Add exception for empty array when publishing data

Add exception for enabling empty array sending (that differs from arrays with one null element)
An empty array with corrrect type is now sent to astarte

Signed-off-by: Eddy Babetto <eddy.babetto@secomind.com>

cmd/appengine/device.go

@@ -1603,6 +1603,7 @@ func parseSendDataPayload(payload string, mappingType interfaces.AstarteMappingT
 	// Default to string, as it will be ok for most cases
 	var ret interface{} = payload
 	var err error
+
 	switch mappingType {
 	case interfaces.Double:
 		if ret, err = strconv.ParseFloat(payload, 64); err != nil {
@@ -1634,32 +1635,42 @@ func parseSendDataPayload(payload string, mappingType interfaces.AstarteMappingT
 	case interfaces.BinaryBlobArray, interfaces.BooleanArray, interfaces.DateTimeArray, interfaces.DoubleArray,
 		interfaces.IntegerArray, interfaces.LongIntegerArray, interfaces.StringArray:
 
-		//wait it's all string?
-		payload = strings.Replace(payload, "[", "", -1)
-		payload = strings.Replace(payload, "]", "", -1)
-		payload_parsed := strings.Split(payload, ",")
-		//always has been
+		//check if payload is an empty array, bypass conversions and just return an empty array of correct type
+		// if it is not, proceed as usual
+		if payload == "[]" {
+			ret = make([]interface{}, 0)
 
-		jsonOut := make([]interface{}, len(payload_parsed))
-		for i, v := range payload_parsed {
-			jsonOut[i] = v
-		}
+		} else {
 
-		retArray := []interface{}{}
-		// Do a smarter conversion here.
-		for _, v := range jsonOut {
-			switch val := v.(type) {
-			case string:
-				p, err := parseSendDataPayload(strings.TrimSpace(val), interfaces.AstarteMappingType(strings.TrimSuffix(string(mappingType), "array")))
-				if err != nil {
-					return nil, err
+			//wait it's all string?
+			payload = strings.Replace(payload, "[", "", -1)
+			payload = strings.Replace(payload, "]", "", -1)
+			payload_parsed := strings.Split(payload, ",")
+			//always has been
+
+			jsonOut := make([]interface{}, len(payload_parsed))
+			for i, v := range payload_parsed {
+				jsonOut[i] = v
+			}
+
+			retArray := []interface{}{}
+
+			// Do a smarter conversion here.
+			for _, v := range jsonOut {
+				switch val := v.(type) {
+				case string:
+					p, err := parseSendDataPayload(strings.TrimSpace(val), interfaces.AstarteMappingType(strings.TrimSuffix(string(mappingType), "array")))
+					if err != nil {
+						return nil, err
+					}
+					retArray = append(retArray, p)
+				default:
+					retArray = append(retArray, val)
 				}
-				retArray = append(retArray, p)
-			default:
-				retArray = append(retArray, val)
 			}
+			ret = retArray
 		}
-		ret = retArray
+
 	}
 
 	return ret, nil