Report devices seen on last scan in ARP/SNMP status

The ARP and SNMP scanner status endpoints and front-end cards now expose
the number of devices found by the most recent successful scan, following
the existing mDNS device-count pattern. The count persists across the
running/waiting transitions, and for SNMP a failed poll keeps the last
good count rather than overwriting it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

TODO.md

@@ -9,7 +9,9 @@
 
 - [x] Add configuration options to enable/disable each scanner
 - [ ] Implement the pushover API call directly to support HTML content and review notification text to use it
-- [ ] Add "devices seen on last scan" to the ARP and SNMP scanners status
+- [x] Add "devices seen on last scan" to the ARP and SNMP scanners status
+- [ ] Modify the passive scanners status to count devices seen in the last hour
+- [ ] Modify the event management to ignore duplicate events if they happen within a time threshold
 - [x] Review the recommended timings for the ARP scanner (change defaults) — SNMP defaults set to 10m/5s
 
 ## Frontend

backend/src/scanners/arp/scanner.rs

@@ -22,6 +22,7 @@ pub async fn scan() -> Result<(), Box<dyn std::error::Error>> {
 
         info!("Done with ARP probes");
         info!("Found {} online devices", devices.len());
+        status::record_scan(devices.len() as u64);
 
         // Process found devices
         for device in devices.iter() {

backend/src/scanners/arp/status.rs

@@ -6,6 +6,8 @@ pub struct ArpScannerStatus {
     pub is_running: bool,
     pub scan_started_at: Option<DateTime<Utc>>,
     pub next_scan_at: Option<DateTime<Utc>>,
+    pub last_scan_devices_seen: Option<u64>,
+    pub last_scan_at: Option<DateTime<Utc>>,
 }
 
 #[derive(Clone)]
@@ -13,6 +15,8 @@ pub struct ArpScannerStatusSnapshot {
     pub is_running: bool,
     pub scan_started_at: Option<DateTime<Utc>>,
     pub next_scan_at: Option<DateTime<Utc>>,
+    pub last_scan_devices_seen: Option<u64>,
+    pub last_scan_at: Option<DateTime<Utc>>,
 }
 
 static STATUS: OnceCell<Mutex<ArpScannerStatus>> = OnceCell::new();
@@ -23,6 +27,8 @@ pub fn init() {
             is_running: false,
             scan_started_at: None,
             next_scan_at: None,
+            last_scan_devices_seen: None,
+            last_scan_at: None,
         }))
         .ok();
 }
@@ -45,6 +51,14 @@ pub fn set_waiting(next_scan_at: DateTime<Utc>) {
     }
 }
 
+pub fn record_scan(devices_seen: u64) {
+    if let Some(m) = STATUS.get() {
+        let mut s = m.lock().unwrap();
+        s.last_scan_devices_seen = Some(devices_seen);
+        s.last_scan_at = Some(Utc::now());
+    }
+}
+
 pub fn get() -> Option<ArpScannerStatusSnapshot> {
     STATUS.get().map(|m| {
         let s = m.lock().unwrap();
@@ -52,6 +66,8 @@ pub fn get() -> Option<ArpScannerStatusSnapshot> {
             is_running: s.is_running,
             scan_started_at: s.scan_started_at,
             next_scan_at: s.next_scan_at,
+            last_scan_devices_seen: s.last_scan_devices_seen,
+            last_scan_at: s.last_scan_at,
         }
     })
 }
@@ -66,6 +82,8 @@ mod tests {
             s.is_running = false;
             s.scan_started_at = None;
             s.next_scan_at = None;
+            s.last_scan_devices_seen = None;
+            s.last_scan_at = None;
         } else {
             init();
         }
@@ -92,6 +110,15 @@ mod tests {
         assert_eq!(snapshot.next_scan_at.unwrap(), next);
     }
 
