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Architecture

Tauri 2 (Rust core) + SvelteKit + Svelte 5 + TypeScript. The frontend talks to FluidNC over WebSocket and HTTP; the Rust side owns the connection, job streaming and the calibration state model.

The split is deliberate: the Rust side owns the live connection and all machine-state truth; the frontend is a thin reactive view that listens for Tauri events and mirrors them into Svelte stores. Frontend code does not replicate state-machine or reconciliation logic.

Rust core (src-tauri/src/)​

  • lib.rs - registers every #[tauri::command] in one invoke_handler.
  • connection.rs - the heart. A connection_loop supervisor task owns the WebSocket (ws://<host>:81/, i.e. web port + 1, subprotocol arduino) and survives automatic reconnects. Binary frames carry the GRBL line stream; text frames carry key:value control messages. It polls ? (status), $MINFO and $GSTATE on tunable intervals (fast while moving, slow at idle), and burst-polls $GSTATE after any user action so the UI reflects state changes within milliseconds instead of waiting for the 1.5 second tick. All polling is suspended while upload_active is set (an SD/flash write stalls both ESP32 cores). The active streaming Job is owned here so it outlives reconnects.
  • grbl.rs - parses <...> realtime status reports into MachineStatus. FluidNC may append [GC:...] after the report; the parser extracts the <...> substring. Maslow reports 5 axes (X, Y, Z, A, B).
  • maslow.rs - Maslow telemetry (MINFO: JSON blob) and the calibration state machine (states 0-9, mirrors firmware MaslowEnums.h). policy_for(state) is the single source of truth for which user actions are allowed in each state. State (Current state: N) arrives separately from MINFO, via [MSG:INFO:...] or $GSTATE.
  • streaming.rs - G-code job streaming via the GRBL character-counting protocol (127-byte RX budget). Only the acked cursor matters for resume; it is persisted to disk (every 25 acked lines plus on state change) so a job survives an app restart, not just a reconnect.
  • calibration.rs - client-side anchor solver behind the AnchorSolver trait (a Levenberg-Marquardt implementation, a faithful port of the firmware's own solver). Exposed as solve_calibration for what-if waypoint-exclusion analysis without touching the machine.
  • http_api.rs - HTTP client for /command, /files, /upload (file ops, ping, firmware version). $/$/ commands return an empty HTTP body: their output is routed to the WebSocket instead, so config reads ($CD) must go over the socket, not HTTP.
  • toolpath.rs - parses G-code into a polyline for the preview canvas.
  • grpc/, http/, mcp/ - the three control API transports. See Using the API.

Frontend (src/)​

  • SPA mode: +layout.ts sets ssr = false (no Node server under Tauri); adapter-static.
  • src/lib/stores/ - one store module per domain (connection, machine, maslow, job, ui, viewport). Each exposes an init*Listeners() registered once in +page.svelte's onMount. These listeners are the only place Tauri events become Svelte state.
  • src/routes/+page.svelte - desktop shell (CSS-grid: topbar + persistent right control rail + 3-tab workspace + bottom console dock). MobileShell.svelte is the touch layout; $layout from viewport.ts switches between them.
  • Tabs are kept mounted and hidden with display:none (not conditionally rendered) so the waypoint canvas and config panels keep their state and don't refetch on tab switch.

Event contract (Rust app.emit to frontend listen)​

Key events: ws-state, grbl-line, machine-status, maslow-info, maslow-state, maslow-waypoint, action-policy, stream-progress, config-dump / maslow-config / maslow-anchors (all filled by one $CD dump), maslow-discord (logged when firmware state reports disagree with the app's reconciliation). action-policy is the reconciled allow-list (FluidNC state + calibration state + job state) computed in Rust and emitted only on change; the UI gates buttons on it rather than re-deriving it.

Conventions​

  • E-Stop is 0x18 (Ctrl-X soft reset), sent as a realtime byte; it stays reachable from app chrome at all times, never gated behind a tab.
  • HTTP vs WebSocket for a machine interaction: $/$/ commands go over WebSocket; [ESP...]//files//upload go over HTTP.
  • Firmware-version-gated features (e.g. apply-tension limiting, v1.22+) hide or no-op on older firmware rather than error.