Check for nil Reading.Value. Scheduler will fail on nil reading.

Makefile

@@ -3,7 +3,7 @@
 #
 
 PLUGIN_NAME    := modbus-ip
-PLUGIN_VERSION := 2.0.6
+PLUGIN_VERSION := 2.0.7
 IMAGE_NAME     := vaporio/modbus-ip-plugin
 BIN_NAME       := synse-modbus-ip-plugin
 

pkg/devices/coils.go

@@ -59,6 +59,8 @@ func bulkReadCoils(devices []*sdk.Device) (readContexts []*sdk.ReadContext, err
 			var readResults []byte
 			readResults, err = client.ReadCoils(read.StartRegister, read.RegisterCount)
 			incrementModbusCallCounter()
+			log.Debugf("[modbus call]: ReadCoils(0x%x, 0x%x), result: %v, len(d%d), err: %v\n",
+				read.StartRegister, read.RegisterCount, readResults, len(readResults), err)
 			if err != nil {
 				log.Errorf("modbus bulk read coils failure: %v", err.Error())
 				if modbusDeviceData.FailOnError {

pkg/devices/common.go

@@ -71,10 +71,12 @@ func UnpackCoilReading(output *output.Output, rawReading []byte, startAddress ui
 	bitIndex = bitIndex % 8
 
 	if int(byteIndex) >= len(rawReading) {
+		// Make a reading with a nil Reading.Value.
+		reading = output.MakeReading(nil)
 		if failOnErr {
-			return nil, fmt.Errorf("failed to get coil data")
+			return reading, fmt.Errorf("failed to get coil data")
 		}
-		return nil, nil // No Reading
+		return reading, nil // Reading with nil reading.Value
 	}
 
 	coilByte := rawReading[byteIndex]
@@ -93,11 +95,13 @@ func UnpackReading(output *output.Output, typeName string, rawReading []byte, fa
 	// Cast the raw reading value to the specified output type
 	data, err := utils.CastToType(typeName, rawReading)
 	if err != nil {
+		// Make a reading with a nil Reading.Value.
+		reading = output.MakeReading(nil)
 		log.Errorf("Failed to cast typeName: %v, rawReading: %x", typeName, rawReading)
 		if failOnErr {
-			return nil, err
+			return reading, err
 		}
-		return nil, nil // No reading.
+		return reading, nil // No reading.
 	}
 
 	return output.MakeReading(data), nil
@@ -400,7 +404,9 @@ func MapBulkReadData(bulkReadMap map[ModbusBulkReadKey][]*ModbusBulkRead, keyOrd
 						// nil reading.
 						log.Errorf("No data. Attempt to read beyond bounds. startDataOffset: %v, endDataOffset: %v, readResultsLength: %v",
 							startDataOffset, endDataOffset, readResultsLength)
-						readings = append(readings, nil)
+						// Make a reading with a nil Reading.Value.
+						reading = theOutput.MakeReading(nil)
+						readings = append(readings, reading)
 						// Append a read context here for the nil reading.
 						readContext := sdk.NewReadContext(device, readings)
 						readContexts = append(readContexts, readContext)

pkg/devices/device_test.go

@@ -224,9 +224,9 @@ func verifyReadContexts(t *testing.T, expected []*sdk.ReadContext, actual []*sdk
 	t.Logf("*** verifyReadContexts end ------------------------\n")
 }
 
-// verifySingleNilReading verifies that there is one read context with one
+// verifySingleNilReadingValue verifies that there is one read context with one
 // reading that is nil.
-func verifySingleNilReading(t *testing.T, readContexts []*sdk.ReadContext) {
+func verifySingleNilReadingValue(t *testing.T, readContexts []*sdk.ReadContext) {
 	if len(readContexts) != 1 {
 		t.Fatalf("Expected 1 read context, got %v", len(readContexts))
 	}
@@ -236,8 +236,14 @@ func verifySingleNilReading(t *testing.T, readContexts []*sdk.ReadContext) {
 		t.Fatalf("Expected 1 reading, got %v", len(readContexts[0].Reading))
 	}
 
-	if readContexts[0].Reading[0] != nil {
-		t.Fatalf("Expected nil reading, got %#v", readContexts[0].Reading[0])
+	// The scheduler was dereferencing ReadContext.Reading.Value here,
+	// so don't give it a  nil reading but a nil reading value.
+	if readContexts[0].Reading[0] == nil {
+		t.Fatalf("Expected non-nil reading, got %v\n", readContexts[0].Reading[0])
+	}
+
+	if readContexts[0].Reading[0].Value != nil {
+		t.Fatalf("Expected nil reading value, got %#v", readContexts[0].Reading[0].Value)
 	}
 }
 
@@ -3511,7 +3517,7 @@ func TestReadHoldingRegisters_NoConnection(t *testing.T) {
 	if err != nil {
 		t.Fatalf(err.Error())
 	}
-	verifySingleNilReading(t, readContexts)
+	verifySingleNilReadingValue(t, readContexts)
 }
 
 // Unable to connect to the device. Fail on error is true, which fails all
@@ -3583,7 +3589,7 @@ func TestReadInputRegisters_NoConnection(t *testing.T) {
 	if err != nil {
 		t.Fatalf(err.Error())
 	}
-	verifySingleNilReading(t, readContexts)
+	verifySingleNilReadingValue(t, readContexts)
 }
 
 // Unable to connect to the device. Fail on error is false, which allows
@@ -3615,7 +3621,7 @@ func TestReadCoils_NoConnection(t *testing.T) {
 	if err != nil {
 		t.Fatalf(err.Error())
 	}
-	verifySingleNilReading(t, readContexts)
+	verifySingleNilReadingValue(t, readContexts)
 }
 
 // We will need a read (modbus over IP call) for each device below due to different IPs.

pkg/devices/holding_register.go

@@ -60,6 +60,8 @@ func bulkReadHoldingRegisters(devices []*sdk.Device) (readContexts []*sdk.ReadCo
 			var readResults []byte
 			readResults, err = client.ReadHoldingRegisters(read.StartRegister, read.RegisterCount)
 			incrementModbusCallCounter()
+			log.Debugf("[modbus call]: ReadHoldingRegisters(0x%x, 0x%x), result: %v, len(d%d), err: %v\n",
+				read.StartRegister, read.RegisterCount, readResults, len(readResults), err)
 			if err != nil {
 				log.Errorf("modbus bulk read holding registers failure: %v", err.Error())
 				if modbusDeviceData.FailOnError {

pkg/devices/input_register.go

@@ -49,6 +49,8 @@ func bulkReadInputRegisters(devices []*sdk.Device) (readContexts []*sdk.ReadCont
 			var readResults []byte
 			readResults, err = client.ReadInputRegisters(read.StartRegister, read.RegisterCount)
 			incrementModbusCallCounter()
+			log.Debugf("[modbus call]: ReadInputRegisters(0x%x, 0x%x), result: %v, len(d%d), err: %v\n",
+				read.StartRegister, read.RegisterCount, readResults, len(readResults), err)
 			if err != nil {
 				log.Errorf("modbus bulk read input registers failure: %v", err.Error())
 				if deviceData.FailOnError {