MF-600 - Handle custom LoRa Server application decoder (#608)

Signed-off-by: Manuel Imperiale <manuel.imperiale@gmail.com>

lora/message.go

@@ -40,4 +40,5 @@ type Message struct {
 	FCnt                int    `json:"fCnt"`
 	FPort               int    `json:"fPort"`
 	Data                string `json:"data"`
+	Object              string `json:"object"`
 }

lora/service.go

@@ -84,9 +84,17 @@ func (as *adapterService) Publish(m Message) error {
 		return ErrNotFoundApp
 	}
 
-	payload, err := base64.StdEncoding.DecodeString(m.Data)
-	if err != nil {
-		return ErrMalformedMessage
+	// Use the SenML message decoded on LoRa server application if
+	// field Object isn't empty. Otherwise, decode standard field Data.
+	var payload []byte
+	switch m.Object {
+	case "":
+		payload, err = base64.StdEncoding.DecodeString(m.Data)
+		if err != nil {
+			return ErrMalformedMessage
+		}
+	default:
+		payload = []byte(m.Object)
 	}
 
 	// Publish on Mainflux NATS broker