Forward request to ws client and wait for response Express

Question

I\'m trying to build an endpoint that will receive a request, emit the request data to a WebSocket client, wait for an event, then send back the response using express + soc

Answer 1

Please note that:

socket.on('res', function (data) {
    res.status(200).json(data);
});

Is being called each time a socket is sending a response, thus showing the above error. You should unbind the listener inside the callback function.

Answer 2

You're trying to do two different async tasks for the same data.

First, take your socket.on('res'...) out of the app.get().

Send back res.status(200) immediately with express to say you received the request and it is processing. Then send the socket message to the client using socket.io when it's complete. You'll want to save the connected users socket client ID and use io.to(socketId).emit(...data...) to do this

the other option is what I always do (assuming it's not a crazy large payload of data you're sending) Just use socket.io for the whole process.

---

client

function makeRequest () {
    socket.on('data-complete--error', function ( error ) {
        // ... message to user :(
        // also remove these handlers when finished
        socket.off('data-complete--error');
        socket.off('data-complete--success');
    });
    socket.on('data-complete--success', function ( data ) {
        // ... message to user :)
        // ... handle data
        // also remove these handlers when finished
        socket.off('data-complete--error');
        socket.off('data-complete--success');
    });
    socket.emit('request-data');
}

makeRequest();

server

move your stuff out and handle without using express at all

Answer 3

Keep an array of express responses and set an id to each request. So it can be used later and delete if needed.

var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);
var timeout = require('connect-timeout');
var uuid = require('uuidv4');
var _ = require('lodash');

app.use(timeout('10s'));

app.get('/', (req, res) => {
    res.sendFile(__dirname + '/index.html');
});

let responses = []

io.on('connection', (socket) => {
    socket.on('res', (e) => {
        var obj = _.find(responses, r => r.id === e.id);
        obj.res.send(e)
        _.remove(responses, r => r.id === e.id);
    })
})

app.get('/endpoint', (req, res) => {
    const id = uuid()
    io.emit('req', { id, ip: req.ip, header: req.headers, method: req.method });
    responses.push({ id, res })
});

http.listen(3000);