QuixiCloud Desktop for Windows
Product & Technical Architecture Brief

Traditional cloud storage clients (like Dropbox, Box, or early Google Drive sync) function as heavy user-space synchronizers: they download entire directory structures to local disks, duplicate gigabytes of payload, and run resource-hungry Chromium/Electron processes that chew up RAM and battery.

QuixiCloud Desktop for Windows completely redesigns this paradigm by integrating directly into the Windows File Explorer using the native operating system Windows Cloud Files API (cfapi).

QuixiCloud is engineered with an ultra-modern, memory-safe systems stack designed for high throughput and near-zero idle resource consumption:

A. "Files On-Demand" (Cloud Hydration)

• Placeholder Creation: When connecting a vault, QuixiCloud inspects cloud metadata and writes lightweight NTFS file placeholders into the local folder. Windows recognizes them natively as cloud files.
• On-Demand Hydration: When any Windows software (File Explorer, Word, Photoshop, Premiere Pro, or CLI) requests to read a file, the Windows kernel intercepts the I/O call and notifies the QuixiCloud background daemon to stream the necessary byte ranges.
• Smart Local Caching: Once opened, the file is locally cached. When local SSD space runs low, users (or Windows Storage Sense) can right-click and click "Free up space" to dehydrate the file back to a 0 KB placeholder without touching the cloud original.

B. Bidirectional Real-Time Synchronization

• Local → Cloud: Newly created, modified, renamed, or deleted files are immediately caught via the Windows USN Journal and file system watchers (notify-debouncer-full), queued, and uploaded via chunked streams.
• Cloud → Local: The desktop client maintains a lightweight Server-Sent Events (SSE) connection and delta query pipeline with the QuixiCloud backend, reflecting remote alterations locally within milliseconds.

C. Native Windows File Explorer Badges & Context Menus

Electron-based sync utilities bundle full Chromium browser engines that routinely idle at 300MB to 800MB of RAM. QuixiCloud utilizes Rust and Tauri v2, idling at a fraction of that memory:

High-Speed Transfer Pipeline

• Direct-to-Cloud Uploads: When backed by Amazon S3, Cloudflare R2, or MinIO storage policies, QuixiCloud transfers files directly to object stores using secure presigned URLs, eliminating server proxy bottlenecks.
• Parallel Multi-Part Uploads: Large media files are divided into optimized chunks and streamed concurrently across multiple threads.
• Automatic Resumption: If a laptop sleeps or Wi-Fi drops, transfers automatically resume from the exact byte offset without restarting from scratch.

• REST API over HTTPS (TLS 1.3): All directory listing, file metadata, quota queries, and policy enforcement run over TLS 1.3 encrypted endpoints.
• Modern OAuth 2.0 with PKCE: Users authenticate via their web browser or custom workspace domain. The desktop client registers the quixicloud://oauth/callback deep-linking scheme to capture the auth token automatically. A built-in manual token fallback is included for restricted enterprise environments.
• Persistent Server-Sent Events (SSE): Remote modifications trigger instantaneous push notifications down an active SSE pipeline, eliminating battery-draining polling loops.
• Adaptive Rate Limiting: A built-in token-bucket algorithm (governor) prevents saturating domestic upload bandwidth or triggering provider rate limits.

• Zero Plaintext Passwords: The desktop client never receives or stores your master account password. It relies entirely on short-lived OAuth 2.0 bearer and refresh tokens.
• Windows Credential Manager (DPAPI): Access tokens and cryptographic keys are saved inside the Windows hardware-backed credential vault, preventing malicious third-party apps from extracting session data.
• SQLCipher AES-256 Local Metadata DB: The local metadata cache (meta.db) is encrypted with AES-256 via SQLCipher, protecting local file names, paths, and timestamps from unauthorized offline extraction.
• MSIX Sandboxed Execution: Distributed in Microsoft's MSIX application container, preventing registry corruption and defending against malicious DLL injection attacks.

Because QuixiCloud hooks into the Windows NTFS filesystem driver via cfapi, other desktop software treats cloud placeholders exactly like local files: