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Node.js running a shell command from the same process

I'm trying to make a way to boot up a Minecraft server from nodejs, but I'm having trouble making a way to run commands from nodejs.
const { spawn } = require('node:child_process')
const express = require('express');
const bodyParser = require('body-parser');
const app = express();
const fs = require('fs');
app.get('/start', (req, res) => {
fs.writeFile('minecraftstatus.txt', 'on', (err) => {
if (err) throw err;
});
const command = spawn('java', ['-jar', '-Xms2048M','-Xmx2048M', '-Dfile.encoding=utf8', 'server.jar', 'nogui'])
// the `data` event is fired every time data is
// output from the command
command.stdout.on('data', output => {
// the output data is captured and printed in the callback
fs.appendFile('console.txt', ("\n" + output.toString()), 'utf-8', err => {
console.log(err)
})
console.log("Output: ", output.toString())
})
res.status(200).send("OK")
});
app.listen(80, () => {
console.log('Server started on port 80');
});
From what you see above, whenever a user sends a GET request, it sends a command and appends any output to a text file. I need to make a way in order to send commands to Minecraft. I need to send commands to the same shell that nodejs ran the command.
I've tried this:
app.get('/mcstop', (req, res) => {
try {
const command2 = spawn('/stop')
// the `data` event is fired every time data is
// output from the command
command2.stdout.on('data', output => {
// the output data is captured and printed in the callback
console.log("Output: ", output.toString())
})
res.status(200).send("OK")
}
catch {
console.log("Oh no...")
}
});
Where it sends /stop to the shell, but it seems like it isn't being ran on the same shell as where the Minecraft server was created from.
How could I achieve this?

SO_REUSEADDR in NodeJs using net package

I have two backends. Backend A and Backend B.
Backend B sends and receives info using a socket server running at port 4243.
Then, with Backend A, I need to catch that info and save it. But I have to also have a socket server on Backend A running at port 4243.
The problem is that, when I run Backend A after running Backend B I receive the error "EADDRINUSE", because I'm using the same host:port on both apps.
If, for Backend A I use Python, the problem dissapear because I have a configuration for sockets that's called SO_REUSEADDR.
Here we have some examples:
https://www.programcreek.com/python/example/410/socket.SO_REUSEADDR
https://subscription.packtpub.com/book/networking-and-servers/9781849513463/1/ch01lvl1sec18/reusing-socket-addresses
But, I want to use JavaScript for coding my Backend A, so I was using the net package for coding the sockets, and I can't get it to work, because of the "EADDRINUSE" error.
The NodeJS documentation says that "All sockets in Node set SO_REUSEADDR already", but it doesn't seem to work for me...
This is my code so far:
// Step 0: Create the netServer and the netClient
console.log(`[DEBUG] Server will listen to: ${HOST}:${PORT}`);
console.log(`[DEBUG] Server will register with: ${AGENT_ID}`);
const netServer = net.createServer((c) => {
console.log('[netServer] Client connected');
c.on('message', (msg) => {
console.log('[netServer] Received `message`, MSG:', msg.toString());
});
c.on('*', (event, msg) => {
console.log('[netServer] Received `*`, EVENT:', event);
console.log('[netServer] Received `*`, MSG:', msg);
});
}).listen({
host: HOST, // 'localhost',
port: PORT, // 4243,
family: 4, // ipv4, same as socket.AF_INET for python
});
// Code copied from nodejs documentation page (doesn't make any difference)
netServer.on('error', function (e) {
if (e.code == 'EADDRINUSE') {
console.log('Address in use, retrying...');
setTimeout(function () {
netServer.close();
netServer.listen(PORT, HOST);
}, 1000);
}
});
const netClient = net.createConnection(PORT, HOST, () => {
console.log('[netClient] Connected');
});
// Step 1: Register to instance B of DTN with agent ID 'bundlesink'
netClient.write(serializeMessage({
messageType: AAPMessageTypes.REGISTER,
eid: AGENT_ID,
}));
With this code, I get the following output in the terminal:
But, with the Python code, the socket connects successfully:
I don't know what to do :(
I hope I get some help here.
Edit 1
By the way, the lsof command, throws me this output for the JavaScript backend:
And this other output for the Python backend:
Edit 2
It really seems to be a problem with JavaScript. I also found this snippet:
var net = require('net');
function startServer(port, host, callback) {
var server = net.createServer();
server.listen(port, host, function() {
callback(undefined, server);
});
server.on('error', function(error) {
console.error('Ah damn!', error);
callback(error);
});
}
startServer(4000, '0.0.0.0', function(error, wildcardServer) {
if (error) return;
startServer(4000, '127.0.0.1', function(error, localhostServer) {
if (error) return;
console.log('Started both servers!');
});
});
From this post:
https://medium.com/#eplawless/node-js-is-a-liar-sometimes-8a28196d56b6
As the author says:
Well, that prints “Started both servers!” which is exactly what we don’t want.
But for me, instead of printing that, I get an error:
Ah damn! Error: listen EADDRINUSE: address already in use 127.0.0.1:4000
at Server.setupListenHandle [as _listen2] (node:net:1319:16)
at listenInCluster (node:net:1367:12)
at doListen (node:net:1505:7)
at processTicksAndRejections (node:internal/process/task_queues:84:21) {
code: 'EADDRINUSE',
errno: -98,
syscall: 'listen',
address: '127.0.0.1',
port: 4000
}
I really cannot make it to run and print "Started both servers!".
Because that's what I want my code to do.
Edit 3
This is the Python server socket: https://gitlab.com/d3tn/ud3tn/-/blob/master/tools/aap/aap_receive.py
This is the important part:
addr = (args.tcp[0], int(args.tcp[1])) # args.tcp[0] = "localhost", args.tcp[1] = "4243"
with AAPTCPClient(address=addr) as aap_client:
aap_client.register(args.agentid) # args.agentid = "bundlesink"
run_aap_recv(aap_client, args.count, args.verify_pl)
It creates an AAPTCPClient, and the only thing that AAPTCPClient does, is the following:
def __init__(self, socket, address):
self.socket = socket
self.address = address
self.node_eid = None
self.agent_id = None
def register(self, agent_id=None):
"""Attempt to register the specified agent identifier.
Args:
agent_id: The agent identifier to be registered. If None,
uuid.uuid4() is called to generate one.
"""
self.agent_id = agent_id or str(uuid.uuid4())
logger.info(f"Sending REGISTER message for '{agent_id}'...")
msg_ack = self.send(
AAPMessage(AAPMessageType.REGISTER, self.agent_id)
)
assert msg_ack.msg_type == AAPMessageType.ACK
logger.info("ACK message received!")
def send(self, aap_msg):
"""Serialize and send the provided `AAPMessage` to the AAP endpoint.
Args:
aap_msg: The `AAPMessage` to be sent.
"""
self.socket.send(aap_msg.serialize())
return self.receive()
def receive(self):
"""Receive and return the next `AAPMessage`."""
buf = bytearray()
msg = None
while msg is None:
data = self.socket.recv(1)
if not data:
logger.info("Disconnected")
return None
buf += data
try:
msg = AAPMessage.parse(buf)
except InsufficientAAPDataError:
continue
return msg
I don't see any bind, and I don't understand why the python code can call "socket.recv", but in my JavaScript code I can't do "netServer.listen". I think it should be the same.

