Description

Fixes an issue where rewrites acting as proxies can return 500 Internal Server Error when running Next.js behind a reverse proxy in standalone production builds.

The request is correctly received by Next.js, proxied upstream, and the upstream responds with 200, but the client still receives a 500 response when response compression is enabled.

I already documented this behavior in PR #87244. That PR aims to fix the same 500 error when using rewrites as proxies, but through a different approach.
The issue still reproduced in this setup.

This PR fixes the problem by explicitly removing the Accept-Encoding header on proxied requests, preventing double compression when running behind a reverse proxy.

#87244 (comment)

Research and Findings

During debugging, the following was observed:

• The request consistently reaches the Next.js server and executes proxyRequest
• The upstream responds successfully with status 200
• The response fully completes inside Next.js
• When running behind Traefik with compression enabled, clients receive 500
• Removing Accept-Encoding or forcing identity resolves the issue

This strongly indicates a double compression or content encoding mismatch when multiple reverse proxies are involved.

Changes

• Remove the Accept-Encoding header for proxied requests to prevent double compression
• Keep proxy behavior otherwise unchanged

Fixes

Fixes #87071