Network connectivity (headless capability crate)

Status: implemented as day-part-network (in parts/, the headless counterpart of pieces/), a headless day-ecosystem crate with no UI Piece: a shared cross-platform API for reading a snapshot of the device’s network connectivity through each platform’s native API. Any Rust code can depend on it and call day_part_network::status(). Verified on macOS (real online reading); iOS-sim/Android clippy-clean and HarmonyOS cross-compiles + links against the native libnet_connection.so.

Authoring

if let Some(n) = day_part_network::status() {
    println!("online: {}, kind: {:?}, expensive: {:?}", n.online, n.kind, n.expensive);
}

status() -> Option<NetworkStatus> returns None where there’s no connectivity API (or the reading failed), which is distinct from a successful reading that says offline (Some with online: false). NetworkStatus { online: bool, kind: NetworkKind, expensive: Option<bool> }; NetworkKind is Wifi | Cellular | Ethernet | Other | None.

There are no crate features; platform selection is purely #[cfg(target_os)], because connectivity is an OS concern rather than a widget-toolkit one. parts/day-part-network/examples/network.rs is a plain main that uses it with no Day framework at all.

Per-platform native realization

What each platform can report

Every field is best-effort; the platforms report different amounts of detail:

• macOS/iOS: reachability answers “could traffic to the default route flow right now?” from the routing table. It sends no packets, so it cannot detect a captive portal or a dead upstream: online means routable, not verified internet. The only transport bit is IsWWAN (iOS-only): cellular reports Cellular + expensive: Some(true); any other reachable iOS connection reports Wifi (the classic “ReachableViaWiFi” reading; it could in fact be wired or a tether). macOS gets no transport info at all, so an online Mac reports Other, expensive: None.
• Android: the richest reading. online is the system’s INTERNET + VALIDATED verdict for the active network, kind comes from TRANSPORT_WIFI/CELLULAR/ETHERNET, and expensive is the inverse of NET_CAPABILITY_NOT_METERED. Requires android.permission.ACCESS_NETWORK_STATE, a normal install-time permission the crate contributes to the manifest itself (see below).
• HarmonyOS: online = a default network is activated; kind from the bearer type, expensive from NETCONN_NET_CAPABILITY_NOT_METERED. The app must declare ohos.permission.GET_NETWORK_INFO in its module.json5 (requestPermissions; normal permission, no prompt) or the calls fail with 201 and status() returns None.
• Linux: no daemon-independent connectivity API is guaranteed (NetworkManager is optional), so the crate scans /sys/class/net: online = a non-loopback interface has operstate up (link-level, not validated internet); kind from the kernel’s predictable name prefixes (wl* wireless, en*/eth* wired, ww* wwan), preferring wired > wifi > cellular when several are up; expensive is always None (meteredness is a desktop-session concept).
• Windows: GetNetworkConnectivityHint (Windows 10 2004+, blind like the rest of the xaml backend) gives a connectivity level (online = internet or constrained-internet access) and a cost (expensive) but no transport, so kind is Other when online. The symbol is resolved at runtime via LoadLibrary/GetProcAddress, so apps still start on older Windows; status() just returns None there.

A snapshot is a point-in-time poll; a change-notification rail (SCNetworkReachability callbacks, Android NetworkCallback, OH_NetConn_RegisterNetConnCallback, NotifyNetworkConnectivityHintChange) is a v2 follow-up.

Connectivity says whether traffic could flow; to actually move bytes through the platform’s HTTP stack (proxies, VPN, platform TLS), see its sibling part day-part-http.

What it shows about the extension system

Like day-part-battery, this is a headless external crate: it has no UI Piece and registers nothing into any backend’s RENDERERS slice. It additionally exercises the manifest-permission overlay (from the webview work, docs/extending.md): [package.metadata.day.android] stages its own Java shim and contributes android.permission.ACCESS_NETWORK_STATE, which day build merges into the app manifest with no changes to any core Day crate. On Android the crate rides on the Day runtime (day-android’s cached JVM + DayBridge.ctx); on every other platform it is fully day-independent.