sanity checks

exporter.go

@@ -164,6 +164,18 @@ func mainImpl() error {
 			if err != nil {
 				return fmt.Errorf("sensor reading error: %v", err)
 			}
+
+			// sanity check sensor outputs:
+			// current = shunt / resistor, but resistor is fixed,
+			// so if current == 0 if and only if shunt == 0
+			if (p.Current == 0) != (p.Shunt == 0) {
+				return fmt.Errorf("current = %v but shunt = %v", p.Current, p.Shunt)
+			}
+			// power = current * voltage, similar logic
+			if (p.Power == 0) != (p.Current == 0 || p.Voltage == 0) {
+				return fmt.Errorf("power = %v but current = %v and voltage = %v", p.Power, p.Current, p.Voltage)
+			}
+
 			busVolts := float64(p.Voltage) / float64(physic.Volt)
 			busVoltageHist.Observe(busVolts)
 			busVoltageSumm.Observe(busVolts)