gridcraft/packaging/web

Hosting GridCraft for the web

gridcraft-web-<version>.zip (from the GitHub release, or packaging/web/package.sh) holds a static site in gridcraft-web-<version>/:

File	What it is
index.html	The page. It loads everything through relative URLs.
gridcraft-web-<hash>.js	wasm-bindgen glue (generated, ES module)
gridcraft-web-<hash>_bg.wasm	The app (compresses to roughly a third with gzip/Brotli)
_headers, .htaccess	Sample header rules for Netlify/Cloudflare Pages and Apache

There is no server-side code. Upload the folder's contents anywhere that serves static files.

Any path works

All URLs in index.html are relative (public_url = "./" in apps/gridcraft-web/Trunk.toml), so the site works at a domain root (https://example.com/), under a prefix (https://example.com/tools/gridcraft/) and from a CDN bucket. The asset names carry a content hash, so they can be cached forever. Only index.html needs revalidation.

Required server settings

• MIME type: serve .wasm as application/wasm. Browsers refuse to stream-compile it under any other type, and the app then loads slowly or not at all. Serve .js as text/javascript. Most hosts already do both. For nginx, check that mime.types has application/wasm wasm;.
• Compression: turn on gzip or Brotli for .wasm, .js and .html. That cuts the download to roughly a third. You can also precompress (brotli -k *.wasm) and let the server send Content-Encoding: br.
• Caching: Cache-Control: public, max-age=31536000, immutable on the hashed .wasm and .js files, and no-cache on index.html.
• HTTPS: WebGPU (and the clipboard) only work in a secure context, which means https:// or http://localhost. Over plain HTTP elsewhere, the app falls back to WebGL2.
• No special isolation headers: GridCraft doesn't use SharedArrayBuffer, so it doesn't need Cross-Origin-Opener-Policy or Cross-Origin-Embedder-Policy. If your site already sends COEP require-corp, also send Cross-Origin-Resource-Policy: same-origin (or cross-origin when the files live on a CDN) on the app's files.

nginx example:

location /gridcraft/ {
    types { application/wasm wasm; text/javascript js; text/html html; }
    gzip on;
    gzip_types application/wasm text/javascript text/html;
    location ~* \.(wasm|js)$ { add_header Cache-Control "public, max-age=31536000, immutable"; }
    location ~* index\.html$ { add_header Cache-Control "no-cache"; }
}

Local test: python3 -m http.server 8765 inside the folder, then open http://localhost:8765/.

Embedding in a page (iframe)

<iframe
  src="https://example.com/gridcraft/"
  title="GridCraft spreadsheet"
  style="width: 100%; height: 720px; border: 0;"
  allow="fullscreen; clipboard-read; clipboard-write"
  allowfullscreen>
</iframe>

• The app fills the iframe and follows its size, so size the iframe and not the app.
• Keyboard shortcuts go to the iframe after the user clicks into it, as with any embedded app.
• Cross-origin embeds work. Preferences are kept in the iframe's localStorage. Browsers that partition or block third-party storage may forget them between visits, and the app then starts with defaults.
• Sandboxed iframes need at least sandbox="allow-scripts allow-same-origin allow-downloads allow-popups". Without allow-same-origin there's no storage. Without allow-downloads, Save and Export (browser downloads) are blocked.
• Don't send X-Frame-Options: DENY or a frame-ancestors CSP that excludes the embedding page.
• Window chrome: ?chrome=none on the iframe src leaves out the title bar and the File tab (whose Backstage view then never opens); ?chrome=notitlebar or ?chrome=nofiletab leave out just one. Use them when the host window already shows the file name and owns the files, so the sheet's own Open or Save As cannot replace what the host thinks is open. Everything stays on by default.

