@schlessera/brain-render-puppeteer

Server-side PNG/PDF rendering for caller-supplied HTML, on headless Chrome (puppeteer-core — bring your own Chrome). Built for one hostile fact: the content being rendered is untrusted, and the renderer usually runs next to a private knowledge repo. A page that can fetch — or open a WebSocket — is an SSRF and exfiltration vector, so the page gets nothing:

• No network. The browser's DNS is blackholed at launch — the load-bearing layer, because request interception cannot see WebSocket handshakes, prerender, preconnect, iframes, or popups. Interception runs as well, belt-and-braces.
• No JavaScript. Scripting is disabled for rendered content.
• Chrome's sandbox stays on by default (opt out only where the process already runs as root, e.g. minimal containers).
• Bounded everything: per-render wall-clock budget (30 s, launch included), bounded concurrency (2) with a bounded queue, clamped output geometry, idle browser shutdown, crash recovery, terminal shutdown().

Practical consequence: remote images and webfonts do not render. Inline assets as data: URIs if they must appear.

import { createRenderer } from "@schlessera/brain-render-puppeteer";

const renderer = createRenderer();
const png = await renderer.renderPng({ html, width: 800 });
const pdf = await renderer.renderPdf({ html });
await renderer.shutdown();

Options

| Option | Default | Notes | |---|---|---| | executablePath | PUPPETEER_EXECUTABLE_PATH / well-known paths | Chrome binary. | | renderTimeoutMs | 30_000 | Per-render wall clock, browser launch included. | | maxConcurrent | 2 | Renders in flight; more queue. | | maxQueue | 16 | Waiting renders beyond the cap before "renderer busy". | | idleTimeoutMs | 5 min | Close the browser after this long without a render. | | allowHosts | [] | Explicit host allowlist excluded from both the DNS blackhole and interception. A predicate was rejected by design — it could only gate the interceptable channels. |

Verification

The unit tests cover the predicates; the suite that matters launches real Chrome against a live listener and proves the page cannot reach it over fetch, WebSocket, prerender, preconnect, iframe, or popup (tests/runtime.test.ts). Predicate-only tests hid exactly these holes once; keep the runtime suite green.