Resumable & Multipart Protocols

tus protocol details

Headers: Upload-Length, Upload-Offset, Tus-Resumable: 1.0.0

• POST → 201 + Location upload URL
• HEAD → current offset (resume after crash)
• PATCH → append chunk, response new offset
• Checksum extension optional

Termination: DELETE to abort.

S3 MPU edge cases

• Incomplete MPU — parts stored, object invisible; lifecycle abort after N days avoids storage leak
• Part size — last part can be smaller; min 5 MB except last (except last part rule)
• CopyObject for server-side assemble when client uploaded parts out of order (must fix order at complete)
• Checksum — new data integrity features; verify on complete

Client SDK design

• Parallel part uploads (4–8 workers)
• Exponential backoff on 5xx
• Persist uploadId + completed part ETags locally (IndexedDB)
• Progress callbacks for UI
• Cancel → AbortMultipartUpload

Download resume

Range: bytes=N- on GET; store partial file + metadata. HTTP 416 when range invalid.

Comparison

	tus	S3 MPU
Abstraction	Protocol	Cloud API
Portability	Any tus server	S3-compatible
Resume	Core spec	ListParts

Many products: tus in front → translates to S3 MPU server-side.