orin-status: publish net_wifi_ssid from iw while WiFi is up, re-read every 10 s

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

README.md

@@ -18,7 +18,7 @@ needed.
 | `recorder` | `yukart-recorder.service` | Raw CAN + GNSS to disk, in sessions, under a storage bound; OBD-II values from the bus beside them |
 | `bus-bench` | not installed: a test tool | Raw CAN and decoded-signal load over MQTT, measured: loss, latency, broker CPU ([report](docs/impl/reports/BUS-BENCH.md)) |
 | `obd-poller` | `yukart-obd-poller.service` | OBD-II mode 01 polling, the single CAN writer: rpm, speed, throttle, load, MAP, MAF ~10 Hz; temperatures and fuel 1 Hz (`yukart/vehicle/*`) |
-| `orin-status` | `yukart-orin-status.service` | The Orin's health on the bus, once a second: temperatures, CPU/GPU load, memory, power, fan, WiFi/LTE/tablet links, UPS battery (`yukart/host/*`) |
+| `orin-status` | `yukart-orin-status.service` | The Orin's health on the bus, once a second: temperatures, CPU/GPU load, memory, power, fan, WiFi (with SSID)/LTE/tablet links, UPS battery (`yukart/host/*`) |
 
 ```bash
 scripts/deploy-recorder.sh                 # build, glibc check, install on the car Orin

src/orin-status/net.rs

@@ -1,6 +1,7 @@
 //! Network links: WiFi, LTE and the USB link to the tablet. Up/down and rates
-//! from sysfs counters; WiFi signal from /proc/net/wireless; the modem's own view
+//! from sysfs counters; WiFi signal from /proc/net/wireless, its SSID from `iw`;
-//! from ModemManager, polled on a thread because `mmcli` can take seconds.
+//! the modem's own view from ModemManager, polled on a thread because `mmcli` can
+//! take seconds.
 
 use std::fs;
 use std::path::Path;
@@ -52,6 +53,18 @@ fn wifi_dbm(iface: &str) -> Option<f64> {
     line.split_whitespace().nth(3)?.trim_end_matches('.').parse().ok()
 }
 
+/// SSID of the associated network, from `iw dev <iface> link` ("\tSSID: name"); None when
+/// not associated. iw prints non-printable bytes as \xNN escapes, which are kept as they are.
+fn wifi_ssid(iface: &str) -> Option<String> {
+    let out = Command::new("iw").args(["dev", iface, "link"]).output().ok()?;
+    let text = String::from_utf8_lossy(&out.stdout);
+    let ssid = text.lines().find_map(|l| l.trim_start().strip_prefix("SSID: "))?;
+    Some(ssid.to_string())
+}
+
+/// How often the SSID is re-read while WiFi stays up; a change of network without a drop is rare.
+const SSID_EVERY: Duration = Duration::from_secs(10);
+
 #[derive(Default, Clone)]
 struct Modem {
     state: String,
@@ -80,6 +93,7 @@ fn poll_modem() -> Modem {
 pub struct Net {
     wifi: Option<String>,
     wifi_rate: Rate,
+    ssid: Option<(Instant, Option<String>)>,
     lte_rate: Rate,
     tablet_rate: Rate,
     modem: Arc<Mutex<Option<Modem>>>,
@@ -97,6 +111,7 @@ impl Net {
         Net {
             wifi: wifi_iface(),
             wifi_rate: Rate { prev: None },
+            ssid: None,
             lte_rate: Rate { prev: None },
             tablet_rate: Rate { prev: None },
             modem,
@@ -110,6 +125,14 @@ impl Net {
         if let Some(w) = self.wifi.clone() {
             let up = attr(&w, "operstate").as_deref() == Some("up");
             out.push(("net_wifi_up", json!(up)));
+            if !up {
+                self.ssid = None;
+            } else if self.ssid.as_ref().is_none_or(|(at, _)| at.elapsed() >= SSID_EVERY) {
+                self.ssid = Some((Instant::now(), wifi_ssid(&w)));
+            }
+            if let Some((_, Some(ssid))) = &self.ssid {
+                out.push(("net_wifi_ssid", json!(ssid)));
+            }
             if let Some(dbm) = wifi_dbm(&w).filter(|_| up) {
                 out.push(("net_wifi_signal_dbm", json!(dbm)));
             }