Simple TCP Port Scanner in Node.JS

port-scanner.js

(async () => {

const net = require('net');
const dns = require('dns');
const fs = require('fs');

const [,,host,portmin,portmax] = process.argv;

let a = Date.now();
const ipv4 = await new Promise((ok,fail) =>
    dns.lookup(host, { family: 4, verbatim: true }, (err, address, family) =>
        err ? fail(err) : ok(address)));
let elapsed = Date.now() - a;

if (ipv4 !== host) {
    console.log(`Resolved hostname ${host} to ${ipv4} in ${elapsed} ms.`);
}

const TIMEOUT = 3*1000;

function probe(host, port, cb) {
    let connect, timeout, hangup, error, data, end, emitted;

    const client = net.createConnection({
        port,
        host: ipv4,
        timeout: TIMEOUT,
        family: 4,
        lookup: () => {},
    }, () => {
        connect = true;
    });
    client.setNoDelay(true);
    client.setKeepAlive(false);
    client.setEncoding('utf8');

    const done = () => {
        if (emitted) return;
        emitted = true;
        clearTimeout(timer);
        cb({ port, connect, timeout, hangup, error, data, end });
    };

    const timer = setTimeout(()=>{
        hangup = true;
        client.end();
        done();
    }, TIMEOUT+1000);

    client.on('timeout', () => { timeout = true; done(); });
    client.on('error', (e) => { error = e; });
    client.on('data', (d) => { null == data ? data = d : data += d; });
    client.on('end', () => { end=true; done(); });
    // other events: close, connect, drain, lookup, ready
}

const CONCURRENCY = 100;

let running = 0;
let port = portmin;
const ports = [];
for (let i=portmin; i<=portmax; i++) ports.push(i);
ports.sort(()=>.5-Math.random());

const next = () => {
    running--;
    if (ports.length > 0) {
        const port = ports.pop();
        probe(host, port, (outcome) => {
            render(outcome);
            process.nextTick(next);
        });
        running++;
    }
    else if (running < 1) {
        console.log('\n\ndone.');
        process.exit(0);
    }
};

for (let i=0; i<CONCURRENCY; i++) {
    running++;
    next();
}

let lastRenderedDot = false;
const render = (outcome) => {
    let out;
    if (outcome.timeout) {
        out = (lastRenderedDot ? '' : '\n') + '.';
        lastRenderedDot = true;
    }
    else {
        out = '\n'+JSON.stringify(outcome);
        lastRenderedDot = false;
    }
    fs.appendFileSync('./out.log', out);
    process.stdout.write(out);
};

})();