fix(images): preserve bodyless responses with size headers

[luvs01]

Summary

• Treat a response with no body as zero bytes before evaluating its Content-Length metadata.
• Preserve bodyless image relay statuses such as 204 even when an upstream sends an oversized or stale Content-Length header.
• Extend the live image relay regression so this header cannot turn a bodyless response into a synthetic 502.

Follow-up to #1346 (comment).

Verification

• Bun 1.3.14: bun test tests/server-images.test.ts — 63 passed.
• bun run typecheck — passed.
• bun run privacy:scan — passed.
• git diff --check HEAD^ HEAD — passed.

Checklist

• Scope stays focused and avoids unrelated cleanup.
• Docs or release notes were updated when needed; none are required for this internal response-body correction.
• Security-sensitive changes were reviewed for untrusted upstream metadata and fail-closed behavior.

Review readiness checklist

• All CI tests are green on my local testing.

• I pushed my PR to the latest dev commit.

• I resolved all correct Codex and CodeRabbit findings.

• My PR is ready for review.

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of image responses with no body.
  • Prevented empty responses with oversized declared content lengths from being incorrectly treated as oversized image data.
  • Preserved expected behavior for successful empty responses.

[coderabbitai]

📝 Walkthrough

Walkthrough

readImageResponseBytes now returns zero bytes for null response bodies without marking them oversized. The related test covers a 204 response with an oversized Content-Length header and no response body.

Changes

Image response handling

Layer / File(s)	Summary
Null body handling and regression coverage src/server/images.ts, tests/server-images.test.ts	At lines 87–89, readImageResponseBytes returns an empty, non-oversized result when the response body is null. The test at lines 786–789 verifies this behavior for a 204 response with an oversized Content-Length header.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• lidge-jun/opencodex#551: Modifies the same image response reader and bodyless response test.

Suggested reviewers: wibias, ingwannu, lidge-jun

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: preserving bodyless image responses when size headers are oversized or stale.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[github-actions]

✅ Deterministic PR hygiene checks passed.

[github-actions]

✅ READY

• all PR quality gates passed; the review readiness checklist is complete.

Review readiness checklist

• ✅ All CI tests are green on my local testing.
• ✅ I pushed my PR to the latest dev commit.
• ✅ I resolved all correct Codex and CodeRabbit findings.
• ✅ My PR is ready for review.

✅ 4/4 boxes ticked.

This pull request is already Ready for Review.
The review-ready label marks this PR as ready; review automation runs independently. If no CodeRabbit review appears, comment @coderabbitai review to request one.
Maintainers: @lidge-jun @Ingwannu @Wibias

[Wibias]

Reviewed current head 9b44acc. The production change correctly handles a null response body before Content-Length validation, which fixes the bodyless-response false oversize case while preserving the existing abort and bounded-body behavior. Cross-platform CI and React Doctor are green. Non-blocking note: the motivating standards-compliant example is a 304 with Content-Length; the regression uses a 204 with Content-Length, which is a malformed upstream case. The implementation still covers both, so this is not a merge blocker.

[Wibias]

Thanks @luvs01! 🙏 This is a clean, focused fix for the bodyless image-response edge case. Merged into dev.