Reconnect net.socket nodejs - node.js

Question

I am new to node.js and would like to connect to a TCP socket. For this I am using the net module.
My idea was to wrap the connect sequence into a function then on the 'close' event, attempt a reconnection. Not that easy apparently.
function conn() {
client.connect(HOST_PORT, HOST_IP, function() {
startSequence();
})
}
client.on('close', function(e) {
log('info','Connection closed! -> ' + e)
client.destroy();
setTimeout(conn(),1000);
});
So when the remote host is closed, I see my logs comming through, howere what seems to be happening is that as soons as the remote host comes online ALL the previous attempts start to get processed - if that makes sense. If you look at client.connect, there is a function called startSequence that sends some data that "iniates" the connection from the remote server side. When the server goes offline and I start reconnecting all the failed attempts from before seem to have been buffered and are all sent together when the server goes online.
I have tried the code from this Stackoverflow link as well to no avail (Nodejs - getting client socket to try again after 5 sec time out)
client.connect(HOST_PORT, HOST_IP, function() {
pmsStartSequence();
})
// Add a 'close' event handler for the client socket
client.on('close', function(e) {
log('debug','connection closed -> ' + e)
client.setTimeout(10000, function() {
log('debug', 'trying to reconnect')
client.connect(HOST_PORT, HOST_IP, function() {
pmsStartSequence();
})
})
});
Is there any advice on how I can reconnect a socket after failure?

Answer 1

Inspired from the other solutions, I wrote this, it's tested, it works !
It will keep on trying every 5 sec, until connection is made, works if it looses connection too.
/* Client connection */
/* --------------------------------------------------------------------------------- */
const client = new net.Socket()
var intervalConnect = false;
function connect() {
client.connect({
port: 1338,
host: '127.0.0.1'
})
}
function launchIntervalConnect() {
if(false != intervalConnect) return
intervalConnect = setInterval(connect, 5000)
}
function clearIntervalConnect() {
if(false == intervalConnect) return
clearInterval(intervalConnect)
intervalConnect = false
}
client.on('connect', () => {
clearIntervalConnect()
logger('connected to server', 'TCP')
client.write('CLIENT connected');
})
client.on('error', (err) => {
logger(err.code, 'TCP ERROR')
launchIntervalConnect()
})
client.on('close', launchIntervalConnect)
client.on('end', launchIntervalConnect)
connect()

Answer 2

The problem is where you set the on-connect callback.
The doc of socket.connect() says:
connectListener ... will be added as a listener for the 'connect' event once.
By setting it in socket.connect() calls, every time you try reconnecting, one more listener (a one-time one), which calls startSequence(), is attached to that socket. Those listeners will not be fired until reconnection successes, so you got all of them triggered at the same time on a single connect.
One possible solution is separating the connect listener from socket.connect() calls.
client.on('connect', function() {
pmsStartSequence();
});
client.on('close', function(e) {
client.setTimeout(10000, function() {
client.connect(HOST_PORT, HOST_IP);
})
});
client.connect(HOST_PORT, HOST_IP);

Answer 3

My solution:
var parentHOST = '192.168.2.66';
var parentPORT = 9735;
var net = require('net');
var S = require('string');
var parentClient = new net.Socket();
var parentActive = false;
var startParentClient = function () {
parentClient = new net.Socket();
parentActive = false;
parentClient.connect(parentPORT, parentHOST, function() {
console.log('Connected ' + cluster.worker.id + ' to parent server: ' + parentHOST + ':' + parentPORT);
parentActive = true;
});
parentClient.on('error', function() {
parentActive = false;
console.log('Parent connection error');
});
parentClient.on('close', function() {
parentActive = false;
console.log('parent connection closed');
setTimeout(startParentClient(), 4000);
});
}
If is necessary connect:
if (!S(parentHOST).isEmpty() && !S(parentPORT).isEmpty()) {
startParentClient();
}

