[lprnmns]

The if-modified-since check in the handler has two problems:

1. It never matches a real file's mtime. last-modified is sent with mtime.toUTCString(), which has second precision. The check then compares the client's echoed date against the full mtime, new Date(ifModifiedSince) >= sourceMeta.mtime. File mtimes almost always have a sub-second part, so the echoed date is always slightly earlier and the request is answered with a full 200. Revalidation only works when the client also sends if-none-match.

With ipxFSStorage over test/assets:

mtime 2026-10-23T13:36:13.675Z
GET /w_10/giphy.gif                                        -> 200, last-modified: Fri, 23 Oct 2026 13:36:13 GMT
GET /w_10/giphy.gif  if-modified-since: <that value>       -> 200 (expected 304)

2. It runs before, and regardless of, if-none-match. RFC 9110 §13.1.3 says a recipient MUST ignore If-Modified-Since if the request contains If-None-Match, because the entity tag is the more accurate validator. Here a request whose if-none-match doesn't match, but whose if-modified-since is not older than the mtime, gets a 304. The client then keeps a response the ETag says is stale:

GET /w_10/giphy.gif  if-none-match: "other"  if-modified-since: <tomorrow>  -> 304 (expected 200)

The fix reads if-modified-since only when there is no if-none-match, and compares it against the mtime truncated to whole seconds. Truncating matches what last-modified sends; Date.parse() returns NaN for an invalid date, so the comparison is false as before. This is the same behavior h3 (utils/internal/cache.ts) and srvx (static.ts) already implement.

Tests: two cases in the conditional requests block of test/server.test.ts, one with a .500 mtime and one with a non-matching if-none-match plus if-modified-since. Both fail without the change. The existing if-modified-since test used a whole-second mtime, which is why it passed. pnpm test passes (lint, tsc --noEmit after pnpm build for the examples, and vitest with coverage).

Summary by CodeRabbit

• Bug Fixes
  • Corrected conditional response handling for cached content. Modification dates are now compared at whole-second precision, so matching dates return a not-modified response even when the underlying timestamp includes milliseconds.
  • When a request includes both an entity tag and a modification date, the entity tag takes precedence. A non-matching entity tag now correctly results in the full response rather than an incorrect not-modified response.

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Reviewing files that changed from the base of the PR and between 28295a0 and e23fc16.

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• src/server.ts
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📝 Walkthrough

The server now ignores If-Modified-Since when If-None-Match is present. Otherwise, it compares the parsed date with the source modification time rounded down to whole seconds. Tests cover both behaviors.

Changes: Conditional request handling

Layer / File(s)	Summary
Conditional header checks src/server.ts, test/server.test.ts	The server checks If-Modified-Since only when If-None-Match is absent and compares dates at whole-second precision. Tests cover a modification time with milliseconds and a nonmatching ETag.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to e23fc

The conditional-request change is ready to merge after normal checks. Clients using only Last-Modified retain its standard one-second ambiguity.

Pre-merge checks: 5

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: updating server handling of If-Modified-Since to follow RFC 9110, including conditional-request precedence behavior.
Docstring Coverage		Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files.
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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.76%. Comparing base (28295a0) to head (e23fc16).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #346      +/-   ##
==========================================
+ Coverage   95.74%   95.76%   +0.01%     
==========================================
  Files           9        9              
  Lines        1011     1015       +4     
  Branches      352      357       +5     
==========================================
+ Hits          968      972       +4     
  Misses         41       41              
  Partials        2        2              

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