+    #[test]
+    fn test_record_scan() {
+        reset_for_test();
+        record_scan(7);
+        let snapshot = get().unwrap();
+        assert_eq!(snapshot.last_scan_devices_seen, Some(7));
+        assert!(snapshot.last_scan_at.is_some());
+    }
+
     #[test]
     fn test_initial_state() {
         reset_for_test();
@@ -99,5 +126,7 @@ mod tests {
         assert!(!snapshot.is_running);
         assert!(snapshot.scan_started_at.is_none());
         assert!(snapshot.next_scan_at.is_none());
+        assert!(snapshot.last_scan_devices_seen.is_none());
+        assert!(snapshot.last_scan_at.is_none());
     }
 }

backend/src/scanners/snmp/scanner.rs

@@ -33,6 +33,7 @@ pub async fn scan() -> Result<(), Box<dyn std::error::Error>> {
         match finder::find(config).await {
             Ok(devices) => {
                 info!("SNMP poll found {} devices in the ARP cache", devices.len());
+                status::record_scan(devices.len() as u64);
                 for device in devices.iter() {
                     process_device(device);
                 }

backend/src/scanners/snmp/status.rs

@@ -6,6 +6,8 @@ pub struct SnmpScannerStatus {
     pub is_running: bool,
     pub scan_started_at: Option<DateTime<Utc>>,
     pub next_scan_at: Option<DateTime<Utc>>,
+    pub last_scan_devices_seen: Option<u64>,
+    pub last_scan_at: Option<DateTime<Utc>>,
 }
 
 #[derive(Clone)]
@@ -13,6 +15,8 @@ pub struct SnmpScannerStatusSnapshot {
     pub is_running: bool,
     pub scan_started_at: Option<DateTime<Utc>>,
     pub next_scan_at: Option<DateTime<Utc>>,
+    pub last_scan_devices_seen: Option<u64>,
+    pub last_scan_at: Option<DateTime<Utc>>,
 }
 
 static STATUS: OnceCell<Mutex<SnmpScannerStatus>> = OnceCell::new();
@@ -23,6 +27,8 @@ pub fn init() {
             is_running: false,
             scan_started_at: None,
             next_scan_at: None,
+            last_scan_devices_seen: None,
+            last_scan_at: None,
         }))
         .ok();
 }
@@ -45,6 +51,14 @@ pub fn set_waiting(next_scan_at: DateTime<Utc>) {
     }
 }
 
+pub fn record_scan(devices_seen: u64) {
+    if let Some(m) = STATUS.get() {
+        let mut s = m.lock().unwrap();
+        s.last_scan_devices_seen = Some(devices_seen);
+        s.last_scan_at = Some(Utc::now());
+    }
+}
+
 pub fn get() -> Option<SnmpScannerStatusSnapshot> {
     STATUS.get().map(|m| {
         let s = m.lock().unwrap();
@@ -52,6 +66,8 @@ pub fn get() -> Option<SnmpScannerStatusSnapshot> {
             is_running: s.is_running,
             scan_started_at: s.scan_started_at,
             next_scan_at: s.next_scan_at,
+            last_scan_devices_seen: s.last_scan_devices_seen,
+            last_scan_at: s.last_scan_at,
         }
     })
 }
@@ -66,6 +82,8 @@ mod tests {
             s.is_running = false;
             s.scan_started_at = None;
             s.next_scan_at = None;
+            s.last_scan_devices_seen = None;
+            s.last_scan_at = None;
         } else {
             init();
         }
@@ -92,6 +110,15 @@ mod tests {
         assert_eq!(snapshot.next_scan_at.unwrap(), next);
     }
 
+    #[test]
+    fn test_record_scan() {
+        reset_for_test();
+        record_scan(7);
+        let snapshot = get().unwrap();
+        assert_eq!(snapshot.last_scan_devices_seen, Some(7));
+        assert!(snapshot.last_scan_at.is_some());
+    }
+
     #[test]
     fn test_initial_state() {
         reset_for_test();
@@ -99,5 +126,7 @@ mod tests {
         assert!(!snapshot.is_running);
         assert!(snapshot.scan_started_at.is_none());
         assert!(snapshot.next_scan_at.is_none());
+        assert!(snapshot.last_scan_devices_seen.is_none());
+        assert!(snapshot.last_scan_at.is_none());
     }
 }

