/_next/data is permanently redirected if a middleware is present and trailingSlash is enabled

Verify canary release

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

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 10 Pro
Binaries:
  Node: 16.10.0
  npm: N/A
  Yarn: N/A
  pnpm: N/A
Relevant packages:
  next: 12.2.1-canary.1
  eslint-config-next: 12.2.0
  react: 18.2.0
  react-dom: 18.2.0

What browser are you using? (if relevant)

Irrelevant

How are you deploying your application? (if relevant)

Irrelevant

Describe the Bug

We have an app that uses the next@12.2 middleware features and at the same time has trailingSlash set to true in next.config.js.

When the app is opened for the first time in a browser tab it works correctly. However, navigating to any page with getServerSideProps via the Link component results in the corresponding /_next/data request getting a 308 response and therefore in the server-side data not reaching the client-side.

The issue reproduces if both, a middleware is present and trailingSlash is set to true. It doesn’t matter what the middleware does (it can just return NextResponse.next()), it just needs to be present.

Expected Behavior

The /_next/data request gets a 200 OK response containing the data from the server-side.

Link to reproduction

https://codesandbox.io/s/trailing-slash-middleware-issue-rhvbbx

To Reproduce

1. Star the app using yarn dev
2. Click on the “Go to dummy” link

[kodkroken]

We’re also experiencing the same issue when upgrading from 12.1.6 -> 12.2.

[github-actions[bot]]

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