[engine.io-client] The client writes the URI into the options object, so a reused object sends one URL's query to the next server #5597

Describe the bug

The client writes the parts of the URI into the options object passed to it: the Socket constructor of engine.io-client sets hostname, secure, port and query on it, and io() in socket.io-client also sets path and query. When the same options object is used for another connection, the query string of the first URI (for example a token) is sent to the second server.

To Reproduce

Socket.IO server version: 4.8.4

Server

const { createServer } = require("node:http");
const { Server } = require("socket.io");

for (const port of [3000, 3001]) {
  const httpServer = createServer();
  const io = new Server(httpServer);

  io.on("connection", (socket) => {
    console.log(`server on port ${port} received token:`, socket.handshake.query.token);
  });

  httpServer.listen(port);
}

Socket.IO client version: 4.8.4 (engine.io-client 6.6.8, also reproduced on main at 545e984)

Client

const { io } = require("socket.io-client");

const opts = { transports: ["websocket"] };

const a = io("http://localhost:3000/?token=secret-for-3000", opts);

a.on("connect", () => {
  const b = io("http://localhost:3001/", opts);
});

Server output:

server on port 3000 received token: secret-for-3000
server on port 3001 received token: secret-for-3000

The same happens with engine.io-client alone (new Socket("ws://localhost:3000/?token=secret-for-3000", opts), then new Socket("ws://localhost:3001/", opts)). After the first call, opts is:

{
  transports: [ 'websocket' ],
  hostname: 'localhost',
  secure: false,
  port: '3000',
  query: 'token=secret-for-3000'
}

Expected behavior

The options object is left as it was, and each connection only sends the query of its own URI:

server on port 3000 received token: secret-for-3000
server on port 3001 received token: undefined

Platform:

• Device: desktop
• OS: Windows, Node.js 24.22.1

Additional context

#5462 fixed the transports part of the same pattern. The remaining writes are in the constructor of Socket in packages/engine.io-client/lib/socket.ts, and in lookup() in packages/socket.io-client/lib/index.ts (opts.query = parsed.queryKey, plus opts.path set by the Manager). I'm opening a PR with a fix and tests.

AI-assisted: found and reproduced with an AI coding agent; the example above was run locally.