There are things to clarify.
1.) The client uses the bind syscall where the kernel selects the source port automatically.
It does so by checking sys local_portrange sysctl settings.
1.) If you want to bind the client to a static source port, be sure to select a TCP port outside the local_portrange range !
2.) You cannot subscribe to event "*", instead you've to subscribe to the event "data" to receive messages.
For best practice you should also subscribe to the "error" event in case of errors !
These links will get you started right away:
How do SO_REUSEADDR and SO_REUSEPORT differ?
https://idea.popcount.org/2014-04-03-bind-before-connect/
So, for all beginners, who want to dig deeper into networking using node.js…
A working server example:
// Step 0: Create the netServer and the netClient
//
var HOST = 'localhost';
var PORT = 4243;
var AGENT_ID = 'SO_REUSEADDR DEMO';
var net = require('net');
console.log(`[DEBUG] Server will listen to: ${HOST}:${PORT}`);
console.log(`[DEBUG] Server will register with: ${AGENT_ID}`);
const netServer = net.createServer((c) => {
console.log('[netServer] Client connected');
c.on('data', (msg) => {
console.log('[netServer] Received `message`, MSG:', msg.toString());
});
c.on('end', () => {
console.log('client disconnected');
});
c.on('error', function (e) {
console.log('Error: ' + e.code);
});
c.write('hello\r\n');
c.pipe(c);
}).listen({
host: HOST,
port: PORT,
family: 4, // ipv4, same as socket.AF_INET for python
});
// Code copied from nodejs documentation page (doesn't make any difference)
netServer.on('error', function (e) {
console.log('Error: ' + e.code);
if (e.code == 'EADDRINUSE') {
console.log('Address in use, retrying...');
setTimeout(function () {
netServer.close();
netServer.listen(HOST, PORT);
}, 1000);
}
if ( e.code = 'ECONNRESET' ){
console.log('Connection reset by peer...');
setTimeout(function () {
netServer.close();
netServer.listen(HOST, PORT);
}, 1000);
}
});
The Client:
/* Or use this example tcp client written in node.js. (Originated with
example code from
http://www.hacksparrow.com/tcp-socket-programming-in-node-js.html.) */
var net = require('net');
var HOST = 'localhost';
var PORT = 4243;
var client = new net.Socket();
client.setTimeout(3000);
client.connect(PORT, HOST, function() {
console.log("Connected to " + client.address().address + " Source Port: " + client.address().port + " Family: " + client.address().family);
client.write('Hello, server! Love, Client.');
});
client.on('data', function(data) {
console.log('Received: ' + data);
client.end();
});
client.on('error', function(e) {
console.log('Error: ' + e.code);
});
client.on('timeout', () => {
console.log('socket timeout');
client.end();
});
client.on('close', function() {
console.log('Connection closed');
});
Best Hannes

