From dadd9ec164e62ef638dbf8cdb94c875ee62d577c Mon Sep 17 00:00:00 2001
From: Thomas Faour <tom@tfao.ca>
Date: Thu, 23 Jul 2026 17:50:27 -0400
Subject: [PATCH] Fix whiteboard render sidecar crash on startup

@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.
---
 server/render-service/README.md | 23 +++++++++++++-----
 server/render-service/server.js | 42 +++++++++++++++++++++++++++++----
 2 files changed, 54 insertions(+), 11 deletions(-)
diff --git a/server/render-service/README.md b/server/render-service/README.md
index 1c641c4..cb344a7 100644
--- a/server/render-service/README.md
+++ b/server/render-service/README.md
@@ -13,12 +13,23 @@ that same container.
 API (used to verify the dependency versions/licenses in `package.json`
 actually exist and resolve). The code is written carefully against each
 library's documented API (`@excalidraw/utils`'s `exportToSvg`,
-`@resvg/resvg-js`'s `Resvg` class), but the first real build
-(`docker compose build`) is the first time this has actually executed
-end to end. If something's off, `docker compose logs` will show it --
-most likely candidates are `exportToSvg`'s actual return type (string vs.
-DOM element -- handled defensively, see server.js) or a font-rendering
-quirk, not a wrong API shape.
+`@resvg/resvg-js`'s `Resvg` class), but `docker compose build`+actually
+running it is the first time this has executed end to end -- and the
+first real run did in fact crash: `@excalidraw/utils`'s bundle touches
+bare browser globals (`devicePixelRatio`, `location`, `matchMedia`, ...)
+the same way inline `<script>` code in a real page would, not as
+`window.foo` -- jsdom only puts those *on* `dom.window`, so only
+copying `window`/`document`/`navigator` onto Node's `global` (the
+original version of this file) left everything else undefined. Fixed
+by copying jsdom's entire `window` onto `global` plus a `matchMedia`
+stub (jsdom doesn't implement it at all). If another crash like this
+shows up, it's almost certainly the same shape -- another bare global
+the bundle expects that this file hasn't stubbed yet. One other gap
+worth knowing about going in: jsdom's `<canvas>` has no real 2D
+rendering context (no `node-canvas` installed), so if Excalidraw's text
+measurement path depends on `canvas.getContext('2d').measureText(...)`
+rather than pure SVG/font-metrics math, that could be a next thing to
+watch for -- not something confirmed broken, just not yet exercised.
 
 ## Local development (if you have Node 20.19+/22.13+ installed)
 
diff --git a/server/render-service/server.js b/server/render-service/server.js
index b14d79f..dad60a3 100644
--- a/server/render-service/server.js
+++ b/server/render-service/server.js
@@ -25,15 +25,47 @@
 
 const { JSDOM } = require('jsdom');
 
-// @excalidraw/utils touches `window`/`document` globals even though
-// exportToSvg's own return value doesn't depend on a live page -- these
-// have to exist before the package is required, not just before it's
-// called.
-const dom = new JSDOM('<!DOCTYPE html><html><body></body></html>');
+// @excalidraw/utils is a browser bundle: it references things like
+// `devicePixelRatio` and `location` as bare identifiers, the same way
+// inline <script> code in a real page would resolve them off the global
+// scope -- not as `window.devicePixelRatio`. Copying jsdom's entire
+// `window` onto Node's `global` (not just window/document/navigator) is
+// what makes those bare references resolve at all; without it, the first
+// one touched throws a ReferenceError. `pretendToBeVisual` is what makes
+// jsdom actually populate devicePixelRatio/requestAnimationFrame in the
+// first place -- both are left undefined otherwise.
+const dom = new JSDOM('<!DOCTYPE html><html><body></body></html>', { pretendToBeVisual: true });
+for (const key of Object.getOwnPropertyNames(dom.window)) {
+  if (key in global) continue;
+  try {
+    global[key] = dom.window[key];
+  } catch {
+    // a handful of window properties throw on read outside a real
+    // browser (e.g. some storage/permissions getters) -- skip those
+    // rather than let one bad property crash startup entirely
+  }
+}
 global.window = dom.window;
 global.document = dom.window.document;
 global.navigator = dom.window.navigator;
 
+// jsdom doesn't implement matchMedia -- Excalidraw's bundle calls it
+// unconditionally (theme/print-media detection), so without a stub this
+// is the next ReferenceError-shaped crash after the one above.
+if (typeof global.window.matchMedia !== 'function') {
+  const stubMatchMedia = () => ({
+    matches: false,
+    media: '',
+    addListener: () => {},
+    removeListener: () => {},
+    addEventListener: () => {},
+    removeEventListener: () => {},
+    dispatchEvent: () => false,
+  });
+  global.window.matchMedia = stubMatchMedia;
+  global.matchMedia = stubMatchMedia;
+}
+
 const express = require('express');
 const { exportToSvg } = require('@excalidraw/utils');
 const { Resvg } = require('@resvg/resvg-js');
