File Download Service

GET /api/v1/files/{id} with resume support

• Create FileDownloader service:

class FileDownloader
  def download(file_id, expected_checksum:, resume_from: 0)
    # Downloads to temp file
    # Supports Range header for resume
    # Returns path to downloaded file
  end
end

• Download to temp directory (tmp/downloads/)
• Track partial download progress for resume capability
• Return downloaded file path for attachment

Verify downloaded files match manifest checksums

• Create ChecksumVerifier service:

class ChecksumVerifier
  def verify!(file_path, expected_sha256)
    actual = Digest::SHA256.file(file_path).hexdigest
    expected = expected_sha256.delete_prefix("sha256:")
    raise ChecksumMismatchError unless actual == expected
  end
end

• Consider using MD5 since active storage uses MD5 for checksums
• Integrate verification before ActiveStorage attachment
• On mismatch: delete file, retry download (up to 3 attempts)

Ensure proper ActiveStorage setup for offline operation

• Verify config/storage.yml uses local disk:
  local:
  service: Disk
  root: <%= Rails.root.join("storage") %>
• Set in config/environments/production.rb:
  config.active_storage.service = :local
• Configure blob cleanup: old blobs purged when TopicFile destroyed
• Add storage/ to backup strategy

Start by reading config/storage.yml and config/environments/production.rb, then locate the FileDownloader, ChecksumVerifier, ActiveStorage attachment flow, and TopicFile model. Done means downloads resume from partial files, checksum failures clean up and retry, local storage is configured for offline use, and TopicFile cleanup and backup requirements are addressed.