Ignoremetrics: add feature to ignore Values returned by modbus device

config/config.go

@@ -213,6 +213,15 @@ type MetricDef struct {
 
 	// Scaling factor
 	Factor *float64 `yaml:"factor,omitempty"`
+
+	// Special return values with meaning
+	IgnoredValues []IgnoredValueDef `yaml:"ignoredValues,omitempty"`
+}
+
+// IgnoredValueDef defines an array of special values and the return error
+type IgnoredValueDef struct {
+	Value   *float64 `yaml:"value"`
+	Meaning string   `yaml:"meaning"`
 }
 
 // Validate semantically validates the given metric definition.

modbus.yml

@@ -42,3 +42,15 @@ modules:
         dataType: bool
         bitOffset: 0
         metricType: gauge
+
+      - name: "some_special_device_with_buggy_values"
+        help: "some help for some coil"
+        address: 301220
+        dataType: int16
+        metricType: counter
+        ignoredValues:
+        - value: 4294934512
+          meaning: Data pending, acquisition in progress
+        - value: 4294934513
+          meaning: Reserved
+

modbus/modbus.go

@@ -263,9 +263,25 @@ func scrapeMetric(definition config.MetricDef, f modbusFunc, modAddress uint64)
 		return metric{}, err
 	}
 
+	// Check Value with special meaning from config.yml
+	for _, iv := range definition.IgnoredValues {
+		if v == *iv.Value {
+			return metric{}, &IgnoredValueMeaningError{fmt.Sprintf("value is %v - %s", *iv.Value, iv.Meaning)}
+		}
+	}
+
 	return metric{definition.Name, definition.Help, definition.Labels, v, definition.MetricType}, nil
 }
 
+// IgnoredValueMeaningError is returned whenever a value equals the ignoredValue defined in config.yaml
+type IgnoredValueMeaningError struct {
+	e string
+}
+
+func (e *IgnoredValueMeaningError) Error() string {
+	return fmt.Sprintf("ignored value returned as value: %v", e.e)
+}
+
 // InsufficientRegistersError is returned in Parse() whenever not enough
 // registers are provided for the given data type.
 type InsufficientRegistersError struct {