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Web server mode (diffcore-web)

Status: v1 implemented (2026-08-21)

Run the Tauri app's UI as a browser-hosted web app so diffs can be reviewed on a remote server without a desktop environment.

Architecture

The existing pieces already do most of the work: the UI runs in plain browsers (IS_TAURI detection + mock demo mode), LLM activity streaming is already an axum SSE server (activity_stream.rs, zero tauri imports), and all commands are plain serde-typed functions.

New pieces:

  1. State shim (crates/diffcore-tauri/src/state_shim.rs): a Deref newtype over &AppState, cfg-swapped for tauri::State when the desktop feature is off. Command signatures change from tauri::State<'_, AppState> to a bare State<'_, AppState> resolved by a conditional use. No per-command splitting.
  2. Feature gating (crates/diffcore-tauri/Cargo.toml): desktop (default) enables tauri + plugins; web enables axum static serving. Both binaries carry required-features. build.rs only calls tauri_build::build() when the desktop feature is enabled. The web binary links no webkit/gtk.
  3. Process-global background runtime (runtime.rs): background jobs and block_on go through one shared tokio runtime instead of tauri::async_runtime, so command logic works identically under tauri and axum.
  4. diffcore-web binary (src/bin/web.rs + src/web_server.rs): axum server with
    • POST /api/invoke/{cmd}: JSON body = command args (camelCase keys, mirroring tauri IPC 1:1), dispatched by a hand-written match; sync commands run under spawn_blocking. Unknown/desktop-only commands → 501.
    • GET /api/health: { "ok": true, "default_repo": <--repo flag> }; the UI probes this to enter web mode.
    • the existing SSE routes merged in (same origin; activity_stream_base_url is set to "" so stream_url comes out relative).
    • static file serving of the built UI (--ui-dir, default crates/diffcore-tauri/ui/dist).
  5. Frontend third mode (ui/src): transport priority is Tauri IPC → web API (same-origin /api/health probe at bootstrap) → mock demo. Branches that mean "real backend vs mock" use HAS_BACKEND; branches that are truly desktop-only (updater, file-watch events, editor opening) stay on IS_TAURI.

v1 cuts (deliberate)

  • No auth. Binds 127.0.0.1 by default; --host to override. Remote access via SSH tunnel or a reverse proxy with auth. Do not expose bare. Requests are still guarded against DNS rebinding and CSRF: Host/Origin headers must name an allowed host (localhost, the bind host, or --allowed-host values, e.g. a reverse-proxy domain), and invoke bodies must be well-formed application/json.
  • Single-user server. One shared AppState: concurrent clients analyzing different repos/refs overwrite each other's last_analysis/refinement state. Fine for the personal-tunnel posture; multi-user needs per-session state.
  • No git-HEAD/manifest watch push on web (tauri events; UI already tolerates the failed watch_git_head invoke). Manual refresh covers it.
  • Updater and open-in-editor stay desktop-only.

Usage

# nix (the package ships all three modes; UI assets are bundled)
nix run .#web -- --repo /srv/checkouts/myrepo --port 4400
nix run .#desktop        # tauri app
nix run .#cli -- --help  # diffcore CLI

# plain cargo
cargo build --release --bin diffcore-web --no-default-features --features web
npm --prefix crates/diffcore-tauri/ui run build
diffcore-web --repo /srv/checkouts/myrepo --port 4400

ssh -L 4400:localhost:4400 server   # then open http://localhost:4400

When binding non-loopback (--host 0.0.0.0) or fronting with a reverse proxy, pass each hostname/IP clients will use via --allowed-host. The Host/Origin guard rejects anything else with 403.

Testing

Rust integration test spins the router and exercises /api/health plus an invoke round-trip. Both feature configurations must compile; the full workspace test suite and the UI build stay green.