Steffen Ullrich was completely right.
In my JavaScript code, I was trying to create a server to listen to the port 4243.
But you don't need to have a server in order to listen to some port, you can listen with a client too! (At least that's what I understood)
You can create a client connection as following:
const netClient = net.createConnection(PORT, HOST, () => {
console.log('[netClient] Connected');
});
netClient.on('data', (data) => {
console.log('[netClient] Received data:', data.toString('utf8'));
});
And with "client.on", then you can receive messages as well, as if it were a server.
I hope this is useful to someone else.

Sails js client native websocket

I'm trying to use websockets with sails-js but I can't make it work with native javascript websockets.
the tutorial example use the sails.io.js library and it goes a little bit like this:
io.socket.on('hello', function (data) {
console.log('Socket `' + data.id + '` joined the party!');
});
function sendHello () {
// And use `io.socket.get()` to send a request to the server:
io.socket.get('/websockets/hello', function gotResponse(data, jwRes) {
console.log('Server responded with status code ' + jwRes.statusCode + ' and data: ', data);
});
}
This does work, but i want to use the native javascript websockets like this:
let ws = new WebSocket("ws://localhost:1337/websockets/hello");
ws.onopen = function (e) {
console.log("[open] Connection established");
console.log("Sending to server");
ws.send("My name is John");
};
ws.onmessage = function (event) {
console.log(`[message] Data received from server: ${event.data}`);
};
ws.onclose = function (event) {
if (event.wasClean) {
console.log(`[close] Connection closed cleanly, code=${event.code} reason=${event.reason}`);
} else {
// e.g. server process killed or network down
// event.code is usually 1006 in this case
console.log('[close] Connection died');
}
};
ws.onerror = function (error) {
console.log(`[error] ${error}`);
console.log(error);
};
Clean and native javascript websockets with no library needed. Unfortunately I can't seem to make it work.
When I try to connect to sails js server using native websockets I get this message:
WebSocket connection to 'ws://localhost:1337/websockets/hello' failed: Connection closed before receiving a handshake response
Impossible to make it connect, it seems like sails js don't even get the message because i make a log when i get a new connection (using the tutorial code):
module.exports = {
hello: function (req, res) {
console.log("web socket received",req.isSocket)
// Make sure this is a socket request (not traditional HTTP)
if (!req.isSocket) {
return res.badRequest();
}
// Have the socket which made the request join the "funSockets" room.
sails.sockets.join(req, 'funSockets');
// Broadcast a notification to all the sockets who have joined
// the "funSockets" room, excluding our newly added socket:
sails.sockets.broadcast('funSockets', 'hello', { howdy: 'hi there!' }, req);
// ^^^
// At this point, we've blasted out a socket message to all sockets who have
// joined the "funSockets" room. But that doesn't necessarily mean they
// are _listening_. In other words, to actually handle the socket message,
// connected sockets need to be listening for this particular event (in this
// case, we broadcasted our message with an event name of "hello"). The
// client-side code you'd need to write looks like this:
//
// io.socket.on('hello', function (broadcastedData){
// console.log(data.howdy);
// // => 'hi there!'
// }
//
// Now that we've broadcasted our socket message, we still have to continue on
// with any other logic we need to take care of in our action, and then send a
// response. In this case, we're just about wrapped up, so we'll continue on
// Respond to the request with a 200 OK.
// The data returned here is what we received back on the client as `data` in:
// `io.socket.get('/say/hello', function gotResponse(data, jwRes) { /* ... */ });`
return res.json({
anyData: 'we want to send back'
});
}
};
How can I make sails js work with native javascript websockets?

