Reconnect net.socket nodejs

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

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 2

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()