NewFileDate (Online File Date & Timestamp Editor)

Change OS file dates, photo EXIF capture dates, and the creation dates stored inside HWP / PPTX / DOCX documents.

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Two processing modes

	File Date (OS)	HWP / PPT (Pro)
Where it runs	Your browser	Server
File leaves the device	No	Yes
Size limit	None	4.5 MB per file (host payload cap)
Formats	Any	HWP, PPTX, DOCX, JPEG

File Date (OS) builds the ZIP in browser memory with JSZip; nothing is transmitted. Pro must upload the document because the target timestamps live inside the container. Uploaded files exist only in memory for the duration of the request and are discarded once the response is written — they are never persisted. The UI states which of the two applies to the selected mode; see privacy.html.

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Timestamp model

Two different kinds of timestamp are involved, and conflating them shifts every result:

• Wall clock, no timezone — ZIP/DOS entry dates and EXIF DateTimeOriginal. Written exactly as the user picked them.
• UTC instant — Windows FILETIME in the HWP summary stream and dcterms:created / dcterms:modified in OOXML.

The client sends the wall clock it displayed plus tz_offset_minutes (the Date.getTimezoneOffset() convention), so the server derives both without assuming any particular timezone.

Other format constraints:

• DOS second snapping — ZIP timestamps have two-second resolution, so seconds floor to an even value (00, 02, ... 58).
• Range clamping — 1980-01-01 to 2107-12-31, the representable DOS range.
• EXIF edits are confined to the APP1 segment, never applied across the whole file, so entropy-coded image data cannot be corrupted.
• A photo carrying no EXIF timestamp is reported as skipped rather than silently counted as changed.

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Security posture

Track B accepts untrusted files from the public internet. The following are enforced in backend/:

Control	Where
Upload filenames stripped to a safe basename (no traversal)	metadata_editor.sanitize_filename
Duplicate names suffixed instead of overwritten	metadata_editor.deduplicate_filename
Decompression-bomb limits (entry count, entry size, total size, ratio)	metadata_editor._assert_archive_safe
Reads capped independently of self-reported ZIP sizes	metadata_editor._read_entry_bounded
Per-file / total / count upload limits	main.py
Extension allowlist	main.py
CORS restricted to known origins (ALLOWED_ORIGINS env var)	main.py
Generic error bodies; details only to logs	main.py
Best-effort per-instance rate limit, checked before any file is read	main.py
CSP (no script-src 'unsafe-inline') and related headers	vercel.json

Rate limiting

main.py enforces 20 requests / 60s per client IP, rejected before any upload is read. This is per-instance. A serverless platform runs many instances concurrently, so a distributed flood still gets roughly instances × limit. It reduces the cost of a sustained single-source flood; it is not a complete control.

For a real limit, add an edge rule — Vercel dashboard → project → Firewall → Custom Rules: match Path starts with /api/, action Rate Limit, e.g. 30 requests per 60s keyed by IP. Edge rules run before the function is invoked, so blocked requests cost nothing.

Content Security Policy

script-src does not include 'unsafe-inline'. The GA bootstrap lives in frontend/public/ga-init.js, and the one remaining inline block (JSON-LD) is allowlisted by sha256 hash in vercel.json.

Editing that JSON-LD changes its hash and the browser will silently block it, so the hash is verified in CI:

cd frontend && npm run build && npm run csp:check   # verify
cd frontend && npm run csp:update                   # rewrite vercel.json

style-src still allows 'unsafe-inline': the UI uses React inline style props, which are governed by that directive.

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Quick start

Frontend

cd frontend
npm ci
npm run dev        # http://localhost:3000

Backend

python3 -m venv backend/venv
source backend/venv/bin/activate
pip install -r backend/requirements.txt
python backend/main.py    # http://127.0.0.1:8000

Tests

cd frontend && npm test          # vitest, jsdom
cd backend  && pytest -q         # pytest

Regenerating the Open Graph image

pip install -r tools/requirements.txt
python3 tools/make_og_image.py

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Layout

api/index.py             Vercel entrypoint -> backend/main.py
api/requirements.txt     Serverless runtime deps (minimal)
backend/main.py          FastAPI routes, request limits, CORS
backend/metadata_editor.py  Format parsers and safety limits
backend/requirements.txt Dev + test deps
frontend/src/lib/timestamp.ts  Track A archive build, EXIF rewriting
tools/make_og_image.py   Regenerates frontend/public/og-image.png

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License

MIT