[🐛 Bug]: Compat: Header values for x-vercel-ip-* headers are appended instead of replaced.

[rphsoftware]

next-on-pages environment related information

System:
Platform: linux
Arch: x64
Version: #1 SMP PREEMPT_DYNAMIC Sat, 23 Sep 2023 22:55:13 +0000
CPU: (20) x64 13th Gen Intel(R) Core(TM) i5-13600K
Memory: 63 GB
Shell: /usr/bin/zsh
Binaries:
Node: 18.12.0
Bun: 1.0.4
pnpm: 7.25.0
Yarn: 1.22.19
npm: 9.2.0
Package Manager Used: npm
Relevant Packages:
@cloudflare/next-on-pages: 1.6.3
vercel: N/A
next: 13.5.4

Description

The header rewrites produce different behavior from running the NextJS application on Vercel.
If a client sends a request with the header x-vercel-ip-city: Atlantis to a deployment hosted on Pages, the API route will see the following header: x-vercel-ip-city: Atlantis, London (assuming the user lives in London).
Meanwhile, the same application hosted on Vercel will see the header as x-vercel-ip-city: London.

Reproduction

Create a next API route with the following code:

export async function GET(request) {
    let headers =  Object.fromEntries(Array.from(request.headers.entries()));
    headers["x-vercel-sc-headers"] = "--redacted--"; // redact private info for deployments on vercel.
    return Response.json({ h: headers })
}

export const runtime = 'edge';

Deploy it to both Vercel and Pages, and send a request with the x-vercel-ip-city: Atlantis header set.

curl -H "x-vercel-ip-city: Atlantis" https://example.com/apiroute | jq '.h["x-vercel-ip-city"]'

Observe that the response differs between Vercel and Pages.

Pages Deployment Method

Pages CI (GitHub/GitLab integration)

Pages Deployment ID

https://0086b0c1.header-accuracy-test.pages.dev

Additional Information

Using set instead of append in https://github.com/cloudflare/next-on-pages/blob/main/packages/next-on-pages/templates/_worker.js/utils/request.ts should fix this problem and make the behavior inline with deployments on Vercel.

Would you like to help?

• Would you like to help fixing this bug?