[BUG] Diacritics in IP geolocation headers causing problems #7641

[Joozty]

Describe the bug

I tried to deploy my Next.js app to Cloudflare Workers, and I followed this tutorial. The build completes successfully, but when I try to preview or deploy it, I encounter the following error:

Invalid header name or value: "Žilina". Per the Fetch specification, the Headers class may only accept header names and values which contain 8-bit characters. That is, they must not contain any Unicode code points greater than 0xFF. As a quirk, we are encoding this string in UTF-8 in the header, but in a browser this would result in a TypeError exception. Consider encoding this string in ASCII for compatibility with browser implementations of the Fetch specification.

Žilina is a city in Slovakia, and I assume that somewhere, a header with this value is being sent. I was able to find the cause, and it throws an error in Miniflare here. I guess the diacritics are causing the problem.

Steps to reproduce

I do not know how to reproduce. VPN maybe?

Expected behavior

not throwing the error

@opennextjs/cloudflare version

0.3.3

Wrangler version

3.99.0

next info output

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.2.0: Fri Dec  6 18:56:34 PST 2024; root:xnu-11215.61.5~2/RELEASE_ARM64_T6020
  Available memory (MB): 32768
  Available CPU cores: 12
Binaries:
  Node: 20.17.0
  npm: 10.8.2
  Yarn: 1.22.22
  pnpm: 9.15.0
Relevant Packages:
  next: 15.1.3 // Latest available version is detected (15.1.3).
  eslint-config-next: N/A
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.7.2
Next.js Config:
  output: N/A

Additional context

cloudflare/workers-sdk#7641

[vicb]

fixed via opennextjs/opennextjs-aws#687