Merge branch 'L2SS-1759-fix-metrics' into 'master'

L2SS-1759: Fix for attributes that return None and then break the prometheus_client

Closes L2SS-1759

See merge request !857

tangostationcontrol/tangostationcontrol/devices/base_device_classes/lofar_device.py

@@ -112,6 +112,10 @@ class AttributePoller:
             try:
                 value = await self._read_attribute(attr_name)
 
+                # check if value could be read
+                if value is None:
+                    continue
+
                 # update metric, if any
                 if attr_data["metric"]:
                     attr_data["metric"].set_value(value)

tangostationcontrol/tangostationcontrol/metrics/_metrics.py

@@ -159,6 +159,9 @@ class AttributeMetric:
     def set_value(self, value: object):
         """A new value for the attribute is known. Feed it to the metric."""
 
+        if value is None:
+            raise ValueError(f"Invalid value for metric: {value}")
+
         # set it, this class will take care of the default labels
         if self.metric_class == Enum:
             self._enum_value(value, self.static_label_values)

tangostationcontrol/test/metrics/test_metrics.py

@@ -563,6 +563,27 @@ class TestMetrics(base.TestCase):
             metrics = parse_prometheus_response(proxy.prometheus_response())
             self.assertIn("ds_foo", metrics)
 
+    def test_set_value_none(self):
+        """Test behaviour of setting None as a value in a metric."""
+
+        @device_metrics()
+        class test_device(TestMetrics.TestDevice):
+            FOO = attribute(
+                doc="This is FOO",
+                dtype=str,
+                fget=lambda obj: None,
+                fset=lambda obj, value: None,
+            )
+
+            @command()
+            def test(device):
+                # writing None should fail
+                with self.assertRaises(ValueError):
+                    device.metrics["FOO"].set_value(None)
+
+        with DeviceTestContext(test_device, process=False) as proxy:
+            proxy.test()
+
     def test_track_value_modification(self):
         """Test whether metrics update if the attribute's value is accessed."""