subzey/cli.js

## cli.js
#!/usr/bin/env node

import { createServer } from 'http';
import { readFile } from 'fs/promises';
import { resolve } from 'path';
import { parse, fileURLToPath } from 'url';


const ALIGNMENT = 60000; // ms
const TTL = 80000; // ms

function promisleep(delay){
    return new Promise(r => setTimeout(r, delay))
}

async function serveIndex(req, res) {
    const fileContents = await readFile(resolve(fileURLToPath(import.meta.url), '..', 'index.html'));
    res.writeHead(200, {
        'content-type': 'text/html;charset=utf-8',
        'content-length': fileContents.byteLength,
    });
    res.end(fileContents);
}

async function serveToken(req, res) {
    console.log(`${new Date().toISOString()} Token request...`);

    await promisleep(1000);

    const now = Date.now(); // ms
    const iat = Math.floor(now / ALIGNMENT) * ALIGNMENT; // ms
    const exp = iat + TTL; // ms
    const age = now - iat; // ms

    const headers = {
        'content-type': 'application/json;charset=utf-8',
        'age': Math.round((now - iat) / 1000),
        'cache-control': `private, max-age=${ ALIGNMENT / 1000 }, stale-while-revalidate=${ (TTL - ALIGNMENT) / 1000 }`,
    };

    res.writeHead(200, headers);
    res.end(
        JSON.stringify({
            iat: new Date(iat).toISOString(),
            exp: new Date(exp).toISOString(),
        })
    );

    console.log(`${new Date().toISOString()} ${JSON.stringify(headers, null, 2)}`);
}

(
    createServer((req, res) => {
        switch (parse(req.url).pathname) {
            case '/':
                return serveIndex(req, res);
            case '/get-token/':
                return serveToken(req, res);
            default:
                res.writeHead(404);
                res.end();
        }
    })
    .on('listening', function() { console.log(`http://127.0.0.1:${this.address().port}/`)})
    .listen(8080)
);

## index.html
<!doctype html>
<html>
    <head>
        <style>pre { margin: 1em; border: 1px dashed gray; min-height: 100px }</style>
    </head>
    <body>
        <button id="fetch">Fetch!</button>
        <pre id="output"><div id="now"></div><div id="response"></div></pre>
        <script>
            document.querySelector('#fetch').addEventListener('click', async (e) => {
                e.preventDefault();
                const output = document.querySelector('#response');

                try {
                    const response = await fetch('/get-token/');
                    if (!response.ok) {
                        throw new Error(`Pas glop! ${response.status}`);
                    }
                    const json = await response.json();

                    const serverDate = new Date(response.headers.get('date')).toISOString();
                    const localDate = new Date().toISOString();

                    output.textContent = `\nLocal time:\t${localDate}\nServer time:\t${serverDate}\n\nIssued at:\t${json.iat}\nExpires at:\t${json.exp}`;
                } catch (e) {
                    output.textContent = `Error: ${e.stack || e.message}`;
                }
            });

            requestAnimationFrame(function frame(){
                document.querySelector('#now').textContent = new Date().toISOString();
                requestAnimationFrame(frame);
            });
        </script>
    </body>
</html>

## package.json
{
    "type": "module",
    "name": "token-cache",
    "version": "0.1.0",
    "bin": "cli.js"
}
	#!/usr/bin/env node

	import { createServer } from 'http';
	import { readFile } from 'fs/promises';
	import { resolve } from 'path';
	import { parse, fileURLToPath } from 'url';


	const ALIGNMENT = 60000; // ms
	const TTL = 80000; // ms

	function promisleep(delay){
	return new Promise(r => setTimeout(r, delay))
	}

	async function serveIndex(req, res) {
	const fileContents = await readFile(resolve(fileURLToPath(import.meta.url), '..', 'index.html'));
	res.writeHead(200, {
	'content-type': 'text/html;charset=utf-8',
	'content-length': fileContents.byteLength,
	});
	res.end(fileContents);
	}

	async function serveToken(req, res) {
	console.log(`${new Date().toISOString()} Token request...`);

	await promisleep(1000);

	const now = Date.now(); // ms
	const iat = Math.floor(now / ALIGNMENT) * ALIGNMENT; // ms
	const exp = iat + TTL; // ms
	const age = now - iat; // ms

	const headers = {
	'content-type': 'application/json;charset=utf-8',
	'age': Math.round((now - iat) / 1000),
	'cache-control': `private, max-age=${ ALIGNMENT / 1000 }, stale-while-revalidate=${ (TTL - ALIGNMENT) / 1000 }`,
	};

	res.writeHead(200, headers);
	res.end(
	JSON.stringify({
	iat: new Date(iat).toISOString(),
	exp: new Date(exp).toISOString(),
	})
	);

	console.log(`${new Date().toISOString()} ${JSON.stringify(headers, null, 2)}`);
	}

	(
	createServer((req, res) => {
	switch (parse(req.url).pathname) {
	case '/':
	return serveIndex(req, res);
	case '/get-token/':
	return serveToken(req, res);
	default:
	res.writeHead(404);
	res.end();
	}
	})
	.on('listening', function() { console.log(`http://127.0.0.1:${this.address().port}/`)})
	.listen(8080)
	);
	<!doctype html>
	<html>
	<head>
	<style>pre { margin: 1em; border: 1px dashed gray; min-height: 100px }</style>
	</head>
	<body>
	<button id="fetch">Fetch!</button>
	<pre id="output"><div id="now"></div><div id="response"></div></pre>
	<script>
	document.querySelector('#fetch').addEventListener('click', async (e) => {
	e.preventDefault();
	const output = document.querySelector('#response');

	try {
	const response = await fetch('/get-token/');
	if (!response.ok) {
	throw new Error(`Pas glop! ${response.status}`);
	}
	const json = await response.json();

	const serverDate = new Date(response.headers.get('date')).toISOString();
	const localDate = new Date().toISOString();

	output.textContent = `\nLocal time:\t${localDate}\nServer time:\t${serverDate}\n\nIssued at:\t${json.iat}\nExpires at:\t${json.exp}`;
	} catch (e) {
	output.textContent = `Error: ${e.stack \|\| e.message}`;
	}
	});

	requestAnimationFrame(function frame(){
	document.querySelector('#now').textContent = new Date().toISOString();
	requestAnimationFrame(frame);
	});
	</script>
	</body>
	</html>
	{
	"type": "module",
	"name": "token-cache",
	"version": "0.1.0",
	"bin": "cli.js"
	}