fix(BunFile): lastModified returns 0 for missing files instead of 2^52-1 sentinel

[robobun]

Repro

const m = Bun.file("/definitely/not/a/real/path");
console.log(m.lastModified);                 // 4503599627370495  (2**52 - 1)
console.log(new Date(m.lastModified).toISOString()); // +144683-05-23T16:29:30.495Z
console.log(m.size, await m.exists());       // 0 false  (these two are already normalized)

await Bun.write("/tmp/real", "x");
console.log(m.lastModified > Bun.file("/tmp/real").lastModified); // true: missing is "newer"

Cause

get_last_modified reads the file store's last_modified field, which is initialized to jsc::INIT_TIMESTAMP ((1u64 << 52) - 1). When the field is still the sentinel it calls resolve_file_stat, but that function silently does nothing on stat failure (ENOENT etc.), so the sentinel is returned to JS unchanged. The fallthrough for in-memory Blobs also returned the raw sentinel.

.size already normalizes this case to 0 via resolve_size; .lastModified was the one getter that leaked the lazy marker.

Fix

After the resolve attempt, if the field is still INIT_TIMESTAMP, return 0 instead of the sentinel. Same for the in-memory Blob fallthrough. new File([...], name) is unchanged and still returns Date.now() when no lastModified option is passed, per the File API.

Verification

USE_SYSTEM_BUN=1 bun test test/js/bun/util/bun-file.test.ts -t lastModified   # 4 fail, all show 4503599627370495
bun bd test test/js/bun/util/bun-file.test.ts                                 # 10 pass

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📥 Commits

Reviewing files that changed from the base of the PR and between 3f5d816 and fa12f28.

📒 Files selected for processing (2)

• src/runtime/webcore/Blob.rs
• test/js/bun/util/bun-file.test.ts

---

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[robobun]

^{Updated 4:53 PM PT - Jul 7th, 2026}

✅ @robobun, your commit fa12f28959d56ed136bbef3c3f603a78387b30d7 passed in Build #70017! 🎉

---

🧪   To try this PR locally:

bunx bun-pr 33652

That installs a local version of the PR into your bun-33652 executable, so you can run:

bun-33652 --bun

[claude]

LGTM — straightforward sentinel normalization mirroring the existing .size behavior.

Extended reasoning...

Overview

This PR fixes Bun.file().lastModified to return 0 instead of the internal lazy-stat sentinel 2**52 - 1 (jsc::INIT_TIMESTAMP) when the underlying file does not exist or stat fails. It touches one getter in src/runtime/webcore/Blob.rs (get_last_modified) and adds four tests to test/js/bun/util/bun-file.test.ts. The fallthrough for in-memory Blobs (non-File) is also changed from the sentinel to 0.

Security risks

None. This is a read-only getter returning a numeric timestamp; no auth, crypto, path handling, or untrusted-input parsing is involved. The change only substitutes one constant return value for another on a path that was already reachable.

Level of scrutiny

Low-to-medium. The diff is ~10 lines of native code plus tests. The fix is a direct analogue of the existing .size → 0 normalization for missing files (resolve_size), so the design decision is already established in the codebase. The S3 branch (which skips resolve_file_stat) now also returns 0 instead of the sentinel when unstatted, which is strictly less surprising than 4503599627370495. The is_jsdom_file path (new File(...)) is unchanged and still returns the stored self.last_modified, so the File API's Date.now() default is preserved — I checked existing structured-clone and fetch tests that assert file.lastModified > 0 and they remain valid.

Other factors

• Tests cover the missing-path case, the deleted-after-creation case, ordering vs. a real file, and the in-memory Blob fallthrough.
• PR description shows the tests fail under USE_SYSTEM_BUN=1 and pass under bun bd, satisfying the repo's test-validity requirement.
• No CODEOWNERS entries cover these paths.
• The bug-hunting system found no issues.

[github-actions]

This PR may be a duplicate of:

1. Allow assigning to Blob#lastModified #32425 - Also fixes the INIT_TIMESTAMP sentinel leaking from get_last_modified in Blob.rs; that PR's primary goal is making Blob#lastModified writable, but it incidentally applies the same sentinel-to-zero fix in the same code area

🤖 Generated with Claude Code

[robobun]

Not a duplicate of #32425. That PR makes Blob#lastModified writable (issue #14257) and only touches the fallthrough at the end of get_last_modified. It does not touch the file-backed branch, so Bun.file("/missing").lastModified still returns 4503599627370495 under that change (the file store's last_modified field stays at INIT_TIMESTAMP when resolve_file_stat fails, and that value is returned directly).

This PR normalizes the sentinel in the file-backed branch, which is the bug reported here. The only overlap is the final fallthrough line; whichever lands second is a trivial rebase.

[robobun]

CI status: this diff is green on every lane that executed tests.

• Build 69869: 75 checks passed (all linux/windows/freebsd/android). darwin-14 aarch64 failed on test/integration/next-pages/test/dev-server.test.ts (puppeteer Chromium DevTools WebSocket "Connection ended" after 3 retries) and test/js/bun/webview/webview.test.ts ("WebView host process killed by signal 5"), both external-browser-process issues unrelated to this change. The other darwin aarch64 attempt died at failed to git clone vendor 'elysia': timeout before running any tests.
• Build 70017 (retrigger): same darwin agent availability problem, jobs expiring in queue.

test/js/bun/util/bun-file.test.ts (the new tests) passed on every platform that ran it. The diff is a 10-line getter normalization in Blob.rs and cannot affect puppeteer WebSocket or WKWebView host processes. Ready for maintainer review.

[claude]

LGTM — straightforward sentinel normalization matching how .size already handles missing files.

Extended reasoning...

Overview

Two-line fix in src/runtime/webcore/Blob.rs get_last_modified: after resolve_file_stat fails to populate last_modified (ENOENT etc.), return 0 instead of leaking the internal jsc::INIT_TIMESTAMP sentinel (2**52 - 1) to JS. The fallthrough for in-memory Blob is normalized the same way. Four new tests in test/js/bun/util/bun-file.test.ts cover missing path, comparison against a real file, post-deletion, and in-memory Blob.

Security risks

None. This is a read-only getter returning a numeric timestamp; no input parsing, no allocation, no I/O added. The change only maps one sentinel constant to 0 at the JS boundary.

Level of scrutiny

Low. The fix is a two-branch value substitution in a getter, directly mirroring the existing pattern where .size already normalizes to 0 for missing files via resolve_size. The is_jsdom_file() branch (which handles new File(...) per the File API spec) is untouched, so spec-mandated Date.now() defaults for File are preserved. The S3 branch also now sees 0 instead of the sentinel when unresolved, which is strictly an improvement.

Other factors

• Tests follow harness conventions (tempDir with using, no hardcoded paths, assert exact values), and the PR description confirms they fail under USE_SYSTEM_BUN=1 and pass under the debug build.
• CI is green on all platforms that ran; the only red checks are expired darwin agent slots, not test failures.
• No outstanding reviewer comments; the duplicate-PR bot flag was addressed by the author (the overlap with #32425 is one line and non-conflicting in intent).

[robobun]

The lastModified sentinel fix here has been folded into #33659 (cdead2d) since that PR already reworks get_last_modified / resolve_file_stat for the same stat-cache root. The four tests from this PR are included there under the BunFile exists()/size/lastModified describe. This PR can be closed once #33659 lands.

[robobun]

Closing as part of a cleanup of stale pull requests. This PR has had no new commits since 2026-07-07 and it conflicts with main. This is not a judgment on the fix itself. If the problem still reproduces on a current build, reopen this PR after a rebase or open a new one against main.