i’m writing an express middleware that know how to respond to many endpoints, most of them pure http, but some of them are special that require bi-directional communication (websockets).

normally, when you have access to the http server you can achive this with the following:

import http from 'http';
const server = http.createServer(app);
app.listen = function serverListen(...args) {
    return server.listen(...args);
};
const wss = new WebSocketServer({ server: server });
wss.on('connection', (ws) => {
    ws.on('message', (message) => {
        console.log('Received:', message);
        ws.send('Message received: ' + message);
    });
});
server.on('upgrade', function upgrade(request, socket, head) {
    wss.handleUpgrade(request, socket, head, function done(ws) {
        wss.emit('connection', ws, request);
    });
});

the above implementation works as expected. the upgrade event provide us request, socket, and head parameters which are crucial in order to call correctly to wss.handleUpgrade.

the things is, that i don’t have access to the underlying http server, and i couldn’t find any implementation on the internet that extract request, socket, head directly from express request and response objects passed to the middlewares. (before anyone suggest, express-ws also relies on http server).

currently, i was able to correctly extract request and socket parameter from express, but i am missing the head parameter.

wss.handleUpgrade(req, req.socket, ???, (websocket) => {
    wss.emit('connection', websocket, req);
});

as you can see: we get request from express.request, socket from express.request.socket but head is missing.

with the help of AI and MDN docs i was able to get one step closer in re-constructing the head parameter.
here the code:

if (path === '/transaction/.websocket') {
    // this is a transaction request
    console.log('Transaction request');

    // Check if the request is a WebSocket upgrade request
    if (!req.headers.upgrade || req.headers.upgrade.toLowerCase() !== 'websocket') {
        return res.status(400).send('Invalid WebSocket upgrade request');
    }

    // Get the value of the 'Sec-WebSocket-Key' header
    const secWebSocketKey = req.headers['sec-websocket-key'];
    if (!secWebSocketKey) {
        return res.status(400).send('Missing Sec-WebSocket-Key header');
    }
    // Construct the `head` buffer according to the WebSocket protocol
    // see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Sec-WebSocket-Accept
    const secWebSocketAccept = crypto
        .createHash('sha1')
        .update(secWebSocketKey + '258EAFA5-E914-47DA-95CA-C5AB0DC85B11=')
        .digest('base64');

    const head = Buffer.from(
        `HTTP/1.1 101 Switching ProtocolsrnUpgrade: websocketrnConnection: UpgradernSec-WebSocket-Accept: ${secWebSocketAccept}rnrn`,
    );
    
    // Handle the WebSocket upgrade
    wss.handleUpgrade(req, req.socket, head, (websocket) => {
        wss.emit('connection', websocket, req);
    });
    
}

but not i get on the server response Uncaught RangeError: Invalid WebSocket frame: RSV1 must be clear.

this is where i was able to get so far. any help would be appreciated.

relevant:

• NodeJS, WebSockets, upgrade head