fix: allow relative paths in fetch cache allow list check

[serhalp]

🔗 Linked issue

N/A

🧭 Context

Soooo we were passing a relative path (with a configured base url) in several places, but the isAllowedDomain() check didn't support this and quietly threw and disallowed these, so they never got cached! 😱

📚 Description

Add the missing logic.

Check this out: warm package page TTFB

Package	Before	After
vite	1.42–1.57s	0.20–0.30s
next	0.74–0.89s	0.27–0.38s
vue	0.19–0.34s	0.12–0.17s

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• test/unit/server/plugins/fetch-cache.spec.ts

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📝 Summary

Summary by CodeRabbit

• Bug Fixes

  • Requests with relative URLs are now checked against the cache allowlist using their resolved address, including when a base URL is provided. Requests that cannot be resolved or aren’t allowed are fetched without caching.
  • Cache entries for allowed requests now use the resolved address, helping equivalent requests share the correct cache entry.

• Tests

  • Added coverage for URL resolution, allowed-domain checks, caching requests resolved through a base URL, and reusing fresh cached entries.

The fetch cache resolves request URLs against an optional base URL before checking the domain allowlist. It bypasses caching for unresolved or disallowed URLs. For allowed requests, it uses the resolved URL to generate cache keys.

Changes: Fetch cache URL resolution

Layer / File(s)	Summary
URL resolution helper and tests shared/utils/fetch-cache-config.ts, test/unit/shared/utils/fetch-cache-config.spec.ts	The new resolveRequestUrl helper resolves strings against an optional base URL, passes through URL inputs and returns null when parsing fails. Tests cover URL resolution and domain allowance.
Resolved URL cache checks and keys server/plugins/fetch-cache.ts, test/unit/server/plugins/fetch-cache.spec.ts	cachedFetch resolves the request URL before checking the allowlist. It fetches without caching when resolution fails or the URL is disallowed. Allowed requests use the resolved URL for cache keys. Tests cover caching, cache hits and bypass cases.

Priority: ➖ Normal

Merge Risk: 🔵 Low · up to 211dc

A protocol-relative request can be cached under a URL different from the one actually fetched, risking an incorrect cache association. Inspected callers use ordinary relative paths, so the current merge risk is bounded but remains open.

Pre-merge checks: 4

Passed checks: 4 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: allowing relative paths in the fetch-cache allow-list check.
Description check		The description directly explains the relative-path issue, the caching impact, and the logic added to resolve it. It is related to the changeset.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
server/plugins/fetch-cache.ts	66.66%	0 Missing and 1 partial ⚠️
shared/utils/fetch-cache-config.ts	75.00%	0 Missing and 1 partial ⚠️

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @server/plugins/fetch-cache.ts:
- Around line 71-80: Update resolveRequestUrl to match ofetch’s withBase and
joinURL semantics before the allowlist check and generateFetchCacheKey call, so
protocol-relative URLs resolve to the same host that $fetch requests.

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📒 Files selected for processing (3)

• server/plugins/fetch-cache.ts
• shared/utils/fetch-cache-config.ts
• test/unit/shared/utils/fetch-cache-config.spec.ts

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[trueberryless]

Could we create an e2e test to validate that cachedFetch('/vite', { baseURL }) reaches the storage? The unit tests do not really cover it end to end...

[serhalp]

Could we create an e2e test to validate that cachedFetch('/vite', { baseURL }) reaches the storage? The unit tests do not really cover it end to end...

We can't with the current integration/e2e stack because the whole real event.context.cachedFetch is replaced in those... but I just pushed tests for the cachedFetch plugin!