Middleware Caches Uploaded Files In Memory

[KakkoiDev]

Link to the code that reproduces this issue

https://github.com/KakkoiDev/try-memory-efficient-nextjs-upload-proxy

To Reproduce

1. Open your system monitor to see how much RAM is available
2. Start project server
3. Upload a file
4. Use the alternative NEXT_PUBLIC_UPLOAD_URL path, to avoid using the middleware to validate the issue disappears

Current vs. Expected behavior

Current

As the file uploads, the sent chunks are cached in memory and not released.

Expected behavior

As the data stream is sent to the server, the cached chunks are released from memory.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #29~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Apr  4 14:39:20 UTC 2
  Available memory (MB): 32012
  Available CPU cores: 6
Binaries:
  Node: 20.12.2
  npm: 10.5.0
  Yarn: 1.22.22
  pnpm: 9.1.0
Relevant Packages:
  next: 14.2.3 // Latest available version is detected (14.2.3).
  eslint-config-next: 14.2.3
  react: 18.3.1
  react-dom: 18.3.1
  typescript: 5.4.5
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Middleware, Performance

Which stage(s) are affected? (Select all that apply)

next dev (local), next build (local), next start (local), Vercel (Deployed), Other (Deployed)

Additional context

My whole team experiences the same issue on their own computers.