[Bug]: Unsanboxed preload running after page with content is loaded (ESM) #40777
Description
Preflight Checklist
- I have read the Contributing Guidelines for this project.
- I agree to follow the Code of Conduct that this project adheres to.
- I have searched the issue tracker for a bug report that matches the one I want to file, without success.
Electron Version
28.0.0
What operating system are you using?
Windows
Operating System Version
Windows 10 Family
What arch are you using?
x64
Last Known Working Electron version
No response
Expected Behavior
Electron 28 added support for ESM, the new doc states that:
Unsandboxed ESM preload scripts will run after page load on pages with no content
If the response body for a renderer's loaded page is completely empty (i.e.
Content-Length: 0), its preload script will not block the page load, which may result in race conditions.If this impacts you, change your response body to have something in it (e.g. an empty
htmltag (<html></html>)) or swap back to using a CommonJS preload script (.jsor.cjs), which will block the page load.
So for an HTML with content, I expect the preload to be run before the page loads:
Actual Behavior
For the following HTML:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="Content-Security-Policy" content="script-src 'self';">
</head>
<body>
<main>
<p>
There is nothing interesting to see here...
</p>
</main>
</body>
</html>Loaded as:
new BrowserWindow({
webPreferences: {
nodeIntegration: false,
contextIsolation: true,
sandbox: false,
preload: /*preload path */,
}
});With in package.json:
"type": "module"The JS file linked to my HTML shows the page is loaded before the preload.
For context, listen is a function exposed on the preload with contextBridge.
Testcase Gist URL
No response
Additional Information
I can't see the Content-Length header in the response headers:
The file is loaded from http://localhost:3000/worker.html