I have setup Nodejs to serve an HttpServer using ExpressJs. I also need to use ws WebSocket in order to connect to my device for fetching data.
My attempt is now this.
import express from 'express';
import cors from 'cors';
import http from 'http';
import { WebSocketServer } from 'ws';
const app = express();
app.use(cors());
//initialize a simple http server
const httpServer = http.createServer(app);
const wsServer = new WebSocketServer({ port: 7777});
wsServer.on('connection', function connection(ws, req) {
app.get('/', (req, res) => {
ws.send('{"msg":"getdata"}');
ws.on('message', function message(data) {
data = JSON.parse(data);
res.json(data);
});
});
//start our server
httpServer.listen(7778, () => {
console.log(`Server started on port ${httpServer.address().port} :)`);
});
});
The problem is that when the API is called more than once. An error code: 'ERR_HTTP_HEADERS_SENT' is thrown. I assume it is because the ws.on('message') is executed multiple times. So, I am trying to find a way to remove the listener but to no avail.
Is there any better way to do this? I just want to have a webserver that calls to another websocket in order to get data from a device.
this will solve your error code: 'ERR_HTTP_HEADERS_SENT'
wsServer.on('connection', function connection(ws, req) {
app.get('/', (req, res) => {
//first This
ws.on('message', function message(data) {
data = JSON.parse(data);
res.json(data);
});
//then use this
ws.send('{"msg":"getdata"}');
});
//start our server
httpServer.listen(7778, () => {
console.log(`Server started on port ${httpServer.address().port} :)`);
});
});
For your code example to work, message on websocket must be sent after the / request is made. Because, before that, on message handler is not registered. Also, once handling the first request successfully, you cannot send a websocket message again. Because, when you do that, the res in the message handler is already completed. So, you will get ERR_HTTP_HEADERS_SENT. Thus proved :-)
So, your API calls must be like in the following pattern
/ Call #1
Websocket message #1
/ Call #2
Websocket message #2
If you do so, you will not get the ERR_HTTP_HEADERS_SENT error. Because, res is send once for every / request.
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);
If you want over multiple instance, you can use redis pub sub.