Design File Storage with Metadata, Access Control, and Chunked Uploads

Design a file-storage service with a drive-style user experience. Focus on the separation of file metadata from file bytes, access-control lists, and large-file uploads split into chunks.

Constraints & Assumptions

• Support authenticated users, file upload and download, and explicit sharing permissions.
• A file can be large enough that an interrupted upload should resume without retransmitting every completed chunk.
• Clarify overwrite/version behavior before choosing identifiers and commit semantics.
• No scale target, availability SLA, or particular storage vendor is supplied. Describe a coherent baseline and identify where those requirements would change it.

Clarifying Questions to Ask

• Are permissions attached to individual files, inherited from folders, or both?
• Is an overwrite a new immutable version or an in-place replacement?
• May clients upload chunks directly to blob storage using scoped authorization?
• What should happen to incomplete uploads and cached download links after access is revoked?

Part 1 — Metadata and access control

Define metadata records, file/blob identifiers, and permission checks for listing, sharing, and downloading.

What This Part Should Cover

• Separation of logical files, immutable content versions, and storage objects.
• ACL entries and server-side authorization on relevant operations.
• A consistent metadata view when content is uploaded or overwritten.

Part 2 — Chunked upload and completion

Describe upload-session creation, chunk transfer, retry/resume, and finalization.

What This Part Should Cover

• Chunk identity, size and integrity checks, and idempotent retry behavior.
• A manifest or equivalent complete-file representation.
• A commit boundary that exposes only a complete, validated version.
• Cleanup of abandoned temporary chunks.

Part 3 — Download and failures

Walk through an authorized download and explain recovery from failures between blob writes and metadata commit.

What This Part Should Cover

• Authorization before granting access to bytes.
• Range or chunk-based retrieval without making clients trust arbitrary storage keys.
• Reconciliation for unreferenced blobs and incomplete metadata transitions.