backend/src/web_server/arp_scanner.rs

@@ -11,6 +11,10 @@ pub struct ArpScannerStatusResponse {
     pub running_for_seconds: Option<f64>,
     /// Seconds until the next scan starts (only set when is_running is false; clamped to 0)
     pub next_run_in_seconds: Option<f64>,
+    /// Number of devices found by the last successful scan (None if none completed yet)
+    pub last_scan_devices_seen: Option<u64>,
+    /// Seconds since the last successful scan completed (None if none completed yet)
+    pub last_scan_seconds_ago: Option<f64>,
 }
 
 #[utoipa::path(
@@ -47,9 +51,15 @@ pub async fn status() -> Result<Json<ArpScannerStatusResponse>, StatusCode> {
         (None, next_run_in)
     };
 
+    let last_scan_seconds_ago = snapshot
+        .last_scan_at
+        .map(|t| ((now - t).num_milliseconds() as f64 / 1000.0).max(0.0));
+
     Ok(Json(ArpScannerStatusResponse {
         is_running: snapshot.is_running,
         running_for_seconds,
         next_run_in_seconds,
+        last_scan_devices_seen: snapshot.last_scan_devices_seen,
+        last_scan_seconds_ago,
     }))
 }

backend/src/web_server/snmp_scanner.rs

@@ -11,6 +11,10 @@ pub struct SnmpScannerStatusResponse {
     pub running_for_seconds: Option<f64>,
     /// Seconds until the next poll starts (only set when is_running is false; clamped to 0)
     pub next_run_in_seconds: Option<f64>,
+    /// Number of devices found by the last successful scan (None if none completed yet)
+    pub last_scan_devices_seen: Option<u64>,
+    /// Seconds since the last successful scan completed (None if none completed yet)
+    pub last_scan_seconds_ago: Option<f64>,
 }
 
 #[utoipa::path(
@@ -47,9 +51,15 @@ pub async fn status() -> Result<Json<SnmpScannerStatusResponse>, StatusCode> {
         (None, next_run_in)
     };
 
+    let last_scan_seconds_ago = snapshot
+        .last_scan_at
+        .map(|t| ((now - t).num_milliseconds() as f64 / 1000.0).max(0.0));
+
     Ok(Json(SnmpScannerStatusResponse {
         is_running: snapshot.is_running,
         running_for_seconds,
         next_run_in_seconds,
+        last_scan_devices_seen: snapshot.last_scan_devices_seen,
+        last_scan_seconds_ago,
     }))
 }

frontend/lib/model/arp_scanner_status.dart

@@ -2,11 +2,15 @@ class ArpScannerStatus {
   final bool isRunning;
   final double? runningForSeconds;
   final double? nextRunInSeconds;
+  final int? lastScanDevicesSeen;
+  final double? lastScanSecondsAgo;
 
   const ArpScannerStatus({
     required this.isRunning,
     this.runningForSeconds,
     this.nextRunInSeconds,
+    this.lastScanDevicesSeen,
+    this.lastScanSecondsAgo,
   });
 
   factory ArpScannerStatus.fromJson(Map<String, dynamic> json) {
@@ -14,6 +18,8 @@ class ArpScannerStatus {
       isRunning: json['is_running'] as bool,
       runningForSeconds: (json['running_for_seconds'] as num?)?.toDouble(),
       nextRunInSeconds: (json['next_run_in_seconds'] as num?)?.toDouble(),
+      lastScanDevicesSeen: (json['last_scan_devices_seen'] as num?)?.toInt(),
+      lastScanSecondsAgo: (json['last_scan_seconds_ago'] as num?)?.toDouble(),
     );
   }
 }

frontend/lib/model/snmp_scanner_status.dart

@@ -2,11 +2,15 @@ class SnmpScannerStatus {
   final bool isRunning;
   final double? runningForSeconds;
   final double? nextRunInSeconds;
+  final int? lastScanDevicesSeen;
+  final double? lastScanSecondsAgo;
 
