Server with ws (Node)

npm install ws
npm install --save-dev @types/ws   # TypeScript

import { WebSocketServer } from "ws";

const wss = new WebSocketServer({ port: 4000 });

wss.on("connection", (ws, req) => {
  const ip = req.socket.remoteAddress;
  console.log(`Client connected from ${ip}`);

  ws.on("message", (data, isBinary) => {
    const text = isBinary ? data : data.toString();
    console.log("received:", text);
  });

  ws.on("close", (code, reason) => {
    console.log("closed:", code, reason.toString());
  });

  ws.on("error", (err) => {
    console.error("ws error:", err);
  });

  ws.send("Hello from server");
});

wss.on("error", (err) => console.error("server error:", err));
wss.on("listening", () => console.log("WebSocket server on :4000"));

ws.send("hello");                          // text
ws.send(Buffer.from([0x01, 0x02]));        // binary
ws.send(data, { binary: true });           // force binary
ws.send(data, { compress: false });        // skip per-message deflate
ws.send(data, { fin: false });             // start fragmented message
ws.send(data, { fin: true });              // last fragment
ws.send(data, (err) => {                   // delivery callback
  if (err) console.error("send failed:", err);
});

const wss = new WebSocketServer({
  port: 4000,
  verifyClient({ origin, req, secure }, callback) {
    const token = new URL(req.url, "http://x").searchParams.get("token");
    if (!isValidToken(token)) {
      callback(false, 401, "Unauthorized");
    } else {
      callback(true);
    }
  },
});

const wss = new WebSocketServer({
  port: 4000,
  perMessageDeflate: {
    zlibDeflateOptions: { chunkSize: 1024, memLevel: 7, level: 3 },
    zlibInflateOptions: { chunkSize: 10 * 1024 },
    clientNoContextTakeover: true,   // saves memory, reduces ratio
    serverNoContextTakeover: true,
    serverMaxWindowBits: 10,
    concurrencyLimit: 10,            // max concurrent zlib ops
    threshold: 1024,                 // only compress if > 1 KB
  },
});

wss.on("headers", (headers, req) => {
  headers.push("Set-Cookie: session=abc; HttpOnly; SameSite=Strict");
  headers.push("X-Custom: value");
});

import WebSocket from "ws";

const ws = new WebSocket("wss://api.example.com/ws", {
  headers: { Authorization: `Bearer ${token}` },  // allowed in Node, not browser
  handshakeTimeout: 5000,
  rejectUnauthorized: true,       // validate TLS cert (true in prod)
  perMessageDeflate: false,
});

ws.on("open", () => ws.send("hello"));
ws.on("message", (data) => console.log(data.toString()));
ws.on("error", console.error);
ws.on("close", (code) => console.log("closed:", code));

function safeSend(ws, data) {
  if (ws.readyState === WebSocket.OPEN) {
    ws.send(data);
  }
}