Found a simple solution!
Used the npm package ws: npm i ws
making a new hook: sails generate hook customWebSocket
in the hook :
/**
* WS hook
*
* #description :: A hook definition. Extends Sails by adding shadow routes, implicit actions, and/or initialization logic.
* #docs :: https://sailsjs.com/docs/concepts/extending-sails/hooks
*/
const WebSocket = require('ws');
module.exports = function defineWsHook(sails) {
return {
/**
* Runs when this Sails app loads/lifts.
*/
initialize: async function () {
sails.log.info('Initializing custom hook (`WS`)');
console.log("custom hook")
const wss = new WebSocket.Server({ port: 3100 });
wss.on('connection', (socket) => {
console.log('New user connected wss');
socket.on('message', function incoming(message) {
console.log(message)
});
});
}
};
};
Done and done, now i can connect to is using native websocket!
now that i have done that i realize that the socket.io library might be better for handling errors.

socket io client lost conection when server restarts

so I am creating a module for the members that are using my services (cloudlist.xyz).
basically, we have a voting system in our service, this module is making a connection using socket io on the server and socket io client on the module, announcing to the user when someone votes on it
Everything is working normally, but when I restart the server to do some maintenance, all users are disconnected from socket io even when the server is on again
Server side code :
var server = app.listen(process.env.PORT || 3000, () => {
console.log("Your app is listening on port " + server.address().port)
});
var io = require('socket.io')(server)
io.on("connection",function(socket) {
console.log("Someone Joined to our server api!")
})
//that's the part that he emits the event when someone votes
io.of(`vote/${bot}`).emit("voted", user_votes.val());
Module/client side:
var https = require('https');
const { EventEmitter } = require("events");
var fetch = require('node-fetch')
const io = require("socket.io-client");
module.exports = class Cloud_client extends EventEmitter {
constructor(id, token) {
super();
if (!id) throw new Error("Missing client instance on contructor");
if (!token) throw new Error("Missing token on constructor");
this.id = id;
this.token = token;
this.socket = io.connect(`https://www.cloudlist.xyz/vote/${id}`, {
reconnect:true,
autoConnect:true,
reconnectionDelay: 1000,
reconnectionDelayMax : 5000,
reconnectionAttempts: Infinity
});
this.socket.on("connect", () => this.emit("connected"));
this.socket.on("disconnect", (...args) => {this.socket.open();
});
this.socket.on("voted", (...args) => this.emit("voted", ...args));
};
this is an example of someone using the module:
var cdl = require("cloud-list")
var cloud_client = new cdl("701456902160121966","5669556617e2a070ada1688")
cloud_client.on("connected", (data) => {
console.log(`Connected to the api Server`)
})
cloud_client.on("voted", (data) => {
console.log(`Thanks,user ${data.user_name} for voting on us :)`)
})
When I connect to the server, it sends the message of this example saying "Connected to the api Server", but when I restart the server, I don't receive anything. Already tried this.socket.on("disconnect", (...args) => {this.socket.open()}); or this.socket.on("disconnect", (...args) => {this.socket.connect()}); ,but still the same thing,user can't reconnect again.
the only way for users to connect again is to restart his project, which is very bad

Socket connections require the server to be serving. Socket.io doesn't seem good for a voting system unless you want it to be real time. It's expected for clients to restart when the server restarts.

As per with working in Socket server we need to restart our node socket server during the restart of the main servers like apache or Nginx.
Because it is not an automatic process on the server.

How can i send data from a UDP server to a browser?

I try to make an application that receives from a third part application UDP packets.
I try to create a server UDP in NodeJS, but now when I receive the data I don't know how can I show it in a browser windows.
I explain better...my application receives data via udp in real time, the server processes them and should show them real time on a web page.
This is my code for UDP server in NodeJS:
const dgram = require('dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
console.log(` messaggio ricevuto ${msg}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind({
adress:'127.0.0.1',
port:'41234'
});
// server listening address :41234
Thanks a lot for the reply

welcome to SO!
You could do something like below...
// Open a connection
var socket = new WebSocket('ws://localhost:41234/');
// When a connection is made
socket.onopen = function() {
console.log('Opened connection 🎉');
// send data to the server
var json = JSON.stringify({ message: 'Hello 👋' });
socket.send(json);
}
// When data is received
socket.onmessage = function(event) {
console.log(event.data);
}
// A connection could not be made
socket.onerror = function(event) {
console.log(event);
}
// A connection was closed
socket.onclose = function(code, reason) {
console.log(code, reason);
}
// Close the connection when the window is closed
window.addEventListener('beforeunload', function() {
socket.close();
});
This link should give you more info : https://www.sitepoint.com/real-time-apps-websockets-server-sent-events/ (above snippet is taken from this link)

You need a web server to send data to browser.
This link https://socket.io/get-started/chat will help you create a webserver.
You could send the message received on UDP port to the websocket as below
server.on('message', (msg, rinfo) => {
socket.emit('sendData', msg);
});