OCPP in Node.js: Build a CSMS with ocpp-ws-io

OCPP in Node.js

OCPP-J is JSON over WebSocket, which makes Node.js a natural fit for a CSMS: one process can hold thousands of charger connections and handle their messages asynchronously. What you don't want to write by hand is the protocol plumbing — message framing, matching responses to requests, timeouts and the OCPP error codes.

ocpp-ws-io is an OCPP RPC WebSocket library for Node.js and TypeScript that does exactly that, for OCPP 1.6J, 2.0.1 and 2.1. It is also what powers this simulator, so the same library sits on both ends of your tests.

What “OCPP RPC” means

OCPP-J sends remote procedure calls as JSON arrays. A CALL is [2, id, action, payload]; the receiver replies with a CALLRESULT [3, id, payload] or a CALLERROR [4, id, code, description, details]. An OCPP RPC library handles that framing, so your code works with typed requests and responses.

What ocpp-ws-io gives you

• OCPP 1.6J, 2.0.1 and 2.1

  Full OCPP-J RPC framing with version-aware handlers.

• Type-safe TypeScript

  Generated types for every OCPP action and payload.

• Schema validation

  Optional strict JSON schema validation of messages.

• All security profiles

  Plain WebSocket, Basic Auth, TLS and mutual TLS.

• Scales out

  Redis pub/sub clustering for multi-node CSMS deployments.

• Client, server and browser

  Server and client for Node.js, plus a browser client.

Build a minimal CSMS

Install the package:

npm install ocpp-ws-io

Then start a server that accepts OCPP 1.6J and 2.0.1 chargers and answers their BootNotification:

import { OCPPServer } from "ocpp-ws-io";

const server = new OCPPServer({
  protocols: ["ocpp1.6", "ocpp2.0.1"],
  logging: { prettify: true, exchangeLog: true, level: "info" },
});

server.on("client", (client) => {
  console.log(`${client.identity} connected`);

  client.handle("ocpp1.6", "BootNotification", ({ params }) => {
    console.log("Boot from:", params.chargePointVendor);
    return {
      status: "Accepted",
      currentTime: new Date().toISOString(),
      interval: 300,
    };
  });
});

await server.listen(9000);

Test it with the simulator

1. Run the server above; it listens on ws://localhost:9000.
2. Open the simulator, keep the endpoint ws://localhost:9000 and select Connect.
3. Your server logs the connection and the BootNotification. Add more handlers — Authorize, StartTransaction, MeterValues — and drive them from the simulator.

Or write a charge point in Node.js

The same library also works on the charger side, for scripted tests and headless simulators:

import { OCPPClient } from "ocpp-ws-io";

const client = new OCPPClient({
  endpoint: "ws://localhost:9000",
  identity: "CP001",
  protocols: ["ocpp1.6"],
});

client.handle("ocpp1.6", "Reset", async ({ params }) => {
  console.log("Reset requested:", params.type);
  return { status: "Accepted" };
});

await client.connect();

const response = await client.call("ocpp1.6", "BootNotification", {
  chargePointVendor: "VendorX",
  chargePointModel: "ModelY",
});
console.log("Status:", response.status);

Full API reference and guides: ocpp-ws-io documentation · npm · GitHub.