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.
I'm writing a WebSocket connection between a JavaScript client and node.JS server.
My client code:
<!DOCTYPE html>
<html>
<head>
<title>Socket Test</title>
</head>
<body>
</body>
<script>
const ws = new WebSocket('wss://mydomain.in:26031/');
ws.onopen = function () {
console.log('WebSocket Client Connected');
ws.send('Hi this is web client.');
};
ws.onmessage = function (e) {
console.log("Received: '" + e.data + "'");
};
</script>
Server code:
const net = require('net');
const server = net.createServer((socket) => {
socket.on('data', (data) => {
console.log(data.toString());
});
socket.write('SERVER: Hello! This is server speaking.\n');
socket.end('SERVER: Closing connection now.\n');
}).on('error', (err) => {
console.error(err);
});
server.listen(26031, () => {
console.log('opened server on', server.address().port);
});
The error i'm Getting:
WebSocket connection to 'wss://mydomain.in:26031/' failed: Error in connection establishment: net::ERR_CONNECTION_TIMED_OUT
I tried other answers in stack overflow, but everything seems perfect from my side. The server port is open for accepting request. What else might be wrong?
Use "wss://" only when you have SSL install
Or else try with ws://
You can also try using Socket.IO for socket connection.
The basic problem can be summarized as follows: When creating a Websocket server in Node using ws with the server option populated by an express server(as in this example), while using that same express server to handle the routing for NextJS (as in this example), the upgrade header seems to not be properly parsed.
Instead of the request being routed to the Websocket server, express sends back an HTTP 200 OK response.
I've searched high and low for an answer to this, it may be that I simply do not understand the problem. A possibly related question was brought up in an issue on NextJS's github. They recommend setting WebsocketPort and WebsocketProxyPort options in the local next.config.js, however I have tried this to no avail.
A minimal example of the relevant server code can be found below. You may find the full example here.
const express = require('express')
const next = require('next')
const SocketServer = require('ws').Server;
const port = parseInt(process.env.PORT, 10) || 3000
const dev = process.env.NODE_ENV !== 'production'
const app = next({ dev })
const handle = app.getRequestHandler()
app.prepare().then(() => {
const server = express()
server.all('*', (req, res) => {
return handle(req, res)
})
server.listen(port, err => {
if (err) throw err
console.log(`> Ready on http://localhost:${port}`)
})
const wss = new SocketServer({ server });
wss.on('connection', function connection(ws, request) {
console.log('Client connected');
ws.on('close', () => console.log('Client disconnected'));
});
wss.on('error', function (error) {
console.log(error);
});
setInterval(() => {
wss.clients.forEach((client) => {
client.send(new Date().toTimeString());
});
}, 1000);
}).catch(ex => {
console.error(ex.stack);
process.exit(1);
});
The expected result, of course, is a connection to the websocket server. Instead I receive the following error:
WebSocket connection to 'ws://localhost:3000/' failed: Error during WebSocket handshake: Unexpected response code: 200
Can anyone elucidate anything for me here?
Ok, after more digging I have solved the problem. Quite simply, the ws.Server object to which I was trying to feed the server = express() object is not strictly speaking an http server object. However, server.listen() returns such an http server object. On such an object we can listen for an 'upgrade' call, which we can pass to our ws.Server object's handleUpgrade() event listener, through which we can connect. I will be updating the examples that I linked in my question, but the relevant code is below:
app.prepare().then(() => {
const server = express()
server.all('*', (req, res) => {
return handle(req, res)
})
const wss = new SocketServer({ server });
wss.on('connection', function connection(ws, request) {
console.log('Client connected');
ws.on('close', () => console.log('Client disconnected'));
});
wss.on('error', function (error) {
console.log(error);
});
let srv = server.listen(port, err => {
if (err) throw err
console.log(`> Ready on http://localhost:${port}`)
})
srv.on('upgrade', function(req, socket, head) {
wss.handleUpgrade(req, socket, head, function connected(ws) {
wss.emit('connection', ws, req);
})
});
I try to make an application that receives from a third part application UDP packets.
I try to create a server UDP in NodeJS, but now when I receive the data I don't know how can I show it in a browser windows.
I explain better...my application receives data via udp in real time, the server processes them and should show them real time on a web page.
This is my code for UDP server in NodeJS:
const dgram = require('dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${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);
});
Is it possible to display the default console output from a node.js Server to the users client? I've tried several plugins like e.g. 'console.re' but not one of them worked for me.
I like to read the 'console.log' output in real time and display all output to a client (mobile device).
Thanks
console.log writes to stdout, so you can listen to it and do whatever with the data.
console.log([data,][args])
Prints to stdout with newline.
https://nodejs.org/api/console.html
Try advancing this code:
const spawn = require('child_process').spawn
const ls = spawn('ls', ['-lh', '/usr'])
const collectedData = []
ls.stdout.on('data', (data) => {
console.log('stdout: ' + data.toString())
collectedData.push({ event: 'CONSOLE_LOG', data })
// now just make the client consume collectedData in real-time
// or on refresh
})
ls.stderr.on('data', (data) => {
console.log('stderr: ' + data.toString())
})
ls.on('exit', (code) => {
console.log('child process exited with code ' + code.toString())
})
Child processes are built in. Take a sample through these docs here:
https://nodejs.org/api/child_process.html
I don't know anything about your setup, but if you want super easy in Express
app.get('/logging', (req, res) => {
res.send(collectedData)
})
Make the client hit it every 2000ms or something.
Otherwise, you need to create a socket with the server and push updates to the client, and handle them in the client.
http://www.socket.io
You can also setup TCP and UDP sockets fairly quick in node.js. Do some Googling.
I have some sample code I can give you:
/**
* SERVER
*/
// Load dgram module
const dgram = require('dgram')
// Create new socket
const server = dgram.createSocket('udp4')
// Listening event
server.on('listening', () => console.log('UDP Server listening'))
// Message event
server.on('message', (msg, rinfo) => {
console.log(`${rinfo.address}:${rinfo.port} - ${msg}`)
});
// Start UDP socket listener
const PORT = 3333
const HOST = '127.0.0.1'
server.bind(PORT, HOST)
/**
* CLIENT
*/
const client = dgram.createSocket('udp4')
const ip = require('ip')
client.send('Sample message', PORT, HOST, (err) => {
if (err) throw err
console.log(`UDP message sent: ${ip.address()}`)
client.close()
})