Make socket.io work within an API endpoint in Node.js

Question

I'm having the following logic (all servers are in Node.js) :

1- Client makes an API call to Server A's "api/request" endpoint.

2- Server A "request" endpoint receives the request, and just passes the original request to Server B with a socket.io emit event.

3- Server B socket.io on event receives the request, handles it, and sends back the response in a new socket.io emit event.

4- Server A socket.io on event receives the response, and is supposed to return the response to the Client who originally made the request.

The issue is that since in Server A I'm passing the request with socket.io emit event, I'm loosing the option to wait for an answer from Server B to return to Client anything. I would like Client to receive the response from Server B, as a response from its original call to Server A.

Any idea on how to achieve this?

Answer 1

I found a way. Since you can only have one io.on('connection', function (socket) {}) in your code, I had to find a way around it.

The issue was that if you place io.on('connection', function (socket) {}) within your router.post('/', async (req, res) => {}), it will only be triggered when you call your endpoint. In my case, I had some sockets events that I wanted to be called at anytime, not only when the endpoint is called. So I had to place the io.on('connection', function (socket) {}) outside of my router.post('/', async (req, res) => {}). Thus I couldn't use var io = req.app.get('socketio'); inside the router. Here is what I have done instead in Server A code:

index.js:

const cors = require('cors');
const express = require('express');
const app = express();
const server = require('http').Server(app);
const io = require('socket.io')(server);
const taskRequest = require('./routes/taskRequest')(io);

app.use(cors())
app.use(express.json());
app.use('/api/taskRequest', taskRequest);

server.listen(4002);

routes/taskRequest.js

const express = require('express');
const router = express.Router();

module.exports = function(io) {

    //we define the variables
    var sendResponse = function () {};

    io.sockets.on("connection",function(socket){
        // Everytime a client logs in, display a connected message
        console.log("Server-Client Connected!");

        socket.on('connected', function(data) {
            //listen to event at anytime (not only when endpoint is called)
            //execute some code here
        });

        socket.on('taskResponse', data => {
            //calling a function which is inside the router so we can send a res back
            sendResponse(data);
        })     
    });

    router.post('/', async (req, res) => {

        //pickedUser is one of the connected client
        var pickedUser = "JZLpeA4pBECwbc5IAAAA";
        io.to(pickedUser).emit('taskRequest', req.body);

        sendResponse = function (data) {
            return res.status(200).json({"text": "Success", "response": data.data});
        }

    });

    return router;

};

Like this, Server A is only sending back to Client the response once it has received the response from Server B.

Solved!