refactor/serializing (#1)

Co-authored-by: matst80 <mats.tornberg@gmail.com>
Reviewed-on: https://git.tornberg.me/mats/go-cart-actor/pulls/1

packet.go

@@ -0,0 +1,76 @@
+package main
+
+import (
+	"encoding/binary"
+	"io"
+)
+
+const (
+	RemoteGetState      = uint16(0x01)
+	RemoteHandleMessage = uint16(0x02)
+	ResponseBody        = uint16(0x03)
+)
+
+type CartPacket struct {
+	Version     uint16
+	MessageType uint16
+	Id          CartId
+	DataLength  uint16
+}
+
+type ResponsePacket struct {
+	Version     uint16
+	MessageType uint16
+	DataLength  uint16
+}
+
+func SendCartPacket(conn io.Writer, id CartId, messageType uint16, datafn func(w io.Writer) error) error {
+	data, err := GetData(datafn)
+	if err != nil {
+		return err
+	}
+	binary.Write(conn, binary.LittleEndian, CartPacket{
+		Version:     2,
+		MessageType: messageType,
+		Id:          id,
+		DataLength:  uint16(len(data)),
+	})
+	_, err = conn.Write(data)
+	return err
+}
+
+func SendPacket(conn io.Writer, messageType uint16, datafn func(w io.Writer) error) error {
+	data, err := GetData(datafn)
+	if err != nil {
+		return err
+	}
+	binary.Write(conn, binary.LittleEndian, ResponsePacket{
+		Version:     1,
+		MessageType: messageType,
+		DataLength:  uint16(len(data)),
+	})
+	_, err = conn.Write(data)
+	return err
+}
+
+// func ReceiveCartPacket(conn io.Reader) (CartPacket, []byte, error) {
+// 	var packet CartPacket
+// 	err := binary.Read(conn, binary.LittleEndian, &packet)
+// 	if err != nil {
+// 		return packet, nil, err
+// 	}
+// 	data := make([]byte, packet.DataLength)
+// 	_, err = conn.Read(data)
+// 	return packet, data, err
+// }
+
+func ReceivePacket(conn io.Reader) (uint16, []byte, error) {
+	var packet ResponsePacket
+	err := binary.Read(conn, binary.LittleEndian, &packet)
+	if err != nil {
+		return packet.MessageType, nil, err
+	}
+	data := make([]byte, packet.DataLength)
+	_, err = conn.Read(data)
+	return packet.MessageType, data, err
+}