Why it matters
An uploaded file is untrusted input. Large uploads, malware, malformed content and misleading extensions all need handling before a file becomes available to other users.
The ingestion boundary should separate temporary upload storage from trusted content. Scanning and validation are asynchronous, so users need a clear pending or rejected state.
Decisions to make
- Choose direct-to-cloud upload and maximum size by file type.
- Define scanning, validation and content-type rules.
- Decide where files wait before approval and who can see them.
- Set retention for rejected or abandoned uploads.
- Plan behavior when scanning is unavailable.
Build checklist
- Use short-lived, scoped upload grants and immutable object keys.
- Treat extension and browser MIME type as hints, not proof.
- Scan or validate in quarantine before publishing a file reference.
- Enforce size, decompression and archive-depth limits.
- Test malicious, truncated, duplicate and oversized files.
Common mistakes
- Making a file downloadable before scanning finishes.
- Trusting the original filename in a storage path.
- Letting a failed scanner default to approval.
Tools & references
3 starting points to compare or study. Check fit, maintenance, terms and current capabilities before choosing one.
