Backend (Rust)

The Tauri 2 Rust backend lives in src-tauri/. It owns all networking, local persistence, background tasks, and keeps the WebView sandboxed. No panic crosses the command boundary: every command returns Result<_, String>.

Here’s the lifecycle of a request, from UI to nhentai.net and back:

flowchart TD
    A[Frontend invoke] -->|"invoke()"| B[Command handler]
    B -->|"calls client"| C[NhDesktopClient]
    C -->|"HTTPS throttled"| D[nhentai.net API]
    D -->|"typed JSON"| C
    C -->|"typed model"| B
    B -->|"Result Ok or Err"| A

🧩 Modules

File	Responsibility
`src-tauri/src/nh_desktop.rs`	`NhDesktopClient` — typed nhentai.net API client (reqwest) + `THROTTLE`
`src-tauri/src/commands.rs`	All `#[tauri::command]` handlers
`src-tauri/src/db.rs`	SQLite persistence (`Db`, `database.sqlite`), compaction, and cache pruning
`src-tauri/src/service.rs`	`BackgroundService` — throttled worker queue (downloads, prefetch, maintenance, sync, auto-refresh)
`src-tauri/src/image_cache.rs`	`ImageCache` — disk image cache at `cache/images`, LRU budget pruning, backing `proxy_image`
`src-tauri/src/error.rs`	Friendly error type
`src-tauri/src/main.rs`	Application entry point

⚡ Commands (the full surface)

All commands are snake_case, registered on the Tauri invoke handler.

🔍 Display & discovery

Command	What it does
`fetch_new`	New/recent galleries (paginated)
`fetch_popular`	Popular galleries (site’s list)
`fetch_tagged`	Galleries for a tag (type, sort, page)
`search_galleries`	Search with query text + sort + page
`fetch_gallery`	Single gallery detail (with favorite state)
`related_galleries`	Related galleries for a gallery id
`fetch_tag_info`	Tag metadata by `type`/`slug`
`fetch_tags_by_type`	Tag listing for a given tag type
`proxy_image`	Fetch image bytes (CDN fallback) → `Vec<u8>` (served from the disk image cache first)

💾 Local DB (key/value)

Command	What it does
`db_get` / `db_set` / `db_del`	Single key operations in `database.sqlite`
`db_dump` / `db_clear`	Full-table dump / clear

🗄️ Storage & Cache Management

Command	What it does
`get_storage_stats`	Return disk usage telemetry (image cache bytes + count, query cache rows, database file size)
`set_cache_budget`	Configure maximum storage budget (bytes) for background LRU pruning
`clear_image_cache`	Wipe cached disk images
`clear_query_cache`	Clear cached API response rows in `database.sqlite` without touching user favorites/blacklist/settings
`optimize_storage`	Reclaim physical disk space via SQLite `VACUUM`

🔑 Account & Authentication

Command	What it does
`set_api_key` / `get_api_key_status` / `clear_api_key`	Store/query/clear the local API key
`login_account`	Authenticate with username and password (`POST /api/v2/auth/login`) and store token
`verify_api_key` / `get_current_user`	Validate key or token; fetch `/api/v2/user` (`UserMeResponse`)
`check_favorite` / `add_favorite` / `remove_favorite`	Account favorite state
`fetch_favorites`	Remote favorites list
`fetch_account_blacklist` / `update_account_blacklist`	Account blacklist sync via `POST /api/v2/blacklist`
`download_gallery`	Fetch official archive URL via `POST /api/v2/galleries/{id}/download` or direct URL

🛰️ Background service & System

BackgroundService (service.rs) runs a single throttled worker; jobs are enqueued as service://job events stream progress to the UI.

Command	What it does
`service_enqueue_download`	Download gallery ZIP/CBZ → disk (progress events); returns job id
`service_enqueue_prefetch`	Prefetch a list of image URLs into the image cache
`service_enqueue_maintenance`	Prune image cache (LRU budget) + cached lists (7d)
`service_enqueue_sync`	Account favorites + blacklist sync into cached mirrors
`service_status`	Pending job count
`service_set_auto_refresh`	Enable/disable Popular auto-refresh (interval `≥15` min)
`service_get_auto_refresh`	Current auto-refresh config
`service_get_downloads_dir` / `service_set_downloads_dir` / `service_reset_downloads_dir`	Downloads folder config
`open_downloads_folder`	Reveal downloaded files in OS file manager
`get_system_locale`	Detect OS locale tag (`sys-locale`)
`app_quit`	Gracefully quit application

🦀 Networking rules

🦀 One client, one place: NhDesktopClient is the only thing touching nhentai.net.
Respect the site: a THROTTLE sleep keeps requests human-paced; single-flight/reuse patterns avoid fan-out. The background service runs one job at a time.
Image hosts: any *.nhentai.net subdomain is accepted (is_allowlisted_image_host), so t./i./static. all work; matching CSP img-src in tauri.conf.json.
Typed serde models mirror the API JSON 1:1; deserialization tests cover the shapes.
TLS: reqwest with rustls (no OpenSSL dependency), gzip enabled.

🚨 Error handling

🚨 error.rs provides friendly error types; commands never return panic!.
Failure to load a resource (image/CDN) is signaled with a clean Err(String) the UI renders as a retryable notice (see Reader & Galleries).
The DB is behind a Mutex<Connection>; all access is short-lived and unlock-and-drop.