Answer 4

As mentioned multiple times in the comments, you need to use .removeAllListeners() before trying to reconnect your client to the server in order to avoid having multiple listeners on the same event.
The code below should do the trick
Note that I try to reconnect the client after the close and end events because these two events can be fired in different orders after closing a connection
const net = require("net")
let client = new net.Socket()
function connect() {
console.log("new client")
client.connect(
1337,
"127.0.0.1",
() => {
console.log("Connected")
client.write("Hello, server! Love, Client.")
}
)
client.on("data", data => {
console.log("Received: " + data)
})
client.on("close", () => {
console.log("Connection closed")
reconnect()
})
client.on("end", () => {
console.log("Connection ended")
reconnect()
})
client.on("error", console.error)
}
// function that reconnect the client to the server
reconnect = () => {
setTimeout(() => {
client.removeAllListeners() // the important line that enables you to reopen a connection
connect()
}, 1000)
}
connect()

Answer 5

I use the following code to achieve reconnection with node.js. I am not a Javascript expert so I guess it can be improved but it nevertheless works fine for me.
I hope this could help.
Best.
//----------------------------------------------------------------//
// SocketClient //
//----------------------------------------------------------------//
var net = require('net');
var SocketClient = function(host, port, data_handler, attempt)
{
var node_client;
var attempt_index = (attempt ? attempt : 1);
this.m_node_client = new net.Socket();
node_client = this.m_node_client;
this.m_node_client.on('close', function()
{
var new_wrapper = new SocketClient(host, port, data_handler, attempt_index + 1);
node_client.destroy();
new_wrapper.start();
});
this.m_node_client.on('data', data_handler);
this.m_node_client.on('error', function(data)
{
console.log("Error");
});
this.start = function()
{
this.m_node_client.connect(port, host, function()
{
console.log('Connected ' + attempt_index);
});
};
};
//----------------------------------------------------------------//
// Test //
//----------------------------------------------------------------//
var test_handler = function(data)
{
console.log('TestHandler[' + data + ']');
};
var wrapper = new SocketClient('127.0.0.1', 4000, test_handler);
wrapper.start();

Answer 6

I have tried re-using the same socket connection, by using this:
const s = net.createConnection({port});
s.once('end', () => {
s.connect({port}, () => {
});
});
that didn't work, from the server-side's perspective. If the client connection closes, it seems like a best practice to create a new connection:
const s = net.createConnection({port});
s.once('end', () => {
// create a new connection here
s = net.createConnection(...);
});
sad but true lulz.

Answer 7

Following this:
//
// Simple example of using net.Socket but here we capture the
// right events and attempt to re-establish the connection when
// is is closed either because of an error establishing a
// connection or when the server closes the connection.
//
// Requires
const net = require('net');
// Create socket
const port = 5555;
const host = '127.0.0.1';
const timeout = 1000;
let retrying = false;
// Functions to handle socket events
function makeConnection () {
socket.connect(port, host);
}
function connectEventHandler() {
console.log('connected');
retrying = false;
}
function dataEventHandler() {
console.log('data');
}
function endEventHandler() {
// console.log('end');
}
function timeoutEventHandler() {
// console.log('timeout');
}
function drainEventHandler() {
// console.log('drain');
}
function errorEventHandler() {
// console.log('error');
}
function closeEventHandler () {
// console.log('close');
if (!retrying) {
retrying = true;
console.log('Reconnecting...');
}
setTimeout(makeConnection, timeout);
}
// Create socket and bind callbacks
let socket = new net.Socket();
socket.on('connect', connectEventHandler);
socket.on('data', dataEventHandler);
socket.on('end', endEventHandler);
socket.on('timeout', timeoutEventHandler);
socket.on('drain', drainEventHandler);
socket.on('error', errorEventHandler);
socket.on('close', closeEventHandler);
// Connect
console.log('Connecting to ' + host + ':' + port + '...');
makeConnection();

Answer 8

function createServer() {
const client = new net.Socket();
client.connect(HOST_PORT, HOST_IP, function() {
console.log("Connected");
state = 1 - state;
client.write(state.toString());
});
client.on("data", function(data) {
console.log("Received: " + data);
//client.destroy(); // kill client after server's response
});
client.on("close", function() {
console.log("Connection closed");
//client.connect()
setTimeout(createServer, 2000);
});
}
createServer();