POC for how to hack Puppeteer to be able to use the JS Self-Profiling API

js-self-profile.mjs

// Usage: node js-self-profile.mjs https://example.com/

import puppeteer from 'puppeteer';
import http from 'http';
import https from 'https';

const PROXY_SERVER_PORT = 8080;

// Create an HTTP server so that we can inject the Document-Policy header in the response. Otherwise, the JS Self-Profiling API is not available.
const server = http.createServer(async (req, res) => {
    const requestUrl = new URL(req.url, 'http://localhost');
    if (!requestUrl.searchParams.get('url')) {
        return;
    }
    const url = new URL(requestUrl.searchParams.get('url'));

    const options = {
        headers: {
            ...req.headers,
            ...{
                host: url.host
            }
        }
    };

    const proxyRequest = https.request(url, options, (proxyResponse) => {
        res.setHeader('Document-Policy', 'js-profiling');
        res.writeHead(proxyResponse.statusCode, proxyResponse.headers);
        proxyResponse.pipe(res); // Forward the response to the client
    });

    req.pipe(proxyRequest); // Forward the request body
});

server.listen(PROXY_SERVER_PORT);

const browser = await puppeteer.launch({
    devtools: false,
    headless: true
});

const page = await browser.newPage();

await page.evaluateOnNewDocument(() => {
    const profiler = new Profiler({sampleInterval: 1, maxBufferSize: 100000});

    async function collectAndSendTrace() {
        if (profiler.stopped) {
            return;
        }
        window.selfProfilingTrace = await profiler.stop();
    }

    profiler.addEventListener('samplebufferfull', collectAndSendTrace);
    window.addEventListener('load', collectAndSendTrace);
});

// Emulate mobile.
await page.emulate({
    userAgent: 'Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/123.0.6312.99 Mobile Safari/537.36',
    viewport: {width: 360, height: 800}
});

// await page.emulateCPUThrottling(4);

const url = new URL(`http://localhost:${PROXY_SERVER_PORT}`);
url.searchParams.append('url', process.argv[2]);

await page.goto(url.href, {timeout: 60000});

await page.waitForFunction(() => {
    return window.selfProfilingTrace !== undefined;
});

const trace = await page.evaluate(() => {
    return window.selfProfilingTrace;
});

process.stdout.write(JSON.stringify(trace));

await browser.close();
server.close();