Resumable Uploads: Why They Matter for Large Files

You're uploading a 1 GB video file. You're 90% done. Your WiFi drops. Standard upload: start over from zero. Resumable upload: reconnect and continue from where you left off.

How Resumable Uploads Work

The file is split into chunks (typically 5–10 MB each). Each chunk is uploaded independently. The server records which chunks have been successfully received. If the connection drops, only the last partially-transferred chunk needs to be retried — all previous chunks are already stored.

The most common open standard for resumable HTTP uploads is tus.io, which provides a simple protocol extension built on standard HTTP.

The Technical Mechanism

1. CREATE — POST to the upload endpoint to reserve a slot; receive an upload URL
2. PATCH — send file chunks sequentially, each with an Upload-Offset header indicating byte position
3. HEAD — query upload progress to resume after disconnection; server returns the current offset
4. Continue — resume PATCH requests from the reported offset

Platforms with Resumable Upload Support

• Google Drive API — supports resumable upload sessions natively
• AWS S3 — Multipart Upload API for files over 100 MB
• Cloudflare R2 — compatible S3 API, same multipart support
• tus.io servers — open-source server implementations for any platform

Should You Worry About This?

For small files (under 50 MB), resumability is rarely a practical concern — a retry is fast. For large files on mobile networks or satellite connections, resumable uploads are the difference between a usable and an unusable workflow. If you regularly share large files, choose a platform built on chunked upload infrastructure.