Node.JS raw socket: how to do repeated connect-disconnect?

Question

Currently I am trying to repeatedly connect and disconnect to a device (TCP socket). Here is the flow

1. Connect to the device
2. Send a "data".
3. Have a delay of 200msec to ensure that the other end receives the data and it has already replied.
4. Process the data
5. Disconnect.
6. Wait for 1 second
7. Go back to 1.

This 1-time connection code is working (I got it from the web):

var net = require('net');
var HOST = '127.0.0.1';
var PORT = 23;

// (a) =========
var client = new net.Socket();
client.connect(PORT, HOST, function() {

    console.log('CONNECTED TO: ' + HOST + ':' + PORT);
    // Write a message to the socket as soon as the client is connected, the server will receive it as message from the client
    client.write('data');

});

// Add a 'data' event handler for the client socket
// data is what the server sent to this socket
client.on('data', function(data) {

    console.log('DATA: ' + data);
    // Close the client socket completely
    client.destroy();
});

// Add a 'close' event handler for the client socket
client.on('close', function() {
    console.log('Connection closed');
});

// (b) =========

Currently, the code above works for 1 time connection. I did put the code from (a) to (b) in a while(true) loops and placed a sleep of 1 second at the end using https://www.npmjs.com/package/sleep and it seems the connect isn't executing on that setup.

Any thoughts on this will be helpful.

Answer 1

I think the best way to do this, is to encapsule what you want to do in a function "loopConnection", and call recursively on each client.on('close') like this :

var net = require('net');
var HOST = '127.0.0.1';
var PORT = 23;

var loopConnection = function() {
    var client = new net.Socket();

    client.connect(PORT, HOST, function() {
        console.log('CONNECTED TO: ' + HOST + ':' + PORT);
        client.write('data');
    });

    client.on('data', function(data) {
        console.log('DATA: ' + data);
        client.destroy();
    });

    client.on('close', function() {
        console.log('Connection closed');
        setTimeout(function() {
            loopConnection(); // restart again
        }, 1000); // Wait for one second
    });
};

loopConnection(); // Initialize and first call loopConnection

Hope it helps.