next.js

8fbd7396 - Automatically compress route handler responses if not already compressed (#101220)

Automatically compress route handler responses if not already compressed (#101220) Route handler responses were never compressed when self-hosted. `NodeNextResponse.appendHeader` stored every header value as an array, even a single value. The compression middleware checks `Content-Type` with the `compressible` package, which only accepts strings, so any response sent through `sendResponse` (all app route handlers, including prerendered ones served from the cache) failed the content-type filter and skipped compression. `appendHeader` now keeps a single value as a plain string, matching Node's own `appendHeader` semantics. Fixes https://github.com/vercel/next.js/issues/101120 Closes https://github.com/vercel/next.js/pull/101201 We must strip CE and CL headers from `Response` returned from route handlers due to https://github.com/vercel/next.js/security/advisories/GHSA-pc58-hwjq-p385. A `Response` from `fech()` is indistinguishable from a synthetic one. Any provenance can get lost via `clone` or manual reconstruction based on headers and body. Instead, the responses from route handlers should be returned uncompressed and be compressed by the outgoing server: now `next start` or your hosting provider e.g. Vercel. Route handlers should not return a `fetch()` without processing the body as this needlessly adds CPU overhead due to `fetch()`'s automatic decompression. Use a dedicated proxy library for that instead. ## test plan - moved dev-only compression test to e2e and extended with small/large and dynamic/static routes <!-- NEXT_JS_LLM --> --------- Co-authored-by: Claude Code (kimi-k3) <noreply@anthropic.com>