fix: server crash on /theme.css request (ERR_STREAM_WRITE_AFTER_END)

[sahillllllllll-bit]

Description

Fixes #39407

Requesting /theme.css may crash the server with:

Error [ERR_STREAM_WRITE_AFTER_END]: write after end

This happens because the middleware ends the response using res.end() but does not stop execution afterward. In some cases the request stream continues and attempts to write to the same response again, causing Node.js to throw ERR_STREAM_WRITE_AFTER_END.

This change ensures the middleware stops execution immediately after sending the response.

Additionally, the Content-Length header now uses Buffer.byteLength instead of string.length to correctly handle UTF-8 characters.

Changes

• Stop middleware execution after res.end()
• Use Buffer.byteLength(style, 'utf8') for accurate Content-Length

Summary by CodeRabbit

• Bug Fixes
  • Fixed Content-Length header calculation for CSS file delivery. The header now accurately reflects the actual byte length of CSS content, ensuring reliable content delivery and preventing potential issues with stylesheet serving.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 0dcb7dd8-cf40-4f65-af56-97b5ed068804

📥 Commits

Reviewing files that changed from the base of the PR and between 46a1774 and 4be8933.

📒 Files selected for processing (1)

• apps/meteor/app/theme/server/server.ts

📜 Recent review details

🧰 Additional context used

📓 Path-based instructions (1)

**/*.{ts,tsx,js}

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Files:

• apps/meteor/app/theme/server/server.ts

🧠 Learnings (2)

📚 Learning: 2026-02-26T19:25:44.063Z

Learnt from: gabriellsh
Repo: RocketChat/Rocket.Chat PR: 38778
File: packages/ui-voip/src/providers/useMediaSession.ts:192-192
Timestamp: 2026-02-26T19:25:44.063Z
Learning: In the Rocket.Chat repository, do not reference Biome lint rules in code review feedback. Biome is not used even if biome.json exists; only reference Biome rules if there is explicit, project-wide usage documented. For TypeScript files, review lint implications without Biome guidance unless the project enables Biome rules.

Applied to files:

• apps/meteor/app/theme/server/server.ts

📚 Learning: 2026-02-26T19:25:44.063Z

Learnt from: gabriellsh
Repo: RocketChat/Rocket.Chat PR: 38778
File: packages/ui-voip/src/providers/useMediaSession.ts:192-192
Timestamp: 2026-02-26T19:25:44.063Z
Learning: In this repository (RocketChat/Rocket.Chat), Biome lint rules are not used even if a biome.json exists. When reviewing TypeScript files (e.g., packages/ui-voip/src/providers/useMediaSession.ts), ensure lint suggestions do not reference Biome-specific rules. Rely on general ESLint/TypeScript lint rules and project conventions instead.

Applied to files:

• apps/meteor/app/theme/server/server.ts

🔇 Additional comments (1)

apps/meteor/app/theme/server/server.ts (1)

40-43: Nice fix on the response framing.

Buffer.byteLength(style, 'utf8') gives the correct Content-Length for UTF-8 CSS payloads, so clients won't see a mismatched body size here.

---

Walkthrough

Modified HTTP response Content-Length calculation in the theme CSS endpoint from using raw string length to using Buffer.byteLength with UTF-8 encoding, ensuring the Content-Length header accurately reflects the actual byte size of the CSS content.

Changes

Cohort / File(s)	Summary
Theme CSS Response Handling apps/meteor/app/theme/server/server.ts	Changed Content-Length calculation from string length to Buffer.byteLength with UTF-8 encoding to correctly represent the actual byte length of CSS content in the HTTP response header.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Suggested labels

type: bug

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title clearly and specifically describes the fix: preventing a server crash caused by writing after stream end on /theme.css requests.
Linked Issues check	✅ Passed	The PR changes align with issue #39407 requirements: using Buffer.byteLength for correct Content-Length calculation to handle UTF-8 properly and stopping middleware execution to prevent writes after end.
Out of Scope Changes check	✅ Passed	All changes in apps/meteor/app/theme/server/server.ts are directly scoped to fixing the /theme.css ERR_STREAM_WRITE_AFTER_END error without unrelated modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[cubic-dev-ai]

No issues found across 1 file