Return NaN for invalid temperature readings

pkg/temperature/ds18b20.go

@@ -184,7 +184,15 @@ func readSensors(hub *sentry.Hub) bool {
 			WithLabelValues(sensor.Name).
 			Set(tw)
 
-		metrics.TemperatureSensorReadingStatus.WithLabelValues(sensor.Name, "ok").Inc()
+		var statusStr string
+		if err == nil {
+			statusStr = "ok"
+		} else {
+			statusStr = "fail"
+		}
+		metrics.TemperatureSensorReadingStatus.
+			WithLabelValues(sensor.Name, statusStr).
+			Inc()
 	}
 
 	// Throw away reading if any sensor failed
@@ -235,28 +243,28 @@ func read(sensor string) (int64, error) {
 	path := filepath.Join("/sys/bus/w1/devices", sensor, "w1_slave")
 	data, err := ioutil.ReadFile(path)
 	if err != nil {
-		return 0.0, err
+		return NaN, err
 	}
 
 	raw := string(data)
 
 	if !strings.Contains(raw, " YES") {
-		return 0.0, fmt.Errorf("%v: %w: checksum failed [%v]", sensor, ErrReadSensor, raw)
+		return NaN, fmt.Errorf("%v: %w: checksum failed [%v]", sensor, ErrReadSensor, raw)
 	}
 
 	i := strings.LastIndex(raw, "t=")
 	if i == -1 {
-		return 0.0, fmt.Errorf("%v: %w: t= not found in [%v]", sensor, ErrReadSensor, raw)
+		return NaN, fmt.Errorf("%v: %w: t= not found in [%v]", sensor, ErrReadSensor, raw)
 	}
 
 	c, err := strconv.ParseInt(raw[i+2:len(raw)-1], 10, 64)
 	if err != nil {
-		return 0.0, err
+		return NaN, err
 	}
 
 	// Ignore magic value -128
 	if c == -128000 {
-		return 0.0, fmt.Errorf("%v: magic value -128 detected", sensor)
+		return NaN, fmt.Errorf("%v: magic value -128 detected", sensor)
 	}
 
 	return c, nil