@extensibility(APPENDABLE)
struct LicencePlateReq
{
    unsigned long index;
    map<string, string> msg;
};

struct LicencePlateRsp
{
    unsigned long index;
    string licence;
};

struct PrintReq
{
    unsigned long index;
    map<string, string> msg;
};

struct PrintRsp
{
    unsigned long index;
    string msg;
};

struct WeighReq
{
    unsigned long index;
    map<string, string> msg;
};

struct WeighRsp
{
    unsigned long index;
    float stable_weight;
    float instantaneous_weight;
};