MF-519 - Refine Message (#567)

* Enable Message JSON mashaling/unmarshaling

Update Protobuf generated files.

Signed-off-by: Dusan Borovcanin <dusan.borovcanin@mainflux.com>

* Update readers and SDK to use Mainflux Message

Signed-off-by: Dusan Borovcanin <dusan.borovcanin@mainflux.com>

* Fix alignment

Signed-off-by: Dusan Borovcanin <dusan.borovcanin@mainflux.com>

message.go

@@ -0,0 +1,74 @@
+package mainflux
+
+import "encoding/json"
+
+// Type messageType is introduced to prevent cycle when calling Message
+// MarshalJSON and UnmarshalJSON methods.
+type messageType Message
+
+// Struct message is an internal representation of Mainflux message to be serialized to JSON.
+// Field `Value` is added to prevent marshaling of corresponding Message field.
+type message struct {
+	messageType
+	Value       isMessage_Value `json:"Value,omitempty"`
+	FloatValue  *float64        `json:"value,omitempty"`
+	StringValue *string         `json:"stringValue,omitempty"`
+	BoolValue   *bool           `json:"boolValue,omitempty"`
+	DataValue   *string         `json:"dataValue,omitempty"`
+	ValueSum    *float64        `json:"valueSum,omitempty"`
+}
+
+// MarshalJSON method is used by `json` package to serialize Message.
+func (m Message) MarshalJSON() ([]byte, error) {
+	msg := message{messageType: messageType(m)}
+
+	switch m.Value.(type) {
+	case *Message_FloatValue:
+		floatVal := m.GetFloatValue()
+		msg.FloatValue = &floatVal
+	case *Message_StringValue:
+		strVal := m.GetStringValue()
+		msg.StringValue = &strVal
+	case *Message_DataValue:
+		dataVal := m.GetDataValue()
+		msg.DataValue = &dataVal
+	case *Message_BoolValue:
+		boolVal := m.GetBoolValue()
+		msg.BoolValue = &boolVal
+	}
+
+	if m.GetValueSum() != nil {
+		valueSum := m.GetValueSum().GetValue()
+		msg.ValueSum = &valueSum
+	}
+
+	return json.Marshal(msg)
+}
+
+// UnmarshalJSON method is used by `json` package to unmarshal data to Message.
+func (m *Message) UnmarshalJSON(data []byte) error {
+	var msg message
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return err
+	}
+
+	*m = Message(msg.messageType)
+	m.Value = nil
+
+	switch {
+	case msg.FloatValue != nil:
+		m.Value = &Message_FloatValue{*msg.FloatValue}
+	case msg.StringValue != nil:
+		m.Value = &Message_StringValue{*msg.StringValue}
+	case msg.DataValue != nil:
+		m.Value = &Message_DataValue{*msg.DataValue}
+	case msg.BoolValue != nil:
+		m.Value = &Message_BoolValue{*msg.BoolValue}
+	}
+
+	if msg.ValueSum != nil {
+		m.ValueSum = &SumValue{Value: *msg.ValueSum}
+	}
+
+	return nil
+}