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.
My client is not receiving the broadcast sent to the room. If I replace socket.to(roomName).emit('join', currentUser); with socket.emit('join', currentUser); the client receives the broadcast, but I'd like to use rooms here. Any help would be greatly appreciated.
app.js
// Game
app.get('/game', (req, res) => {
const cookies = req.cookies;
const currentUser = cookies['current_user'];
const roomName = cookies['room_name'];
if (roomName) {
res.render('pages/game', {
room: roomName
});
io.of('/game').on('connection', socket => {
console.log('a user connected');
socket.on('disconnect', () => {
console.log('user disconnected');
});
socket.join(roomName);
socket.to(roomName).emit('join', currentUser);
});
} else {
res.redirect('/login');
}
});
game.ejs
const socket = io("/game");
socket.on('join', function(user) {
console.log(`${user} joined`);
});
Also, could I replace this:
if (roomName) {
// stuff
} else {
// other stuff
}
with this:
if (!roomName) {
// other stuff
return;
}
// stuff
According to the documentation, if you use socket.to('room').emit(...) instead of io.in('room').emit(...), it will be broadcasted to all sockets in the room except the sender. That's where your problem lies.
The reason socket.emit(...) works is because you're sending it directly and only to the sender.
This emit cheatsheet is quite useful to figure out which combinations of io/socket and to etc affect where messages get sent to.
the issue that occurs here, is that, when i connect between sample socekt.io client with this socket.io server by node.js ( just running two terminals and opening socket connection between client and server)
I have no problems. But, when I am trying to inject this socket.io-client into my Ember.js application, precisely to ember-cli-mirage it redirects my client from given address : ( 'http: //localhost:8080') to something like http: //localhost:8080/socket.io/?EIO=3&transport=polling&.....
also Mirage displays me an error that I cannot handle, even by setting up precise namespace, routing the wsClient.connect() method or calling this.passthrough() , before calling wsClient.connect() .
I also paste the the screenshot of error from inspect console in browser:
error image
Do you have any idea how to resolve this problem? Thank you in advance and I also hope that the topic is not duplicated.
// server.js
var app = require('http').createServer(handler);
var io = require('socket.io')(app);
app.listen(8080);
function handler(req, res) {
res.writeHead(200);
res.end('default.index');
}
var rooms = {
'room1': [
],
'room2': [
]
};
io.on('connection', function(socket) {
console.log('client connected');
socket.on('join', function(roomName) {
rooms[roomName].push(socket.id);
socket.join(roomName);
});
socket.on('leave', function(roomName) {
var toRemove = rooms[roomName].indexOf(socket.id);
rooms[roomName].splice(toRemove, 1);
socket.leave('roomName');
});
socket.on('eNotification', function(data) {
console.log(data);
io.to(socket.id).emit('eNotificationCall', data);
io.to('room2').emit('eventNotification', data);
});
socket.on('gNotification', function(data) {
console.log(data);
io.to(socket.id).emit('gNotificationCall', data);
io.to('room1').emit('diagram1Notification', data);
});
socket.on('close', function() {
console.log('client disconnected');
});
});
//client.js
var wsClient = {
socket: null,
connect: function() {
this.socket = io.connect('http://localhost:8080');
this.socket.on('connect', function() {
console.log('mirage client connected!');
});
},
send: function(eventData, graphData) {
this.socket.emit('eNotification', eventData);
this.socket.emit('gNotification', graphData);
}
};
export default wsClient;
//config.js
import wsClient from './websockets/client';
export default function() {
wsClient.connect();
console.log(wsClient.socket);
var graphData = {X: "2", Y: "3"};
var eventData = {myDAta: 'myDAta', message: 'message'};
setInterval(function() {
wsClient.send(graphData, eventData);
}, 5000);
}
If you call this.passthrough() with no args it only allows requests on the current domain to passthrough. It looks like the websocket connection is on a different port, so try specifying it directly:
this.passthrough('http://localhost:8080/**');
See the docs for more information.
I am wondering what websocket events exist So far I have only been using the ws.on('message') event, but I would like to use an event that is triggered when the connection is established and closed. I tried adding ws.on('connection'), but that didn't get triggered.
My code:
app.ws('/', function (ws, req) {
ws.on('message', function (textChunk) {
//do stuff
}
});
});
Do I need some client side programming to do this?
I tried adding this, but it didn't trigger when I connected from my client.
ws.on('request', function () {
console.log("request");
});
The function provided to app.ws is the one executed when a new websocket is opened. So use it this way:
app.ws('/', function (ws, req) {
console.log("New connection has opened!");
ws.on('close', function() {
console.log('The connection was closed!');
});
ws.on('message', function (message) {
console.log('Message received: '+message);
});
});
After looking at the source code for express-ws it looks like you can do the following.
var express = require('express');
var app = express();
var expressWs = require('express-ws')(app);
// get the WebsocketServer instance with getWss()
// https://github.com/HenningM/express-ws/blob/5b5cf93bb378a0e6dbe6ab33313bb442b0c25868/index.js#L72-L74
expressWs.getWss().on('connection', function(ws) {
console.log('connection open');
});
// ... express middleware
// ... websocket middle ware
app.ws('/', function(ws, req) {
ws.on('message', function(msg) {
console.log(msg);
});
});
app.listen(3000);
Old Response
There are the following:
close
error
message
open
https://developer.mozilla.org/en-US/docs/Web/API/WebSocket#Attributes
Okay I found one more event that actually triggers. Now if only I would find one that gets called once on open connection.
app.ws('/', function (ws, req) {
ws.on('close', function() {
console.log('close connection');
});
ws.on('message', function (textChunk) {
//do stuff
}
});
});
Just searched all the web to find how can I track inside node.js server when a channel is subscribed or unsubscribed. What I can do right know is the connect and disconnect bindings, but no clue how to do it with channels.
io.sockets.on('connection', function (socket) {
console.log("["+socket.id+"] Connected");
// handler to know when a socket subscribed a channel (*) ?
// handler to know when a socket unsubscribed a channel (*) ?
socket.on('disconnect', function () {
console.log("["+socket.id+"] Disconnect");
});
});
Is it possible?
You are looking for "socket.of('channelName')" ...
See Socket.io docs
SERVER:
var io = require('socket.io').listen(80);
var chat = io
.of('/chat')
.on('connection', function (socket) {
socket.emit('a message', {
that: 'only'
, '/chat': 'will get'
});
chat.emit('a message', {
everyone: 'in'
, '/chat': 'will get'
});
});
var news = io
.of('/news')
.on('connection', function (socket) {
socket.emit('item', { news: 'item' });
});
CLIENT:
<script>
var chat = io.connect('http://localhost/chat')
, news = io.connect('http://localhost/news');
chat.on('connect', function () {
chat.emit('hi!');
});
news.on('news', function () {
news.emit('woot');
});
</script>