Send simple TCP messages in JavaScript, similarly to Python .socket

Question

Coming from Python, I am trying to achieve a similar result using JavaScript and node.js.

I am trying to send a simple TCP message across a network. In Python, I would achieve this in the following way:

import socket

device_ip = '192.168.0.10'
device_port = 20000

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(5)
s.connect((device_ip, device_port))

command = ('Message to be sent to device here')
s.sendall(command.encode())
s.recv(4096)

I have looked at node's socket.io module, but I couldn't find anything as simple as the above solution in Python.

The device at the end of device_ip will respond to the message so long as it is TCP encoded, it will then just send back an Ack message which the JS can effectively ignore. The Ack messages only exist as a simple handshake before sending another message. I have the Python code working as desired, but I find myself needing to run this with JS and Node.

eol · Accepted Answer · 2020-07-10 18:25:31Z

3

Node provides the Net-module which basically allows you to create tcp-server and client sockets. Here's a very simple example for a server-socket:

const net = require('net');
const server = net.createServer((c) => {
    console.log('client connected');
    c.on('end', () => {
        console.log('client disconnected');
    });
    c.write('hello\r\n');
    c.pipe(c);
});

server.listen(20000, () => {
    console.log('server socket listening ...');
});

And here's the code for a corresponding client-socket:

const net = require('net');
const client = net.createConnection({ port: 20000}, () => {
    client.write('world!\r\n');
});
client.on('data', (data) => {
    console.log(data.toString());
    client.end();
});

answered Jul 10, 2020 at 18:25

eol

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2 Comments

rHumphries Over a year ago

So this didn't fully answer the question, but it did give me the means to work my way around it, so thank you for that. I have ended up with the following. var client = new net.Socket(); client.connect(PORT, IP_ADDRESS, function() { client.write('Command1'); client.write('Command2'); } However what i now need is to acknowledge the ACK message the client is returning before 'Command2' is being sent. I think this would be done in the callback part of socket.write(data[, encoding][, callback]) however i am completely lost on how to achieve this...

eol Over a year ago

I'm not 100% sure, but maybe something like this? codesandbox.io/s/recursing-cray-6kvdi (this won't run in codesandbox, but you can copy the files and execute it on your machine). Basically what I'm doing is wrapping both the server and the client in a class and restrict sending/receiving messages in the client until the server has sent ACK. Check it out :)

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