The parent bridge (?host=parent)

A page framing GridCraft in a same-origin iframe can add ?host=parent to the iframe's URL (https://example.com/gridcraft/?host=parent) and have GridCraft hand its files over instead of downloading them. The two sides talk postMessage with plain window messages that carry a type:

Message	Direction	Fields
gridcraft:ready	app → page	version, appVersion: the app is listening; send a file now
gridcraft:open	page → app	name, bytes (an ArrayBuffer or Uint8Array): open like File › Open
gridcraft:save	app → page	name, bytes (a transferred ArrayBuffer): every file the app would otherwise download (Save, Save As, Export as PDF). The page stores it and reports failures itself.
gridcraft:dirty	app → page	dirty: unsaved changes appeared or went away
gridcraft:failed	app → page	error: the app couldn't start

In host mode the app starts with an empty workbook instead of a sample, so the framing page should guard leaving the page while changes are unsaved. &author= names the user for the notes and comments the app creates. Opening ?host=parent outside an iframe gives the normal app with downloads.

Embedding without an iframe (page host mode)

A page that loads the GridCraft module into its own document — its own <canvas id="gridcraft_canvas"> inside a component, sized to a box beside the page's own header and controls — opts in with data-host="page" on that canvas. The behaviour is the same as the parent bridge, except the transport is DOM CustomEvents on the canvas instead of postMessage: the app dispatches gridcraft:ready, gridcraft:save, gridcraft:dirty and gridcraft:failed on the canvas with the message fields above as the event's detail, and the page dispatches gridcraft:open on the canvas with detail: { name, bytes } to open a workbook. Events don't bubble, so two editors on one page can't hear each other; listen on the canvas itself.

<canvas id="gridcraft_canvas" data-host="page" style="width: 100%; height: 600px; border: 0;"></canvas>

import init from "./gridcraft-web-<hash>.js"; // the wasm-bindgen glue shipped with the app

// Listen first: the app announces itself while `init` runs.
const canvas = document.getElementById("gridcraft_canvas");

canvas.addEventListener("gridcraft:ready", async () => {
  // Open a workbook of the page's own, as with File › Open.
  const bytes = await workbookBytes(); // an ArrayBuffer or Uint8Array
  canvas.dispatchEvent(new CustomEvent("gridcraft:open", {
    detail: { name: "Budget.xlsx", bytes },
  }));
});

// Every file GridCraft would otherwise download (Save, Save As, Export as PDF) arrives here.
canvas.addEventListener("gridcraft:save", (event) => {
  const { name, bytes } = event.detail; // bytes is an ArrayBuffer
  storeFile(name, bytes);
});

canvas.addEventListener("gridcraft:dirty", (event) => {
  warnBeforeLeaving(event.detail.dirty);
});
canvas.addEventListener("gridcraft:failed", (event) => {
  showError(event.detail.error);
});

await init({ module_or_path: "./gridcraft-web-<hash>_bg.wasm" });

As with the parent bridge, the app starts with an empty workbook instead of a sample, and ?author= on the page's URL names the user for new notes and comments. The data-host value must be exactly page; anything else is ignored, and the app runs as a standalone page with downloads.

The messages and both transports are the shared contract of craft-web-host (storytold/craft-libs#420), the same for every Craft app: its README lists every message, including saved, with the compatibility notes. In gridcraft:ready, version is the contract's ("1") and appVersion is this app's release. GridCraft reads bytes, so a host sends bytes, not a File.

Trust and limits

• Who is trusted. In page host mode the page and GridCraft share one document, so any script on the page can drive the app: open files in it and receive what it saves. Use this mode only for a page you control. The iframe mode (?host=parent) answers only the parent window, on the page's own origin.
• Files from the host are untrusted input. An opened file goes through the same reading as one picked with File ▸ Open or dropped on the window, with the same format limits; before it is copied into the app's memory, its size is checked against the host open limit (512 MiB) and a larger file is refused, and a name is cut to 255 characters.
• The event and message names are the interface. gridcraft:ready, gridcraft:open, gridcraft:save, gridcraft:dirty and gridcraft:failed, and the fields they carry (the same as the ?host=parent messages), stay stable; changing one is a breaking change.

Renderer selection

GridCraft's web build is the same egui app as the desktop one, compiled to wasm (apps/gridcraft-web). It renders with the backend apps/gridcraft-web selects (WebGPU where available, otherwise WebGL2). If the web app adds URL flags to force a backend (as the sibling Craft apps do with ?webgl / ?cpu), document them here; they also work on the iframe src.

A browser with neither WebGPU nor WebGL2 gets a message in place of the app.