[fix] Fixed mobile signal missing case

In some cases, the mobile signal info may be missing,
therefore we need the code to be resilient and not
crash in this case (simply do not try to write mobile
signal data).

openwisp_monitoring/device/api/views.py

@@ -207,6 +207,8 @@ def _get_extra_tags(self, device):
         return tags
 
     def _get_mobile_signal_type(self, signal):
+        if not signal:
+            return
         # if only one access technology in use, return that
         sections = list(signal.keys())
         if len(sections) == 1:
@@ -221,6 +223,8 @@ def _get_mobile_signal_type(self, signal):
 
     def _write_mobile_signal(self, interface, ifname, ct, pk, current=False, time=None):
         access_type = self._get_mobile_signal_type(interface['mobile']['signal'])
+        if not access_type:
+            return
         data = interface['mobile']['signal'][access_type]
         signal_power = signal_strength = None
         extra_values = {}

openwisp_monitoring/device/tests/test_api.py

@@ -906,6 +906,42 @@ def test_gsm_charts(self):
         self.assertEqual(charts[0]['summary']['signal_power'], None)
         self.assertEqual(charts[0]['summary']['signal_strength'], -70.0)
 
+    def test_mobile_signal_missing(self):
+        org = self._create_org()
+        device = self._create_device(organization=org)
+        data = {
+            'type': 'DeviceMonitoring',
+            'interfaces': [
+                {
+                    'name': 'mobile0',
+                    'mac': '00:00:00:00:00:00',
+                    'mtu': 1900,
+                    'multicast': True,
+                    'txqueuelen': 1000,
+                    'type': 'modem-manager',
+                    'up': True,
+                    'mobile': {
+                        'connection_status': 'connected',
+                        'imei': '865847055230161',
+                        'manufacturer': 'QUALCOMM INCORPORATED',
+                        'model': 'QUECTEL Mobile Broadband Module',
+                        'operator_code': '22250',
+                        'operator_name': 'Iliad',
+                        'power_status': 'on',
+                        'signal': {},
+                    },
+                }
+            ],
+        }
+        self._post_data(device.id, device.key, data)
+        response = self.client.get(self._url(device.pk.hex, device.key))
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.data['charts'], [])
+        dd = DeviceData(name=device.name, pk=device.pk)
+        self.assertEqual(
+            dd.data['interfaces'][0]['mobile'], data['interfaces'][0]['mobile']
+        )
+
     def test_pre_metric_write_signal(self):
         d = self._create_device(organization=self._create_org())
         data = {'type': 'DeviceMonitoring', 'resources': {'cpus': 1, 'load': [0, 0, 0]}}