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@excalidraw/utils is a browser bundle -- it references devicePixelRatio, location, matchMedia etc. as bare globals the way inline <script> code would, not as window.foo. Only copying window/document/navigator onto Node's global left everything else undefined, so the very first bare reference threw a ReferenceError as soon as the module loaded. Copy jsdom's entire window onto global instead, enable pretendToBeVisual so jsdom actually populates devicePixelRatio/requestAnimationFrame, and stub matchMedia since jsdom doesn't implement it at all.
132 lines
5.6 KiB
JavaScript
132 lines
5.6 KiB
JavaScript
// Local render sidecar for whiteboard frame mode: turns Excalidraw scene
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// JSON (the format Nextcloud Whiteboard's .whiteboard files use --
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// {"elements", "appState", "files"}, see app/webdav_client.py) into a
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// PNG, using the real Excalidraw export code rather than a hand-rolled
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// reimplementation of its element types/styling/fonts. That's the whole
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// reason this exists as Node rather than more Python: @excalidraw/utils
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// IS the renderer real whiteboards are drawn with, so this reproduces
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// whatever a user actually sees in their whiteboard exactly, and never
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// drifts out of sync with new element types as Excalidraw adds them.
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//
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// Runs as a second process inside the main Python server's own
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// container (see ../Dockerfile installing Node, and ../start.sh
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// launching this in the background before exec'ing uvicorn) -- not a
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// separate deployment, no independent scaling/restart needs, so one
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// container is simpler than a second docker-compose service. Bound to
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// 127.0.0.1 only: reachable from the Python process in the same
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// container, never from outside it, so there's no auth on top of that
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// -- the network boundary IS the access control here.
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//
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// No headless browser (Puppeteer/Playwright) -- jsdom provides just
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// enough of a browser-like global environment for @excalidraw/utils'
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// internal DOM calls (e.g. text measurement) to work, and
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// @resvg/resvg-js (a native Rust SVG rasterizer, no browser process)
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// turns the resulting SVG into the actual PNG.
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const { JSDOM } = require('jsdom');
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// @excalidraw/utils is a browser bundle: it references things like
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// `devicePixelRatio` and `location` as bare identifiers, the same way
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// inline <script> code in a real page would resolve them off the global
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// scope -- not as `window.devicePixelRatio`. Copying jsdom's entire
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// `window` onto Node's `global` (not just window/document/navigator) is
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// what makes those bare references resolve at all; without it, the first
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// one touched throws a ReferenceError. `pretendToBeVisual` is what makes
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// jsdom actually populate devicePixelRatio/requestAnimationFrame in the
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// first place -- both are left undefined otherwise.
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const dom = new JSDOM('<!DOCTYPE html><html><body></body></html>', { pretendToBeVisual: true });
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for (const key of Object.getOwnPropertyNames(dom.window)) {
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if (key in global) continue;
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try {
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global[key] = dom.window[key];
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} catch {
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// a handful of window properties throw on read outside a real
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// browser (e.g. some storage/permissions getters) -- skip those
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// rather than let one bad property crash startup entirely
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}
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}
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global.window = dom.window;
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global.document = dom.window.document;
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global.navigator = dom.window.navigator;
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// jsdom doesn't implement matchMedia -- Excalidraw's bundle calls it
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// unconditionally (theme/print-media detection), so without a stub this
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// is the next ReferenceError-shaped crash after the one above.
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if (typeof global.window.matchMedia !== 'function') {
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const stubMatchMedia = () => ({
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matches: false,
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media: '',
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addListener: () => {},
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removeListener: () => {},
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addEventListener: () => {},
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removeEventListener: () => {},
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dispatchEvent: () => false,
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});
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global.window.matchMedia = stubMatchMedia;
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global.matchMedia = stubMatchMedia;
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}
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const express = require('express');
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const { exportToSvg } = require('@excalidraw/utils');
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const { Resvg } = require('@resvg/resvg-js');
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const PORT = process.env.RENDER_SERVICE_PORT || 3001;
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const HOST = '127.0.0.1';
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// A whiteboard scene is normally tiny (KB, not MB) -- this is a sanity
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// cap against something going wrong upstream, not a real expected size.
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const MAX_BODY_BYTES = 25 * 1024 * 1024;
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const app = express();
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app.use(express.json({ limit: MAX_BODY_BYTES }));
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app.get('/health', (req, res) => {
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res.json({ status: 'ok' });
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});
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app.post('/render', async (req, res) => {
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const { elements, appState, files, width, height } = req.body || {};
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if (!Array.isArray(elements)) {
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res.status(400).json({ error: 'elements must be an array (a parsed .whiteboard/Excalidraw scene)' });
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return;
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}
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try {
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const svg = await exportToSvg({
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elements,
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appState: appState || {},
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files: files || {},
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exportPadding: 20,
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});
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// Depending on the installed version, exportToSvg resolves to either
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// an SVGSVGElement (needs serializing) or already a string -- handle
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// both rather than assume, since this isn't runtime-tested against a
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// live install in this environment (no Node available to verify
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// during development, see the server README's whiteboard mode notes).
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const svgString = typeof svg === 'string' ? svg : svg.outerHTML;
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const targetWidth = Number(width) || undefined;
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const resvg = new Resvg(svgString, {
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fitTo: targetWidth ? { mode: 'width', value: targetWidth } : { mode: 'original' },
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background: 'rgba(255, 255, 255, 1)',
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font: {
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// No bundled Excalidraw font assets (Virgil/Cascadia) in v1 --
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// text renders in whatever fonts fontconfig finds in the image
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// (see ../Dockerfile's fonts-dejavu-core), not pixel-identical
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// to the browser editor's handwriting-style font. Good enough
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// for "what does the board say", not a design-fidelity tool.
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loadSystemFonts: true,
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},
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});
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const pngBuffer = resvg.render().asPng();
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res.set('Content-Type', 'image/png');
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res.send(pngBuffer);
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} catch (err) {
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console.error('Whiteboard render failed:', err);
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res.status(500).json({ error: String((err && err.message) || err) });
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}
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});
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app.listen(PORT, HOST, () => {
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console.log(`whiteboard-render listening on ${HOST}:${PORT}`);
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});
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