[Bug]: Electron net.fetch can't handle non-ASCII characters in headers

[shadaxv]

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

30.0.6

What operating system are you using?

Windows

Operating System Version

Windows 10 22H2 19045.4291

What arch are you using?

x64

Last Known Working Electron version

Unknown

Expected Behavior

Electron should encode unsupported characters in HTTP headers so that they do not cause uncaught errors

Actual Behavior

Electron does not check HTTP headers, and because of this, Node.js throws unexpected errors. This can be worked around by encoding headers in webRequest.onHeadersReceived, but it won't work, for example, on a modified User Agent.

When net.fetch is replaced with the regular fetch from Node.js, this issue does not occur for HTTP requests (just like in web browsers). Unfortunately, in Node.js, it is not possible to set non-ASCII headers, and I cannot demonstrate this example.

I understand that using non-ASCII headers is against the HTTP standard, but sometimes servers send such headers (e.g., when a file being downloaded has a non-standard name and that name is placed in the header), and developers using Electron cannot cover all cases (such as a wrong User Agent).

Testcase Gist URL

https://gist.github.com/shadaxv/742cd824de5a8dfc7893c40432ee4ce1

Additional Information

There was a similar ticket, but it was closed, I am sending this as a new issue to better mark the details in the template

#39469

webRequest.onHeadersReceived workaround:

// Electron's net.fetch does not support non-ASCII characters in the headers
for (const [key, value] of Object.entries(responseHeaders)) {
  // normalize and convert all non-ASCII characters to ASCII using Buffer
  responseHeaders[key] = value.map((entry) => {
    const normalized = entry.normalize("NFKD");
    const buffer = Buffer.from(normalized, "utf8");
    return buffer.toString("ascii");
  });
}