`TypeError: fetch failed` for Edge API Routes running locally

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 21.6.0: Sat Jun 18 17:07:22 PDT 2022; root:xnu-8020.140.41~1/RELEASE_ARM64_T6000
Binaries:
  Node: 16.15.1
  npm: 8.13.2
  Yarn: 1.22.19
  pnpm: N/A
Relevant packages:
  next: 12.2.4-canary.8
  eslint-config-next: 12.2.3
  react: 18.2.0
  react-dom: 18.2.0

What browser are you using? (if relevant)

Edge

How are you deploying your application? (if relevant)

next dev

Describe the Bug

When accessing an API route setup to use the Edge Runtime, we’d get an error saying TypeError: fetch failed

Expected Behavior

The API should work normally and have a valid response.

Link to reproduction

https://github.com/jahirfiquitiva/sponsors-edge-api

To Reproduce

Run the project using next dev and access http://localhost:3000/api/sponsors-edge to see the error.

Also, I created a normal API route at http://localhost:3000/api/sponsors which works fine.

Worth mentioning this issue is not present in Next.js 12.2.2, but started happening after updating to 12.2.3 (I didn’t try the canary versions between 12.2.2 and 12.2.3, but I tried the latest canary 12.2.4-canary.8 and this issue is still present)

[balazsorban44]

Edge API routes and Middleware use the same runtime. 👍

[github-actions[bot]]

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