prune network interfaces that no longer exist

extension.js

@@ -575,6 +575,17 @@ var VitalsMenuButton = GObject.registerClass({
             if (/^network-(?!rx$|tx$)/.test(typeKey)) typeKey = 'network';
             let key = '_' + typeKey + '_' + label.replace(' ', '_').toLowerCase() + '_';
 
+            // issue #557 - interface is gone, drop it rather than show its last reading
+            if (value == 'destroy') {
+                this._values.removeNetworkSensor(key, label, type.replace('network-', ''));
+                if (key in this._sensorMenuItems) {
+                    this._sensorMenuItems[key].destroy();
+                    delete this._sensorMenuItems[key];
+                }
+                this._removeHotItem(key);
+                return;
+            }
+
             // if a sensor is disabled, gray it out
             if (key in this._sensorMenuItems) {
                 this._sensorMenuItems[key].setSensitive((value!='disabled'));

sensors.js

@@ -47,6 +47,9 @@ export const Sensors = GObject.registerClass({
 
         this.resetHistory();
 
+        // interfaces seen by the last network query, to spot the ones that go away
+        this._network_interfaces = [];
+
         this._last_processor = { 'core': {}, 'speed': [] };
 
         this._settingChangedSignals = [];
@@ -311,6 +314,24 @@ export const Sensors = GObject.registerClass({
         let netbase = '/sys/class/net/';
 
         new FileModule.File(netbase).list().then(interfaces => {
+            // 'lo' is always present, so an empty listing means the read failed
+            if (!interfaces.length) return;
+
+            // issue #557 - forget interfaces the kernel no longer has
+            for (let iface of this._network_interfaces) {
+                if (interfaces.includes(iface)) continue;
+
+                for (let direction of directions) {
+                    if (iface == 'lo' && direction == 'rx') continue;
+
+                    let name = iface + ((iface == 'lo')?'':' ' + direction);
+                    let type = 'network' + ((iface=='lo')?'':'-' + direction);
+                    this._returnValue(callback, name, 'destroy', type, 'storage');
+                }
+            }
+
+            this._network_interfaces = interfaces;
+
             for (let iface of interfaces) {
                 for (let direction of directions) {
                     // lo tx and rx are the same

values.js

@@ -470,6 +470,17 @@ export const Values = GObject.registerClass({
         return output;
     }
 
+    // issue #557 - forget a removed interface, so its last counters stop being totalled
+    removeNetworkSensor(key, label, direction) {
+        for (let type of ['network', 'network-rx', 'network-tx'])
+            if (type in this._history) delete this._history[type][key];
+
+        delete this._networkSpeedOffset[key];
+
+        if (direction in this._networkSpeeds)
+            delete this._networkSpeeds[direction][label];
+    }
+
     resetHistory(numGpus) {
         // don't call this._history = {}, as we want to keep network-rx and network-tx
         // otherwise network history statistics will start over