printer.id, {
      printerId: printer.id,
      status: "offline",
      jobName: null,
      progress: null,
      nozzleTemp: null,
      bedTemp: null,
      errorCode: error instanceof Error ? error.message : "poll_failed",
      capturedAt: new Date()
    });
  }
}

setInterval(() => {
  void Promise.all(printers.map((printer) => pollPrinter(printer)));
}, 20_000);

app.get("/api/printers/snapshots", (_request, response) => {
  response.json(Array.from(latestSnapshots.values()));
});

app.listen(3000, () => {
  console.log("Printer monitor listening on port 3000");
});