   const SnmpScannerStatus({
     required this.isRunning,
     this.runningForSeconds,
     this.nextRunInSeconds,
+    this.lastScanDevicesSeen,
+    this.lastScanSecondsAgo,
   });
 
   factory SnmpScannerStatus.fromJson(Map<String, dynamic> json) {
@@ -14,6 +18,8 @@ class SnmpScannerStatus {
       isRunning: json['is_running'] as bool,
       runningForSeconds: (json['running_for_seconds'] as num?)?.toDouble(),
       nextRunInSeconds: (json['next_run_in_seconds'] as num?)?.toDouble(),
+      lastScanDevicesSeen: (json['last_scan_devices_seen'] as num?)?.toInt(),
+      lastScanSecondsAgo: (json['last_scan_seconds_ago'] as num?)?.toDouble(),
     );
   }
 }

frontend/lib/widgets/arp_scanner_card.dart

@@ -24,14 +24,20 @@ class ArpScannerCard extends StatelessWidget {
     ArpScannerStatus status,
     double elapsed,
   ) {
-    final successColor =
-        Theme.of(context).extension<AppColorExtension>()!.success;
+    final successColor = Theme.of(
+      context,
+    ).extension<AppColorExtension>()!.success;
     final neutralColor = Theme.of(context).colorScheme.outline;
+    final lastScan = status.lastScanDevicesSeen != null
+        ? '${status.lastScanDevicesSeen} devices on last scan'
+        : null;
     if (status.isRunning) {
-      final sub = status.runningForSeconds != null
-          ? ['Running for ${formatSeconds(status.runningForSeconds! + elapsed)}']
-          : <String>[];
-      return (color: successColor, label: 'Running', sublabels: sub);
+      final sublabels = <String>[
+        if (status.runningForSeconds != null)
+          'Running for ${formatSeconds(status.runningForSeconds! + elapsed)}',
+        ?lastScan,
+      ];
+      return (color: successColor, label: 'Running', sublabels: sublabels);
     }
     if (status.nextRunInSeconds != null) {
       final remaining = (status.nextRunInSeconds! - elapsed).clamp(
@@ -41,7 +47,7 @@ class ArpScannerCard extends StatelessWidget {
       return (
         color: neutralColor,
         label: 'Waiting for next run',
-        sublabels: ['Next run in ${formatSeconds(remaining)}'],
+        sublabels: ['Next run in ${formatSeconds(remaining)}', ?lastScan],
       );
     }
     return (color: neutralColor, label: 'Not started', sublabels: []);

frontend/lib/widgets/snmp_scanner_card.dart

@@ -28,11 +28,16 @@ class SnmpScannerCard extends StatelessWidget {
       context,
     ).extension<AppColorExtension>()!.success;
     final neutralColor = Theme.of(context).colorScheme.outline;
+    final lastScan = status.lastScanDevicesSeen != null
+        ? '${status.lastScanDevicesSeen} devices on last scan'
+        : null;
     if (status.isRunning) {
-      final sub = status.runningForSeconds != null
-          ? ['Running for ${formatSeconds(status.runningForSeconds! + elapsed)}']
-          : <String>[];
-      return (color: successColor, label: 'Running', sublabels: sub);
+      final sublabels = <String>[
+        if (status.runningForSeconds != null)
+          'Running for ${formatSeconds(status.runningForSeconds! + elapsed)}',
+        ?lastScan,
+      ];
+      return (color: successColor, label: 'Running', sublabels: sublabels);
     }
     if (status.nextRunInSeconds != null) {
       final remaining = (status.nextRunInSeconds! - elapsed).clamp(
@@ -42,7 +47,7 @@ class SnmpScannerCard extends StatelessWidget {
       return (
         color: neutralColor,
         label: 'Waiting for next run',
-        sublabels: ['Next run in ${formatSeconds(remaining)}'],
+        sublabels: ['Next run in ${formatSeconds(remaining)}', ?lastScan],
       );
     }
     return (color: neutralColor, label: 'Not started', sublabels: []);