cloudflare/vinext

App Router: `reactMaxHeadersLength` config not respected

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#1,552 opened on May 22, 2026

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Description

This issue was created by an agent analysing CI failures from the Next.js Deploy Suite (vinext main vs Next.js v16.2.6, 2026-05-22).

Problem

The reactMaxHeadersLength config option (which controls how much React inlines into HTTP headers like Link preload hints) is not honored — the expected header that should be set when this option is configured is always null.

With `reactMaxHeadersLength` configured, expected Link preload header set; received null

Estimated Impact

~3 test failures across the deploy suite.

Affected Test Suites

  • test/e2e/app-dir/react-max-headers-length/react-max-headers-length.test.ts (3 failures)

Recommendation

  1. Reproduce first in vinext's own test suite. Configure reactMaxHeadersLength: 16000 and assert the expected Link header is emitted.

  2. Forward the option into the React renderer. Pass reactMaxHeadersLength to renderToReadableStream/renderToPipeableStream so React inlines preload hints into headers up to the limit.

Part of #1328.

Contributor guide

Research direction
Ensure that the `reactMaxHeadersLength` configuration value is forwarded to the React rendering function (e.g., `renderToReadableStream` or `renderToPipeableStream`), and verify that the generated Link headers respect the set limit.
Tech stack
typescriptreactvite
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
TypeScriptReact
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
55