Messenger/docs/adr/0004-media-storage.md

ADR 0004: Media behind an S3-like interface

• Status: accepted
• Date: 2026-09

Context

Attachments (images, files, videos) need storage, thumbnails for images, and bounded upload size. Storage must survive container restarts and, ideally, be swappable without touching API code.

Decision

Define a Storage interface (Save/Open/Delete keyed by opaque keys) in internal/media. Phase 2 ships Local — files on disk with atomic temp-file+rename writes and path-traversal protection. API handlers depend only on the interface.

Consequences

• Metadata lives in Postgres (media table); bytes live in storage.
• Replacing disk with MinIO/S3 means a new Storage implementation, no handler changes.
• Image thumbnails are generated with stdlib decoding + x/image/draw, avoiding CGO and external binaries.